Initial characterization results of metal wick capillary pumps

In the past 5 years considerable effort has been invested in understanding and improving capillary pumped loop (CPL) technology and many advances have been made, particularly with respect to evaporator designs. With the development of looped heat pipe (LHP) manufacturing capability and expertise outside the former Soviet Union there has been a push to incorporate LHP technology in CPLs to improve their performance. Of particular interest has been the application of sintered metal wicks in the evaporators. Conventional CPL evaporators used polyethene wicks that are generally limited to a minimum pore size of 10 to 15 microns, which severely limited the wicking height of a system against gravity. Metal wicks allow pore sizes to 1 micron and sometimes even less, potentially increasing the wicking height by orders of magnitude. Not only can metal wicks increase the wicking height of the CPL, easing the ground testing restrictions, but they can also theoretically increase the heat flux density of an evaporator, and the maximum allowable temperature for manufacturability and survival. In addition to the possible benefits stated, there are also disadvantages including heaver evaporators and the higher thermal conductivity of the wick itself, possibly leading to deprime with low power loads and/or power cycling. In this paper the test results of seven metal wick CPL evaporators will be discussed, including two evaporators built by DTX, and five built by the Institute of Thermal Physics in Ekaterinburg, Russia. Initial testing shows very promising results with respect to robustness in power cycling and heat flux capability.