Modeling a fire whirl generated over a 5-cm-diameter methanol pool fire

We conducted a series of laboratory-scale fire whirl experiments spinning 5-cm-diameter methanol pool fires and observed elongated flame height compared with the pool fire without spin. A simple scaling analysis was conducted to obtain dependency of the axial flame height on the momentum-controlled circulation and the effect of buoyancy. To obtain a specific functional relationship for the parameters obtained by the scaling analysis, we developed an analytical model consisting of coupled species and energy equations and Burgers vortex for circulation generated by a fire whirl. The solution of the coupling equations shows that the average rate of heat transfer from the flame to the fuel surface is a function of the vortex core radius; a smaller vortex core radius provides more heat to the fuel surface enhancing evaporation thereby producing the longer flame height. This new model predicts both flame height and flame shape. The flame height prediction compare favorably with results from the scaling analysis and experiment.

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