Study On Droplet Collisions In Seawater Circulatiing Cooling System

Droplet collision is a widely existed natural phenomenon in life and modern technology.Seawater droplets collision in impinging seawater shower cooling tower will change the distribution of droplets velocity and diameter and affect the flow of droplets,which will further affect the performance of shower cooling towers.Studies on the collision of seawater droplets will provide useful reference for the optimization design of shower cooling tower,which have great practical importance for engineering applications.In the present work,seawater droplets collision was simulated using volume of fluid and an adaptive mesh method was employed to improve the calculation efficiency.First,the head-on and off-center binary collisions of tetradecane droplet were simulated at various Weber number and impact parameter.And the results are in good agreement with the experiments,which validates the accuracy of numerical method.Next,simulations of head-on and off-center binary collision of alumina droplets with equal-sized were carried out and three different types of outcomes:coalescence,reflexive separation and stretching separation were covered.The We-x map of the binary collision outcomes of seawater droplets is captured,the formation mechanism of different outcomes are presented.Finally,the numerical simulations of different droplet diameter and seawater concentration were carried out,and the influence of droplet diameter and seawater concentration on the droplet collision was discussed.The dissertation contents and conclusions are as follows:?1?For equal-sized seawater droplets head-on collisions under the conditions of We:0.5²00,u₀:0.21m/s⁴.22m/s,Re:89.56¹791.12,x=0,D₀=200?m,Oh=0.0079.Two kinds of outcomes are obtained,which are coalescence and reflexive separation.The critical Weber number of coalescence and reflexive separation is 23.?2?For equal-sized seawater droplets off-centre collisions under the conditions of We:5²00,u₀:0.66m/s⁴.22m/s,Re:283.20¹791.12,x:0.1⁰.8,D₀=200?m,Oh=0.0079.Three kinds of outcomes are obtained,which are coalescence,reflexive separation and stretching separation.The deformations of droplets between head-on collision and off-centre collision are similarity,except rotation motion exists in the deformation.?3?For equal-sized seawater droplets collisions with diameter D₀=20?m,200?m,2000?m.The critical Weber number of coalescence and reflexive separation are 29,23,14,respectively,which is similar to 30.88,19.88,16.41 calculated by the model of Gotaas et al.The Ohnesorge number determines the distribution of collision regimes while the Weber number and impact parameter determine the deformation processes and results of collision.As the droplet diameter increases,the Ohnesorge number decreases,the critical Weber of coalescence and reflexive separation decreases,and the coalescence region is obviously shrunken.?4?For equal-sized seawater droplets collisions and two-fold concentrated seawater droplets collision,the critical Weber number of coalescence and reflexive separation are 20,23,25,respectively,which is similar to 19.62,19.88,20.07 calculated by the model of Gotaas et al.As the droplet concentration increases,the Ohnesorge number increases,the critical Weber of coalescence and reflexive separation increases,the coalescence region gradually broadens,and the separation region moves to lager Weber number region.