摘要
在中国华东地区最炎热的月份,舍外高温高湿的气候条件,降低了低屋面横向通风(low profile cross ventilated,LPCV)牛舍的环境调控效果。为了研究LPCV牛舍温湿度场的分布规律,该文在现场实测的基础上,采用计算流体动力学CFD(computational fluid dynamics)方法,对LPCV牛舍的温度和相对湿度参数进行了三维数值模拟。现场实测的结果表明,舍外空气温度为36.2℃,相对湿度为55.5%的条件下,舍外空气流经湿帘后的降温幅度为7.7℃,湿帘出口处的相对湿度为99.9%;模拟结果表明,舍内温湿度场受气流场的影响,分布不均匀,风速高的区域温度相对较低,舍内相对湿度与温度呈现强烈的耦合关系。随着空气的流动,沿气流方向平均每米长度温度升高0.014℃、相对湿度下降0.04%,THI增加0.025。模拟值与实测值的对比表明,9个测点温度和相对湿度的测试值与模拟值之间相对误差的平均值分别为0.89%和0.59%,理论计算和数值模拟得到的奶牛显热散热量的相对误差为14.5%,说明现场实测与数值模拟有较好的吻合度。该研究可为中国LPCV牛舍结构优化设计和环境调控提供参考。
With the ever increasing scale and intensivism in pasture in China, low profile cross ventilated (LPCV) dairy cattle barn, as a main building style in cattle house, is increasingly applied. The most obvious benefit of LPCV building is the ability to control the cow’s environment during all seasons of the year. It increases the percentage of time cows are in the thermal neutral zone, which allows both milk production and feed efficiency to be increased. However, during the hottest period in eastern China, the hot and humid climate, reduces the control effectiveness inside the building. In order to understand temperature and humidity distribution inside, the field experiment, which measured the parameters including environment temperature, humidity and surface temperature of dairy cattle, was conducted. The experimental dairy houses were located in the east part of China, with the demotions of length 376.6 m×width 90.4 m, and a slop roof of 1/12.5 pitch. Measured results showed that in the LPCV cattle house in eastern China, when the outdoor temperature and relative humidity were 36.2℃ and 55.5% respectively, the wet pad system could cool the air with a decline of up to 7.7℃, but increase the relative humidity to 99.9%, which led to a high temperature and high moisture condition. Meanwhile, three-dimension computational fluid dynamics (CFD) method was carried out to simulate thermal condition inside the cattle building. Multiple parameters of cattle were included in the CFD model to effectively express the heat and moisture released from cattle bodies as well as provide more realistic air flow patterns. In order to save the computer resource, a model of simplified cattle was considered to reduce the number of meshes with the legs and tails in the original. The temperature of the surface of cattle and building was measured by thermal camera in the field experiment. Multi-phase transport model was adopted to calculate the moisture generation. Simulated results showed that the indoor temperature and humidity were influenced by fluent field and unevenly distributed. Low temperature was found in place that had high air velocity, and humidity was significantly coupled with temperature variation. With the air movement, temperature increased by 0.014℃ while humidity decreased by 0.04% per meter in width dimension. Temperature-humidity index (THI) was applied to analyze and estimate environment comfort in different locations inside the cattle building. The THI had a same tendency with the change of environment outdoors. When the wet pad worked properly, THI increased in width dimension. Inlet position had a better thermal condition than outlet position, and THI increased by 0.025 per meter in this dimension (width dimension). The CFD model was validated via the comparison with the field experimental results at the same locations where the temperature and relative humidity sensors were installed. Comparison between simulations and measurements showed that the average relative error between simulated and measured results in temperature and humidity were 0.89% and 0.59%, respectively. Theoretical heat generation of dairy cow was calculated, and the discrepancy between calculated and simulated values was 14.5%. The high agreement in simulation and measurement proved the reliability and feasibility of the model and boundary condition in the simulation. And this study can provide references for the optimization design and environment regulation of LPCV dairy cattle barn in China.
出处
《农业工程学报》
EI
CAS
CSCD
北大核心
2015年第9期209-214,共6页
Transactions of the Chinese Society of Agricultural Engineering
基金
国家奶牛产业技术体系资助项目(CARS-37)
公益性行业(农业)科研专项资助项目(201303091)
中央高校基本科研业务费专项资金资助(2012YJ015)
关键词
计算流体动力学
温度
湿度控制
低屋面横向通风
奶牛舍
数值模拟
computational fluid dynamics
temperature
humidity control
low profile cross ventilated
dairy cattle barns
numerical simulation