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Reducing Contact Resistance Errors In Measuring Thermal Conductivity Of Porous Media
Values of thermal conductivity (k) of glass beads, quartz sand, stone dust and clay were determined using a thermal probe with and without heat sink compounds (arctic silver grease (ASG) and white grease (WG)) at different water contents, bulk densities and particle sizes. The heat sink compounds (HSC) increased k at air-dry condition, thereby reducing the thermal contact resistance (TCR), but reduced values of k when water was added. The increase in values of k was higher with application of high-conductivity ASG than low-conductivity WG. The maximum percentage increase in k with application of ASG was 25, 118, 22 and 25 % in glass bead, quartz sand, stone dust and clay, as compared with increase of 10, 22, 23 and 22 % respectively for WG. The increase in k for 1 mm samples exceeded the increase in 2 mm samples. At water saturation, application of HSC on the probe did not change the values of k suggesting almost a non-existent TCR at such conditions. The values of k increased with water content (Vw) and bulk density (ρ). The highest increase was attained when 200 mL of water was added to air-dry samples, where k in quartz sand was increased by 132 % on application of WG as compared to increase of 307 % on application of ASG.
Journal of Applied Science and Technology Vol. 12 (1&2) 2007: pp. 58-64