Condensation in two phase and desuperheating zone for R1234ze(E), R134a and R32 in horizontal smooth tubes

• Experimental measurement and discussion of condensation in superheated zone.
• Effect of mass flux, saturation temperature and heat flux on HTC.
• Comparison of HTC and pressure drop for R1234ze(E), R134a and R32.
• Experimental data in agreement with Kondo–Hrnjak and Cavallini correlations.

Condensation is usually assumed to begin when the bulk enthalpy reaches the saturated vapor enthalpy, which leads to discontinuity of heat transfer coefficient calculation in modeling. This paper addresses the discontinuity by showing the presence of condensation in desuperheating region when the wall temperature decreases below the saturation temperature at any operating condition. The experiments have been conducted with R134a, R1234ze(E) and R32 for mass fluxes of 100–300 kgm−2 s−1, saturation temperatures of 30°C–50 °C and from x = 0.05 to superheat of 50 °C in a horizontal smooth tube with 6.1 mm inner diameter. R134a is observed to have approximately 10% higher and 20% lower HTC compared to R1234ze(E) and R32 respectively. Cavallini correlation predicted the data within an accuracy of 12% while Kondo-Hrnjak correlation predicted HTC for condensation in de-superheating zone within accuracy of 23%.