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Summary In this study, an experimental rig representing a deep enclosure was designed to be used to validate a CFD‐based fire model in predicting the outcome. The model then can be used for further study to investigate physical phenomenon within a deep enclosure and to develop an engineering fire severity (heat release rate, HRR, vs time vs position [1]) model. Two empirical models (the VU model [1] and Kawagoe model [2]) were used along with Fire Dynamics Simulator (FDS) in designing the experimental rig. For a specific‐sized enclosure, when the HRR was prescribed to the FDS as input from the VU model, it was accurately reproduced, while the HRR from the Kawagoe was used as the input, the FDS calculated much lower value. The experimental rig of that specific size was then built, and various parameters were measured from the tests with liquid fuel fire within this experimental rig. The measured HRR was prescribed into the FDS, and the FDS could reproduce HRR values well. However, the predicted temperature and radiation flux was not as good, especially when the flames were near the opening. This may be due to the tendency of flames over‐projecting outside the opening in FDS simulations.

Summary Water‐mists are emerging as an effective agent for the suppression of fires. However, the mechanisms of suppression are complex and the behaviour of individual water droplets in a smoke layer generated by fires must be quantified. This study investigates the behaviour of individual droplets injected from a nozzle into a hot air environment induced by a room fire. A semi‐empirical model has been developed based on the conservation of mass, momentum and energy to evaluate the heat and mass transfer phenomena in an air‐water droplet system. The model has considered the effect of change of momentum of an evaporating droplet. A forward finite difference approach is applied to solve the governing time dependent ordinary differential equations. The droplets are considered to be ‘lumped mass’ and variable thermo‐physical properties of water and air and the change of Reynolds number of the droplets, due to the change of their diameter and velocity are considered. The effect of high evaporation rate on the mass and heat transfer coefficient and the contribution of radiation emanating by a flame and the surrounding boundary walls are also considered in the model which were not taken into account in the previous studies. Experimental data on terminal velocity and adiabatic saturation temperature are used to validate and verify the model. The validation and verification indicate that the proposed model predicted the terminal velocity within 4% of the experimental data and predicted the saturation temperature within 5% of the adiabatic saturation temperature. This semi‐empirical model is also used as a tool to validate a more comprehensive computational fluid dynamics (CFD) based tool, Fire Dynamics Simulator (FDS). It is found that FDS results agree well with the results of the proposed model. Furthermore, the proposed model can be used to evaluate the temperature, velocity, diameter and other physical properties of a droplet travelling through a layer of hot air. Copyright © 2014 John Wiley & Sons, Ltd.

The physical characteristics of water sprays profoundly influence the efficacy with which fires are extinguished. One of the most important physical characteristics of water sprays is the median diameter of the water droplets. However, this parameter is difficult to measure without resorting to the use of specialised equipment. Furthermore, the distribution of the size of water droplets and their initial velocity are profoundly sensitive to the pressure at the nozzle head. This paper presents a simple technique to determine the median droplet size of a water spray produced by a nozzle. The method required only two experiments to determine the mass flux distribution generated by a nozzle operating at two known pressures. A computational fluid dynamics (CFD) program was then used to estimate the median diameter of the water spray under these conditions. The median droplets generated when the nozzle was operating under a different pressure can be calculated using an established empirical relationship. The approach advocated in this paper is supported by invoking Whewell’s principle of consilience of inductions. This was achieved by observing that the CFD software accurately predicts the mass flux distribution when the new pressure and estimated median diameter of the droplets were used as inputs. This provides independent evidence that the proposed approach has some merit. The findings of this research may contribute to establish a technique in calculating the median diameter of droplets when direct measurement of droplet diameter is not available.