| The fine-grained water in the oil-water emulsion not only affects the quality of the oil,but also causes energy consumption in the oil processing.In practical engineering applications,electric dehydration technology is the most widely used,but it has high energy consumption,poor adaptability,and its efficiency hits a plateau.Therefore,in recent years,new methods of applying external force have been continuously explored to combine the electric field to promote dehydration effects.Adding a cylindrical flow to the electric field and multiphase flow field improves the shear efficiency of the oil relative to the droplets,studies the deformation and coalescence of droplets,and provides a theoretical basis for the application of new dehydration technologies.The main work content and research results are as follows:(1)Using the phase field method,a two-dimensional model of the oil-water emulsion in the flow field in the wake area around a cylinder and the steady flow field is established.By comparing and analyzing the coalescence and deformation characteristics of droplets in the steady flow field and the wake field around the cylinder,the effect of the wake field around the cylinder on the coalescence of droplets is studied.In the two-phase flow/cylindrical flow,the effects of different inlet velocity distributions,flow velocities and droplet pair relative position on the deformation and coalescence of droplets were compared and analyzed.The results show that when the average velocity is equal,the parabolic inlet velocity is more conducive to droplet coalescence than the steady flow,and the coalescence time can be shortened to 1/15 of the steady flow;As the inlet velocity increases,the coalescence efficiency of droplet pair and the extent of droplet extension increase.When the inlet velocity increases by0.5m/s,the coalescence time of droplets decreases by 1/5 approximately,but when the inlet velocity is greater than 2m/s,the coalescence efficiency tends to be a fixed value;When the angle between the droplet pairs increases from 0° to 90°,the coalescenceefficiency gradually decreases.When the angle increases by 15°,the collision coalescence time between droplets increases by 0.1s.When the included angle increases to 90°,the droplets will not collide;this indicates that the flow field in the wake area around a cylinder promotes the droplet coalescence.(2)The effect of the multi-field coupling of the flow around a cylinder/electrostatic field/two-phase flow on the deformation and coalescence process of the droplet pair was studied.Based on the study of the droplet motion characteristics in the electrostatic field,the same electrostatic field was used in the flow field,and the effect of the flow coalescence on the coalescence and deformation of the droplet was compared and analyzed.The results show that the droplets can be stretched and deformed toward the electric field.The axial deformation of the large droplets is larger than that of the small droplets.The coalescence efficiency of the electrostatic field is much smaller than that of the flow field around a cylinder.The coalescence efficiency and deformation degree of the pair is greater than that of small droplets;the greater the flow velocity,the smaller the effect of the electric field in the electric coalescence of the flow around the flow,and the change range of the coalescence efficiency and deformation of the droplet in the flow field of 1m/s are stronger than the flow-through electrical coalescence field with a velocity of 2m/s;a comprehensive comparison of the coalescence and deformation processes of the droplet pair in the three physical fields is most conducive to droplet coalescence and the flow-around electrical coalescence,followed by Around the flow field,the last is the electrostatic field.(3)A two-dimensional model of flow field around a cylinder/electrostatic field/level set was established to analyze the coalescence effect of oil-water emulsions in the flow field and the flow coalescence field from the perspective of macroscopic droplet groups,and to explore the effects of flow velocity and electric field strength.The results show that in the flow field,within a certain flow velocity range,the larger the flow velocity,the larger the droplet at the outlet,and the more conducive to the coalescence between the droplets;the greater the intensity of the applied electric field,the larger the droplet at the outlet,the more conducive to coalescence between droplets,the growth rate of the droplet at the outlet is parabolic;the flow field/level set and electrostatic field/level set compared with the results of coalescence,the effect of the flow field on coalescence between droplets is more significant than that of the electric field.The effect of coalescence for each 1m/s increase in flow velocity is approximately 11 times that for 1 k V/cm increase in electric field strength. |
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