- Author
-
Blevins, L.
- Title
- New Perspective on Thermocouple Behavior in Room Fires. BFRL Fire Research Seminar. VHS Video.
- Coporate
- National Institute of Standards and Technology, Gaithersburg, MD
- Report
-
Video
April 21, 1998
- Keywords
-
room fires
|
thermocouples
|
temperature measurements
|
aspirated thermocouples
- 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 thermcouples were developed and used to study the expected effects of varying the gas and average effective surroundings temperatures on the percent error in measured temperature of each type of thermocouple. The models indicate that thermocouples respond differently in a hot upper layer than they do in a relatively cooler lower layer of a room fire. In an upper layer, for a given gas temperature, the percent error in the temperature is relatively insensitive to surroundings temperature. In a lower layer, much larger errors which increase rapidly with surroundings temperature are possible. The most extreme errors occur in a lower layer when gas temperature is low and surroundings temperature is high. Aspriated thermocouples reduce the magnitude of errors in both the upper and lower layers of a room fire, and they reduce the likelihood that large errors will occur in a lower layer. Using an aspirated thermocouple reduces the error in a measurement, but does not eliminate it entirely. Under certain conditions, the predicted error associated with an ASTM-recommended sigle-shielded aspirated thermocouple probe with the recommended aspiration velocity of 5 m/s is very large. This seminar focuses on the development of working thermocouple models which can be used side-by-side with experiments to determine the potential severity of measurement errors.