Development of a Two‐Phase Capillary Pumped Heat Transport for Spacecraft Central Thermal Bus

Thermal requirements of future spacecraft and satellites will certainly outgrow the capability of conventional heat pipes in terms of heat transport, heat density, and temperature control. Emerging passive heat transport technologies such as Capillary Pumped Loop (CPL) and Loop Heat Pipe (LHP) have demonstrated in both ground testing and micro‐gravity flight experiments that they have the potential to replace heat pipes as primary heat transport devices in next generation thermal control technology. Like heat pipes, CPLs and LHPs are completely passive systems which have no mechanical moving part to wear out or to introduce unwanted vibration to the spacecraft. However, the heat transport capabilities of CPLs and LHPs are at least one order of magnitude higher than those of heat pipes. Despite sharing many operational characteristics. CPLs and LHPs do have differences. CPLs require a lengthy and tedious start‐up procedure to prime the wicks before heat is applied to the evaporator plate. Even with the start‐up procedure, start‐ups are not always successful. LHPs, on the other hand, do not require a wick pre‐conditioning process. But the LHP effective thermal conductance is not as high as that of a CPL. Temperature control of a LHP is not easily achieved. A novel concept, which combined a CPL and a LHP into one loop, was proposed to take advantage of selective features of each system without inheriting their shortcomings. The resultant loop was called Advanced Loop Heat Pipe (A‐LHP). A proof‐of‐concept testbed was put together and tested at the Naval Research Laboratory. Test results showed that the A‐LHP performed like a CPL without start‐up problems associated with CPLs.