Simulation Of Interior And Exterior Environmental Air Quality Of Pig Buildings Based On CFD

Air velocity,temperature,relative humidity and harmful gases such as ammonia,carbon dioxide are main influencing factors to the health of pigs and their production performance,a good assessment of these internal environmental parameters can effectively help find deficiencies existing in pig buildings and contribute to providing improvements design,and reduce economic loss of the farm.At the same time,with the increase of scale and intensive degree of the pig farm,the air pollutants emitted by farms can not be ignored any more.The simulation method of air pollutants dispersion is the main approach to evaluate the effect of air pollution.This research used computational fluid dynamics(CFD)technology for pig internal and external environment quality assessment,and compared the impact of two different manure removal methods on piggery environment as well as the impact of three different dominant wind directions on the ammonia dispersion produced from pig farm.The results can provide theoretical basis and guidance for the intensive pig farm site layout and construction.Two typical pig farms were selected to conduct the field experiments.Navier-stokes and Species transport equations,RNG k-? turbulence model were chosen and applied in this research.With the tools of GAMBIT 2.4.6 and FLUENT 16.0,three dimensional steady simulation of air velocity,temperature,relative humidity and ammonia concentration were taken in a typical gestation swine house.On the other hand,three dimensional steady simulations of ammonia dispersion were also taken around an intensive pig farm.Conclusions can be drawn from the simulated results as followings:1)In the gestation swine house equipped with mechanical ventilation and manure pit system,the air velocity,temperature,relative humidity and ammonia concentration were simulated using FLUENT 16.0 software.The results showed that,the air velocity,temperature,relative humidity and ammonia concentration ranged from 0?0.83m/s,11.5?25'C,35.3%?51.5%and 1.5?7.5 mg/m~3,respectively.And the averaged values in the animal occupied zone were 0.31m/s,17.1?,43.6%and 4.72 mg/m~3,respectively.Although the internal environment suited the requirements of gestation in winter,yet the uniformity of ventilation was not satisfying.According to that,an optimum design of a mechanical solid-liquid separation manure cleaning system was generated and simulated by CFD.Compared with the manure pit system,the results showed that the mechanical solid-liquid separation manure cleaning system has a better-distributed ventilation and more comfortable environment for the sows.2)In a typical intensive pig farm,field experiments were conducted to examine the ammonia concentrations in pig houses of different growth stages.The ammonia concentrations in finishing pig house,weaned pig house,gestation pig house and farrowing pig house were 6.91 ±4.59 mg/m~3?5.02±3.13 mg/m~3?4.37±2.96 mg/m~3 and 3.68±2.68 mg/m~3,respectively.Based on the ammonia concentrations from the sources,ammonia dispersion in three different dominant wind directions was simulated with software of FLUENT 16.0.The simulated results showed that:correction factors needed to adjust predicted ammonia levels to those observed ranged from 0.05 to 1.38,the larger the wind speed,the farther the dispersion distance of ammonia,the furthest distance in winter was 700 m.Downwind of the pig farm were crowded places,ammonia concentrations in these areas in winter even reached 3 mg/m~3,the impact of the ammonia produced from the pig farm on the surrounding residents should not be neglected.