Effect of Heat and Mass Transfer on the Cellular Plastic Insulation and the Long-Term Aging

摘要

To produce environmental-friendly products, foamed plastic industries are facingthe challenge to replace the traditional blowing agents chlorofluorocarbons (CFCs) with zero ozone depletion potential (ODP) alternatives. Problems arose from such a change are far from manufacturing difficulties. Quality changes, control and evaluation of the new products are among the important issues that have to be considered in selecting a new production formula. Such tasks have formed the contents of the authors' studies on the rigid closed-cell cellular plastic insulation which are composed, originally, by the low thermal conductivity cell gases (the blowing agents) and the solid polymer matrix/ or skeleton. After a plastic insulation was produced, the blowing agents are diffusing out off the foam whilst the relatively high thermal conductivity air components are diffusing into it, the aging occurs. Such a gaseous transfer process will not only change the overall thermal conductivity of the foam but also change its dimensions because the mass transfer rate of blowing agents and air could be dramatically different. After a series of studies were completed, more understandings and new findings have been achieved with respect to the rigid closed-cell cellular plastic insulations or foamed plastic insulations (FPIs). The mechanism of heat transfer within the FPIs was examined. The foamed plastic deformation was also discussed. A new model has been established for predicting the elastic modulus of the foamed plastics. In comparison to the published measurements, it was found that the new model gives fairly good results. (Copyright (c) Valtion teknillinen tutkimuskeskus (VTT) 1997.)