Transition from momentum to buoyancy-controlled turbulent jet diffusion flames and flame height relationships

Abstract

Based on dimensional arguments for the physics in turbulent diffusion flames, an analysis is presented for the transition characteristics from momentum-to buoyancy-controlled turbulent jet diffusion flames. This analysis extends previous correlations and investigations on the dynamics of buoyant jet flames and pool fires [ Combust. Flame 70:33–46, (1987)]. A new correlation is derived and compared with experiments for flame heights in turbulent diffusion jet flames ranging from buoyancy-to momentum-dominated cases. The same methodology is used for correlating entrainment rates in turbulent diffusion flames, buoyancy or momentum dominated. The present results have been used to delineate various regimes characteristic of jet diffusion flames such as laminar, turbulent, buoyancy-dominated, momentum-dominated, and lift-off (turbulent jet) flames. Differences and similarities between the present approach and published results are also discussed. A practical contribution is the enhancement of the classical Hottel and Hawthorne laminar-turbulent transition plot by emphasizing that, in most cases, prior to the turbulent momentum regime there exists a considerable turbulent buoyant regime.