Abstract
Two phase flow experiments with different superficial velocities of gas
and water were performed in a vertical upward isothermal cocurrent
air-water flow column with conditions ranging from bubbly flow, with very
low void fraction, to transition flow with some cap and slug bubbles and
void fractions around 25%. The superficial velocities of the liquid and
the gas phases were varied from 0.5 to 3 m/s and from 0 to 0.6 m/s,
respectively. Also to check the effect of changing the surface tension on
the previous experiments small amounts of 1-butanol were added to the
water. These amounts range from 9 to 75 ppm and change the surface
tension. This study is interesting because in real cases the surface
tension of the water diminishes with temperature, and with this kind of
experiments we can study indirectly the effect of changing the temperature
on the void fraction distribution. The following axial and radial
distributions were measured in all these experiments: void fraction,
interfacial area concentration, interfacial velocity, Sauter mean diameter
and turbulence intensity. The range of values of the gas superficial
velocities in these experiments covered the range from bubbly flow to the
transition to cap/slug flow. Also with transition flow conditions we
distinguish two groups of bubbles in the experiments, the small spherical
bubbles and the cap/slug bubbles. Special interest was devoted to the
transition region from bubbly to cap/slug flow; the goal was to understand
the physical phenomena that take place during this transition A set of
numerical simulations of some of these experiments for bubbly flow
conditions has been performed by coupling a Lagrangian code, that tracks
the three dimensional motion of the individual bubbles in cylindrical
coordinates inside the field of the carrier liquid, to an Eulerian model
that computes the magnitudes of continuous phase and to a 3D random walk
model that takes on account the fluctuation in the velocity field of the
carrier fluid that are seen by the bubbles due to turbulence fluctuations.
Also we have included in the model the deformation that suffers the bubble
when it touches the wall and it is compressed by the forces that pushes it
toward the wall, provoking that the bubble rebound like a ball.
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