How does a faucet use the Venturi principle

[TheWonderer1]

I've noticed that a slight opening of the faucet releases less water which makes sense intuitively but I don't notice an increase in velocity. Since a slight opening in the stopper would be a convergence in cross sectional area. Am I missing something? I read about resistance affect but still thought I would ask the question.

 

[FactChecker]

Good question. But remember that the velocity at the spigot outlet should be compared to the velocity in the supply pipe, which IS much slower. It should not be compared to the velocity of some other valve setting, where all velocities are higher or lower.

 

[TheWonderer1]

Good question. But remember that the velocity at the spigot outlet should be compared to the velocity in the supply pipe, which IS much slower. It should not be compared to the velocity of some other valve setting, where all velocities are higher or lower.

So I guess it's like I suspected? If the supply pipe is much slower than the velocity at the spigot outlet? I would just be interested bc I'm trying to learn more about fluid dynamics.

 

[russ_watters]

I've noticed that a slight opening of the faucet releases less water which makes sense intuitively but I don't notice an increase in velocity. Since a slight opening in the stopper would be a convergence in cross sectional area. Am I missing something?

WHERE is the velocity higher in a Venturi tube?

 

[FactChecker]

So I guess it's like I suspected? If the supply pipe is much slower than the velocity at the spigot outlet? I would just be interested bc I'm trying to learn more about fluid dynamics.

I should have said the velocity within the valve restriction. Once the water gets beyond that and into the larger spigot pipe, it will slow down again.

 

[TheWonderer1]

WHERE is the velocity higher in a Venturi tube?

At the restriction, I believe at the vena contracta to be exact is where it has the least diameter and max velocity. I see that I was over thinking it.

 

[russ_watters]

At the restriction, I believe at the vena contracta to be exact is where it has the least diameter and max velocity. I see that I was over thinking it.

Right, so in a faucet, the opening is full size and the restriction is at the valve...which you can't see, but might be able to hear.

 

[Nidum]

In most domestic water supplies the pressure in the primary mains does not usually vary much in the short term .

Pressure may vary more within a connected property depending on how much water is being used but assume that your faucet is the only one that is turned on at the time of your experiment .

So you effectively have a constant pressure water source and a variable area nozzle . What conclusion can you reach about the flow velocity and the flow rate of water through the nozzle as the nozzle area is varied ?

 

[TheWonderer1]

It's my understanding at this point that the velocity would only change at the valve. If the pressure is constant except at the valve and the velocity decreases soon after the valve, it seems I was over thinking the image in my head.

I think according to the principle of contuity in fluid dynamics, the flow rate should stay the same. Pressure getting slightly lower usually means a transfer of energy so more kinetic energy. Therefore, a slight change in velocity at that point but the increase is dampened by the return to normal pressure levels. Overall, the velocity should remain constant as it flows out of the faucet. By the way, I am assuming this from articles telling me that flow rate can only change through a force or change in mass. I got to thinking about it since I noticed a smaller stream but velocity doesn't increase by a noticeable amount. I assume a smaller area at the valve would mean that a smaller stream comes out. Obviously, this needs to be case since it happens via observation that the stream cross section area is not as wide.

 

[Nidum]

Can you write down any simple formula showing how the velocity of water through the nozzle varies with the pressure drop across the nozzle ?

 

[FactChecker]

It's my understanding at this point that the velocity would only change at the valve. If the pressure is constant except at the valve and the velocity decreases soon after the valve, it seems I was over thinking the image in my head.

Yes. A better example would be a hose with a spray head. There the increased velocity of the water coming out of the restriction is very easy to see. (Or just putting your thumb over part of the end of a hose.)