Absolute measurements of the thermal conductivity of liquids at pressures up to 500 MPa

An apparatus for the accurate measurement of the thermal conductivity of liquids is described. The instrument, which is of the transient hot‐wire type, operates over the pressure range 0.1 to 700 MPa and the temperature range 20–200°C. The precision of the thermal conductivity measurements is estimated to be one of ±0.2% over the entire range. — Experimental data are reported for the thermal conductivity of n‐heptane in the temperature range 35–75°C and the pressure range 50–500 MPa. The accuracy of the present results is estimated to be one of ±0.5%, which is slightly worse than their precision because the lack of suitable data for the optical properties of the liquid at high pressures only allows an approximate correction to be applied for the systematic effects of radiative heat transfer. Along an isochore the thermal conductivity of n‐heptane is found to increase with temperature although along an isobar the temperature derivative is negative. The density dependence of the thermal conductivity is almost independent of temperature.