Study On Temperature And Humidity Control Of Open Cultural Relic Grottoes

There are many precious fresco cultural relics preserved in the Mogao Grottoes of Dunhuang.Due to historical and natural reasons,the internal frescos of the cultural relics caves have suffered serious diseases,such as succinate,hollow drums,and nails.A large number of studies have shown that changes in temperature and humidity inside the cave are an important reason for the destruction of cultural relics.This thesis studies the hot and humid environment in the Dunhuang Mogao Grottoes,aiming to provide the most favorable environment for the preservation of the wall paintings and cultural relics in the caves.Firstly,the thesis introduces the principle of temperature and humidity changes in open caves,and compares and analyzes the temperature and humidity control methods commonly used in underground buildings.Combined with the characteristics of open caves,it is preliminarily determined to use a dehumidifier to control the temperature and humidity of the cave.Secondly,taking an open cave in Mogao Grottoes of Dunhuang as the research object,the wall moisture dispersion was calculated under the design conditions of summer and winter respectively.The calculation results show that the wall moisture dispersion is about 41.65g/(m~2·h)in summer and 34.20g/(m~2·h)in winter.Thirdly,when the cave is in the natural state,the numerical simulation of different design conditions in summer is carried out based on Fluent software.The simulation results show that the critical conditions of dew condensation in summer are the average temperature outside the cave is 27℃,the average relative humidity is65%,the average temperature of the inner wall of the cave is 20.8℃,and the dew point temperature in the cave is 21.3℃.The numerical simulation of the design conditions in winter shows that the dew point temperature of the air in the hole is lower than the temperature of the inner wall of the hole,so the open cave will not produce dew condens ation in winter.Finally,when the average temperature outside the cave is 26℃and the average relative humidity is 80%in summer,dew condensation will occur on the cave wall.According to the dew condensation in the cave under the design working condition s in summer,the temperature and humidity in the cave are controlled by a dehumidifier.Optimize the working conditions of the dehumidifier placement position,dehumidifier supply air temperature,and supply air speed.When the dehumidifier is placed 2.5m away from the wall that is prone to condensation,the supply air temperature is 18℃,and the supply air speed is 5m/s.,The average air temperature in the cave is 21.3℃,the average relative humidity is 48.9%,the average wall temperature is 20.4℃,the air dew point temperature is 11℃,the wall temperature is higher than the air dew point temperature,and no condensation occurs on the wall.In addition,at this time,the air velocity near the inner wall of the cave is 0.3m/s as a whole,which meets the requirement of 0.2～0.5m/s for the wind speed of the cave in summer,that is,this working condition is the best optimized working condition.