دراسة محاكاة للسلوك الهيدروديناميكي لفقاعات الهواء المتدفقة خلال عمود المفاعل لزيت الوقود الثقيل المتبقي

Simulation Study for Hydrodynamic Behaviour of Air Bubbles Flowing Through a Reactor Column of Heavy Fuel Oil Residue

Abstract

Several industrial operations rely on the rise of air bubbles through heavy
fuel oil residue (HFOR), including oil recovery and wastewater treatment.
To increase efficiency and decrease expenses, it is necessary to
understand the characteristics of this process. With the help of COMSOL
Multiphysics, numerically simulate the ascent of a single air bubble via
HFOR. The dimensions of the container used in the simulations are 100
mm in diameter and 200 mm in height, with one and three, and five
nozzles, each one with a diameter (3,5,7) mm, with HFOR temperatures
at (20, 40, 60, 80) °C. For an air bubble ascending through an HFOR
column, the predicted numerical outcomes are compared with two models
for the comparison. As the bubble rose higher, the region with the
greatest number of vortices is located on its side. The remaining vortex is
contained inside the bubble. In addition, since drag decreases the flow, a
lighter fluid usually exhibits a region of strong vortex and low pressure.
Because of the wavy motion, the results reveal that the rising velocity initially
rises and then gradually falls between 0.6 and 0.65 seconds as bubbles coalesce,
according to the data. Finally, it was discovered that the rising bubble behaved
chaotically, shifting its path from the surface to the bottom to generate vortices. The
bubbles split before reaching the surface when the air injection speed increased. The
wavy motion of the air bubbles is due to the high liquid density, which deteriorated
with increased air velocity or raised HFOR temperature. As the air injection velocity
value 0.15 m/s at 20 °C increases to 0.28 m/s at 80 °C at the top of HFOR column, the
drag coefficient values increase significantly 20% for Dn = 3mm and 25% for Dn =
5mm and 30% for Dn =7mm. The study also discovers that liquid height is correlated
inversely with pressure