Experimental study on flow boiling of R134a and R410A in a horizontal microfin tube at high saturation temperatures

This paper presents an experimental study on vaporization of R134a and R410A inside a horizontal microfin tube at 30 degrees C and 40 degrees C saturation temperatures. A wide range of operating conditions is investigated: mass flux from 80 to 600 kg m(-2) s(-1), heat flux from 14 to 83.5 kW m(-2) and vapour quality from 0.1 to 0.99. The experimental database includes measurements of heat transfer coefficient and dry-out inception vapour quality. The heat transfer data are compared with those for a plain tube at similar operating conditions. The experimental data are then used to assess the accuracy of models for the prediction of the heat transfer coefficient and dry-out vapour quality. The present data are measured at high evaporating temperature, covering values of reduced pressure between 0.19 and 0.49, which are higher than usual for air-conditioning applications with halogenated refrigerants. The main applications for the present study are related to heat pumps reaching high condensing temperature (above 70 degrees C) and high evaporating temperature (above 30 degrees C), although other applications of evaporators operating at high reduced pressure may also benefit from the present data. (C) 2011 Elsevier Ltd. All rights reserved.