Wall temperature and system mass effects in a reciprocating gas spring

Reciprocating-piston devices can be used as high-ef ficiency compressors or expanders in small-scale Ra nkine cycle engines for power generation or in energy storage s ystems. The thermodynamic performance of piston-cyl inder devices is adversely affected by the unsteady heat transfer between the compressed/expanded gas and the surrou nding cylinder walls. Gas springs are an excellent model for the s tudy of these losses because they exhibit the same co plex heat transfer due to periodic pressure oscillations while avoidin g the complexities of gas intake or exhaust. In thi s paper, results from CFD simulations of gas springs are compared to expe rimental data obtained in a piston-cylinder cranksh aft-driven gas spring that experiences mass leakage. The temperatu r of the walls of the gas spring and the system ma ss are not known precisely in the experiments and are important para meters that determine the operation and performance of the system. The aim of this paper is to use complementary exper imental and computational data in order to study th e effects of these two parameters. Initial (mass) and boundary (wall t emperature) conditions of the CFD are varied to mat ch experimental measurements. It is found that the mass of the syst m has little influence on the temperature while an increase leads to a higher mean cyclic pressure without affecting the p ressure ratio. In other words, the mass in a perfec tly sealed gas spring only influences the operational pressure but not th e performance of the system.