Reciprocating, compressor, pressure, pulsation, impedance
In a hermetic reciprocating compressor the suction pressure pulsations affect compressor performance and noise. The pressure pulsations are created due to the dynamic flow of refrigerant through the suction valve into the cylinder bore. One dimensional (1D) acoustic method, Finite Element Method (FEM) calculated impedance transfer matrix method, and Computational Fluid Dynamics (CFD) are three commonly used methods to calculate these pressure pulsations. With CFD being used most often to solve this type of analysis; however CFD is often time consuming and requires significant computer resources. In order to solve the pressure pulsation analyses faster, the suction plenum geometry is often simplified by reducing the model size. This simplification could lead to inaccuracies in pressure pulsation modeling. This paper will use the FEM calculated impedance transfer matrix method to analyze a hermetic HVAC reciprocating compressor to show that geometry simplifications could result in poor predictions of pressure pulsation. The FEM calculated impedance transfer matrix method was chosen due to its short solution time and the inherent ability to compare similarities and differences in the plenum’s impedances between the full model which includes volume inside the compressor shell, and a simplified model. This paper will specifically look at the influence of the compressor shell volume on simulating suction pressure pulsations. In the compressor analyzed, the compressor shell volume influences the pressure pulsation at the first compressor speed harmonic. A pressure pulsation at the first harmonic has the greatest influence on the compressor performance. This paper will compare measured pressure pulsations to simulated pressure pulsations. The pressure pulsations are in good agreement when the full model is analyzed but when simplifications are done to the model it fails to provide good agreement.