liquid pressure and speed

[mir]

Hi.
a fairly simple question of fluid dynamics: I have a circuit equipped with a pressure gauge and pump. the circuit is not closed and the liquid flows into the plant. I don't have any change in altitude.

the pressure gauge reads me 2 bar and the diameter of the tube is ø48.9 sp. 2.0.

Can I just get this data flow?

greetings
♪

 

[MBT]

Let's see if I say after lunch cow. . .
between point 1 (subito after the pump)
and point 2 (to the fluid outlet mouth)
It is worth bernoulli that tells us:

p1/rho + c^2/2 + gz1 = p2/rho + c2^2/2 + gz2
now if the tube is horizontal, z1=z2 that can be eliminated
at the mouth, the pressure is zero (if you talk about relative pressure) then also p2/rho disappears
a moment before the pump the fluid is steady, so c1 is zero and disappears from the equation

remains therefore p1/rho = c2^2/2
of course with consistent units you should get a speed in m/s
knowing the area of the duct, you will have the flow in m3/sec

 

[gerod]

m^3/s if we want to be consistent!!! no sec!!!
We say that, unless the losses, the formula is fine.
I don't understand if the pressure gauge is put before or after the pump. I would put it after not before and therefore change the null terms.

 

[MBT]

m^3/s if we want to be consistent!!! no sec!!!
We say that, unless the losses, the formula is fine.
I don't understand if the pressure gauge is put before or after the pump. I would put it after not before and therefore change the null terms.

If I put it before, I would read zero pressure... :tongue:
so my pressure needed to make the fluid flow out would be unknown and I could not solve the problem.. .

You're consistent... I a little tick in cul@ :biggrin:

 

[gerod]

but then immediately after the pump c1 > 0. If anything before the pump I can have speed!
I'm full of digestion, maybe I'm wrong? ? ?
:

 

[stevie]

Hi.
a fairly simple question of fluid dynamics: I have a circuit equipped with a pressure gauge and pump. the circuit is not closed and the liquid flows into the plant. I don't have any change in altitude.

the pressure gauge reads me 2 bar and the diameter of the tube is ø48.9 sp. 2.0.

Can I just get this data flow?

greetings
♪

negative, to calculate the flow rate you should know the difference in pressure between two sections having different surface (principle on which venturimeters, claws and diaphragms are based)

 

[mir]

negative, to calculate the flow rate you should know the difference in pressure between two sections having different surface (principle on which venturimeters, claws and diaphragms are based)

Yes, I do, too, because if I have a pressure gauge (bottom of the pump) that measures 2 bars and I know the diameter I could have different speeds/ports to check bernoulli.... even the static condition for absurd.... or wrong?

 

[MBT]

negative, to calculate the flow rate you should know the difference in pressure between two sections having different surface (principle on which venturimeters, claws and diaphragms are based)

Um...
what you say is true, but because you look for two points known within a circuit that you do not know anything about.
then insert the diaphragm to have quesit points "notes"
but he knows that the discharge is free, then pressure = 0
and knows the downstream pressure of the pump

 

[MBT]

Yes, I do, too, because if I have a pressure gauge (bottom of the pump) that measures 2 bars and I know the diameter I could have different speeds/ports to check bernoulli.... even the static condition for absurd.... or wrong?

in static condition, absurdly, your pressure at point 2 should be equal to that at point 1

 

[meccanicamg]

the reasoning is the one attached. with due considerations it is possible to obtain the flow value. in reality the flow rate will be lower but quite proportional if you want to use the gauge as a reference index (2 bar = x flow rate, 4 bar x*n flow)

 

[Er Presidente]

the reasoning is the one attached. with due considerations it is possible to obtain the flow value. in reality the flow rate will be lower but quite proportional if you want to use the gauge as a reference index (2 bar = x flow rate, 4 bar x*n flow)

quoto, pitot tube, static and dynamic fluid pressure, the difference is linked to the fluid speed.
knowing the diameter of the pipe, the rest is boring.

 

[mir]

the reasoning is the one attached. with due considerations it is possible to obtain the flow value. in reality the flow rate will be lower but quite proportional if you want to use the gauge as a reference index (2 bar = x flow rate, 4 bar x*n flow)

but "g" is gravity?

 

[mcdue]

but "g" is gravity?

Yes, "g" is the acceleration of gravity.
I also checked myself and the reasoning of mechanicsmg is correct.

 

[riccardot5765]

Sorry, but I say my...

between sections 1 and 2 there is a given dp, the sections are placed at a known distance, the tube I suppose all wet and for simplicity ipotizzo only the losses per friction. being the incomprehensible fluid, as said by mg, there is the consistency of the volumetric flow rates and therefore the average speed to be considered is that of the whole section and not the two average flow rates to the sections.
of the mir tube can know everything, as well as fluid.

said this, shouldn't you use formulas of colebrook, churchill or blasius depending on the range in which you are located? Of course, it would be a calculation not by hand or with different reiterations.

 

[haga78]

I try to say my mouth.

If you have the pressure gauge on the pump's output at a close distance to the pump and if you have the pump's characteristic curve (available from the manufacturer's site/catalogue) you can read the flow rate on the characteristic curve.

 

[paulpaul]

Hi.
a fairly simple question of fluid dynamics: I have a circuit equipped with a pressure gauge and pump. the circuit is not closed and the liquid flows into the plant. I don't have any change in altitude.

the pressure gauge reads me 2 bar and the diameter of the tube is ø48.9 sp. 2.0.

Can I just get this data flow?

greetings
♪

Haga 78 is right. valley-mount pressure difference (mounted pressures close to the flanges of the pump), divide by density and by acceleration of gravity to find the prevalence in meters, then enter the pump curve and revenues the flow.

if you do not have the curve impose a problem of energy conservation considering load losses in the tube: However, you must know the roughness of the tube and its length, in addition to the singularities that may occur (curves, etc.), and the problem is iterative, in the sense that the load losses depend on the flow and the flow depends on the load losses! :smile:

the extra data you need if you want to make an account of this type (I can do it) are:
1. water temperature (to calculate viscosity)
2. Roughness tube (to determine relative roughness) or at least material
3. pipe length ( directly affects load losses)
4. possible singularities (curves, shrinkages, etc.)

there are cmq network of free programs that allow you to solve simple problems of this type.