Variable Mixing Chamber Waste-Heat Driven Ejector Cycle For CommercialRefrigeration

Abstract

International audienceEjectors are commonly studied for heat-driven refrigeration systems. Constant mixing area ejectors are limited incooling capacity because of the presence of a shocked flow in the mixing chamber in normal conditions. Besides,this geometric constraint makes ejectors extremely sensitive to the outlet pressure variations usually associated withambient temperature variations; at high temperatures, ejectors can suddenly stall leading to zero power. The authordeveloped a variable mixing chamber ejector concept that helps in reducing the drawbacks of ejectors. It makes itpossible to increase the mixing chamber cross-sectional area at moderate temperatures and reduce it at hightemperatures. This results in an extended range of operation. In this paper, the benefits of using this new ejector as aheat-driven compressor booster stage are quantified. The ejector-based booster stage can be driven by low gradeheat or solar power. The variable mixing chamber ejector opening is adapted to the condensation temperature tomaximize the entrained flow rate for every operating condition; this maximizes the cooling capacity whatever thecondensation temperature is. New system architecture for commercial refrigeration is explored in the paper. Thegains are computed by common thermodynamic models and a specific ejector reduced model derived from CFDmodeling. The refrigeration efficiency gains of the studied architectures are compared to a classical vaporcompression refrigeration system