The effect of curvature ratio on flow structure and fluids mixing in 90o bent square duct

Abstract EN

Many mechanical and chemical problems rely mainly on the mixing characteristics of a dispersed liquid and the carrier gas which is strongly affected by the rates of mass and heat exchanged.

The secondary flow generated by the centrifugal forces accompany a substantial change in flow direction leads to the presence of counter rotating vortices.

The study investigates the effect of curvature ratio on the flow structure and turbulence intensity during a liquid-gas mixing process prior to a bent duct.The study employs the experimental Particle Image Velocimetry technique (PIV) in purpose tracking the secondary flow structure when the water-air mixture travelling through a bent duct.

The curvature ratios were taken to be (0.25, 0.5, 0.75) at average velocities of 2.5 and 5m/s for air flowing through a square duct.

The PIV images illustrate the appearance of a Pair of rotating Dean vortices (four-cell pattern) generated for all curvature ratios with the vortices near the inner side of the bend moved outward while decreasing the curvature ratio as a result of centrifugal effect and flow separation.

The design and the configuration of the water nozzles matrix is decided according to the numerical simulation using ANSYS FLUENT 19.R1, with RNG-k-ε turbulent model.

The numerical analysis showed that the swirl intensity has little effect on mixing due to changing Reynolds number and was more influenced by the changing of the curvature ratio.

The phenomenal comparison between experimental and numerical results showed good agreement as the maximum deviation recorded is about (7.1%).