Simulation Of Internal And External Environmental Of House-type Cowshed Based On CFD

With the large-scale development of animal husbandry,people pay more and more attention to the environmental quality of livestock and poultry houses.China is a big country raising cattle,and cattle breeding is one of the important components of Chinese animal husbandry.In order to resist the cold environment in the cold regions of northern China,the house-type cowshed are widely used.However,in order to keep cattle warm,there are some environmental problems,such as uneven airflow,high humidity and high ammonia(NH3)concentration.Environmental factors such as wind speed,temperature,relative humidity and ammonia concentration in the cowshed are closely related to the healthy growth and efficient production of cattle.Therefore,it is of great significance to simulate and evaluate the environmental quality in the the house-type cowshed to maintain the normal growth and production of cattle and improve the welfare and breeding level of cattle.The optimization simulation for the existing problems in the cowshed can provide theoretical reference for optimizing the layout of the cowshed and the ventilation mode.Meanwhile,the discharge of ammonia from the intensive cattle farm will also cause certain pollution to the surrounding environment.The simulation of ammonia pollution diffusion in the intensive cattle farm can provide beneficial reference for the optimization of the breeding mode and the prevention and control of ammonia pollution in the intensive cattle farm.Based on the computational fluid dynamics(CFD)method,this study adopts Navier-stokes and Species transport equations and RNG k-s turbulence model.With Solidworks 2017,ANSYS Mesh 15.0,ANSYS Fluent 15.0 and CFD-POST 15.0 software,CFD numerical simulation was carried out on two intensive cattle farms in Fengning Manzu Autonomous County,Chengde City,Hebei Province.According to the boundary conditions determined by the field measured data,the three-dimensional steady-state simulation of the wind speed,temperature,relative humidity and ammonia concentration in one of the cattle farms was carried out,and the optimization simulation of ventilation scheme was carried out.The ammonia gas pollution diffusion outside another cattle farm was simulated under different dominant wind direction and wind speed.The study reached the following conclusions:(1)The temperature,relative humidity and ammonia concentration parameters in the cowshed are related to the wind speed parameters.The higher the wind speed is,the lower the temperature is,the lower the relative humidity is,the lower the ammonia concentration is.The simulation results show that,under the ventilation mode of corridor longitudinal ventilation,the wind speed in the corridor is between 0.50～1.29m/s,the wind speed in the cattle activity area is basically between 0～0.40m/s,and the wind speed in most areas is below 0.10m/s.The air distribution in the cowshed is not uniform,the ununiformity coefficient of wind speed was 48.10%,and some ventilation dead zones exist.The temperature in the cattle activity area is about 10～13.50 ℃,but the local temperature is too low.The relative humidity in the cattle activity area was kept between 50%～60%.The wind speed in the aisle was high,and the ventilation effect was good,with ammonia concentration between 11.10～19.50mg/m3.However,the ammonia concentration in the cattle activity area was the highest,between 19.50～22.30mg/m3,due to the small wind speed away from the vent and poor ventilation effect.In autumn,the space structure of the cowshed is relatively close,and the ventilation condition is good.The wind speed,temperature and relative humidity of the cattle in the cowshed can basically guarantee the cattle’s demand for ventilation and warmth in the cowshed environment.However,the ammonia concentration in the cowshed is high,slightly higher than the industry standard 20mg/m3,which isn’t conducive to the cattle’s health.(2)The ventilation mode of corridor longitudinal ventilation was improved to that of transverse ventilation.After the optimization of ventilation scheme,the wind speed in the cowshed was between 0.10～0.60m/s,and the wind speed was uniformly distributed in the cowshed without obvious ventilation dead angle,the ununiformity coefficient of wind speed was 20%;The temperature distribution in the cowshed is uniform,and the temperature in most areas is about 10℃.The relative humidity in most areas in the cowshed ranges from 40%～46%.The ventilation effect of the cattle activity area was improved,and the ammonia concentration was reduced between 11.10～17.30mg/m3,lower than the 20mg/m3 stipulated by the industry standard,meet the comfort requirements of cattle.In general,the optimized ventilation scheme is better than the original ventilation scheme,so this study can provide a useful reference for the environmental assessment and ventilation scheme optimization of house-type cowshed in cold areas of northern China.(3)CFD technology was used to simulate the diffusion of ammonia gas discharged outside the intensive cattle farm under four dominant wind directions:southeast,southwest,northeast and northwest.The simulation results show that different dominant wind direction and wind speed have different influences on ammonia diffusion outside the house.The greater the wind speed,the greater the concentration of ammonia in the buffer zone and the farther the diffusion distance.The ammonia concentration in the farm was 3.80～5mg/m3,and the ammonia concentration in the buffer zone was less than 2mg/m3,which did not exceed the Environmental Quality Standards for Livestock and Poultry Farms.When the concentration of NH3 emission source is about 18mg/m3,the location of cattle farm should be no less than 500m away from residents,so as to ensure that the normal life of nearby residents is not affected by NH3 emission from cattle farm.This study can provide useful reference for optimization of breeding mode and prevention of ammonia pollution in intensive cattle farms.