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Modeling of Bare and Aspirated Thermocouples in Compartment Fires.


pdf icon Modeling of Bare and Aspirated Thermocouples in Compartment Fires. (1747 K)
Blevins, L. G.; Pitts, W. M.

NISTIR 6310; 25 p. April 1999.

Fire Safety Journal, Vol. 33, 239-259, 1999.

Available from:

National Technical Information Service (NTIS), Technology Administration, U.S. Department of Commerce, Springfield, VA 22161.
Telephone: 1-800-553-6847 or 703-605-6000;
Fax: 703-605-6900.
Website: http://www.ntis.gov
Order number: PB99-131948

Keywords:

thermocouples; compartment fires; instruments; radiative heat transfer; temperature measurements

Abstract:

As part of an effort to characterize the uncertainties associated with temperature measurements in fire environments, models of bare bead single-shielded aspirated, and double-shielded aspirated thermocouples were developed and used to study the effects of varying the gas and average effective surroundings temperatures on the thermocouple error of each configuration. The models indicate that thermocouples respond differently to changes in effective surroundings temperature in a hot upper layer than in a relatively cooler lower layer of a room fire. In an upper layer, for a given gas temperature, the thermocouple error is relatively insensitive to surroundings temperature. In a lower layer, errors which increase rapidly with surroundings temperature are possible. The most extreme errors occur in a lower layer when the gas tmperature is low and the surroundings temperature is high. Aspirated thermocouples reduce the errors in both the upper and lower layers of a room fire, but do not eliminate them entirely. The present study is intended to provide fire researchers with a methodology for developing working models of thermocouples which are tailored to their own configurations.