Discovery of the Peltier effect in 1834 led to the development of solid-state heat pumps, but the devices became commercially available only in the 1960s, when the combination of ceramic substrates with advanced semiconductor thermocouple materials made it possible. Solid-state heat pumps or thermoelectric modules utilize the Peltier effect to dissipate heat through a heat exchanger.
While operating, DC current flowing through the thermoelectric module creates heat transfer and a temperature differential across the ceramic surfaces. This causes one side of the thermoelectric module to be hot, while the other side grows cold. Although single-stage standard thermoelectric module can achieve temperature differentials up to 70°C, modern semiconductor materials can exceed this limitation.
Regular cooling technologies such as fans have moving parts that can wear out and need maintenance. However, thermoelectric modules, being solid-state with no moving parts, are highly reliable. While single thermoelectric modules can cool devices well below the ambient temperature, use of multistage thermoelectric modules in a vacuum environment can achieve colder temperatures, down to -100°C.
Simply reversing the polarity of the current flowing through a thermoelectric module can reverse its ability to heat and cool, as the reversal of current direction also changes the direction of heat transfer. This allows achievement of a very precise temperature control under steady state conditions—to the order of ±0.01°C. While heating, thermoelectric modules are much more efficient as compared to conventional resistance heaters, as they can generate heat from two sources—one, the input power supplied, and two, the additional heat generated by the heat pumping action.
A typical thermoelectric module physically measures 30X30X3.6 mm. However, they can have geometric footprints as small as 2X2 mm or as large as 62X62 mm, while being very lightweight. Therefore, thermoelectric modules are well suited for applications with space or weight constraints as compared to much larger cooling technologies offered by conventional compressor-based systems. Some applications also use thermoelectric modules as small power generating sources, converting waste heat into energy in remote locations.
Thermoelectric modules are well suited for applications where active cooling is required for reaching temperatures below ambient with cooling capacity requirements up to 600 W. Design engineers consider using thermoelectric modules when faced with system design criteria such as high reliability, precise temperature control, low weight, compact geometrical constraints, and other environmental requirements. Thermoelectric modules are in use in industries such as food and beverage, consumer, telecom, medical, photonics and many more.
Manufacturers offer several types of thermoelectric modules suitable for different applications. For instance, some have a wide breadth suitable for higher current and higher heat pumping applications and operating temperatures of 80°C. Other modules have several surface finish options such as pre-tinning or metallization to allow soldering the thermoelectric module to the mating conduction surfaces.
For achieving higher temperature differentials, designers stack thermoelectric modules one on top of another to create a multistage module. However, these multistage modules are suitable only for lower heat pumping applications.
Manufacturers design special modules that will work in both heating and cooling modes reversibly. Standard modules are not suitable here as they will be unable to withstand the thermal stresses these applications generate.
