| Due to the mass transfer heat transfer of the evaporative cooling technology,it can improve the heat transfer capacity under the condition of small temperature difference.The traditional water cooling and air cooling are affected by the dry bulb temperature of the air,and the heat transfer efficiency is very low during the high temperature season.Therefore,the evaporative cooling technology is widely used in chemical,refrigeration,metallurgy and other fields.The distribution method of the traditional water film evaporative condensers tube is generally horizontal pipe arrangement.When horizontal tube evaporative condenser working,it cannot quickly discharge condensate out of the tube,resulting into the back pressure rise,pipe burst and other security risks.At the same time,these effects can lead to a decrease in heat transfer capacity of the equipment.Therefore,it is necessary to study the distribution method of evaporative condenser tube.When the thickness of the liquid film outside the tube is too large,the vaporization resistance increases,which is detrimental to heat transfer;If the liquid film is thin,there will be "dry spots",seriously affecting equipment life.The distributions of air velocityin the evaporator not only affect taking away heat and saturated steam,but also affect the flow of fluid outside the tube.Therefore,the film thickness and air velocity distribution are two key factors influencing the inclined tube evaporative condensers.However,test conditions of film thickness distributions and air flow rates between the various tubes are limited,and there are too many impact factors,the accuracy of the experimental data can not be guaranteed,the workload is too large,and investment is huge.So,it is valuable to carry out the numerical simulation experiments on the factors such as the film thickness and the air flow rate.And it can provide some important theoretical basis and references to build a mass transfer heat transfer test bed and production practice.In this paper,the evaporation tube of the evaporator was set as an elliptical tube with a long half shaft of 28.5mm and a short half axis of 19 mm.First,UG software was used for physical modeling,followed by grid partitioning by ANSYS ICEM CFD software.The boundary conditions and each discrete equations were defined using the numerical simulation software FLUENT 15.0.The study of flow characteristics of liquid film outside the tube started from the VOF model;Simulated of air flow field characteristics from RNG k-ε Turbulence Model,and then selected the appropriate grid size by grid-independent verification,compared the numerical results with the experimental results to verify the correctness of the numerical calculations.Used the post-processing software Tecplot and CFD-Post on the simulationresults to do a reasonable follow-up.At the same time,draw the experimental results of the data with the Origin software.The qualitative analysis of the calculation results was carried out according to the experimental data.The effects of different spray flows,spray locations,elliptical tube inclination angles and head wind speeds on the flow of liquid outside the tube were simulated and analyzed,The results showed: When the spray flow rate is1.8 cm3/s(v = 0.8m/s),the distributor position is C1 = 6.0mm,the head wind speed is v = 2.4m/s,the elliptical tube inclination angle is θ = 15°,the distributions of liquid film outside the tube is stable and uniform,it improve the ability of heat transfer cooling.The tilted piping approach causes the air flow above the heat transfer tube to shift,and the movements is basically concentrated near the outlet of the heat transfer tube.When the number of layers increased to 18 layers,the air flow out of the box stability.With the increase of the number of layers,the rate of pressure decline is significantly slowed down,and the negative pressure at the exit is gradually increased,the negative pressure and the low pressure space region are gradually increased and appear in the vicinity of the elliptical tube,and are concentrated in the region between the elliptical tube circumferential angle of 30 ° to 150 °.The results of this study can provide important theoretical basis and reference for building mass transfer heat transfer test bed and production practice and application... |
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