I need to determine the size of the tube having the flow rate of the liquid (water) which is 5 ml/min and assuming the diameter of the tube is 4mm. How can i determine the size of the tube that takes approx one minute for 5ml water to flow along the tube?
If the flow rate is 5ml/min, and you want to know how long a tube it will take 1 min to pass through, you’re effectively asking how long a tube contains 5ml.
Volume of a cylinder is $\pi*r^2*h$.
5ml = 5000mm^3.
Pi*r^2 = Pi*2mm^2 = 4pi mm^2
Your length therefore is 5000/4pi or around 400mm.