Constant conductance heat pipes
Constant conductance heat pipes (CCHPs) transport heat from a heat source to a heat sink with a very small temperature difference. Axial groove capillary wick structures are utilized because of the relative ease of manufacturing (aluminum extrusions) and their demonstrated heritage in spacecraft and instrument thermal control applications. CCHPs can transport heat in either direction and are typically used to transfer heat from specific thermal loads to a radiator panel or as part of an integrated heat pipe radiator panel or as part of an integrated heat pipe radiator panel. Common working fluids include: ammonia, propylene, ethane, and water.
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 Precision axial groove extrusion with integral flange
 Examples of CCHPs manufactured with various evaporator/condenser lengths and 90° bends Applications:
ACT has specialized equipment required to manufacture CCHPs to achieve aerospace quality. This includes: multi stage cleaning baths for chemically cleaning raw extrusions, triple distillation apparatus for working fluid purification, state-of-the-art helium mass spectrometer leak detector, dedicated charging, processing and non-condensable gas venting stations, and specialized test setups for testing and characterization at various temperatures.
 Multi bath chemical cleaning station |
 Triple distillation apparatus After the rigorous physical/chemical cleaning process, the heat pipes are further cleaned in-situ by operation at elevated temperatures with a high purity working fluid charge that is subsequently vented. A second high purity charge is loaded and the pipe is operated over a number of days with several checks for non-condensable gases at extremely low temperatures, where the slightest amount of non-condensable gas can be detected and removed before final hermetic sealing. ACT has proprietary heat pipe models to simulate each design application and these models are used to assist with the selection of the right extrusion for each application. This software calculates the capillary limit of the heat pipe taking into account the exact extruded groove geometry. The optimum fluid charge is determined for the specific application and the effect of excess fluid charge is determined for both 0-G and 1-G operations. The figure below compares the model predictions and test data on two specific CCHPs.
 Predictions/data comparison (click graph to enlarge)
 An example of a precision test setup specific to the application - before insulation
 An example of a precision test setup specific to the application - in actual test configuration with only top few layers of insulation removed |