Variable Conductance Heat Pipe (VCHP) Solutions

When precise and reliable temperature control is needed in addition to heat rejection, typically in applications where temperatures can adversely affect electronic components, variable conductance heat pipes can be a cost-effective solution.

Aavid’s variable conductance heat pipes (VCHPs) control the evaporator temperature change by altering the amount of condenser area available. Decreasing ambient temperatures cause the vapor pressure of the working fluid to decrease and the volume of Non-Condensable Gas (NCG) to increase, lowering the condenser area. The result is an efficient cooling method with no moving parts.

Aavid’s variable conductance heat pipes operate efficiently within ambient temperatures ranging from -5° C to 65° C and work in conjunction with copper plates that can be as thin as 0.2 inches. They are compatible with numerous heat pipe assemblies.



Three types of VCHP configurations are available:

•Wicked with cold reservoir
•Wickless with hot reservoir
•Actively controlled with heated reservoir

These heat pipe solutions are more efficient than thermal electric controls, are easier to configure, and require little or no power input. VCHPs are at work in a wide variety of demanding, extreme-temperature applications and can be incorporated in custom thermal solutions from Aavid.

How Does a Variable Conductance Heat Pipe Work?

By introducing a small mass of NCG (shown schematically below), most heat pipes can be created as a Variable Conductance Heat Pipe. Because NCG is swept to the end of the condenser by the condensing working fluid vapor, it blocks a portion of the condenser, effectively reducing its conductance. If the ambient temperature increases, decreasing the available temperature difference between the condenser and the ambient, the operating temperature of the heat pipe will increase. This causes the operating pressure or saturation pressure of the working fluid at the heat pipe operating temperature to increase and compresses the NCG into a smaller volume. The result is that more of the condenser area is available to condensing working fluid. This limits the increase in the operating temperature of the heat pipe and the component mounted to it, much as in the case of a Constant Conductance Heat Pipe (CCHP). Ideally, the increased conductance of the condenser offsets the increase in the ambient temperature and the heat pipe operates at a constant temperature.

The degree of control depends on the working fluid saturation curve, the desired operating temperature set point, the ranges of ambient temperature and heat load and the volume of gas relative to the volume of the vapor space in the condenser.



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