| Summary: | 碩士 === 國立臺北科技大學 === 能源與冷凍空調工程系碩士班 === 105 === This study investigates the evaporation heat transfer performance of R-134a falling film in a wavy channel at saturation temperatures of 5 and 10oC. The fluid drips from pores of a tubular distributor onto a pair of gliding plate with a tilting angle of 30 degree, and then fluid is introduced into the wavy channel. The wavy channel made by two wavy copper blocks. The wavelength is 9.5mm, and its amplitude is 3mm. The wavy channel is 2.5mm in width and 64mm in depth. The liquid flow rates were 250, 350 and 500 ml/min, and heat fluxes varied from 7.908 to 43.49kW/m2. The experimental results show that the heat transfer is enhanced as the flow rate increases because that the fluid film increases and the low velocity region reduces with increasing flow rate. The temperature curve of the wavy channel wall is in jigsaw shape because more fluid flows through the convex section and results in a lower temperature than those of the concave section. Low heat transfer coefficient is found at high flow rates and low heat fluxes as single phase convection dominates. As the heat flux increases, the fluid evaporates forms thin film. Then, the heat transfer shift to thin film evaporation mode and heat transfer is enhanced. At low flow rates and high heat fluxes, the surface of the lower channel section becomes dry-out and heat transfer performance degraded. In this study the highest heat transfer coefficient of 14.919 kW/m2K is obtained at the flow rate of 500ml/min and heat flux of 43.49 KW/m2 at saturation temperatures of 10 oC.
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