Study on the turbo expansion characteristic of a reverse Brayton air refrigerator

For the purpose of investigating the cooling down and refrigerating performance of a reverse Brayton air refrigerator, a simulation method using CFX was firstly adopted to research flow and thermodynamics process in the cold end of the turboexpander and then the thermal performance of the whole turboexpander was analyzed. The influence of brake power on cooling characteristics of expander was discussed on this basis. The test apparatus was improved with closed blower circuit and tests with fixed brake pressure and fixed characteristic ratio which were two typical braking strategies were carried out to study the cooling down performance of the refrigerator. The result indicated that it was feasible to match the variation of working condition of expander by adjusting brake pressure of the closed blower circuit, and theoretical predictions agreed well with experimental results. The efficiency of the turboexpander reached 62%, the lowest outlet temperature reached -170℃ within 120 minutes, and the reverse Brayton air refrigerator with turboexpander had excellent refrigerating performance.