Heat transfer characteristics of an array of impinging pre-mixed slot flame jets

An experimental study was carried out to investigate the shape and the heat transfer characteristics of an array of three laminar pre-mixed butane/air slot flame jets impinging upwards normally on a horizontal water-cooled flat plate. The effects of jet-to-jet spacing and nozzle-to-plate distance were examined at the Reynolds number (Re) of 1000 and the equivalence ratio (ϕ) of unity. Comparisons of the heat transfer characteristics between single and multiple slot flame jets, as well as multiple slot and round jets, were made. The between-jet interference decreased with increasing jet-to-jet spacing (s/de) and nozzle-to-plate distance (H/de). Strong interference was obtained at s/de = 1 and H/de = 2, at which the central jet was suppressed while the side jets were deflected towards their free sides. In addition, there was no minimum heat flux found in the inter-jet interacting zone, instead, a peak heat flux was obtained. Thermal performance was reduced when H/de became smaller than the length of the conical luminous reaction zone of the flame. A maximum average heat flux occurred at the moderate jet-to-jet spacing of s/de = 2.5 at Re = 1000, ϕ = 1 and H/de = 2. The resultant heat flux distribution of the central jet of a multiple slot jets system was higher than that of a single slot jet when the jet-to-jet spacing was small, but this advantage in thermal performance diminished when the jet-to-jet spacing was increased. Besides, the area-averaged heat flux of the multiple slot flame jets was higher than that of the multiple round flame jets arranged at the same geometric configuration.