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Scott catalogue

The Scott catalogue of postage stamps, published by Scott Publishing Company, now a subsidiary of Amos Media, is updated annually and lists all the stamps of the world that its editors recognize as issued for postal purposes. It is published in fourteen large volumes (as of 2021) that include twelve volumes containing all the countries of the world that have ever issued postage stamps, the United States Specialized Catalog, and the 1840–1940 Classic Specialized Catalogue (covering the world for the first 100 years that stamps were issued). The numbering system used by Scott to identify stamps is dominant among stamp collectors in the United States, Canada and Mexico.

Background
The first Scott catalogue was a 21-page pamphlet with the title Descriptive Catalogue of American and Foreign Postage Stamps, Issued from 1840 to Date, Splendidly Illustrated with Colored Engravings and Containing the Current Value of each Variety. It was published in September 1868 by John Walter Scott, an early stamp dealer in New York, and purported to list all the stamps of the world, with prices for each. A notice inside does caution the reader that "it is simply impossible for any one to always have every stamp" in stock. The original catalog has been reprinted.

In subsequent years, the Scott company gave up dealing in stamps but continued to publish the catalog, gradually providing more detail as the hobby evolved and collectors became more sophisticated. In addition to the factual information about the stamps, the catalog includes price information based on market analysis and reported sales from the previous year. As of 2006, and despite annual changes to save space, the catalog was more than 5,000 pages.

The Scott numbering system assigns plain numbers for regular mail stamps, and uses capital letter prefixes for special-purpose types, such as "B" for semi-postals and "C" for airmail. The numbers are generally consecutive; there are gaps among older stamps, where some numbered types were later renumbered, and among newer stamps where Scott has left numbers unassigned in the anticipation of additional stamps in a series. If more stamps than expected appear, Scott will add a capital letter as suffix, or if the change is very recent, it will renumber stamps. Minor variations, such as shades or errors, get a lowercase letter; so the "C3a" above indicates a variation (error in this case) on what is listed as the third U.S. airmail stamp.

Because of its commercial importance the publishers of the Scott Catalogue claim copyright on their numbering systems, and grant only limited licenses for their use by others. The inconsistency with which Scott enforced these licenses resulted in a lawsuit by Scott against Krause Publications (publishers of the Minkus Catalogue) for copyright infringement. After Krause filed a defense, the suit was settled out of court, and Krause continued to reference the Scott numbers.

Editors of this, the dominant catalog in the United States, have great influence over what is and is not considered to be a valid postage stamp. For instance, in the 1960s the countries of the United Arab Emirates issued many stamps that were likely never actually on sale in a post office, so Scott does not list most of them. One must go to a Michel catalog, for instance, to see them described. The lack of a Scott listing, though, means that most American dealers will refuse to trade in such stamps.

Similarly, Scott lists most stamps from countries embargoed by the U.S. government, and in some cases lists them without catalog values. To some extent, this is unavoidable, since the ban on importation means that Scott's editors are unable even to acquire copies of the stamps to be described. Moreover, since American dealers and collectors are unable to buy the stamps legally, they are unlikely to have any need of the data. (Again, interested persons typically use Michel or other catalogs instead.) The policy changes with government policy; stamps of Cuba, Libya and North Vietnam now appear in the Scott catalogues after an absence of some years.

The dominance of Scott is such that U.S. collectors know many of the numbers by heart, and dealers need only mention the number in their price lists. For instance, United States no. "C3a" is instantly recognized as the Inverted Jenny, a rare airmail inverted error stamp.

Contents
The contents for each of the twelve volumes (2021 catalogs) are listed below. Scott has chosen to identify the current twelve volume format of catalogs as only six volumes with an alphabetical suffix (vol 1b is actually vol 2, etc).
 * Volume 1a: United States, United Nations, 'A' countries to Australia
 * Volume 1b: Austria to 'B' countries
 * Volume 2a: 'C' countries to Curacao
 * Volume 2b: Cyprus to "F" countries
 * Volume 3a: 'G' countries
 * Volume 3b: 'H' through 'I' countries
 * Volume 4a: 'J' through 'L' countries
 * Volume 4b: 'M' countries
 * Volume 5a: 'N' countries through 'P' countries (Philippines)
 * Volume 5b: 'P' countries (Pitcairn Islands) to 'S' countries (Samoa)
 * Volume 6a: 'S' countries (San Marino) to 'T' countries (Tete)
 * Volume 6b: 'T' countries (Thailand) to 'Z' countries

Covers
For many years, the stamps featured on the cover of the catalogue follow a specific theme as follows:
 * 1993: Trains and Birds
 * 1994: Ships and Butterflies
 * 1995: Space and Mushrooms
 * 1996: World War II
 * 1997: Olympics
 * 1998: No specific topic
 * 1999: Used stamps
 * 2000: Millennium
 * 2001: Space exploration
 * 2002: Paintings
 * 2003: Airplanes (for the 100th anniversary of the first airplane flight)
 * 2004: Famous Buildings
 * 2005: Earth's Features
 * 2006: Mail Transport
 * 2007: Scouting
 * 2008: Odd-shaped stamps
 * 2009: Abraham Lincoln
 * 2010: Birds
 * 2011: UNESCO World Heritage Sites
 * 2012: Bridges
 * 2013: Lighthouses
 * 2014: Women
 * 2015: Stamps from "Dead Countries"
 * 2016: New York City
 * 2017: Royalty
 * 2018: Stamp Collecting (Scott's 150th Anniversary)
 * 2019: Trains

Illustrations
In May, 2001 Scott announced a project to include a scan of each stamp in its catalogues. Many were made from its own reference collection and introduced in the six volume 2002 edition as black and white images. Color images were introduced in 2003 in the Classic Specialized Catalogue and in 2005 in the Specialized Catalogue of United States. In 2006 color images were included in the main Scott catalogues. Shortly after the program was announced, Scott Publishing received a letter from Hsien-ming Meng, a physician in Dayton, Ohio, and worldwide collector of mint stamps with a nearly complete collection. Dr. Meng offered to permit scanning of his collection, an offer that was eagerly accepted by Scott Publishing. Scans from Dr. Meng's collection began appearing in volume 4 of the 2002 catalog. Together with generous access by many other collectors, Meng's cooperation has resulted in creation of scanned images of all but about 1300 stamps by Scott as of 2024 catalogue series. About 120 are specialized stamps from the US Specialized Catalogue. About 1180 are used stamp images that Scott is replacing with mint images in the general world catalogues or are poorly centered stamps that they are replacing with F to VF centered stamps. Only a handful of black and white images are left in the world catalogues. Meng, born in 1926, died February 8, 2011.

Scott Specialized Catalogue of United States Stamps and Covers
Scott Publishing Co also produces a related volume which more comprehensively lists all United States Postage Stamps and Postal History. It is generally known as the Scott Specialized and is regarded by many as the definitive single volume reference to USA postage stamps. The catalogue provides more detail than Volume One, with particular emphasis on varieties and errors. A new edition of the catalogue is produced annually with a particular edition year date generally indicating production in the middle of the previous year. Biannual Valuing Supplements are also issued in the Spring and Fall.

Scott Classic Specialized Catalogue: Stamps and Covers of the World
Scott Classic Specialized Catalogue: Stamps and Covers of the World is limited to stamps and covers that were produced between 1840 and 1940 or for the British Commonwealth nations to 1952. It covers all postage stamp producing nations in one volume for those years.

title: Scott catalogue


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Vega 2

Vega 2 (along with Vega 1) was a Soviet space probe part of the Vega program to explore Halley's comet and Venus. The spacecraft was a development of the earlier Venera craft. The name VeGa (ВеГа) combines the first two letters Russian words for Venus (Венера: "Venera") and Halley (Галлея: "Galleya"). They were designed by Babakin Space Centre and constructed as 5VK by Lavochkin at Khimki. The craft was powered by large twin solar panels. Instruments included an antenna dish, cameras, spectrometer, infrared sounder, magnetometers (MISCHA) and plasma probes. The 4,840 kg craft was launched on top of a Proton 8K82K rocket from Baikonur Cosmodrome, Tyuratam, Kazakh SSR. Both Vega 1 and 2 were three-axis stabilized spacecraft. The spacecraft were equipped with a dual bumper shield for dust protection from Halley's Comet.

Venus mission
The descent module arrived at Venus on 15 June 1985, two days after being released from the Vega 2 flyby probe. The module, a 1500 kg, 240 cm diameter sphere, contained a surface lander and a balloon explorer. The flyby probe performed a gravitational assist maneuver using Venus, and continued its mission to intercept the comet.

Lander
The surface lander was identical to that of Vega 1 as well as the previous six Venera missions. The objective of the probe was the study of the atmosphere and the exposed surface of the planet. The scientific payload included a UV spectrometer, temperature and pressure sensors, a water concentration meter, a gas-phase chromatograph, an X-ray spectrometer, a mass spectrometer, and a surface sampling device. Several of these scientific tools (the UV spectrometer, the mass spectrograph, and the devices to measure pressure and temperature) were developed in collaboration with French scientists. Since the probe made a nighttime landing, no images were taken.

The Vega 2 lander touched down at 03:00:50 UT on 15 June 1985 at around, in the northern region of Aphrodite Terra. The altitude of the touchdown site was 0.1 km above the planetary mean radius. The measured pressure at the landing site was 91 atm and the temperature was 736 K. The surface sample was found to be an anorthosite–troctolite rock, rarely found on Earth, but present in the lunar highlands, leading to the conclusion that the area was probably the oldest explored by any Venera vehicle. It transmitted data from the surface for 56 minutes.

Balloon

The Vega 2 Lander/Balloon capsule entered the Venusian atmosphere (125 km altitude) at 02:06:04 UT (Earth received time; Moscow time 05:06:04) on 15 June 1985 at roughly 11 km/s. At approximately 2:06:19 UT the parachute attached to the landing craft cap opened at an altitude of 64 km. The cap and parachute were released 15 seconds later at 63 km altitude. The balloon package was pulled out of its compartment by parachute 40 seconds later at 61 km altitude, at 7.45 degrees S, 179.8 degrees east. A second parachute opened at an altitude of 55 km, 200 seconds after entry, extracting the furled balloon.

The balloon was inflated 100 seconds later at 54 km and the parachute and inflation system were jettisoned. The ballast was jettisoned when the balloon reached roughly 50 km and the balloon floated back to a stable height between 53 and 54 km some 15 to 25 minutes after entry. The mean stable height was 53.6 km, with a pressure of 535 mbar and a temperature of 308-316 K in the middle, most active layer of the Venus three-tiered cloud system. The balloon drifted westward in the zonal wind flow with an average speed of about 66 m/s at nearly constant latitude. The probe crossed the terminator from night to day at 9:10 UT on 16 June after traversing 7400 km. The probe continued to operate in the daytime until the final transmission was received at 00:38 UT on 17 June from 7.5 S, 76.3 E after a total traverse distance of 11100 km. It is not known how much further the balloon traveled after the final communication.

Halley mission
After their encounters, the Vegas' motherships were redirected by Venus' gravity to intercept Halley's Comet.

The spacecraft initiated its encounter on March 7, 1986, by taking 100 photos of the comet from a distance of 14,000,000 km.

Vega 2 made its closest approach at 07:20 UT on March 9, 1986, at 8,030 km. The data intensive examination of the comet covered only the three hours around closest approach. They were intended to measure the physical parameters of the nucleus, such as dimensions, shape, temperature and surface properties, as well as to study the structure and dynamics of the coma, the gas composition close to the nucleus, the dust particles' composition and mass distribution as functions of distance to the nucleus and the cometary-solar wind interaction.

During the encounter, Vega 2 took 700 images of the comet, with better resolution than those from the twin Vega 1, partly due to the presence of less dust outside the coma at the time. Yet Vega 2 recorded an 80% power loss during the encounter as compared to Vega 1's 40%.

After further imaging sessions on 10 and 11 March 1986, Vega 2 finished its primary mission.

Post Halley
A 6 million kilometer distant flyby of 2101 Adonis was considered, however, Vega 2 didn't have enough fuel left to make the necessary orbital changes for the flyby. Instead the Vega probes took the opportunity to measure the dust as they passed through the orbits of 72P/Denning–Fujikawa, Biela's Comet and 289P/Blanpain.

Contact with Vega 2 was lost on 24 March 1987. Vega 1 had previously exhausted its attitude control propellant on 30 January 1987.

Vega 2 is currently in heliocentric orbit, with perihelion of 0.70 AU, aphelion of 0.98 AU, eccentricity of 0.17, inclination of 2.3 degrees and orbital period of 281 days.

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/

title: Vega 2


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Sacramento Monarchs

The Sacramento Monarchs were a professional basketball team based in Sacramento, California. They played in the Women's National Basketball Association (WNBA) from 1997 until folding on November 20, 2009. They played their home games at ARCO Arena.

The Monarchs were one of the WNBA's eight original franchises and were noted early on for standout players Ticha Penicheiro, Ruthie Bolton and Yolanda Griffith. They were the sister franchise of the Sacramento Kings National Basketball Association (NBA) team. They were one of the more successful WNBA franchises on the court, though they often trailed behind perennial Western Conference champions the Houston Comets and the Los Angeles Sparks. However, in 2005, the team brought Sacramento its first championship, winning the WNBA Finals for the only time.

Origins (1997–2003)
The Monarchs made an impact in the WNBA almost immediately. With the hiring of Portuguese national team player Ticha Penicheiro, popular player Ruthie Bolton and prolific scorer Yolanda Griffith, all of whom have been WNBA All-Stars, the Monarchs have been able to make the playoffs almost every year so far, but were normally eliminated before reaching the WNBA Finals.

Championship window (2004–2006)
After losing to the Seattle Storm in the 2004 WNBA Western Conference Championship, the Monarchs made major roster moves to improve the team – obtaining younger players and emphasizing Head Coach John Whisenant's defense-oriented system. Bolton, one of the team's original players, became a free agent and the Monarchs made the difficult decision not to keep her on the active playing roster, though they did offer her a position in their front office. Edna Campbell, a breast cancer survivor and another fan favorite, was not signed by the Monarchs and later signed with the San Antonio Silver Stars.

On March 3, 2005, the Monarchs traded Tangela Smith and a 2006 second round draft pick to the Charlotte Sting in exchange for former Stanford University standout Nicole Powell, Olympia Scott-Richardson, and Erin Buescher. After signing two Chinese players, Miao Lijie and Sui Feifei, the Monarchs traded Chantelle Anderson to the San Antonio Silver Stars for a 2006 draft pick. During the 2005 WNBA draft, the Monarchs drafted point guard Kristin Haynie from Michigan State University and Chelsea Newton from Rutgers University. The Monarchs did sign Ruthie Bolton as a free agent for the purpose of her trying to win a spot on team's roster during its pre-season training camp, but eventually waived her. Bolton later joined the Monarchs to work in their promotions and public relations department.

The offseason moves immediately paid off for the Monarchs as the team finished with a franchise-best 25–9 win–loss record. Whisenant was later named the WNBA Coach of the Year, and Powell received the WNBA Most Improved Player Award. After previous seasons of being eliminated from the WNBA Playoffs by either the Houston Comets or the Los Angeles Sparks, the Monarchs finally defeated both, sweeping both teams en route to their first appearance in the WNBA Finals. The Monarchs won their first ever WNBA Finals by defeating the Connecticut Sun, three games to one in a best-of-five playoff series, which brought the city of Sacramento its second major championship in a professional sport. After winning the championship, the Monarchs became the first women's professional team to appear on a Wheaties box.

The Monarchs remained strong in 2006, finishing second place in the West. The Monarchs would catch fire in the playoffs, once again sweeping both Houston and then top seeded LA to reach the Finals for the second straight season. But in the Finals, they were defeated by the Detroit Shock 3 games to 2, in the first WNBA Finals to go 5 games.

Decline (2007–2009)
In 2007, the Monarchs finished strongly again, but blew a chance to get the #2 seed at the end of the season. They were matched up against the San Antonio Silver Stars. After defeating the Silver Stars in game 1 at home, the Monarchs would lose games 2 & 3 (and the series) in San Antonio, ending their two-year run as Western Conference champions.

In 2008 the Monarchs were markedly less strong, but hung around the Western Playoff picture all season and finished with the #4 seed. Facing the Silver Stars again in the first round, the Monarchs were hoping for some payback for 2007. The series did not start well for the Monarchs, as they dropped Game 1 at home 85–78. Now the series shifted to San Antonio, and it seemed the series would come to a quick end. But the Monarchs would not back down, blowing out the Silver Stars in Game 2 84–67, forcing the critical Game 3. In Game 3, the Stars came out strong and at one point had a 14-point lead. But the Monarchs put together a furious rally, scoring seven points in the final 90 seconds of play to even the game and force it to overtime. But unfortunately for the Monarchs, the Silver Stars came out strong in the extra period and won the game, 86–81, ending the Monarchs' season.

In 2009, the Monarchs had one of their worst seasons in franchise history. It also led to the firing of head coach Jenny Boucek during the season, after which she was replaced by John Whisenant, the coach that led the Monarchs to their first championship in 2005. They finished 12–22, last in the conference and the league. They also missed the playoffs for the first time since the 2002 season and tied the record for the most losses with 22, the same number of losses they made 11 years ago.

Dissolution
It was revealed on November 20, 2009, that the Maloof family would no longer operate the Monarchs. The league attempted to re-locate the Monarchs to the San Francisco Bay Area, but on December 8, 2009, it was announced that new ownership could not be found and a dispersal draft would be held on December 14, 2009. As of 2024, the Monarchs were the last WNBA team to cease operations.

Possibility of rebirth
In October 2009, there were plans to relocate the Monarchs to Oakland but they never came to fruition. The ownership group of the Sacramento Kings, led by Vivek Ranadivé, have indicated a desire to bring back the Monarchs as shared tenants for the new Golden 1 Center an intention shared with former Sacramento mayor Kevin Johnson, himself a former professional basketball player in the NBA.

Head coaches

 * Mary Murphy (1997)
 * Heidi VanDerveer (1997–1998)
 * Sonny Allen (1999–2001)
 * Maura McHugh (2001–2003)
 * John Whisenant (2003–2006, 2009)
 * Jenny Boucek (2007–2009)

General managers

 * Jerry Reynolds (1997-2003)
 * John Whisenant (2003–09)

Hall of Famers

 * Bridgette Gordon
 * Ruthie Bolton
 * Ticha Penicheiro
 * Yolanda Griffith

Retired numbers
1 The Monarchs' first General Manager, has a retired jersey marked "GM", that was hung onto the ARCO Arena's rafters in 2004.

Notable players

 * Chantelle Anderson
 * Cass Bauer-Bilodeau
 * Cindy Blodgett
 * Rebekkah Brunson
 * Erin Buescher
 * Latasha Byears
 * Edna Campbell
 * Bridgette Gordon
 * Lady Grooms
 * Yolanda Griffith
 * Kristin Haynie
 * Kedra Holland-Corn
 * Kara Lawson
 * Hamchetou Maiga-Ba
 * Pamela McGee
 * Courtney Paris
 * Ticha Penicheiro
 * Nicole Powell
 * Scholanda Robinson
 * Laure Savasta
 * Olympia Scott-Richardson
 * Tangela Smith
 * Kate Starbird
 * Katy Steding
 * Chantel Tremitiere
 * DeMya Walker
 * Kara Wolters
 * Adrian Williams-Strong

All-Stars

 * 1999: Ticha Penicheiro, Ruthie Bolton-Holifield, Yolanda Griffith
 * 2000: Ticha Penicheiro, Yolanda Griffith
 * 2001: Ticha Penicheiro, Ruthie Bolton-Holifield, Yolanda Griffith
 * 2002: Ticha Penicheiro
 * 2003: Yolanda Griffith
 * 2004: None but Yolanda Griffith on USA Olympic Team
 * 2005: Yolanda Griffith, DeMya Walker
 * 2006: Yolanda Griffith
 * 2007: Yolanda Griffith, Kara Lawson, Rebekkah Brunson
 * 2008: No All-Star Game
 * 2009: Nicole Powell

title: Sacramento Monarchs


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Heat transfer

Heat transfer is a discipline of thermal engineering that concerns the generation, use, conversion, and exchange of thermal energy (heat) between physical systems. Heat transfer is classified into various mechanisms, such as thermal conduction, thermal convection, thermal radiation, and transfer of energy by phase changes. Engineers also consider the transfer of mass of differing chemical species (mass transfer in the form of advection), either cold or hot, to achieve heat transfer. While these mechanisms have distinct characteristics, they often occur simultaneously in the same system.

Heat conduction, also called diffusion, is the direct microscopic exchanges of kinetic energy of particles (such as molecules) or quasiparticles (such as lattice waves) through the boundary between two systems. When an object is at a different temperature from another body or its surroundings, heat flows so that the body and the surroundings reach the same temperature, at which point they are in thermal equilibrium. Such spontaneous heat transfer always occurs from a region of high temperature to another region of lower temperature, as described in the second law of thermodynamics.

Heat convection occurs when the bulk flow of a fluid (gas or liquid) carries its heat through the fluid. All convective processes also move heat partly by diffusion, as well. The flow of fluid may be forced by external processes, or sometimes (in gravitational fields) by buoyancy forces caused when thermal energy expands the fluid (for example in a fire plume), thus influencing its own transfer. The latter process is often called "natural convection". The former process is often called "forced convection." In this case, the fluid is forced to flow by use of a pump, fan, or other mechanical means.

Thermal radiation occurs through a vacuum or any transparent medium (solid or fluid or gas). It is the transfer of energy by means of photons or electromagnetic waves governed by the same laws.

Overview
Heat transfer is the energy exchanged between materials (solid/liquid/gas) as a result of a temperature difference. The thermodynamic free energy is the amount of work that a thermodynamic system can perform. Enthalpy is a thermodynamic potential, designated by the letter "H", that is the sum of the internal energy of the system (U) plus the product of pressure (P) and volume (V). Joule is a unit to quantify energy, work, or the amount of heat.

Heat transfer is a process function (or path function), as opposed to functions of state; therefore, the amount of heat transferred in a thermodynamic process that changes the state of a system depends on how that process occurs, not only the net difference between the initial and final states of the process.

Thermodynamic and mechanical heat transfer is calculated with the heat transfer coefficient, the proportionality between the heat flux and the thermodynamic driving force for the flow of heat. Heat flux is a quantitative, vectorial representation of heat-flow through a surface.

In engineering contexts, the term heat is taken as synonymous to thermal energy. This usage has its origin in the historical interpretation of heat as a fluid (caloric) that can be transferred by various causes, and that is also common in the language of laymen and everyday life.

The transport equations for thermal energy (Fourier's law), mechanical momentum (Newton's law for fluids), and mass transfer (Fick's laws of diffusion) are similar, and analogies among these three transport processes have been developed to facilitate prediction of conversion from any one to the others.

Thermal engineering concerns the generation, use, conversion, storage, and exchange of heat transfer. As such, heat transfer is involved in almost every sector of the economy. Heat transfer is classified into various mechanisms, such as thermal conduction, thermal convection, thermal radiation, and transfer of energy by phase changes.

Mechanisms
The fundamental modes of heat transfer are:

 * Advection
 * Advection is the transport mechanism of a fluid from one location to another, and is dependent on motion and momentum of that fluid.

 * Conduction or diffusion
 * The transfer of energy between objects that are in physical contact. Thermal conductivity is the property of a material to conduct heat and evaluated primarily in terms of Fourier's Law for heat conduction.

 * Convection
 * The transfer of energy between an object and its environment, due to fluid motion. The average temperature is a reference for evaluating properties related to convective heat transfer.

 * Radiation
 * The transfer of energy by the emission of electromagnetic radiation.

Advection
By transferring matter, energy—including thermal energy—is moved by the physical transfer of a hot or cold object from one place to another. This can be as simple as placing hot water in a bottle and heating a bed, or the movement of an iceberg in changing ocean currents. A practical example is thermal hydraulics. This can be described by the formula: $$\phi_q = v \rho c_p \Delta T$$ where
 * $$\phi_q$$ is heat flux (W/m2),
 * $$\rho$$ is density (kg/m3),
 * $$c_p$$ is heat capacity at constant pressure (J/kg·K),
 * $$\Delta T$$ is the difference in temperature (K),
 * $$v$$ is velocity (m/s).

Conduction
On a microscopic scale, heat conduction occurs as hot, rapidly moving or vibrating atoms and molecules interact with neighboring atoms and molecules, transferring some of their energy (heat) to these neighboring particles. In other words, heat is transferred by conduction when adjacent atoms vibrate against one another, or as electrons move from one atom to another. Conduction is the most significant means of heat transfer within a solid or between solid objects in thermal contact. Fluids—especially gases—are less conductive. Thermal contact conductance is the study of heat conduction between solid bodies in contact. The process of heat transfer from one place to another place without the movement of particles is called conduction, such as when placing a hand on a cold glass of water—heat is conducted from the warm skin to the cold glass, but if the hand is held a few inches from the glass, little conduction would occur since air is a poor conductor of heat. Steady state conduction is an idealized model of conduction that happens when the temperature difference driving the conduction is constant, so that after a time, the spatial distribution of temperatures in the conducting object does not change any further (see Fourier's law). In steady state conduction, the amount of heat entering a section is equal to amount of heat coming out, since the change in temperature (a measure of heat energy) is zero. An example of steady state conduction is the heat flow through walls of a warm house on a cold day—inside the house is maintained at a high temperature and, outside, the temperature stays low, so the transfer of heat per unit time stays near a constant rate determined by the insulation in the wall and the spatial distribution of temperature in the walls will be approximately constant over time.

Transient conduction (see Heat equation) occurs when the temperature within an object changes as a function of time. Analysis of transient systems is more complex, and analytic solutions of the heat equation are only valid for idealized model systems. Practical applications are generally investigated using numerical methods, approximation techniques, or empirical study.

Convection
The flow of fluid may be forced by external processes, or sometimes (in gravitational fields) by buoyancy forces caused when thermal energy expands the fluid (for example in a fire plume), thus influencing its own transfer. The latter process is often called "natural convection". All convective processes also move heat partly by diffusion, as well. Another form of convection is forced convection. In this case the fluid is forced to flow by using a pump, fan or other mechanical means.

Convective heat transfer, or simply, convection, is the transfer of heat from one place to another by the movement of fluids, a process that is essentially the transfer of heat via mass transfer. Bulk motion of fluid enhances heat transfer in many physical situations, such as (for example) between a solid surface and the fluid. Convection is usually the dominant form of heat transfer in liquids and gases. Although sometimes discussed as a third method of heat transfer, convection is usually used to describe the combined effects of heat conduction within the fluid (diffusion) and heat transference by bulk fluid flow streaming. The process of transport by fluid streaming is known as advection, but pure advection is a term that is generally associated only with mass transport in fluids, such as advection of pebbles in a river. In the case of heat transfer in fluids, where transport by advection in a fluid is always also accompanied by transport via heat diffusion (also known as heat conduction) the process of heat convection is understood to refer to the sum of heat transport by advection and diffusion/conduction.

Free, or natural, convection occurs when bulk fluid motions (streams and currents) are caused by buoyancy forces that result from density variations due to variations of temperature in the fluid. Forced convection is a term used when the streams and currents in the fluid are induced by external means—such as fans, stirrers, and pumps—creating an artificially induced convection current.

Convection-cooling
Convective cooling is sometimes described as Newton's law of cooling: "The rate of heat loss of a body is proportional to the temperature difference between the body and its surroundings." However, by definition, the validity of Newton's law of Cooling requires that the rate of heat loss from convection be a linear function of ("proportional to") the temperature difference that drives heat transfer, and in convective cooling this is sometimes not the case. In general, convection is not linearly dependent on temperature gradients, and in some cases is strongly nonlinear. In these cases, Newton's law does not apply.

Convection vs. conduction
In a body of fluid that is heated from underneath its container, conduction and convection can be considered to compete for dominance. If heat conduction is too great, fluid moving down by convection is heated by conduction so fast that its downward movement will be stopped due to its buoyancy, while fluid moving up by convection is cooled by conduction so fast that its driving buoyancy will diminish. On the other hand, if heat conduction is very low, a large temperature gradient may be formed and convection might be very strong.

The Rayleigh number ($$\mathrm{Ra} $$) is the product of the Grashof ($$\mathrm{Gr} $$) and Prandtl ($$\mathrm{Pr} $$) numbers. It is a measure which determines the relative strength of conduction and convection.

$$ \mathrm{Ra} = \mathrm{Gr} \cdot \mathrm{Pr} = \frac{g \Delta \rho L^3} {\mu \alpha} = \frac{g \beta \Delta T L^3} {\nu \alpha}$$ where
 * g is acceleration due to gravity,
 * ρ is the density with $$\Delta \rho$$ being the density difference between the lower and upper ends,
 * μ is the dynamic viscosity,
 * α is the Thermal diffusivity,
 * β is the volume thermal expansivity (sometimes denoted α elsewhere),
 * T is the temperature,
 * ν is the kinematic viscosity, and
 * L is characteristic length.

The Rayleigh number can be understood as the ratio between the rate of heat transfer by convection to the rate of heat transfer by conduction; or, equivalently, the ratio between the corresponding timescales (i.e. conduction timescale divided by convection timescale), up to a numerical factor. This can be seen as follows, where all calculations are up to numerical factors depending on the geometry of the system.

The buoyancy force driving the convection is roughly $$g \Delta \rho L^3$$, so the corresponding pressure is roughly $$g \Delta \rho L $$. In steady state, this is canceled by the shear stress due to viscosity, and therefore roughly equals $$\mu V/L = \mu / T_\text{conv} $$, where V is the typical fluid velocity due to convection and $$T_\text{conv}$$ the order of its timescale. The conduction timescale, on the other hand, is of the order of $$T_\text{cond} = L^2/ \alpha$$.

Convection occurs when the Rayleigh number is above 1,000–2,000.

Radiation
Radiative heat transfer is the transfer of energy via thermal radiation, i.e., electromagnetic waves. It occurs across vacuum or any transparent medium (solid or fluid or gas). Thermal radiation is emitted by all objects at temperatures above absolute zero, due to random movements of atoms and molecules in matter. Since these atoms and molecules are composed of charged particles (protons and electrons), their movement results in the emission of electromagnetic radiation which carries away energy. Radiation is typically only important in engineering applications for very hot objects, or for objects with a large temperature difference.

When the objects and distances separating them are large in size and compared to the wavelength of thermal radiation, the rate of transfer of radiant energy is best described by the Stefan-Boltzmann equation. For an object in vacuum, the equation is: $$ \phi_q=\epsilon \sigma T^4. $$

For radiative transfer between two objects, the equation is as follows: $$ \phi_q=\epsilon \sigma F (T_a^4 - T_b^4), $$ where
 * $$\phi_q$$ is the heat flux,
 * $$\epsilon $$ is the emissivity (unity for a black body),
 * $$\sigma $$ is the Stefan–Boltzmann constant,
 * $$F$$ is the view factor between two surfaces a and b, and
 * $$ T_a$$ and $$ T_b$$ are the absolute temperatures (in kelvins or degrees Rankine) for the two objects.

The blackbody limit established by the Stefan-Boltzmann equation can be exceeded when the objects exchanging thermal radiation or the distances separating them are comparable in scale or smaller than the dominant thermal wavelength. The study of these cases is called near-field radiative heat transfer.

Radiation from the sun, or solar radiation, can be harvested for heat and power. Unlike conductive and convective forms of heat transfer, thermal radiation – arriving within a narrow angle i.e. coming from a source much smaller than its distance – can be concentrated in a small spot by using reflecting mirrors, which is exploited in concentrating solar power generation or a burning glass. For example, the sunlight reflected from mirrors heats the PS10 solar power tower and during the day it can heat water to 285 °C.

The reachable temperature at the target is limited by the temperature of the hot source of radiation. (T4-law lets the reverse-flow of radiation back to the source rise.) The (on its surface) somewhat 4000 K hot sun allows to reach coarsely 3000 K (or 3000 °C, which is about 3273 K) at a small probe in the focus spot of a big concave, concentrating mirror of the Mont-Louis Solar Furnace in France.

Phase transition
Phase transition or phase change, takes place in a thermodynamic system from one phase or state of matter to another one by heat transfer. Phase change examples are the melting of ice or the boiling of water. The Mason equation explains the growth of a water droplet based on the effects of heat transport on evaporation and condensation.

Phase transitions involve the four fundamental states of matter:
 * Solid – Deposition, freezing and solid to solid transformation.
 * Liquid – Condensation and melting / fusion.
 * Gas – Boiling / evaporation, recombination/ deionization, and sublimation.
 * Plasma – Ionization.

Boiling
The boiling point of a substance is the temperature at which the vapor pressure of the liquid equals the pressure surrounding the liquid and the liquid evaporates resulting in an abrupt change in vapor volume.

In a closed system, saturation temperature and boiling point mean the same thing. The saturation temperature is the temperature for a corresponding saturation pressure at which a liquid boils into its vapor phase. The liquid can be said to be saturated with thermal energy. Any addition of thermal energy results in a phase transition.

At standard atmospheric pressure and low temperatures, no boiling occurs and the heat transfer rate is controlled by the usual single-phase mechanisms. As the surface temperature is increased, local boiling occurs and vapor bubbles nucleate, grow into the surrounding cooler fluid, and collapse. This is sub-cooled nucleate boiling, and is a very efficient heat transfer mechanism. At high bubble generation rates, the bubbles begin to interfere and the heat flux no longer increases rapidly with surface temperature (this is the departure from nucleate boiling, or DNB).

At similar standard atmospheric pressure and high temperatures, the hydrodynamically quieter regime of film boiling is reached. Heat fluxes across the stable vapor layers are low, but rise slowly with temperature. Any contact between fluid and the surface that may be seen probably leads to the extremely rapid nucleation of a fresh vapor layer ("spontaneous nucleation"). At higher temperatures still, a maximum in the heat flux is reached (the critical heat flux, or CHF).

The Leidenfrost Effect demonstrates how nucleate boiling slows heat transfer due to gas bubbles on the heater's surface. As mentioned, gas-phase thermal conductivity is much lower than liquid-phase thermal conductivity, so the outcome is a kind of "gas thermal barrier".

Condensation
Condensation occurs when a vapor is cooled and changes its phase to a liquid. During condensation, the latent heat of vaporization must be released. The amount of the heat is the same as that absorbed during vaporization at the same fluid pressure.

There are several types of condensation:
 * Homogeneous condensation, as during a formation of fog.
 * Condensation in direct contact with subcooled liquid.
 * Condensation on direct contact with a cooling wall of a heat exchanger: This is the most common mode used in industry: Dropwise condensation is difficult to sustain reliably; therefore, industrial equipment is normally designed to operate in filmwise condensation mode.

Melting
Melting is a thermal process that results in the phase transition of a substance from a solid to a liquid. The internal energy of a substance is increased, typically through heat or pressure, resulting in a rise of its temperature to the melting point, at which the ordering of ionic or molecular entities in the solid breaks down to a less ordered state and the solid liquefies. Molten substances generally have reduced viscosity with elevated temperature; an exception to this maxim is the element sulfur, whose viscosity increases to a point due to polymerization and then decreases with higher temperatures in its molten state.

Modeling approaches
Heat transfer can be modeled in various ways.

Heat equation
The heat equation is an important partial differential equation that describes the distribution of heat (or variation in temperature) in a given region over time. In some cases, exact solutions of the equation are available; in other cases the equation must be solved numerically using computational methods such as DEM-based models for thermal/reacting particulate systems (as critically reviewed by Peng et al. ).

Lumped system analysis
Lumped system analysis often reduces the complexity of the equations to one first-order linear differential equation, in which case heating and cooling are described by a simple exponential solution, often referred to as Newton's law of cooling.

System analysis by the lumped capacitance model is a common approximation in transient conduction that may be used whenever heat conduction within an object is much faster than heat conduction across the boundary of the object. This is a method of approximation that reduces one aspect of the transient conduction system—that within the object—to an equivalent steady state system. That is, the method assumes that the temperature within the object is completely uniform, although its value may be changing in time.

In this method, the ratio of the conductive heat resistance within the object to the convective heat transfer resistance across the object's boundary, known as the Biot number, is calculated. For small Biot numbers, the approximation of spatially uniform temperature within the object can be used: it can be presumed that heat transferred into the object has time to uniformly distribute itself, due to the lower resistance to doing so, as compared with the resistance to heat entering the object.

Climate models
Climate models study the radiant heat transfer by using quantitative methods to simulate the interactions of the atmosphere, oceans, land surface, and ice.

Engineering
Heat transfer has broad application to the functioning of numerous devices and systems. Heat-transfer principles may be used to preserve, increase, or decrease temperature in a wide variety of circumstances. Heat transfer methods are used in numerous disciplines, such as automotive engineering, thermal management of electronic devices and systems, climate control, insulation, materials processing, chemical engineering and power station engineering.

Insulation, radiance and resistance
Thermal insulators are materials specifically designed to reduce the flow of heat by limiting conduction, convection, or both. Thermal resistance is a heat property and the measurement by which an object or material resists to heat flow (heat per time unit or thermal resistance) to temperature difference.

Radiance or spectral radiance are measures of the quantity of radiation that passes through or is emitted. Radiant barriers are materials that reflect radiation, and therefore reduce the flow of heat from radiation sources. Good insulators are not necessarily good radiant barriers, and vice versa. Metal, for instance, is an excellent reflector and a poor insulator.

The effectiveness of a radiant barrier is indicated by its reflectivity, which is the fraction of radiation reflected. A material with a high reflectivity (at a given wavelength) has a low emissivity (at that same wavelength), and vice versa. At any specific wavelength, reflectivity=1 - emissivity. An ideal radiant barrier would have a reflectivity of 1, and would therefore reflect 100 percent of incoming radiation. Vacuum flasks, or Dewars, are silvered to approach this ideal. In the vacuum of space, satellites use multi-layer insulation, which consists of many layers of aluminized (shiny) Mylar to greatly reduce radiation heat transfer and control satellite temperature.

Devices
A heat engine is a system that performs the conversion of a flow of thermal energy (heat) to mechanical energy to perform mechanical work.

A thermocouple is a temperature-measuring device and widely used type of temperature sensor for measurement and control, and can also be used to convert heat into electric power.

A thermoelectric cooler is a solid state electronic device that pumps (transfers) heat from one side of the device to the other when electric current is passed through it. It is based on the Peltier effect.

A thermal diode or thermal rectifier is a device that causes heat to flow preferentially in one direction.

Heat exchangers
A heat exchanger is used for more efficient heat transfer or to dissipate heat. Heat exchangers are widely used in refrigeration, air conditioning, space heating, power generation, and chemical processing. One common example of a heat exchanger is a car's radiator, in which the hot coolant fluid is cooled by the flow of air over the radiator's surface.

Common types of heat exchanger flows include parallel flow, counter flow, and cross flow. In parallel flow, both fluids move in the same direction while transferring heat; in counter flow, the fluids move in opposite directions; and in cross flow, the fluids move at right angles to each other. Common types of heat exchangers include shell and tube, double pipe, extruded finned pipe, spiral fin pipe, u-tube, and stacked plate. Each type has certain advantages and disadvantages over other types.

A heat sink is a component that transfers heat generated within a solid material to a fluid medium, such as air or a liquid. Examples of heat sinks are the heat exchangers used in refrigeration and air conditioning systems or the radiator in a car. A heat pipe is another heat-transfer device that combines thermal conductivity and phase transition to efficiently transfer heat between two solid interfaces.

Architecture
Efficient energy use is the goal to reduce the amount of energy required in heating or cooling. In architecture, condensation and air currents can cause cosmetic or structural damage. An energy audit can help to assess the implementation of recommended corrective procedures. For instance, insulation improvements, air sealing of structural leaks or the addition of energy-efficient windows and doors.
 * Smart meter is a device that records electric energy consumption in intervals.
 * Thermal transmittance is the rate of transfer of heat through a structure divided by the difference in temperature across the structure. It is expressed in watts per square meter per kelvin, or W/(m2K). Well-insulated parts of a building have a low thermal transmittance, whereas poorly-insulated parts of a building have a high thermal transmittance.
 * Thermostat is a device to monitor and control temperature.

Climate engineering
Climate engineering consists of carbon dioxide removal and solar radiation management. Since the amount of carbon dioxide determines the radiative balance of Earth atmosphere, carbon dioxide removal techniques can be applied to reduce the radiative forcing. Solar radiation management is the attempt to absorb less solar radiation to offset the effects of greenhouse gases.

An alternative method is passive daytime radiative cooling, which enhances terrestrial heat flow to outer space through the infrared window (8–13 μm). Rather than merely blocking solar radiation, this method increases outgoing longwave infrared (LWIR) thermal radiation heat transfer with the extremely cold temperature of outer space (~2.7 K) to lower ambient temperatures while requiring zero energy input.

Greenhouse effect
The greenhouse effect is a process by which thermal radiation from a planetary surface is absorbed by atmospheric greenhouse gases and clouds, and is re-radiated in all directions, resulting in a reduction in the amount of thermal radiation reaching space relative to what would reach space in the absence of absorbing materials. This reduction in outgoing radiation leads to a rise in the temperature of the surface and troposphere, until the rate of outgoing radiation again equals the rate at which heat arrives from the Sun.

Heat transfer in the human body
The principles of heat transfer in engineering systems can be applied to the human body in order to determine how the body transfers heat. Heat is produced in the body by the continuous metabolism of nutrients which provides energy for the systems of the body. The human body must maintain a consistent internal temperature in order to maintain healthy bodily functions. Therefore, excess heat must be dissipated from the body to keep it from overheating. When a person engages in elevated levels of physical activity, the body requires additional fuel which increases the metabolic rate and the rate of heat production. The body must then use additional methods to remove the additional heat produced in order to keep the internal temperature at a healthy level.

Heat transfer by convection is driven by the movement of fluids over the surface of the body. This convective fluid can be either a liquid or a gas. For heat transfer from the outer surface of the body, the convection mechanism is dependent on the surface area of the body, the velocity of the air, and the temperature gradient between the surface of the skin and the ambient air. The normal temperature of the body is approximately 37 °C. Heat transfer occurs more readily when the temperature of the surroundings is significantly less than the normal body temperature. This concept explains why a person feels cold when not enough covering is worn when exposed to a cold environment. Clothing can be considered an insulator which provides thermal resistance to heat flow over the covered portion of the body. This thermal resistance causes the temperature on the surface of the clothing to be less than the temperature on the surface of the skin. This smaller temperature gradient between the surface temperature and the ambient temperature will cause a lower rate of heat transfer than if the skin were not covered.

In order to ensure that one portion of the body is not significantly hotter than another portion, heat must be distributed evenly through the bodily tissues. Blood flowing through blood vessels acts as a convective fluid and helps to prevent any buildup of excess heat inside the tissues of the body. This flow of blood through the vessels can be modeled as pipe flow in an engineering system. The heat carried by the blood is determined by the temperature of the surrounding tissue, the diameter of the blood vessel, the thickness of the fluid, velocity of the flow, and the heat transfer coefficient of the blood. The velocity, blood vessel diameter, and the fluid thickness can all be related with the Reynolds Number, a dimensionless number used in fluid mechanics to characterize the flow of fluids.

Latent heat loss, also known as evaporative heat loss, accounts for a large fraction of heat loss from the body. When the core temperature of the body increases, the body triggers sweat glands in the skin to bring additional moisture to the surface of the skin. The liquid is then transformed into vapor which removes heat from the surface of the body. The rate of evaporation heat loss is directly related to the vapor pressure at the skin surface and the amount of moisture present on the skin. Therefore, the maximum of heat transfer will occur when the skin is completely wet. The body continuously loses water by evaporation but the most significant amount of heat loss occurs during periods of increased physical activity.

Evaporative cooling
Evaporative cooling happens when water vapor is added to the surrounding air. The energy needed to evaporate the water is taken from the air in the form of sensible heat and converted into latent heat, while the air remains at a constant enthalpy. Latent heat describes the amount of heat that is needed to evaporate the liquid; this heat comes from the liquid itself and the surrounding gas and surfaces. The greater the difference between the two temperatures, the greater the evaporative cooling effect. When the temperatures are the same, no net evaporation of water in air occurs; thus, there is no cooling effect.

Laser cooling
In quantum physics, laser cooling is used to achieve temperatures of near absolute zero (−273.15 °C, −459.67 °F) of atomic and molecular samples to observe unique quantum effects that can only occur at this heat level.
 * Doppler cooling is the most common method of laser cooling.
 * Sympathetic cooling is a process in which particles of one type cool particles of another type. Typically, atomic ions that can be directly laser-cooled are used to cool nearby ions or atoms. This technique allows cooling of ions and atoms that cannot be laser cooled directly.

Magnetic cooling
Magnetic evaporative cooling is a process for lowering the temperature of a group of atoms, after pre-cooled by methods such as laser cooling. Magnetic refrigeration cools below 0.3K, by making use of the magnetocaloric effect.

Radiative cooling
Radiative cooling is the process by which a body loses heat by radiation. Outgoing energy is an important effect in the Earth's energy budget. In the case of the Earth-atmosphere system, it refers to the process by which long-wave (infrared) radiation is emitted to balance the absorption of short-wave (visible) energy from the Sun. The thermosphere (top of atmosphere) cools to space primarily by infrared energy radiated by carbon dioxide at 15 μm and by nitric oxide (NO) at 5.3 μm. Convective transport of heat and evaporative transport of latent heat both remove heat from the surface and redistribute it in the atmosphere.

Thermal energy storage
Thermal energy storage includes technologies for collecting and storing energy for later use. It may be employed to balance energy demand between day and nighttime. The thermal reservoir may be maintained at a temperature above or below that of the ambient environment. Applications include space heating, domestic or process hot water systems, or generating electricity.

Newton's law of cooling
In 1701, Isaac Newton anonymously published an article in Philosophical Transactions noting (in modern terms) that the rate of temperature change of a body is proportional to the difference in temperatures (graduum caloris, "degrees of heat") between the body and its surroundings. The phrase "temperature change" was later replaced with "heat loss", and the relationship named Newton's law of cooling. In general, the law is valid only if the temperature difference is small and the heat transfer mechanism remains the same.

Thermal conduction
In heat conduction, the law is valid only if the thermal conductivity of the warmer body is independent of temperature. The thermal conductivity of most materials is only weakly dependent on temperature, so in general the law holds true.

Thermal convection
In convective heat transfer, the law is valid for forced air or pumped fluid cooling, where the properties of the fluid do not vary strongly with temperature, but it is only approximately true for buoyancy-driven convection, where the velocity of the flow increases with temperature difference.

Thermal radiation
In the case of heat transfer by thermal radiation, Newton's law of cooling holds only for very small temperature differences.

Thermal conductivity of different metals
In a 1780 letter to Benjamin Franklin, Dutch-born British scientist Jan Ingenhousz relates an experiment which enabled him to rank seven different metals according to their thermal conductivities:

"You remembre you gave me a wire of five metals all drawn thro the same hole Viz. one, of gould, one of silver, copper steel and iron. I supplyed here the two others Viz. the one of tin the other of lead. I fixed these seven wires into a wooden frame at an equal distance of one an other ... I dipt the seven wires into this melted wax as deep as the wooden frame ... By taking them out they were covred with a coat of wax ... When I found that this crust was there about of an equal thikness upon all the wires, I placed them all in a glased earthen vessel full of olive oil heated to some degrees under boiling, taking care that each wire was dipt just as far in the oil as the other ... Now, as they had been all dipt alike at the same time in the same oil, it must follow, that the wire, upon which the wax had been melted the highest, had been the best conductor of heat. ... Silver conducted heat far the best of all other metals, next to this was copper, then gold, tin, iron, steel, Lead."

Benjamin Thompson's experiments on heat transfer
During the years 1784 – 1798, the British physicist Benjamin Thompson (Count Rumford) lived in Bavaria, reorganizing the Bavarian army for the Prince-elector Charles Theodore among other official and charitable duties. The Elector gave Thompson access to the facilities of the Electoral Academy of Sciences in Mannheim. During his years in Mannheim and later in Munich, Thompson made a large number of discoveries and inventions related to heat.

"New Experiments upon Heat"
In 1785 Thompson performed a series of thermal conductivity experiments, which he describes in great detail in the Philosophical Transactions article "New Experiments upon Heat" from 1786. The fact that good electrical conductors are often also good heat conductors and vice versa must have been well known at the time, for Thompson mentions it in passing. His intention was to measure the relative conductivities of mercury, water, moist air, "common air" (dry air at normal atmospheric pressure), dry air of various rarefication, and a "Torricellian vacuum". "From the striking analogy between the electric fluid and heat respecting their conductors and non-conductors (having found that bodies, in general, which are conductors of the electric fluid, are likewise good conductors of heat, and, on the contrary, that electric bodies, or such as are bad conductors of the electric fluid, are likewise bad conductors of heat), I was led to imagine that the Torricellian vacuum, which is known to afford so ready a passage to the electric fluid, would also have afforded a ready passage to heat." For these experiments Thompson employed a thermometer inside a large, closed glass tube. Under the circumstances described, heat may—unbeknownst to Thompson—have been transferred more by radiation than by conduction. These were his results.

After the experiments, Thompson was surprised to observe that a vacuum was a significantly poorer heat conductor than air "which of itself is reckoned among the worst", but only a very small difference between common air and rarefied air. He also noted the great difference between dry air and moist air, and the great benefit this affords. "I cannot help observing, with what infinite wisdom and goodness Divine Providence appears to have guarded us against the evil effects of excessive heat and cold in the atmosphere; for if it were possible for the air to be equally damp during the severe cold of the winter ... as it sometimes is in summer, its conducing power, and consequently its apparent coldness ... would become quite intolerable; but, happily for us, its power to hold water in solution is diminished, and with it its power to rob us of our animal heat.""Every body knows how very disagreeable a very moderate degree of cold is when the air is very damp; and from hence it appears, why the thermometer is not always a just measure of the apparent or sensible heat of the atmosphere. If colds ... are occasioned by our bodies being robbed of our animal heat, the reason is plain why those disorders prevail most during the cold autumnal rains, and upon the breaking up of the frost in the spring. It is likewise plain [why] ... inhabiting damp houses, is so very dangerous; and why the evening air is so pernicious in summer ... and why it is not so during the hard frosts of winter."

Temperature vs. sensible heat
Thompson concluded with some comments on the important difference between temperature and sensible heat. "The ... sensation of hot or cold depends not intirely upon the temperature of the body exciting in us those sensations ... but upon the quantity of heat it is capable of communicating to us, or receiving from us ... and this depends in a great measure upon the conducing powers of the bodies in question. The sensation of hot is the entrance of heat into our bodies; that of cold is its exit ... This is another proof that the thermometer cannot be a just measure of sensible heat ... or rather, that the touch does not afford us a just indication of ... real temperatures."

Coining of the term "convection"
In the 1830s, in The Bridgewater Treatises, the term convection is attested in a scientific sense. In treatise VIII by William Prout, in the book on chemistry, it says: "This motion of heat takes place in three ways, which a common fire-place very well illustrates. If, for instance, we place a thermometer directly before a fire, it soon begins to rise, indicating an increase of temperature. In this case the heat has made its way through the space between the fire and the thermometer, by the process termed radiation. If we place a second thermometer in contact with any part of the grate, and away from the direct influence of the fire, we shall find that this thermometer also denotes an increase of temperature; but here the heat must have travelled through the metal of the grate, by what is termed conduction. Lastly, a third thermometer placed in the chimney, away from the direct influence of the fire, will also indicate a considerable increase of temperature; in this case a portion of the air, passing through and near the fire, has become heated, and has carried up the chimney the temperature acquired from the fire. There is at present no single term in our language employed to denote this third mode of the propagation of heat; but we venture to propose for that purpose, the term convection, [in footnote: [Latin] Convectio, a carrying or conveying] which not only expresses the leading fact, but also accords very well with the two other terms."Later, in the same treatise VIII, in the book on meteorology, the concept of convection is also applied to "the process by which heat is communicated through water".

title: Heat transfer


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Sanitation

Sanitation refers to public health conditions related to clean drinking water and treatment and disposal of human excreta and sewage. Preventing human contact with feces is part of sanitation, as is hand washing with soap. Sanitation systems aim to protect human health by providing a clean environment that will stop the transmission of disease, especially through the fecal–oral route. For example, diarrhea, a main cause of malnutrition and stunted growth in children, can be reduced through adequate sanitation. There are many other diseases which are easily transmitted in communities that have low levels of sanitation, such as ascariasis (a type of intestinal worm infection or helminthiasis), cholera, hepatitis, polio, schistosomiasis, and trachoma, to name just a few.

A range of sanitation technologies and approaches exists. Some examples are community-led total sanitation, container-based sanitation, ecological sanitation, emergency sanitation, environmental sanitation, onsite sanitation and sustainable sanitation. A sanitation system includes the capture, storage, transport, treatment and disposal or reuse of human excreta and wastewater. Reuse activities within the sanitation system may focus on the nutrients, water, energy or organic matter contained in excreta and wastewater. This is referred to as the "sanitation value chain" or "sanitation economy". The people responsible for cleaning, maintaining, operating, or emptying a sanitation technology at any step of the sanitation chain are called "sanitation workers".

Several sanitation "levels" are being used to compare sanitation service levels within countries or across countries. The sanitation ladder defined by the Joint Monitoring Programme in 2016 starts at open defecation and moves upwards using the terms "unimproved", "limited", "basic", with the highest level being "safely managed". This is particularly applicable to developing countries.

The Human Right to Water and Sanitation was recognized by the United Nations (UN) General Assembly in 2010. Sanitation is a global development priority and the subject of Sustainable Development Goal 6. The estimate in 2017 by JMP states that 4.5 billion people currently do not have safely managed sanitation. Lack of access to sanitation has an impact not only on public health but also on human dignity and personal safety.

Definitions
There are some variations on the use of the term "sanitation" between countries and organizations. The World Health Organization defines the term "sanitation" as follows: ""Sanitation generally refers to the provision of facilities and services for the safe disposal of human urine and faeces. The word 'sanitation' also refers to the maintenance of hygienic conditions, through services such as garbage collection and wastewater disposal.""

Sanitation includes all four of these technical and non-technical systems: Excreta management systems, wastewater management systems (included here are wastewater treatment plants), solid waste management systems as well as drainage systems for rainwater, also called stormwater drainage. However, many in the WASH sector only include excreta management in their definition of sanitation.

Another example of what is included in sanitation is found in the handbook by Sphere on "Humanitarian Charter and Minimum Standards in Humanitarian Response" which describes minimum standards in four "key response sectors" in humanitarian response situations. One of them is "Water Supply, Sanitation and Hygiene Promotion" (WASH) and it includes the following areas: Hygiene promotion, water supply, excreta management, vector control, solid waste management and WASH in disease outbreaks and healthcare settings.

Hygiene promotion is seen by many as an integral part of sanitation. The Water Supply and Sanitation Collaborative Council defines sanitation as "The collection, transport, treatment and disposal or reuse of human excreta, domestic wastewater and solid waste, and associated hygiene promotion."

Despite the fact that sanitation includes wastewater treatment, the two terms are often used side by side as "sanitation and wastewater management".

Another definition is in the DFID guidance manual on water supply and sanitation programmes from 1998:

""For the purposes of this manual, the word 'sanitation' alone is taken to mean the safe management of human excreta. It therefore includes both the 'hardware' (e.g. latrines and sewers) and the 'software' (regulation, hygiene promotion) needed to reduce faecal-oral disease transmission. It encompasses too the re-use and ultimate disposal of human excreta. The term environmental sanitation is used to cover the wider concept of controlling all the factors in the physical environment which may have deleterious impacts on human health and well-being. In developing countries, it normally includes drainage, solid waste management, and vector control, in addition to the activities covered by the definition of sanitation.""

Sanitation can include personal sanitation and public hygiene. Personal sanitation work can include handling menstrual waste, cleaning household toilets, and managing household garbage. Public sanitation work can involve garbage collection, transfer and treatment (municipal solid waste management), cleaning drains, streets, schools, trains, public spaces, community toilets and public toilets, sewers, operating sewage treatment plants, etc. Workers who provide these services for other people are called sanitation workers.

Purposes
The overall purposes of sanitation are to provide a healthy living environment for everyone, to protect the natural resources (such as surface water, groundwater, soil), and to provide safety, security and dignity for people when they defecate or urinate.

The Human Right to Water and Sanitation was recognized by the United Nations (UN) General Assembly in 2010. It has been recognized in international law through human rights treaties, declarations and other standards. It is derived from the human right to an adequate standard of living.

Effective sanitation systems provide barriers between excreta and humans in such a way as to break the disease transmission cycle (for example in the case of fecal-borne diseases). This aspect is visualised with the F-diagram where all major routes of fecal-oral disease transmission begin with the letter F: feces, fingers, flies, fields, fluids, food.

Sanitation infrastructure has to be adapted to several specific contexts including consumers' expectations and local resources available.

Sanitation technologies may involve centralized civil engineering structures like sewer systems, sewage treatment, surface runoff treatment and solid waste landfills. These structures are designed to treat wastewater and municipal solid waste. Sanitation technologies may also take the form of relatively simple onsite sanitation systems. This can in some cases consist of a simple pit latrine or other type of non-flush toilet for the excreta management part.

Providing sanitation to people requires attention to the entire system, not just focusing on technical aspects such as the toilet, fecal sludge management or the wastewater treatment plant. The "sanitation chain" involves the experience of the user, excreta and wastewater collection methods, transporting and treatment of waste, and reuse or disposal. All need to be thoroughly considered.

Economic impacts
The benefits to society of managing human excreta are considerable, for public health as well as for the environment. As a rough estimate: For every US$1 spent on sanitation, the return to society is US$5.50.

For developing countries, the economic costs of inadequate sanitation is a huge concern. For example, according to a World Bank study, economic losses due to inadequate sanitation to The Indian economy are equivalent to 6.4% of its GDP. Most of these are due to premature mortality, time lost in accessing, loss of productivity, additional costs for healthcare among others. Inadequate sanitation also leads to loss from potential tourism revenue. This study also found that impacts are disproportionately higher for the poor, women and children. Availability of toilet at home on the other hand, positively contributes to economic well-being of women as it leads to an increase in literacy and participation in labor force.

Types and concepts (for excreta management)
The term sanitation is connected with various descriptors or adjectives to signify certain types of sanitation systems (which may deal only with human excreta management or with the entire sanitation system, i.e. also greywater, stormwater and solid waste management) – in alphabetical order:

Basic sanitation
In 2017, JMP defined a new term: "basic sanitation service". This is defined as the use of improved sanitation facilities that are not shared with other households. A lower level of service is now called "limited sanitation service" which refers to use of improved sanitation facilities that are shared between two or more households.

Community-based sanitation
Community-based sanitation is related to decentralized wastewater treatment (DEWATS).

Dry sanitation
The term "dry sanitation" is not in widespread use and is not very well defined. It usually refers to a system that uses a type of dry toilet and no sewers to transport excreta. Often when people speak of "dry sanitation" they mean a sanitation system that uses urine-diverting dry toilet (UDDTs).

Environmental sanitation
Environmental sanitation encompasses the control of environmental factors that are connected to disease transmission. Subsets of this category are solid waste management, water and wastewater treatment, industrial waste treatment and noise pollution control. According to World health organization (WHO) Environmental sanitation was defined as the control of all those factors in the physical environment which exercise a harmful effect on human being physical development, health and survival. One of the primary function of environmental sanitation is to protect public health.

Lack of sanitation
Lack of sanitation refers to the absence of sanitation. In practical terms it usually means lack of toilets or lack of hygienic toilets that anybody would want to use voluntarily. The result of lack of sanitation is usually open defecation (and open urination but this is of less concern) with associated serious public health issues. It is estimated that 2.4 billion people still lacked improved sanitation facilities including 660 million people who lack access to safe drinking water as of 2015.

Onsite sanitation or non-sewered sanitation system
Onsite sanitation (or on-site sanitation) is defined as "a sanitation system in which excreta and wastewater are collected and stored or treated on the plot where they are generated". Another term that is used for the same system is non-sewered sanitation systems (NSSS), which are prevalent in many countries. NSSS play a vital role in the safe management of fecal sludge, accounting for approximately half of all existing sanitation provisions. The degree of treatment may be variable, from none to advanced. Examples are pit latrines (no treatment) and septic tanks (primary treatment of wastewater). On-site sanitation systems are often connected to fecal sludge management (FSM) systems where the fecal sludge that is generated onsite is treated at an offsite location. Wastewater (sewage) is only generated when piped water supply is available within the buildings or close to them.

A related term is a decentralized wastewater system which refers in particular to the wastewater part of on-site sanitation. Similarly, an onsite sewage facility can treat the wastewater generated locally.

The global methane emissions from NSSS in 2020 was estimated to as 377 Mt CO2e per year or 4.7% of global anthropogenic methane emissions, which are comparable to the greenhouse gas emissions from wastewater treatment plants. This means that the GHG emissions from the NSSS as a non-negligible source.

Safely managed sanitation
Safely managed sanitation is the highest level of household sanitation envisioned by the Sustainable Development Goal Number 6. It is measured under the Sustainable Development Goal 6.2, Indicator 6.2.1, as the "Proportion of population using (a) safely managed sanitation services and (b) a hand-washing facility with soap and water". The current value in the 2017 baseline estimate by JMP is that 4.5 billion people currently do not have safely managed sanitation.

Safely managed sanitation is defined as an improved sanitation facility which is not shared with other households, and where the excreta produced is either treated and disposed in situ, stored temporarily and then emptied and transported to treatment off-site, or transported through a sewer with wastewater and then treated off-site. In other words, safely managed sanitation is a basic sanitation service where in addition excreta are safely disposed of in situ or transported and treated offsite.

Wastewater management
Wastewater management consists of collection, wastewater treatment (be it municipal or industrial wastewater), disposal or reuse of treated wastewater. The latter is also referred to as water reclamation.

Sanitation systems in urban areas of developed countries usually consist of the collection of wastewater in gravity driven sewers, its treatment in wastewater treatment plants for reuse or disposal in rivers, lakes or the sea.

In developing countries most wastewater is still discharged untreated into the environment. Alternatives to centralized sewer systems include onsite sanitation, decentralized wastewater systems, dry toilets connected to fecal sludge management.

Stormwater drainage
Sewers are either combined with storm drains or separated from them as sanitary sewers. Combined sewers are usually found in the central, older parts or urban areas. Heavy rainfall and inadequate maintenance can lead to combined sewer overflows or sanitary sewer overflows, i.e., more or less diluted raw sewage being discharged into the environment. Industries often discharge wastewater into municipal sewers, which can complicate wastewater treatment unless industries pre-treat their discharges.

Solid waste disposal
Disposal of solid waste is most commonly conducted in landfills, but incineration, recycling, composting and conversion to biofuels are also avenues. In the case of landfills, advanced countries typically have rigid protocols for daily cover with topsoil, where underdeveloped countries customarily rely upon less stringent protocols. The importance of daily cover lies in the reduction of vector contact and spreading of pathogens. Daily cover also minimizes odor emissions and reduces windblown litter. Likewise, developed countries typically have requirements for perimeter sealing of the landfill with clay-type soils to minimize migration of leachate that could contaminate groundwater (and hence jeopardize some drinking water supplies).

For incineration options, the release of air pollutants, including certain toxic components is an attendant adverse outcome. Recycling and biofuel conversion are the sustainable options that generally have superior lifecycle costs, particularly when total ecological consequences are considered. Composting value will ultimately be limited by the market demand for compost product.

Food safety

Sanitation within the food industry means the adequate treatment of food-contact surfaces by a process that is effective in destroying vegetative cells of microorganisms of public health significance, and in substantially reducing numbers of other undesirable microorganisms, but without adversely affecting the food or its safety for the consumer (U.S. Food and Drug Administration, Code of Federal Regulations, 21CFR110, USA). Sanitation Standard Operating Procedures are mandatory for food industries in United States. Similarly, in Japan, food hygiene has to be achieved through compliance with food sanitation law.

In the food and biopharmaceutical industries, the term "sanitary equipment" means equipment that is fully cleanable using clean-in-place (CIP) and sterilization-in-place (SIP) procedures: that is fully drainable from cleaning solutions and other liquids. The design should have a minimum amount of deadleg, or areas where the turbulence during cleaning is insufficient to remove product deposits. In general, to improve cleanability, this equipment is made from Stainless Steel 316L, (an alloy containing small amounts of molybdenum). The surface is usually electropolished to an effective surface roughness of less than 0.5 micrometre to reduce the possibility of bacterial adhesion.

Hygiene promotion
In many settings, provision of sanitation facilities alone does not guarantee good health of the population. Studies have suggested that the impact of hygiene practices have as great an impact on sanitation related diseases as the actual provision of sanitation facilities. Hygiene promotion is therefore an important part of sanitation and is usually key in maintaining good health.

Hygiene promotion is a planned approach of enabling people to act and change their behavior in an order to reduce and/or prevent incidences of water, sanitation and hygiene (WASH) related diseases. It usually involves a participatory approach of engaging people to take responsibility of WASH services and infrastructure including its operation and maintenance. The three key elements of promoting hygiene are; mutual sharing of information and knowledge, the mobilization of affected communities and the provision of essential material and facilities.

Indicator organisms
When analyzing environmental samples, various types of indicator organisms are used to check for fecal pollution of the sample. Commonly used indicators for bacteriological water analysis include the bacterium Escherichia coli (abbreviated as E. coli) and non-specific fecal coliforms. With regards to samples of soil, sewage sludge, biosolids or fecal matter from dry toilets, helminth eggs are a commonly used indicator. With helminth egg analysis, eggs are extracted from the sample after which a viability test is done to distinguish between viable and non viable eggs. The viable fraction of the helminth eggs in the sample is then counted.

Sustainable Development Goal Number 6
In the year 2016, the Sustainable Development Goals replaced the Millennium Development Goals. Sanitation is a global development priority and included Sustainable Development Goal 6 (SDG 6). The target is about "clean water and sanitation for all" by 2030. It is estimated that 660 million people still lacked access to safe drinking water as of 2015.

Since the COVID-19 pandemic in 2020, the fight for clean water and sanitation is more important than ever. Handwashing is one of the most common prevention methods for Coronavirus, yet two out of five people do not have access to a hand-washing station.

Millennium Development Goal Number 7 until 2015
The United Nations, during the Millennium Summit in New York in 2000 and the 2002 World Summit on Sustainable Development in Johannesburg, developed the Millennium Development Goals (MDGs) aimed at poverty eradication and sustainable development. The specific sanitation goal for the year 2015 was to reduce by half the number of people who had no access to potable water and sanitation in the baseline year of 1990. As the JMP and the United Nations Development Programme (UNDP) Human Development Report in 2006 has shown, progress meeting the MDG sanitation target is slow, with a large gap between the target coverage and the current reality. In December 2006, the United Nations General Assembly declared 2008 "The International Year of Sanitation", in recognition of the slow progress being made towards the MDGs sanitation target. The year aimed to develop awareness and more actions to meet the target.

There are numerous reasons for this gap. A major one is that sanitation is rarely given political attention received by other topics despite its key importance. Sanitation is not high on the international development agenda, and projects such as those relating to water supply projects are emphasised.

The Joint Monitoring Programme for Water Supply and Sanitation of WHO and UNICEF (JMP) has been publishing reports of updated estimates every two years on the use of various types of drinking-water sources and sanitation facilities at the national, regional and global levels. The JMP report for 2015 stated that:
 * Between 1990 and 2015, open defecation rates have decreased from 38% to 25% globally. Just under one billion people (946 million) still practise open defecation worldwide in 2015.
 * 82% of the global urban population, and 51% of the rural population is using improved sanitation facilities in 2015, as per the JMP definition of "improved sanitation".

Initiatives to promote sanitation
In 2011 the Bill & Melinda Gates Foundation launched the "Reinvent the Toilet Challenge" to promote safer, more effective ways to treat human waste. The program is aimed at developing technologies that might help bridge the global sanitation gap (for example the Omni Processor, or technology for fecal sludge management). In 2015, the Bill & Melinda Gates Foundation published their "Water, sanitation, and hygiene strategy portfolio update and overview" called "Building demand for sanitation".

The latest innovations in the field of public health sanitation, currently in the testing phase, comprise - use of 'locally produced alcohol-based hand rub'; 'novel latrine improvement'; and 'container-based sanitation'. Centers for Disease Control and Prevention (CDC), the national public health agency of the United States has recognized the stated three initiatives.

Capacity development
Capacity development is regarded as an important mechanism to achieve progress in the sanitation sector. For example, in India the Sanitation Capacity Building platform (SCBP) was designed to "support and build the capacity of town/cities to plan and implement decentralized sanitation solutions" with funding by the Bill & Melinda Gates Foundation from 2015 to 2022. Results from this project showed that capacity development best happens on the job and in a learning organization culture. In a government capacity development initiative, it is critical to have an enabling policy and program funding to translate capacity development input into program and infrastructure outputs. Capacity development aims to empower staff and institutions, develop a learning strategy, learning content and training modules, as well as strengthened partnerships and institutions of learning. The Capacity Development Effectiveness Ladder Framework (CDEL) identifies five critical steps for capacity development interventions: Developing original learning content, partnerships for learning and outreach, learning strategy, visioning change and designing solutions, contribution to capacity development discourse.

Costs
A study was carried out in 2018 to compare the lifecycle costs of full sanitation chain systems in developing cities of Africa and Asia. It found that conventional sewer systems are in most cases the most expensive sanitation options, followed, in order of cost, by sanitation systems comprising septic tanks, ventilated improved pit latrines (VIP), urine diversion dry toilets and pour-flush pit latrines. The main determinants of urban sanitation financial costs include: Type of technology, labour, material and utility cost, density, topography, level of service provided by the sanitation system, soil condition, energy cost and others (distance to wastewater treatment facility, climate, end-use of treatment products, business models, water table height).

Some grassroots organizations have trialled community-managed toilet blocks whose construction and maintenance costs can be covered by households. One study of Mumbai informal settlements found that US$1.58 per adult would be sufficient for construction, and less than US$1/household/month would be sufficient for maintenance.

History
Major human settlements could initially develop only where fresh surface water was plentiful, such as near rivers or natural springs. Throughout history people have devised systems to get water into their communities and households, and to dispose (and later also treat) wastewater. The focus of sewage treatment at that time was on conveying raw sewage to a natural body of water, e.g. a river or ocean, where it would be diluted and dissipated.

The Sanitation in the Indus Valley Civilization in Asia is an example of public water supply and sanitation during the Bronze Age (3300–1300 BCE). Sanitation in ancient Rome was quite extensive. These systems consisted of stone and wooden drains to collect and remove wastewater from populated areas—see for instance the Cloaca Maxima into the River Tiber in Rome. The first sewers of ancient Rome were built between 800 and 735 BCE.

Society and culture
There is a vast number of professions that are involved in the field of sanitation, for example on the technical and operations side: sanitation workers, waste collectors, sanitary engineers.

title: Sanitation