The Tibetan Plateau is characterized by low-pressure, cold, hypoxic, and dry ambient conditions. Thus, in addition to heating, buildings in the region need humidification and oxygenation. It is noted here that the existing specifications of the resistance coefficients of the gas flow in the HVAC pipeline do not consider the effect of the variation in air components on the local resistance of the pipeline due to the low air pressure conditions as well as the humidification and oxygenation. In this paper, the effects of various parameters on the local resistance loss are investigated and reported, including the atmospheric pressure, inlet velocity, humidity, oxygen concentration, pipe diameter, wall roughness, velocity ratio, and area ratio between the branch and the main pipes. The results showed that the decrease in atmospheric pressure leads to a shorter longitudinal distance of effective dissipation of the secondary flow, primarily concentrated in 25D-27D. Additionally, the resistance losses generated in the elbow, the tee straight branch pipe, and the side branch pipe are reduced, with a maximum reduction of 42 %, 33 %, and 46 %, respectively, under low pressure conditions. Also, with the increase in the inlet velocity and the decrease in the pipe diameter, the local resistance of the elbow pipe is increased by a maximum of 14 times and 22 %. Moreover, when the velocity ratio increases and the area ratio between the branch pipe and the main pipe decreases, the local resistance loss of the straight branch pipe and the side branch pipe increases. Based on this study, the recommended value of the local resistance coefficient of the elbow and tee under low pressure is identified. This can provide a reference for the proper design of heat-moisture-oxygen transport pipelines in the plateau area.

中文翻译：

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青藏高原建设热湿氧输送管道局部构件流动特性及阻力系数

青藏高原的特点是低压、寒冷、缺氧、干燥。因此，除了供暖之外，该地区的建筑物还需要加湿和充氧。这里需要说明的是，现有暖通空调管道中气流阻力系数的规范没有考虑低气压条件以及加湿情况下空气成分变化对管道局部阻力的影响。和氧合。本文研究并报道了各种参数对局部阻力损失的影响，包括大气压力、入口速度、湿度、氧气浓度、管道直径、壁粗糙度、速度比以及支管与主管之间的面积比。管道。结果表明，大气压降低导致二次流纵向有效消散距离变短，主要集中在25D~27D。此外，弯头、三通直支管、侧支管产生的阻力损失也减少，在低压工况下最大分别减少42%、33%、46%。并且，随着入口速度的增加和管径的减小，弯管的局部阻力最大增加了14倍和22%。而且，当速度比增大、支管与主管之间的面积比减小时，直支管和侧支管的局部阻力损失增大。根据这项研究，确定了低压下弯头和三通的局部阻力系数的推荐值。这可为高原地区热湿氧输送管道的合理设计提供参考。