Evaporative heat transfer of R410A flow in an annular duct under oscillatory wall heat flux

Abstract

In this investigation, the evaporative heat transfer characteristics of R410A flow in a slender annular duct under an oscillatory heat flux are studied experimentally with emphasis on the influences of mean mass flux, heat flux, and oscillating amplitude and period of heat flux. The applied heat flux is varied in ranges of q = 5,000 to 15,000 W m−2 and the mean mass fluxes of 300 and 400 kg.(m−2s−1) are considered, respectively. The results reveal that increasing either oscillating amplitude or period of heat flux enhances the oscillation of surface temperature and evaporation heat transfer coefficient (HTC). The prevailing influence of heat flux oscillations on the evaporation heat transfer causes notable variations in the vapour quality and liquid film thickness. At a high level of vapour quality, the thickness of refrigerant liquid film on the hot surface is decreased, leading to the increase of the evaporation HTC. Furthermore, the oscillation in the wall temperature is slightly stronger as the period of heat flux oscillation boosts in the range of 120 s to 600 s. Based on the present measured data, some correlations are provided for the evaporation HTC of R410A as the function of the heat flux and vapour quality.