C Tison

D Hauser

L Delaye

T Koleck

N Lamquin

M Planells

F Gouillon

P Castillan

PROCESSING OF THE CFOSAT-SWIM DATA: ALGORITHM PROTOTYPING AND SIMULATIONS

Keywords: Oceanography, radar, CFOSAT, SWIM, wave scatterometer

This paper presents the under-going development of the ground segment algorithms of the SWIM instrument. SWIM is a wave scatterometer which will be embarked on the Chinese French oceanography mission, CFOSAT. SWIM aims at measuring the 2D oceanic wave spectra; it is a Ku band real aperture radar. Simulations are performed to get data along the satellite track: radar signals are obtained simulated interaction with a realistic sea surface and taking into account the radar geometry. Then, the simulated data are processed with software prototypes.

INTRODUCTION

The Chinese and French Space Agencies (resp. CNSA and CNES) have proposed to jointly carry out an innovative mission, CFOSAT (China France Oceanography SATellite) devoted to the monitoring of the ocean surface and its related science and applications. Currently under Phase D (manufacturing phase), the launch and the Assessment Phase completion should lead to deliver a fully validated system in orbit in 2018. The primary objective of CFOSAT is to monitor, at the global scale, ocean surface winds and waves. CFOSAT will embark two payloads, SWIM a wave scatterometer provided by France [START_REF] Enjolras | a state of the art multi-incidence beams Ku-band waves scatterometer to go beyond current radar systems[END_REF], and SCAT a wind scatterometer provided by China [START_REF] Zhu | Calibration and estimation of attitude errors for a rotating fan-beam scatterometer using calibration ground stations[END_REF]. The paper focuses on SWIM data processing. This instrument is a real aperture radar scanning with 6 incidence angles from 0° to 10°, inherited of the concept described in [START_REF] Hauser | SWIMSAT: a real aperture radar to measure directional spectra of ocean waves from space main characteristics and performance simulation[END_REF]. The three beams 6°, 8° and 10° are dedicated to the directional wave spectrum measurements. This spectrum will provide information on energy, propagation direction and wavelength of oceanic waves which wavelengths are between 70 m and 500 m with an accuracy step of 15° in azimuth.

OVERVIEW OF THE PRODUCTS

The French mission center, CWWIC (CNES Waves and Wind Center) localized at CNES (France) will deliver in near real time the SWIM and SCAT products. Fig. 1 illustrates the SWIM products which will be processed at the CWWIC. Three major kinds of products will be made available:

 backscattering coefficient profiles over [0°,11°] of incidence angles,  nadir significant wave height and wind speed,  2D wave spectra and associated geophysical parameters (energy, dominant wavelengths and dominant azimuth) per sea states.

Level 0: raw data (backscattered power versus range) @ 0, 2, 4, 6, 8, 10°W

ave products (6°, 8°, 10°) σ 0 products (0°, 2°, 4°, 6°, 8°, 10°) Nadir products (0°)

PROCESSING AND PRODUCTS OF EACH WAVE LEVEL

L1A processing and products

The level 1a processing will provide calibrated radar echoes from the six beams (normalized radar cross-section in radar geometry), and the associated localization of each range gate (coordinates with respect to nadir track and geographical North). This processing requires the use of calibration parameters provided independently by the processing of the calibration sequences which will be regularly updated. The main steps of the processing are:  correction by the mean level of thermal noise,  normalization of the received power to get an averaged power,  computation of the geometry for each gate (range distance, ground distance from nadir point, elevation, incidence, latitude and longitude),  inversion of the radar equation taking into account the integrated antenna gain.  In order to test the processing software, a simulation tool, named SimuSWIM has been developed [START_REF] Tison | Latest advances of the SWIM instrument[END_REF]: it enables to generate L0 data on orbit parts. The inputs are a pre-defined wave spectrum either provided by hindcasts of the wave model MFWAM from the French Meteorological Institute Meteo-France or from empirical spectra wave spectra. Figure 2 and 3 illustrate the level 0 and level 1a products. The different processing steps applied to the L1a are: calculate the mean value and mean trend of 0 using a polynomial fit, calculate the relative fluctuations 0 (r) around the mean trend, as a function of radial distance,  resample radial fluctuations to get fluctuations in the surface reference frame  0 (x),  calculate the fluctuation spectrum,  calculate the modulation spectrum due to ocean waves by correcting for the impulse response function and for the density spectrum of speckle (the impact of thermal noise is neglected in this step). Different options for speckle estimation are included in the software [START_REF] Hauser | A study of speckle properties over the ocean surface from the airborne radar Kuros[END_REF]. This a major point for investigation in order to estimate the proper level of the modulation spectrum.

L2 processing and products

The Level2 products refer to geophysical data representative of geographic boxes of about 70 x 90 km. These boxes are defined so as to construct the directional wave spectra by concatenation and fusion of the radial spectra either from a single antenna beam (6 or 8 or 10°) or from the three antenna beams (6, 8, and 10°). For each box, the Level 2 from products the spectrum beams (6°, 8°, 10°) will contain:

 the directional spectra of wave slopes (F(k,)) in about 50 wavenumber intervals and 24 azimuth intervals with a 180° ambiguity in the direction of propagation.  partitions of the 2D wave spectra, and associated parameters of wave partitions (direction, wavelength, energy);  mean  values as a function of incidence and azimuth. In addition, products from the nadir processing will be merged to the L2 products (significant wave height, normalized radar cross-section and wind speed.

To construct the Level2 product, the processing steps applied to Level 1b products are the following:

 average the modulation spectrum in 50 wave number bins and 15° azimuth intervals,  apply the tilt modulation transfer function to estimate wave slope spectra k 2 F,  apply a partitioning algorithm to detect up to three wave components of the 2D polar spectrum; the partitioning algorithm is based on the detection of the maxima and a watershed detection [START_REF] Hanson | Automated Analysis of Ocean Surface Directional Wave Spectra[END_REF].  calculate the main parameters of the 2D spectrum and of its partition (total energy, peak direction, peak wavelength). In order to quantify the accuracy of the Level 2 products, test sets #1a and #1b have been used. The errors on the energy E, wavelength  and direction  are calculated on each partition. Figure 6 illustrates the result of a performance analysis based on a simulation of a 10-min of L2 products in a case of high wind and waves. It shows the very good agreement between the inverted products and the reference, except on the energy where a bias can be observed. The energy is the tricky parameter to be estimated and researches are still ongoing to improve its estimation.

Figure 6: Histograms of relative error on the energy (left), wavelength (middle) and azimuth (right) of the wave spectrum between simulation and reference for 10 minutes of data of the 6, 8 and 10° beams of SWIM. Energy: relative bias = 14-22%, scatter index = 30%; wavelength: relative bias=1-2%, scatter index = 19%; azimuth direction: relative bias=1°, scatter index=10-17°.

CONCLUSION

The SWIM instrument will provide innovative data (global coverage of directional wave spectrum) which will help for sea state forecast and climate studies. The synergy with the SCAT instrument will be of great interest as for the first time wind and wave will be observed at the very same time. For the present time, the processing algorithms are under definition and tests. Some trade-offs have to be made, mostly on the speckle spectrum estimation and on the tilt modulation transfer function estimation. Several algorithms are implemented and tested on simulated data. All this work will lead to an operational ground segment for the CFOSAT launch. Synergies between SWIM and SCAT products will be mainly performed at levels 3 and 4. On French side, these levels are under IFREMER responsibilities. In the levels 1 and 2, we plan to use the SCAT wind product to complete the information provided by the nadir beam. This has not been tested yet. It will be a major research axis for the future as having wind and wave information at the same place is the major innovation of the project.

Fig. 1 .

 1 Fig. 1. Overview of the SWIM products from level 0 to level 2.

Fig. 2 .

 2 Fig.2. Example of the L0 output power on the six beams (simulation). The blue line is the output power and the green line is the maximal expected power (without thermal noise) from the radar equation.

Fig. 2 .

 2 Fig. 2. Example of the L0 output power on the six beams (simulation).The blue line is the output power and the green line is the maximal expected power (without thermal noise) from the radar equation.

Figure 3 :

 3 Figure 3: Simulation of Level 1a products for the six SWIM illumination beams: normalized radar cross-section as a function of elevation angles.

3. 2 .

 2 L1b processing and productsThe L1b products are intermediate products specific of the spectrum beams (6°, 8°, 10°). They will contain: flags on probability of presence of sea ice and rain and flags on the observed mean trend 0 with incidence angle,  moments of the fluctuations of signal (mean variance, kurtosis, skewness of 0) and associated flags,  density spectra of modulation Pm(k,f), corrected from impulse response function and speckle density spectra and provided for each spectrum beam and each azimuth (approximately every 7.5° in azimuth).

Figure 4

 4 Figure 4 illustrates a modulation spectrum for a signal simulated for the 8° incidence beam.

  link budget / without thermal noise) SimuSWIM output power (with thermal noise and speckle)

Figure 4 :

 4 Figure 4: Example of L1b product for a simulated echo obtained with the 8° incidence beam: density spectrum of signal fluctuations and of speckle with 3 different estimates of speckle spectrum as a function of wave number (in rad/m).

Figure 5

 5 Figure 5 illustrates an example of a simulated 2D and omni-directional wave spectrum contained in the L2 product.

Figure 5 :

 5 Figure 5: Example of simulated 2D (left) and omnidirectional (right) wave spectrum for a case a high sea state (Hs= 5.3 m). The black (resp. red) line on the right plot is the simulation (resp. reference)


Valérie Legrand

Peter Stockinger

Francis Lemaitre

The social and economic context for the sharing of video resources in a non-profit setting

ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

1) Background

In 2002, the R&D lab ESCoM (Equipe Sémiotique Cognitive et Nouveaux Médias) of the Fondation Maison des Sciences de l'Homme (FMSH) in Paris has launched the "Audiovisual Research Archive" Program (acronyme: ARA). The mission of ARA is two-folded:

-1 st to produce a digital audiovisual online library that documents the scientific and cultural heritage in social and human sciences;

-2 nd : to do research and development in the use and exploitation of audiovisual content.

Ten years after, the ARA Program is composed of:

1) A collection of almost 6000 hours of online video resources produced by an international community of 2500 authors (researchers, teachers, journalists, artists, ...) from some 85 countries and accessible through a main web portal and several specialized portals 1 ;

2) A digital environment for working with audiovisual corpora called ASW 2 Studio (Studio ASA in French). This working environment is constituted on the one hand by tools for segmenting, describing, annotating and indexing as well as publishing of audiovisual corpora and, on the other hand, of meta-linguistic resources -the ASW ontology -for building libraries of description models necessary for the concrete work (segmentation, analysis, publishing) with an audiovisual text (a video);

3) The necessary technical infrastructure for storing, streaming, using and preserving audiovisual data (essentially a group of servers that are maintained by the Computer Resources Department of FMSH); 4) A small team dedicated to the different tasks of the ARA program (one part-time research director, one full-time computer engineer, one part-time digital archivist, one part-time technician). The ARA working group is advised by a scientific board of researchers, engineers and representatives of user stakeholders.

1 http://www.archivesaudiovisuelles.fr/EN/ and http://www.semiosphere.msh-paris.fr/semiospherefr.aspx 2 « ASW » stands for « Audiovisuel Semiotic Workshop » which has been developed thanks to an ANR (Agence Nationale de la Recherche) founded R&D project called « ASA-SHS » (Atelier de Sémiotique Audiovisuelle pour l'analyse de corpus audiovisuals en SHS): http://www.asa-shs.fr/ (also: http://asashs.hypotheses.org/78)

Since 2006 and thanks to a series of European and French founded R&D projects3 as well as a special targeted financial help from the French Ministry of Higher Education and research, one of the main R&D activities has been to disclose the intellectual and technical opportunities of the ARA program for a public composed mainly of people and institutions of higher education and research.

The willingness to disclose the intellectual and technical opportunities of the ARA program to this public has been motivated by the following two observations:

1) In the "academic world", a growing number of individual actors (i.e. researchers, teachers, researchers, doctoral students,...) and collective ones (research labs and teams, educational centers, associations, archives and libraries,...) make more and more use of digital audiovisual resources (namely videos) in their professional activities (research, education, scientific and cultural heritage preservation and valorization, ...) and are themselves engaged in concrete activities of collecting, processing, analyzing, publishing, using and reusing as well as, finally, preserving an intellectual heritage.

2) But without an appropriate working environment, it is difficult if not impossible to generalize and to "standardize" this new interests and activities -sometimes summarized under the heading of digital humanities; it's a serious drawback for enabling the targeted public of the ARA program to become an active actor in the production, diffusion and use of digital audiovisual resources.

Based on these observations, a small R&D project has been started at the very beginning of 2012 aiming to provide, in fine, an appropriate environment for individual and collective actors of the "academic world" working with audiovisual resources. The name of this project is ARA Campus (the Campus of the Audiovisual Research Archives). In a nutshell, ARA Campus is intended:

1) to become a video portal for accessing the audiovisual productions of individual or collective actors belonging to the "academic world"

2) and to provide these actors with the necessary tools and services (software, ...) for creating and managing their own archives, working and publishing their video collections, using and/or reusing their own collections and/or those of third parties.

The functionalities and services which ARA Campus is intended to provide from the end of 2014/beginning 2015 on, are identified in the next section.

2) Output

The ARA Campus is intended to be a technical and scientific platform (mainly in form of downloadable software, ontologies and description models, procedures and "best practices") that enables, in principle, any individual or collective actor of the "public academic world":

1. to create and manage his/her own online audiovisual archive (its own "video channel" in the sense of You Tube) that is to say, via a CMS, to adapt the interfaces of his/her archives and the main access to the videos that are provided by the Campus AAR;

2. to upload (to add), to delete or to change,... audiovisual resources in his/her archives;

3. to develop and manage his/her own ontology (concepts, description models and thesaurus) on the basis of a common ontology provided by the ARA Campus;

4. to define his/her own publishing formats of audiovisual resources on the basis of a "library" of models provided by the ARA Campus;

5. to segment, analyze, publish and republish, in his/her archives own audiovisual resources;

6. to moderate the inclusion in his/her archives, videos of a third party (other researcher, other institution, etc.); 7. to moderate the segmentation, description and republication of his/her resources by a third party; 8. to moderate the possible adjustments to his/her regional ontology -changes requested by third parties using his/her archives as a platform for storage and dissemination;

9. to moderate requests of third parties to use in a non-commercial or commercial way records belonging to his/her archives; 10. to launch, through the social media, bits of resources belonging to his/her archives.

In addition, ARA Campus is also intended to be a central web portal for accessing content of all archives using ARA Campus as a platform for storage and distribution of their own audiovisual resources. In other words the ARA is also a content provider:

1. of third party videos, 2. of third party video archives, 3. of third party video descriptions and video publications (in form of interactive video books, thematic folders, video-lexica, etc.).

As shown in Figure 1, ARA Campus will be made up of several services (or "workshops") for the management of videos, semantic resources, analyses and channels: a common thesaurus defining the vocabulary of Real World Objects (RWOs), as well as the vocabulary specific to the video analysis domain;

7

a common set of analysis and publication templates usable by any channel;

user ontologies defining the templates specific to each channel: subjects, indexing sequences and schemes, as well as the definition of the channel publication models: thesaurus access, thematic access, contextualization of results, etc.

2) A Production Workshop providing tools to video material owners for:

-Publishing, creating licenses, and making their videos available for streaming

3) An Analysis Workshop providing tools to analysts for:

-Subscribing to and downloading videos in a secure environment -Analyzing videos (segmentation and semiotic description) 4) A Publication Workshop providing tools to video channels owners for:

-Creating and managing their channel (interface and content personalization)

-Subscribing to videos and analyses -Posting videos and analyses on their channel

3) Description and size of market

As already mentioned in section 1, the principal market of the ARA Campus project is, globally speaking, the public academic world first of all in France (individual actors: researchers, teachers, doctorate and post-doc students; institutional actors: research labs, research networks, but also associations ...). In this part we will describe:

the market of Web video platforms in scientific, cultural and educational fields the target market: his profile and needs the ARA Campus' strategy to answer to the market's needs

Web video platforms in scientific and cultural fields

Audiovisual archives online: new interactive and attractive Internet use

The advantage of new technologies and internet is undeniable and, actually, these new media provide the necessary conditions for processing intangible material, such as cultural or scientific audiovisual content. Ever since the 1980s, the Internet revolution has been highly beneficial for publishing audio-visual data which had previously not been, or at least under represented institutionally. Such as a representative example, since 2006 over 20 million Internet users visited the INA website which offers a referenced and catalogued by search engine, keywords associated, or via a custom space and sharing: the success of this site shows that this heritage digitized encounters a memory appetite in public. Note: This poll was made with Internet users from 15 and over, on more than 200 websites.

France: 36,6 % of Internet users have consulted videos online France : the most common operations on the web -Source : Ipsos, enquête profiling*, 2005

The interactivity of the Internet, coupled with its ease of access and exchange between the far corners of the world makes this media a vector for publishing and promoting global audiovisual heritages, thereby enabling all the users to view hitherto unpublished and inaccessible cultural or scientific phenomena.

% of Internet video amateur users adhere to content sharing platforms

At the same time, the popularity of internet and new media platforms allow indeed to develop new popular ways of sharing videos on the net, or UGC (User Generated Content). The popular web video platforms (such as You Tube, Vimeo or Daily Motion) and social networks (such as Facebook, or Twitter) offer various informal ways of disseminating audiovisual data. These "popular" media could actually be used for academic communication, but they won't allow an advanced user to manage specific rights on sensitive video contents or to index in detail video data.

It is therefore necessary to conduct a reflection on the articulation and differentiation of scientific and popular audiovisual platforms to meet the diverse needs of multiple users and to develop new way of broadcasting and protecting video material.

Research, knowledge transmission and education through video data

Nowadays, with implementations of audiovisual and digital technologies the needs and uses of video materials are increasing in cultural, scientific and educational domains. Indeed, since one decade many researchers are working with digital audiovisual material to documents their researches, especially in the domain of social sciences. In the educational area, a lot of teachers are using video as pedagogical resources, especially in linguistics studies, language learning and distance education. In this framework, many universities, scientific institutions (such as the CNRS and the CCSD4 or INRIA), cultural heritage institutions (such as INA, UNESCO or Louvre) as well as governmental institutions (such as the Directorate of audiovisual resources of the Ministry of Higher Education and Research with CERIMES5 , Canal U6 -the online video-library and web tv for higher education -, the digital universities network (UNT)7 and the UOH -the Open University of Humanities)8 have already developed their own systems to archive videos, which are not always compatible with one to another.

Since the last three years and thanks to big national infrastructure projects (such as the TGE Adonis for Humanities) 9 , the "digital humanities market" is becoming more and more structured enabling individual as well as small institutional actors (research labs, groups working for a research project, ...) to have a better use of new information technologies for producing, disseminating and sharing scientific information. Main services in this are, as far as France is concerned, the ISIDORE gateway 10 for human and social sciences, Revue.org 11 for the production and management of digital research magazines, the HAL gateway 12 for gathering and disseminating scientific reports, articles, still images (and soon videos), the Hypothese.org portal 13 for the creation and management of scientific logs (documenting research "in progress") and finally the Calenda portal 14 for announcing scientific events such as workshops, symposia, etc.

In the field of archives, for a decade, digitization projects respond to major issues related to the exercise of democratic culture: save large segments of audiovisual history threatened by technical obsolescence and physical deterioration of the collections, increase backed up volumes and enhance audiovisual heritage by ensuring wider access to the public. Furthermore, digitization was accompanied by widespread battle content with the appearance of "technological convergence" 15 as of 2006.

With the inflation of Web audiovisual contents, servers and internet are now at the heart of the system of archive. The perimeter of the audiovisual archive is deeply modified, having been so far confined to the activities of storage, backup, indexing, and -often limitedprovision of resources. Today, heritage institutions define themselves so more and more in terms of activities and not only storage, making the audiovisual archives of an "archivestock" system to a system "of archive-stream". In general, the emergence of networks led the heritage institutions to more focus on the user and its practices. This means that they are the gateway to cultural contents in developing dynamic interfaces between the users and the knowledge, in relying on collaborative tools and devices of mediation. Also we see emerge new activities such as online archives of television or even production targeted educational and cultural content. Therefore, digitalized online multimedia archives can also be used as a means of communication not only for the conservation purposes. In this direction, FMSH -ESCoM-AAR through the development of various online audiovisual archiving programs has ensured the important protection and wide dissemination of audiovisual heritages whether through interviews with specialists, seminars, or cultural events. The creation of thematic folders and networks of links between different recordings of videos enables the conception of a dynamic approach to audiovisual heritages.

Profile of the target market

In this part we will describe the main targets markets identified for (CONVERGENCE-derived) services provided by FMSH -ESCOM-AAR structure, considered as a Technology provider.

So the main concerns of the target market actors, concerning their activities related to audiovisual data, could be resumed as:

1) individual or institutional actors already possessing audiovisual data and who want to digitize them in order to preserve and disseminate them.

2) individual or institutional actors who want to create their own audiovisual archive system for research, education or culture 3) individual or institutional actors who want to use or reuse (and so modifiy, adapt and enhance) already existing digital resources for their specific activities (in research, in education, in documentation, etc.)

It is very difficult to find "official" data allowing to quantify this market with respect to these three roles.

However, since 2001 ESCoM has realized for its ARA (Audiovisual Archives Research) Program, several surveys and reports on user communities in the "public academic world" and their typical needs and expectations with respect to audiovisual corpora in research, education, heritage management and preservation 16 (See chapter 4).

Needs of the target market

In the context of Web video platform market for purposes of research, knowledge transmission or education, the main and current issues are:

-The lack of an equivalent non-commercial management service for the production, dissemination, management and preservation of audiovisual resources in higher education and research (a sort of "academic YouTube") open to all actors in human and social sciences (and beyond) ;

-The lack of a scientific media allowing researchers and institutions to properly broadcasting their videos in a legal and scientific framework;

-The lack of interoperability and compatibility between the different existing audiovisual archive systems.

We point out 7 main needs:

Differentiation of approaches: popular-informal / scientificacademic Issue

Currently we are witnessing the emergence of a generation of UGC "User Generated Contents », the large public producing and annotating its own documents, while it generally ignores all of the traditional archival.

Audiovisual "academic" culture is then counterbalanced by consumers of images becoming themselves new « memory producers ».

Need

Need for differentiation between the informal popular approach and the academic scientific one proposed by the archives or libraries and residing in the documentary quality and levels of indexing.

Strategy of the ARA Campus to answer to the market's needs

As already explained in section 2, the ARA Campus project has three main objectives:

1) it should provide the necessary services for the targeted public -services such as archive creation, indexing, diffusion, republishing of digital audiovisual resources;

2) it should further provide relevant (audiovisual) content : i.e. a digital resource itself as well as the relevant metadata for the (intellectual, cognitive) appropriation of the resource and its practical "exploitation".

3) it should develop a new scientific framework for intellectual properties on videos

Modern-day information society relies on increasing the number of digital resources. Music, films, software, and sensitive personal data (bank accounts, medical records, billing etc.) are stored and moved as digital files and broadcasted, in their own formats. Designed to route information between computers, the Internet is rapidly evolving into an Internet of things where services, media, and Real World Objects (RWOs) (e.g. products, people and places) and their corresponding data are individually identified.

In the context of this new Internet, the main center of interest is content. At present, the content management solutions are proprietary, non-interoperable, and restricted to certain types of information. Hence, there is an increasing need for more effective means of managing and organizing information resources, ensuring their traceability and the ability to search and filter them, as well as to copy, protect, and synchronize them while guaranteeing their integrity and controlling access to them and their usage.

With audiovisual data, considered as a new object for scientific purposes and from the international legacy perspective, we have to face with a legal vacuum concerning rights and intellectual properties. The creation of a Web audiovisual portal which publishes living cultural heritages in the public domain raises legal questions, notably about rights over content and publication rights concerning data collection practices and using oral data. Beyond the current "Image Reproduction Rights" and "Author Rights", we have to consider the "Contents Holders' Rights" concerning the speech and ideas developed by the person filmed/interviewed in the video. At the present, the current technologies can't allow us to recognize and protect these Contents Holders' Rights. For example, if a Video Material Owner specify the names and participation of Content Holder on the videos credits at the end, this part could ever be cut and this information could disappear, there is no way to ensure and record it permanently on the video with current technologies. On this specific point, a future technology should allow to specify these rights in the video permanent metadata.

In some cases, the copyright in the audiovisual materials limited the distribution of these materials via the internet. It is important that the interests of the authors, actors and other right holders are taken into account in the search for satisfactory solutions to enable a wide public access to audiovisual material. So, special attention should be given to the research and education objectives allowed by copyright laws. European recommendations on copyright are therefore essential: some legal mechanisms for the producer of a film to grant rights of use for non-commercial purposes for a public institution in charge of film heritage institution are under study [START_REF]Doc.12929: Protection and provision of audiovisual cultural heritage[END_REF] .

4) Results of an online survey (2009/2010) on the relevancy of the ARA Campus for the target market

Based on a cumulative experience of almost 9 years in the production and management of digital audiovisual archives and in order to prepare the ARA Campus project, a detailed online survey has been realized on the web portal "Audiovisual Research Archive" 18 during the period of 2009-2010. The objective of this survey has been:

1) to get an input form the visitors and users of the about 6000 hours of scientific and cultural videos diffused on the ARA web portal concerning the evolution of the ARA program itself;

2) to understand the expectations of the ARA public as far as the uses and potential exploitations of video material is concerned.

The survey -provided in French and English -has been composed of the following principal headings:

1) general personal information;

2) access to collections of videos/audiovisual resources: satisfaction of existing solutions; desired new solutions;

3) the diffusion of videos/audiovisual resources: satisfaction of existing solutions; desired new solutions;

4) the content of videos/audiovisual resources: satisfaction of existing content; actual and potential use of content by the visitors; 5) the publishing formats of videos: satisfaction of actually existing, desired, expected ones and for which use;

6) ARA as a service provider: satisfaction of actually existing ones, desired, expected ones.

Here is a small list of 8 salient results of this survey 19 which have been proved to be extremely precious for the definition of the different services of the ARA Campus.

Result 1) 265 persons have answered the survey (54% male; 46% female, figure 2) -63% are from France, the rest is coming from some 35 different countries (major representation of the francophone world, Africa and Europe, figure 3).

It is not surprising that the two principal languages are French (98%) and English (73%); among the 25 represented languages, the most important are, further, Spanish, Italian, German and Arabic (spoken between 29% and 13,4% of the panel; figure.4) Indeed, 35% of the panel confirm to consult either one time or more than one time per day the ARA program (14, 9%) or at least several times a week (20,1%). These 35% are completed by 41% of the surveyed panel who confirms that they visit a few times a month the ARA portal (only 21% of the surveyed panel confirms to be "occasional" users of the ARA program.

In taking into account that the average daily number of visitors for the period 2009-2010 has been about 620 visitors (spending an average time of 6 to 9 minutes on a video page) 20 , the 20 This data are provided by an FMSH external service -Xitiand, since 2011, also by Google Analytics. It also has to be mentioned that the in 2009-2010, the daily average of visitors of the ARA content has been significantly be more important than to-day (to-day, 2012, the average number of visitors is about 450 visitors spending however more or less the same time on a video page). The relative decline of visitors between 2010 and 2012 ha several internal reasons: important reduction of means in the production of new content, reorganisation of the service, etc. But an other reason is that the priority in the last three years has been given to research and development and the consequences of these activities only will be visible (and hopefully positive) from 2013 on.

"kernel" of daily ARA customers can be situated between 180 to 220 visitors and those of potential customers between 200 and 250 visitors. However, it is impossible to have an idea of the absolute number of "de facto" or potential customers of the ARA programme21 . This figures show that the ARA Campus is -a priori -a credible project for the targeted public composed of individual and collective actors in the academic world (figure 6).

Fig. 6: Professional Category

Result 4) Concerning the content itself provided through the ARA portal(s), it is strongly claimed by more than 52% (+ 39,3%) of the respondents to include third party videos (and not only videos produced by the FMSH-ESCOM).

This figure echoes the "strategic" choice of opening the ARA opportunities to the academic public in order to enable every researcher or research unit to become an authentic producer and author of audiovisual resources and to use or reuse third-party resources in his/her own work (figure 7).

Fig.7: About ARA Audiovisual Content

Result 5) Concerning the appropriation ("lecture") of video content provided through the ARA portal, the respondents provide, among other, following interesting data (figure 8):

-73% of respondents confirm to try to proceed to "a partial viewing (of a video) based on what you need to find";

-70% of respondents confirm to opt for a "full event video (reading)", i.e. the reading of the whole video of a lecture, a conference, an interview, a documentary, etc.

-Only 20% of the respondents confirm "to flip through sets of videos as if you where changing T.V. channels".

These data are very important for the ARA Campus project because they show that the targeted "consumer public" is extremely different from that of the standard passive "TV consumer".

Indeed, videos are used here for professional activities (in research, in education, in heritage management, etc.) and constitute a genuine "working resource" for the concerned public. ARA Campus has to provide therefore the necessary tools in order to enable the targeted public to effectively work with videos.

One specific question pointed out here is the particular access problem of long videos: as the 73% of respondents confirm, they access (try to access) video resources with respect to specific themes they are interested in. This presupposes however that on a video portal not only an entire video has to be accessible but also segments or sequences of it which possess a specific thematic profile.

Once more again, for developing such accesses, tools have to be developed enabling the owner of an archive to segment and to index his/her videos. As already shown in section 2, this is another main objective of the ARA Campus. -62,4% of the respondent strongly believe that the ARA videos "can serve as teaching aids in the university classroom" (only 2,5% disagree or strongly disagree);

-61,1% of the respondent strongly believe that the ARA videos "are a way of fostering dialogue between science, culture and the citizen" (only 6,5% disagree or strongly disagree);

-54% of the respondents strongly believe that the ARA videos "are a way of improving the diffusion of information and of increasing scientific exchanges among researchers" (10% disagree or strongly disagree);

-53,4% of the respondent strongly believe that the ARA videos "can serve as teaching aids in lifelong learning" (only 9,1% disagree or strongly disagree);

-52% of the respondents strongly believe that the ARA videos can serve as "incubators for new research themes or issues" (11% disagree or strongly disagree);

-42,5% of the respondents strongly believe that the ARA videos can "be used for vulgarizing research in the human and social sciences" (15% disagree or strongly disagree).

These data (and again a series of other, thematically related one) show more precisely potential uses of videos such as those of the ARA portal -uses as imagined or experienced by the respondents of the survey.

Indeed, this does not mean necessarily that the video as such published on the ARA portal is already a "working resource" in this or that direction but that it can be a working resource.

In any case, publishing tools have to be provided for adapting, transforming existing videos in "real" resources. And this, as already argued in section 2, one of the main objectives of the ARA Campus. -48,2% strongly agree and 42,2% simply agree on "theme-based browsing that links several independent videos in one narrative path" (9,6% disagree; 0% strongly disagree);

-53, 8% strongly agree and 33,8% simply agree on "online video-encyclopaedia to one issue, one domain" (12% disagree; 0% strongly disagree);

-45, 6% strongly agree and 39,2% simply agree on "interactive video-book" (13,9% disagree; 1,3% strongly disagree); -45% strongly agree and 40% simply agree on "enhanced video (with comments, suggestions, links, etc.)" (13,9% disagree; 1,3% strongly disagree);

In order to satisfy these and related expectations, one of the main objectives of the ARA Campus project is, as explained in section 2, to provided users of the ARA Campus with a publishing service of single videos and/or video segments as well as of video corpora in form of predefined but adaptable publishing models. -Service enabling users to download lists of video segments (!!) provided by third party video collections (54,7% strongly agree and 30,2% simply agree; 12,8% disagree; 2,3% strongly disagree);

-Personal web space for working with videos (43,7% strongly agree and 34,5% simply agree; 18,4% disagree; 3,4% strongly disagree);

-Service for building my own audiovisual archives containing my own videos and those from third parties (42,7% strongly agree and 28,4% simply agree; 22,2% disagree; 7,4% strongly disagree).

These and related expectations concern more particularly the role of the (individual or collective) user as a producer and manager of an audiovisual archive (or channel) including activities such as creating and managing a web portal, up/downloading own or third partyvideos, etc. The objective of the ARA project is to provide such a service. -The use of multilingual resources, as more than 1/3 of users are working out of France and speak more than 25 different languages.

-Developing the loyalty and interest of customers by providing personal subscription and notifications features.

-Better help end users to find content of their interest by the use of semantic queries, direct access to relevant video segments, and the development of advanced access such as theme-based videos, video-encyclopedia, etc.

-Taking into consideration the needs of users, mainly coming from Research, Education and Culture, who are more concerned about the intellectual value than the commercial value of their content, by providing features for tracing the usages of their resources.

-Securing the sharing of videos and, this way, giving guarantees to third party videos owners.

-Providing tools for building analysis and publication templates dedicated to specific themes and contexts of use: support for teaching, promoting sciences and culture, improving the exchanges between researchers, teachers and students.

1

  The social and economic context for the sharing of video resources in a non-profit setting. A preparatory study for the development of the community research platform ARA Campus (Campus of the Audio-visual Research Archives) Valérie Legrand-Garlarza (INALCO, FMSH -ESCoM-AAR) Peter Stockinger (INALCO, FMSH -ESCoM-AAR) Francis Lemaitre (FMSH -ESCoM-AAR) Fondation Maison des Sciences de l'Homme (FMSH) Equipe Sémiotique Cognitive et Nouveaux Médias (ESCoM) -Programme « Archives Audiovisuelles de la Recherche » (AAR) ............................................................................................................................................... 2) OUTPUT .............................................................................................................................................................. 3) DESCRIPTION AND SIZE OF MARKET .................................................................................................................. 3.1 WEB VIDEO PLATFORMS IN SCIENTIFIC AND CULTURAL FIELDS ..................................................................... 3.2 PROFILE OF THE TARGET MARKET ............................................................................................................... 3.3. NEEDS OF THE TARGET MARKET ................................................................................................................. 3.4 STRATEGY OF THE ARA CAMPUS TO ANSWER TO THE MARKET'S NEEDS .................................................... 4) RESULTS OF A DURING 2009/2010 ONLINE SURVEY ON THE RELEVANCY OF THE ARA CAMPUS FOR THE TARGET MARKET ..................................................................................................................................................

Fig. 1 :

 1 Fig. 1: ARA Campus Services

Fig. 2 :Fig. 3 :

 23 Fig. 2: Gender distribution of the survey

Fig. 5 :

 5 Fig. 5: Consultation Frequency

Fig. 8 :

 8 Fig. 8: Visiting the ARA, user want…

Fig. 9 :

 9 Fig. 9: ARA Audiovisual Content Objectives

Fig. 10 :

 10 Fig. 10: Formats and Genres of Publication

Fig. 11 :

 11 Fig. 11: Expected services

  Technological convergence is the result of digital technology which provides different types of content (audio, video, text) on multiple technologies as the computer, mobile telephone, television. Internet practice diversity by converge all previous media that he welcomes and broadcasts. While until the early 2000s, the canvas was constituted 95% of hypertext, the web has quickly overwhelmed by the arrival of successive sounds, music and finally of the moving image with YouTube and Dailymotion video sharing platforms.

	10 http://www.rechercheisidore.fr/
	11 http://www.revues.org/
	12 http://hal.archives-ouvertes.fr/
	13 http://hypotheses.org/
	14 http://calenda.org/
	15

(See the report of the European Parliamentary Assembly on audiovisual cultural heritage (May 09, 2012): "Doc.12929: Protection and provision of audiovisual cultural heritage": http://assembly.coe.int/ASP/Doc/XrefViewHTML.asp?FileID=18707&Language=FR, following the European Convention on the protection of the audiovisual heritage (ETS No. 183))

Mainly the two ANR (Agence National de la Recherche) founded projects SAPHIR (2006 -2009) and ASA-SHS (2008 -2011) and the two FP6 founded projects LOGOS (2006 -2009) and DIVAS (2007 -2009)

http://ccsd.cnrs.fr/

http://www.cerimes.fr/

http://www.canal-u.tv/

http://www.universites-numeriques.fr/

http://www.uoh.fr/front

http://www.tge-adonis.fr/

The second vague of the survey will try to find trustful ("quantifiable") data for this. However, there are different indirect evidences for the rather important popularity of the ARA program as can be shown through an impressive number of collected and online published endorsements from individuals and institutions (http://semioweb.msh-paris.fr/corpus/aar/fr/_petitionMessages.asp), the inclusion of the ARA portal in many university and research labs portals, etc.

/a. videos.html CRDO -The Description of Oral resource Centre http://crdo.risc.cnrs.fr/exist/cr do/ Resource centre attached to the CNRS (National Centre for Scientific Research): open archive and documentation centre on oral data Research Research Laboratory LACITO -Languages and Civilizations in Oral Tradition http://lacito.vjf.cnrs.fr/ http://lacito.vjf.cnrs.fr/archivag e/presentation.htm Audiovisual archives of students and researchers. Research Research Laboratory CERLOM -Centre for research on the literature and http://www.cerlom.fr/ Audiovisual archives of students and researchers, but not yet exploited. Research Audiovisual archives and multimedia projects. Research


Sofia H Rodrigues

Anne Forret

F Montjovet

M Lance

Thierry Gauthier

Sofia S Rodrigues

CFD modeling of riser with Group B particles

Keywords: CFB, riser, Geldart Group B, CFD, sphericity, hydrodynamics

come   L'archive ouverte pluridisciplinaire

Introduction

Chemical Looping Combustion (CLC) is an oxy-combustion like technology where oxygen carrying particles are used to supply oxygen for combustion [START_REF] Yazdanpanah | Investigation of a Chemical Looping Combustion (CLC) Configuration with Gas Feed[END_REF][START_REF] Hossain | Chemical-looping combustion (CLC) for inherent separation -a review[END_REF][START_REF] Adánez | Progress in Chemical-Looping Combustion and Reforming technologies[END_REF]. The CLC process comprises two separate reactors, an Air Reactor and a Fuel Reactor. The oxygen carrier circulates between the Air Reactor, where it is oxidized in contact with air, and the Fuel Reactor, where it is reduced by burning fuels. CO 2 can be easily recovered from the Fuel Reactor flue gases after steam condensation, since it is not diluted by N 2 . Based on energy penalty criteria, the CLC process is considered as one of the most promising routes for CCS (Carbon Capture and Storage).

The Air Reactor, as developed by IFPEN and Total, is a riser type reactor where the oxygen carrier, a metal oxide, is transported upwards by the air flow as it is being oxidized. In order to minimize the energy penalty of the CLC process, it is necessary to minimize pressure drop across the reactor while simultaneously achieving efficient oxidation of the oxygen carrier. This requires good control of contact time between air and oxygen carrier along the riser and therefore, an accurate knowledge of solid concentration as a function of operating conditions.

The oxygen carriers being considered for the CLC process are particles belonging to Group B of the Geldart classification. Indeed, these types of particles allow the use of non-mechanical valves (like the L-valve) that are employed for solids flow control at very high temperatures (around 900°C) required for the CLC process [START_REF] Yazdanpanah | An experimental investigation of L-valve operation in an interconnected circulating fluidized bed system[END_REF]. In addition, Group B particles can be straightforwardly separated from unburned solid fuel at the Fuel Reactor exit based on size and density differences [START_REF] Bourgeon | Chemical Looping Combustion: Development status and perspectives[END_REF].

Most of the studies on riser hydrodynamic have been conducted with Group A powders, mostly for the FCC process [START_REF] Yang | Investigation on slip velocity distributions in the riser of dilute circulating fluidized bed[END_REF][START_REF] Yan | Scale-up effect of riser reactors (3) axial and radial solids flux distribution and flow development[END_REF]. However, Group B oxygen carrier particles are larger and heavier than FCC catalysts, which results in different overall flow behavior. There is a general lack of reliable modeling and experimental information in the literature on Circulating Fluidized Beds (CFBs) working with large materials. Furthermore, published work on Group B particles does not focus on the impact of particles shape [START_REF] Chew | Cluster characteristics of Geldart Group B particles in a pilot-scale CFB riser. I. Monodisperse systems[END_REF][START_REF] Chew | Reverse core-annular flow of Geldart Group B particles in risers[END_REF]. Further studies are required for the reliable scale-up and optimization of the CLC process.

The broader goal of this study was, therefore, to gather basic experimental data on a circulating fluidized bed riser with different kinds of Group B particles closely related to CLC applications. The experimental results can then be used to improve understanding of gas-particle interactions and the real impact of particle properties such as size, density and sphericity, on riser flow. Experimental data, using three different Group B solids can be found on [START_REF] Rodrigues | Flow modeling of Group B particles in the transport regime for CLC[END_REF]. The development of a 1D model of the riser and the development of a new drag force correlation for Group B solids has been achieved [START_REF] Rodrigues | Riser hydrodynamic study with different Group B powders[END_REF].

In this paper, the principal results concerning sand and glass beads are recalled and results concerning local information are presented. Afterwards, simulation results by a commercial CFD code of the riser with Group B particles are discussed. The final objective of this study is to evaluate the ability of Barracuda to simulate the solid flow inside the riser and the impact of particle properties such as sphericity. Comparison of simulation results with experimental profiles allows the evaluation of the implemented drag law.

Experimental set-up

All experimental tests were conducted in a large scale cold flow circulating fluidized bed built at IFPEN Lyon. The cold flow mock-up is composed of two solid loops with a central riser, the primary loop being used for all stationary hydrodynamic tests. Besides the riser, both loops consist of a fluidized bed, a standpipe, an orifice valve, primary and secondary cyclones, and a filter as shown on Fig. 1.

The steel riser is 18 m high and has a 30 cm diameter. The riser is grounded and has a blind-T exit where slide valves can be inserted in each branch, in order to isolate one loop from another. Air is fed in the riser by a central jet with a diameter of 0.1 m. Air relative humidity is controlled and kept constant at around 12%. Gas velocity is determined from the values of the flowmeter feeding the riser.

A fluidization ring, operating around 10•umf, is placed at the bottom of the riser. Particles are fed 0.5 m below the main gas inlet pipe to ensure symmetrical solid flow conditions downstream the riser.

Several pressure taps, located along the riser, allow the measurement of axial pressure profiles. At 12 m, extraction probes can be inserted in the riser for local solid flux measurements.

On the bottom of the standpipe, there is an interchanging orifice valve with aeration injections. The valve and aerations allow for the solid flux to be controlled. Solid mass fluxes are measured by a batch operation and are then correlated directly to riser pressure drop for a given gas flow rate. The batch operation consists on discharging the main fluidized bed of the CFB into the secondary fluidized bed through the riser and by recording bed level as a function of time. Correlations were developed for each solid and each gas velocity, to determine solid flux during normal operation from the continuously measured riser pressure drop. More information can be found in [START_REF] Rodrigues | Flow modeling of Group B particles in the transport regime for CLC[END_REF].

Extraction probes

Flux of solids can be measured inside the riser using extraction probes [START_REF] Chew | Reverse core-annular flow of Geldart Group B particles in risers[END_REF][START_REF] Herb | Solid mass fluxes in circulating fluidized beds[END_REF][START_REF] Zhang | Momentum probe and sampling probe for measurement of particle flow properties in CFB boilers[END_REF]. The probe tip, with an angle of 90°, is inserted in the riser either facing upwards or downwards to measure downflow or upflow of solids, respectively. Net flux is defined as the difference between the upflow and the downflow of solids. The extraction probes were operated at pseudo-isokinetic conditions, i.e., the vacuum velocity at the tip of the probe equals the superficial gas velocity in the riser [START_REF] Zhang | Momentum probe and sampling probe for measurement of particle flow properties in CFB boilers[END_REF][START_REF] Bader | Gas solid flow patterns in a 30.5 cm diameter circulating fluidized bed[END_REF][START_REF] Kruse | 2D gas and solids flow prediction in circulating fluidized beds based on suction probe and pressure profile measurements[END_REF]. The complete extraction system is shown on Fig. 2. Suction rate is controlled by a rotameter connected to the solids collection pot that sits on top of an electronic scale. The measurement duration is controlled with a standard stopwatch.

During the first extraction measurements, plugging issues were found for several experimental conditions. Plugging was detected all along the probe. These problems are not well documented on literate mostly because most studies focus on Group A particles, which are more easily transported.

In an attempt to solve these issues, different designs of extraction probes were tested. The initial probe (probe (a) on Fig. 3) has an 8 mm inside diameter and a quite severe angle to place the probe tip perpendicular to the solids flow. The solids travel 14 cm vertically and 44 to 50 cm horizontally to reach the collection pot. The line connecting the extraction probe to the collection pot has the inside diameter of 8 mm. A first attempt was made to solve the plugging issues a probe with a less abrupt angle, that would improve the solids passage (probe (b) on Fig. 3). This probe did not allow measurements to be made over the total riser diameter. However, the plugging problems persisted, which led to a probe (probe (c) on Fig. 3) with a smaller horizontal portion of 33 cm. The last probe tested (probe (d) on Fig. 3) had a smaller horizontal portion and a wider entrance of 9,5 mm, but the same 8 mm inside diameter on the rest of the probe.

The last probe tested was the one that presented less plugging issues. Therefore, probe d was used for all the ensuing tests and the detailed geometry is represented on Fig. 4. This probe has a tip of 9.5 mm diameter, an inner diameter of 8 mm, a vertical portion of 14 cm and a horizontal portion of 33 cm.

Operating conditions and materials

A wide range of operating conditions have been tested on the large scale CFB, but this paper will focus on two experimental conditions corresponding to potential operating conditions encountered in the air reactor of the CLC process in the following ranges: gas velocities of 8 and 10 m/s and solid fluxes of about 55-60 kg/m²s Additional details and results can be found in [START_REF] Rodrigues | Flow modeling of Group B particles in the transport regime for CLC[END_REF].

The reported experimental tests were conducted with two different monodispersed Group B particles of the Geldart classification [START_REF] Geldart | Types of gas fluidization[END_REF]: sand and glass beads. The different materials were chosen to study the impact of particle sphericity on riser flow. Microscopic images of sand and glass beads can be seen on Fig. 3 and Fig. 4, respectively. Particle properties for irregularly shaped sand and for spherical glass beads can be seen on Table 1. The mean diameter presented is the mean Sauter diameter calculated from several PSD measurements at experiments equilibrium state. Fig. 5 shows the particle size distribution (PSD) for the powders at equilibrium state. More detailed information can be found in [START_REF] Rodrigues | Flow modeling of Group B particles in the transport regime for CLC[END_REF].

The sphericity of a particle is defined as the ratio of the surface area of a sphere (with the same volume of the particle) to the surface area of the particle. Sphericity was determined experimentally through the method suggested by Kunii [START_REF] Yazdanpanah | Investigation of a Chemical Looping Combustion (CLC) Configuration with Gas Feed[END_REF][START_REF] Kunii | Fluidization Engineering[END_REF] and that uses the Ergun equation (see equation [START_REF] Bader | Gas solid flow patterns in a 30.5 cm diameter circulating fluidized bed[END_REF].

∆P h = 150 µ 𝑔 •𝑢 𝑔 (𝜙•𝑑𝑝 2 ) (1-𝜀) 2 𝜀 3 + 1.75 𝜌 𝑔 •𝑢 𝑔 2 𝜙•𝑑𝑝 (1-𝜀) 𝜀 3
Eq.1

The value of sphericity is calculated through the fit of the Ergun equation to experimental points of pressure drop and voidage, at fixed gas velocity. These data points were obtained at a variety of gas velocities (inferior to the minimum fluidization velocity) by tapping the column between pressure drop measurements, to achieve different values of voidage.

As expected, sand particles and glass beads exhibit a large difference in particle sphericity (see Table 1). Based on literature, lower particle sphericity means higher drag force coefficient [START_REF] Tran-Cong | Drag coefficients of irregularly shaped particles[END_REF][START_REF] Xu | Effects of particle properties on flow structure in a 2-D circulating fluidized bed: Solids concentration distribution and flow development[END_REF]. As shown in Table 1, terminal velocity of a single particle was calculated with the Haider & Levenspiel [START_REF] Yang | Handbook of Fluidization and Fluid-Particle Systems[END_REF] correlation, with (u tϕ ) and without (u t ) particle shape correction.

Results and discussion

Pressure profiles

Solid hydrodynamic behavior inside the CFB riser was characterized through the measurement of axial pressure profiles. Profiles were obtained with the help of several pressure taps located along the riser at different experimental conditions for sand and glass beads [START_REF] Rodrigues | Flow modeling of Group B particles in the transport regime for CLC[END_REF]. A focus on the bottom 5 m of the riser was made to better characterize the acceleration region. Axial pressure profiles are shown on Fig. 6 for sand and glass beads at 8 m/s and 55 kg/m²s and on Fig. 7 at 10 m/s & 60 kg/m²s. Pressure at each elevation H is computed relative to the pressure at the riser gas inlet. Therefore, pressure profiles represent the difference between P 0 -P H as a function of height H. The direct comparison between similar operating conditions aims at identifying the impact of sphericity on riser hydrodynamics.

The experimental axial pressure profiles exhibit the same trend, regardless of operating conditions. Therefore, the riser can be divided into three zones, according to pressure drop evolution. At the bottom of the riser, the nearly exponential increase of the pressure drop suggests the presence of a dense solid phase. In this region, particles are being accelerated by the inlet gas producing high pressure drop that can be as high as 50% of the total riser pressure drop. For this reason, more data was collected on the first 5 m of the riser. Higher in the riser, in between 5 and 13 m approximately, pressure increases linearly with riser height. This evolution suggests that after a given height, particles will be fully accelerated and the flow becomes established. This nonlinear evolution of pressure in the riser is consistent with literature findings [START_REF] Chew | Reverse core-annular flow of Geldart Group B particles in risers[END_REF][START_REF] Zhou | Hydrodynamics of gas-solid flow in the circulating fluidized bed reactor for dry flue gas desulfurization[END_REF][START_REF] Grace | Circulating Fluidized Beds[END_REF].

Finally, close to the riser exit (above 13 m) pressure gradient increases due to the riser outlet configuration which decelerates particles. The blind-T pressure drop is not shown, but its impact is significant on the last two pressure points of the riser profile. Since velocities are moderate, the impact is also moderate. Pressure drop generated by the riser exit is dependent on the exit geometry [START_REF] Gupta | Evaluation of the gas solid suspension density in CFB risers with exit effects[END_REF][START_REF] Kim | Effects of solids feeder and riser exit configuration on establishing high density circulating fluidized beds[END_REF]. Therefore, riser upper part results were not taken into account in further calculations.

As already described in [START_REF] Rodrigues | Riser hydrodynamic study with different Group B powders[END_REF], for identical operating conditions, sand pressure profiles are about twice as high as glass beads pressure profiles. This is a very large, significant and unexpected difference.

Since density for sand and glass beads is almost identical, the results suggest a substantial impact of particle nature, i.e. diameter or sphericity, on riser hydrodynamics. Consequently, results imply that particle sphericity should be accounted for when studying solid flow inside the riser.

The development of a new cross section averaged drag force using the axial pressure profiles as a base to study the flow inside the riser has been made [START_REF] Rodrigues | Flow modeling of Group B particles in the transport regime for CLC[END_REF]. The developed drag force correlation applies to a 1D model. In this paper, the analysis of drag force expressions for multi-dimension starts. Because it is much more difficult to derive a multi-dimensional drag force than in 1D, an evaluation of the performance of the existing drag force laws is first needed.

Radial solid flux profiles

Radial solid flux profiles were obtained for sand and glass beads at 12 m which corresponds to the developed region of the riser. Measurements were conducted along the riser radius at 12 different positions. In a few cases, profiles were conducted over the whole diameter. Results are not reported here but radial symmetry was found [START_REF] Rodrigues | Flow modeling of Group B particles in the transport regime for CLC[END_REF]. The measurements of solid flux were repeated at identical conditions and radial positions with the probe facing upwards and facing downwards. This method allows the measurement of upflow and downflow of solids in the vertical direction in the riser. Fig. 10 shows the upflow and downflow radial solid flux profiles for sand at 60 kg/m²s and gas velocity of 10 m/s, where zero corresponds to the center of the riser and 0.15 m corresponds to the riser wall. It can be seen how the solid flow is not homogeneous over the riser diameter. The majority of solids upflow is made in the center of the riser. The flow of solids moving upwards decreases rapidly with the distance from the center. Close to the riser walls, there are solids moving downwards. This solid distribution suggests the presence of the core-annulus regime in the developed region of the riser. The core-annulus regime is well established in the literature as typical solid flow inside the riser [START_REF] Bader | Gas solid flow patterns in a 30.5 cm diameter circulating fluidized bed[END_REF][START_REF] Rhodes | Particle motion at the wall of a circulating fluidized bed[END_REF][START_REF] Karri | A comparison of annulus solids flow direction and radial solids mass flux profiles at low and high mass fluxes in a riser[END_REF].

Glass beads radial net solid flux profile at 60 kg/m²s and gas velocity of 10 m/s is shown on Fig. 11.

The net solid flux is obtained by subtracting the downward solid flux to the upward solid flux at each point. The core-annulus regime is found for glass beads in the developed region as well as for sand.

High solid flux moves upwards in the center of the riser as a smaller amount of solids moves downwards at the riser walls. The same conclusion can be made from Fig. 12 of the radial net solid flux profile at 57 kg/m²s and gas velocity of 8 m/s. However, when comparing glass beads profiles at similar solid flux and different gas velocity (see Fig. 13), solid downflow of solids close to the walls is more pronounced for the smaller gas velocity.

To study the impact of particle sphericity on riser radial flow, a comparison of the radial net solid flux profiles of sand and glass beads at 60 kg/m²s and gas velocity of 10 m/s is made on Fig. 14. It can be seen that sand presents higher solid flux moving upwards in the center and moving downwards at the walls. A smaller amount of solids moving downwards and a slightly smaller annulus region would be coherent with the smaller pressure drop profiles presented by glass beads.

As discussed before, on the axial pressure drop profiles, sphericity seems to have an important and unexpected impact on solid flow inside the riser.

CFD modeling

Barracuda

Barracuda ® is a hybrid Eulerian-Lagrangian model developed by Computational Particle Fluid Dynamic's (CPFD's). The gas is described as a continuous phase in the Eulerian description, where the Reynolds Averaged Navier Stokes equations (RANS) are used. The Lagrangian description of the solids considers it as a disperse phase where the equations for each particle will be solved using Newtonian equations [START_REF] Gupta | Modeling of Fluid Catalytic Cracking Riser Reactor: A Review[END_REF]. The energy of the two phase mixture is conserved by exchange terms in the gas phase mass, momentum and energy equations [START_REF] Ryan | Multi-phase CFD modeling of solid sorbent carbon capture system[END_REF]. Barracuda uses a multiphase particle-in-cell approach to decrease calculation time [START_REF] Snider | An Incompressible Three-Dimensional Multiphase Particle-in-Cell Model for Dense Particle Flows[END_REF][START_REF] Chen | CPFD simulation of circulating fluidized bed risers[END_REF]. This approach consists in representing a large number of real particles by a smaller number of computational particles. It is in this computational particles that the mass and momentum conservation laws are calculated.

The volume averaged mass and momentum equations, that describe the continuous fluid phase are shown below [START_REF] Chen | CPFD simulation of circulating fluidized bed risers[END_REF].

𝜕�𝜀 𝜌 𝑔 � 𝜕𝑡 + ∇�𝜀 𝜌 𝑔 𝑢 𝑔 � = 0 Eq.2 𝜕�𝜀 𝜌 𝑔 𝑢 𝑔 � 𝜕𝑡 + ∇�𝜀 𝜌 𝑔 𝑢 𝑔 𝑢 𝑔 � = -∇p -F + 𝜀 𝜌 𝑔 𝑔 + ∇�𝜀 𝜏 𝑔 � Eq.3
The rate of momentum transfer per unit volume between the fluid and the particle phases (F) is defined as:

𝐹 = ∬ 𝑓𝑚 �𝐹 𝑡 �𝑢 𝑔 -𝑢 𝑠 � - 1 𝜌 𝑠 ∇𝑝� 𝑑𝑚𝑑𝑣 Eq.4
The Lagrangian method is used to model the particles. This method considers a control volume in which the velocity of the control volume surface equals the local fluid velocity. The numerical particles in Barracuda contain a number of real particles with identical properties located at a certain known position. Particle acceleration is defined on equation 5.

𝑑𝑢 𝑠 𝑑𝑡 = 𝐹 𝑡 �𝑢 𝑔 -𝑢 𝑠 � - 1 𝜌 𝑠 ∇𝑝 + 𝑔 - 1 (1-𝜀)𝜌 𝑠 ∇𝜏 𝑝 Eq.5
Solids movement is given by the displacement equation shown on equation 6.

𝑑𝑥 𝑠 𝑑𝑡 = 𝑢 𝑠 Eq.6
Particle properties are mapped from the particles to the Eulerian grid to obtain grid-based properties such as the particle volume fraction at cell i.

𝜀 𝑠𝑖 = 1 𝑉 𝑖 ∑ 𝑉 𝑠 𝑛 𝑝 𝑁 𝑝 1 𝑆 𝑝𝑖 Eq.7
And at cell i, the interphase momentum transfer is defined as:

𝐹 𝑖 𝑛+1 = 1 Ω 𝑖 ∑ 𝑆 𝑖 �𝐹 𝑡 �𝑢 𝑔,𝑠 𝑛+1 -𝑢 𝑠 𝑛+1 � - 1 𝜌 𝑠 ∇𝑝 𝑝 𝑛+1 � 𝑝 𝑛 𝑝 𝑁 𝑝 Eq.8
A numerical particle in Barracuda contains a number of real particles that can be adjusted. Therefore, the "number density" used in Barracuda can be described as the total number of real particles in the feed divided by the number of real particles per numerical particle and by solid hold up.

In Barracuda, a series of drag force correlations can be used to determine the force acting on a particle by the fluid. The drag function chosen for the glass beads simulations conducted in this work is the Wen-Yu and Ergun correlations. Because the Wen-Yu correlation is more adapted for more dilute flows and the Ergun correlation is better for higher solids concentration flows, this is an appropriate choice for modeling the riser [START_REF] Chen | CPFD simulation of circulating fluidized bed risers[END_REF][START_REF] Gidaspow | Multiphase Flow and Fluidization: Continuum and Kinetic Theory Descriptions[END_REF].

The equations used to determine drag force as a function of solids concentration are detailed below.

𝐹 𝑡 = 𝐶 𝑑-𝑊&𝑌 The range of use of each equation is relative to the close packing solid concentration. A transition (equation 9) was developed to prevent numerical problems on the transition phase.

To simulate sand particles, that present smaller sphericity than one, the non-spherical Haider-Levenspiel model in Barracuda was used. The drag force on a particle is calculated by the following expression.

𝐹 𝑡 = 𝐶 𝑑 The drag force coefficient takes into account particle sphericity (ϕ) as seen on equation 14.

𝐶 𝑑 = 𝜀 -2.65 � 24 𝑅𝑒 �1 + 8.1716𝑒 -4.0655𝜙 𝑅𝑒 (0.0964+0.5565𝜙) � + + 73.69𝑒 -5.0748𝜙 𝑅𝑒 𝑅𝑒+5.378𝑒 6.2122𝜙 � Eq.14

In Barracuda, solids are defined as part of a "Particle Species". Each "Particle Specie" is defined by the material, particle density, particle size and particle sphericity. In this work no kinetics were studied inside the riser. Therefore, particle material is of no importance for simulation results. The "Particle Specie" size is defined by the real particle size distribution function for each solid studied.

Geometry

To simulate the hydrodynamics inside the riser with Group B solids, a simplified version of the experimental riser was used. The riser geometry used in Barracuda simulations does not include the blind-T exit. Therefore, comparison to experimental results will be made in the acceleration and developed regions only. The riser bottom is defined with the central air jet as shown on Fig. 15.

The small fluidization ring on the bottom of the real riser was not included in the numerical geometry.

However, to simulate fluidization on the bottom, air injection points were created where the ring should be.

Riser geometry was created with CATIA ® software, a 3D CAD program. Fig. 16 shows the CAD file (a), a zoomed view of the riser bottom (b) and a transparent image of the riser bottom (c). A grid can be generated automatically from an initial set of major grid lines over the geometry input. Then, the initial grid was adjusted to the riser geometry. For Barracuda it is very important to create a grid as uniform as possible with very small differences between neighboring cells. From the adjusted grid, Barracuda generated the mesh over the riser geometry.

In Barracuda two numbers of cells are displayed. The total number of cells includes all cells created in the grid, independently of the input geometry. The real number of cells are the ones created within the input geometry that will be part of the fluid domain. Therefore, the total number of cells displayed includes the real number of cells and the number of null cells, that are outside the fluid domain. The mesh system shown above has generated 186760 real and null cells. The cells inside the riser are cubes with sides of 0.03 m.

To simplify the simulation case, it was chosen not to describe the reactor top exit. The goal was only to evaluate the capability of the code to simulate a riser with Group B particles. Because geometry is simple, no mesh related problems were encountered.

The "number density" controls the rate at which computational particles are fed through the boundary, by increasing it the number of clouds per mesh cell will increase. Simulations were run with an initial "number density" of 200, which was increased to 700 in some simulations in an attempt to improve the match between the inlet and the outlet solid flux. The total number of particles was about 9.1 x 10 9 and the number of numerical particles, or clouds, of about 1.7 x 10 6 . A study on the effect of the number density was not made in this work, the values used were chosen so the mass balance would of the riser would match.

Boundary and initial conditions

Boundary conditions allow for the definition and control of the entries and exits of the 3D mesh. The user chooses the location of the boundary conditions to define whether a discontinuity on the geometry wall is a flow inlet or outlet. There are also used to impose pressure, solid or gas flow rate.

The riser geometry used in all simulations has three boundary conditions, as shown on Fig. 17. The riser top, without exit geometry, is defined as flow outlet and pressure condition is imposed at the top of the riser. The top of the inlet air jet is defined as a gas entry where the gas flow rate is imposed.

And the angled solids feed line is defined as solid and gas entry.

The state of the riser, gas and solids at the start of the simulations (initial conditions) will determine how long the system will take until reaching steady state. In order to decrease simulation time, at the initial condition the riser bottom is full of particles close to minimum fluidization solid concentration (0.5), as shown on Fig. 18.

The inlet air jet is defined as full gas flow rate as initial condition.

Before starting Barracuda simulations, it is known in advance the information needed to compare to experimental results available. Therefore, a series of points are set along the riser to obtain local information about pressure, particle velocity and solids concentration, called transient data points. Ten points are set along the riser axis to determine the axial pressure profile of the riser. And ten points are set over the diameter of the riser at 12 m high to determine radial particle concentration and velocity.

The information collected on the transient data points can be averaged over time since calculation convergence is reached and then be used to compare experimental and simulation results.

The time step of simulations varied between 5x10 -4 and 1x10 -2 s, auto-adjusted by Barracuda.

Glass beads simulations

Glass beads flow inside the riser were simulated with the Wen-Yu/Ergun drag force correlation for 200 seconds. The operating conditions were chosen to match an experimental case for glass beads. The simulation was done at gas velocity of 10 m/s, solid flux 60 kg/m²s and a top pressure of 109000 Pa.

The evolution of pressure drop with simulation time along the riser is presented on Fig. 19.

It can be seen that it takes about 75 s (average between 65 to 85 s) to approach the final pressure drop profile. However, until 150 s (average between 140 to 160 s) higher pressure drop on the first 5 m can be seen, indicating a flow not yet fully developed. With time solid concentration stabilizes along the riser. After 150 s, steady state condition is assumed and pressure drop data was therefore averaged over the period 150-200 s to compare with experimental results. To verify simulation convergence, the inlet and outlet solid fluxes were also compared to ensure there is no mass balance changes.

Fig. 20 shows the pressure profile of the riser (as a line) resulting from the Barracuda simulation and averaged over the last 50 s (dotted line on Fig. 19).

As stated before, Barracuda has as an entry point, the pressure at the top of the riser. The pressure at the top is imposed by the respective boundary condition. This pressure value can only be estimated from the experimental results because the value is influenced by the exit geometry. As the riser geometry in Barracuda does not have the blind T exit, pressure drop at the top should be lower.

The pressure at the top of the riser assigned for the simulation was slightly too small. Direct correction of the results to match pressure at 12 m was made. The pressure outlet adjustment is minor (1.2 kPa)

and the impact on simulations should be negligible.

It can be seen from Fig. 20 that the experimental pressure profiles obtained with glass beads is very close to the one obtained from the Barracuda simulation at identical conditions.

Barracuda is able to correctly predict the slope of the first meter of the riser and the different slope of the accelerated zone. The CFD code is able to simulate the acceleration zone at the bottom of the riser as the experimental pressure profiles showed. The evidence of the bottom region with higher solids concentration can also be seen on Fig. 21. The solids concentration mapping shows the solids inlet and the lower riser region where solid concentration can be very high due to particle acceleration.

A second glass beads simulation was made with the Wen-Yu/Ergun drag force correlation for 200 seconds. The simulation was done at gas velocity of 8 m/s, solid flux 54 kg/m²s and a top pressure of 106821 Pa. Fig. 22 shows the experimental pressure profile at identical conditions (pressure adjusted) as well as the Barracuda simulation.

The commercial CFD code is able to predict the bottom zone acceleration responsible for a great part of the total pressure drop. The difference in pressure drop (between 0.15 and 11 m) between the experimental profile and Barracuda is of 2 %.

Local vertical solid velocities over the riser diameter at 12 m from the gas inlet are shown on Fig. 23.

The radial solids velocity profile shows the high gradient existing between the center of the riser (at radial position of 0.15 m) and the riser walls. At the center of the riser particles travel at a faster velocity, approaching the gas velocity. Yet, close to the riser walls, vertical velocity is much smaller.

The profile suggests the existence of a core-annulus regime, where the particles travel upwards in the center. However, the Barracuda simulation does not predict a time-averaged downward solid flow close to the wall like it was shown on experimental results, by local flux measurements.

The radial profile of local voidage values at 12 m from the gas inlet is shown on Fig. 23.

It can be seen how the solids volume fraction is higher closer to the riser walls. The profiles seem slightly asymmetrical, this could be linked to average time used to calculate the profiles. Experimental results of radial solid flux have shown rather symmetrical radial profiles. This result shows how Barracuda can partially predict the core-annulus regime on the developed region of the riser.

From the local results of velocity and voidage shown above, the local solid flux can be calculated through equation 15.

𝑊 𝑠 = 𝑢 𝑠 • 𝜌 𝑠 • 𝜀 𝑠 Eq.15

To determine the values presented on Fig. 24, the values of solid flux were calculated for each point and then divided by the integrated value of the solid flux, 57 kg/m²s.

The values of dimensionless local solid flux from the Barracuda simulation are smaller than the experimental results. Because there is experimentally downward solids flow on the wall, there has to be higher upward solid flux in the center to obtain a similar value of integrated solid flux. Considering that Barracuda does not predict averaged downward solid flow at the wall, a flat profile, like the one shown on Fig. 24, would be expected. The difficulty on predicting a correct core-annulus flow in the riser may partially come from the lack of cluster formation and interaction. Yang et al. [START_REF] Yang | CFD simulation of concurrent-up gas-solid flow in circulating fluidized beds with structure-dependent drag coefficient[END_REF] revealed CFD simulations where the core-annulus regime was found in a 2D, 10 m riser with fine particles (54 µm). However, negative solid velocities were found only at 3. 5 m high. At 8.75 m, velocity and voidage profiles became much flatter, like in this work. The author recognizes that the difficulty in simulating cluster formation impacts CFD results.

One could also argue that the absence of blind-T exit in the simulations may impact the riser flow as well. However, based on experimental pressure profiles, results suggest that riser exit effect does not affect the flow structure in the first 13 m. Therefore, the lack of blind-T is not enough to explain differences observed between experimental and simulated profiles. It can be seen that Barracuda cannot predict the pressure drop generated by the non-spherical particles.

The acceleration zone may present a correct slope initially compared to the experimental results, butacceleration length is clearly under predicted. Barracuda generates a shorter dense bottom region and therefore, smaller pressure drop in this zone.

In the developed region, Barracuda predicts an overall smaller pressure drop than the experimental results. It can be seen from the smaller slope of the Barracuda pressure profiles that the impact of the particle sphericity seems to be underpredicted by the CFD code.

The difference in pressure drop (between 0.15 and 11 m) between the experimental profile and Barracuda simulation is of 43 %. The conclusion made from the glass beads simulations, that the coreannulus regime is only partially predicted may also be a reason for the poor performance of Barracuda with sand particles. It was seen experimentally that the annulus region of sand flow is bigger than for glass beads and should account for a great portion of the pressure drop along the riser. If Barracuda cannot correctly predict the core-annulus regime in the riser then the pressure drop will be systematically underpredicted.

Conclusion

Experimental tests were conducted with two different Group B particles on a large scale CFB to study the impact of particle shape on riser hydrodynamic. Simulations at identical conditions were then conducted using a commercial CFD code, Barracuda.

For identical operating conditions, sand and glass beads experimental axial pressure drop profiles show a difference of approximately 50%. Pressure drops for glass beads, with sphericity of 1, are consistently smaller than those of sand, with sphericity of 0.83. The results, for a wide range of operating conditions, suggest a substantial impact of particle shape on the flow inside the riser. Such impact could also be detected on radial solid flux profiles. In the developed region, the flow can be characterized by a core-annulus structure. Particle sphericity seems to impact the structure of the coreannulus regime, suggesting that lower sphericity results in larger annulus region. Differences seen on the axial pressure profiles of sand and glass beads would be explained in part by the larger annulus region.

Barracuda has been shown to predict quite well the pressure drop profiles of glass beads. The Wen & Yu/ Ergun drag force correlation for spherical particles is capable of simulating glass beads pressure profiles along the riser.

However, the CFD code has not been able to accurately predict pressure profiles for sand particles.

The use of the Haider and Levenspiel model for non-spherical particles seems to underestimate the pressure drop generated by particles with sphericity of 0.83.

The core annulus regime is partially predicted by Barracuda, with significant deformation of radial particle velocity and voidage profiles. However, the downward solids flow at the wall seems underpredicted and the radial solid flux profiles are quite flat. This result could be the effect of several parameters, like the drag force correlations used but also from mesh impact.

In the present work, standard drag correlations and CFD simulation parameters were used. Based on the discrepancy between experimental results and simulations, more detailed investigations should be conducted in order to evaluate, for instance, the impact of alternative drag correlations and select more appropriate closure equations.

Notation

4. 5

 5 Sand simulationsThe flow of sand particles inside the riser were simulated with the Haider & Levenspiel drag force correlation for 170 seconds. Steady state was reached after around 100 s. The simulation was done at gas velocity of 10 m/s, solid flux 60 kg/m²s and a top pressure of 113000 Pa. Fig.25shows the comparison between the Barracuda simulation and the corresponding experimental results.

Fig. 1 -

 1 Fig. 1 -Schematic representation of the cold flow mock up used in the present work.

Fig. 2 -

 2 Fig. 2 -A schematic view of the extraction system collecting particles from the riser (on the right).

Fig. 3 -

 3 Fig. 3 -Different extraction probes tested in this work.

Fig. 4 -

 4 Fig. 4 -Detailed geometry of the extraction probe used in this work.

Fig. 5 -

 5 Fig. 5 -Microscopic image of sand particles.

Fig. 6 -

 6 Fig. 6 -Microscopic images of glass beads particles.

Fig. 7 -

 7 Fig. 7 -Particle size distribution at equilibrium state for sand, and glass beads.

Fig. 8 -

 8 Fig. 8 -Axial pressure drop profiles for sand and glass beads at gas velocity of 8 m/s and solid flux of 55 kg/m²s.

Fig. 9 -

 9 Fig. 9 -Axial pressure drop profiles for sand and glass beads at gas velocity of 10 m/s and solid flux of 60 kg/m²s.

Fig. 10 -

 10 Fig. 10 -Upwards and Downwards radial solid flux profiles for sand at 10 m/s and solid flux of 60 kg/m²s.

Fig. 11 -

 11 Fig. 11 -Net radial solid flux profile for glass beads at gas velocity of 10 m/s and solid flux of 60 kg/m²s.

Fig. 12 -

 12 Fig. 12 -Net radial solid flux profile for glass beads at gas velocity of 8 m/s and solid flux of 57 kg/m²s.

Fig. 13 -

 13 Fig. 13 -Dimensionless radial solid flux profiles of glass beads at two different conditions.

Fig. 14 -

 14 Fig. 14 -Dimensionless radial solid flux profiles of sand and glass beads at 10 m/s and solid flux of 60 kg/m²s.

Fig. 15 -

 15 Fig. 15 -Schematic view of the riser with measurements used in Barracuda simulations.

Fig. 16 -

 16 Fig. 16 -Images of the CAD file as introduced on Barracuda.

Fig. 17 -

 17 Fig. 17 -Boundary conditions for all Barracuda simulations.

Fig. 18 -

 18 Fig. 18 -Initial solids condition for all Barracuda simulations, scale of solids concentration on left.

Fig. 19 -

 19 Fig. 19 -Pressure drop evolution with simulation time of glass beads.

Fig. 20 -

 20 Fig. 20 -Comparison between Barracuda simulation and glass beads experimental values of pressure along the riser at gas velocity of 10 m/s and solid flux of 60 kg/m²s.

Fig. 21 -

 21 Fig. 21 -Simulation still image of solid concentration at the bottom of the riser at 200 s.

Fig. 22 -

 22 Fig. 22 -Comparison between Barracuda results and glass beads experimental values of pressure along the riser at gas velocity of 8 m/s and solid flux of 54 kg/m²s.

Fig. 23 -

 23 Fig. 23 -Solid velocity radial profile (left axis) and solid fraction (1-ε) radial profile (right axis) 12 m from the gas inlet at gas velocity of 8 m/s and solid flux of 54 kg/m²s..

Fig. 24 -

 24 Fig. 24 -Comparison between experimental and Barracuda radial dimensionless solid flux at gas velocity of 8 m/s and solid flux of 54 kg/m²s..

Fig. 25 -

 25 Fig. 25 -Comparison between Barracuda results and sand experimental values of pressure along the riser at gas velocity of 10 m/s solid flux of 60 kg/m²s.

  𝐸𝑟𝑔𝑢𝑛 -𝐹 𝑡-𝑊𝑒𝑛&𝑌𝑢 � + 𝐹 𝑡-𝑊𝑒𝑛&𝑌𝑢 0.75𝜀 𝑚𝑓 < 𝜀 𝑠 < 0.85𝜀 𝑚𝑓

			3 8	𝜌 𝑔 𝜌 𝑠	�𝑢 𝑔 -𝑢 𝑠 � 𝑟 𝑝	𝜀 𝑠 < 0.75𝜀 𝑚𝑓	Eq.9
	𝐹 𝑡 =	𝜀 𝑠 -0.75𝜀 𝑚𝑓 0.85𝜀 𝑚𝑓 -0.75𝜀 𝑚𝑓	�𝐹 𝑡-Eq.10
	𝐹 𝑡 = 𝐹 𝑡-𝐸𝑟𝑔𝑢𝑛 = 0.5 � 180(1-𝜀 ) 𝜀 𝑅𝑒	+ 2�	𝜌 𝑔 �𝑢 𝑔 -𝑢 𝑠 � 𝑟 𝑝 𝜌 𝑠	𝜀 𝑠 > 0.85𝜀 𝑚𝑓	Eq.11
	Where the Wen & Yu drag force coefficient is defined by,
			⎧		24 𝑅𝑒	𝜀 -2.65	𝑅𝑒 < 0.5
	𝐶 𝑑-𝑊&𝑌 =	⎩ ⎨ 𝑅𝑒 𝜀 -2.65 (1 + 0.15𝑅𝑒 0.687 ) 0.44 • 𝜀 -2.65 24	𝑅𝑒 > 1000 0.5 ≤ 𝑅𝑒 ≤ 1000	Eq.12

Table 1 -

 1 Particle properties for sand and glass beads.

	Sand	Glass beads