tions (125 We at a temperature ratio of 2). The engine may also achieve an overall thermal efficiency of approximately 27% if integrated with a generator. Engine Components Heat Exchanger An electrical heater with an maximum thermal input of 2 kW was used as an external heat source rather than using solar energy. Input heat is supplied to the engine heater assembly, which consists of 15 U-shaped tubes and is heat-shielded by packing the cylindrical enclosure with ceramic fiber refractories. Temperature of the outside wall of the heater can be kept constant with a heater input controller. An annular regenerator configuration was designed which consisted of a stack of woven 316 stainless steel wire screens sandwiched between the heater and cooler. The matrix design was done according to the method as given by K. Hamaguchi [14]. Three mesh sizes for the regenerator matrix (100, 150 and 200 mesh) were provided, but for present testing the 150 mesh was used, giving a porosity of 0.671 with 165 stacked screen layers. The annular cooler was water-cooled with a tube-in-shell configuration with the working fluid passing through the tubes. Water was supplied to the engine cooler through a gear pump with maximum flow of 1.8 liters/min. The cooler inlet temperature ranged from 287 to 350 K with a hot water supply device. Seal Device To avoid any gas leakage in the displacer and power pistons, ring-like devices were used. The displacer piston seal was a one-stage straight-cut ring, with a plane bearing used for linear sliding of the displacer rod. The power piston seal was a one-stage two- piece assembly of a straight-cut ring and backup metal ring. The ring seal materials were all PTFE composites.
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