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The objective of the research work is to predict the volume of fluid drained from a cylindrical vessel without entrapping air through the drainpipe, and hence predict the location of the free surface of the liquid in the vessel.

A two‐dimensional axi‐symmetric numerical simulation has been made using a finite volume method that employs unstructured grids with cell‐wise local refinement and an interface capturing scheme to predict the shape of the free surface of water in a cylindrical vessel, thus simulating the entrapment of air in the drainpipe connected to the vessel.

A drain cover was placed on top of the drainpipe to delay the entry of air into the drainpipe. It was found that an increase in the diameter of the drain cover increases the amount of liquid to be drained out before the air could enter into the drainpipe. It was found that air enters the drainpipe at a particular height of the liquid in the vessel. However, when an initial rotational velocity was imparted to the liquid, the height of liquid when air enters the drainpipe depends on the initial bath height. As the initial bath height increases, air enters the drainpipe at a progressively higher bath height. But surprisingly when the drain cover is put in place the initial bath height, again, has no effect on the height of the liquid (in the vessel).

The outcome of the present research work has direct implications for steel making. If the drainpipe can be connected to the ladle the way it has been discussed in this paper then more steel can be drained before stopping the drainage in order to avoid air or slag entrapment.

The idea of putting a drain cover, using a larger diameter drainpipe and making the drainpipe connection to the vessel different so as to delay the appearance of air at the drainpipe is a new finding and the idea can be used by steel makers.

Two‐dimensional numerical simulations have been performed using a finite volume method that employs unstructured grids with cell‐wise local refinement and an interface‐capturing scheme to predict the shape of the free surface, thus simulating the surface wave that is created in a mold due to the flow from the submerged entry nozzle (SEN). Simulation has been done for 1:6.25 aspect ratio of the mold having a height of 2 m with parallel rectangular ports as well as 15° upward and downward ports. It has been found that for low inlet velocity of the SEN (<1 m/s) the maximum wave amplitude of the surface remains below 12 mm and no outside air is entrapped by the wave to form a bubble. However, for high inlet velocity (2 m/s or more) there is considerable fluctuations on the free surface and the maximum wave amplitude shoot up beyond 70 mm at the start up and slowly falls to about 30 mm entrapping air bubbles from the surroundings. The movement of the air bubble within the mold and its rise to the free surface where it subsequently collapses has been captured well in the numerical simulation. The overall shape of the free surface matches well, excepting the initial transience, with that of the experimentally observed free surface, although the free surface never attains a perfect steady shape neither in the experiment nor in the numerical simulation due to its continuous oscillation and breaking.