Robust Two-Phase Cooling Technology for Megawatt Space-Based Systems

Loop Heat Pipe (LHP) has been the leading two-phase heat transport technology for space-based thermal control subsystems (TCS) for more than 20 years.nbsp; LHPs are capillary-pumped devices having no mechanical moving parts to wear out or break down.nbsp; Due to the excellent phase-change heat transfer efficiency, for the most part, two-phase loops are lightweight and more compact than the single-phase counterparts.nbsp; Hence, it has become popular among the thermal engineers for the operational reliability, robustness, long life, and more importantly, requiring no maintenance.nbsp; Nevertheless, after more than two decades in service, the thermal requirements ndash; imposed on the TCS by the ever-increasing demand for the payload power ndash; are finally outpacing the LHP capability.nbsp; Sintered metal powder wicks of todayrsquo;s technology generate a maximum capillary pumping head of about 5psid with Ammonia as the working fluid.nbsp; Nominal room-temperature Ammonia LHPs have heat transport capacities of approximately 5kW-m, which is sufficient for most space-based TCS at the present.nbsp; However, the NASA Artemis program ndash; in which an astronaut lunar base camp is planned ndash; shall require the heat management in excess of hundreds (if not thousands) of kilo-Watts over long distances.nbsp; In addition, the lunar human base includes many heat-dissipating equipment situated at far-apart locations. nbsp;The heat collection would be a serious challenge for a single-evaporator LHP for it has only one heat collection site with a limited external surface to interface the heat source.nbsp; Hence, more capable heat transport technologies (with multiple evaporators and condensers) need to be developed and flight qualified quickly to achieve the Technology Readiness Level (TRL) of 7-8 for the LHP replacement in 10-20 years.nbsp;