EXPERIMENTAL STUDY ON ADIABATIC TWO-PHASE EXPANSION IN A CYLINDER FOR TRILATERAL CYCLE

asme-orc2015 Tracking Number 29

ABSTRACT Trilateral cycle is one of heat cycles in which working fluid is pressurized and kept as a single liquid phase during the heating process [1]. The exergy loss can be drastically reduced because of favorable temperature profile matching between the heat source and the working fluid. In the expansion process, working fluid is flashed and becomes liquid-vapor two-phase. This two-phase expander is one of the key components to realize the trilateral cycle system. In the present study, visualization and measurement of two-phase adiabatic expansion in a cylinder for trilateral cycle are carried out. Experimental setup with piston and cylinder which mimics reciprocating expander is constructed and boiling phenomenon is visualized. Working fluids are water and ethanol, and initial temperatures are 100 and 80 ℃ in this study. The piston and cylinder are made of polycarbonate with diameter of Dp = 38, 44 and 55 mm. The piston velocity vp is ranged from 1 to 300 mm/s and inner pressure is measured by the pressure sensor embedded in the piston. Output work is calculated from the P - V diagram. In addition, filter-type sintered metal is fixed on the bottom of the cylinder to enhance boiling. The average pore diameter is ranged from 5 to 75 μm and the effect of initial bubbles on boiling is evaluated. The difference between measured and quasi-static pressures becomes larger and the adiabatic efficiency decreases as piston velocity is increased. When using water, adiabatic efficiency is about 83 % for Dp = 55 mm and vp = 300 mm/s, while the adiabatic efficiency is about 78 % when using ethanol for the same condition. With sintered metal on the bottom of the cylinder, the deterioration of adiabatic efficiency becomes moderate for both working fluids. The adiabatic efficiency for pore diameter 20 μm is about 87 % for water and about 92 % for ethanol when Dp = 55 mm and vp = 300 mm/s. From these results, the initial bubbles captured in the porous metal are effective to improve the efficiency of the expander for trilateral cycle. In an actual reciprocating expander, heat transfer from the working fluid to the setup wall may reduce the adiabatic efficiency while the initial bubbles in the cylinder can improve the boiling. Therefore, a new experiment reproducing the intake and exhaust process is conducted. The feasibility of the two-phase expander is evaluated through this experiment. REFERENCES [1] Smith I.K., Development of the trilateral flash cycle system. 1. Fundamental considerations., Journal of Power and Energy 207 (1993), pp. 179-194.