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Pressure Of Water Spraying Out Of Tank

spraying pressure storage tank

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#1 raisie

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Posted 24 April 2015 - 07:16 AM

Hi guys,

I have a question regarding the spraying pressure of a water tank.
Suppose I have a storage tank for water with the following parameters:

Height: 10 m
Capacity: 651900 liters

There is a hole on the tank shell, almost at the bottom of the tank (assume that it is at the bottom) and the hole has a diameter of approximately 11 mm.

What would be the pressure of the water spraying out at that depth?

What I know so far, is the hydrostatic pressure at that depth in the tank, which is 14.2 psi.
But the pressure increases when it is sent through the small hole right?
Can I apply Bernoulli's formula to calculate the pressure of the water spraying out?
I'm not sure. And even if I could use that, I don't have any speeds of fluid.

Any ideas? 



#2 latexman

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Posted 24 April 2015 - 07:31 AM

I recommend you obtain Crane Technical Paper No. 410, it is an excellent reference.

 

http://www.flowofflu...ane-tp-410.aspx



#3 Art Montemayor

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Posted 24 April 2015 - 10:34 AM

Raisie:

 

Latexman has given you the best advice:  Learn the basics which you are writing about.

 

First define the term you use: "pressure".  Pressure is force imposed on a unit area.

 

Next, understand what you have been asked to specifically do.  I don't believe you understand what it is that you have been asked to find.  Do you understand that once the water leaves the hole in the tank, it has NO PRESSURE?  Under the driving force of hydrostatic pressure, it develops momentum and an outgoing force.  There is no specific "area" that this force is acting on as it goes into the atmosphere and dissipates the force developed.

 

The water, before it exits the hole, can only have the hydrostatic pressure developed by the height of the water column (which is the height times the water density at that depth.

 

Have you been asked to find the hydrostatic pressure?  Perhaps that is what is confusing you.  Or maybe you haven't transmitted the homework problem correctly?



#4 katmar

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Posted 24 April 2015 - 12:44 PM

Bernoulli's equation is the corect route to take.  Inside the tank at the level of the hole the (gauge) pressure is the 10 m or 14.2 psi you have calculated and the velocity is zero.  Outside the tank the (gauge) pressure is zero and in accordance with Bernoulli the "missing" pressure of 14.2 psi is now converted to velocity head.  This allows you to calculate the actual velocity through the hole.

 

This is all based on ideal (frictionless) behavior and in reality there will be some losses, but they will be small and the Bernoulli solution will be very close to what you would find experimentally.

 

I don't know where you got the idea that the pressure would increase if the water is sent through a small hole. This is not true.

 

The Crane manual recommended above is a good reference, but just about any fluids textbook will have an explanation of Bernoulli's Equation.  A Google search will probably tell you more than you need to know.



#5 raisie

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Posted 27 April 2015 - 05:16 AM

Thank you all for your kind advice.



#6 RAHUL123ok

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Posted 29 May 2015 - 07:03 AM

According to the Bernoulli principle:

For constant flow of fluid in a pipe, as the diameter decrease the velocity increases and the pressure decreases.  But according to the expression Pressure = Force/Area, it should increase.

I am confused about this.

 

What is actually the meaning of it?


Edited by Art Montemayor, 29 May 2015 - 10:14 AM.
Spelling, content, formatting


#7 katmar

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Posted 30 May 2015 - 03:07 AM

From your formula, pressure would increase with decreasing area if the force were constant.  But there is no "conservation of force" principle that operates here.  In fact the force would be calculated from Force = Pressure x Area, with the pressure calculated from Bernoulli.



#8 samayaraj

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Posted 30 May 2015 - 05:11 AM

What ever the pressure you're seeing in a flow of pipe, its dynamic pressure. For the constant flow, as the flow area increases the velocity will decrease, pressure will increase and vise versa. Ultimately the energy in to the pipe is equal to energy out. This is Bernoulli's principle.
 
The question Pressure = Force/ Area is applicable for fluid in static. You should refer "Pascal's Law".


#9 RAHUL123ok

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Posted 30 May 2015 - 07:11 AM

P=Force/Area=F/A= (F*d/A*d)=W/V=Energy/Volume=Energy Density

 

How Can I understand that energy density will decrease in smaller diameter pipe compare to larger diameter pipe ?

 

Is there any relation between internal energy or something?

 

How can I know it with fundamentally without go into mathematical equation.






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