Numerical Simulation Of Falling Film Of Vertical System For Circular Tube Under Conical Distributor

Vertical tube falling film evaporation condenser with high efficiency and energy saving,heat transfer temperature difference is small,and the advantages of small filling quantity,is widely used in industry,vertical tube falling liquid film thickness is thinner,high Reynolds number under the intensity of heat transfer and mass transfer of strength is several times under the same conditions of laminar flow,thus reach the same heat transfer effect,heat exchange equipment may be greatly reduced,equipment cost is reduced,raised the working efficiency of the equipment.The conical distributor is selected as the distribution device of the liquid film in the standpipe falling-film evaporative condenser.The annular gap formed between the conical distributor and the pipe maked the liquid film distribute on the pipe wall.However,scholars seldom studied the falling film of the standpipe under the conical distributor,and the distribution mechanism of the liquid film on the pipe wall was not clear enough.In view of this,this paper studied the influence of the flow distribution characteristics of the liquid film on the tube wall on the condensation heat transfer efficiency by means of numericalsimulation,and discussed the possibility of enhancing heat transfer under the optimal falling film condition,so as to provide reliable data support for the optimal design of the vertical falling film evaporative condenser.In the numerical simulation,CFD software was used to simulate the distribution characteristics of the liquid film when the flow rate of the vertical circular tube in the tube wall was 0.37kg/(m · s)~1.48kg/(m · s)under the conditions of conical membrane distributor and constant wall temperature.The numerical simulation results under different spray flow rates were compared with the theoretical results of predecessors,and it was found that the overall simulation results were reliable when the Reynolds number was from 2000 to10000.On this basis,the shape distribution,temperature distribution and velocity distribution of the liquid film were discussed,and the heat transfer effect of the pipe wall on the liquid film under the condition of different spray amount was studied.On the whole,in the low Reynolds number,the forms of vertical tube falling film was divided into two sections: the period of stability and the oscillation of the next paragraph,when spray to increase,the thickening of liquid membrane,liquid membrane under the period of the degree of fluctuation is abate,but increasing average heat transfer coefficient of tube wall of liquid membrane,this is because the spray quantity increase,makes the liquid film on the wall to speed up the update rate.Falling film width of the vertical tube falling film structure,falling filmlength and air inlet was simulated optimization analysis,analysis of the film thickness,temperature,speed and Nu numeral change rule,it was concluded that the increase of the width of the falling film on the nusselt numeral Nu with the increase of the effect was not obvious,air inlet width and length of heat-exchange reinforcement effect were obvious,especially the factors of length,when the L =0.7m,Nu is 1.72 times than L =0.3m.So,proper air inlet width and tube length can prevent the rupture of the liquid film.