Abstract
To recovering a throttling loss by an expander is effective to improve the performance of a CO_2 refrigeration cycle. Leakage in the expander is dominant factor on the expander performance, and it is to be estimated correctly by an analytical model. Since the leakage in the expander flows from super-critical region to two-phase region, i.e. the trans-critical flow, the flow characteristic is complicated. In this study, the flow characteristics of the trans-critical flow are examined experimentally and analytically. It is found that oil circulating with refrigerant is separated and stratified in a pipe under the super-critical condition. The position where the transition from super-critical to two-phase condition occurs is identified by observation in the leakage path. The calculated result by an analytical model taking account of the oil effect agrees well with the experimental one.
