物理降温缓解奶牛热应激的喷淋水滴特性研究

The dairy heat stress caused by high temperature in summer is one of the significant reasons for restricting China's dairy industry, and the spray evaporation as physical cooling to reduce heat stress effectively has been widely applied. The relationship between the dynamic characteristics of the spray droplets and the spray pressure, nozzle diameter, environmental parameters were studied by using the three dimensional laser Doppler instruments and the high-speed camera, than got the rule change of spray droplets in space collisions and crushing. At the same time, the mathematic model of spray droplet size, water film features and surface evaporation cooling in diary were studied, than established the relationship between the characteristics of spray droplets under the different conditions of temperature, humidity and ventilation and alleviating heat stress in dairy. The experimental test were taken place in the experiment barn, the mechanism action between characteristics of spray droplets under different environmental parameters and alleviating heat stress in dairy under were studied by focusing on production performance of dairy physiological indices. This research will provide the theoretical and technical basis of optimization of spray cooling technique in dairy, and the new ways for energy conservation and emission reduction.

夏季高温造成的奶牛热应激问题一直是制约我国奶业发展的重要原因之一，喷淋蒸发作为缓解奶牛热应激有效的物理降温措施得到了广泛应用。本项目通过三维激光多普勒测试技术并结合高速摄像仪，直观真实的再现喷淋水滴的特性，明确喷淋压力、喷嘴直径、环境参数等影响因子与喷淋水滴动力学特性的关系，并研究喷淋水滴的空间碰撞和破碎变化规律；同时研究模拟不同喷淋水滴粒径尺度、水膜特性与奶牛体表蒸发散热的数学模型，建立不同温、湿度环境和通风条件下喷淋水滴特性与奶牛体表降温、缓解奶牛热应激之间的关系。并在实验牛舍中进行实验测试，通过关注奶牛的生产性能、生理指标，研究不同环境参数下喷淋水滴的特性与缓解奶牛热应激的作用机理。为奶牛喷淋降温技术的优化提供理论依据和技术基础，从而为节能减排提供新的途径。

夏季高温造成的奶牛热应激问题一直是制约我国奶业发展的重要原因之一，目前从环境控制角度对奶牛进行物理降温缓解其热应激的最常用方法是蒸发降温喷淋系统。本项目采用激光雨滴谱并结合高速摄像仪，研究测试6种喷头的喷淋水滴特性，明确喷淋压力、流速、喷嘴直径、环境温度、湿度、风速等影响因子与喷淋水滴动力学特性关系，并研究喷淋水滴的空间碰撞和破碎变化规律；研究不同喷淋水滴粒径与奶牛体表蒸发散热的作用模型，建立不同温、湿度环境和通风条件下喷淋水滴特性与奶牛体表降温、缓解奶牛热应激之间的关系；在现场牛舍中进行实验测试，验证喷淋水滴粒径与奶牛体表空气层之间的蒸发散热关系，通过关注奶牛的生理指标，研究不同环境参数下喷淋水滴的特性与缓解奶牛热应激的作用机理。解决了奶业发展的基础性课题，为奶牛健康节约养殖以及精准环境控制系统提供了理论依据。.通过项目研究得到如下主要结论：①实测6种喷淋水滴粒径分布在0.125mm-4mm范围内，但是喷淋水滴粒径<0.5mm的水滴易雾化飘移，不利于奶牛蒸发降温，故不建议作为喷淋降温系统使用。②喷淋水滴群在奶牛体表的运动现象主要为：随机散落、融合聚集、多样形变和流动滑落四类。③平均粒径为0.56、0.80mm的喷淋水滴群出现随机散落现象的频率较高，平均粒径为1.10mm时水滴群出现融合聚集现象频率较高，该2种现象不利于喷淋降温过程，故不建议采用。当γ集中在5～30区域内，We则在500～3000范围内变化时，喷淋水滴群平均粒径在0.80mm~1.0mm范围内发生多样形变，有利于奶牛体表的喷淋降温过程。④环境影响因子中风速起主要且促进喷淋降温换热量的作用，通过Merkel焓差理论计算了奶牛体表的换热量，得到0.914~0.995mm喷淋水滴粒径换热效果最好。⑤现场试验采用帽檐式扰流风机提高舍内风速，测试得出0.947mm平均喷淋水滴粒径下，奶牛脖颈区域平均降温为1.1℃，腹部区域平均降温分别为1.4℃，平均呼吸频率降低4.2次/min，奶牛单位时间平均换热量469.9W。项目研究明确了缓解奶牛热应激的最佳喷淋降温水滴平均粒径为0.947mm。