Heat And Mass Transfer Characteristics Research On The Vertical Tubular Falling Film Evaporation Solar Desalination Device

With the continuous development of global industrialization,the shortage of fossil energy and water resources is becoming more and more serious.Although many studies have been conducted on solar desalination technology in the world,the existing small-scale solar desalination systems still have disadvantages such as low efficiency and high cost,which limited the popularization and application of solar desalination technology.To improve these obstacles,this paper designs a novel vertical tubular falling film evaporation solar desalination device with solar concentrator heating the water tank directly.During the conversion process of from radiation to heat,the energy flow and the heat and mass transfer in the salt-water separation process in the desalination device are studied.Firstly,the 3D model of the concentrator that can be used as co-transmitting concentrator for the energy supply of the vertical tubular falling film evaporation solar desalination device is established by Solid Works software.The 3D model is imported into the optical simulation Trace Pro software,the effect of the depth of the water in the heating water tank on the area of focal and the density of energy flow is simulated.The results show that,the energy distribution area increases with the increase of water body depth,and the energy flow density decreases with the increase of water body depth.Based on optical simulation results,for exploring the photo-thermal conversion performance the concentrator,the test set-up of photo-thermal conversion performance the concentrator is built.The experimental results indicated that,in the sunny weather conditions,the photo-thermal conversion efficiency of the concentrator is about 40.8%.Secondly,based on the laws of thermodynamics,the heat and mass transfer process in the vertical tubular falling film evaporation solar desalination device are analyzed theoretically.The formulas for calculating the heat transfer by evaporation,radiation,and natural convection in the heat transfer process of the vertical tubular falling film evaporation solar desalination device are obtained.By analyzing the experiment data of the vertical tubular falling film evaporation solar desalination device,the variation of the proportion of three heat transfer ways mentioned above of in the process of the desalination device running with operating temperature is revealed.Based on the vertical tubular falling film evaporation solar desalination device of theoretical analysis,the vertical tubular falling film evaporation solar desalination device which angle of evaporation surface is 45°is designed.The effect of the feeding water flow,heating power and operating temperature on the device is studied.When the heating power is 160 W and M_W=0.3 kg/h,the Gain Output Ratio(GOR)of the device is 0.64,which is0.06 higher than that of unit with the heating power is 240 W.When the operating temperature is 80℃,the maximum water productivity of the device is 0.19 kg/h,which is2.98 times higher than that of the operating temperature at 50℃.Through the testing of the vertical tubular falling film evaporation solar desalination device,the heat loss and cover area of the device can be decreased with the decrease of the evaporation surface angle.Combined with research results,an improved vertical tubular falling film evaporation solar desalination device which the evaporation surface angle is 70°is designed and manufactured.The test set-up of the improved device was built,and the effect of the feeding water flow,heating power and operating temperature on the performance of the improved device is studied under the same operation conditions.The water productivity performance and thermal characteristics of the improved device and the former device are compared and tested.The radiative heat transfer in the device is decreased by selecting polishing mirror condensation surface.When the heating power is 160 W,M_w=0.3 kg/h,the GOR of the improved device is 0.79.When operating temperature is 80℃,the water productivity per unit cover area of the improved device is 548.41 g/20min,is 2.08times higher than that of the former device.In the experiment of heat and mass transfer enhancement by polishing the condensation inner surface,when the feeding water flow is0.6 kg/h and the heating power is 200W,the water productivity of using mirror condensation surface is increased 7.1%compared with the normal condensation surface.This experiment provided data reference and theoretical basis for the popularization and application of solar desalination device.