Multiphase Flow Through Inlet Manifolds of HVAC Systems

Abstract

Inlet manifolds in HVAC systems are required to deliver specified amounts of refrigerant and oil to multiple compressors. However, multiphase flow through such manifolds is quite sensitive to upstream geometry and flow conditions. This paper reports a CFD investigation done to understand the sensitivity of oil flow (the minor component) in such manifolds with a T junction and 3 outlet pipes to the design of the inlet feed pipe geometry. The main objective was to understand the effect of upstream bends and settling length on the nature of flow through the outlets, particularly with reference to the delivery of the required amount of oil and refrigerant to each compressor. The results indicated that the refrigerant flow was not sensitive to upstream effects, while the oil flow was quite sensitive to distortions introduced in to the upstream flow field by lack of sufficient settling length and bends. It further showed that the sensitivity increased with oil droplet size.