An Improved High Power Hybrid capillary pumped loop

The High-Power Spacecraft Thermal Management (HPSTM) system was modified and upgraded to facilitate improved performance testing. Modifications to the system included augmenting the heat dissipation capacity of the condenser sink for steady-state high power operation, adding more pressure transducers to monitor pressure drops in various components of the system, installing pressure contact thermocouples on the evaporators to measure the heating surface temperature, providing a coolant loop to one of the evaporator plates for heat load sharing operation, installing a load cell on the reservoir to monitor transient fluid flows, and re-orienting the reservoir to reduce the effects of compressed vapor during transient operations. The system demonstrated a steady, continuous operation at a power input of 20 kW for 10 hours in the capillary mode. Test results also showed about 33% less variation of the reservoir set point temperature during power transients. The evaporative heat transfer coefficient was determined to be about 10,000 W/m2/°C. The condensation heat transfer coefficient was found to be about 16,000 W/m²/°C. One of the evaporator plates was used to demonstrate its ability to share heat from the other evaporator plates. The evaporator's operation as the sole condenser in the loop was also verified.