Augmentation of heat transfer during convective boiling inside flattened Microfin Icrofin tubes

Abstract

In the present research, augmentation of heat tranfer rates during convective boiling of HFC-134a inside a horizontal round tube and different flattened smooth and microfined tubes has been carried out experimentally. The test set-up was a well instrumented vapor compression refrigeration system. Smooth and microfined round tubes were flattened into oblong shapes with inside height of 6.6 mm, 5.5 mm, 3.8 mm, and 2.8 mm. Refrigerant HFC-134a flowing inside the tubes was heated by an electrical coil heater wrapped around them. Analysis of the collected data showed that, by flattening the round tube, the heat tranfer enhancement relative to the round tube values were achieved by the flattened tubes with the lowerst internal height. The maximum heat tranfer enhancement due to the presence of microfin inside the tube, was achieved by the tube with height internal height of 6.6 mm. It was 63% and gained at mass velocity of 107 kg/s.m2 and vapor quality of about 35%. based on the present collected dat, two different correlations were developed to predict the average boiling heat tranfer coefficients inside smooth and microfined flattened tubes.