| dc.description.abstract | Thermal conductivities of refractory bricks made
from the materials; fireclay, kaolin, siaya clay and
Kisii soap stone have been measured. The thermal
conductivities of the bricks in dry air at atmospheric
pressure were determined at different porosity
percentages and as a function of temperature from room
temperature to about 800°C. The effects of particle
size distribution, chemical composition, grain structure,
firing shrinkage, weight loss on firing, density, casting
pressure and firing temperature for each material on
the thermal conductivity values were investigated.
The thermal conductivity values were determined by an
unsteady state method, the transient hot wire method
of comparison, which is based 6n the model of heating
a cylinder of a perfect conductor surrounded by an
infinite amount of a reference material on one side
and on the other side the material whose thermal
conductivity is being measured.
The porosities of the prepared bricks ranged; from
23.3 to 56.0 per cent for fireclay, from 21.1 to 56.7
per cent for kaolin and from 21.3 to 57.6 per cent for
Siaya clay.
The thermal conductivities of the refractory bricks
increased with decreasing percentage porosity. For all
the brick materials studied, the thermal conductivity
values measured increased with increasing temperature.
The rate of increase of these thermal conductivity
values was higher at low temperatures below 500°C and
and lower at higher temperatures above 500°C.
The results obtained from experiment were compared
to those predicted by theoretical models of heat
transfer in porous materials. The model of Imura et ale
gave the best explanation of the variations.
These results are useful to designers who will
require to calculate heat losses in refractory
material applications. | en |
