Thermal Conductivity 16 pp 451-469 | Cite as

# Extending the Capabilities of the Multiproperty Apparatus for Thermophysical Property Determinations

## Abstract

The unique multiproperty apparatus developed at Purdue University has proven to be a powerful scientific and engineering tool. Efforts were made to increase its usefulness even further. Successful efforts were made to relax geometrical constraints on the samples, as a result of which the multiproperty apparatus can handle larger diameter samples. In addition to weakening geometrical limitations on samples, thermal conductivity measurement in an inert argon atmosphere was also demonstrated. Agreement within 5% was obtained with data obtained in vacuum. Since the presence of an atmosphere restricts sample vaporization, higher measurement temperature should be attainable.

Efforts were also made to increase the accuracy of Thomson coefficient values. The iterative approach was adopted to develop computer programs. Our experience in their use showed that the uncertainty in the measurement was reduced, but that the scatter is still unacceptable.

A new method to measure Seebeck Coefficient on multiproperty apparatus was attempted by using AC direct heating rather than DC heating. A signal conditioning unit, which measures very low level DC signals in the presence of large AC signals, was constructed. The results obtained by its use show large errors are associated with this method and further efforts are needed to identify the sources of errors in order to improve it.

## Keywords

Seebeck Coefficient Thermal Conductivity Measurement Radial Temperature Gradient Thomson Coefficient Inert Argon Atmosphere## Nomenclature

- A
cross sectional area of a sample

- A(z)
cross sectional area of sample at position z

- h
convection heat transfer coefficient

- h
_{r} overall radiation heat transfer coefficient

- I
current flowing through conductor (amps)

- j
current density

- M
Equation (6)

- \(\vec{n}\)
unit normal vector

- P
perimeter of sample cross section

- r
radial position

- S
_{AB} Seebeck coefficient (many times denoted as thermopower of thermocouple in literature)

- T
temperature

- T(r,z)
temperature as a function of position r and z

- T
_{1} temperature of position 1

- T
_{2} temperature of position 2

- T
_{m} maximum temperature

- T
_{o} ambient temperature

- T
_{s} temperature at surface

- V
potential

- z
longitudinal position

- z
_{m} longitudinal position on sample where temperature is maximum

- z1
longitudinal position 1

- z2
longitudinal position 2

- \(\nabla\)
delta operator

- Δ
delta — refers differential quantity (e.g., ΔT — temperature difference, ΔV — voltage difference, etc.)

- ε
_{H} total hemispherical emissivity

- ε
_{C} convection emissivity factor

- ε
_{EQ} overall heat transfer emissivity factor

- ρ
electrical resistivity

- σ
Stephen Boltzmann constant

- λ
the thermal conductivity

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## References

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