Heat Flux Measurements: Experiments and Modelling
Robbins A. P. and Collier P. C. R. 2009.
BRANZ Study Report 206
BRANZ Ltd, Judgeford, New Zealand
Plate thermometers for estimating incident radiative flux were investigated using a range of experiments: cone calorimeter tests, furniture calorimeter tests using a burner or a mattress as the heat source, and ISO room experiments also using a burner or a mattress as the heat source. A series of experiments in the ISO room were also performed with the door of the ISO room sealed off. The results from these experiments and the subsequent analysis are summarised in this report. Overall reasonable agreement was found between Gardon gauge results and the estimates of incident radiative heat flux for steady sources of heat once the results of each type of instrument reached a quasi steady state or when the heat source was increased relatively slowly compared to a distinct stepped increase. When considering the use of plate thermometers for non-steady state heat sources, care must be applied when analysing and applying the results. For non-steady state heat sources, it is recommended that particular aspects of the theory used in the calculation of the estimated incident radiative heat flux be considered or an alternative approach be developed. Such aspects include: the parameters affecting the response time of the plate thermometer to a stepped change in heat source; the different errors associated with the estimates based on plate thermometer temperatures for the initial rise and then (when or if a quasi steady state value is reached) effective convective and conductive coefficients for different orientations and local conditions; and observed oscillatory behaviour of the recorded temperature data and subsequent incident radiation estimates. This is discussed in detail in this report. Experimental results were compared to Computational Fluid Dynamics (CFD) using the Fire Dynamics Simulator (FDS) model predictions for an example ISO room test. The results showed reasonable agreement for the incident radiative heat flux.
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