Measurements of Heat and Combustion Products in Reduced-Scale Ventilation-Limited Compartment Fires
Matthew F. Bundy, Anthony P. Hamins, Erik L. Johnsson, Sung C. Kim, Gwon Ko, David B. Lenhert
The present study investigated the flow and heat transfer characteristics of aspirated thermocouples using a simple energy balance model and a 3D CFD model. The calculations quantify the systematic measurement error, providing an estimate of the measurement uncertainty. At the same time, the model provides information on the time to achieve steadystate, which should be carefully considered in terms of the development of an experimental procedure and in the interpretation of the results. Despite the application of additional assumptions and idealizations, calculations using the previously developed algebraic energy balance model generally showed good agreement with the results of the 3D CFD model. The algebraic model can be useful, particularly in parametric studies used to evaluate thermocouple measurement error. Consistent with previous findings, calculations show that use of the double shield aspirated thermocouple can greatly reduce the thermocouple error especially for low gas temperatures. The results, however, can still be biased by hundreds of degrees, depending on the conditions. Figure A8 provides information on the magnitude of the measurement error for a given value of the surrounding temperature. Since the surrounding temperature takes on multiple values and is a complex function of thermocouple location and fire conditions, a representation of the surrounding temperature can be made based on estimated temperature averages. Precise determination of the surrounding temperature is impossible, and engineering judgment is a key component of the uncertainty analysis. 137 The results of the CFD model allow determination of the transient response of the double shield aspirated thermocouple, which is helpful in the interpretation of measurement results and possibly for design of the experiment itself. The calculated time response of the aspirated thermocouples suggests that while the measurements provide an adequate representation of the a
, Hamins, A.
, Johnsson, E.
, Kim, S.
, Ko, G.
and Lenhert, D.
Measurements of Heat and Combustion Products in Reduced-Scale Ventilation-Limited Compartment Fires, Technical Note (NIST TN), National Institute of Standards and Technology, Gaithersburg, MD, [online], https://doi.org/10.6028/nist.tn.1483
(Accessed August 17, 2022)