Experimental and Theoretical Study of High Velocity Multi-Flame Direct Flame Impingement Heating

In recent years, there has been an increased interest in applying the direct flame impingement (DFI) concept in industrial furnaces to enhance the convective heat transfer rates. In some applications, DFI is emerging as an attractive and cost effective alternative to conventional radiant heating. Use of DFI offers several potential advantages over radiant heating such as increased heat fluxes, which reduces processing time, fuel consumption and undesirable scale fonnation (oxidation), and improves product quality. In addition, with multi-flame DFI, the heating can be locally targeted by adjusting the firing rate of the individual flames. Applications for DFI include continuous heating of tubes and strips, and reheating of billets and slabs. In conventional gas fired furnaces used for these processes, the convective heat transfer coefficient is usually less than 50 W/m2 K (9.0 Btu/ft2h-F). With DFI, however, it can be increased to several times this value. During the past 10 years, a number of rapid heating technologies, using different jet impingement approaches, have been investigated. The primary differences between these approaches are in the type of jets used and their makeup: