Heat transfer characteristics of an impinging premixed annular flame jet

The heat transfer behaviors of an annular jet flame impinging vertically normal to a flat surface were investigated experimentally. The relationship between the flow/flame structure of the annular jet flame and the local heat transfer behavior along the surface was analyzed. Further, the effects of Reynolds number (Re), equivalence ratio () and nozzle-to-plate distance (H) on the local and overall heat flux distributions were examined. The flame has two stable patterns, the 'V' shaped flame under lean conditions and the 'M' shaped flame under rich conditions. The two stable flames have similar heat flux distribution characteristics: (1) local heat flux in the region close to the jet axis is low; (2) peak heat flux occurs at a radial position at small H while at large H it coincides with the jet axis. Comparison of impinging annular jet and round jet flames under identical fuel/air flow rates shows that at low H, the annular jet flame has higher heat fluxes in the region near to the jet axis because a cool core is present in the round jet flame. Compared to the round jet flame, the annular jet flame achieves the highest heat transfer rate at smaller H and the maximum value is slightly lower, indicating that the annular jet flame is favorable for uniform heating.