Numerical Simulation Of Particulate Matter From A Laying Hen House In Northeast China

Particle pollution is considered to be the most representative and most harmful type of pollution,and it has become an important factor affecting the quality of the atmospheric environment.A large amount of particulate matter generated in the production process of livestock and poultry has become an important source of agricultural particulate matter emissions.The microorganisms in the house rely on the relative stability of the colloidal dispersion system to spread with the particulate matter as a medium,which seriously affects the health of livestock and poultry and field workers.Part of the particulate matter in the livestock and poultry house is discharged into the atmospheric circulation through the exhaust system,polluting the surrounding atmospheric environment and causing serious harm to the health of the surrounding residents.Due to the seasonal characteristics of the north,the chicken house needs to take into account the thermal insulation factor in winter,resulting in a low ventilation rate in the house and a high concentration of particulate matter in the house;however,in summer,it is necessary to increase the ventilation volume to discharge the excess heat in the house,thereby reducing the ventilation rate higher than in winter,resulting in a higher rate of particulate matter emissions outside the house.The application of computational fluid dynamics（CFD）technology can save a lot of measurement time and repetitive labor to better understand the diffusion fundamentals and spatial and temporal distribution differences of PM.Carrying out the use of CFD technology to study the distribution law of particle concentration inside and outside the laying hen house is of great significance to the improvement of the environmental quality in the house,and provides a theoretical basis for evaluating the air quality in the area around the livestock and poultry house and controlling the emission of atmospheric particulate matter.In this paper,the concentration of particles with different particle sizes(PM₁,PM_2.5,PM₁₀and total suspended particles TSP)inside and outside the house in winter and summer of a laying hen farm in Jilin Province was monitored and the distribution characteristics of particles with different particle sizes were analyzed,carry out three-dimensional simulation analysis of the temperature,humidity field,airflow field and particle concentration field inside and outside the mechanically ventilated test laying hen house,and verify it in combination with the test results,and optimize the simulation design for unreasonable places.On the basis of the plume diffusion model,a Gaussian plume diffusion model suitable for livestock and poultry houses was established and verified.By raising the height of the fan to reduce the concentration of particles settled to the ground,the main conclusions are as follows:（1）An experimental study was carried out to analyze the correlation between various environmental parameters and the concentration of particulate matter in the laying hen house.There was a positive correlation between temperature and PM₁ and PM_2.5,and a negative correlation between humidity and particulate matter of each particle size.The concentration of TSP was mainly affected by the activity of chickens.There was also a correlation between particulate matter,in which TSP was strongly correlated with PM₁₀（P<0.001）,and PM_2.5 was strongly correlated with PM₁ concentration（P<0.001）.（2）Using CFD simulation technology to analyze and optimize the environmental quality of the laying hen house.The relative error and normalized mean squared error（NMSE）were used to verify the accuracy of the model.It is proved that the establishment of the CFD model can effectively evaluate the house environment,and the reasons for the unreasonable ventilation in the house in winter are analyzed.By optimizing the angle of the deflector and increasing it to67.5°,the uniformity of the air flow in the house is significantly enhanced,and the air distribution is more reasonable.The PM₁ concentration in the house decreased by 17.4%,the PM_2.5 concentration decreased by 15.9%,the PM₁₀ concentration decreased by 18.1%,and the TSP concentration decreased by 21.6%.（3）CFD simulation technology was used to explore the influence of different factors on particle diffusion concentration and propagation path.The simulation results show that the larger the particle size,the longer the diffusion distance in the atmosphere and the higher the propagation height.The diffusion distance and height of the particles are mainly affected by the force of the particles themselves and the turbulent phenomenon.The propagation direction of the particles is mainly related to the direction of the airflow and the direction of mechanical ventilation.When the atmospheric environment is relatively stable at night,the diffusion distance of PM₁₀ is longer than that in the daytime.When the natural wind direction is the same as the diffusion direction of particles,the propagation distance of particles is greater than that of other wind directions.（4）The diffusion concentration and propagation path of particulate matter in the atmosphere were explored by changing the height of the fan.Considering the environmental characteristics of the Northeast region,combined with the Gaussian plume diffusion model and CFD simulation technology,increasing the height of the fan by 1m can significantly reduce the concentration of particulate matter when it diffuses to the ground.Effectively improve the environmental quality around livestock and poultry houses and reduce the harm of particulate matter to residents’health.This paper provides a theoretical reference for the control of particulate matter inside and outside of caged laying hen houses in the north in winter and summer,and reveals the diffusion laws and propagation paths of different particle sizes in the atmosphere.Minimize the impact of particulate matter on residents’health and air quality.