Abstract Due to the accumulation of residual gas, vacuum failure may occur in the annulus of evacuated collector tube in solar trough thermal power system, resulting in the changes of flow and heat transfer mechanism and characteristics. In this paper, based on the actual situation of solar radiation in summer of Chongqing, China, the flow and heat transfer characteristics of the annulus in slip regime were numerically studied. The effects of gas pressure, gas types (N2, H2 and He), heat transfer fluid temperature were analyzed and discussed. The results show that the temperature jump under lower gas pressure directly affects the heat loss and temperature distribution of the annulus. The temperature jump is most obvious for the residual gas of H2 at gas pressure of 130Pa, while it basically disappears for N2 and He (the corresponding Knudsen numbers Kn are 0.0019 and 0.0040; 0.0022 and 0.0046; 0.0026 and 0.0052 respectively under heat transfer fluid temperatures of 473.15 K, 573.15 K and 673.15 K). The heat loss and the outer wall temperature of glass envelope rise with the increasing of heat transfer fluid temperature and gas pressure, and are related to the thermo-physical properties and thermal adaptation coefficient of gas. For gas pressure being less than 70Pa (Kn > 0.0048) or greater than 20000Pa (continuous gas flow regime), the heat loss of N2 keeps increasing with gas pressure, and the heat losses of H2 and He are even more than 1200 W·m−1 under heat transfer fluid temperature of 673.15 K. When the temperature of heat transfer fluid is 573.15 K and the pressure increases from 1.83Pa to 130Pa, the declining relative values of first law efficiency (thermal efficiency) and second law efficiency (exergic efficiency) for N2, H2 and He are 1.59%, 10.07% and 8.48% respectively.

中文翻译：

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非均匀太阳通量边界条件下真空集热管环在滑移状态下的流动和传热特性

摘要 由于残余气体的积聚，太阳能槽式热电系统中真空集热管环空可能发生真空失效，导致流动传热机理和特性发生变化。本文结合重庆夏季太阳辐射的实际情况，对滑移状态下环空的流动和传热特性进行了数值研究。分析和讨论了气体压力、气体类型（N2、H2和He）、传热流体温度的影响。结果表明，较低气压下的温度跃变直接影响环空的热损失和温度分布。130Pa气压下H2残余气体温度跃变最明显，而N2和He基本消失（相应的Knudsen数Kn分别为0.0019和0.0040；0.0022和0.0046；在传热流体温度为473.15 K、573.15 K和673时，分别为0.0026和0.0052）。玻璃外壳的热损失和外壁温度随着传热流体温度和气体压力的增加而升高，并与气体的热物理性质和热适应系数有关。气体压力小于70Pa（Kn>0.0048）或大于20000Pa（连续气体流态）时，N2的热损失随气体压力不断增加，H2和He的热损失甚至超过1200W·m -1 在传热流体温度为 673.15 K 时。 当传热流体温度为 573.15 K，压力从 1.83Pa 增加到 130Pa 时，