Influence of Burner Geometry on Heat Transfer Characteristics of Methane/Air Flame Impinging on Flat Surface

Abstract

An experimental study has been conducted to find the heat transfer characteristics of methane/air flames impinging normally to a flat surface using different burner geometries. The burners used were of nozzle, tube, and orifice type each with a diameter of 10 mm. Due to different exit velocity profiles, the flame structures were different in each case. Because of nearly flat velocity profile, the flame spread was more in case of orifice and nozzle burners as compared to tube burner. Effects of varying the value of Reynolds number (600-2500), equivalence ratio (0.8-1.5) and dimensionless separation distance (0.7-8) on heat transfer characteristics on the flat plate have been investigated for the tube burner. Different flame shapes were observed for different impingement conditions. It has been observed that the heat transfer characteristics were intimately related to flame shapes. Heat transfer characteristics were discussed for the cases when the flame inner reaction cone was far away, just touched, and was intercepted by the plate. Negative heat fluxes at the stagnation point were observed when the inner reaction cone was intercepted by the plate due to impingement of cool un-burnt mixture directly on the surface. Different heat transfer characteristics were observed for different burner geometries with similar operating conditions. In case of tube burner, the maximum heat flux is around the stagnation point and decay is faster in the radial direction. In case of nozzle and orifice burner, the heat transfer distribution is more uniform over the surface.

Heat transfer distribution for three interacting methane–air premixed impinging flame jets

“…Studies on numerical investigation are reported in the work of Conolly and Davies [7], Som et al [8], Chander and Ray [9] and Remie et al [6]. Different burner geometries (employing single and multiple jets) have been used, the inverse diffusion flame (IDF) burners have been employed by Dong et al [10][11][12][13][14] and burners with induced swirl by Huang et al [15], Chander and Ray [16,17] and Singh et al [18]. Following conclusions are drawn from the literature.…”

“…The tube burner when compared with the orifice and nozzle has the maximum heat flux and surface temperature near the stagnation region, for the nozzle and orifice burners it is shifted away from the stagnation point [17]. The reason attributed to this is the velocity profile of the unburnt mixture exiting from these burners is different.…”

Heat transfer characteristics of three interacting methane/air flame jets impinging on a flat surface

“…The non-equilibrium nature of the flow in this region also contributes to high heat flux values. Close to the high temperature reaction zone, large concentration of active species such as atoms and free radicals exist which augment convective heat transfer rates by diffusion and exothermic recombination in the boundary layer surrounding the heat receiving body [31,32]. Fig.…”

“…It has been seen that the heat flux distribution on the impingement surface is dependent upon the impinging flame shapes [15,16,[27][28][29][30][31]. All the flames were laminar (Re = 800) and appeared to be conical in shape with blue inner reaction zone and light blue outer layer.…”

“…There was impingement of cool fuel/air mixture directly on the surface around the stagnation points of individual jets. This resulted in very low heat flux at all three stagnation points of the impinging flames [15,16,[27][28][29][30][31]. Fig.…”