Condensation of R-134a inside dimpled helically coiled tube-in-shell type heat exchanger

In this study, condensation heat transfer coefficients and frictional pressure drops of R-134a inside a dimpled helically coiled tube are experimentally investigated. The inner tubes comprise of one smooth straight tube, one smooth helically coiled tube and one dimpled helically coiled tube. The experimental measurements are carried out at saturation temperature of 35 degrees, and 45 degrees C with mass flux of 75, 115, 156 and 191 kg m(-2) s(-1). The experimental data of a smooth and dimpled helically coiled tube have been plotted on the mass flux versus vapor quality flow map and Tailtel and Dukler flow map. The transitions between different flow regimes have also been discussed. Moreover, the effect of mass flux, vapor quality and saturation temperature of R-134a on the heat transfer coefficients and pressure drops are examined. Comparisons between smooth straight tube, smooth helically coiled tube and dimpled helically coiled tube are also discussed. The dimple helically coiled tube produces a higher heat transfer coefficient and frictional pressure drop compared to smooth helically coiled tube and smooth straight tube. The correlations have been proposed to predict the Nusselt number and frictional pressure drop multiplier during condensation of R-134a inside horizontal dimpled helically coil tube. (C) 2017 Elsevier Ltd. All rights reserved.