Thermal conductivity and permeability of consolidated expanded natural graphite treated with sulphuric acid

The thermal conductivity and permeability of consolidated expanded natural graphite treated with sulphuric acid (ENG-TSA) were measured both parallel and perpendicular to the direction of compression used to produce the samples. Results showed that the thermal conductivity and permeability were highly anisotropic. The thermal conductivity perpendicular to the direction of compression was 50 times higher than that parallel to the direction of compression and the permeability was 200 times higher. The maximum thermal conductivity measured was 337 W m−1K−1 at a bulk density of 831 kg m−3. The permeability perpendicular to the direction of compression varied in the range of 10−11 to 10−16 m2 as the density increased from 111 to 539 kg m−3. The specific heat was measured, and the average value is 0.89 kJ kg−1K−1 in the temperature range 30–150 °C. As a type of heat transfer matrix the thermal diffusivity was about five times higher than that of, for example, pure aluminium due to the combination of improved thermal conductivity with comparatively low density and reasonable specific heat.