Study on the coupled characteristics of high-speed centrifugal compressor and turboexpander of a reverse Brayton air refrigerator

Abstract

Reverse Brayton air refrigerators are environmentally friendly and have broad application prospects, which can work under various conditions. In this paper, the characteristics of a open-loop air cycle for room temperature applications were investigated. The compressor and turboexpander in the cycle were modeled by numerical simulation. Based on coupled characteristics of the compressor and expander, a system model was established. The effects of the first stage compression ratio and the expander inlet temperature on the refrigerator performance were studied by experiments. The accuracy of the system model is verified by comparing with the experiments, and the maximum deviations of expander rotating speed and supplied mass flow are 3.1% and 4.83%, respectively. With the increase of the first-stage compression ratio and the decrease of expander inlet temperature, the mass flow rate of supplied air and cooling capacity of the cycle increase. The expander efficiency can be maintained near the optimal value. At the expander inlet temperature of 313.2 K, COP drops by 31.7 % when the cooling capacity is reduced from 3.34 kW to 0.74 kW.