Review on the experimental studies of refrigerant flow mechanisms inside short-tube orifices

A short-tube orifice is a kind of an expansion device. The advantages of a short-tube orifice are simplicity, low cost, and low starting torque of the compressor as the pressures across the short-tube orifice equalise during the off-cycle. The two-phase flow mechanisms of refrigerant inside the short-tube orifice are very complicated although its physical configurations are simple. During the past decade, investigations of the mass flow rate of various refrigerants inside short-tube orifices, which is useful for selecting the proper size in practical applications, have been reported by many researchers. However, few researchers focused on the flow pattern, choked flow, and metastable flow phenomena inside short-tube orifices, which are necessary for a clear understanding of the flow behaviour and developing suitable calculation techniques. The aim of this paper is to summarise the evolution of the experimental research on refrigerant flow characteristics inside short-tube orifices to provide guidelines for future research.