Modeling of oil retention and pressure drop in vertical suction risers

A semi-empirical model for prediction of oil retention and pressure drop in vertical suction lines of an air-conditioning system is presented. The model was developed using experimental data for R134a with polyol ester oil International Organization for Standardization 32 oil in a 10.2-mm-inside-diameter pipe and was supported by data for R410A with polyol ester oil 32 flows in 7.1- and 18.5-mm-inside-diameter pipes. The model predicts 90% of oil retention data within ±20% relative error and pressure drop data within ±30% relative error. A model was also developed for prediction of minimum refrigerant mass flux, which ensures oil returns as annular film in vertical suction lines. The oil return model was used to develop minimum cooling capacity tables versus vertical suction line diameter for R134a.