An Experimental Study of Condensation Heat Transfer of Natural Refrigerants on Aluminum Surface Coated Tubes

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Trial test tubes and plates, which were coated with repellant and hydrophilic on a surface of aluminum, were produced in this study. The effect that the repellant and hydrophilic was to enhance the condensation heat transfer which was verified experimentally by using pure water, ethanol and HCFC123. The effects of the surface coats were also measured quantitatively by measuring static, dynamic contact angle and downfall angle. The results were obtained as follows.(1)As the value of surface tension of test fluids increases, static contact angle becomes larger independent of surface coats. Static contact angle on the plates that were coated with repellant showed that AL4 βhad the largest value in the case of pure water and ammonia solution and AL4 αhad the largest value in the case of ethanol. Static contact angle on the plates that were coated with hydrophilic confirmed higher wettability independent of the difference of surface tension and coats.(2)Dynamic contact angle whose forward a … More nd backward angle on the plates that were coated with repellant showed a tendency to be the same as the static contact angle, AL4α had the largest value in the case of pure water and AL4 had the largest value in the case of ammonia solution. Also the value of forward angle showed a constant value independent of the difference of surface tension, and the value of backward angle showed lower results with increased surface tension.(3)As the value of surface tension of test fluids increased, a liquid-drop on the plates that were coated with repellant fell down quickly with relatively a small liquid-drop. Also a liquid-drop on the plates of AL4α and AL6 could be seen to fall down quickly with relatively a small liquid-drop, and the effect of the surface coating was verified as superior.(4)Test tubes that were coated with repellant showed the dropwise condensation pattern, high heat flux for surface superheat, and high condensation heat transfer in the case of pure water had the largest surface tension. However, all test tubes that were coated with repellant showed the film condensation pattern, and the condensation heat transfer agreed with the Nusselt Solution for a horizontal tube in the case of ethanol and HCFC123 had a smaller surface tension. The effect of surface coating could not be verified as superior in this case. Less