| Thousands-Armed Guanyin Statue in the Dazu Rock Carved,which is the largest Cliff carving integrated carving,painting,and gilding in China country,has extremely high historical,artistic and modern social value.However,due to long-term exposure to a semi-closed environment with high temperature,high humidity,and serious air pollution,Thousands-Armed Guanyin is plagued by various diseases due to the interaction of various environmental factors.Among them,condensation disease is one of the root causes of many other diseases.If we can predict the condensation risk of relics,so that control relevant important environmental parameters effectively through control measures to create a suitable preservation environment,it is of great significance for the long-term preservation of cultural relics.This article first carried out fixed monitoring and artificial observation of the air environment parameters in the core and surrounding areas of the Thousand-Armed Guanyin.Then the temporal and spatial distribution characteristics and dynamic changes of meteorological parameters,main air pollutant parameters,and wall temperature of the statue are analyzed.As a result,the current situation of the preservation environment of relics has been fully grasped.Combined with the problem of condensation and disease of cultural relics,it is proposed that key observations of air temperature,humidity,and particulate pollutants are required.Wall temperature is an important parameter for judging the risk of condensation on the statue.However,the non-contact instruments will lead to large errors in wall temperature measurement.Based on the heat and moisture transfer characteristics of the Thousand-Armed Guanyin rock mass,this article utilizes unsteady heat and moisture simulation technology to obtain the statue's wall temperature.First,a mathematical model of heat and moisture transfer with temperature and water content as driving potential is established,and the model's assumptions,initial conditions,and boundary conditions are given.Next,through experimental research,the unknown parameters in the mathematical model including the material thermal conductivity,specific heat,water vapor permeability coefficient,liquid water diffusion coefficient,and isothermal moisture absorption and desorption curve were measured,which provides thermal and moisture physical parameters data for subsequent simulations.Based on the above research,the multi-physics simulation software COMSOL Multiphysic is used to dynamically simulate wall temperature of the statue in 2020.By comparing the simulated wall temperature with the near-wall air dew point temperature,the seasonal and daily changes of the risk of condensation on the statue are analyzed.Then,the concept of wall-dew temperature difference is used to measure the risk of condensation levels.Based on the above research,we construct a stone cultural relics condensation prevention and control system with field monitoring,unsteady heat and moisture coupling simulation technology,and condensation risk levels to guide subsequent cultural relics protection jobs.In view of the poor dehumidification effect of the preservation environment around relics,and the serious problems of condensation on the surface of the statue at this stage,effective prevention and control measures need to be implemented to further control the environment.Based on the actual situation,three condensation prevention and control measures are proposed,and CFD simulation technology is used to compare these measures.The simulation results show that in the semi-closed environment where the Thousands-Armed Guanyin statue is located,the optimized measure of closed water vapor inlet with additional dehumidifiers can effectively reduce the air relative humidity and near-wall air dew point temperature,thereby effectively reducing the condensation risk and lighten the statue's condensation disease. |
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