A simple needle-probe method for measuring thermal diffusivity of unconsolidated materials

Abstract

A potential difficulty in the measurement of heat flow in sea or lake floor sediments is the possibility that the measured temperatures are not in equilibrium, being affected by thermal disturbances such as seasonal fluctuations in bottom water temperature and rapid recent sedimentation. Correction for such transient disturbances requires an estimate of thermal diffusivity, a parameter that is not usually measured in sediments. A method for measuring diffusivity of sediments or other unconsolidated material has been developed and tested. It is a modification of the needle-probe method for measuring thermal conductivity; the modification is the use of a second probe recording temperature at a finite distance from the conductivity probe such that diffusivity can be measured using the theory of a line heat source. Tests of the method suggest that it is a useful one for measuring both conductivity and diffusivity of the same sample in a single heating-cooling cycle usually used for measuring conductivity alone. Only heating cycle data should be used for calculating diffusivity, owing to the poor resolution available from the cooling curve data. Probe separation should be approximately 20–25 mm for measuring diffusivity of water-saturated sediments.