Compact Heat Exchangers for Space Power Systems

For missions to dark, dusty, or distant destinations, solar power is not practical. General-purpose heat sources used in conjunction with a heat engine represent a viable solution. The critical challenge is minimizing the size and mass of the system components without compromising reliability. Regardless of the cycle used for the dynamic power converter, the heat exchangers are frequently one of the larger/heavier components, particularly when one of the fluids is a gas rather than a liquid. In this project, Ultramet will design, fabricate, and test compact heat exchangers based on open-cell graphite foams with extremely low pressure drops. With foam-based heat exchangers, the ligaments comprising the foam are the extended surface used for heat transfer. Because of their high volumetric surface area, foam-based exchangers can be far more efficient than a fin-based heat exchanger. The foams to be used in this project, which are fabricated by chemical vapor deposition, have very low pressure drops and have demonstrated heat transfer coefficients that are 3.4 times greater than those of wavy aluminum fins. The technology is cycle-agnostic and can be used in Stirling, Brayton, and/or Rankine cycles. The high efficiency of these heat exchangers will allow them to be much smaller and weigh considerably less than a conventional heat exchanger, which will significantly reduce the overall mission cost.