Vortexing during draining through twin drain ports in a cylindrical tank

In this paper, the results of an investigation on the formation of vortex air core commonly known as ‘vortexing’ occurring during draining of a liquid (water) column from a cylindrical tank through two eccentric ports (diameters d1 and d2) simultaneously, are presented and discussed; d1 is fixed whereas d2 is varied. Before draining, the liquid column is induced with a rotation (N rpm) using a motorized stirrer where rotational speed can be controlled. Drain port eccentricities are equal (e). During draining, as the liquid level reaches certain height called ‘critical height’ (Hc), a vortex air core develops and extends down touching the drain port. Results show that as N is increased, Hc is increased. At N=200rpm (highest speed tested), at the smallest eccentricity, lowest critical height occurs for the largest value of d2 (equal to d1). At larger eccentricities, a significantly different highly non-linear variation of Hc w.r.t N is seen with vortexing nearly suppressed for the case with drain port sizes equal. In many engineering systems, occurrence of ‘vortexing’ is reported and hence, the present study carries significant practical relevance. All the studies reported so far were with single drain port and hence, the present study is first of its kind.