Numerical Investigation of a Large-Scale Two-phase Pumped Loop Thermal Management System With Variable-Volume Pressure Control

A series of physical models were developed using MATLAB Simscape to investigate the operation of a mechanically pumped, two-phase thermal management system that is subjected to a pulsed multi-kilowatt, high-flux heat load. An experimental system built and operated at the Air Force Research Laboratory was found to suffer from uncontrolled pressure rise during heating pulses. Model analysis showed that the uncontrolled pressure rise was due to the experimental system not providing a means of either transporting or condensing the generated vapor at a rate sufficient to maintain system pressure within a prescribed range. A second model was developed to demonstrate a variable volume that would expand as vapor was generated and be recompressed as vapor generation slowed. Results show this architecture, when subjected to a series of high-heat flux heating pulses, is capable of maintaining the evaporator temperature within 1℃ of the target temperature during heating. Further, the condenser heat transfer rate is reduced to 40% of the evaporator heating rate by storing vapor during heating pulses and recondensing over a longer period between heating pulses. These results indicate that applying a pressure-driven variable volume apparatus to a two-phase pumped loop cooling system can maintain evaporator saturation pressure during high-heat flux transient heating.