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

After 20 years serving the American space thermal control systems amicably, the leading capillary-pumped heat transport technology - Loop Heat Pipes (LHPs) - has finally run out of capacity to offer the ever-increasing demand for spacecraftnbsp;power.nbsp; LHPs contained no mechanical moving part to wear out or break down, hence, highly reliable for space applications.nbsp; The simplest and most rational approach was to employenbsp;a mechanical pump to augment the capillary pumping head of the LHP.nbsp; In fact, NASA Goddard had tried in in the 1980s time frame and the results were not very well-received simply because the mechanical pumps especially the gear-type were notoriously unreliable, lasting no more than 1,000 hours of service.nbsp; In 2004-2005, TTH Research Inc. introduced an Advanced concept of LHP - called Advanced LHP or A-LHP - in which any pumping device could be utilized to assist the capillary pumping.nbsp; One variant of the A-LHP called for a bearingless pumpnbsp;to be added in-line to the LHP liquid return line.nbsp; Since the bearingless pump was originally developed for the bio-medical technology as a blood pump, it could not withstand the high fluid pressure of Ammonia.nbsp; Nevertheless, a Freon 11 breadboard test unit was constructed and performance tested and the results were very encouraging. Subsequent efforts to design an Ammonia version of the Freon 11 pump ended up in a complete failure and the researched had to be put a shelf for 10 years.nbsp; In 2015, by sheer serendipity, another type of bearingless pump manufactured by Levitronix was discovered.nbsp; The pump was of centrifugal (impeller) type having a single impeller embedded with permanent magnets to (i) employ magnetic levitation (MagLev)nbsp;to suspend itself in the fluid while inside a hermetically-sealed casing AND (ii) be magnetically driven by an external electro-manetic motor.nbsp; The MagLev allowed liquid to flow through without impedance.nbsp; More importantly, more than one unit can be used for redunancy or enhanced capacity.