Experimental Study on Condensation Heat Transfer of Ethanol-Water Vapor Mixtures on Vertical Micro-tubes

The paper presents an experimental investigation of Marangoni condensation heat transfer of ethanol-water vapor mixtures on vertical micro-tubes with an outer diameter of 0.793 mm, 1.032 mm, and 1.221 mm. Experiments were performed over a wide range of ethanol mass fractions in vapor mixtures for different vapor velocities and pressures. Condensation heat transfer coefficients behaved nonlinear characteristics, increased, and then decreased with increasing vapor-to-surface temperature difference. Under the same experimental conditions, the condensation heat transfer coefficient at a 2 % ethanol mass fraction in vapor was the highest. At low ethanol mass fractions, the condensation heat transfer coefficient of the ethanol-water vapor mixture was 2 to 3 times greater than that for pure steam. The effect of vapor pressure and velocity on condensation heat transfer suggested a positive tendency on each micro-tube for all vapor mixtures with different ethanol mass fraction. Results showed that condensation heat transfer coefficients on micro-tubes with a diameter of 1.032 mm were higher than those on the other two micro-tubes, suggesting that there existed a critical diameter which gave the largest condensation heat transfer coefficient.