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Show The differences in swirl and flow reversal between adjacent burners can also be phenomenal. When a combustion system is being designed for low excess air and minimum pollutant emissions a variation of air flows of the magnitude above rapidly makes the whole system a joke. Once the air flow mapping is complete the model is then connected to a purpose built water circulation system Fig. 3. The system comprises of a storage/recovery vessel, de-aeration facility, pumps, flow meters, surge tanks and control valves. De-mineralised water containing polystyrene beads as a tracer are then pumped through the model. Polystyrene is utilised due to its density similarity with water and the size of bead is critical. Too small a bead and many operating problems are experienced with the pump, flow meters and control valves. Too large a bead results in the beads picking up their own momentum and their not remaining in the flow lines of the fluid being utilised. The use of a black-out room plus high intensity collimated lights (quartz halogen) allows discrete sections of the model to be illuminated and the flow regime in each section to be studied in detail Fig. 7 I and 7 F. Photographic and/or video recordings are taken of the model as deemed necessary. Dye or air bubble injection are sometimes utilised to enhance the photographic results as required Fig. 5. The water flow technique allows a very positive visual display of the flow regimes, and immediately illustrate areas of stagnation, flow reversal and system pulsing. - 9 - |