Experimental validation of a homogeneous equilibrium model for two-phase flow in capillary tubes using R290 refrigerant

This work aims to validate a Homogeneous Equilibrium Model using experimental data from a dedicated apparatus to forecast two-phase flows in capillary tubes using R290. The experimental setup consists of a 1.05 m long capillary tube painted with high emissivity black paint. It is integrated into a refrigeration cycle. Pressure transducers are placed at 0 cm, 53 cm, and 105 cm along the tube, each accompanied by a T-type thermocouple in close contact with the tube's surface. Moreover, temperature distribution along the tube's surface is obtained via thermography. The model was tested using experimental data from published studies on R12 refrigerant fluid: it showed high accuracy in predicting pressure trends and capillary tube's length. Comparison of model prediction with original experimental data obtained with R-290 showed remarkable accuracy in predicting the overall capillary length, single-phase length, and pressure trends within a restricted mass flow rate. The model performs worse as the mass flow rate increases. This discrepancy is presumed to be due to the presence of oil in the circuit. Therefore, further work is underway to develop a model that includes the presence of oil, to understand its influence more comprehensively.