Study On Hygric Properties Of Porous Building Materials By Parameter Identification Method

The hygric properties of the porous building materials are the vital parameters in the analysis of heat and moisture transfer in building envelopes.These reliable parameters are the basis for solving a large number of engineering problems.Therefore,this paper explored how to use parameter identification method to confirm these parameters basis on the measurement of partial moisture content and temperature transfer in porous building materials.The main work is as follows.Firstly,a model of coupled heat and moisture transfer was established according to the laws of conservation of energy,conservation of mass and the laws of Darcy’s,Fick’s,Fourier’s studies.This model made the temperature and relative humidity as driving potential.Used parameter identification method to ensure these parameters in the heat and moisture coupled equation and then established the liquid diffusion coefficient formula and water vapor diffusion coefficient formula.Taking autoclaved aerated concrete as an example,according to the distribution of heat and moisture in one-dimensional direction,liquid diffusion coefficient formula and water vapor diffusion coefficient formula were solved.Then,in order to verify the feasibility of the parameter identification method,the moisture transfer coefficient of aerated concrete was studied by capillary water absorption experiment and steam permeation experiment.The results showed that though little deviation between the parameter identification method and the experimental value,the two were consistent and in the same magnitude order.Finally,In order to analyze the deviation of the hygric parameters under actual climatic conditions how to impact the heat and humidity distribution in the wall,we selected Nanchang,a typical hot summer and cold winter area,as the research object.The COMSOL Multiphysics simulation software was used to analyze the aerated concrete walls in Nanchang.Results showed that,in hot summer and cold winter area,when the diffusion coefficient of liquid water changed between 10-9 and 10-7,it made little influence on the temperature and humidity distribution in the wall.But water vapor permeability coefficient could make important affect to the temperature and humidity distribution when it changed between 10-13 and 10-11.The higher of water vapor permeability coefficient was,the more wall temperature and relative humidity distribution fluctuated.In the meantime the instantaneous heat transferred in the wall would cause greater fluctuation to bring more prominent impact to the indoor load.