Velocity Versus Pressure relation

[madhavank007]

Dear friend

Is there any relation between pressure and velocity

i like to know using line pressure is it possible to calculate velocity of the fluid.

i got following data line pressure,line size, fluid property .
velocity ?

regards
K Madhavan



K Madhavan

 

[quark]

Unfortunately there is no such relationship. Flow depends upon the pressure drop or difference in pressures. You can calculate flow by using Darcy-Weisbach equation if you know the pressure drop.

http://me.queensu.ca/courses/mech451/losses.htm

Regards,


Believe it or not : Goldbach's conjecture says any even number can be written as a sum of two prime numbers. Postulated in 16th century, nobody could, so far, prove it nor disproove it.

 

[quark]

PS: At any pipeline pressure you can have zero flow (by closing the valve)

Believe it or not : Goldbach's conjecture says any even number can be written as a sum of two prime numbers. Postulated in 16th century, nobody could, so far, prove it nor disproove it.

 

[25362]

to quark, I've read that Goldbach's conjecture is from the middle of the 18th century, not the 16th. Besides, Goldbach has another one: any integer larger than 5 can be expressed by the sum of three primes. I think it also hasn't been proven yet.

 

[Guidoo]

Indeed, Goldbach lived in the 18th century and Euler was involved as well, as can be seen in following exerpt from

http://www.sciencenews.org/20000819/mathtrek.asp

"In a letter written in 1742 to Leonhard Euler (1707–1783), the historian and mathematician Christian Goldbach (1690–1764) expressed the belief that every integer greater than 5 is the sum of three primes. (See the letter at

http://www.euler2007.com/Letter_1742-Mathematics.htm.)

Euler replied, pointing out that Goldbach's statement is equivalent to the conjecture that every even integer greater than or equal to 4 is the sum of two primes. He went on to note, "that every even number is a sum of two primes, I consider an entirely certain theorem in spite of that I am not able to demonstrate it."

 

[quark]

You both are right. I noticed the error as soon as I posted it.

Believe it or not : Pythagorus theorem was used 2500 years before Pythagorus was born.

 

[25362]

Pythagoras' theorem may have been known about 1000 earlier by the babylonians, but there is a consensus among historians that its original proof was the work of Pythagoras himself.

BTW, there are many proofs to the Pythagorean theorem, among them one attributed to the 20th US president Garfield.

 

[ixchawla]

Madhav,
If the flow is considered constant, a relation between pressure and velocity can be made for gas system. At higher pressure, the density reduces, thus decreasing the velocity and vice versa. A gas law can be used to deduce the relation.

 

[madhavank007]

Dear Friends
Thanks lot for your replies.

In my plant i like to calc utility flow rate
i got Pressure gauges in utility inlet and outlet of the reactor.
i want to calc the flow rate of the utility.

I just thought that if i got any correlation between pressur and velocity i can just calc velocity of the inlet.

Now i have to assume the velocity for 1 1/2" pipe velocity has 1.5 m/s max.

i got one idea

Shall i collect data from pump discharge

i got Pressure gauge in the pump discharge
so i know the flow rate of the pump and line size
from this is it possible for me to get an idea between pressure and velocity
but not with valve closed ! ( quark)

regards
K Madhavan

K Madhavan

 

[quark]

ixchawla!

For liquids(to be more precise, for incompressible fluids), flow is constant then there is only one pressure drop and one velocity correspondingly.

Where as for compressible fluids, you can increase mass flow rate eventhough the flow is choked in terms of volumetric flow. This is because, the density of compressible fluids increase with increase in pressure (this is correction to your post). Even then, you should know the upstream and downstream pressures and not at a single point.

Madhavan!

You can check the total flow rate from pump discharge pressure (for accuracy, it should be the differential pressure between discharge and suction), power consumption and the performance curve of the pump. Mark the head on the pump curve and go down vertically to know the flow rate. Check actual power consumption vs power consumption from the performance. This gives you a fair idea about the actual condition of the pump. Now you have got total volumetric flow.

Now if you have a battery of reactors connected to same watr circuit (by supply and return headers) then you should go for Hardy Cross Method to check the flow rates or you can check individual flow rates through coils as given in Perry's Chemical Engineers Handbook.

Check this link

http://www.lmnoeng.com/Pipes/PipeNetwork.htm

25362!

The first (with evidence) use of the above said theorem dates back to Circa 2500BC at Egypt (pyramids) and England (stonehenge). But much earlier, a description was given in Indian Religious Texts which described a method of constructing 'Yagna Kund'(the holy fire) and also the value of Pi. But in those times science was closely gaurded from a probable misuse. That is where we lost.

Regards,


Believe it or not : Pythagorus theorem was used 2500 years before Pythagorus was born.

 

[25362]

To quark, used, may be; proved, definitely not.

 

[quark]

25362!

Infact I forgot to mention about the proof. You are correct (with historical evidence). But still there is a chance for me to be patriotic(let me go and learn Sanskrit first)

Regards,


Believe it or not : Pythagoras theorem was used 2500 years before Pythagoras was born.

 

[25362]

To madhavank007, you need pressure differences. If you can introduce a known flow "resistance" such as a valve, an orifice, a venturi nozzle, or a pitot tube, and measure the pressure drop across this resistance by suitably located taps, you may estimate the flow rate from the velocities therein, based on Bernouilli's theorem. Nothing new, however. These are methods used to measure flow rates in pipes. Rotameters can also be used.

There are formulas to estimate flow rates by letting the fluid exit the pipe to the atmosphere or flowing over a notched weir. By measuring distances (vertical and horizontal, as the case may be) from the open nozzle or weir, one can get a reasonable flow rate appraisal.

Once you can measure flows, you may construct a table based on pump discharge pressures, keeping the piping geometry and head at the receiving point unchanged, to relate these pressure readings to measured liquid flowrates.

To quark, it has been shown that the Babylonians used tables of squares to solve multiplications based on the formula:

a.b=[(a+b)²-(a-b)²]/4

and that the old egyptians and chinese used the 3,4,5 "rule" to construct right angle gardens and buildings.

Amazing feats by themselves, thousands of years before Newton's famous binomial and Pythagoras' theorem proof.