CFD Simulation And Optimization Of Vertical Ventilation In Nursery Pig House

In winter in cold areas of North China,closed feeding mode is usually adopted to ensure the temperature of pig houses is comfortable,which leads to insufficient ventilation of pig houses and a large amount of harmful gases such as NH₃and CO₂accumulate in pig houses.Vertical ventilation technology is a new technology applied to pig house ventilation in recent years.Compared with common horizontal ventilation and vertical ventilation,vertical ventilation can significantly improve the uniformity of airflow distribution.Vertical ventilation can accurately ventilate and preheat the air flow.It can not only keep warm but also eliminate polluting gases while exchanging air.And the short air flow path can effectively reduce the spread of bacteria.However,there are few studies related to the use of vertical ventilation in the nursery pig house in the cold winter area in the north,which has research value.This research can provide a theoretical basis for the optimal design of the vertical ventilation structure of the nursery pig house and the environmental regulation in the cold area of the north.In this study,the porous media model（PMM）was used to simplify the slatted floor and the pig activity area in the model simplification.Computational fluid dynamics（CFD）was used to simulate,evaluate and analyze the distribution of air flow,wind speed,NH₃concentration,CO₂concentration and mean age of air（MAA）in the nursery pig house,explored the ventilation effect of the vertical ventilation model,and optimized the shortcomings of the original model.The research results can evaluate the environmental impact on the nursery pig house and provide theoretical support for improving the ventilation effect.The main research contents and conclusions were as follows:（1）The viscous resistance coefficient and inertia resistance coefficient of the slatted floor and pig activity area in vertical ventilation were explored,and the PMM was verified.Research shows that it was feasible to simplify the slatted floor and pig activity area into PMM.The viscous resistance coefficient D in the Z direction of the slatted floor was 4.11×10⁵m^-2,and the inertial resistance coefficient C was 126.7 m^-1.The viscous resistance coefficients D in the X,Y,and Z directions of the nursery pigs were 65.6 m^-2,10.9 m^-2,and 71.0 m^-2,respectively,and the inertial resistance coefficients C were 0.20 m^-1,0.18 m^-1,and 0.30 m^-1.（2）Simplified nursing pig house model based on PMM and resistance coefficient research results.The error analysis between the simulation value of the simplified model and the values measured at 13 verification points in the field showed that the average relative error of the wind speed field was 13.98%,the average relative error of the NH₃concentration simulation was10.14%,and the average relative error of the CO₂concentration simulation was 10.14%.The relative error was 6.10%.The results showed that it was feasible to apply CFD simulation to evaluate and analyze the wind speed,NH₃and CO₂in the nursery pig house.This model had a high degree of simulation and can be used for subsequent simulation analysis.（3）Through the analysis of the simulation value under the vertical ventilation mode of the current nursery pig house,it was found that the wind speed below the tuyere was greater than 0.4m/s,which exceeded the wind speed standard of the nursery pig house;it was found that there was a problem of excessive CO₂concentration in the area between the pig pens.The average wind speed,CO₂average concentration,and NH₃average concentration in the pig pen area all meet the standards of nursery pig houses.The average air age was small,and the air in the pig house was fresh.（4）In view of the problems existing in vertical ventilation,five ventilation angles were designed,which were 15°,30°,45°,60°,and 75°.The distribution of wind speed,NH₃concentration and CO₂concentration were better when the ventilation angle was 45°,and the MAA distribution was better when the ventilation angle was 60°.Considering the wind speed distribution,polluting gas distribution and MAA distribution at ventilation angles of 45°and 60°,it was concluded that the ventilation effect was better when the ventilation angle was 45°.