Performance of radial piston type reciprocating expander for CO2 refrigeration cycle

• A new piston type expander which has four cylinders arranged radially is developed.
• The radial piston expander can be operated adequately with small mass flow rate.
• Total efficiency of the expander is 0.4 and relatively good as such small expander.
• It is necessary to reduce the frictional loss at seal devices.

Various types of expanders have been investigated to recover a throttling loss and to improve the performance of CO2 refrigeration cycle. However, the capacity of the expander studied so far is so large that it cannot be used for a small cycle such as a vending machine, since the performance of small expander tends to get worse due to influence of leakage. In this paper, a novel reciprocating expander which can be applied to the small cycle is designed and its performance is examined. The expander has four cylinders and pistons arranged radially, and controls supply and discharge of refrigerant by a reciprocating motion of an adjacent piston. It is found that the developed expander can be operated with a small flow rate and the total efficiency attains to 0.4 over the wide range of rotational speed.