Draining of liquids through cylindrical tanks is very common phenomena. An interesting but undesirable Aircore is generated during draining process. Therefore understanding of air core formation and its growth is of quite interest in literature. In present study, water draining through cylindrical tanks is studied by experimental techniques. Rotational Froude number is varied based on different initial heights of water in the cylinder. Spatial and temporal variation of critical height and critical time against experiments performed is reported in paper. From comparison of critical height ratio against Froude numbers under consideration, it is found that air core generates slower for lower Froude numbers. Therefore, for higher initial heights of liquid column in the tank, the Aircore generates later as compared to lower initial liquid height case, and this seems to be the reason for the same drain time for all the initial water heights being used in the study. In order to validate the concept, further experiments are performed without initial swirl of tank. Thus causing no Aircore to generate during draining. It is found that with decreasing height the drain time decreases. This validate the concept that early Aircore generation was the major reason behind same drain times with different volumes of water in the cylinder.
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