Numerical Simulation Of CO₂ Desorption In Bundles Of Falling Film Evaporation Outside Horizontal Tubes

Horizontal tube falling film evaporation technology has the advantages of high heat transfer efficiency,simple pretreatment,low temperature waste heat waste heat and so on,and has become the main technology of hot desalination.The non-condensable gas produced in the falling film evaporation not only deteriorates the heat transfer,but also causes the fouling and corrosion of the desalination equipment.As a result,the cost and running cost of desalination are greatly increased.Therefore,it is necessary to research the CO₂ desorption process.In this paper,the micro-phase transition heat transfer characteristics and the sea water flow characteristics are combined with the CO₂ desorption process.The mathematic model of CO₂ desorption in the process of falling film falling was established,considering microscopic heat transfer,flow,chemical reaction and mass transfer process,that dividing microelement in the tube circumference,the axial and adjacent pipe.The desorption process of CO₂ in falling film vaporization was simulated by Matlab software.This paper calculates the distribution laws of CO₂ desorption unit area,carbonate concentration,evaporation rate and CO₂ desorption in seawater,and analyzing the effects of thermal parameters and geometric parameters to CO₂ desorption during falling film evaporation.The simulation results show that the calculated values of the heat transfer coefficient inside and outside the tube are in good agreement with the experimental data,and the accuracy of the heat transfer model is verified.The chemical reaction time gradually decreases along the vertical tube row,and the rate of decrease is slowed down.The chemical reaction time increases along the length of the horizontal tube,and this trend increases with the increase of the vertical pipe row nodule.The concentrations of HCO3-and CO32-ions in CO₂ desorption were significantly higher in seawater than in CO₂ and H+.The distribution of carbonate ion concentration in seawater is closely related to CO₂ desorption and seawater evaporation rate.The evaporation rate per unit area is the same as change of CO₂ desorption per unit area per ton of seawater,and decreases along the vertical tube row and tube length direction under the combined action of tubes heat transfer and seawater flow rate.The effect of evaporation temperature and diameter on the unit body distribution and CO₂ desorption is greater than that of heating steam flow rate and tube spacing.With the increase of the evaporation temperature,the number of preheating units and the total number of units increased,but the CO₂ desorption decreased,and the rate was declining.With the increase of diameter,the number of preheating unit and the total unit volume increase,CO₂ desorption increased,and the rate is declining.With the increase of the heating steam flow rate,the CO₂ desorption decreases,and the rate is increasing.When the tube spacing changes within 0.2 to 0.5 times the tube diameter,the CO₂ desorption increases firstly and then stabilizes as the tube spacing increases.