Thermal Modeling of Multiple-Line-Heat-Source Guarded Hot Plate Apparatus.
Thermal Modeling of Multiple-Line-Heat-Source Guarded
Hot Plate Apparatus.
Healy, W. M.; Flynn, D. R.
Insulation Materials: Testing and Applications, 4th
Volume. ASTM STP 1426. 2002, ASTM International, West
Conshohocken, PA, Desjarlais, A. O.; Zarr, R. R.,
Editor(s)(s), 79-97 pp, 2002.
insulation; heat transmission; conductive heat transfer;
heat transfer; thermal analysis; thermal conductivity;
thermal insulation; thermal resistance
The National Institute of Standards and Technology is
building an advanced-design guarded hot plate apparatus
of advanced design to provide very accurate thermal
transmission properties for specimens of thermal
insulation 500 mm in diameter, with thicknesses up to
110 mm, at mean temperatures from 90 K to 900 K. This
paper documents some of the extensive thermal modeling
and analyses that were carried out in the course of
designing this apparatus and characterizing potential
errors and uncertainties. In an idealized guarded hot
plate apparatus, the effective thermal conductivity is
simply computed from the measured power input to the
meter plate heater, the effective area of the meter
plate, the temperature of the hot plate and the two cold
plates, and the specimen thickness. In an actual
apparatus, there may be (a) temperature variations in
the hot plate and cold plates, (b) radial heat flow
within the specimen, and (c) transient temperature
fluctuations that add uncertainty to the measured
thermal conductivity. For the new 500 mm apparatus, both
analytical solutions and finite element analyses were
used to model temperature distributions in critical
thermal components, heat flows that might affect the
measured thermal conductivity values, and the effects of
departures from ideal steady-state conditions on test
results. This paper focuses on the results of these
analyses and computations.