Abstract
In this study, the effect of lubricating oil on the heat transfer characteristics of R600a condensing flow inside a horizontal micro-fin tube is experimentally investigated. The results are presented in three parts, including the characteristics of pure R600a condensation inside a smooth tube, the impact of using a micro-fin tube, and the effect of adding lubricating oil on the condensing heat transfer inside a micro-fin tube. The test condensers are smooth and micro-fin copper tubes of 14.18 mm inner diameter which are installed in a 6 cm polyethylene pipe to form double-pipe heat exchangers. The test conditions include mass velocity of 54 to 90 kg/m2s and vapor quality of 0.03 to 0.78, while condensation pressure is between 550 to 700 kPa. The results show that in the case of pure R600a, using the micro-fin tube may enhance the local heat transfer coefficients up to 79%. In addition, for the refrigerant-oil mixture condensing flow, by increasing the vapor quality, the heat transfer coefficient increases up to a critical value after that it starts to decrease due to the effect of oil on the condensation liquid film.
Published Version
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