Reconstruction Of Three-Dimensional Geometric Model And Surface Tension Of Non-Axisymmetric Droplet Based On Orthogonal Two-Dimensional Images

In many industrial applications,droplets are attached to fibers under capillary force,such as the gas-liquid separation process in filter paper air filters,and the penetration process of water droplets in the gas diffusion layer in proton exchange membrane fuel cells.So studying the interaction between fibers and droplets is a hot topic.Based on image recognition and mathematical analysis and experiment,this paper conducts indepth research on static droplet force on fiber,which paves the way for future dynamic droplet force analysis.The main research contents of this paper are:(1)The equilibrium and dynamic droplet experimental research system was designed and constructed to obtain the stress state of droplet on horizontal fiber and inclined fiber.The design ideas of the test system and the design requirements of the test system are introduced in detail,and fibers of different diameters and liquids with different tension coefficients are selected during the experiment,and the control variable method is adopted for the test.At the same time,the key components of the test system were selected,the test plan was formulated,the relevant parameters in the test process were calibrated,and the droplet dynamics model was established.(2)Based on the orthogonal two-dimensional droplet image,the reconstruction of the threedimensional model of non-axisymmetric droplet was completed.Aiming at the problem of incomplete droplet contour shooting,the three-phase contact line of the droplet is completed by polynomial fitting method,and the complete droplet contour is obtained,and the reconstruction of the non-axisymmetric droplet and fiber three-dimensional model is completed with the help of orthogonal two-dimensional images.Based on the Young-Laplace equation,the radius of curvature of the droplet profile,the pressure generated by the surface tension of the droplet,and the horizontal and vertical components were obtained by combining the image method.Subsequently,the droplet surface tension calibration test was carried out,which verified the effectiveness of the 3D model reconstruction method.(3)Based on the change of the width of the droplet neck,the length of the contact line and the shape of the droplet,combined with the change of local Bond number in the two parts.It is found that the Bond number at the droplet neck rises significantly faster than at the contact line,that is,the neck is the weak point of the droplet’s force.The conclusion is verified: firstly,the shear stress of each part of the droplet is calculated,and then the force cloud of the droplet is presented through the threedimensional software,and the results show that the droplet is subjected to the largest shear stress at the neck,that is,the droplet first falls off from the maximum stress.(4)Based on the Young-Laplace equation,the integral force of the surface tension is calculated,and finally the capillary force between the droplet and the fiber is obtained.For the inclined fiber test,the tangential drag force between the fiber and the droplet is obtained by the droplet three-dimensional geometric model reconstruction method,which solves the problem of the tangential capillary force test method of non-axisymmetric droplet.The results show that the surface tension integration method is significantly better than the contact angle hysteresis method.As the inclination angle of the fiber increases,the tangential drag force of the droplet increases.