Thermophysical Properties Research Laboratory, Inc.

Phone : 765-463-1581

Kohlrausch Apparatus

The Kohlrausch method involves the determination of the product of the thermal conductivity (λ) and the electrical resistivity (ρ). Since the electrical resistivity is also measured at the same time, conductivity can be calculated. The method involves passing constant direct current through the specimen to heat the sample while the ends are kept at constant temperature. Radial heat losses are minimized by an external heater maintained at the sample's midpoint temperature. With these provisions, at steady state a parabola-like axial temperature profile is obtained. Thermocouples are placed at the center and one centimeter on each side of the center. The thermocouples also act as voltage probes. Numbering the center thermocouple as the "2" position and the other positions as "1" and "3", it is possible to get the product of λ and ρ:

_{1}+T_{3} are summed and the middle, T_{2},
is the middle temperature. Since the electrical resistivity can be obtained during measurements
from the following equation:

_{1}, T_{2}, T_{3}, V_{3} - V_{1}, I)
are computerized and the results calculated for a set of measurements performed while the sample is under vacuum
and the heater temperature matched to that of T_{2}. For a new temperature point, additional current is used,
a new set of equilibrium conditions is obtained, and the process repeated.

The Kohlrausch method involves the determination of the product of the thermal conductivity (λ) and the electrical resistivity (ρ). Since the electrical resistivity is also measured at the same time, conductivity can be calculated. The method involves passing constant direct current through the specimen to heat the sample while the ends are kept at constant temperature. Radial heat losses are minimized by an external heater maintained at the sample's midpoint temperature. With these provisions, at steady state a parabola-like axial temperature profile is obtained. Thermocouples are placed at the center and one centimeter on each side of the center. The thermocouples also act as voltage probes. Numbering the center thermocouple as the "2" position and the other positions as "1" and "3", it is possible to get the product of λ and ρ:

λρ=V^{2}/(4[2T_{2}-(T_{1}+T_{3})]

ρ=(A/L)(V/I)

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West Lafayette, IN 47906

3080 Kent Avenue

West Lafayette, IN 47906

Last updated 1/5/2012