Experimental Investigation of a Mechanically Assisted Suction Reed Valve in a Small Hermetic Reciprocating Compressor

Abstract

Reed valves are widely used in hermetic reciprocating compressors and are responsible for a major share of thermodynamic losses. In particular, the suction valve movement of a hermetic reciprocating compressor contains a potential for further improvement. The self-actuated valve is opened only by the pressure difference created by the moving piston, which leads to a characteristic flutter. Furthermore, the suction valve is usually preloaded in order to close properly before the compression phase, causing additional flow resistance. In this work a mechanically assisted suction valve is experimentally investigated. A mechanically actuated spring element generates an additional force acting on the conventional suction reed valve. This force leads to a completely different valve motion. While a conventional reed valve motion is characterized by several opening-and closing periods during one suction phase, the mechanically assisted valve remains open during the whole suction phase. Furthermore, the maximum impact velocity of the valve can be reduced significantly. Thus, not only the suction losses but also the valve stress can be reduced. To investigate the mechanically assisted suction valve, a conventional small capacity hermetic reciprocating compressor is fitted with measurement equipment and additional components for the mechanical valve actuation. Preliminary investigations are made without the hermetic shell to find an appropriate design. Finally, measurement results of the compressor running at steady-state conditions on a calorimeter test bench (R600a) show significant improvements of the coefficient of performance (COP) at different rotational speeds and operating conditions.