Study On The Variation Characteristic And Distribution Law Of Thermal And Humidity Environment For Underground Corridor/cavern Based On Hydropower Engineering

With the accelerating process of urbanization,developing and utilizing underground space resources,especially deep space resources,is an inevitable trend of social development.The calculation and control of thermal and humid environment in underground caverns,such as underground hydropower stations,subway or civil air defense projects and national defense engineering,is a problem that needs further research and solution.Deep underground caverns are different from above-ground buildings,which is not exposed to sunlight.It is influenced by topography and permeation and moisture transfer from wall and other factors.The thermal and humid environment of deep underground buildings has an important influence on the work efficiency and even life and health of people.At the same time,the humid environment will also cause short circuit of electromechanical equipment in the plant,thus causing major accidents and causing major personnel and property losses.The heat and moisture transfer characteristics of the underground cavern envelopes and the control methods and technical measures of the thermal and humid environment are particularly important.In this paper,the heat and moisture transfer characteristics and environmental control method of the underground power station cavern/corridor are put forward by theoretical analysis,numerical simulation and field measurement.The main contents are as follows:Firstly,in this paper,a general mathematical equation of heat and moisture transfer between rotating curved underground corridor walls and air were established based on the underground corridor structural shape and mathematical rotational surface.The relationship of heat and moisture transfer between underground corridor and air was obtained.Meanwhile,The simplified heat and moisture transfer prediction formulas of circular,arched(horseshoe)and rectangular shaped corridor were put forward,and the field test data verified the practicality of its application in engineering calculations.It was found that under the equal cross section area,the average temperature cooling amplitude of rectangular corridor is 0.25% higher than that of arch corridor,and 0.8% higher than that of circular corridor.Under the equal cross section perimeter,the average temperature cooling amplitude of rectangular corridor is 0.51% higher than that of arch corridor,and 1.37% higher than that of circular corridor.In the case of the same equivalent diameter,the effect of heat and moisture transfer is almost no difference between the three kinds of shape corridors.Secondly,field test of heat absorption and exothermic effect of ventilation in underground corridor in the typical summer and winter conditions of Xianyou Pumped Storage Power Station,Dagangshan Hydropower Station,and Jinping I Power Station were carried out to complement and improve the thermal and humid physical property boundary conditions of the underground corridor envelope structure.Also the mathematical formula of air temperature and humidity distribution in underground corridors of each power station is obtained.By comparing the indexes of ventilation temperature drop(rise),heat dissipation and moisture gain of underground corridors in different climate zones,it was found that in summer,Xianyou and Dagangshan Hydropower Station underground corridor can cool down the air flowing,and the supplying air was dehumidified.In winter,the underground corridors have heating effect on the air flow,while the relative humidity is decreasing in the corridor of Xianyou power station and the air flow is humidified by traffic corridor of Dagangshan power station.The traffic corridor moisture dissipation of Jinping I Power Station was 0 in summer.The air is cooled and humidified in winter.Therefore,it is concluded that the main factors affecting the heat and humidity change characteristics of underground corridor include: the structure size of corridor(section size,depth length,wall temperature)and the physical parameters of air flow(air velocity,temperature,relative humidity).In addition,according to the measured thermal and humid physical property boundary conditions,numerical model for prediction the heat and mass transfer between underground corridor and air was established.And the full size numerical simulation of underground hydropower corridor is carried out by CFD(Computational Fluid Dynamics)to further compare and analyze the specific influence of corridor section size,wall temperature,depth,inlet air velocity,temperature and relative humidity on the heat and moisture transfer characteristics of underground corridor.It is found that under the same conditions in summer,with the increase of the equivalent diameter and the wall temperature of the corridor,the cooling and humidifying effect of the corridor on the air decreases gradually.With the increase of inlet velocity,the cooling effect of corridor on air decreases.When the inlet air supply velocity v > 2 m/s,the effect of increasing the air supply velocity on the corridor wall and the air absorption or exothermic is not obvious.Research shows different equivalent diameters and velocities,there exists an effective length of corridor which provides the maximum cooling capacity.The lower air temperature at the entrance of the corridor,the smaller air temperature(wet)difference between the inlet and outlet of the corridor,and the lower cooling efficiency of the corridor to the air.Relative humidity(moisture content)of inlet air is the main factor affecting fog formation in corridor.The air temperature and humidity in the corridor change periodically with the depth of the corridor,and the fluctuation range decreases gradually with the depth of the corridor.Finally,the dynamo floor of underground large plant cavern for Xianyou Hydropower Station was taken as an example in this paper.The heat and humidity distribution law of the underground high space cavern was studied by means of field measurement and numerical simulation at different air supply velocities and heat source intensity.The influence of different air supply modes on velocity field,temperature field and humidity field in dynamo floor was also analyzed.Based on the evaluation index of air distribution effect in the working area,the optimal air supply velocity suitable for the top air supply mode of Xianyou underground hydropower station is proposed.It provides a basis for the optimization design of complex air flow ventilation and thermal and humidity environment of underground cavern.The study shows that v=8 m/s is the optimal air velocity value of Xianyou Hydropower Station nozzle jets from the perspective of energy saving and comfort of large space air flow.This paper provides a theoretical reference and numerical simulation design tool for the related industry standards and ventilation and air conditioning design in the field of HVAC in hydropower industry.