Thermoelectric Module-Variable Conductance Heat Pipe Assemblies for Reduced Power Temperature Control

Abstract

Thermoelectric modules (TEMs) are used to precisely maintain the setpoint temperature of photonic components generating variable heat loads under varying ambient conditions. The non-component side of TEMs is mounted onto conventional heat sinks (CHSs). At any combination of setpoint temperature, heat load and ambient temperature, there is a unique thermal resistance between the non-component side of a TEM and the ambient corresponding to minimal TEM power consumption. Indeed, a zero thermal resistance heat sink minimizes power consumption when a TEM operates in refrigeration mode, but when it operates in heating mode a relatively high thermal resistance one is optimal. This paper considers replacing a CHS with a variable thermal resistance heat sink in the form of a finned variable conductance heat pipe (FVCHP). An FVCHP passively and (generally) favorably alters its thermal resistance in response to changes in operating conditions, thereby reducing TEM power consumption. An analytical model of a TEM-FVCHP assembly is developed in order to quantitatively estimate achievable energy savings. The model assumes that there is 1-D flow of heat and charge through a TEM and that a “flat front” divides the condenser section of an FVCHP into thermally active and inactive regions. Calculations are performed for representative TEM-FVCHP assemblies that maintain the setpoint temperature of a photonics component over prescribed ranges of heat loads and ambient temperatures. Average TEM power consumption is reduced by up to 55% compared to a comparable TEM-CHS assembly. Finally, further optimization of the TEM and FVCHP design parameters is considered.