# Velocity of efflux in a piston cylinder arrangement.

• dE_logics
In summary, the velocity of efflux off a pipe is a function of the width of the pipe, the rate at which the cylinder empties, and the pressure inside the pipe.
dE_logics
I did a few derivations to calculations to figure out the velocity of efflux off a pipe which is situated on the piston of a piston cylinder arrangement.

Attached is the attempt...though I have a doubt in it -

But h will not be the distance if we're considering the upper particles of the block...

An attachment follows...can someone confirm if it's correct?

#### Attachments

• Fluids.pdf
55.7 KB · Views: 374
There's a reason why I dropped science.

I don't see what you are trying to do here - I see a lot of words and not a lot of meaning in that pdf to describe a situation that at face value looks very simple (if poorly defined): flow rate is equal to rate of volume displacement of the cylinder for an incompressible fluid. Your force and acceleration and velocity analysis math doesn't look at all meaningful/useful.

With this and your other thread, you seem to be putting a lot of effort into making simple issues more complicated than they really are without adding any meaning. I don't see any point/value to any of this, nor do I understand why you have an attitude about it.

russ_watters said:
I don't see what you are trying to do here - I see a lot of words and not a lot of meaning in that pdf to describe a situation that at face value looks very simple (if poorly defined): flow rate is equal to rate of volume displacement of the cylinder for an incompressible fluid. Your force and acceleration and velocity analysis math doesn't look at all meaningful/useful.

With this and your other thread, you seem to be putting a lot of effort into making simple issues more complicated than they really are without adding any meaning. I don't see any point/value to any of this, nor do I understand why you have an attitude about it.

Well it is a simple situation actually, but I don't find computing what I want simple.

Obviously I do not know the rate of volume displacement of the cylinder, that's why I'm computing it with pressure...the rate at which fluid from the arrangement will flow out is a function of the width of the pipe, which is also unknown; and I have to find the velocity with all these unknown things.

With this and your other thread, you seem to be putting a lot of effort into making simple issues more complicated

I can't help it!...I am that way!

So what I'm trying to do here is compute the velocity of efflux through that pipe without knowing the area of cross section of that pipe nor having any information about the rate at which the cylinder empties, these are my attempts and I really do not find any attitude in it...it appears to me simple scientific derivations which might be wrong...so I'm trying to see what's wrong in it, or get another right derivation...simple.

BTW this doesn't have to do anything with the dam.

My answer above was considering a positive displacement (a given displacement) of the piston. More, coming closer to what you were describing...

-The scenario is ill-defined. You can't figure out the flow rate if you don't know the area of the pipe.
-Using an acceleration calculation isn't really correct unless the force is huge and then it becomes more complicated than we can easily deal with here anyway (you have dynamic effects such as compressibility of the fluid, inertia of the piston, etc). The situation will quickly reach a dynamic equilibrium so you should just use a Bernoulli's principle calculation to find the velocity out the pipe.

There is so very much wrong with your math. Start with your first statement: force=p*k. But above that you said p is force. Well if p is force (so is f?) then p*k can't also be force. In fact, force times area isn't anything useful.

My answer above was considering a positive displacement (a given displacement) of the piston.

The question does not state a positive displacement.

-The scenario is ill-defined. You can't figure out the flow rate if you don't know the area of the pipe.

I do not want to figure out the flow rate, I want to figure out the velocity of efflux which is possible without knowing the thickness of the pipe.

There is so very much wrong with your math. Start with your first statement: force=p*k. But above that you said p is force. Well if p is force (so is f?) then p*k can't also be force. In fact, force times area isn't anything useful.

Yes, that's wrong...my fault.

The force should have been f*k/A.

Ok, so I'll try it with Bernoulli's principle which I absolutely do not understand or any attempts to understand it results in failure.

All I've known is that as the velocity of the fluid increases, it's pressure decreases, I cannot make relations between this and law of conservation of energy...they say the decrease in pressure of the ideal fluid is used up to increase the K.E. but everyone also agrees with the fact that significant work cannot be done by the pressure stored in an ideal fluid.

Last edited:
So I'll give another few attempts to compute the answer using the block theory, then proceed to calculate using bernaulli's principal, i.e if I succeed understanding it.

Can someone please do something? I'll try and make the question clearer again -

There's a piston cylinder arrangement, and there's a pipe on top of the piston. What I know -

Dimensions of the piston and cylinder arrangement (not the pipe).
Force on the piston and so pressure in the fluid.
Density of the fluid.
Assume ideal fluid and conditions.

The reason why I bumped this question -

I hit a log 0!

## 1. What is the velocity of efflux in a piston cylinder arrangement?

The velocity of efflux in a piston cylinder arrangement is the speed at which a fluid or gas is discharged from a small opening in the bottom of a piston cylinder setup.

## 2. How is the velocity of efflux calculated?

The velocity of efflux can be calculated using the equation v = √(2gh), where v is the velocity, g is the acceleration due to gravity, and h is the height of the fluid or gas above the opening.

## 3. What factors affect the velocity of efflux?

The velocity of efflux is affected by the size of the opening, the density of the fluid or gas, and the height of the fluid or gas above the opening.

## 4. How does the velocity of efflux change with different fluids or gases?

The velocity of efflux will vary for different fluids or gases due to differences in density and viscosity. Heavier and thicker fluids or gases will have a lower velocity of efflux compared to lighter and thinner ones.

## 5. Can the velocity of efflux be controlled?

Yes, the velocity of efflux can be controlled by adjusting the size of the opening or the height of the fluid or gas above the opening. It can also be controlled by changing the properties of the fluid or gas, such as temperature or pressure.

• Thermodynamics
Replies
0
Views
880
• Classical Physics
Replies
5
Views
654
• Science and Math Textbooks
Replies
7
Views
2K
• Introductory Physics Homework Help
Replies
39
Views
2K
• Mechanical Engineering
Replies
7
Views
1K
• Engineering and Comp Sci Homework Help
Replies
20
Views
3K
• Engineering and Comp Sci Homework Help
Replies
31
Views
2K
• Other Physics Topics
Replies
1
Views
1K
• Engineering and Comp Sci Homework Help
Replies
3
Views
1K
• Engineering and Comp Sci Homework Help
Replies
19
Views
3K