Experimental investigation of vapor condensation of iso-butane over single horizontal plain tube under different vapor pressures

• Heat transfer coefficient (HTC) reduces with increase in wall sub-cooling temperature.
• HTC decreases as heat flux increases.
• Heat flux increases as wall sub-cooling temperature increases.
• For plain tube, Nusselt model underpredicts the experimental results at higher pressure.
• For plain tube, Nusselt model overpredicts the experimental results at lower pressure.

In this study, condensation heat transfer coefficients of refrigerant R-600a (iso-butane) over a single horizontal smooth tube of diameter 19 mm were measured at different vapor pressures and different wall sub-cooling temperatures. Like other refrigerants, condensation heat transfer coefficients of R-600a showed the same trend with wall sub-cooling that external condensation HTCs decrease as wall sub cooling temperatures increase. All data were taken under three different pressures of 0.52 MPa, 0.48 MPa, and 0.43 MPa of the refrigerant-vapor with wall sub-cooling temperatures of 5–12 °C on a plain tube of 19 mm outside diameter under a heat flux of 8–20 kW/m2. Based upon the Data taken in this study, different graphs were plotted varying different parameters to show their dependency on other parameters. The experimental data were validated by comparing them against the standard model for condensation over plain tube. In this study, Nusselt's model was used as the standard model for validating the experimental results. The values given by Nusselt's equation were in the range of −10% to +12% of the experimental values.