Experimental Investigation of R134a and Its Alternative Refrigerant R513A Flow Boiling in Microchannel Tube

This study investigates the flow boiling characteristics of R134a and its alternative refrigerant R513A in a microchannel tube. The effects of vapor quality, saturation temperature, heat flux, and mass flux on the heat transfer coefficient and pressure gradients were explored. Additionally, a comparative analysis of R134a and R513A was conducted. The test conditions covered vapor quality from 0 to 1, inlet saturation temperature from 10 ℃ to 30 ℃, heat flux from 2 kW/m² to 8 kW/m², and mass flux from 100 kg/(m²·s) to 200 kg/ (m²·s). Results show that saturation temperature has almost no effect on the heat transfer coefficient of R134a but slightly influences that of R513A. At high saturation temperatures, the pressure gradient of R513A is low. Heat flux significantly affects the heat transfer coefficients of both refrigerants, and the peak heat transfer coefficient increases by more than 30%. Moreover, under low vapor quality, the heat transfer coefficient increases by more than 80%; however, its effect on pressure gradients is negligible. Mass flux significantly affects the heat transfer coefficient under intermediate vapor quality, and doubling its value causes the heat transfer coefficient to increase by more than 50%. In addition, mass flux significantly affects the pressure gradient. A comparison of the flow boiling characteristics of R134a and R513A under the same test conditions shows that R513A has higher heat transfer coefficients and lower pressure gradients than R134a.