Drift Measurement Technique Applied to Poor Conductors Available to Purchase

Many applications require knowledge of thermal properties, over a wide range of temperature, to within 5 percent. The speedy and economical acquisition of the data is often a prime concern. We are investigating the potential of the very simplest system (an unguarded plate system), used in a drift mode rather than in a steady-state mode, to fulfill this need.

When heat flows across a specimen whose mean temperature is drifting slowly and linearly with time, a term of the form C_F(dT/dt) must be added to the steadystate equation. Data are taken over a given temperature range with the temperature both increasing and decreasing; the value of C_F is then adjusted until the two sets of data produce the same value of conductivity. Since C_F is a function of the density of the specimen and its specific heat at constant pressure, an approximate value of the thermal diffusivity is obtained as a by-product in this drift mode of operation.

The successful application of the technique is illustrated by both drift technique and steady-state measurements on microconcrete over the temperature range -20 to +60°C. Corrections for heat losses and nonlinear heat flow have been appraised by finite-element analysis and by comparisons with data from adiabatic linear heat flow systems. Our objective is to develop the apparatus for use up to 500°C.