Variable Mixing Chamber Waste-Heat Driven Ejector Cycle For Commercial Refrigeration
Résumé
Ejectors are commonly studied for heat-driven refrigeration systems. Constant mixing area ejectors are limited in
cooling 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 with
ambient temperature variations; at high temperatures, ejectors can suddenly stall leading to zero power. The author
developed a variable mixing chamber ejector concept that helps in reducing the drawbacks of ejectors. It makes it
possible to increase the mixing chamber cross-sectional area at moderate temperatures and reduce it at high
temperatures. This results in an extended range of operation. In this paper, the benefits of using this new ejector as a
heat-driven compressor booster stage are quantified. The ejector-based booster stage can be driven by low grade
heat or solar power. The variable mixing chamber ejector opening is adapted to the condensation temperature to
maximize the entrained flow rate for every operating condition; this maximizes the cooling capacity whatever the
condensation temperature is. New system architecture for commercial refrigeration is explored in the paper. The
gains are computed by common thermodynamic models and a specific ejector reduced model derived from CFD
modeling. The refrigeration efficiency gains of the studied architectures are compared to a classical vapor
compression refrigeration system.