Bernoulli's principal and law of conservation of energy

[dE_logics]

Ok, just for simplicity morph the original question by a bit, with only 1 image -

And assume that we have another piston towards the narrower cross section just to not allow the fluid to 'spill', i.e ensure that the whole cross section is filled with the fluid; both the pistons are mass-less.

If, initially the piston towards the LHS applies a force so as to make the fluid gain a momentum, then, after a while, the force application stops, but the pistons keeps pace with the fluid to avoid it's spilling...ensuring that the fluid fills the cross section.

Assuming the length of the narrow cross section is long enough, will all the fluid in the wider cross section move into the narrow cross section without application of any additional force?...i.e solely by virtue of the momentum gained by the fluid?

 

[dE_logics]

I really have no idea what you are trying to describe with that first diagram. For the second diagram, the system will accelerate and quickly reach an equilibrium with steady flow, based on the applied pressure equalling the total pressure required to move the fluid at a certain velocity through the small pipe.

Ok...by this I conclude, it might happen that all the fluid (referring to the above description) will not move to narrower cross section.

 

[SystemTheory]

For a practical application of fluid models go to this link:

http://dynast.net/course/index.html

Course parts for printing:

Modeling and Simulation (This is a link to a 140 page modelsim.pdf. Chapter 5 covers fluid models. The paper itself is an introduction to multidomain system models).

 

[russ_watters]

And assume that we have another piston towards the narrower cross section just to not allow the fluid to 'spill', i.e ensure that the whole cross section is filled with the fluid; both the pistons are mass-less.

First, could you tell me whether we are talking about air or water?

Next, massless or not, the second piston has to be applying a force (there is a pressure due to the presence of the fluid), so you need to be more specific about what you want it to do. How much force, exactly does the second piston apply? A force equal to "F"? Something lower than "F"? It makes a difference.

If, initially the piston towards the LHS applies a force so as to make the fluid gain a momentum, then, after a while, the force application stops, but the pistons keeps pace with the fluid to avoid it's spilling...ensuring that the fluid fills the cross section.

The piston cannot "keep pace" without applying a force. The fluid is under pressure!

Assuming the length of the narrow cross section is long enough, will all the fluid in the wider cross section move into the narrow cross section without application of any additional force?...i.e solely by virtue of the momentum gained by the fluid?

Though your scenario is still being described in an incomplete and contradictory way, I can see is no reason to believe the fluid would completely move through the narrower tube. I can't think of any variant of your problem description where it would.

Do you have a specific real-world scenario that you are trying to understand or is this completely hypothetical?

 

[dE_logics]

For a practical application of fluid models go to this link:

http://dynast.net/course/index.html

Course parts for printing:

Modeling and Simulation (This is a link to a 140 page modelsim.pdf. Chapter 5 covers fluid models. The paper itself is an introduction to multidomain system models).

It's a guide to a software which's proprietary and works only on windaz.

 

[dE_logics]

First, could you tell me whether we are talking about air or water?

Water.

Next, massless or not, the second piston has to be applying a force

The force is applied on the second piston...and the first piston applies the force (initially). The force on the second piston is a consequence.

I think it's impossible to describe this.

So just leave it for now...really appreciated the help.