Flow boiling heat transfer characteristics of R407C inside a smooth tube with different tube inclinations

• Experimental analysis of flow boiling in inclined smooth tube is presented.
• Refrigerant R407C has been tested.
• Effects of tube inclination, vapor quality, heat flux and mass velocity on heat transfer coefficient are considered.
• Experimental results are compared with some recognized correlations.
• New correlation for flow boiling of R407C through inclined tube has been proposed.

This paper presents the results of experimental investigations carried out with refrigerant R407C during flow boiling inside a smooth tube of inside diameter 7.0 mm at different tube inclinations. The experiments included five different tube inclination angles from 0° to 90° of the direction of refrigerant flow. The test runs were carried out at inlet temperature range of 6 °C to 9 °C, refrigerant mass velocities from 100 to 300 kgm−2 s−1 and heat fluxes between 3 and 6 kW m−2. The average quality of boiling refrigerant was between 0.1 and 0.9. The influences of the above parameters on the boiling heat transfer coefficient with tube inclinations are presented. The heat transfer coefficients predicted by some available models and correlations in the open literature are compared with the present data. An empirical correlation has also been developed to predict the heat transfer coefficient of R407C during flow boiling inside an inclined plain tube.