Heat transfer characteristics of impinging methane diffusion and partially premixed flames

Abstract

Flame jet impingement heat transfer is a well-established technique for obtaining high heat transfer rates in many domestic and industrial applications. The flame structure and the heat transfer characteristics of the impinging methane diffusion flame and partially premixed flame are experimentally investigated. The heat transfer characteristics of the impinging methane flame are determined using the minimization technique wherein the target surface is impinged by a methane flame from the bottom and is simultaneously cooled from the top by air jets of different Reynolds number. At steady state, one-dimensional energy balance across the impingement surface provides an over-determined system of equations which when solved using the minimization technique give the heat transfer coefficient of the flame jet, the reference temperature and the emissivity of the gas/flame beneath the impingement surface.The stagnation point heat transfer coefficient and reference temperature are found to be maximum for the case of flame just touching the impingement surface. The radial variation of the non-dimensional heat transfer coefficient and reference temperature is found to have a Gaussian profile. For low H/d’s where the flame is impinging the target surface, the temperature at the stagnation zone is lower than in the radial position as the hot jet turns in the radial direction and impinges at a distance slightly away from the stagnation region.The separation of heat transfer components indicates that the heat transfer is convective dominant with radiation accounting to 10% of the total incident heat flux in the case of methane diffusion flame and 3.5% in the case of partially premixed flame. Re-radiation becomes a significant component of heat transfer, accounting to 25–30% of the incident heat flux, due to higher wall temperatures. The present study also investigates the effect of tube burner to plate spacing.