A promising new class of working fluids / refrigerants (i.e. water azeotropes) has been identified, which offer the potential to provide advanced capabilities for next-generation spacecraft thermal control systems. Water-based azeotropes have been identified as a class of working fluids that offer the following: high thermodynamic performance than ammonia above 25ºC, low global warming potential, capability to be used in high heat lfux applications, capability to be used in applications requiring a high turn-down ratio, significantly lower freezing points than water, near-zero density change upon freezing, low environmental impact, and low toxicity. Important auxiliary applications are possible for related applications, including refrigeration / AC systems and pumped loops. A development program is proposed to evaluate their potential, define their properties, identify leading candidate mixtures, and complete operational tests on a representative water azeotrope heat pipe. Potential NASA Applications (Limit 1500 characters, approximately 150 words) Water azeotropes can be used for spacecraft high-performance / freeze-proof heat pipes, loop heat pipes, and pulsating heat pipes. Related important applications include pumped single-phase and two-phase pumped loops, thermosiphons and loop thermosiphons, Rankine cycle power generation systems, i.e. power plants, reverse Rankine cycle refrigeration systems, especially ones for use in manned areas, and higher temperature reverse Rankine cycle refrigeration / air conditioning systems for electronics cooling systems. Potential Non-NASA Applications (Limit 1500 characters, approximately 150 words) The largest application for this technology will be next-generation freeze-proof commercial heat pipes for electronics cooling and air conditioning equipment. The technology would also be applicable to Rankine cycle power generation, reverse Rankine cycle refrigeration/AC systems, pumped single-phase and two-phase cooling systems, thermosiphons, loop thermosiphons etc.
