Calculation of the suction power of a venturi?

[Christophe]

Hello,

I would like to estimate the suction power of a venturi (air or water or any fluid or gas of known density and viscosity), so I would have to estimate the pressure and flow to get power. I'm talking about the "aspiration" part of course.

All this obviously correlates with the flow rate of the "primary" source (the flow which passes through the venturi) and the dimensions of the venturi.

We talked a lot about venturi on these forums, so if anyone has some ready-made formulas, I'm interested.

Thank you friends!

[chatelot16]

is this really the power you want?

what is easy to calculate is depression! there is a simple formula to calculate the depression in a venturi, with the speed in the narrowest part ... or with the flow and the passage section

so when the venturi is used as a measuring device, it's simple ... but when the venturi is used as a vacuum cleaner and you want a certain power, so power = depression x flow rate is more complicated because all the details of venturi have an influence on the flow it can suck

[Christophe]

Yes I would like the power: with the vacuum (+ suction section) we get a flow ...
And with a flow + (of) pressure we have a power.

So having depression will give power ... indirectly

No?

[sen-no-sen]

What do you mean by power?
Do you want to know the speed difference between section 1 (pipe) and 2 (venturi)?

[Christophe]

I would like to know the suction power that a venturi is capable of doing ... obviously related to the speed of the fluid passing through the venturi ... and to the "tapping" section ...

[chatelot16]

the simple formula gives the vacuum at zero flow, is useful when the venturi is just a measuring instrument ... but when the venturi must make power there is no simple formula ... as soon as the venturi sucks a significant flow the depression decreases and the output is often poor

I often use venturi but I have no means of calculation: my only way is to try

conclusion: when the conditions allow to use a centrifugal or helical fan directly it is the preferable solution ... I use the venturi only when I cannot do otherwise, for example to ventilate an oven at high temperature that none fan would not support: ventilation by venturi works and it doesn't matter if the energy efficiency is not good since it is the only solution

other special case: ventilation in an incubator: a fan may cause vibrations harmful to the eggs, ventilation by venturi is better to avoid vibrations and it does not matter if the performance is poor since the power is low

[sen-no-sen]

My courses in fluid mechanics are distant but from memory to get the speed in section (2) of the venturi you have to multiply the speed in section 1 by the area of ​​section1 divide by the area of ​​section2 ...
Basically the speed of the fluid increases in proportion to the degrees of shrinking of the tube, taking into account a perfect and incompressible fluid of course.

[Christophe]

I often use venturi but I have no means of calculation: my only way is to try

Uh? Are you sure about that?

Venturi has been used for over 100 years in aeronautics! It would surprise me that this was done without precise equation ...

And given the speeds in aviation, a venturi, even if it is "of measure" must make power (even if it is only a few watts at 800 km / h ...)

[chatelot16]

when the venturi is used to measure a flow it makes a vacuum with zero flow in the pressure gauge which measures ... therefore zero power!

when the venturi is used as a vacuum cleaner to make power it is more complicated ... when I say that I have no way to calculate it that does not mean that there is no way to calculate it but just that I don't have them

there is a multitude of venturi, so not to search in a vacuum it would be better to describe the venturi you need, there might be something calculable ... or measurable

[Christophe]

Obviously the power is zero ... but there is a potential for power (I meant): because the depression must be far from negligible at 800 km / h. After obviously the instruments are dimensioned, at the level of the probe for the measurement and not to create a power ...

Here is an example on Cesna: https://fr.wikipedia.org/wiki/Tube_de_Venturi

Not to be confused with pitot probes which only use dynamic pressure.

Ok for the calculations, bin let's look together then ...

For the idea, it is only theoretical: I would like to know the potential of hydraulic power of a venturi ...

In Chemistry class I remember glass venturis that we put on the taps: the suction was far from being negligible while the water flow remained "reasonable" (tap not fully open) ... obviously it still cost tens of liters of drinking water for each experiment.