TAILIEUCHUNG - Heat Transfer Handbook part 103

Heat Transfer Handbook part 103. The Heat Transfer Handbook provides succinct hard data, formulas, and specifications for the critical aspects of heat transfer, offering a reliable, hands-on resource for solving day-to-day issues across a variety of applications. | 1016 HEAT TRANSFER IN ELECTRONIC EQUIPMENT where 0 is a configuration factor which must be determined empirically. However to obtain engineering estimates of the thermal performance Bar-Cohen et al. 1987 have proposed a value of for 0. The upper bound on the performance maps is therefore marked with both the CHF limit and the condensation limit. THERMOELECTRIC COOLERS The Peltier effect is hie basis for the thermal electtic coo er CEC which is a solidstate heat pump. If a potential is placed across two junctions heat will be absorbed into one junction and expelled from the other in proportion to the current. Most material combinations exhibit the Peltier effect to some degree. However it is most obvious across a p-n junction as shown in Fig. . As electrons are transported from the p-side of a junction to the n-side they are elevated to a higher-energy state and thus absorb heat resulting in cooling the surrounding area. When they are transported from the p-side to the n-side they release heat. The materials that have been used to make TEC include bismuth telluride Bi2Te3 lead telluride PbTe and silicon germanium SiGe . To obtain optimum parameters these semiconductors are doped during fabrication. Bi2Te3 has the best performance at temperatures of interest for electronic components and is most commonly used. A T C device is constructed by placing from one to several hundred thermocouples electrically in series and thermally in parallel between two pieces of metallized thermally conductive ceramic acting as an electrical insulator. For continuous cooling at the low-temperature side of the T C the heat absorbed at the cold side as well as the heat generated by the flow of electricity must be removed from the hot side by one of the thermal transport mechanisms described previously. Solution of the governing equations for a thermoelectric couple yields a relation for the maximum temperature differential obtainable with such a device as ATmax 0 2KR

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