VOF, CFD, Slugging, Muffler
Liquid slugging in reciprocating compressors is highly concerning due to the exceptionally harmful effects of liquid hammering. The high pressure generated by the liquid compression leads to high stresses on the structural components, resulting many times in compressor failure. The suction muffler is a path to the compression chamber for the slugging flow, therefore its design influences the amount of liquid that reaches the compression chamber. This paper depicts the numerical study of the liquid flow in four typical muffler designs, aiming to analyze the influence of the muffler design parameters in the liquid mass flow rate reaching the compression chamber. It has been considered only non-hermetic suction mufflers. The Volume of Fluid Method (VOF), available in the software ANSYS CFX, was employed to simulate the unsteady two phase flow in the suction system of a R134a compressor of 9.5 cc. The physical domain consists of the suction system only, which is composed by the suction tube, suction muffler and the compressor internal cavity, simplified by a two-dimensional geometry. The inlet mass flow is an important variable and its correct prediction is quite challenging, due to the relationship with the refrigerant charge, running condition and pressure losses in the suction line, so it has been defined a range for the inlet mass flow rate in order to properly account its influence. For simplification purposes, in the presented study the effect of the liquid evaporation through the suction system due to the heat transfer and pressure pulsation was not considered. VOF method was used, therefore the procedure shall lead to higher rate of outlet liquid mass flow, providing a conservative analysis. The main conclusions of the present work are the muffler design can influence significantly the flow towards the compression chamber and the numerical procedure can provide insightful information about the slugging flow in the reciprocating compressors suction system.