Single Bubble Behavior in Newtonian and Non-Newtonian Liquids
Sprache des Vortragstitels:
Jahrestreffen der ProcessNet-Fachgruppen Computational Fluid Dynamics und Mehrphasenströmungen
Sprache des Tagungstitel:
Comparing the gases, CO2 and air bubbles showed nearly identical trajectories and velocity at small bubble sizes there the form drag is insignificant. By increasing the bubble size, the differences between the velocity of them become more significant so that the differences between the velocity of large CO2 and air bubbles (d ? 6 mm) become clearly visible there the the form drag plays a major role and brings about a noticeable change in drag coefficient. The trajectories instead are still identical.
In water and low concentrations of CMC (up to 0.50%), small and large bubbles (d ? 1.5 mm, d ? 6 mm) move in a rectilinear path, and the terminal velocity increases by increasing the diameter. On the other hand, bubbles with medium sizes tend to move in a zig-zag path in the same liquids. This area was called the ?reverse area? because the terminal velocity of bubbles decreases by increasing the diameter. The onset of the reverse area occurs at the Weber number equal to 3.1, that is in great agreement with literature indicating that in systems with low Morton number (Mo < 107), bubbles start to meander at critical weber number equal to 3.18 (Brenner, 1994). An interesting phenomenon that was observed in the mentioned liquids is the shape fluctuation of some bubbles (5.5 mm ? d ? 6.5 mm). The shape of these bubbles fluctuates between a hemisphere and a disc continuously that cause the bubble velocity to fluctuate between a maximum and a minimum point and not to reach terminal velocity at all. These bubbles alter the liquid field of velocity violently, making heat and mass transfer more efficient inside the system. In kerosene and high concentrations of CMC (higher than 0.50%), bubbles are more spherical and tend to move in a rectilinear path, and the terminal velocity increases by increasing the diameter for all sizes of bubbles. In fact, in these liquids, no ?reverse areas? were observed.