Study On Indoor Radon Migration Under Natural Convection

With the development of urbanization,a large number of associated radioactive industrial waste residue(such as fly ash,coal cinder,etc.)are used in the production and production of building materials,resulting in an increasing trend of indoor radon level in our country.Especially in the houses in northern China,the temperature is low all the year round,and the residents are heated by hot kangs,and the indoor environment is often in a closed state,resulting in natural convection caused by the temperature gradient.in this process,radon migrates from the building wall to the indoor air,resulting in indoor air radon pollution and causing certain harm to the health of the residents in the house.The control standard of indoor radon concentration in civil buildings stipulated in China’s national standards is also increasing year by year,and residents pay more and more attention to indoor air quality,so it is very important to study the law of indoor radon migration under natural convection.In order to study the above problems,through the methods of experimental measurement,theoretical analysis and multi-physical field numerical simulation,this paper takes the indoor residence as the research object to study the indoor radon migration law under the condition of natural convection.The specific research contents are as follows:(1)By using the improved closed cavity method,the cumulative radon concentration measurement experiments of building material samples under different temperature conditions are constructed,and the radon diffusion coefficient is solved based on the radon diffusion coefficient solution theory.the non-linear fitting of the solution results is carried out,and the relationship between temperature and radon diffusion coefficient is obtained.(2)The porosity of building wall materials was measured by mercury porosimetry,and the porosity and pore size distribution of building wall materials were obtained.According to the theory of unidirectional seepage field,the permeability experiment of building wall material is constructed,and the gas permeability of building wall material is obtained.(3)Based on the theory of radon migration in porous media and indoor air,as well as the theory of natural convection,an indoor radon migration model under natural convection is established.Darcy equation is used to provide buoyancy drive in building wall area,buoyancy flow caused by temperature difference is used in indoor air area,relevant boundary conditions are set,and the control equation is dimensionless,and the solution method of the model is analyzed.(4)The parameters of the model are set,and the finite element method is used to solve the model.The indoor radon concentration distribution under different temperature gradients,the radon flux of indoor building wall and indoor air,and the radon exhalation rate of building wall-indoor air interface are obtained.By setting different Darcy numbers and solving the average Nusselt number (?) and average Sherwood number (?) of building wall-indoor air interface under different Grashof number (Gr),the effects of dimensionless groups related to heat and mass transfer on radon migration in building materials and indoor atmosphere are obtained.The migration law of indoor radon under the condition of natural convection is obtained,which provides a theoretical basis for improving indoor air quality.