Thank you for your prompt response sir.
Yes volume in flow domain can also be used for this purpose but the problem is i am dealing with a 2D geometry (like a computer disk). We can calculate the area of a sphere (V=1.33*3.14*r3) but cannot calculate the volume of a circle as my geometry is 2D. Therefore, i cannot use volume of liquid for liquid holdup calculation. For L.H i need area of liquid instead.