Abstract
An unguarded longitudinal heat flow apparatus designed for measuring the apparent thermal conductivity, k//a, of thermal insulations under steady-state conditions has yielded significant results when operated under nonsteady-state conditions. A large, unguarded, electrically heated Nichrome wire screen is sandwiched between two horizontal layers of insulation with flat isothermal bounding surfaces. Steady-state results for k//a on a standard reference material and a calibration transfer standard from 300 to 335 K are within 1% of values assigned by the National Bureau of Standards. Nonsteady-state operation of the apparatus involves starting the system from an isothermal state with a step increase in the electric power applied to the Nichrome screen heater and recording the resulting heater temperature versus time for analysis. The experimental thermal diffusivity for the insulation test samples is less than the thermal diffusivity calculated from the steady-state value for k//a by as much as 40%. This anomalous behavior is attributed to heat transfer by radiation in the insulation that is not accounted for by the transient heat conduction equation.
Original language | English |
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Pages (from-to) | 395-401 |
Number of pages | 7 |
Journal | High Temperatures - High Pressures |
Volume | 17 |
Issue number | 4 |
Publication status | Published - 1 Dec 1985 |
Externally published | Yes |
ASJC Scopus subject areas
- Fluid Flow and Transfer Processes
- Physical and Theoretical Chemistry
- Computational Mechanics
- Mechanics of Materials
- Materials Science (miscellaneous)