Effects of discharge angle of jet from a slot orifice on cooling performance for a perforated air ducting system in dairy cattle barn
Effects of discharge angle of jet from a slot orifice on cooling performance for a perforated air ducting system in dairy cattle barn
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槽孔射流出射角对奶牛舍穿孔通风系统冷却性能的影响
DOI：
10.1016/j.compag.2023.107890
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发表时间：
2023
期刊：
影响因子：
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通讯作者：
Xiaoshuai Wang
中科院分区：
文献类型：
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作者：
Mengbing Cao;Ruimin Yang;Christopher Y. Choi;L. Rong;Guoqiang Zhang;Kaiying Wang;Xiaoshuai Wang
通过采用一种依赖于穿孔空气管道 (PAD) 和槽孔的通风系统，奶农可以帮助他们的奶牛避免热应激，从而提高牛奶产量。然而，从孔口喷出的空气会以一定角度输送，即排出角，即流出射流方向与风道轴线之间的角度。排放角度会影响系统的效率，如果喷射角度无法正确瞄准奶牛，喷射将无法输送足够量的空气。因此，本研究通过计算流体动力学模拟，寻求优化排气角对PAD系统冷却效率的影响，首先研究影响排气角的因素（如气流速率和风道直径），然后评估两种类型的喷气偏转器（矩形风道和矩形板）以及改变槽孔之间的间距所产生的影响。结果表明，第一个孔口（从管道入口到末端计算）主要受这两个研究因素的影响。将气流速率从 376.3 增加到 564.5 m3h−1 并将管道直径从 0.8 m 增加到 1.0 m 对排放角的影响有限（排放角相差约 2°）。而且，随着连续孔口数量的增加，排出角度逐渐增大，最后一个孔口的排出角度保持恒定的90°。在所有测试的排放角缓解中，矩形风管导流板产生最高的蒙皮表面平均对流换热率 (98.37 W m−2) 和最低的标准偏差 (±1.25 W m−2)。修改孔口之间的间距后（与原始情况相比），位于第一个孔口下方的奶牛记录的对流换热率将增加多达 27.5%，而其他奶牛的对流换热率则观察到增加和减少。鉴于这些发现，得出的结论是，通过添加带有矩形管道的导流板来调整排放角，可以最好地提高 PAD 系统的性能。
By employing a type of ventilation system that relies on perforated air ducting (PAD) and slot orifices, dairy farmers can help their cows avoid heat stress and in so doing increase milk production. However, the air jets from the orifices would be delivered at an angle, namely the discharge angle, which is the angle between the outflowing jet direction and the axis of the air duct. The discharge angle can affect the system’s efficiency and the jet will fail to deliver a sufficient amount of air if the angle is such that the jet does not properly target the cow. Consequently, by means of computational fluid dynamic simulation, this study sought to optimize the discharge angle on the cooling efficiency of PAD system, first by examining the factors (such as airflow rate and duct diameter) that affect the discharge angle and then by evaluating two types of air jet deflector (rectangular duct and rectangular plate) and also the effects produced by varying the spacing between the slot orifices. Results showed that the first orifice (counting from the inlet to the end of the duct) was mostly affected by the two investigated factors. Increasing the airflow rate from 376.3 to 564.5 m3h−1and the duct diameter from 0.8 m to 1.0 m had a limited effect on the discharge angle (around a 2° difference in the discharge angle). Also, as the number of sequential orifices increased, the discharge angle increased gradually, and the discharge angle of the last orifice remained at a constant 90°. Of all the discharge-angle mitigation tested, the rectangular-duct deflector produced the highest mean-convection heat transfer rate of the skin surface (98.37 W m−2) and the lowest standard deviation (±1.25 W m−2). The convection heat transfer rate registered by the cow positioned under the first orifice would increase by as much as 27.5% after the spacing between the orifices was modified (in comparison with the original case), while both an increase and a decrease in the convective heat transfer rate were observed to occur among the other cows. Given these findings, it was concluded that the PAD system’s performance could best be improved by adding a deflector with a rectangular duct to adjust the discharge angle.