The Mechanism Research On Formaldehyde Diffusion Within Porous Building Material In Multi Physical Fields

IAQ?Indoor Air Quality?is closely related to people's healthy and good IAQ can make people energetic and happy.However,different kinds of architecture and interior decoration materials such as density board,particle board,and wooden floor are widely used,which send out a lot of VOCs?Volatile Organic Compounds?in indoor leading to poor indoor air quality.What's more,formaldehyde is one of the main ingredients of VOCs.Therefore,it's significant to understand the diffusion and distributing law of formaldehyde in porous building materials for engineering application.In traditional research,the research of distributing characteristics of VOCs within building materials is still in the macroscopic and mesoscopic level.Related research in the micro level is missing and the effect of external field except temperature on formaldehyde diffusion within building materials is not clear.In that case,this paper conducted a study to solve the above problems and the results and conclusions are summarized as follows:Firstly,the experimental study of effect of external high-voltage electric field on formaldehyde emission from building materials was proposed.The effect of different electric intensities on equilibrium concentration and emission rate of formaldehyde emission from middle density fiberboard was studied.The experimental results indicated that equilibrium concentration of formaldehyde increased with the greater electric intensity and the increase of electric intensity speed up the emission process of formaldehyde from middle density fiberboard.In addition,the relationships between electric intensity and three key parameters?initial concentration,diffusion coefficient and partition coefficient?of formaldehyde emission from building materials were analyzed.It was found that partition coefficient decreased 30%with the electric field of 100 kV/m compared with no electric field action.The changing rules of three parameters provided reference and guidance for understand the effect of high-voltage electric field on formaldehyde emission from building materials.Secondly,combined effect of temperature and high-voltage electric field on formaldehyde emission from building materials was studied experimentally.The new calculation method of three key parameters was proposed,with the advantages of shorter experimental time and simple procedures.The experimental results showed that both temperature and electric field made a promoting effect on formaldehyde emission.What's more,the promoting effect of temperature was more obvious than electric field.When the temperature was 298 K,303 K,308 K and 313 K,the electric field intensity increased from 0kV/m to 160 kV/m,and the separation coefficient decreased by 17.7%,16.8%,22.2%and 22%respectively,and the decrease trend was not significant.When the electric field intensity is 0kV/m,80 kV/m,120 kV/m and 160 kV/m,the temperature increases from 298 K to 313 K,and the separation coefficient decreases by 59.8%,58.8%,60.3%and 62%respectively,and the variation of the decline trend is basically the same.Thirdly,the adsorption characteristic of formaldehyde within porous building materials was studied in the micro level.Cellulose was chosen as the study object representing building materials in microcosmic.Furthermore,the effects of different electric intensities on adsorption model,structure parameters and energy were studied by density functional theory.The relationship between adsorption potential and electric field was obtained.When the electric field intensity increased from 0 to 10^-3 a.u.,the adsorption potential of structure I decreased by about 50%,while the adsorption potential of structure II decreased by more than60%.The simulation work provided theoretical basis for macro experimental results,which was one of the important research method to study the formaldehyde emission from building materials.Finally,the diffusion process of formaldehyde within cellulose I?region and amorphous region was simulated by molecular dynamics.The effect of temperature and electric intensities on diffusion coefficient,hydrogen bonds and interaction energy was studied.The simulation results indicated that diffusion coefficient increased both with the greater temperature and electric intensity.In addition,the relationship between diffusion coefficient and electric field,and relationship between diffusion coefficient and temperature were obtained,which were verified by experimental results.