Computational evaluation of air jet cooling from a perforated air ducting system to mitigate heat stress of cows in free stalls
Computational evaluation of air jet cooling from a perforated air ducting system to mitigate heat stress of cows in free stalls
复制标题
通过穿孔空气管道系统进行空气喷射冷却以减轻散栏奶牛热应激的计算评估
DOI：
10.1016/j.compag.2022.107198
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发表时间：
2022
期刊：
影响因子：
--
通讯作者：
Xiaoshuai Wang
中科院分区：
文献类型：
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作者：
Menbing Cao;L. Rong;Christopher Y. Choi;Kaiying Wang;Xiaoshuai Wang
缓解奶牛的热应激，提高奶牛的生产效率，有赖于有效的通风系统。为此，本研究评估了穿孔空气管道(PAD)系统的散热性能，并特别关注了与射流流动模式及其相应的冷却效率有关的重要设计参数(例如，孔口的形状和大小以及空气射流的速度和流量)。具体地说，本工作旨在通过数值模拟来评估四种不同类型的喷气孔(即三圆喷口、单圆喷口、矩形喷口和缝隙喷口)所产生的影响，以及不同的喷流速度和室内空气的整体运动对喷流特性及其与奶牛在自由牛栏中的降温性能的影响。结果表明，从狭缝孔口喷出的射流更有效地将空气分配到斜卧奶牛的表面，并产生更均匀的皮肤温度范围。当射流流量为470.4 m3h−1(625公斤奶牛推荐通气量的50%)、射流温度为28°C时，所实现的喷射降温性能相当于相同气温的2米S−1气流通过模型奶牛身体所获得的降温性能。另外，随着射流流量从212.0增加到564.5−1，斜卧奶牛的对流散热速率从63.47W/m−2增加到91.27W/m−1，表明增加通过缝隙孔口的射流流量可以提高对流散热速率，但对流换热的增加率同时降低。室内空气的整体运动(>；0.2米S−1)对射流和相应的冷却性能产生负面影响。因此，配备槽孔的PAD系统很可能在大气条件不太动荡时更有效(例如在侧风速度最小的自然通风谷仓或封闭谷仓内)。简而言之，这项研究的结果应该证明，使用PAD系统为自由放养的奶牛牛舍通风，以缓解奶牛的热应激。
Alleviating the heat stress suffered by dairy cows in order to increase their productivity depends on an effective ventilation system. For this reason, this study evaluated the heat mitigating performance of a perforated air ducting (PAD) system with special attention given to significant design parameters (e.g., the shape and size of the orifices and the speed and flow rate of the air jets) having to do with the jet flow pattern and its corresponding cooling efficiency. More specifically, this work aimed to evaluate, using numerical simulation, the effects produced by four different types of air-jet orifice (i.e., three-circular orifice, single-circular orifice, rectangular orifice, and slot orifice) and also the effects produced by different jet flow rates and by the bulk movement of indoor air with respect to the jet properties and their cooling performance in relation to cows reclining in free stalls. The outcomes show that the jet emitted from the slot orifice distributes air more effectively over the surface of a reclining cow and produces a more even range of skin temperatures. The jet cooling performance achieved with a jet flow rate of 470.4 m3h−1(50% of the recommended ventilation rate for 625 kg cow) and a jet temperature of 28 °C was equivalent to the cooling performance achieved by a 2 m s−1wind stream of the same air temperature passing over the model cow’s body. Additionally, the convective heat dissipation rate of the reclining cow increased from 63.47 to 91.27 W m−2as the jet flow rate increased from 212.0 to 564.5 m3h−1, indicating that increasing the flow rate of a jet emitted through the slot orifice could improve the convective heat dissipation rate, but the rate of the increase in the convective heat transfer decreased simultaneously. The bulk movement of the indoor air (>0.2 m s−1) negatively affects jet flow and the corresponding cooling performance. Therefore, a PAD system equipped with slot orifices will most likely be more effective when atmospheric conditions are less agitated (such as those in naturally ventilated barns with minimal cross wind speeds or inside enclosed barns). In short, the findings of this study should warrant using the PAD system to ventilate free-stall dairy barns to mitigate heat stress of dairy cows.