Research On The Cooling And Condensation Feature And Calculation Model Of The Air In Deep Buried Large Section Ventilation Tunnel

The underground power station is a common building form used in the development of hydropower stations,especially large hydropower stations.It has the advantages of high structural stability,safety and reliability,and is usually buried deep underground and equipped with traffic tunnels.In actual projects,in order to save energy consumption of air conditioner,it will make full use of the heat and humidity treatment capacity of the tunnel to the air.In most cases,the tunnel is not only a communication connection between the underground power station and the ground,but also an introduction of the ventilation and air conditioning system of the entire plant,that is ventilation tunnel.However,in the actual operation,the ventilation tunnel has reduced the temperature and dehumidification of the intake air in summer,but it has brought more serious fogging to the tunnel itself,even reduced the visibility inside the tunnel,and influenced the safe operation for driving and equipment.At the same time,by reading relevant literature,it is found that similar problems exist in other underground projects.Therefore,in-depth study of the fogging and condensation laws of the underground ventilation tunnel can not only reveal the characteristics of the air cooling and condensing,but also guide the comparison of the tunnel length in the design stage of the power station.It provides an important basis for solving the fogging problem in tunnels and analyzing the effectiveness of existing engineering demisting measures.At the same time,as a ventilation tunnel of a deep-buried building,it often has the characteristics of large sectional area and long longitudinal distance.Through the observation and analysis of the measured data of different underground tunnels,it is found that the air parameters of the tunnels in the same section and at different locations are unevenly distributed.The air temperature near the wall of the tunnel is low and the relative humidity is large.The air away from the wall has a high temperature and a relatively low relative humidity.The larger the difference between the average air temperature and the wall temperature at the same section,the more obvious the parameter distribution unevenness.The problems existing in the calculation method of heat and moisture transfer of existing underground ventilation tunnel are pointed out.Combined with the actual situation of the field,it is analyzed that the air flows through the large section of the underground ventilation tunnel to reduce the temperature and humidity,and then it will undergo dry cooling,condensation(partial wet cooling)and fogging(complete wet cooling),three stages,rather than just two stages of dry cooling and saturated condensing.And based on this,a new accurate calculation model of heat and condensation is proposed,which improves engineering calculation accuracy without increasing the difficulty of calculation.This paper focuses on the analysis of the measured results of air and wall parameters of the underground ventilation tunnel of Hongping Power Station in summer and winter.Then,through the analysis and summary of a large number of measured data from different underground areas and multiple underground ventilation tunnels in China,and the data fitting,two self-determined parameters that determine the air cooling and dehumidification process line in the ventilation tunnel are obtained.The relationship between the starting relative humidity and the temperature-humidity ratio of the condensation as a function of operating conditions is showed,and the corresponding results are programmed and embedded in the improved MATLAB dynamic implicit calculation model.The comparison between the two sets of engineering measured data shows that the improved program calculation results are more consistent with the measured data,and when the length of the ventilation tunnel is small,the error improvement effect is very significant.Finally,by establishing the CFD multiphase flow model of the underground ventilation tunnel,the characteristics of uneven distribution of air section parameters during the cooling and condensing process of the large section ventilation tunnel are further verified.