Measurements of thermal conductivity and thermal diffusivity of carbon dioxide near critical region

摘要

In the present study, the thermal conductivity and thermal diffusivity of CO{sub}2 at temperatures from 0 to 33°C, pressures up to 10 MPa, and specific volumes from 0.001 to 0.0025 kg{sup}(-1)m{sup}3 were measured by a transient short-hot-wire (SHW) technique. A special hot-wire support and a high pressure cell with a volume of about 30 ml were made. In the measurements, a platinum (Pt) wire with the diameter of 10 μm and length of 15mm serves both as a heat source and as an electrical resistance thermometer. The effective length and diameter of the wire were calibrated using water and toluene with known thermophysical properties. The measurements were performed in less than 0.5 s and the heating rates were adjusted to assure the wire temperature increases to be smaller than 0.15 K to suppress the effect of natural convection. The experimental data show that the thermal conductivity increases with very large slope when the condition approaches the region near the critical point, and then decreases quickly when the condition leaves this region, exhibiting a pronounced maximum near the critical region. The specific heats of the measured CO{sub}2 were also calculated from the relation among the specific heat, density, thermal conductivity, and thermal diffusivity.