Modeling and experimental testing of periodic flow regenerators for sCO2 cycles

Abstract

Supercritical CO2 cycles have the ability to reach high efficiency because of their high turbine inlet temperatures. However, high effectiveness recuperators (>90%) are needed to achieve high efficiencies. Periodic flow regenerators have been proposed as an alternative to conventional heat exchanger designs such as Printed Circuit Heat Exchangers (PCHEs) or micro-tube heat exchangers. Regenerators use a packed bed of spheres to alternatively store and release heat. Since the hot and cold fluid streams are not in direct contact, the design of the regenerator is much simpler and less expensive than a recuperator. A model of the regenerator has been created that can predict the effectiveness, pressure drop, and carryover when given the regenerator size and operating conditions. To verify this model, an experimental test facility has been constructed that is capable of testing regenerators at temperatures up to 550 °C and pressures up to 2400 psi at a heat transfer rate of approximately 10 kW. Experimental data was collected and compared to the model predictions. The model was able to predict effectiveness to within approximately 2% and pressure drop to within approximately 20%; both results are acceptable. However, it was necessary to develop a correction for carryover to account for the differences between the model predictions and experimental data. The final result of this work is a verified model of the regenerator that can be used to quickly and accurately design and optimize a regenerator for a sCO2 Brayton cycle.