| With the rapid growth towards scale,modernization and intensification of the livestock industry in China,multi-floor buildings for raising pigs become very attractive as an emerging model of intensive livestock farming.Multi-floor pig buildings make full use of vertical space which can greatly save land space,improve the production per unit area and reduce the area of environmental pollution.However,there were few studies about whether this new design could provide a proper indoor environment for the growth of pigs and whether it would affect the environment outside the building.In recent years,with the development of computational fluid dynamics(CFD),it has been widely used to simulate airflow and concentration distribution due to its advantages of being controllable,low cost and providing detailed results in the computational domain.Based on CFD simulation,the simplification of lying pigs in the multi-floor pig building,the ammonia distribution in the pig houses on different floors and the ammonia dispersion outside the multi-floor pig building were studied as follows:(1)Due to the great computational cost and difficulty of the direct modeling of high-density multi-floor pig buildings,CFD simulation was conducted on the slatted floor and four lying pig models under six body weights,respectively,to investigate the inertial resistant coefficients of the slatted floor based on the multi-floor pig building and analyze which type of simple geometric lying pig models could replace lying pigs and the relationship between the inertial resistant coefficients and body weight.The results showed that the inertial resistant coefficients and the viscous resistant coefficients of the slatted floor were 173.44 1/m and 118408.41 1/m~2 in Y direction,20.99 1/m and 16251.26 1/m~2in Z direction,and the slatted floor could be simplified into porous medium model according to the resistant coefficients.When the body weight of pigs was 60 kg,the relative errors of the inertial resistant coefficients between half ellipsoid model and pig model in X,Z and Y directions were-5.0%,-9.4%and 16.2%,respectively.Taking all the three directions into consideration,the half ellipsoid model was more suitable for replacing lying pigs compared with the ellipsoid model and the half cylinder model.The average of the mean relative errors of pressure drop per unit length between ellipsoid model,half ellipsoid model,half cylinder model and pig model of six body weights in three directions were 16.18%,12.73%and 18.43%,respectively.The half ellipsoid model was still closest to the pig model.Therefore,the half ellipsoid model was the most suitable model for the simplification of lying pigs.The inertial resistant coefficients were linearly correlated to the body weight,providing reference for calculating the inertial resistant coefficients of different pig models in different directions changing with body weight.(2)Based on the results of porous medium model and resistant coefficients,CFD simulation was conducted on the airflow and ammonia distribution on different floors of the multi-floor pig building.The measured results were used to verify the simulation results and the difference of ammonia distribution between different floors was investigated.The results showed that the average of relative errors between the simulation and measured results of ammonia concentration was 5.72%,which was within the acceptable error range of CFD simulation,indicating that the simulation results agreed well with the measured results and verifying the accuracy of simulation results and porous medium model.The average wind speeds on the second floor and the sixth floor of the multi-floor pig building were 0.68 m/s and 0.70 m/s at the plane of Y=0.3 m,and 1.44 m/s and 1.47 m/s at the plane of Y=1.5 m,respectively,indicating that the wind speed on the sixth floor was higher.At the plane of Y=1.5 m,the wind speed distribution was not uniform and there was obvious stagnant zone near the sidewall,this might be because that the airflow passing through the wet pad on the sidewall into the pig house.The average ammonia concentrations on the second floor and the sixth floor were 2.55 ppm and 2.48 ppm at the plane of Y=0.3 m,respectively,and 1.21 ppm and 1.17 ppm at the plane of Y=1.5 m,respectively.The results showed that the ammonia concentration on the sixth floor was lower than that on the second floor.In addition,the study found that the maximum ammonia concentration of 15.6ppm in the pig house did not appear at the position with the lowest wind speed,this might be because the airflow direction in the ventilation area under the solid floor was opposite to the overall airflow direction in the pig house,and the airflow flowed upward with low wind speed at the corner where the two airflows met,causing the ammonia accumulation at the corner.Therefore,ventilation facilities should be added on the sidewalls near the fans to reduce the adverse effect of long-term ammonia accumulation on pigs.(3)Due to the ammonia concentrated emission from the multi-floor pig building,CFD simulation was conducted on the ammonia dispersion emitted from the multi-floor pig building and the traditional flat-floor pig farm to investigate the difference of the ammonia dispersion between the two different modes of pig farming,and analyze the influence of wind direction,wind speed and emission source concentration on the ammonia concentration distribution and dispersion distance.The results showed that the ammonia dispersion distance of the multi-floor pig building was much greater than that of the flat-floor pig farm at the plane of Z=1.5 m.When the wind direction was 67.5°,the wind speed was 2.03 m/s and the emission source concentration was 20 ppm,the dispersion distance could reach 1380 m.And the ammonia would accumulate in the yard with the concentration of 7.68 ppm.Under different wind directions,ammonia always dispersed along the dominant wind direction,but the influence of wind direction on the dispersion distance was not significant.The ammonia concentration and dispersion distance decreased with the increase of wind speed,but higher wind speed values were more likely to lead to ammonia accumulation in the yard.The ammonia concentration and dispersion distance decreased with the decrease of emission source concentration.In addition,when the emission source concentration decreased from 20 ppm to 15 ppm,the dispersion distance decreased from 1380 m to 727 m,indicating that the reduction of emission source concentration could reduce the dispersion distance.Therefore,wind speed and emission source concentration should be taken into consideration during the site selection of multi-floor pig buildings.The dispersion distance was only 46 m in the actual operation process of the multi-floor pig building in Yiwu and the maximum ammonia concentration was 1.6 ppm in the yard,which would not affect the surrounding residents.In the future site selection,when the emission source concentration was controlled at 20 ppm,the multi-floor pig building should be located 1400 m away from residential areas to ensure that it would not affect the surrounding residents. |
PDF Full Text Request