Influence of water distribution and evolution on measurement accuracy of unconsolidated porous media thermal conductivity

This paper has experimentally studied thermal conductivity measurement accuracy of unconsolidated porous media with a Hot Disk thermal constant analyzer and water distribution and evolution at pore scale by a Charge Coupled Device (CCD) combined with a microscope. It found that thermal conductivities of samples with low moisture content (<25%) can not be accurately measured. For samples with low moisture content, analysis showed that the water in the analyser sensor adjacent region, which mainly existed as isolated liquid bridges between/among sand particles, will evaporate and diffuse to relatively far regions for being heated by the sensor during measuring. Water evaporation and diffusion causes the sample construction of the sensor adjacent region varies throughout the whole measuring process, and accordingly the obtained thermal conductivities have low accuracy. In relatively high moistures content samples, water in different pores has high water connectivity and mainly exists as water mass, thus water evaporation and diffusion rates are relatively slow compared with that in low moisture content ones during measuring, meanwhile, water in the relatively far region flows back to the sensor adjacent region by capillary force. Therefore, sample construction of sensor adjacent region maintains constant and thermal conductivities of unconsolidated porous media with relatively high moisture content can be measured with high accuracy.