Design or selection of the heat sink is crucial to the overall thermoelectric system operation and cooler selection. For proper thermoelectric management, all TECs require a heat sink and will be destroyed if operated without one. The system temperature difference is typically quite different from the cooler temperature gradient. A typical design parameter might be to limit the heat sink temperature rise above ambient to 10°C to 20°C. The heat sink temperature directly affects the cooler hot side temperature, which in turn affects the cold side temperature that can be achieved with a TEC. Heat sink resistance is the measure of the ability of the sink to dissipate the applied heat and is given by:

• HSR = (T₁ -T₂)/Q

where:

• HSR = Thermal resistance in C/w
• T₁ = Heat sink temperature in C
• T₂ = Ambient or coolant input temperature in C
• Q = Heat load into heat sink in watts (includes absorbed + TEC power)

The goal of the heat sink design is to minimize thermal resistance. This is achieved through exposed surface area and may require forced air or liquid circulation.

The following schematic shows how the heat sink resistance can be determined. Ambient temperature is 27°C, the desired rise across the heat sink is 10°C, or heat sink temperature at 37°C. The load that must be dissipated is 10W. This gives a resistance of 10°C / 10W or 1°C / W.

The three basic types of heat sinks are: natural convective, forced convective, and liquid cooled, with liquid cooled being the most effective. Typical values of HSR for natural convective range from 0.5°C/W to 5°C/W, forced convective from 0.02°C/W to 0.5°C/W and liquid cooled from 0.005°C/W to 0.15°C/W. In general, most applications involving thermoelectric cooling require forced convective or liquid cooled heat sinks.