09. Heat and Mass Transfer

In recent years, global warming has been progressing worldwide. In addition, in the urban area, the artificial land cover expands with the population concentration, and the deterioration of the thermal environment becomes serious by the heat island phenomenon which originates from it. As a measure for mitigating these problems, improvement of thermal insulation performance is considered as a part of energy saving in buildings. On this realization, the development of low thermal conductivity heat insulating material is advanced. The thermal conductivity of vacuum insulation material is about one-tenth or less, while the thermal conductivity of foam polyurethane, rock wool, glass wool, etc. used in the building until now is 0.02 ~ 0.05 W/(m･K), and the utilization and popularization to building materials such as refrigerators and freezers, household electric appliances, houses, etc. are expected. On the other hand, for the popularization of the material, the standardization of the performance and the establishment of the evaluation method with high reliability are necessary. In this study, heat transfer phenomena inside vacuum insulation materials are modeled and their thermal characteristics are numerically evaluated. In the analytical model, it is assumed that glass fiber is used as a core material and aluminum film is used as a covering material. Radiative transport properties about absorption and scattering of the fibrous material is evaluated on the basis of scattering theory, and radiative heat transfer in the core material is analyzed by the radiation transport equation. Heat conduction through the solid fibrous material is modeled by use of apparent thermal conductivity taking into account the parameters such as fiber diameter and fiber density of the core material. The effect of adding a small amount of carbon black particles to the core material on radiation transport is also evaluated. The effect of the fiber diameter and fiber density on the apparent thermal conductivity of vacuum insulation panel (VIP) in is evaluated. Three conditions of fiber diameter, 1um, 4um and 8um, are set. It is resulted that radiative heat transfer is more reduced as the fiber diameter is smaller. In the conditions of fiber diameter 4um and 8um with carbon black particle, it is resulted that the effect of extinction of scattering in core material is enhanced and the heat flux of radiation is suppressed. From these results, it is possible that addition of carbon particles to VIP with fibrous core material is effective to improvement of the insulation performance.