Pressure and flow

[keltrem]

Is it possible for a known pressure and diameter of tube that liquid flowrate in litres per sec (for example) can be calculated?

 

If so what data is necessary for calculation and what is the formula?

 

Thanks,

 

Noel

 

[Country Boy]

You would also need to know the viscosity of the fluid.

[keltrem]

If all factors including viscosity, pressure, diameter of tube are known how is flowrate calculated?

[Sriman Dutta]

I think we have to use Hagen-Poiseuille equation.....

[studiot]

I think we have to use Hagen-Poiseuille equation.....

 

 

That would be a good start +1

 

But for 'ordinary' fluids and pipe sizes, not very thick liquids like concrete or very fine pipes like blood capilliaries.

 

Sriman, since you introduced it, you might like to find a link for the OP?

Edited October 2, 2016 by studiot

[keltrem]

What I am trying to find a solution for is this.

 

A production unit to operate at its optimum requires a flow rate within a specific range of +/- 10% of its optimum flow rate (which is known). We want to install a delta pressure valve to to ensure that the unit is only operable within the specified parameters.

 

We need to calculate the minimum and maximum pressure to achieve the desired operational minimum and maximum flow rates. All other information is available to us; flow rate, viscosity, pipe diameter, length of pipe (this is only relevant to the extent within the confines of the pressure valve).

 

I reviewed the Hagen-Poiseuille equation but it seems to me to only calculate pressure loss.

 

Any further guidance would be much appreciated.

[Tim88]

Is it possible for a known pressure and diameter of tube that liquid flowrate in litres per sec (for example) can be calculated?

 

[..]

 

What I am trying to find a solution for is this.

 

A production unit to operate at its optimum requires a flow rate within a specific range of +/- 10% of its optimum flow rate (which is known). We want to install a delta pressure valve to to ensure that the unit is only operable within the specified parameters.

 

We need to calculate the minimum and maximum pressure to achieve the desired operational minimum and maximum flow rates. All other information is available to us; flow rate, viscosity, pipe diameter, length of pipe (this is only relevant to the extent within the confines of the pressure valve).

 

I reviewed the Hagen-Poiseuille equation but it seems to me to only calculate pressure loss.

 

Any further guidance would be much appreciated.

 

The Poisseuile equation tells you flow as function of pressure difference for a circular pipe. In your fist post you say that is what you need to know.

https://en.wikipedia.org/wiki/Hagen%E2%80%93Poiseuille_equation

 

Fill in the flow through the pipe (or the pressure drop over the pipe segment), as well as the other variables, and you obtain the required pressure (or flow).

 

Note: if you require high flow rates, you should verify with the Reynolds number that the Poisseuille equation is the right one to use.

- https://en.wikipedia.org/wiki/Reynolds_number

 

Edited October 2, 2016 by Tim88

[John Cuthber]

Controlling the pressure will only control the flow if the viscosity is constant. Viscosities vary a lot with temperature.

You ought to measure and control the flow directly.

[studiot]

What I am trying to find a solution for is this.

 

A production unit to operate at its optimum requires a flow rate within a specific range of +/- 10% of its optimum flow rate (which is known). We want to install a delta pressure valve to to ensure that the unit is only operable within the specified parameters.

 

We need to calculate the minimum and maximum pressure to achieve the desired operational minimum and maximum flow rates. All other information is available to us; flow rate, viscosity, pipe diameter, length of pipe (this is only relevant to the extent within the confines of the pressure valve).

 

I reviewed the Hagen-Poiseuille equation but it seems to me to only calculate pressure loss.

 

Any further guidance would be much appreciated.

 

So why didn't you say so in the first place?

More importantly you have omitted the most important imformation, which you clearly know.

What is the fluid? what are the throughput rates? What sort of pump are you employing? What is the delivery length?

 

 

This appears not to be a causal shoot the breeze question to while away the hours in a coffee house.

 

This is an attempt to gain commercial information for free, thereby putting someone who has put in years of (study) effort out of a job.

 

Employ a real Engineer for a proper fee.

 

He will ask those questions above and more, and then likely start by studying a Colebrook-White chart or Moody diagram for your installation.

 

Since you did not understand the simplest equation, I would not recommend trying the engineering for yourself.

[keltrem]

Studiot,

 

The purpose of the OP was to ascertain whether or not there is a calculation or formula that provides a relationship between pressure and flow rate. I now know there is. if I wanted a specific answer to our problem I would have noted the liquid and other relevant data. I deliberately did not do this .

 

The engineering development group we are dealing with seem all at sea when trying to resolve this question which has caused undue frustration. Gratuitous advice as above is not helpful either. From the responses on this forum, not yours Studiot, it is now apparent we need to change Consulting Engineers who better understand pressure and flow.

 

To all other posters thank you, it has provided certainty of direction.

[Tim88]

Studiot,

 

The purpose of the OP was to ascertain whether or not there is a calculation or formula that provides a relationship between pressure and flow rate. I now know there is. if I wanted a specific answer to our problem I would have noted the liquid and other relevant data. I deliberately did not do this .

 

The engineering development group we are dealing with seem all at sea when trying to resolve this question which has caused undue frustration. Gratuitous advice as above is not helpful either. From the responses on this forum, not yours Studiot, it is now apparent we need to change Consulting Engineers who better understand pressure and flow.

 

To all other posters thank you, it has provided certainty of direction.

 

OK. As an after thought, it may be useful to clarify that typically the flow resistance of a whole length of pipe should be calculated, between two points at which the pressure can be known or regulated. If you are familiar with electrical circuits, it's similar to calculating the current through a number of resistors in series, between two points of known Voltage.

[keltrem]

Tim88,

 

In a discussion with Hydraulic engineers yesterday we addressed that point. It is not a big issue for us as we require a specific flow rate within a narrow range of tube length plus flowrate can vary within an optimal range giving ample allowance for resistance.

[sethoflagos]

For the record, the Hagen-Poiseuille equation is only applicable to low velocities in small pipes (laminar flow regime). It only crops up (typically) in small chemical dosing systems and the like.

 

Friction loss in the vast majority of process liquid systems is calculated via the Darcy-Weisbach equation (https://en.wikipedia.org/wiki/Darcy%E2%80%93Weisbach_equation) with friction factor f read off a Moody diagram. It simplifies to Hagen-Poiseuille at low Reynolds number.

 

But all this is irrelevant in the context of the OP. The wrong question has been asked, The '....engineering development group we are dealing with seem all at sea' comment tells me a lot about the quality and style of management.

Edited October 7, 2016 by sethoflagos