Convective heat transfer from a partially premixed impinging flame jet. Part II: Time-resolved results

Abstract

This is the second of a two-part paper on heat transfer from an impinging flame jet reporting time-resolved results. Axial and radial profiles of time-resolved local heat fluxes of methane-air jet flames impinging normal to a cooled plate are reported, including the root mean square (RMS), probability distribution function (PDF), and the power spectral density (PSD) of the heat flux fluctuations as a function of equivalence ratio, Reynolds number, and nozzle-plate spacing. The RMS, PDF, and PSD of the heat flux signal from the stagnation point and along the plate revealed correlation of the local heat flux to the flame structure. Impingement heat flux from premixed nozzle-stabilized flames was characterized by small RMS fluctuations and frequency behavior indicating the formation of weak, buoyancy-driven vortex structures at the shear layer between the hot gases surrounding the flame and the ambient air. Conversely, diffusion flames were characterized by much larger RMS fluctuations and PSDÕs indicating the development of much larger vortex structures. Time-resolved heat flux for lifted flames varied according to flame structure and combustion intensity. PSD magnitudes were related to the range of temperatures in the flow; greater temperature ranges produced larger heat flux variations. The contributing frequencies were related to the duration of the heat flux fluctuation; more rapid changes in heat flux produced higher frequency content.

Large eddy simulation of impinging flames: Unsteady ignition and flame propagation

“…CO emissions of both non-premixed and premixed impinging flames were studied experimentally/numerically in [8,9]. Turbulent impinging inverse diffusion flames [10,11,12] and turbulent partially premxied impinging flames [13,14] were investigated where results for different wall-nozzle distances and equivalence ratios were compared. When analyzing impinging flames, it is of great value to measure the flame temperature and flow quantities near the stagnation point.…”

Analysis of the heat transfer of an impinging laminar flame jet

“…Most studies concern the stationary flame impinging on a (flat) surface. Tuttle et al [11,12] however examined the unsteady characteristics of the impingement heat transfer. Lately, research has been performed by Dong et al [13,14] and Kwok et al [15,16] concerning the heat transfer characteristics of single and multiple impinging flame jets and slot and round impinging flame jets.…”

Flame Shapes and Heat Transfer Characteristics of an Impinging Flame Jet

“…Flame jets are also used in breaking under sea rocks, cutting steel plates, concretes and ceramics to dismantle underwater structures. S.G.Tuttle et al [1] studied axial and radial profiles of timeaveraged local heat flux of Methane-air jet flames impinging to a cooled plate by changing the equivalence ratio, Reynolds number and nozzle-plate placing. L.L.Dong et al [2] conducted experiment to study the heat transfer characteristics of a premixed butane/air slot flame jet impinging on a rectangular plate by varying the Reynolds number and nozzle to plate distance.…”