Research Of The Law Of Oil Droplets Motion And The Shearing Field Around The Droplets In Complicated Channels

As the motion phenomenon of oil droplets is very complicated in complicated channels, experimental methods are limited and measurement is very difficult, in order to find the law of oil droplets motion in complicated channels, the way of combining theoretical analysis and simulated computation is used in this study. The law of oil droplets motion and the shearing field around the droplets in complicated channels is presented in this paper.First, aiming at slow weakening disturbance of oil droplets in complicated channels under the condition of low Reynolds number, the theory of low Reynolds number is adopted. As the motion of oil droplet is affected by boundary, environment and viewing oil droplet as fluid sphere, the motion resistance is corrected. Moreover, the boundary integral equation is set up which can be used in shearing field of complicated channels in gravity separator.Second, simulated computation of law of oil droplets motion in flat board, inclined board and corrugated board. is done by way of Fluent software and UDF, based on corrected motion resistance. In this simulated computation, water phase is looked on as laminar flow model, while oil phase is looked on as discrete phase modal. The result shows that:The law of traditional Stokes oil droplet motion is different from that while the oil droplet is in another immiscible liquid in limited space. For liquid-liquid system, oil drop is fluid sphere, which has little positive influences; compared with traditional limitless Stokes, oil droplet trajectory is greatly different by the action of boundary and Poiseuille environmental flows. It has a postponed effect on oil droplets up-floating time, and the impact of its border is major, while Poiseuille flow environment takes the second place; compared to the traditional Stokes oil droplet, the time of oil droplet up-floating in the flat board delay 17.211% because of the synergy, inclined board in counter flow delay 18.753% , corrugated board delay 20.304%. Therefore, synergy impact is more significant when the flow channel is more complex.Third,The up-floating efficiency will drop sharply while the velocity is increased or the size is decreased in flat board, inclined board and corrugated board.â‘ For flat board , vertical velocity of the oil droplet terminal has nothing with the velocity of the flow field ; but relates to the size of oil droplet. The migration velocity of oil droplet in horizontal direction has nothing to do with the size of oil droplet, while the migration velocity is synchronous with the change of Poiseuille flow between the boards, and in line with the conditions of zero resistance; Stokes oil droplets between the boards have a strong independent up-floating and migration movement. As oil droplets collision depend much on geometric parameters, the initial location, physical properties of oil droplets and the velocity gradient of the flow field , a mathematical model of the oil droplets collision is set up according to this. This modal provides a judgement for the oil droplets collision. And the calculated results are in line with the simulation results by Fluent software.â‘¡For inclined board , the vertical velocity of the oil droplets is the same whether in flat board, inclined board or corrugated board, and it has nothing to do with flow pattern; However, if the oil droplets are affected by synergy under the condition of low Reynolds number, the velocity of the oil droplets is different and there is something to do with flow patterns; The effects on migration velocity of oil droplets along the direction of the board are different from flat board. The migration velocity of oil droplets has somthing to do with the size of oil droplets, however does not couple with the velocity of Poiseuille flow between the boards, and there is a motion resistance; The migration velocity of oil droplets is lower if the oil droplets are larger in counter flow in inclined board. While in parallel flow, the situation is on the contrary; Both the motion displacement and up-floating time of oil droplets increase while the angle of the inclined board increases, The up-floating time of oil-droplets in counter flow is shorter than in cross flow and in parallel flow, so adopting counter flow pattern has more advantages than cross flow pattern or parallel flow pattern;â‘¢As one kind of coalescing internals, the flat board has shorter up-floating time and horizontal displacement , so it has more advantages; However, flow field is often torrential and unstable when the angle of inclined board and velocity of the flow field are great. And then the effects on oil droplets become more complicated which can result in volution, fluctuated trajectory, can not free self or even result in back flow, the angle of inclined board and velocity of the flow field should be considered delicately in order to have a good use of corrugated board. Through the simulation of the separator which are inserted with the flat board and corrugated board and the simulation of velocity field, the contour line of symmetric plane concentration in coalescing internal and the contour line of the board concentration both of the head and the tail, by way of multiphase mix modal, the conclusion that separate efficiency of corrugated board is much better than the flat board has a further verification.Finally, as the dimensional analysis has pointed out that the deformation and crush of oil droplets are difficult to give an quantitative description, however, by way of VOF the two-dimension simulation of oil droplets deformation in shear field is feasible. The results are as follows:The viscosity of oil and surface tension inhibit the deformation of oil droplets, however, oil droplets are easier to deform and crush if the diameter is bigger. Oil droplets are easier to deform and crush if the velocity gradient is greater. So, by way of bringing in many kinds of coalescent pack, the efficiency is increased while at the same time the risk of deformation and crush of oil droplets in shear field is increased too. The emulsification of oil and water is increased when there is a larger relative velocity, so there must be emulsification of oil and water in hydrocyclone.We have achieved some progress in this study. However, because of the simplification of practical problems during the process of setting up modal and simulation, the application category of the results is limited. Deficiency still exists at the aspect of quantification, and so, a lot of further experimental research need to be developed.