MODELLING VALVE DYNAMICS AND FLOW IN RECIPROCATING COMPRESSORS – A SURVEY

Abstract

Thermodynamic performance (delivery rate and power intake) and reliability of reciprocating compressors are largely dependent upon the valves. Since the valves open and close automatically, there is a high degree of coupling between the gas flow through the valve and the sealing element dynamics; a mismatch between the two leads inevitably to degradation of the compressor performance and/or short valve life. The latter is due to excessive impact forces between the sealing element and other parts of the valve assembly. Therefore, matching the valves to the compressor application at hand is a complex task that calls for the use of the corresponding simulation models. Surveyed in the paper are mathematical models for the prediction of the valve performance, consisting of the submodels describing compressible gas flow through the valves, sealing element dynamics, and the interaction of the latter with the flow. It is concluded that flow models based on the discharge coefficient are intrinsically not able to predict the critical flow regime with sufficient accuracy, requiring thus experimental data that are not always available. It is also suggested that other loss calculation approaches, such as e.g.. the stagnation pressure loss model, should be investigated as possible alternatives to the discharge coefficient concept.