Experimental investigation of mass flow rate difference between forward flow and reverse flow of sub-cooled R-22 through stepped short tube orifices

•The low cost stepped short tube orifice (SSTO) was firstly proposed.•The mass flow rates in opposite way of R-22 through SSTO are distinguishing.•11# SSTO has good two-way throttling characteristics. An expansion device of two capillary tubes with a by-pass check valve is popularly used in domestic heat pump systems. In order to reduce the manufacturing cost and improve reliability of the heat pump systems, a stepped short tube orifice consisting of two serial-connected short tube orifices with different diameters is employed as an alternative. The effects of upstream pressure, downstream pressure, upstream degree of sub-cooling and the geometric sizes of stepped short tube orifices on mass flow rate difference between forward flow and reverse flow of R-22 through stepped short tube orifices were investigated in this study. The results showed that there was a distinguishing mass flow rate difference between forward flow and reverse flow of R-22 through stepped short tube orifices under upstream pressure ranged from 1460kPa to 1940kPa, downstream pressure ranged from 420kPa to 680kPa and degree of sub-cooling ranged from 2 to 12°C. The mass flow rate difference is about 10kg/h between forward flow and reverse flow of R-22 through the stepped short tube orifice with sizes of D1=0.8mm, D2=1.0mm, L1=3mm, L2=6.5mm at the upstream pressure of 1940kPa, downstream pressure of 500kPa and the degree of sub-cooling ranging between 2°C and 12°C.