| Summary: | 碩士 === 國立臺北科技大學 === 能源與冷凍空調工程系碩士班 === 100 === This study investigates the condensation heat transfer experiments for two pure refrigerants, R-410A and R-22, in the U-bend smooth and micro-fin tubes. U-bend situated in a vertical plane, including two straight and a bend section. Refrigerants flow from the upper horizontal straight section to the lower horizontal straight section. Experiments were performed at saturation temperatures of 30℃ and 40℃. The mass flux varied from 50 to 200 kg/m2s, and the inlet quality varied from 0.2 to 0.9. The heat transfer rate of the test section was controlled to a decrease of vapor quality of 0.2 in the present experiment.
The test results showed that heat transfer coefficient increased as mass flux and quality increased. Condensation heat transfer coefficient of R-22 was higher than R-410A in both the smooth and microfin tubes. The average condensation heat transfer coefficient of the microfin tubes for R-22 and R-410A were 1.63-2.2 and 1.5-1.97 times larger than those of the smooth tube, respectively. In average, the local heat transfer coefficients of R-22 and R-410A in the bend section were, 1.21 and 1.12 times larger than those in the upper straight section, respectively. The maximum local heat transfer coefficient occurs at the midle (90° position) of the bend. Heat transfer correlations of straight horizontal condensation on smooth and microfin tubes predict the data in this study with r.m.s. 9.68% and 5.49% respectively. A correlation of local heat transfer coefficient of the U-bend section based on the straight tube is provided. It predicts the present data of smooth and finned tubes with r.m.s. 9.16% and 5.8%.
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