Analytical and experimental investigation of rotary-vane two-phase expanders in vapor compression refrigeration systems

The refrigeration and air-conditioning community has been searching for environmentally friendly refrigerants and ways to improve energy efficiency and to increase the potential for reductions in system size and weight for some time. These system improvements may manifest themselves in numerous ways but significantly impact terrestrial logistics differently. This study investigates the analytical and experimental utilization of rotary-vane expanders as throttle valve replacements in vapor compression refrigeration systems with a specific application of these expanders in smaller deployable environmental control units. The findings support the conclusion that utilizing two-phase expanders in refrigeration systems is very promising.;Mathematical models for a system-level parametric cycle analysis were developed to assess potential gains in the cycle coefficient of performance for R-22, R-134 and transcritical CO2 vapor compression technology. Optimization studies were conducted to determine the optimum performance of a refrigeration system subject to constraints of size and weight of both the condenser heat transfer area and the size and weight of the two-phase expander.;An exhaustive literature survey aids and validates the suitability of the type of positive-displacement expander used, after which comprehensive component level thermodynamic and fluid dynamic models of a rotary-vane expander were developed to establish the performance of this expansion device as a function of design and fluid parameters. This included rigorous modeling of irreversible loss mechanisms such as throttling in the intake and exhaust ports, two-phase internal leakage, friction, re-compression, and under or over-expansion due to incorrect sizing of the expander or off-design operation.;Results from these models were used to establish the operating principles of a two-phase rotary-vane expander. Experimental data gathered after modifying a conventional chiller with an alternative flow path, where a rotary-vane expander and dynamometer have been installed, were used to improve the fidelity of the analytical model developed. Issues such as real-time control to satisfy system-level constraints, expander sizing and operational speed and inadequate operation were addressed. The analytical model developed along with single-phase experimentation were used to understand and overcome component-level complications and inadequacies due to irreversible effects.