Calculating Volumetric Flow Rate (Q) of Non-Water Liquids

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Discussion Overview

The discussion revolves around calculating the volumetric flow rate (Q) of non-water liquids, specifically addressing the influence of viscosity on flow rate through a hole at the bottom of a tank. Participants explore theoretical and practical aspects of flow rate calculations, particularly in relation to Newtonian fluids and specific scenarios involving viscosity.

Discussion Character

  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant presents the formula Q = V.A and relates it to the velocity of the liquid and the area of the hole, questioning how to account for viscosity in non-water liquids.
  • Another participant suggests that for most oils, unless they are highly viscous, the flow rate can be approximated using Q = AV, indicating that viscosity complicates the calculation of velocity.
  • A participant queries whether viscosity has no effect on flow rate for Newtonian fluids in simple scenarios, expressing skepticism about the lack of relationship.
  • It is noted that while viscosity may not significantly affect flow rate in simple cases, it becomes important in more complex systems involving pipes and fittings, where it contributes to pressure drops.
  • One participant asserts that viscosity will matter, but suggests that for larger holes or lower viscosity fluids, it might be reasonable to neglect viscosity for initial estimates.
  • The original poster emphasizes the need for precision in their calculations for a real-world application, seeking further resources for more accurate methods of accounting for viscosity.

Areas of Agreement / Disagreement

Participants express differing views on the significance of viscosity in determining flow rate, particularly in simple versus complex systems. There is no consensus on the extent to which viscosity should be considered in the calculations for non-water liquids.

Contextual Notes

Participants acknowledge that the calculations may depend on specific conditions such as the size of the hole and the viscosity of the liquid, which could affect the accuracy of flow rate estimates.

Noushka
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Hey, I was wondering how to calculate the volumetric flow rate (Q) of a liquid other than water through a hole at the bottom of a tank.

I know that

Q= V.A

and

1/2.ρ.V^2 = ρ.g.h

Where,

V: Velocity of the liquid coming out of the hole
A: Area of the hole
h: Height of the liquid above the hole in the tank

But how can I calculate Q accounting for the viscosity of the liquid, like oil for instance?

Thanks!
 
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Unless your oil is some thick lubricant or residual distillate, Q = AV works.
Calculating V is the tricky part for fluids with high viscosity.
 
Thanks for the reply SteamKing.

So do you mean that the flow rate is unaffected by the liquid viscosity, as long as we are dealing with Newtonian fluid?
It seems strange that these are not related.
 
Not necessarily. A can with a hole in the bottom is a pretty simple situation. Now, if the fluid were flowing through a piping system with runs of straight pipe combined with valves and other fittings, then viscosity plays a role in determining the pressure drop in the piping system. Fluids with higher viscosity have a larger pressure drop.
 
So for a simple situation with a hole at the bottom of a can or a tank, viscosity would not play in the volumetric flow rate out of the hole ?

I am trying to estimate the flow rate of oil with a very low density, out of a pierced tank.
 
Viscosity will matter, but unless the hole is small or viscosity is large, you can probably get an OK estimate by neglecting it. Including viscosity is a non-trivial computation, so I'd start by ignoring it and seeing how close your result is.
 
Ok thank you.

I will need to have it as precise as possible though, this is for a real case not a homework exercise.

Would you know where I could find information on the way to calculate it (even if if it s not trivial)?
 

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