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ISSN Online: 2377-424X

ISBN Print: 1-56032-797-9

International Heat Transfer Conference 11
August, 23-28, 1998, Kyongju, Korea

HEAT TRANSFER IN POROUS CERAMIC MATERIALS IN THE PRESENCE OF GAS EMISSION

Get access (open in a dialog) DOI: 10.1615/IHTC11.4010
pages 399-404

要約

Thermal diffusivities, k, of several types of industrial refractories measured in vacuum by monotonous heating method with the rate of about 1.5×103 K/h, exhibit an abnormal behavior. In particular, k of magnesite refractories, with porosity ε=24% measured in vacuum, exceeds the comparable data registered at atmospheric pressure. A similar effect was found for thermal diffusivity of several insulating materials. However, for many materials this phenomenon is absent or less pronounced.
It was shown that several heterogeneous physico-chemical processes, taking place on pore surfaces of ceramic materials, may be responsible for this effect. These processes include heterogeneous chemical reactions, accompanied by emission of gaseous products. These processes affect thermophysical properties, especially during fast heating or cooling.
A physico-mathematical model for the gas motion inside the pore, its removal from the pore, as well as gas emission and adsorption on the pore surface, accompanied by heat release and adsorption, is developed. The influence of these processes on the heat transfer within ceramic material is investigated.
We show that thermal conductivity and diffusivity are not material properties in the cases where gas is released in open pores and withdrawn from the specimen. However, when the gas withdrawal from the specimen is negligible, compared to its intrapore transport, these quantities can be used as material properties. Applicability of these properties is discussed.