Abstract: The sufficent vapor velocity should be considered to insure adequate oil return, when designing the suction pipe. The error in reported KESIM model for oil return is analyzed and the KESIM model is revised. The new oil return model is presented based on fluid mechanics principle, and the method of calculating the minimum refrigerant velocity is proposed according to nil oil volumetric flow rate and the relation between refrigerant velocity and interface velocity. The comparison between the models and experimental data shows that the new model can predict the minimum velocity of oil return more accurate than the revised KESIM model. The velocity can be converted to refrigeration capacity through a saturated thermodynamic cycle for R410A and two types of copper suction pipe.

Key words: Minimum refrigerant velocity, Oil return, Refrigerant vapor, Suction pipe