Temperature Uncertainties for Bare-Bead and Aspirated Thermocouple Measurements in Fire Environments

Abstract

Two common approaches for correcting thermocouple readings for radiative heat transfer are aspirated thermocouples and the use of multiple bare-bead thermocouples with varying diameters. In order to characterize the effectiveness of these approaches, two types of aspirated thermocouples and combinations of bare-bead thermocouples with different diameters were used to record temperatures at multiple locations during idealized enclosure fires, and the results were compared with measurements using typical bare-bead thermocouples. The largest uncertainties were found for thermocouples located in relatively cool regions subject to high radiative fluxes. The aspirated thermocouples measured significantly lower temperatures in the cool regions than the bare-bead thermocouples, but the errors were only reduced by 8090%. A simple model for heat transfer processes in bare-bead and aspirated thermocouples successfully predicts the experimental trends. The multiple bare-bead thermocouples could not be used for temperature correction because significant temperature fluctuations were present with time scales comparable to the response times of the thermocouples.

Evaluation of the ability of fire dynamic simulator to simulate positive pressure ventilation in the laboratory and practical scenarios

“…Again some differences were displayed in the gas temperatures due to radiative effects but that has been documented in other experiments as well [13]. …”

Assessment of crown fire initiation and spread models in Mediterranean conifer forests by using data from field and laboratory experiments

“…Although the limitations of the thermocouples to reflect the true values of temperature in the flaming area are well known (e.g. Pitts et al, 2002;Shannon & Butler, 2003;Bova & Dickinson, 2008), the errors when fine thermocouples are used can be considered as to relatively be minor for peaks temperatures (Butler et al, 2004b). Still, in our study, temperature records were primary used to determine fire spread in the full-scale experiment and the distance between fire front and crown to initiate a passive crown fire in the small-scale experiment.…”

Radiation-corrective gas temperature measurement in a circular channel

“…All the heat transfer coefficient increase with the gas temperature. In the high temperature region, the convective and radiation heat transfer coefficients on the sheath tube are large enough to neglect the conduction effect as the energy balance of equation (1). After 42000 sec, the dust from the heaters blocked the micro flow channels of the PCHE, so the mass flow rate was suddenly decreased.…”

“…The radiation absorption effect is negligible in nitrogen, because the nonpolar symmetrical molecular structure of nitrogen results in little absorption of the thermal radiation except ultraviolet region. When it was assumed that the RRE corrected temperature was a true gas temperature, the effective radiation surroundings temperature could not be calculated from equation (1). It resulted from the overestimated radiation bias effect by the conduction heat loss in the sheath tubes.…”

“…When a thermocouple is placed in a gas-flow stream, the measured temperature has two bias sources including the thermal radiation [1] between the sheath tube of the thermocouple between the tube wall and the conduction [2] through the sheath tube as shown in Figure 1.…”