Heat transfer characteristics of an impinging inverse diffusion flame jet. Part II: Impinging flame structure and impingement heat transfer

This paper is the second part of the experimental study on exploring the feasibility of inverse diffusion flame (IDF) for impingement heating. The structures and heat transfer characteristics of an impinging IDF jet have been studied. Four types of impinging flame structure have been identified and reported. The distributions of the wall static pressure are measured and presented. The influences of the global equivalence ratio (ϕ), the Reynolds number of the air jet (Reair), and the non-dimensional burner-to-plate distance (H/dair), on the flame structure, and the local and averaged heat transfer characteristics, are reported and discussed. The highest heat transfer occurs when the tip of the flame inner reaction zone impinges on the plate. The heat transfer rate from the impinging IDF is found to be higher than that in the premixed flame jet due to the augmented turbulence level originated from the flame neck. This high heat transfer rate, together with its in-born advantage of no danger of flashback and low level of nitrogen oxides emission, demonstrates the blue, dual-structured, triple-layered IDF is a desirable alternative for impingement heating.