Environmental Simulation Study And Ventilation Optimization Design Of Winter Piglet House Based On CFD

The environmental parameters（air velocity,temperature,relative humidity）and pollutant concentration（harmful gas,particulate matter）in the pig house are the most important factors affecting the health and production performance of pigs.Because the piglets have just experienced weaning stress,they are more sensitive to the changes of the surrounding environment and have high disease susceptibility,so it is necessary to evaluate the environmental quality in the pig house under natural ventilation,It is helpful to judge whether the growth environment in the house meets the requirements,so as to provide basis for corresponding improvement and optimization.In this paper,the piglet house in large-scale pig farms are selected as the research object,and the environmental parameters and pollutant concentration distribution of pig houses are evaluated and analyzed by means of the combination of experimental method and numerical simulation method.In view of the influence of air distribution under different working conditions of natural ventilation mode on the environmental quality of the house,the most suitable air distribution form is selected,the problems existing in the current ventilation mode are analyzed,and the model is established for optimization research.The results are as follows:（1）For large-span transverse natural ventilation piglet house,different number and size of windows have different effects on the environment of the piggery.Increasing the window opening can improve the uniformity of flow field to a certain extent,but it will lead to excessive head-on wind speed of piglets,exceeding the maximum allowable wind speed by 0.2m/s.At the same time,the head-on temperature of piglets decreases slightly,but the surrounding temperature of piglets is still in the comfortable range of 20℃～25℃;Increasing the number of windows can significantly improve the uniformity of flow field,keep the head-on wind speed of piglets unchanged,and reduce the average temperature in the unit column;Increasing the window opening and the number of windows will reduce the relative humidity around the piglets,which is slightly lower than the minimum critical value of 50%.However,due to the appropriate temperature distribution around the piglets,the relative humidity has little effect on the piglets.In general,the four different air inlet conditions designed according to the number and size of windows can basically meet the growth needs of winter piglets for the environmental parameters in the house（air velocity,temperature and relative humidity）.For the phenomenon of excessive head-on wind speed of piglets,the adverse effect of head-on wind speed can be effectively reduced by setting wind deflectors.（2）For the simulation of particulate matter in the piggery,it is found that simply increasing the opening of the window can significantly improve the discharge effect of particulate matter in the house,and the residence time of particulate matter in the room will be greatly shortened,which is conducive to the prevention and control of diseases in the pig house;Simply increasing the number of windows can control the diffusion of particulate matter to adjacent areas,but the residence time of particulate matter in the room has not been effectively improved,and the discharge effect per unit time may not be guaranteed.For the air distribution optimization mode of side supply and side return plus top exhaust,due to the joint action of thermal pressure and wind pressure in the house,the top exhaust can effectively and in a very short time discharge the particulate matter floating near the roof,which has a positive impact on the health of piglets in the house.In addition,the top exhaust plays a major role in the discharge of particulate matter.The symmetrical inlet and exhaust windows mainly play the role of uniforming air flow field and make the inlet and outlet air flow coherent and at the same time,it ensures the rationality of environmental parameters in the house.（3）The distribution of pollutants in the house is related to the distribution of air flow in the house.Generally speaking,the air distribution form of side supply side plus top exhaust under the natural ventilation mode has a good effect on the discharge of pollutants in the house.Due to the dilution effect of top exhaust,after ventilation for a period of time,the NH₃ concentration in pig respiratory area and human respiratory area gradually tends to be stable,distributed between 1.62～4.85mg/m~3 and 3.23～5 mg/m~3 respectively,which is far lower than the maximum allowable concentration of 20 mg/m~3;As the CO₂ source is generated in the pig body breathing area in the central area,it is mainly diluted by the inlet air flow and discharged outdoors through the South exhaust window and the top exhaust window.The concentration around the pig body and the human body breathing area is mostly distributed between 386～772ppm,which is lower than the health limit of1540ppm,while the single column on the north side of the walkway is hardly affected by the CO₂ concentration.The concentration distribution of NH₃ and CO₂ basically meets the requirements.Due to the blocking effect of pig body and the influence of inlet air flow,NH3 is easy to accumulate at the leaky floor,while CO₂ is easy to accumulate on the leeward side of pig breathing area.It is suggested to improve the incidence angle of air flow or carry out multi window ventilation regularly.Figure 53 table 10 reference 89...