冷凝对隧道通风热压的影响分析

为研究空气水分冷凝现象对隧道通风热压的影响,采用现场实测的某地下通风隧道空气参数以及文献中某隧道自然通风的测试数据,对选用的有限差分法隧道通风传热传质过程及热压计算数学模型进行了验证;并采用数值模拟方法研究分析了不同隧道入口空气温度、相对湿度及通风速度条件下,隧道内空气冷凝现象、沿程空气温度以及热压的变化规律。研究结果表明:冷凝会增大空气与壁面的传热量,使隧道内的空气降温速度减慢,导致通风热压变小,并且该影响会随入口空气温度与相对湿度的升高而增强,随风速提高而减弱;当未发生冷凝时,隧道沿程空气温度分布及热压几乎不受空气湿度的影响。以一个全纵向通风的地下隧道为例,在4~8月,隧道会出现较大范围的冷凝现象,考虑冷凝计算所得热压比不考虑冷凝时低30%,对应的自然风风速平均偏差为0.5 m·s^-1;在其余月份,不考虑空气冷凝计算所得通风热压与考虑冷凝时相同。因此计算湿热季节通风热压或对应的自然风风速时,应考虑冷凝的影响;其余季节可按不考虑冷凝的方法简化计算隧道热压。

Thermal Pressure Analysis of the Influence of Condensation in Tunnel Ventilation

In order to study the influence of air moisture condensation on the thermal pressure of tunnel ventilation,the air parameters of an underground ventilation tunnel measured on-site,and field test data of the natural ventilation of a tunnel from the literature were used to analyze the selected mathematical model of the finite difference method for the tunnel ventilation heat,mass transfer,and thermal pressure.The model was then verified.The numerical simulation method was used to study and analyze the changes in air condensation,air temperature along the tunnel,and thermal pressure under different conditions of tunnel entrance air temperature,relative humidity,and ventilation velocity.The results show that compared with when condensation does not occur,condensation will increase the heat transfer between the air and the wall,and at the same time will slow the air-cooling rate in the tunnel,resulting in a lower ventilation thermal pressure.This effect increases with an increase in inlet air temperature and relative humidity,and decreases with an increase in the ventilation velocity.When the moisture in the air is not condensed,the air temperature distribution and thermal pressure along the tunnel are hardly affected by the amount of air humidity.Taking a fully longitudinally ventilated underground tunnel as an example,from April to August,a large range of condensation occurs in the tunnel.The thermal pressure calculated by considering the condensation was 30% lower than that ignoring consideration,and the corresponding average deviation in the natural wind velocity was 0.5 m·s^-1.In the remaining months,the ventilation thermal pressure calculated without considering air condensation was the same as when considering it.Therefore,the influence of condensation should be considered when calculating the ventilation thermal pressure or the corresponding natural wind velocity in the hot and humid seasons.A method that does not consider condensation can be used to simplify the calculation of the tunnel thermal pressure in the remaining months.