2011

Thermal Management Solutions for Medical Applications

TEMs are composed of two ceramic substrates that serve as electrically insulating materials and house P-type and Ntype semiconductor elements. Heat is absorbed at the cold junction by electrons as they pass from a low-energy level in the P-type element onto a higher energy level in the N-type element. At the hot junction, energy is expelled to a thermal sink as electrons move from a high-energy element to a lower-energy element.

Reversing the polarity changes the direction of heat transfer. TEMs are rated at maximum parameters (ΔTmax, Imax, Vmax, and Qmax) under no load conditions, with temperature control accuracy achieving ±0.01 °C under steady-state conditions. TEMs can be used as power generators and create 1 to 2 Watts of energy per TEM. They can cool to –100 °C (6-stage) and pump up to 150 Watts of heat, with higher heat pumping capacities achieved by wiring TEMs into an array. Their geometry can vary from 2×2 mm to 62×62 mm and are much more efficient in heating mode than resistant heaters. They also fit into tight geometric space constraints that cannot accommodate a much larger compressor-based system.

Various Transfer Systems

Different TEAs are used to meet the thermal demands for specific applications. Air-to-Air Assemblies offer dependable, compact performance by cooling objects via convection. Heat is absorbed and dissipated by heat exchangers equipped with fans. Specifications apply to ambient temperature of 32 °C and nominal voltage with tolerances ±10%.

Direct-to-Air Assemblies offer dependable, compact performance by cooling objects via conduction. Heat is absorbed through a cold plate, pumping the heat through the TEM and dissipating it into the air through a heat sink. Speci fications apply to an ambient temperature of 32 °C and nominal voltage with tolerances ±10%.

Liquid-to-Air Assemblies cool or heat liquids that flow through a heat exchanger. The liquid heat exchanger is designed for a re-circulating system, absorbs heat and pumps it through the TEM, where it dissipates into the outside environment through an air heat sink. Specifications apply to an ambient temperature of 32 °C and nominal voltage with tolerances ±10%.

Direct-to-Liquid Assemblies cool or heat objects attached directly to the cold plate. Heat is dissipated into a liquid heat exchanger on the hot side. The liquid circuit is normally a re-circulating type that requires a pump and additional liquid heat exchanger that dissipates heat into the ambient environment. Specifications apply to the warm side liquid temperature of 32 °C and nominal voltage with tolerances ±10%.

Liquid-to-Liquid Assemblies cool or heat liquids as they pass through a heat exchanger. Heat is then transferred onto another heat exchanger on the hot side. The liquid circuit is normally a re-circulating type that requires a pump and additional liquid heat exchanger that dissipates heat into the ambient environment. Specifications apply to the warm side liquid temperature of 32 °C and nominal voltage with tolerances ±10%.

This technology was done by Laird Technologies, Chesterfield, MO. For more information, visit http://info.hotims.com/34458-192.