Study On Condensation Mechanism Of Wet Air On Cold Surface

In today's society,saving energy and strengthening heat exchange are the themes of improving energy utilization.The heat transfer method of wet air condensation is widely used in many industrial fields,for example,aerospace engineering,steam power engineering,chemical engineering and so on.But so far,because the size of droplets condensed by wet air extends from nanometer to micrometer to millimeter from nucleation to growth and merging and falling off,this process is six orders of magnitude different,and the existing equipment is limited,and it unable clearly observe the change of nanometer scale at the beginning of nucleation,so there are few experimental researches on condensation.So far,the growth process and heat transfer process of wet air condensation droplets are not very clear.In this paper,the growth process and heat transfer process of condensate droplets are analyzed through experiments.Based on the above analysis,this paper uses polytetrafluoroethylene(PTFE)materials,mainly doing the following research:(1)Study on droplet size under different temperature and humidityIn this paper,the condensation process and the change of the diameter of the droplets on the Teflon material of the horizontal plate under different temperature(273k,275 k,277K)and air humidity(50%,60%,70%,80%,90%)were observed by using the hirox three-dimensional video microscope.It was found that there was a positive correlation between the droplet diameter and the condensation time.The higher the humidity,the faster the condensation occurs,the lower the humidity,and the slower the condensation occurs.The linear regression equations of droplet diameter and setting time are established and variance analysis was carried out.(2)Dynamic contact angle change of droplets is observed during condensation under different temperature and humidityIn this paper,the contact angle of droplets condensed on the horizontal cold surface was measured by using the kruss droplet shape analyzer(dsa100),that then the dynamic change curve of contact angle was drawn,that the change rule under different temperature and humidity conditions was analyzed.It was found that under a certain temperature and humidity condition,the contact angle of droplets was fixed in a certain range.In addition,the wet air with higher humidity and supercooling degree is more likely to form bead like condensation on the PTFE plate.(3)Study on the number of droplets coagulated and the area ratio of droplets under different temperature and humiditythe number and area ratio of droplets on the horizontal cold surface with time change under different temperature and humidity conditions were calculated through Photoshop Image analysis software.The results show that the number of droplets and the setting time were in normal distribution.When the second generation of droplets occurs,the number of droplets will have double peaks.The area ratio will increase rapidly in the nucleation and growth stage of the droplets,and finally stabilize in the range of 70% ? 80%.