Analysis of Convective Heat Losses in a Full-scale Compartment Fire Experiment

Abstract

This paper presents a methodology to quantify the convective heat losses in a full-scale compartment fire experiment, and presents an analysis of the key uncertainties in the experimental procedure, with the purpose of reducing uncertainty, and establishing robust error bars to the methodology. Uncertainties in the experimental flow measurements were assessed through a wind tunnel study of the bi-directional probe-transducer assembly at a range of Reynolds numbers. It was shown that at low Reynolds numbers, the probe-transducer assembly gains Reynolds dependence, for which the correction factor can be described as a piecewise function over the voltage of the differential pressure transducer used, with a minimum correction factor of 0.60. Numerical modelling in FDS is used to validate the assumptions driving the proposed methodology, and to provide the upper bound to the methodology. Due to the limited resolution of bi-directional probes in the experiment, the flow profile was mapped using a high resolution of thermocouples positioned near the opening, which allowed for the definition of the thermal interface height within the range (0.51-0.56)H0, which was in proximity to the numerically determined neutral plane height within the range (0.61-0.64)H0. Based on the numerical study and the literature, static inflows are assumed, and thus the convective heat losses through the opening are calculated. Similar to the underpinning work of the Compartment Fire Framework for well-ventilated fires, convective heat losses through the opening are calculated to account for 80% of the input fire. Sensitivity analyses of the hot layer temperatures and the interface height reveal a key dependency of the total convective heat losses to an accurate estimation of the interface height. The work presented herein will be utilised to characterise the fire dynamics of a set of full-scale experiments in order provide an accurate representation of thermal boundary conditions, either to the structure or out of the compartment, into adjacent spaces or windows