Novel flow visualization technology for industrial furnaces

The flow inside furnace chambers influences processes as fuel burn out, NOx formation and build-up of ash deposits. In this study, a new video visualization technology was developed for large-scale flow measurements in high temperature environments. The dedicated experimental equipment mainly consists of several water-cooled stainless-steel probes, needed to inject seeding particles, for the LED light source and to acquire video camera recordings, which are inserted into the furnace through inspection ports. Pressurized air is used on the tip of the probes to avoid dirt and soot, to protect optics and LEDs from the strong thermal radiation and heat, as well as to inject the seeding. The underlying idea is to exploit the fact that flames mainly emit thermal light in the red part of the visible spectrum, and therefore the use of a strong deep blue LED light source can minimize the flame light interference. Small size aluminium oxides particles are employed as seeding material, since they are good reflectors of light and follow the flow accurately. The video camera and the light source are synchronized through a pulse delay generator. The post-processing of the images consists in correcting both their optical and geometrical aberrations before importing them in PIVlab, a particle image velocimetry (PIV) tool created for Matlab. This allows tracking the aluminium oxides clouds as they move in the furnace and, by cross-correlating pairs of consequent images, to obtain their velocity vectors. The experimental results can then be compared with computational fluid dynamics (CFD) simulations of the same area of interest. The described technology will serve to determine the influence of changes in operation conditions on the flue gas and/or ash flow pattern in the furnace chamber. This paper contains the concept validation of the flow visualization technique through well-controlled laboratory experiments, at ambient temperature, in an open wind tunnel.