Off-design operating characteristics of an open-cycle air refrigeration system

Air cycle refrigeration based on the reverse Brayton cycle is a potential solution to environmental problems. In this study, the operating characteristics of an open-air cycle refrigeration system were simulated and analyzed. First, optimal design conditions were found through a design parametric study. Then, the operation of the system was simulated using off-design models. Two partial load operating strategies were compared: fixed shaft speed operation and variable speed operation. Fixed shaft speed operation requires a decrease in the refrigeration temperature as the refrigeration capacity decreases. Variable speed operation can operate with any specified refrigeration temperature. Both operations accompany a reduction in the coefficient of performance compared to the design value, but variable speed operation exhibits much less reduction at the same refrigeration capacity. We presented system performance maps and demonstrated that all of the operating conditions, which differ in refrigeration capacity and refrigeration temperature, can be addressed by varying both the speed and target refrigeration temperature simultaneously.