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Understanding Thermoelectrics

To better understand how a TEC system works, we will investigate TE cooling of a heat generating electronic component. 

There is a heat generating electronic component that produces 5 Watts of heat. A TEC (Marlow’s DT12-6) is placed on top of the electronic component with a thin layer of thermal grease (with a thermal resistance of 0.1 K/W) in between.  An extruded heat exchanger is placed on the other side of the TEC again with a thin layer of thermal grease.  The heat exchanger has a thermal resistance of 0.9 K/W.  To design a system to ensure that the electronic component remains less than 10ºC, you will need to provide the following information about your system:

1. HSR, in this case this includes both the grease and the heat exchanger and is approximately 1.0 K/W
2. CSR, which in this case is the thermal resistance of the grease of 0.1 K/W
3. Qc, this is the heat that is pumped by the TEC and in this example is 5 Watts
4. Tamb, is the ambient temperature of the heat exchanger and can be assumed to be 25ºC
5. Tc, is the desired temperature of the electronic component to ensure proper operation, and in this example it is less than 10ºC

Pertinent information about the DT12-6 performance is as follows:

1. Approximate COP which for this device at this operating point is 0.697
2. I and V needed to drive the TEC, which in this example is 1.5 Amps and 4.779 Volts
3. Temperature drop across TEC, is approximately:

 
 ºC and ºC

 

The DT12-6 COP is 0.697 and will give you a temperature difference of 28.05ºC under your operating conditions.  Since a TEC is simply a heat pump, the equation can be described by the following.

The power needed to run the TEC can be calculated using the following equation for electrical power.

The heat leaving the TEC and going through the HRS is described by the conservation of energy.

This quantity is the heat that passes through the hot side heat exchanger.  To estimate the hot side temperature of the TEC, you can use the following equation.
°C

And you will calculate  to be 37.18ºC.  Marlow gave you a temperature difference across the TEC of 28.05ºC so the cold side of the TEC will be 9.13ºC.  But since there is a thin layer of grease between the TEC and the electronic component, you must adjust for the CSR by using the following equation.
°C

You should calculate the electronic components temperature to be 9.63ºC, which meets your design criteria.