A. Heat Sinks
Design or selection of the heat sink is crucial to the overall thermoelectric system operation and cooler selection. All thermoelectric coolers 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 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
HSR = Thermal resistance (°C/W)
T1 = Heat sink temperature (°C)
T2 = Ambient or coolant input temperature (°C)
Q = Heat load into heat sink (W) (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 10 W. This gives a resistance of 10°C / 10 W or 1°C/W.
The three most common 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.