Patrick De Wever
email: patrick.de-wever@mnhn.fr

François Baudin

Dolores Pereira

Annie Cornée

Grégoire Egoroff

Kevin Page

The importance of geosites and heritage stones in citiesa review by

Keywords: Geoheritage, geotourism, urban geology, heritage stones, geosites

Geology, as a scientific discipline, is often viewed as most applicable in high mountains or in deserts or coastal areas -or more generally in 'natural areas' where rock exposures are most conspicuousand, therefore, not to be experienced by most visitors and tourists. In contrast, most geoscientists are convinced that geology can be practiced on an everyday basis, as it is part of our daily life as a facet of the natural environment that humans have used for 100s of 1000s of years. Even in places where the natural world seems far from its original condition, one can still experience geology. This consideration is of increasing importance as today, more than half the world's population lives in towns and cities. In this context, we can still present geology to an interested public, through establishing leisure walks, either guided or using leaflets, easily carried booklets and even web 'apps'. The style chosen aims to be accessible to a broader public, but crucially, in a urban context, there should always be an aim to demonstrate the relationship between geology and society, as well as architecture and history. Indeed, the realization of many participants in such activities that building stones can belong to, and provide evidence of, both a natural and a build heritage can be a revelation.

Introduction

To many, geology is a subject most applicable to areas where rock exposures are most prominent, such as mountain, coasts and large natural open spaces such as deserts. In addition, geology is for most people, a discipline out of reach and accessible only to geologists, and hence disconnected from their everyday reality. This view can create barriersalmost as a sort of selfprotection from this supposedly inaccessible scienceand many people do not admit to an interest in geology, hence abandoning this mysterious 'dry' topic to specialists. They are convinced that geology is not a part of their daily lifea feeling probably strengthened by the fact that today, half of the world's population lives in the artificial environment of towns and cities. Many geological themes suffer from this 'grey reputation, including its cultural, educational, and touristic aspectsand sometimes this attitude is not helped by geologists themselves. As stated by the English landscape historian, Professor W.G. Hoskins (https://en.wikipedia.org/wiki/William_George_Hoskins): "Geologists have a habit of talking as dull and dusty as their rocks".

Despite its history of secular development and knowledge-contribution to the scientific and technological development of modern society, geology still attracts little attention from people who fail to perceive the time dimension of slow processes and the transformation they cause on the planet [START_REF] Clarke | Geology and the public at the Natural History Museum[END_REF][START_REF] Boulton | The earth system and the challenge of global change[END_REF][START_REF] Mansur | Popularización del conocimiento geológico: metodología del proyecto Caminhos Geológicos[END_REF]Mondéjar, 2008). However, if they can read them, there are some visible signs that can help, such as the commemorative plate of Figure 1, whose bending shape attests that rock can fold within a few decades, not necessarily just over millions of years. The usual long timescales, however, are not easily appreciated, since most geological phenomenona seem to occur spectacularly abruptly, for instance volcanic eruptions, landslides, tsunamis and earthquakes. There is also still a predominant view that geology is a science mainly related to the search for oil and minerals for the economic development of a country. It is also sometimes linked to pollution of the planet: as a well-known Earth-photographer once observed at a meeting during the 'International Year of Planet Earth' declared that geologists are responsible for all types of pollutants -heavy metals in soils, oil slicks, roads and raised levels of CO2 in the airwhilst ignoring that his plane was flying because all these gas, metals and plastics -which also made up his cameras Fig. 1. A commemorative plate on the Observatoire de Paris (14e arrondissement), fixed in 1672 at the time of the inaugural ceremony, but now distorting due to surface weathering processes. "Observatoire construit de 1667-1672 sur les plans de Claude Perrault1 , membre de l'Académie des sciences" The wall is comprises Lutetian limestone (Eocene) and is full of the molds of molluscan shells. © P. De Wever Some other examples can be find on walls of buildings telling that limestones are made of fossils, usually microscopic. However, one of the most incredible piece probably is the skull of a white shark of 5-6 meters long (a Lamniform, probably of Cretaceous age), which is clearly visible but almost ignored, and geologists do not dare to underline this important skull which could be carved out in a night (the reason why we do not provide here neither the address nor the name of the town, only that it is in France (fig. 2) Figure 2 : A stone with the skull of a shark used for facing a house

In a street of this town in France (we do not provide its name purposely) a pink Mesozoic limestone from Ravenne is visible. Being ignored nobody try to steal it. The detail of the left part of the skull show the quality of the preservation. © P. De Wever) Internationally, the geological content of national curricular has often been significantly reduced in both primary and secondary schools and, in consequence, many people have a very limited knowledge of the subject, confirming its inaccessibility. Although attempts at improving this situation have been made, including through international projects such as 'Geoschools ' (geoschools.geol.uoa.gr;[START_REF] Fermeli | Geoscience teaching and student interest in secondary schools-Preliminary results from an interest research in Greece, Spain and Italy[END_REF] and even proposals for an international Geoscience school syllabus [START_REF] King | The International Geosciences Syllabus and its development[END_REF], much work still has to be done to improve the background to geological education in schools. This is why most laypersons are unprepared for the interconnected world of the Earth system operating at all space and time dimensions [START_REF] Stewart | Earth stories: context and narrative in thecommunication of popular geosciences[END_REF].

This reputation also often impacts news and broadcast media and, therefore, only a limited collaboration with geoscientists exists, limiting diffusion of this science. But one has also to admit that the geological community globally often shows little interest in popularizing its subject -not a new phenomena as indicated by the Hosking's quote used above… However, it only requires a slightly closer look to realise just how geological matters are present in all people's lives, whether in the planning and occupation of towns and cities, in construction of roads and buildings, or in their leisure activities.

The UNESCO convention concerning the Protection of World Heritage of 1972 states that it is not possible to separate natural from built heritagealthough in the context of towns and cities where cultural heritage is prominent, the natural aspects of the same heritage is often forgotten, with only a few examples of the promotion of 'Urban geology' being notable (but including the 1996 volume 'Geology on your Doorstep' [START_REF] Bennett | Geology on your Doorstep: The role of urban geology in earth heritage conservation[END_REF] and the work of the London Geodiversity Forum (http://www.londongeopartnership.org.uk/downloads/LGAP%202014-2018.pdf)).

The aim of this paper is to demonstrate how the importance of this natural heritage reflected in the sites and the natural stones used for building towns and cities can be presented, using as a primary example Paris, a vast urban location, but where Geology is easily available to a large audience in the shape of geoheritage.

Underground urban geosites

The sites of all towns and cities were initially parts of a 'pure' nature, but with settlement, successive inhabitants have adapted and exploited natural resources, including rocks and other geological deposits to build shelters, houses, or even palaces. As a consequence, urban sites range from areas retaining some of their original geological characteristics, such as natural or manmade outcrops (e.g. quarries) to architectural and sculptural complexes and streets. When stones were not available, or the accessible resource was soon quarried away, mines and caverns were often created, effectively underground quarries. Examples of such underground urban geosites are quite abundant in some towns. Under Paris, for example, an estimated 280-300 km of underground tunnels and quarries are known at different levels, excavated for working different materials, mainly limestones and gypsum. As a result, Paris is a like a 'Gruyere cheese' and it is not surprising that almost every year, there are instances of street collapse.

The Romans were the first to extract stones to build Lutetia, their proto-Paris. They began to excavate the Montagne Sainte-Geneviève (in the 5 th district, where the Pantheon is now) along the valley of the Bièvre, a tributary of the river Seine, to obtain a good limestone for construction -the Lutetian (Eocene) 'calcaire grossier' -continued southwards (fig. 03). Some of the best known remains of these workings are the 'catacombs' (in reality ossuaries) and the Musée du Vin, which provide good exposures of Lutetian limestones, and small geological exhibits have now been added. In other locations old quarrying tools are exhibited (fig. 04). Several of these underground quarries were once used to grow the mushroom Agaricus bisporus (J. E. Lange) which became known as the 'Champignon de Paris'. By the end of the 19 th century, quarries below the Museum National d'Histoire Naturelle, were being used by the zoologist, Pr. Armand Viré, as a biospeleological laboratory to study the adaptation of various organisms (insects, batrachians, etc) to darkness. His intention was to show the influence of darkness upon surface living forms and, in contrast, the action of light on cavernicoles. The laboratory was used until the First World War, when Armand Viré was conscripted into the army (fig. 05).

To the north of Paris (18th, 19 th and 20th arrondissements and Seine Saint Denis), the upper Eocene (Ludian Stage) gypsum was extracted to make plaster (the famous 'plaster of Paris'). Some old underground quarries also survive, some with high vault-like, ribbed roofs, evoking the structure of cathedrals (fig. 06).

Similar underground mines are widespread across Europe. One very well studied case is the underground mining under Brussels, where the Lede Formation (shallow-marine limestone and sandstone deposited during the Eocene) has been actively exploited since the Middle Ages. Lede stone has been proposed as a candidate for nomination as a Global Heritage Stone Resource (GHSR) [START_REF] De Kock | Lede Stone: a potencial "GlobalHeritage Stone Resource[END_REF], which adds an extra value to these sites. These underground workings are mainly known through old manuscripts, although sometimes major modern constructions have thrown more light on these historical cavities (Camerman 1955a,b). [START_REF] Devleeschouwer | Brussels Urban Geology (BUG): a 2D and 3D model of theundergroundbymeans of GIS[END_REF] designed a 2D and 3D model for the underground workings to serve as an educational resource, but also for stakeholders connected with urban development and underground transport in the city. Other towns and cities have similar stories, including, although for many others, such as the remarkable 18 th century planned townscape-construction of Middle Jurassic (Bathonian) limestones of the World Heritage city of Bath, south-west England, the extensive underground mines remained largely outside of the city limits, and some are still exploitated, in particular for restoration work [START_REF] Perkins | Bath stone: a quarry history[END_REF][START_REF] Devon | Bath in stone: A guide to the city's building stones[END_REF]. Not all underground excavations in towns and cities, however, were sources of building stone, others were dug simply for underground storage or refuge. Notable amongst those in England are the excellent exposures of Triassic sandstones ('Buntsandstein' equivalents) in former storage cellars incorporated England's oldest inn, the Ye Olde Trip to Jerusalem (1189) nestled beneath the rocky crags on upon which are the remains of the famous Nottingham Castle of the Robin Hood legend.

Urban surface geosites

Historical buildings in European towns were usually built using the easiest available stones. Sometimes those stones were from the area of the same city (e.g. [START_REF] Nespereira | Opal cementation in tertiary sandstones used as ornamental stones[END_REF] or close to the city (e.g. [START_REF] Pereira | The Global Heritage Stone concept[END_REF]; also Bath, as noted above). Some of these historical quarries may become historical sites for their strategic position as is the case of the Salamanca sandstone, quarried in the Los Arapiles, hills outside the city that were witnesses of the Independence War in 1812 [START_REF] Pereira | The Global Heritage Stone concept[END_REF] and may consequently acquire cultural designations or significance in their own right. In England, important stone mines such as those in the Middle Jurassic (Bathonian) near Bath, also became important at times of war, acquiring use as storage areas for munitions and even as secure underground 'bunkers' during the second world war [START_REF] Perkins | Bath stone: a quarry history[END_REF].

Extraction of stone to build massive buildings such as the cathedral of Notre-Dame de Paris resulted in the exhaustion of open quarries that had to extend laterally, southwardly, even when the topographic surface was elevating. Then they began to dig and todays some scares are still visible (fig. 07). When the topography was still elevating, there was too much overlaying terranes to take off, so the open quarry progressively became an underground gallery (as we have see on fig. 04,05). This was also very much the case in many southern and eastern English examples, especially where the need for a hard stone for the construction of monumental buildings, for instance in areas dominated by relative soft Mesozoic to Quaternary deposits, meant that it was economically viable to start mining. Examples where surface quarries became extensive underground workings include the Beer Stone mines (Upper Cretaceous, Turonian) of east Devon which became important for the medieval construction of the City of Exeter [START_REF] Dove | Exeter in Stone: an urban geology[END_REF] and medieval workings of Portland Stone in the Vale of Wardour, Wiltshire (Upper Jurassic, Tithonian) and the Isle of Purbeck, Dorsetboth used to construct World Heritage buildings (including Salisbury cathedral in the former case), but curiously not included with the established GHSR for Portland Stone which focusses on the geological type locality of the Isle of Portland, also in Dorset.

In more northerly and western areas of Britain, i.e. with a older and harder Palaeozoic bedrock, it was not necessary to 'import' the stone from long distances, and traces of the quarries that yielded the materials of which the cities were constructed can often still be discerned amongst the buildings and in open spaces. Some of the most notable of these are those amongst Carboniferous igneous rocks in Edinburgh, Scotland, which benefited from one of the first conservation-linked legal decisions in the UK in 1831 (Cleal and Warren 2008). In the first 'Urban' Global Geopark in Torbay, Devon, SW England, first declared as a European Geopark in 2007 (www.englishrivierageopark.org.uk) this relationship if often very obvious, with former quarry faces in Devonian limestones being conspicuous wherever the limestone outcrops, but now surrounded by, and even filled with, houses and other buildings constructed from the same limestones. Indeed, quarrying was so intensive, that virtually none of the orginal limestone Tors that once characterized the Bay, survives today. Returning to Paris, northwards, one can find gypsum quarries such as in the Buttes-Chaumont. The name of this park is tied to geology, as it takes its name from the bleak hill which occupied the site, which, because of the chemical composition of its soil, was almost bare of vegetation-hence 'Chauve-mont', or bare hill, which became Chaumont by contraction. This area, just outside the limits of Paris until the mid-19 th century, had a sinister reputation as it was close to the site of the Gibbet of Montfaucon, the notorious place where the bodies of hanged criminals were displayed after their executions from the 13 th century until 1760. The site is a former gypsum quarry which yielded Eocene mammal fossils, including Palaeotherium, (Fig. 08) which were studied by Georges Cuvier (see also Table 01) . The most famous feature of the park is the Temple de la Sibylle, a miniature version of the famous ancient Roman Temple of Vesta in Tivoli, Italy -which also inspired similar architectural follies in the English landscape gardens of the 18 th century. Elsewhere in Paris, other outcrops are visible in old quarries or underground, however, in areas of harder bed-rock geology some other towns (such as Brest : Jonin & Chauris, 2012; La Rochelle : Moreau, 2008 and Niort : Branger, 2012 in western France,;;) and Edinburgh and Nottingham, as noted above, natural outcrops remarkable remain. In many southern European areas, these outcrops can be spectacular, such as at Bonifacio in Corsica, where the old town is built on a promontory (Orsini et al., 2015, fig. 10). This stone, known as the 'Pierre de Bonifacio, was also used to build the town and is Miocene in age. Similarly in Porto, also in Corsica, red granite is part of the whole landscape (Gauthier, 1992, fig. 11) and it was used in construction World Heritage city. Besides the rocks which are visible in situ, a great variety of other ones are accessible in towns either on buildings or on pavement or on curbstones. These rocks are usually more diversified than those found in situ, having been brought from many sources as reported by [START_REF] Billet | Promenade géologique à Etampes. Biotope, Mèze -MNHN[END_REF], Obert et al., (2012a, b) for Paris, France, [START_REF] Borghi | Fragments of the Western Alpine Chain as Historic Ornamental Stones in Turn (Italy): Enhancement of Urban Geological Heritage through Geotourism[END_REF] for Turin, Italy, Del [START_REF] Lama | Urban Geotourism and the pld centre of Sao Paulo City, Brazil[END_REF], for São Paulo, Brazil and von [START_REF] Gnielinski | Self-guided walking tour featuring building stones through Brisbane CPD[END_REF] for Brisbane, Australia. Nevertheless, as discussed below, this variety can become an important resource for education, in its own right by providing a much more varied selection of rock types for study.

As well as obvious geological features and materials, some references to the geosciences in towns and cities can be more subtle, and survive only as place names. For instance old street names often evoke a physical or practical character of the area, for instance, rue des sablons ('fine sand street'), rue du plâtre ('plaster street'), while others may be dedicated to some local or national celebrity, who may or may not have had a specific connection with the locations. In Paris, a significant number are dedicated to geoscientists (table 01).

Heritage stones

Heritage stones and history

The link to local territory and thus to local geology is most pronounced for the oldest monuments. The maximum use was made of local materials, everything resembling a stone found at or near-surface was put to use, sometimes after allowing time for hardening, or even accelerating this natural process by using carbonated liquids and other 'consolidants'.

Churches generally have a very good representation of local geology, even if only the 'best' stones were used. Notre-Dame de Paris is constructed with different types of Lutetian limestones, the usage of each depending on the location in the building (e.g. miliolid limestone for statues, microbial and algal limestone for lower areas), with other French examples including Strasbourg cathedral which is made of a Triassic red sandstone, Autun cathedral with a grey Lower Jurassic limestone rich in Gryphea and Clermont-Ferrand's cathedral is mainly made of Volvic stone (a trachy-andesite lava from Quaternary age, in the Central Massive). This pattern of usage is characteristic of older ecclesiastical buildings throughout Europe being representative of a regional geology, as generally they are amongst the oldest surviving buildings of high status in most towns and cities and the long distance transport of materials was expensive. Salisbury Cathedral in southern England, as noted previously, is another good example, where even in mediaeval times (from 1220 to around 1266; http://www.salisburycathedral.org.uk/) it was worth transporting high quality Portland (dimension) Stone around 18 kilometres for use in a high status construction.

The oldest and most modest buildings, however, are often constructed of the most local of building stones, and are often a clear testimony to the nature of the very local geology at such a point that it can be used to spot some wine types [START_REF] Wever | Géologie et vin[END_REF]. This situation changed radically, however, as new methods of transportation were established. especially by barge on rivers and canals and later by train [START_REF] Cailleaux | Un chargement de pierres de Saint-Leu pour le chantier de la cathédrale de Sens à la fin du Moyen-Age[END_REF][START_REF] Pomerol | Terroirs et Monuments de France[END_REF], 2006 ;and Pereira and Cooper, 2014). For sophisticated buildings, of course, the cost being less of a constraint when the most suitable, or even fashionable stones where imported from distant places. In France the most spectacular change occurred with Louis XIV in the 17 th century, most famously as he redeveloped the Versailles palace. For this ambitious construction, decorative and construction materials were sought from across Europe, including many from Pyrenees mountains bordering France and Spain, including Sarrancolin marble, or Sienne Brocatelle, Florence green marble (in fact a serpentinite) and the famous Carrare marble from Italy, and from the Ardennes massive, the 'Marbre rouge des Flandres' (also known as 'Rance's Stone') -a reefal limestone of Frasnien (Upper Devonian) age [START_REF] Groessens | La diffusion du Marbre de Rance en France[END_REF][START_REF] Groessens | Les marbres de Flandres et du Hainaut à Versailles[END_REF][START_REF] Tourneur | Belgian black and red marbles" as potential candidates for Global Heritage Stone Resource[END_REF] More recently, during the 19 th century, with the construction of the 'Canal de Bourgogne', a route for transporting stones from Burgundy opened up. As a result Paris and its surroundings were literally invaded by stones from this region, including many of Jurassic age such as the Oxfordian oolitic limestones (Calcaire d'Euville) and the very fine grained, pinkish Mid Jurassic Comblanchian limestone (see 'Stop 13' below and figs.17 and 18) A spectacular example is the main city hall of Paris: Originally build with Lutetian limestone (Fig. 11) during the reign of François Ist (16 th century), but burnt during the Paris Commune in 1871, it was mainly rebuild with Jurassic oolitic limestone from Bourgogne in 19 th century [START_REF] Obert | Geological Walk in the 5th arrondissement of Paris. Biotope, Mèze-MNHN[END_REF]. A very similar pattern of several generations of the use of different stone types can probably be found in most towns and cities, even where monumental architecture is not such a dominant part of the 'townscape'. An excellent example of this is the city of Exeter in the county of Devon in south-west England. Based on a pre-existing celtic settlement, when construction of Roman Isca Dumnoniorum began in around 55 AD, local Permian basic volcanic rockshistorical known as 'Exeter Traps' -were used (the site of quarrying survives in the centre of Exeter, although occupied by the much later 'Rougemont Castle'). The resource was limited, however, and by medieval times, the much inferior Heavitree Breccia, also of Permian age and quarried from the east side of the city, was being extensive usedwindow and door frames, however, were commonly still being constructed of 'Exeter Traps' (much, no doubt, recycled from earlier Roman use). The same is true for the remains of the city walls, which show a mixture of 'Traps', as used originally by the Romans, with later 'Breccia' additions are repairs [START_REF] Dove | Exeter in Stone: an urban geology[END_REF].

Meanwhile, new excavations and mines on the coast of East Devon in Cretaceous sandy limestone known as 'Salcombe Stone' (Albian) were providing better quality stones for facing walls, in particular for the rebuilding of Exeter Cathedral between 1270 and 1370again, the status of the building meaning that the long journey necessary, including around 28 km by sea and river was not significantly prohibitive factor. In addition, high quality Turonian 'Beer Stone', a pale limestone large composed of finely fragmented Inoceramus bivalve shells, from the same area was being used for door and window frames and statuesremarkably this stone had been worked since Roman Times and extensive underground mines now exist.

Although other stones arrived into Exeter later, such as Ham Hill Stone from Somerset for door and window frames (Toarcian, Lower Jurassic), Middle Devonian limestone from Torquay (south Devon) for whole buildings, Dartmoor granite (central Devon, Variscan) for kerbstones, it was the new railways that provided large quantities of Lower Carboniferous 'Westleigh Limestone' from central east Devon for later 19 th century and 20 th century constructions, especially walling (as many other buildings were now being constructed of local brick, made from Upper Carbonifereous mudrocks). The successive arrival of each material can be seen as a sort of 'stratigraphy' in some of the cities older surviving buildings and other structures such as the wallsespecially where they have been repaired several times, with Permian lavas and breccia in the lowest, and hence oldest parts, but with blocks of Cretaceous and Salcombe Stone above, and sometimes capped by Lower Carboniferous 'Westleigh Limestone'.

By the 19 th century, however, the use of a variety of stones in a construction of status had become more a matter of contemporary taste and decorative style and the Royal Albert Memorial Museum, opened in 1865, provides an excellent example, with at least 12 regionally sourced stone types being used in its construction (as listed in Dove 1994).

This dramatic change from the use of locally sourced to much more distantly sourced stones is widespread in Europe, and typically associated with the industrial revolution from the mid19th century. The arrival of steam machines facilitated the extraction of high quality stones from deeper and deeper quarries, and crucially, railways allowed these materials to be transported further and easier than ever before. Local diversity was definitely being replaced by national and European diversity. A second abrupt change had arisen by the mid-20th century, with increasing globalization created international markets for building materials that have often virtually terminated two millennia of building embedded in local and regional geology. Today, the European market is often dominated by both exotic and everyday stone products from countries such as India, China and Brazil. And even within Europe, local roofing slates, flooring and wallcovering materials have been replaced by materials from countries such as Portugal, Spain and Italy. But this trend had already started earlier, as imperial trades routes bought materials from distant parts of empires back to Europe, and vice-versa, for instance Cornish granite from Bodmin Moor (SW Britain) has been used in constructions in Brussels, Copenhagen, Bombay, (India), Singapur, Gibralter and many other places across the UK and globally [START_REF] Macadam | Potential European Geoparks, and the present state of geotourism, geoconservation, and geo-education in Cornwall, south-west Britain[END_REF].

Products such as these are sold under various commercial names that are often misleading with respect to their intrinsic physical and chemical properties, for instance inferior quality cleaved mudrocks with limited actual resistance to normal weathering, but sold as roofing materials. Certificates and quality control procedures are consequently urgently needed here, not only taking into account existing standards for mechanical properties, but also specific aesthetic and durability parameters that are also important, including in restoration projects, such as sulphate attack resistance, discoloration, etc [START_REF] Dreesen | Historical building stones in the province of Limburg (NE Belgium): role of petrography in provenance and durability assessment[END_REF][START_REF] Fronteau | Variability of some Lutetian building stones from the Paris Basin, from characterization to conservation[END_REF][START_REF] Malfilatre | -Petrographical and geochemical characterization of Comblanchain limestone (Bourgogne, France): a fingerprint of the building Stone provenance[END_REF][START_REF] Malfilatre | Fingerprinting the provenance of building stones : a case study on the Louvigné and Lanh lin granitic rocks (Armorica massif, France)[END_REF]. Such certification and quality assessment is a major goal for the new IUGS Geoheritage commission (Pereira et al 2016).

But the movement of such materials is not one-directional, with some French stones, such as the Sarrancolin marble for instance, now being little used in France but exported to the Middle East as a luxury decorative stone. In addition, the 'Norwegian national stone', Larvikite, in widely used in France (and Britain also) as a facing stone for shops, whilst Provencal rudist limestone (fig 13) is used for flooring in prestigious buildings in Iceland such as the headquarters of the main geothermal unit of Nesjavellir and Portuguese and German limestones are widely used for floors and wall facings in England, even within the campus of Plymouth University itself. It seems that there is no more 'local stones', as in music, economy and art, these are now 'world music', 'world economy, or world stones' … A very good example of the expansion of uses for a stone is illustrated by the 'Pierre de Caen' from Normandy. This white limestone of Bathonian (Middle Jurassic) age is famous as it is clear when just extracted, but becomes white and harder in contact with air. It has been used since prehistoric times and famous early usages include the Merovingian sarcophagus (VII th century) and extensive use by William the Conqueror (11 th century; [START_REF] Dugué | Des dinosaures aux cathédrales[END_REF]. The Pierre de Caen was the original 'pierre de taille', a term that, over time, expanded to include other natural stones with a similar coloration and ease of carving [START_REF] Pereira | The value of original natural stone in the context of architectural heritage[END_REF]. Originally, the stone was extracted from area of the city of Caen, but as it was more and more widely used, quarries were installed on the flanks of the valley around the town [START_REF] Juignet | De Pont-Audemer au Mont-Saint-Michel[END_REF]. William wanted to use the stone to build his English capital, but it was much later that it was most extensive used in London, including for the Tower and London bridges, the parliament building, Westminster Abbey as well as constructions in Chichester and Durham. Indeed, until the XIV th century, the Pierre de Caen was almost exclusively used for English constructions [START_REF] Dujardin | L'aire de dispersion de la pierre de Caen[END_REF] and some quarries still had English owners during the 19 th century. Because of this huge demand, the quarries started to work underground (fig. 14), the workings now extending to more than 300 hectares.

By the end of the 19 th century the Pierre de Caen had spread across Europe, with important constructions in Belgium, the Netherlands and Germanybut was also in use much further afield, for instance in Canada (Montreal), the USA (New York) and in the Bermuda's Islands The history of building of each town is not continuous in time; it is punctuated by periods of war, economic crisis, destruction, restructuring and reorganization (for instance the creation grand boulevards in Paris by Baron Haussmann in 19 th century) and periods of recovery, population growth, reconstruction, or even some very specific circumstances. For example, Napoléon named Gaspard de Chabrol, Baron de Volvic, as the prefect of the Seine Department in 1812. And to favour his home country he choose to use an exotic stone for Paris: a lava from the Central Massive, the 'Pierre de Volvic' mentioned previously, for several parts of the capital such as the Pantheon place and some paved roadways and curbstones). In this way, significant changes can occur in the relationship between building periods and styles, and the associated use of building materials.

Heritage stones and education

Although some specialists consider that the use of the term 'geoheritage' should be restricted to sites exposing on demonstrating geological materials and processes (De [START_REF] Egoroff | Outreach geology with the « balades géologiques » project based on smartphone technology[END_REF], we believe that including buildings, monuments and other man-made features constructed of geological materials is entirely consistent with the concept of geodiversity and crucially, may also be used for the promotion of geological values, contributing to the dissemination of knowledge about the Earth sciences and raising public awareness (see also [START_REF]Geoheritage within cities: urban geosites in Mexico city[END_REF]. We are convinced that it is possible to demonstrate to a large audience that a strong connection exists between their everyday life and geology and, moreover, that this science can be understandable to most people and not just specialists.

One of the most efficient ways to achieve such aims is through outreach. Many different methods are possible such as public conferences, illustrated books, newspapers and formal education. However, a well-established and effective way of raising awareness is through the production of self-guided walks or 'trails' using guide books and leafletsalthough increasingly, downloadable internet sources and 'Apps' are also now being used. The goal of such media is not only to show how geological materials have been used through timeand hence their cultural context and significancebut also to raise awareness of the geological processes that formed the materials in the first place, that is their intrinsic, geological story. These guides reveal to both local residents and the richness of building stones in common use, as well as the link to famous buildings which are part of a common, human heritage and our culture. Increasingly, the most cultural significant of these stones have been proposed as candidates for nomination as Global Heritage Stone Resourcesbuilding stones that have a cultural history encompassing a significant time period and have been utilized in significant works, either in buildings, sculpture or more utilitarian applications [START_REF] Cooper | Establishment of the "Heritage Stone Task Group[END_REF]. Such guides can also be invaluable for school education, as resources for field visits to in-situ geological localities becomes scares or health and safety regulations make such visits difficult or (virtually) impossible.

The concept of geological trails focused building stones is not a new one, but the sophistication and quality of guides has dramatically increased in recent yearsso has availability through web applications. In the UK, the concept of guides to building stones first probably became popular in the 1990s, with production often being led by local voluntary organisations, such as RIGS groups (Regionally Important Geological sites), some of which even selected key buildings as geoconservation 'sites' to be protected through spatial planning regulations. Of particular note is a series of 'Thematic Trails', focused on English cities, including Exeter as noted above, which applied an analytical framework for identifying target audiences and encouraging active participationtypically with educational aims -and not just passive observance (as described by [START_REF] Keene | Self-guided trails as a technique for site interpretation; a review of nature Conservancy Council site-guide projects[END_REF]. Many UK cities and towns have ultimately received one or more guides of different technical levels, some specifically designed with school-level education in mind. A common problem, however, is associated with production and printing costs and distributionultimately meaning that once a limited print-run was exhausted, the guide was no longer available in any form. Some, however, are now available for download, but the private printing costs can be significant for appropriately 'attractive' guides produced with full color illustrations -and the size of most hand-held electronic devices is simply not large enough (or bright enough in out-door conditions) for even the simplest geological illustrations to be understood by a non-specialist user. In reality, there is still no more attractive (i.e. to a general public) or practical alternative to a well-produced and widely available printed guide.

In France some geological visits were organized in the late 1980 by Pr. Maurice Mattauer in the town of Montpellier and since 1990, around establishments which are visited by public for scientific exhibitions such as the Cité des Sciences in Paris by Christiane Sabouraud in charge of the geological sciences in this institution and then the Palais de la Découverte, in Paris. To allow the public to keep a memory of the visit a picture (fig. 15) was distributed were the different kinds of stones used in the building were represented by colors. With this objective in mind the Société Géologique de France and the Muséum National d'Histoire Naturelle launched a national collection of small booklets in France entitled 'Balades géologiques' ("geological walks"). The guides cover different towns and cities, and occasionally specific places such as the UNESCO building or particular districts within Paris (fig. 16). One of these districts is the "La Défense" area, a major business district within the Paris Metropolitan Area and of the Île-de-France region [START_REF] Baudin | Geologic walk around La Défense. Biotope, Mèze -MNHN[END_REF]. This district is characterized by high-rise architecture (fig. 17), and provided an interesting challenge to inspire people working there about geology, despite it not being their reason for being present. This collection is now recognized by the Internal Union of Geological Sciences (IUGS) and by UNESCO.

As an example of the content of the guides, two stops in the La Défense business district are presented below (taken from Baudin 2015):

Figure 16: Three examples of the 'Balades géologiques' series focused on Paris-The booklet for Etampes [START_REF] Billet | Promenade géologique à Etampes. Biotope, Mèze -MNHN[END_REF] was the first published and more than 8000 copies were printed. The second booklet (De Wever et al., 2015b) was prepared for the 70th anniversary of UNESCO. The third examines the La Defense business district [START_REF] Baudin | Geologic walk around La Défense. Biotope, Mèze -MNHN[END_REF].

"Stop 12 -A woman's face set in stone"

"Sitting slightly above the Mastaba, we find a mosaic by Fabio Rieti which can only be appreciated from above (Fig. 17). It shows a woman's face in a rapakivi granite oval frame, resembling a huge mirror. Three shades of marble stone were used to trace the woman's features, hair and the reflection in the mirror, with a few blue fragments used for her eyes (Fig. 17). Red fine-grained limestone is used for her skin. This is a reef limestone from the Ardennes, dating from the Devonian age (380 million years ago). If we look closely, we can see numerous traces of white coral and fractures filled with calcite. Pieces of the same marble, but darker red with white veins, were used for the mouth and hair. White Carrara marble is used to depict the mirror's reflections. The green stone used to outline the hair is a variety of serpentine, thus named because of its color that varies from dark green to black and its mottled appearance that looks like snake skin. It is a magmatic rock called peridotite, formed in the middle of an ocean and altered by water flowing in the vicinity of the magmatic chamber. The whitish veins are where pressurised hot fluids flowed, leading to the formation of new calcium-rich minerals. The rock then formed outcrops after tectonic movements. In France, serpentine massifs are found in the Alps, the Pyrenees and the Massif Central." "Now head back towards the Quatre Temps shopping centre. In front of the Courbevoie entrance, there is a ramp and a small surrounding wall, built from greyish beige fine-grained limestone, with a series of pinkish marks and fossil remains (Fig. 18). This is Comblanchien limestone, named after a town between Dijon and Beaune in Burgundy. The limestone was deposited 155 million years ago during the Middle Jurassic, while the Paris Basin was covered by a carbonate shelf, resembling the present-day Bahamas. The Comblanchien limestone was therefore deposited in a shallow tropical lagoon environment. The fossils we can see include fragments of coral and lamellibranch shells; the fact that their two valves are still connected confirms that the environment was relatively calm. The pink-colored marks are secondary transformations (Fig. 18). This limestone is famous in France as many buildings have it for their roofs (Orly airport, Lyon train station in Paris, University of Dijon etc.) and also overseas (Saint-Louis Union Station, USA, Hiroshima Prince Hotel in Kobe, Japan etc.)." roofs

Conclusion

Geology is often considered to be a discipline restricted to specialists, namely geologists, and the amount of touristic information based on the physical aspects of environments is often limited, including in connection with types of stone, geomorphological evolution of the landscape and the relationships of both with the history of local communities. A contributing factor to this deficit, can be a lack of systematic programmes for registering (i.e. 'inventorying') national geological heritage, a process which is essential for identifying geosites not only of scientific value, but also of potential touristic significance (although this deficiency is on the way to being addressed in France; De Wever et al. 2015[START_REF] Egoroff | The national geological heritage inventory in France In Cornée A[END_REF]. Another reason for the deficiency of geoinformation is the almost total ignorance of a general public about geology, which makes it difficult to implement programs related to the conservation of natural landscapes and hence they are often relegated to a low priority.

It is argued that geotourism should include aspects of built heritage or urban geotourism since many historical monuments and buildings consist of many types of different stones, just as there are many notable outcrops of rocks within cities and towns. These sites can help promote geoheritage within cities from both an educational and geoconservation perspective, through geological trails linking sites. Nevertheless, it is important to consider that, due to their accessibility, urban geosites can offer a great potential for promoting geotourism, with the integration of historical and artistic aspects of the city showing that geology is truly a part of a human life and culture. Today, urban geotourism can be considered to be one of the most effective ways to acquaint people with geology, promoting and understanding, i.e. how to read the occupation of urban space and the constraints imposed by the physical environment, including the settlement of the city in the geological terrain and the use of geological materials in its construction.

The 'Balades géologiques' booklets (fig. 16,19), demonstrate the relationships between local stones (geoheritage), their physical properties and their different uses throughout France (e.g. waterproof at base, used in roof construction, porous on the sides, easy or difficult to sculpt ...). Besides these technical aspects, we have shown how some elements reveal their environmental conditions of formation. In addition, when some historical, social or architectural peculiarities exist, we emphasise these elements, showing that stones are associated with human life. These booklets are generally associated with guided tours and they can act to systematically raise the awareness of eye-opener for the public. To improve this outreach, some 'balades' are also available on applications ('Apps') for mobile phones [START_REF] Egoroff | Outreach geology with the « balades géologiques » project based on smartphone technology[END_REF]. This collection was launched in 2008 and by mid 2016, around 30 had been published for different towns across France and they have proved to be very popular. A positive sign was received by the end of last year.

Although geological guides to towns and cities have been being widely produced by geological and educational groups over the last 30 years or so, it is not until relatively recently, that their touristic and general educational potential has been grasped by administrations and decision makers. As a result there are now professionally produced and promoted building stone itinerary guides for many several European cities, many designed as tools for outreach activities, such as the Stone Town Guide for Helsinki and the Stone Town Guide for Kotka, both available from the website of the Geological Survey of Finland (http://newprojects.gtk.fi/ENPI/results/history/city_guides.html) and the geological heritage guide to Segovia in Spain [START_REF] Díez Herrero | De roca a roca: Descubre el Patrimonio Geológico de la ciudad de Segovia[END_REF], published by the City's council and widely available in touristic shops

The IUGS Heritage Stone initiative [http://globalheritagestone.com ] is also important in this context, as its scientific focus helps spread scientific information among stakeholders dealing with construction and restoration. Many different stones from around the world have already been proposed as GHSRs, and their intrinsic characteristics published, crucially providing advice on their proper use for new construction and restoration. Some of the stones mentioned in this paper are already on that interim list (www.globalheritagestone.com), and designation as Heritage stones. Other natural stones, such as those used in France for heritage buildings, will be presented for inclusion in this important list in terms of promotion them from a geoheritage perspective besides the books already published [START_REF] Blanc | Nature et origine des pierres des monument[END_REF], Collectif, 1998) .

Fig. 03

 03 Fig. 03 Map of Paris' underground mine exploitations. The orange areas (to the south) are limestone quarries, green ones (to the north) are gypsum.

Fig. 04 -

 04 Fig. 04-Underground quarries below Cochin hospital, Paris. The pillars, bed rock and tools bear witnesses to the work used to extract these stones for building Paris. © P. De Wever

Fig. 05 -

 05 Fig.05-A view of the biospeleogical laboratory under the Muséum. The white plaque on the wall locates the laboratory with respect to the surface: "Rue du Jardin des Plantes, côté du levant" (Jardin des Plantes street, east side). The carved table is made of Cararre marble. ©DR

Fig. 07 -

 07 Fig. 07-: The "Jardin alpin" : an old quarry in the center of Paris This area of the Jardin des Plantes (Muséum National d'Histoire Naturelle) is devoted to plants living on hard rocks and appropriate named. It corresponds to an old quarry in Lutetian limestones (Eocene)the old quarry face is to the left. © De Wever

Fig. 08

 08 Fig. 08 The lower jaw of a Palaeotherium from Buttes-Chaumont studied by Georges Cuvier, as seen at the entrance of the Bâtiment de Géologie (Museum National d'Histoire Naturelle, Paris)© P. De Wever

  Fig. 10-Bonifacio. The old part of Bonifacio (Corsica), built on Miocene calcarenites. © Archives de l'Office municipal de tourisme de Bonifacio.

Figure 11 "

 11 Figure 11 "Rouge de Porto" granite in the village of Girolata, an isolated village (no road for access) in the center of the Scandola reserve, a UNESCO World Heritage Site Porto-Ota (Corsica). The bed rock and traditional houses shows the same red color due to rhyolitic volcanism of Permian age © P. De Wever

Fig. 11 :

 11 Fig. 11 : Lutetian limestone used for buildings: This example was used in the 'Grand amphithéâtre' of the Muséum National d'Histoire Naturelle in 1788. This rock is characterized by abundant moulds of gastropods (mainly ceriths) © P. De Wever

Fig. 13 .

 13 Fig. 13. Paving slabs in Aix-en-Provence TGV stationa local Cretaceous rudist limestone (the rudists are 5-10 cm long) © P. De Wever

Fig. 14 -

 14 Fig. 14-Winch used to bring to the surface heavy blocks of Pierre de Caen from underground quarries -note the white colour of the stone © D. Peeters

Figure 15

 15 Figure 15Post card of the entrance of the Palais de la Découverte with colours differentiating the stones red-orange (stairs) : Upper Eocene lacustrine limestone orange : fossiliferous shallow water limestone, mid Jurassic yellow : Mid Eocene (Lutetain) miliolids limestone blue : crinoidic limestone, upper Jurassic green : oolothic limestones , middle Jurassic limestones © A. Blanc

Figure 17 -

 17 Figure 17 -Above: The Face, a work by Fabio Rieti, can only be seen from above. (© Defense-92). Below: Three different marbles trace the woman's features. The red is of Devonian age from the Ardennes; the white from Carrara in Italy; the green is a variety of serpentine. The marble strips are 4 to 5 cm wide. (c) F.Baudin

Figure 18 -

 18 Figure 18 -(left) One of the ramps leading to the Quatre Temps shopping centre, built from Comblanchien limestone from Burgundy. (Right) Comblanchien limestone often has pink veins. These are iron oxides that recrystallized after deposit. Fossils, including the 5 cm long mollusc shell are also present.

Figure 19 -

 19 Figure 19 -Map of the 33 available booklets in the 'Balades' series: Red dots = published booklets; Orange dots: booklets in preparation.

Claude Perrault, is the brother of the Charles Perrault, a famous French author who laid the foundations for a new literary genre, the fairy tale (Le Petit Chaperon Rouge (Little Red Riding Hood), Cendrillon (Cinderella), Le Chat Botté (Puss in Boots), La Belle au bois Dormant (The Sleeping Beauty), and Barbe Bleue (Bluebeard).

Acknowledgements

Two anonymous reviewers helped in improving a previous version of the manuscript. Thanks to Alexandre Lethiers for his work on illustrations and to Maryse Aymes. This work was supported by ASM Patrimoine géologique, of the Muséum National d'Histoire Naturelle (Paris). D. Pereira thanks F. Tourneur for the introduction to underground geology in Brussels. This report is a joined contribution among members of the IUGS Geoheritage Task Group and Heritage Stone Task Group. Authors appreciate the continuous support of IUGS to both working groups.


Said Madaoui
email: said.madaoui@stellantis.com

Bartlomiej Guzowski
email: bartlomiej.guzowski@p.lodz.pl

Roman Gozdur
email: roman.gozdur@p.lodz.pl

Zlatina Dimitrova
email: zlatina.dimitrova@stellantis.com

Nicolas Audiot
email: nicolas.audiot@stellantis.com

Jocelyn Sabatier
email: jocelyn.sabatier@u-bordeaux.fr

Jean-Michel Vinassa
email: jean-michel.vinassa@ims-bordeaux.fr

Franck Guillemard
email: franck.guillemard@stellantis.com

Eval- Uation

Evaluation of Dual Side Cooling System for Prismatic Batteries for Vehicle Aplications

Keywords: Electric vehicle, batteries, thermal management, cooling plate, thermal gradient, lifespan

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

Introduction

The battery pack is the only and main source of energy of an electric car, and to be able to replace an internal combustion engine vehicle, several technical challenges exist that engineers and specialists must face, in order to both increase the autonomy and lifespan while reducing the charging time. Lithiumion batteries (LIBs) have gradually evolved from a variety of technologies due to their low self-discharge rate, high energy density and lack of memory effect, this type of batteries has revolutionized the energy storage technology and enabled the mobile revolution [START_REF] Maisel | A forecast on future raw material demand and recycling potential of lithium-ion batteries in electric vehicles[END_REF]. Li-ion batteries are available in different shapes and configurations, including cylindrical, prismatic and pouch cells. Temperature is one of the key limiting factors for battery pack performance and lifetime. Temperature heterogeneity inside LIBs causes different electrochemical reaction rates within the cells. This can lead to uneven current density distributions, local State of Charge (SoC) differences and local ageing differences, which may not only accelerate the global ageing, but also reduce the accessible energy of the battery. Temperature rise and spatial temperature gradient minimization inside the cell is among the main thermal challenges during fast charge [START_REF] Steinhardt | Thermal conductivity inside prismatic lithium-ion cells with dependencies on temperature and external compression pressure[END_REF]. Thermal Management Systems (TMS) are employed in majority of vehicles to counter these challenges [START_REF] Zhou | Parametric Investigation on the Performance of a Battery Thermal Management System with Immersion Cooling[END_REF]. A 5°C variation in temperature can reduce the battery pack's capacity by 1.5-2% [START_REF] Hunt | Surface Cooling Causes Accelerated Degradation Compared to Tab Cooling for Lithium-Ion Pouch Cells[END_REF], and its power capabilities by 10% [START_REF] Feng | Mechanisms for the evolution of cell variations within a LiNixCoyMnzO2/graphite lithium-ion battery pack caused by temperature non-uniformity[END_REF]. To improve cooling capability of LIBs, various researchers have incorporated different cooling techniques. Nowadays, liquid cooling, air cooling and phase change material are widely adopted for battery thermal management. Depending on the technical requirements and cost, battery pack manufacturers can use one or several cooling methods. The TMS can be classified into active cooling and passive cooling. Active cooling consumes extra energy for pumps and fans powering but still more efficient than passive cooling [START_REF] Amalesh | Liquid cooling vs hybrid cooling for fast charging lithium-ion batteries: A comparative numerical study[END_REF]. The active liquid cooling can also be classified into direct-contact and indirect contact. For indirect contact, the liquid is a combination of water and ethylene glycol to avoid liquid freezing at low temperatures inside the cooling plates, while for direct contact, the liquid must be dielectric to avoid any short-circuits. Recently, the direct-contact liquid cooling method has gained increased attention due to its high cooling efficiency [START_REF] Liu | Feasibility study of a novel oil-immersed battery cooling system: Experiments and theoretical analysis[END_REF]. The battery thermal management serves to monitor, control and maintain the optimum operating temperature conditions of a battery. The items that are considered in designing the cooling plate are: (a) the cooling plate should maintain the temperature of batteries at the manufacturer's recommended temperature during normal operation, (b) the cooling plate should dissipate maximum possible heat from the batteries in case of thermal runaway, (c) the coolant pressure drop inside the cooling plate should be minimized, and (d) the size and weight of the TMS should be minimized [START_REF] Mohammed | Dual-purpose cooling plate for thermal management of prismatic lithium-ion batteries during normal operation and thermal runaway[END_REF].

Although the above research has achieved remarkable results in battery thermal management, some challenging questions remain: (a) there is little previous literature on battery inner thermal gradient minimization based on both experimental tests and simulations, (b) so far, little work has investigated the benefits of cooling and heating the batteries by putting a cooling plate on top of the battery module, and its role in the battery thermal management. The aim of this study is to better manage the battery temperature by reducing not only the pick maximum temperature but also the inner thermal gradient, by adding a cooling plate on top of the battery module. The objectives of the present work are as follow:

-perform different experimental tests on a battery module managed thermally in the first case by a bottom cooling plate and then by a top and bottom cooling plates -compare the results of both technologies in term of thermal management -build a model and do the calibration using the data acquired during the experimental tests -use the model to investigate other scenarios in extreme conditions (current and temperature), and of course assess the role of top cooling plate in the battery temperature variation. The last sections conclude and give perspectives on the research topic

Electrothermal modelling of Li-ion batteries 2.1. Battery module model

The battery module consists of 12 prismatic cells connected with busbars to form a 3p4s battery module as represented in the Fig. 1(a). To model the battery module, a fine modeling of its constituents is necessary, by modeling the cells in Fig. 1(b) and also the busbars. One of the most critical steps for developing battery prognostics solutions is to establish a battery model which enables the auto-maker to simulate battery behavior and interpret battery issues in a form that can be understood by users and designers [START_REF] Rezvanizaniani | Review and recent advances in battery health monitoring and prognostics technologies for electric vehicle (EV) safety and mobility[END_REF]. Different methods from the electrical, thermal, mechanical and electrochemistry perspectives have been used to establish different battery models, and the dynamic behaviors of the battery regarding different charging/discharging rates and temperatures have been investigated. Among the various battery models, electro-thermal modeling is commonly used to study the relationship between the current and the temperature of battery. The battery electro-thermal model couples the electrical and thermal models closely. The initial inputs of the electrical model are the discharge current, the SOC level and the temperature. The inputs of the electrical model generates heat for the thermal model, this last provides a temperature output signal. Then this temperature signal is fed back to the electrical model, since the new temperature affects the electrical parameters such as the internal resistance.

Generally, the heat generation of the battery during charge and discharge contains two parts: reversible and irreversible heats, and it can be expressed by Eq. ( 1). The entropy change is responsible for the reversible heat which can be expressed by Eq. ( 2), and the irreversible heat the heat generated by ohmic resistance is expressed by Eq. ( 3

) = + (1) = (2) = ² (3)
In order to avoid the accumulation of heat at the level of the cell, this heat is often exchanged with the neighboring elements of the cell by conduction , or dissipated by different TMS by convection . The two modes of heat exchange are detailed in the two equations below Eq. ( 4) and Eq. ( 5) respectively

= (4) = ℎ ( -) (5)
The battery temperature is affected by various heat transfer paths. To reduce the battery temperature, part of the heat generated has to be dissipated to the external environment in order to avoid the heat accumulation and thus reduce the temperature raise [START_REF] Gozdur | An energy balance evaluation in lithium-ion battery module under high temperature operation[END_REF].

Battery cell model

The research object is a commercial 67 Ah prismatic battery cell. The battery cell specifications are tabulated in table 1 The battery cell is a complex system since it consists of several elements such as JRs, a casing, a cover and electrical insulating films. To finely model the cell, the JRs and the casing are modeled in order to be able to represent the thermal behavior of the battery by having a temperature response at each point of the cell whether at inside or outside. The JR and the casing modeling approaches are now described.

2220

https://doi.org/10.52202/069564-0200

JR modeling

The challenge is to be able to visualize and quantify the temperature gradients within the cell, while having a model that can be simulated in seconds so that it can be embedded on an electric vehicle.

Considering the complex geometry of the JR, it was necessary to design a mesh which makes it possible to represent all the heat exchanges in all directions inside the cell. To successfully reproduce the thermal behaviour of the JR, it is essential to provide a reliable mesh able to represent as good as possible the heat exchanges within the JR, and good assessment of the cell inner thermal gradient. The proposed model consists of meshing the JR in thickness as well as in height. The particularity of this mesh compared to what could be found in literature, is that it takes into account the orthoradial direction which shows that the heat can be exchanged between the meshes by going around the windings. The Fig. 2 shows the proposed mesh by considering the three directions, axial (according to the height of the JR), radial (normal to the winding), orthoradial (parallel to the winding).

Figure. 2. The proposed mesh of the JR

The JR is obtained by wrapping the electrodes around a hollow space. Each turn is qualified as an elementary layer which is made of different sub layers. Each elementary sub layer has its own thermal conductivity and capacity, its own thickness as well as its own density. All these essential data for the thermal model are taken from literature in absence of having been able to obtain them from the supplier. The JR model is well detailed in [START_REF] Madaoui | A detailed Electro-thermal model of an NMC lithium-ion prismatic cell[END_REF] with all the equations that represent the physics at the JR level.

To summarize, the heat generated by a mesh i,j can be calculated according to the following equation:

̇ , = , , + , , , , (6)

Casing modeling

To get a full model of the cell, the JR have to be linked to the other elements of the cell that surround it, starting with the casing which acts as a thermal bridge between the JR and the external environment.

In order to visualize the thermal gradient on the casing, the latter is meshed in height, and each mesh j of the casing is connected with a mesh imax,j of the JR. Since the casing is made of aluminium, its specific characteristics are known.

Busbar modeling

The busbar modeling strategy consists of breaking down the busbar into meshes and assign to each mesh the following Fourier equation:

= + + ℎ (7)
where is the mass of a mesh i,j of a busbar, , specific heat capacity, and represents the heat generated mostly by Joule effect according to eq. ( 8) ,

= * (8)
, denotes the heat dissipated either by natural or forced convection, and represents the heat that could be exchanged between the busbar and the upper part of the tab and also with the neighbouring meshes of the busbar. The fig. 3 shows the meshed busbar. The heat exchange by radiation was neglected in this paper.

Battery module model

Once the battery cell model is well obtained, it is duplicated 12 times to form the 3p4s module model, thus the module is made of 4 blocks of 3 cells each. The cells of the same block are coupled thermally through the busbars as well as through the meshes of their casings. Once the block is built, it is duplicated four times by assuming that the cells are identical, and they have all the same characteristics. Then the four blocks are coupled thermally together through busbars to form what we call a 3p4s battery module. Figure 4(b) shows the temperature responses of the 12 cells for the current profile represented in the Fig. 4(a). This current profile was chosen to represent both charge and discharge scenarios, and also investigate the electrical resistance variation as function of SoC. The hypothesis are not detailed for this part, because the goal is to show that the model allows to have the temperature responses of the twelve cells for a given current profile, the assumptions will be detailed in the part dedicated to (results and comparison).

Model calibration

Before starting the calibration of the module model, some assumptions have been considered.

Assumptions

The following assumptions have been made for model calibration -the cells inside a module are all identical -the presence of thermal spacers between the blocks means that the only thermal path between the block of cells becomes the busbars -the electrical resistances between the busbars and the tabs are considered null.

-the temperatures of the air in the climatic chamber and of the liquid circulating inside the plates are constant throughout the test.

-the initial and boundary conditions of the model are supposed to be suitable to the experiment conditions https://doi.org/10.52202/069564-0200

Battery module without any cooling plate

In order to calibrate the model detailed above, some electrothermal tests have been carried out on the 3p4s module. The first tests have been carried out on the module without any cooling plate as shown in the Fig. 5(a), and the goal is to reproduce correctly the thermal and electrical responses of the twelve cells. At first the battery module has been put in a climate chamber. So, the first parameter to be determined was the heat exchange coefficient ℎ . The second parameter was the contact electrical resistances between the electrical load and the battery module terminals. These contact electrical resistances can play a very important role in the thermal behavior of the batteries, especially when the contact is bad.

Battery module with a top and bottom cooling plate

The same electrothermal tests have been carried out, first on the battery module coupled to a bottom cooling plate (first case see the Fig. 5(b)) and then on the battery module coupled to the top and bottom cooling plates (second case as shown by the Fig. 5(c)).

Once the data acquisition is done through thermocouples, the goal was to assess the benefits of adding the cooling plates and then compare the technologies in term of efficiency in thermal management of the batteries. At the model level the only parameters that had to be determined in order to reproduce the thermal responses of the cells were: (a) the thermal resistances between the bottom cooling plate and the bottom surfaces of the cells for the first case and (b) the thermal resistance between the top cooling plate and the busbars for the second case.

Measurement setup and test procedures

A dedicated test stand has been developed to assess the efficiency of the cooling system extended with a cooling plate through the upper surface on which the connection electrodes are installed. All experimental tests were performed for the same battery module at the same, strictly controlled conditions. Each time, preconditioning procedure was preceded to reach the same initial state of charge and state of health of the tested battery module before tests. The test stand consists of the Li-Ion battery module, the thermal management system, charging/discharging system and a control and acquisition system.

Tested battery module

For the evaluation of the cooling improvements, the high-power battery module has been selected. The battery module was made of 12 Li-Ion prismatic cells connected in the 3s4p setup. Technical parameters of the cells were listed in subsection 2.1.

Thermal Management system and thermal test procedure

The thermal management system consists of two water cooling plates, water chiller and thermal chamber. As shown in Fig. 6, the battery module was placed in the thermal chamber. The bottom dedicated cooling plate was connected in parallel with top cooling plate and supplied from the chiller CW-6100AN. The inlet temperature of purified water was control by the chiller. Cooling plates were integrated with battery module through 3 mm thick thermal pad. In this section a comparison between the three configurations presented in the Fig. 5 has been done in order to assess the benefits of adding the cooling plates regarding the battery module thermal management. According to the Fig. 13, the third configuration (module with top and bottom cooling plates) represented by the blue color is the most efficient in term of thermal management, and it's the 2226 https://doi.org/10.52202/069564-0200 best way of extracting and dissipating the calories generated by the battery during charge and discharge. As a consequence, the maximum pick temperature is reduced compared to the configuration represented by the black curve where the module is cooled only by the bottom cooling plate. Also, one can note that the time constant is shortened which proves the efficiency of this configuration.

6.Conclusion

In this study, a methodology of battery module modelling is proposed, by taking into account the battery cells, the busbars and also the thermal spacers between the battery cells. A qualitative study is done on a battery module by investigating the benefit of adding the top cooling plate in the overall battery module thermal management. According to simulations and experiments regarding one case study, the configuration with top and bottom cooling plates makes it possible to not only cool the module more quickly by reducing the thermal time constant by 47% but also reduces the battery maximum pick temperature reached with a conventional cooling system by 6°C. Different electrothermal tests have been carried out to validate the battery module model with different scenarios in term of air/coolant temperatures and current profiles in (charge and discharge). It stands out that the model has a good reproducibility, and the error is always below the thermocouple's uncertainty. It stands out also that it gets easier and more efficient to extract calories from the batteries by adding the top cooling plate. In this paper, only the prismatic cells are concerned, but the methodology can be applied on different battery types and for different battery module topologies.

  Fig.1(c) shows the cover detached from the casing and also the Jelly roll (JR) which represents the heart of the cell and the main part of the battery. In this section the proposed model is established. With the current, the initial temperature, and the environment temperature as inputs, the model can predict the internal temperature distribution and the state of charge of the battery. The battery module model consists of three sub models, a thermal model, an electrical model based on Electrical Circuit Network ECN and a heat generation model.

Figure. 1 .

 1 Figure. 1. Structure of the studied system: a) battery module, b) battery cell, c) Cover detached from the casing and JR inside the battery cell (a) (b) (c)

Figure. 3 .

 3 Figure. 3. The meshed busbar connecting six cells 2.1.1.4 Battery module modelOnce the battery cell model is well obtained, it is duplicated 12 times to form the 3p4s module model, thus the module is made of 4 blocks of 3 cells each. The cells of the same block are coupled thermally through the busbars as well as through the meshes of their casings. Once the block is built, it is duplicated four times by assuming that the cells are identical, and they have all the same characteristics. Then the four blocks are coupled thermally together through busbars to form what we call a 3p4s battery module. Figure4(b) shows the temperature responses of the 12 cells for the current profile represented in the Fig.4(a). This current profile was chosen to represent both charge and discharge scenarios, and also investigate the electrical resistance variation as function of SoC. The hypothesis are not detailed for this part, because the goal is to show that the model allows to have the temperature responses of the twelve cells for a given current profile, the assumptions will be detailed in the part dedicated to (results and comparison).

Figure. 4 .

 4 Simulation results after building the model: a) Input current, b) cells temperatures

Figure. 5 .

 5 Figure.5. Battery module thermal management: a) module without any cooling plate, b) module with bottom cooling plate, c) module with top and bottom cooling plates (a) (b) (c)

Figure. 6 .. Experimental results 4 . 1 .

 641 Figure. 6. The diagram of the thermal management system

Figure. 7 .Figure. 8 .

 78 Figure. 7. Thermal response of battery module with bottom cooling plate during charge process, where TA = 25 ºC, TC =20 ºC

Figure 9 . 4 . 2 .

 942 Figure 9. Layout of the temperature sensors4.2. Discharging battery moduleAfter charging tests, the discharge test was conducted with TA = 25°C and TC = 30°C. In Fig.10, thermal response of battery module with only bottom cooling plate during the investigation is given. The same test was conducted once again for battery module equipped with bottom and top cooling plates. Thermal behavior of the module is shown in Fig.11. Differences in C-rate profile caused longer time constant for cooling process which was equaled to τ = 7260s. For this case study, the time constant was decreased by 55% in the tests with two cooling plates. Maximum temperatures before and after adding the top cooling plate (45°C and 43°C) were recorded on terminals of battery module. Maximum recorded temperature after improvement inside the battery module dropped by 2°C, but on the other hand the temperature inside the module was more uniform in a test with top and bottom cooling plates. At t = 6000 s, the temperature difference measured inside the battery module and on external walls dropped by half from 5°C to 2.5°C. It stands out that the average relative improvement rate was 31%.

Figure. 10 .

 10 Figure. 10. Thermal response of battery module with bottom cooling plate during discharge process, where TA = 25 ºC, TC =30 ºC

Figure. 13 .

 13 Figure. 13. Thermal management system performance

  heat exchanged with the battery by conduction, W heat generated by the battery, W ℎ thermal resistance, K/W cross-sectional area of the busbar, m² ambient temperature, ºC temperature of the busbar mesh, K coolant temperature, ºC ℎ, neighbour elements of the cells, K Greek symbols density, Kg/ 3 Subscripts and superscripts jelly roll lithium-ion batteries open circuit voltage state of charge thermal management system

Table 1 .

 1 . Specifications of the battery cell

	Specification
	Cathode material	NMC
	Anode material	Graphite
	Nominal capacity	67Ah
	Cut off voltages	2.8-4.2V
	Dimensions	150mm 30mm
		100mm
	Thermal conductivities	40-2.5-40 W/m.K
	Thermal capacity	1200 J/Kg.K

https://doi.org/10.52202/069564-0200

busbar specific heat, J/(kg K) ℎ convective heat transfer coefficient, W/(m 2 K) current flowing through the battery and busbar, A charge current, A discharge current, A heat dissipated by the battery, W irreversible heat, W reversible heat, W length of the busbar mesh, m busbar mesh mass, Kg battery temperature, K environment temperature, K

2225

https://doi.org/10.52202/069564-0200

Acknowledgments

This work took place in the framework of the OpenLab 'Electronic and Systems for Automotive' combining IMS Laboratory, Lodz Laboratory and Stellantis. This work was carried out under a CIFRE agreement and granted by the ANRT Nomenclature