THE THERMAL DIFFUSIVITY MEASUREMENT OF ANTHRACITE BY THE FLASH METHOD IN THE GREEN AND CALCINED STATE

Abstract

Since introducing of the flash method of thermal diffusivity measurement, a large scale of devices and evaluation methods has been developed with various levels of sophistication. Widening the application field of the method is going on continuously and thanks to the computer technology available today, the evaluation of experiments and the determination of thermal parameters can be performed in the case of non-ideal measurement data. With the help of the classical solution of the heat conduction equation, we give a short analysis of influencing factors like the sample thickness-to-diameter ratio, the heat losses, the effect of the flash duration and prolonged heat penetration on the front side. The knowledge of the anthracite properties is essential in the determination of the thermal characteristics of packed coal beds. Because of the unavailability of these data for coals of different origin, the author´s objective was to test whether the flash method is applicable for determining the thermal diffusivity of anthracite. A number of anthracite grains with different size were embedded in acrylic resin and after cutting and polishing we got the proper specimens. Samples were made with layers both parallel and perpendicular to the direction of the energy input. The thermal diffusivities in the parallel and the perpendicular directions are characteristically different. While this difference is only around 30% in the green state, it has been increased to about 300% or more for some samples in the calcined state.