The effect of wire-coil inserts on the heat transfer and pressure drop of R1234yf flow boiling

Due to growing environmental concerns about global warming, eco-friendly HFO refrigerants such as R1234yf have been recently introduced as an alternative to conventional HFC ones. The present research work investigates the boiling heat transfer coefficient and pressure drop of R1234yf flow as a replacement refrigerant for R134a in horizontal plain and wire-coil inserted tubes of 8.7 mm inside diameter. Meanwhile, the accuracy of some well-known correlations to predict R1234yf flow boiling thermo-hydraulic properties are evaluated. The results show that the studied correlations may predict the heat transfer coefficient and pressure drop of R1234yf flow boiling in plain tubes with an acceptable accuracy. The effect of main operating parameters including the vapor quality, the heat flux, and the mass velocity is also thoroughly studied using a well-instrumented test apparatus. According to the results, at constant vapor quality, the heat transfer coefficient increases with both the heat flux and the mass velocity. In addition, inserting a wire-coil in the tube may enhance the heat transfer coefficient as much as 72% while leads up to 85% increment in the pressure drop. This study and its result is helpful in design of next generation of heat exchangers use R1234yf refrigerant as a working fluid.