Conference Year

2012

Keywords

reed valve, valve dynamics, valve flutter, compressor efficiency

Abstract

The current work directly relates valve dynamics to the compressor energy efficiency. Majority of the previous studies have focused on reducing pressure losses due to valve geometry, towards improved compressor performance. On a complimentary note, analyzing the valve ‘flutter’ leads to a holistic valve development methodology. Traditionally, pressure actuated reed valves have been used in reciprocating hermetic compressors on the suction and discharge ports. A characteristic of these valve operation is the multiple opening and closing motions, during a single suction and discharge pulse, often referred to as the ‘valve flutter’. This is more prominent for the suction reed considering the longer (crank-angle) duration of the suction process. The valve dynamics is a highly coupled fluid structure interaction problem. In the present work, the reed valve dynamics has been simplified to a single degree of freedom spring mass system and is captured by a mathematical model within a 15% accuracy range for displacement prediction. Considering the current stage of development, this is within acceptable limits. To validate this model, in-compressor valve lift measurements (direct strain gauge measurements) in a closed loop refrigeration rig have been used. Considering the complexity and time involved with the in-compressor measurements, a simplified framework to characterize the dynamics of reed valves outside the compressor (indirect measurements) has also been proposed and developed. Since the basis of this study is analyzing the characteristic valve dynamics, physics-based transfer functions can translate these measurements to the actual compressor reed motion leading to a faster design cycle. Also, CFD has been used to provide a detailed insight to the flow physics. With all of the above inputs, the mathematical models help identifying key design parameters and help evaluate conceptual designs towards an ideal/ chosen valve response.

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