How Does a Variable Conductance Heat Pipe (VCHP) Work?

ACT has years of experience providing VHCPs to challenging aerospace applications, providing fabrication to exact aerospace requirements. These devices are manufactured under ACT’s ISO 9001:2015 and AS9100D certified Quality System. The materials used for manufacturing are certified and qualified to meet the demanding level of aerospace quality. Each extrusion is fully characterized to determine thermal and pressure containment capabilities as functions of operating temperature and fluid charge. The welding processes are performed by welders certified to AWS 17.1 Specification for Fusion Welding for Aerospace Applications.

ACT has proprietary heat pipe models to simulate each design application using VCHPs and more. These models are used to assist with the selection of the right extrusion for each application. The capillary limit, and the associated thermal transport capability of the heat pipe, is determined by taking into account the exact extruded groove geometry.

A standard heat pipe is filled with a two-phase working fluid, and a wick to return the condensate from the condenser to the evaporator. In a Variable Conductance Heat Pipe (VCHP) a Non-Condensable Gas (NCG) is added to the heat pipe, in addition to the working fluid. Depending on the operating conditions, the NCG can block all, some, or none of the available condenser length. When the VCHP is operating, the NCG is swept toward the condenser end of the heat pipe by the flow of the working fluid vapor. At high powers, all of the NCG is driven into the reservoir, and the condenser is fully open; see Figure 1 As the power is lowered, the vapor temperature drops slightly. Since the system is saturated, the vapor pressure drops at the same time. This lower pressure allows the NCG to increase in volume, blocking a portion of the condenser. At very low powers, the vapor temperature and pressure are further reduced, the NGC volume expands, and most of the condenser is blocked. This change in active condenser length minimizes the drop in evaporator and associated electronics temperatures over large changes in power and evaporator sink conditions.

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