ln this study, the insulation performance of mixed powders was investigated by measuring the effective thermal conductivity. Silica (Si0
2) which was semi-transparent for thermal radiation was used as a main powder and opaque powders for the thermal radiation, namely, titanium oxide (Ti0
2), carbon black, fly ash, and iron oxide (Fe
20
3) were mixed in the main powder. The effective thermal conductivity was measured by the dual cylindrical method with a steady heat flow as shown in Fig.1 in the range of room temperature to 600°C. Experimental results were analyzed by the theoretical equation of Wang and Tien
(1) for heat transfer in a semi-transparent medium. The heat transfer in the mixed powders was divided by two contributions of pure conduction and thermal radiation and the ratios of those were calculated qualitatively for the mixed powders.
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