NONSTEADY-STATE BEHAVIOR OF THERMAL INSULATIONS.

David L. McElroy, Ronald S. Graves, David W. Yarbrough, Wai Cheung Timothy Tong

Research output: Journal article publicationJournal articleAcademic researchpeer-review

3 Citations (Scopus)

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 languageEnglish
Pages (from-to)395-401
Number of pages7
JournalHigh Temperatures - High Pressures
Volume17
Issue number4
Publication statusPublished - 1 Dec 1985
Externally publishedYes

ASJC Scopus subject areas

  • Fluid Flow and Transfer Processes
  • Physical and Theoretical Chemistry
  • Computational Mechanics
  • Mechanics of Materials
  • Materials Science (miscellaneous)

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