The thermal conductivity of heavy water between 75° and 260° c at pressures up to 300 atm

Abstract The thermal conductivity of heavy water having an isotopic purity of 99-85 per cent was measured with a vertical coaxial cylinder apparatus at pressures between 24 and 294 atm in the temperature range 75° to 260°C. The pressure range of the experiments included the critical pressure (218 atm). Identical with the trend exhibited by water, the thermal conductivity of heavy water was found to increase with rising temperature to a shallow maximum near 110°C and to fall with a further rise in temperature. The influence of pressure on thermal conductivity was small, and at 75°C amounted to an increase of 0.77 per cent for a pressure rise from 1 to 100 atm. This is similar to the values reported for natural water by previous investigators [9, 11]. In comparison with natural water, the thermal conductivity of heavy water, in the range investigated, was always lower. According to these tests the ratio k H 2 O / k D 2 O increased almost linearly from 1·045 at 75°C to a value of 1·34 at 260°C. No measurements of the thermal conductivity of heavy water have previously been reported at temperatures above 82°C. Below this temperature the present data are in good agreement with earlier work.