Supercritical Heat Transfer and Pressure Drop in Refrigerant R410A

This paper presents the results of an experimental study on heat transfer and pressure drop at critical and supercritical pressures of refrigerant R410A inside a horizontal 9.4 mm I.D. tube. Knowledge of heat transfer and pressure drop in such refrigerants blends at elevated pressures is gaining increasing attention for the design of vapor-compression space-conditioning and water heating systems at high heat rejection temperatures. Local heat transfer coefficients and pressure drops were measured for the mass flux range 200 < G < 800 kg/m²-s for the temperature range from 30–110°C. A technique that simultaneously allows accurate measurement of low local heat duties and deduction of the tube-side heat transfer coefficient from the measured overall resistance was used. A primary cooling loop using water at high flow rates ensures that the refrigerant side presents the governing thermal resistance. Heat exchange with a secondary cooling water stream at a much lower flow rate amplifies the coolant temperature difference, which in turn enables accurate heat duty measurements. The results show that the heat transfer coefficient exhibits a sharp peak in the vicinity of the vapor-liquid dome. These data are compared with the most relevant correlations from the literature and possible explanations for agreement and discrepancies between the data and predictions are provided.