CONVECTION

In most cases TEC specifications advise by manufacturers show module performance for vacuum conditions. It means that ambient does not affect TEC operation.

In many practical applications TEC operates in gas filled ambient. In the case the TEC gives performance less then specified.

Ambient gas supply additional heat load to TEC, even is nothing else load heat to TEC - gas convection and thermal conductance transfer heat from ambient (from base wall etc) to TEC cold side.

This heat load must be taken into account at designing stage of cooling system.

It is possible to reduce this "passive" heat load by:

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preferable vacuum conditions of application

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or use of gases with low thermal properties - heavy gases like as Ar, Xe, Kr

Special gases are expensive but better performance is much more important for many applications.

Particularly it is a solution for multi-stage TEC applications where deep cooling is required and gas thermal lead can reduce TEC performance considerable.

Thermoconductive properties of some widely used gases for thermoelectric cooling systems are given in the table.

Gas Thermocondictivity, W/mK Typical reduction of maximal cooling capacity (to vacuum conditions)  dT, K
Single-stage Two-stage Three-stage Four-stage
Dry Air 0.026 -4.0 -9.0 -12.0  -18.0
Argon 0.016 -3.0 -6.0  -9.0 -14.0
Xenon 0.0057 -1.5 -3.5  -5.0 -10.0

Deeper cooling (multistage TECs) - more effect of gas

Example

The example shows four-stage TEC performance (power consumption) depending on gas ambient.

The TEC cool down a photodetector:

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Four-Stage TEC 4MD04-116-05

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Cooling level - to 200K (-73°C)

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Active heat load - 50 mW

Worth case - dry air, best - inert heavy gases like as xenon, krypton.