Influence of moisture content on measurement accuracy of porous media thermal conductivity
Thermal conductivity measurement accuracy of sands was experimentally studied with a hot disk thermal constant analyzer and water morphologies,distribution and evolution at pore scale were observed with charge coupled device(CCD)combined with microscope.It was found that thermal conductivities of samples with a low moisture content(25%)could not be accurately measured.For samples with a low moisture content,the analysis showed that the water in the region adjacent to the analyser sensor mainly existed as isolated liquid bridges between/among sand particles and would evaporate and diffuse to relatively far regions because of being heated by the sensor during measurement.Water evaporation and diffusion caused the sample composition in the region adjacent to the sensor vary throughout the whole measurement process,and accordingly low accuracy of the obtained thermal conductivities.Due to high water connectivity in pores,the rate of water evaporation and diffusion in porous media of high moisture content was relatively slow compared with that in porous media of low moisture content.Meanwhile,water in the relatively far region flowed back to the region adjacent to the sensor by capillary force.Therefore,sample composition of the region adjacent to the sensor maintained constant and thermal conductivities of porous media with a relatively high moisture content could be measured with high accuracy.