Determination of thermal diffusivity of fired clay bricks produced from cow pie mixed with selected Ugandan clays

Abstract

This study was designed to determine the thermal diffusivity of fired clay samples produced by mixing cow pie with clays from selected districts in Uganda. The focus of the study was to find out the effect of clay particle sizes and the ratio of kaolin clay, ball clay and cow pie on thermal diffusivity. The clay particle sizes considered were 0-74, 75-89, 90-149, 150-299 and 300-349 μm, the cow pie particle sizes considered were 75-149 and 150-299 μm and the clay-cow pie ratios considered were 9:7:4, 9:6:5 and 9:7:0. The samples used in the study were compacted by using a compression machine International, England at a pressure of 50 MPa and were fired in a heating chamber (CARBOLITE, GERO, HTF 1700) up to a temperature of 950 0C at different firing rates of 1.2 0C/s, 1.3 0C/s, 1.5 0C/s and 0.5 0C/s. Thermal conductivity was measured by using a QTM-machine, density was obtained from mass per unit volume and specific heat capacity was obtained by using a simple calorimeter and applying the method of mixtures. The average values obtained for the thermal properties in the order of increasing particle sizes were as follows; for the kaolin: ball clay: cow pie ratio 9:7:4, thermal conductivity values were 0.2254, 0.2210, 0.2214, 0.2204 and 0.2195 Wm-1K-1, density values were 1.1800, 1.1535, 1.1537, 1.1433 and 1.1490 gcm-3, specific heat capacity values were 1.0670, 1.0510, 0.9810, 1.0490 and 1.0100 Jg-10C-1, the average calculated thermal diffusivity values were 0.1924 e -6, 0.2021 e-6, 0.1883 e-6, 0.2441 e-6, and 0.2039 e-6 m2s-1, for the kaolin: ball clay: cow pie ratio 9:6:5 thermal conductivity values were 0.2237, 0.2221, 0.2188, 0.2200 and 0.2178 Wm-1K-1, density values were 1.1866, 1.1661, 1.1945, 1.1789 and 1.2002 gcm-3, specific heat capacity values were 1.0490, 1.0810, 1.0630, 1.0450 and 1.0020 Jg-10C-1, the average calculated thermal diffusivity values were 0.1919 e-6, 0.2005e-6, 0.2046 e-6, 0.2080e-6, and 0.2031 e-6 m2s-1 and for the kaolin: ball clay: cow pie ratio 9:7:0, thermal conductivity values were 0.2871, 0.2781, 0.2771, 0.2654 and 0.2654 Wm-1K-1, density values were 1.1685, 1.1578, 1.1379, 1.1450 and 1.1280 gcm-3, specific heat capacity values were 1.0690, 1.0490, 1.0460, 1.0200 and 1.0510 Jg-10C-1, the average calculated thermal diffusivity values were 0.2546 e-6, 0.2439 e-6, 0.2427 e-6, 0.2466 e-6, and 0.2254 e-6 m2s-1. From the results, thermal diffusivity increased with the decrease in particle sizes of kaolin and ball clay; however, it was lower for the ratio 9:6:5. Thermal diffusivity values for the control experiment were very high and this implies that cow dung was a good pore former and should be incorporated into clay bricks to improve on their thermal insulation.