Tag Archives: Thermoelectric Modules

What Are Thermoelectric Modules?

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.

How Are Industrial Lasers Cooled?

There are several varieties of industrial lasers. Some lasers, such as fiber lasers, have specific arrangements that enable spreading the heat they generate over a larger surface area. This arrangement gives fiber lasers better cooling characteristics over other media. Other lasers need extra cooling arrangements to remove the heat they generate. For example, ion lasers generate extreme heat when active and need elaborate cooling methods. Other lasers, emitting energy in the microwave and far-infrared region of the spectrum such as carbon dioxide lasers are immensely powerful, and cut hard material such as steel. The laser essentially melts through the material it focuses on. The problem is these industrial lasers have a limited surface area from where to exchange heat.

Although people traditionally use thermoelectric modules as heat exchangers, their efficiency has always limited their application. Now, thermoelectric modules are available which exhibit high heat flux density and are able to achieve higher heat pumping capacity compared to standard thermoelectric modules.

For instance, the UltraTEC series of thermoelectric modules from Laird has heat-pumping capacity of up to 340 Watts, which is fully adequate to cool applications such as industrial lasers that offer only a limited surface for heat exchange.

Industrial laser applications are numerous, including drilling, additive manufacturing, micro machining, welding, and cutting. Irrespective of the application, industrial lasers generate tremendous amounts of heat, which needs to be quickly and effectively removed to allow the laser to perform long-term and properly. Cooling lasers efficiently has always been a significant challenge for the industry.

Typical methods of cooling include transferring the excess heat by conduction or convection. Air may be used to remove the heat directly, or the heat could be transferred to a coolant, usually circulating water. The water carrying the heat is then circulated through a chiller or any heat transfer system. However, these arrangements depend on the system size and configuration, and can be expensive, complex, and noisy.

The UltraTEC series of thermoelectric modules offers excellent heat pump density, and allows precise temperature control. In fact, under steady state conditions, temperatures can remain within ±0.01°C. As these thermoelectric modules offer solid-state operation, these cooling solutions do not produce noise or vibrations. Moreover, they are available in multiple configurations, making them simple to implement.

Any laser system needs to be accurate and repeatable. Stability of the laser system is highly dependent on balanced, controlled cooling. The advantage of using UltraTEC thermoelectric modules for cooling is they can deliver highly reliable cooling solutions under conditions where the laser is in continuous use and even when cycling at high powers.

Laird assembles UltraTEC thermoelectric modules from Bismuth Telluride semiconductor materials. They use aluminum oxide ceramics, which are thermally conductive. This makes the UltraTEC thermoelectric modules capable of carrying high currents that are necessary for large heat-pumping applications. For instance, with Qmax rating of 340.6 W at 25°C, these thermoelectric modules can operate continuously up to 80°. This adequately ensures that the laser system will never overheat when being cooled by the high heat pump density UltraTEC series of thermoelectric modules. These modules are RoHS compliant and DC operated.