F. A. Hamad

Numerical study to invistigate the effect of inlet gas velocity and Reynolds number on bubble formation in a viscous liquid

Bubble formation dynamics has great value in mineral recovery and the oil industry. In this paper, a single bubble formation process through an orifice in a rectangle domain is modelled to study the bubble formation characteristics using the volume of fluid (VOF) with the continuum surface force (CSF) method. The effect of gas inlet velocities, Ug ~ 0.1 - 0.3 m/s on bubble formation stages (i.e., expansion, elongation and pinch off), bubble contact angle, dynamics and static pressure, bubble departure diameter etc. was investigated through an orifice diameter of 1 mm. The method was also used to study the effect of Reynolds number, Reμ ~ 1.32 - 120 on bubble formation when all other parameters were kept constant. It is found that a high inlet gas velocity accelerated the reducing of the bubble contact angle from an obtuse angle to an acute angle and the faster development of hemispherical shape of the bubble. It is also found that an increasing of Reynolds number caused speeding up of the bubble pinch-off and formed a smaller bubble neck height due to stronger vortex ring around the bubble neck.

Effect of impeller type and rotational speed on flow behavior in fully baffled mixing tank

1. Mech. Eng. Dept, College of Engineering, al-Mustansiriya University, Baghdad, Iraq. 2. Mech. Eng. Dept, College of Engineering, al-Mustansiriya University, Baghdad, Iraq. 3. School of Science & Engineering, Teesside University, Middlesbrough, TS1 3BA, UK. ...................................................................................................................... Manuscript Info Abstract ......................... ........................................................................ Manuscript History

Flow structure and cooling behavior of air impingement on a target plate

An experimental data of flow field, pressure coefficient and heat transfer of a jet impinging normally on a flat target plate are presented. The measurements of temperatures and static pressures were carried out for flow from three orifices of 5, 10 and 20 mm diameter for orifice-to-target plate distances of 5, 10, 25, 50, 70, 100 and 120 mm from the orifice exit. The axial development of flow structure of the jet from the orifice was investigated by measuring the radial jet velocity distributions at the same axial distances used to measure heat transfer and static pressure. The results show that pressure coefficients distributions on the target plate are similar to the velocity distributions in the impinging jet which indicates the strong relationship between the two parameters. The pressure coefficients from large orifice diameter are higher than the values from the small orifice diameter for same orifice-to-target plate distance. The results also show a nonlinear increase of heat transfer rate with orifice size and the ratio of axial distance to orifice diameter (X/d). The nonlinear behaviour may be attributed to the complex nature of flow structure at the stagnation region. The high velocity gradients at the stagnation zone leads to higher turbulence and comparatively higher values of heat transfer rates for large orifice diameter.