| With the rapid development of the economy,the consumption of energy has increased significantly,and the development of various high-efficiency and energy-saving technologies and equipment has become an effective means to reduce energy consumption.Evaporative cooler is a high-efficiency heat exchange equipment using indirect evaporative cooling technology,which is widely used in pharmaceutical,chemical and mechanical industries due to its advantages of energy saving,water saving and small footprint,but is relatively less used in agriculture.In this thesis,the evaporative cooler is combined with the heliostat in agriculture,and has good practical application value when improving the thermal performance of the evaporative cooler and sending the outlet air of the evaporative cooler into the heliostat for ventilation.This thesis takes the evaporative cooler as the research object and uses a combination of MATLAB programming calculation and CFD numerical simulation,the main research contents and the conclusions obtained are as follows:1.A complete mathematical model of heat and mass transfer of evaporative cooler is established according to the principle of heat and mass exchange and the law of conservation of mass and energy,and the calculation is programmed by MATLAB software,and the calculated results are compared with the experimental data in the relevant literature,and the deviation between the obtained simulated and experimental values is within 10%,which proves the correctness of the mathematical model.2.Based on the outdoor meteorological parameters around 11:00 a.m.on a typical winter weather day in Jinan,preliminary calculations of the evaporative cooler were carried out to obtain the laws of change of each physical parameter of air,spray water and hot water in the direction of tube length and tube discharge.The results show that the air temperature and relative humidity and other physical parameters in the direction of the pipe row are monotonically increasing trend,and gradually become slower,the trend of a slight decline in the direction of the pipe length;spray water temperature in the direction of the pipe row is increasing and then decreasing trend in the direction of the pipe length is almost no change,the average value of its change is 0.08 ℃,spray water evaporation in the pipe row and the direction of the pipe length are decreasing trend,the direction of the pipe row In the direction of the pipe row,the evaporation of the second row of tubes is about 1.8 times the evaporation of the last row of tubes;hot water outlet temperature in the direction of the pipe row is on the rise,the second row of tubes and the last row of tubes,the difference between the hot water outlet temperature of about1.4 ℃,the direction of the pipe length,the same amount of change in the hot water temperature of the pipe section gradually reduced,0.5m-1m,1.5m-2m,2.5m-3m average reduction in the pipe section were 1.2 ℃,1.05℃,and 0.83℃.3.The thermal performance of the evaporative cooler was optimized in terms of three aspects: air speed,spray density,and structural parameters:(1)The study of the effect of different air velocities on the thermal performance of evaporative coolers.The results show that when the structural parameters and spray density are maintained at a certain level,the wind speed increases from 1.3m/s to 3.4m/s,the total heat transfer coefficient,water film-air mass transfer coefficient,evaporated water volume and other parameters show a trend of first increasing and then slightly decreasing,and the change of the heat transfer coefficient of the outer wall of the tube-water film is not obvious;the thermal performance of the evaporative cooler reaches the best when the wind speed is about 2.5m/s;when the spray density is respectively 0.025 kg/(m/s),0.045 kg/(m/s)and 0.065 kg/(m/s),the heat transfer coefficients are 523 kW,582 kW and 599 kW at the wind speed of 2.5m/s respectively.(2)Study of the effect of different spray densities on the thermal performance of evaporative coolers.The results show that when the structure parameters and wind speed are maintained at a certain level,the spray density increases from 0.03 kg/(m·s)to 0.08 kg/(m·s),the total heat transfer coefficient,the heat transfer coefficient of the outer wall of the tube-water film and the evaporated water volume show a trend of increasing first and then keeping stable,and the water film-air mass transfer coefficient does not change obviously;when the spray density is about 0.07 kg/(m·s),the thermal performance of the evaporative cooler reaches the best;when the spray density is about 0.07 kg/(m·s),the evaporative cooler When the wind speed is 2m/s,2.5m/s and 3m/s,the heat transfer coefficient is 530 kW,612 kW and598 kW respectively at the spray density of 0.07kg/(m/s).(3)Study of the effect of different tube types on the thermal performance of evaporative coolers.The results show that when the spray density and wind speed are maintained at a certain level,the heat transfer performance of elliptical tube with the length-short axis ratio of 2 is better than that of round tube and elliptical tube with the length-short axis ratio of 3.At the wind speed of 2.5 m/s and the spray density of 0.07 kg/(m·s),the heat transfer of the three tube types are658 kW,616 kW and 585 kW respectively.4.It was investigated whether the air obtained could be used for ventilation of the heliostat under the conditions of optimum air speed,spray density and heat transfer tube type.The results show that when taking the optimum air speed(2.5m/s),the optimum spray density(0.07kg/(m·s))and the optimum heat exchange tube type(elliptical tube with the long and short axis ratio of 2),the air outlet parameters of the evaporative cooler are: air volume 11.5kg/s,temperature26.8℃,humidity 88.5%,and it is verified that the outlet air parameters meet the ventilation conditions of the heliostat. |
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