Classification of thermal conductivity of porous insulation using measurement result by high precision GHP

Abstract

In this study, the thermal conductivity of porous insulation materials and vacuum insulation panel (VIP) composed of glass wool were measured under different temperature conditions using a high-precision guarded hot plate (GHP) apparatus developed by author’s research group. This GHP device used a Peltier module to measure the temperature difference between the main plate and the guard plate. The temperature fluctuation of the Peltier module is ± 20 μK, which is 500 times more accurate than the commonly used thermopile. The element of the thermal conductivity of the porous heat insulating material were classified. The expanded uncertainty calculated with the inclusion coefficient kcf = 2 was 0.25% or less for the porous insulation and 0.51% or less for the VIP composed of glass wool. It can be expected that the measurement of thermal conductivity is highly accurate. Moreover, it was confirmed that the measured value of effective thermal conductivity was linearly proportional to the cubic of temperature. It has been experimentally shown that the equivalent radiative thermal conductivity of the porous insulating material and VIP composed of glass wool occupy from 30% to 50% and 36.0% under normal temperature environment 20 °C respectively. Furthermore, the effective thermal conductivity of VIP and its punched one were compared. It was clarified that the thermal conductivity of the porous insulating material was suppressed by about 75% under the vacuum environment. Evaluating the thermal conductivity component of effective thermal conductivity in the porous insulation material, the variation of the solid thermal conductivity by the changing of the porosity was discussed qualitatively.

Keywords

• porous insulation materials
• vacuum insulation panel
• radiative thermal conductivity
• ghp
• expanded uncertainty
• classification of thermal conductivity