Experimental Study On Flow And Heat Transfer Characteristics Of Wavy Condensate Film

The heat transfer process of steam condensation is often accompanied by waves on condensate film,which contain rich dynamic behaviors in space and time.The dynamic behaviors of waves,which are complexly coupled with the heat transfer process of steam condensation,enhance the condensation heat transfer.Therefore,it is of great scientific and practical significance to study the influence of wavy condensate film on the heat transfer of steam condensation and to explore the mechanism of heat transfer enhancement in order to develop efficient heat transfer technology.An experiment unit of wavy condensate film flow in a horizontal tube was designed and built up.The regulator of vapor quality was used to adjust the vapor quality at the entrance of the horizontal tube,and a function generator was used to control the speaker to introduce periodic sinusoidal disturbances of different frequencies.Based on the optical total reflection technology(TIR),the base film thickness at the bottom(0~°),side(90~°)and top(180~°)of the horizontal tube was measured.The LED/phototransistor optical technology was used to measure the wave frequency,wave velocity and wavelength of wavy condensate film.The two visual measurement technologies,which are non-contact quantitative can avoid interfering liquid film flow.The mechanism of heat transfer enhancement of wavy film characteristics was explored by analyzing the variation of base film thickness,wave frequency,wave velocity,wavelength and local heat transfer coefficient with vapor quality and disturbance frequency.The experimental results show that introduced periodic sinusoidal perturbations of specific frequencies can sustain waves in the condensate film.The wave frequency distribution of wavy condensate film for different perturbation frequencies reflects the inheritance of wave frequency to the perturbation frequency.The wave velocity and wavelength decrease with the decrease of vapor quality.When the disturbance frequency is 18Hz,the wave velocity and wavelength approach the maximum.Compared to the absence of the disturbance,the introduced disturbance has a significant effect on thinning the base film thickness at the bottom,side and top of the horizontal tube.The base film thickness at the bottom decreases most significantly.Thinning rate of base film thickness is the most at 18Hz.The base film thickness decreases with the increase of vapor quality.For small steam mass flow rate,the average thickness of base film mainly depends on the thickness of base film at the bottom of the tube.The local steam condensation heat transfer coefficient was enhanced round the tube.The enhancement of the local heat transfer coefficient at the tube bottom is the most.The wave effect on heat transfer enhancement is the most significant at 18Hz.In the range of experimental running parameters,the maximum contribution of thinning base film thickness to the enhancement of condensation heat transfer was 76%for high vapor quality and 30%for low vapor quality.