Effect Of Vapor Flow Direction On Spontaneous Movement Of Drops During Marangoni Condensation

In the condensation process of some binary mixed vapors conforming to the "positive system"(for example,water-alcohol mixture),local disturbances will cause a temperature difference at the gas-liquid interface,which in turn causes uneven concentration distribution at the gas-liquid interface,thereby causing surface tension Poor,driven by the difference in surface tension,the form of the condensate condenses into beads,called "bead-like condensation",which is Marangoni condensation.When the heat transfer surface has a significant temperature gradient,the condensed droplets will move spontaneously,and the condensed droplets will always move from the low temperature area to the high temperature area.And the experimental results show that the condensation droplets will still move spontaneously during the condensation process of the water-alcohol mixed vapor on the horizontal heat transfer surface.Many scholars at home and abroad have studied the mechanism and influencing factors of Marangoni condensation,but have not studied the influence of vapor flow direction on the movement of condensed droplets.In this thesis,an experimental study on the condensation of water-alcohol mixed vapor is carried out in view of the influencing factor of vapor flow.In this paper,a visual observation condensation experimental system is designed.The experimental system operates under local atmospheric pressure and is equipped with a deaerator to eliminate the influence of non-condensable gases on the experimental results.The condensation chamber adopts two-way adjustable jet cooling mode,which can realize different temperature distributions on the heat transfer surface.The effects of vapor flow direction on the movement of condensed droplets on heat transfer surfaces without and with obvious temperature gradients were studied respectively.According to the experimental results,this paper proposes that the direction of vapor flow is a major factor affecting the movement of droplets.The experimental results of this paper show that for the heat transfer surface without obvious temperature gradient,the condensed droplets will move spontaneously along the direction of the vapor inlet,and the average speed of droplets movement increases with the increase of surface subcooling.During the condensation process of mixed vapor,the concentration of alcohol vapor at the gas-liquid interface has a gradient along the vapor flow direction,causing a difference in surface tension.Driven by the difference in surface tension,the condensed droplets spontaneously move toward the vapor inlet.On the heat transfer surface with obvious temperature gradient,the movement characteristics of condensed droplets are different from the heat transfer surface without obvious temperature gradient.When the mixed steam flows from right to left and the heat transfer surface has a positive temperature gradient,the condensed droplets always move to the right;when the heat transfer surface has a negative temperature gradient,the two influencing factors of the temperature gradient and the steam flow direction interact The condensed droplets move either to the left or to the right.The movement direction of the droplets is determined by the relative size of the vapor flow direction and the temperature gradient.When the vapor flow direction plays a leading role,the droplets move along the vapor inlet side and the temperature gradient When playing a leading role,the droplets move from the low temperature area to the high temperature area.