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Heat transfer

Heat transfer is a discipline of thermal engineering that concerns the generation, use and exchange of thermal energy between physical systems. Heat transfer is classified into various mechanisms, such as thermal conduction, thermal convection, thermal radiation, transfer of energy by phase changes. Engineers consider the transfer of mass of differing chemical species, either cold or hot, to achieve heat transfer. While these mechanisms have distinct characteristics, they occur in the same system. Heat conduction called diffusion, is the direct microscopic exchange of kinetic energy of particles 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 bulk flow of a fluid carries heat along with the flow of matter in the fluid. The flow of fluid may be forced by external processes, or sometimes by buoyancy forces caused when thermal energy expands the fluid, thus influencing its own transfer; the latter process is called "natural convection". All convective processes move heat by diffusion, as well. Another form of convection is forced convection. In this case the fluid is forced to flow by use of fan or other mechanical means. Thermal radiation occurs through any transparent medium, it is the transfer of energy by means of photons in electromagnetic waves governed by the same laws. Heat is defined in physics as the transfer of thermal energy across a well-defined boundary around a thermodynamic system; the thermodynamic free energy is the amount of work. Enthalpy is a thermodynamic potential, designated by the letter "H", the sum of the internal energy of the system plus the product of pressure and volume. Joule is a unit to quantify work, or the amount of heat.

Heat transfer is a process function, as opposed to functions of state. 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 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 that can be transferred by various causes, and, common in the language of laymen and everyday life. The transport equations for thermal energy, mechanical momentum, mass transfer are similar, 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 and exchange of heat transfer; as such, heat transfer is involved in every sector of the economy. Heat transfer is classified into various mechanisms, such as thermal conduction, thermal convection, thermal radiation, transfer of energy by phase changes.

The fundamental modes of heat transfer are: Advection Advection is the transport mechanism of a fluid from one location to another, 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 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. 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: ϕ q = v ρ c p Δ T where ϕ q is heat flux, ρ is density, c p is heat capacity at constant pressure, Δ T is the difference in temperature, v is velocity.

On a microscopic scale, heat conduction occurs as hot moving or vibrating atoms and molecules interact with neighboring atoms and molecules, transferring some of their energy 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 t

Giovanni Francesco Gemelli Careri

Giovanni Francesco Gemelli Careri was a seventeenth-century Italian adventurer and traveler. He was among the first Europeans to tour the world by securing passage on ships involved in the carrying trade; some suspected him of spying for the Vatican on his journey. Gemelli Careri was born in Taurianova, 1651, died in Naples, 1725, he obtained a doctorate in law at the College of Jesuits in Naples. After completing his studies he entered the judiciary. In 1685 he took time off to travel around Europe. In Hungary he was wounded. In 1687 he re-entered the judiciary, he began work on his first two books: "Relazione delle Campagne d'Ungheria" with co-author Matteo Egizio, "Viaggi in Europa". At this time Gemelli encountered frustrations with his legal profession, he was denied certain opportunities. He decided to suspend his career for a round-the-world trip; this five-year trip would lead to Giro Del Mondo. Gemelli Careri realized that he could finance his trip by purchasing goods at each stage that would have enhanced value at the next stage: at Bandar-Abbas on the Persian Gulf, he asserts, the traveler should pick up "dates, wine and all the fruits of Persia, which one carries to India either dried or pickled in vinegar, on which one makes a good profit".

Gemelli Careri started his world trip in 1693, with a visit to Egypt and the Holy Land. At the time, this Middle Eastern route was becoming a standard ingredient of any excursion into foreign lands, a hike, not worth writing home about. However, from there the Italian'tourist' would take less traveled paths. After crossing Armenia and Persia, he visited Southern India and entered China, where the Jesuit missionaries assumed that such an unusual Italian visitor could be a spy working for the pope; this fortuitous misunderstanding opened for Gemelli many of the most closed doors of the country. He got to visit the emperor at Beijing, attended the Lantern Festival celebrations and toured the Great Wall. "Almost all the structure, as has been said, is of brick, so well built that it does not only last but looks new after several ages. It is above 1800 years since the Emperor Xi-hoam-ti caused it to be built against the incursions of the Tartars; this was one of the greatest, most extravagant works, undertaken.

In prudence the Chinese should have secured the most dangerous passes: But what I thought most ridiculous was to see the wall run up to the top of a vast high and steep mountain, where the Birds would hardly build much less the Tartar horses climb... And if they conceited those people could make their way climbing the clefts and rocks it was a great folly to believe their fury could be stopped by so low a wall."From Macau, Gemelli Careri sailed to the Philippines, where he stayed two months while waiting for the departure of a Manila galleon, for which he carried quicksilver, for a 300% profit in Mexico. In the meantime, as Gemelli described it in his journal, the half-year-long transoceanic trip to Acapulco was a nightmare plagued with bad food, epidemic outbursts, the occasional storm. In Mexico, he became friends with Mexican creole patriot and savant Don Carlos de Sigüenza y Góngora, who took the Italian traveler to the great ruins of Teotihuacan. Sigüenza spoke with Gemelli about his theories of the ancient Mexicans and entrusted him with information about the Mexican calendar, which appeared in Gemelli's account.

As well as having visited the pyramids at Teotihuacan, he visited several mining towns. After leaving Mexico city he visited the city of Puebla de Los Angeles and several towns as he traveled to the port city of Veracruz, where he joined a Spanish fleet to Cuba. After five years of wandering around the world, Gemelli was on his way back to Europe when he joined the Spanish treasure fleet in Cuba. Relazione delle Campagne d'Ungheria Viaggi in Europa Giro Del Mondo Part 1 Part 2 Part 3 Part 4 Part 5 Part 6 Voyage Round the World Voyage du Tour du Monde The aim of Giro Del Mondo - a faithful description of the countries visited - was emphasized by Giosef-Antonio Guerrieri in his preface. While pointing out the difference between the account of a journey and "an imaginary journey", Guerrieri praised Gemelli Careri for the reliability of his experiences, criticized those who were prone to fantasize over geographic maps. For many years scholars and experts did not consider Gemelli Careri's adventurous journey authentic.

With time, its truthfulness was proved, it was ascertained that he collected important historical documents in order to know those exotic realities in greater detail. Indeed, the sixth volume of Giro Del Mondo, which covers only Mexico, contains information gathered from codices that existed prior to the Conquest, which he got access to via Don Carlos de Sigüenza y Góngora. In New Spain, Gemelli Careri had the opportunity to study the pyramids which Sigüenza had long held. Due to lack of funds, Sigüenza himself had been

Betsy Nagelsen

Helen Elizabeth "Betsy" Nagelsen McCormack is an American former professional tennis player. Nagelsen was the world's top junior in 1973, she won the 1973 U. S. Champion Girls' 16 and under singles, she won the USTA Girls' Sportsmanship Award in 1974. As a professional, she won the doubles championship at the 1978 and 1980 Australian Opens, reached the singles final of the 1978 Australian Open, losing to Christine O'Neil. Over her 21-year career on the WTA Tour, Nagelsen won four singles titles. Nagelsen reached her career-high singles ranking by the end of 1981, when she became the world No. 23. She reached a career-high ranking in doubles of No. 11 on March 4, 1988. She had career wins over Martina Navratilova, Arantxa Sánchez Vicario, Sue Barker, Pam Shriver, Claudia Kohde-Kilsch, Rosie Casals, Betty Stöve, Sylvia Hanika, she was a four-time member of the U. S. Wightman Cup Team in 1974, 1985, 1988 and 1989. After her retirement in 1996, Nagelsen became a commentator for ABC and ESPN in the United States and Australia's Nine Network.

She married Mark McCormack, founder of the sports management group IMG. The couple donated money for the McCormack-Nagelsen Tennis Center at the College of William and Mary in Williamsburg, Virginia; the Intercollegiate Tennis Association's Women's Tennis Hall of Fame is located on the site. Note: The Australian Open was held twice in 1977, in January and December. Performance timelines for all female tennis players who reached at least one Grand Slam final Betsy Nagelsen at the Women's Tennis Association Betsy Nagelsen at the International Tennis Federation ITA Profile on William & Mary McCormack-Nagelsen Tennis Center on tribeathletics.com