Construction And Optimization Of Atmospheric PM_2.5 Removal System By Water Vapor Phase Change Coupled With Natural Convection

As an important component of smog,PM_2.5is still a hot spot in environmental research.At present,the most fundamental way to control PM_2.5in the atmospheric environment is to control it from the source.However,due to the large number of emission sources,the emission process and scale vary greatly,the investment in controlling PM_2.5emissions from the source is large and effective time.Long,and will slow down the economic development to a certain extent.Another method is to directly remove PM_2.5particles that already exist in the atmosphere.This method takes effect quickly and will not affect the local economy.However,due to the small particle size of PM_2.5particles,traditional dust removal methods want to filter them efficiently,and need to overcome large air resistance,high energy consumption,and high operating costs.Therefore,they can only be applied to small-scale indoor air treatment.When processing the air in a local area,most of the water spray methods with low processing efficiency and high energy consumption are currently used.Water vapor phase change technology can solve the problem of small PM_2.5particles.Using water vapor phase change technology can make fine particles nucleate and condense and grow,reduce the resistance in the process of particle removal,and make PM_2.5easier to be removed by conventional dust Technology removed.This paper proposes a gravity air dust removal system using water vapor phase change technology.Air flows through the dust removal system through natural convection.The water vapor phase change technology is used to grow fine particles in the air and be removed.The air flow of this system mainly relies on natural convection,which greatly reduces the energy consumption in the processing process,can process a large amount of air for a long time,and the equipment is simple.In order to study the supersaturation distribution characteristics of gravity air dust removal system,this paper first used Fluent user-defined variables（UDS）to numerically calculate the supersaturation field in gravity air dust removal system,the influence of several factors such as pipe diameter,inlet air temperature,wall hot water temperature,inlet air humidity and hot water addition position on the distribution of supersaturation in the pipe under natural convection were studied.The results show that:as the pipe diameter increases,the average supersaturation first increases and then decreases;The average supersaturation increases with the increase of temperature difference between air and hot water.The relative humidity of the inlet air has a small effect on the supersaturation.Compared with the full coverage of hot water,it is more conducive to increase the supersaturation level of the pipeline that the hot water is added to the position close to the pipe outlet.Therefore,the supersaturation of the system can reach the optimal value by selecting suitable working conditions.In order to comprehensively evaluate the gravity air dust removal system,this article analyzed the economic cost of the system in Chapter 3,and used the entropy method to comprehensively evaluate the system with multiple indicators.Based on the BBD method,the system was designed with three factors and three levels.Analyzed the degree of influence of various factors on the response,and obtained the optimal working condition parameters when the pipeline length was 10m,20m,and 30m.The results show that:the results show that the entropy method determines the weight of supersaturation,air flow,and economic cost.The weight coefficient of the air flow index always accounts for the largest proportion,and the weight coefficient of the economic cost index always accounts for the smallest proportion.Among the factors,the diameter of the pipe affects the air.The influence of flow rate and comprehensive index is always the strongest,and the influence of hot water temperature on supersaturation and economic cost is always the strongest;under the three pipe lengths,the optimal working conditions are basically the same,the pipe diameter and heat the water temperature is close to the maximum value of the experimental design conditions,and the hot water addition position（z/L）is basically around 0.8.In order to study the particle growth effect of the gravity air dust removal system,this paper designed an experimental device to measure the supersaturated atmosphere of water vapor and the growth effect of fine particles.The average supersaturation of the system was measured by changing the temperature of the hot water on the wall.Used silica as the source of fine particles to measure the growth of the particle size of the gravity air dust removal system.The results show that when the air temperature and humidity are constant,the supersaturation degree will increase with the increase of the hot water temperature;when other working conditions are constant,the particle growth effect will be enhanced with the increase of the hot water temperature;the number and concentration of particles will affect The water vapor heterogeneous phase change and growth characteristics of the particles,as the particle number concentration increases,the particle growth effect becomes worse.