Experimental study on two-phase adiabatic expansion in a reciprocating expander with intake and exhaust processes

In the present study, visualization and measurement of two-phase adiabatic expansion in a reciprocating cylinder with intake and exhaust processes is carried out. Experimental setup with piston and cylinder which mimics reciprocating expander was constructed and boiling phenomenon is visualized. Working fluids are water and ethanol, and their inlet temperatures are 100 and 80 °C, respectively. The piston and cylinder are made of polycarbonate with diameter of D_p = 55 mm. The inner pressure is measured by the pressure sensor embedded in the piston. Indicated work and indicated adiabatic efficiency are calculated from the P–V diagram. The effects of heat capacity loss from the working fluid to the inner wall and the remained liquid, injection loss and non-equilibrium loss are evaluated. Evaporated gas velocity at the interface is calculated from the volume and density of the vapor phase, which is found to be almost proportional to the piston velocity. The adiabatic efficiency increases with the piston velocity due to the reduction of heat capacity loss. When the maximum piston velocity exceeds 300 mm/s, the effect of heat capacity loss becomes negligible. Measured indicated adiabatic efficiency of water is about 86% at maximum piston velocity of v_p,max = 380 mm/s, while that of ethanol is about 82% for the same condition.