Calculation of flow and mixing properties in a two-dimensional dilution tunnel
by Sunil Katragadda, Reda Bata, Michael McCawley
International Journal of Computer Applications in Technology (IJCAT), Vol. 11, No. 3/4/5, 1998

Abstract: A computational fluid dynamic analysis was performed to study flow characteristics and mixing performance in a full-flow dilution tunnel. The tunnel, 0.457 m diameter and 4.878 m (16 ft) long, consists of tracer (propane gas) and dilution air introduced as co-current flow, with turbulent mixing enhanced by an orifice. The velocity and concentration profiles of a propane gas tracer were predicted at the tunnel sampling zone for 0.18, 0.47, and 0.94 m3 s−1 volumetric flow rates. Due to limited access of the mixing zone, the characterisation of the flow field under different flow conditions were impractical. A fluid dynamic code, FLUENT, which uses the primitive variable approach, solves the full equations of motion, energy and species mass fraction, was employed to simulate the velocity and species concentration fields. The flow characteristics and the mixing phenomena of the tunnel equipped with one hole, and three hole orifices were studied. For the same tunnel geometry, the mean residence-time of gas from the entrance to the sampling zone location were predicted. The mean residence-time and mixing parameter (p) predictions were in agreement with the experimental measurements. The results indicate that the gas mean residence-time in the tunnel was larger for a lower flow rate. Also, the predicted mixing parameter was mainly dependent on the Peclet number, Pe (i.e. the ratio of convection to dispersion), and the orifice configuration. The results of this study show how a computational fluid dynamic analysis of the dilution tunnel could aid in optimising the tunnel size, and obtain its fluid flow and mixing characteristics, with less cost and effort.

Online publication date: Sun, 01-Jun-2014

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