Vapor Compression and Thermoelectric Heat Pumps for a Cascade Distillation Subsystem: Design and Experiment
Humans on a spacecraft require significant amounts of water for drinking, food, hydration, and hygiene. Maximizing the reuse of wastewater while minimizing the use of consumables is critical for long duration space exploration. One of the more promising consumable-free methods of reclaiming wastewater is the distillation/condensation process used in the Cascade Distillation Subsystem (CDS). The CDS heats wastewater to the point of vaporization then condenses and cools the resulting water vapor. The CDS wastewater flow requires heating for evaporation and the product water flow requires cooling for condensation. Performing the heating and cooling processes separately would require two separate units, each of which would demand large amounts of electrical power. Mass, volume, and power efficiencies can be obtained by heating the wastewater and cooling the condensate in a single heat pump unit. The present work describes and compares two competing heat pump methodologies that meet the needs of the CDS: 1) a series of mini compressor vapor compression cycles and 2) a thermoelectric heat exchanger. In the paper, the CDS system level requirements are outlined, the designs of the two heat pumps are described in detail, and the results of heat pump analysis and performance tests are provided. The mass, volume, and power requirement for each heat pump option is compared and the advantages and disadvantages of each system are listed.
Analytical Study on Gas-Oil Separation of a Heat Pump System under Lunar Gravity
A heat pump in the aerospace industry can significantly reduce the area of radiator by elevating the rejection temperature. Especially for a Lunar base, the heat pump can improve the heat rejection capability of the thermal control system to adapt the high-temperature environment. However, gravity on the Lunar (about 1/6 g) may have an adverse impact on a gas-oil separator of the heat pump, and solving this problem is the key for a heat pump used on Lunar base. At present, the gas-oil separator all based on gravity separation theories, the researches under low or micro gravity were blank. In this work, a gravity separation model based on a single-particle principle was built, and the effects of the vapor velocity, the oil droplet initial velocity, and the oil droplet diameter were investigated under normal gravity. Then the variations of the separation efficiency under Lunar gravity were discussed and the numerical calculation results showed that the separation efficiency was reduced when the vapor velocity or droplet initial velocity increased in a certain height of the separator whenever under normal or Lunar gravity. Particularly, the separation efficiency under Lunar gravity was reduced from 99% to 55% than it under normal gravity.
Performance Assessment of ISS Water Processor Assembly Reactor
Due to modifications to the ISS waste water composition, the concentration of volatile organic contaminants in the original baseline has significantly increased in the feed to the Water Processor Assembly (WPA). In parallel, the specified ISS oxygen supply pressure to the WPA increased, resulting in a higher flow rate of oxygen to the WPA catalytic oxidation reactor. Preliminary testing at Hamilton Sundstrand indicated that the higher oxygen flow rate would increase the WPA capacity for volatile organics. Following an analysis of the expected waste water composition, personnel at NASA MSFC and Hamilton Sundstrand conducted a test of a flight-like reactor to assess its capacity for the higher organic loads. The results of this test verify the WPA can accommodate the expected organic load in the ISS waste water with margin.