The Study On Mass Transfer Mechanism In Vacuum Degassing Of Artificial Board

Artificial board is popular in furniture making,interior architectural and decoration.The pollution gas mainly comes from its internal adhesive layer.The indoor air pollution has caused wide public concern.There are two major ways to treat indoor air pollution,treat the air and treat the source.Treat the source is considered as a more fundamental and thorough approach.Vacuum degassing treatment is considered as effective way to reduce the emission of artificial board through experiments.In this research,the process of formaldehyde diffuse in two typical kinds of artificial boards were analyzed theoretically according to their structure and mass transfer characteristics.In this research,mathematical and geometry model of diffusion process of multilayer composite plates was established under the condition of normal pressure and vacuum degassing.Through the simulation,the concentration distribution in the model was changed from symmetry to asymmetry,the high concentration area was shift to the lower diffusion rate part at a certain angle because of the anisotropy of wood.The drift of concentration also caused the phenomenon of concentration gradient in the lower diffusion rate part from one direction into positive and negative direction interval.Gas in the lower diffusion part transfer in a form of a wave.By comparing the change rate of the gas content in the model under normal pressure and vacuum degassing state,it was found that the diffusion rate under normal pressure keeps below the other one.Vacuum pressure and the rate of diffusion is not a linear relationship,after a certain point,diffusion speed rate was reduced,or even stopped rising but reducing,so the choice of degassing pressure is not the lower the better.Mathematical and geometry model of diffusion process of particleboard was established under normal pressure and vacuum degassing conditions.It was found in the simulation that the lowest concentration was created by a high concentration encirclement in the lowest diffusion rate part.Diffusion of particleboard was happened in each particle as the unit,the particle was spread evenly in the board,so the gas concentration in particle board is different from part to part but overall evenly distributed.Through the simulation the vacuum degassing was found less effective than the multilayer compound plates.In addition to the diffusion theory study of the process in vacuum degassing.Depending on physical properties of the adhesive itself,this research brought out a method to test the diffusion coefficient of adhesive layer using porous ceramics as physical support.Analytical calculation process and the test method was given,too.Due to the physical entities part of porous ceramics as a hindrance of diffusion,a correction coefficient ? was brought in to correct the influence.By establishing a geometric model and solving the model,the relation expression between correction coefficient co and porous ceramics equivalent diameter-thickness of the adhesive layer ratio ? was found.Consolidate the basis of mass diffusion theory in the future.