Influence of Participating Radiation on Measuring Thermal Conductivity of Translucent Thermal Insulation Materials with Hot Strip Method

The hot strip method, as one typical transient method, is widely used to measure the effective thermal conductivity of thermal insulation materials at various temperatures. Since the test theory is based on solving the energy equation via heat conduction, the test result will be questionable when measuring thermal insulation materials, such as silica aerogel and photovoltaic glazing, in which the participating thermal radiation is a dominant heat transfer mode at high temperature. In this study, numerical investigation is employed to reveal the measurement reliability of hot strip method when applied to translucent thermal insulation materials. By reproducing the dynamic conduction-radiation coupled heat transfer process within the translucent materials numerically, the effective thermal conductivity of translucent materials with varying extinction coefficients are obtained at various temperatures. Comparisons are made for the effective thermal conductivity of translucent materials determined by the hot strip method, one-dimensional steady state method, transient plane source method and Rosseland model. Large discrepancies are found among the effective thermal conductivity determined by different methods for translucent materials with low extinction coefficient. The thermal conductivity obtained from the hot strip method is overestimated at elevated temperature when compared with that from one-dimensional steady state method. In order to measure the effective thermal conductivity of translucent materials accurately, the effect of thermal radiation should be considered for different transient methods.