Optimization Of Membrane Module Structure In Separation Process Of Saline Water By Direct Contact Membrane Distillation

DN50-16 single seat regulating valve is a kind of universal machinery widely used,which has the advantages of simple structure and stable operation.Cavitation is a special hydrodynamic phenomenon,which is closely related to the flow medium,velocity,pressure and temperature.Cavitation is an unavoidable phenomenon in the single seat regulating valve.Long-term collapse of a large number of bubbles will cause damage to the surface material of the internal runner,especially the sealing surface of the valve disc and seat,and even cause vibration and noise of the single-seat control valve,thereby reducing its service life.Therefore,it is of great significance to explore the cavitation flow law in single seat control valve under various working conditions,and to optimize the structure parameters of the valve disc and then suppress the cavitation phenomenon.In view of the cavitation phenomenon inside the single seat control valve,this paper mainly studies the following parts:(1)The CFD software FLUENT was used and the Realizable K-εturbulence model,Mixture multiphase flow model and Schnerr-Sauer cavitation model was selected to simulate the internal cavitation flow of the original single-seat valve model under different opening,pressure difference and flow rate.(2)Orthogonal test method was used to optimize the structural parameters of the valve disc,and the optimized valve models were calculated and analyzed separately.Then a set of optimal valve parameters were selected by range analysis method,and the transient calculation and comparison of the valve models before and after optimization were made.(3)At last,the flow characteristic curves of the control valve under different pressure differences were measured by experiment,and then the flow characteristic curves of the control valve were calculated by using the same boundary conditions as the experiment,and the flow characteristic curves of the experimental value and the calculated value were compared,which indirectly verifies the validity of the numerical simulation calculation model.Through the above analysis,the following conclusions can be drawn:(1)At 5%opening of DN50-16 single seat control valve,with the increase of pressure difference,the cavitation area,the maximum vapor volume proportion and the maximum vapor volume proportion area all increase.The lowest pressure decreases,the lowest pressure area increases,and the maximum velocity increases.(2)At the same flow rate,the volume of vapor phase decreases rapidly with the increase of the opening.When the opening is 25%,the volume of vapor phase decreases by only 1/15 of that when the opening is 5%.(3)Under the same pressure difference,with the opening increasing gradually,the volume of vapor phase increases slowly at first,and increases rapidly after the opening reaches 20%.(4)Orthogonal test and range analysis were used to obtain the optimized valve disc parameters ofα=25~°,L=5.5mm,R=2mm.The vapor volume of the optimized model was only 20.05%of that before optimization.(5)The maximum error between the calculated data and the theoretical value is 8.76%,which meets the accuracy requirement.