Pressure and Velocity

you are going to get a lot hammering here by such kind of question !!

Thank you So much Bravo for your respone.

I know what is pressure and Velocity .

Pressure is Force acting on Unit area of Surface, and Velocity is Rate of Change of Displacement with respect to time.

My Doubt is how Velocity will Increase when Pressure Decreases

means Velocity is nothing but speed of any Fluid ,if speed is more subsequently pressure also should be more.,but as per therotical it will be said that velocity decreases , pressure increases.

For eg : if a liquid flowing through a pipe of 10 m/s if the pressure increase / decrease subsquently velocity should vary.

I am Little bit Confused between these 2 parameters. I Need Little bit more practical Clarification.

Bravo , Pl Dont Underestimate the Person who ask Question , there may be some logic behind any Question.

Hope, you i understood my doubt, I hope my doubt will clarify by you.

Regards

Nithin

Yes of course, this takes us back to the Course Fluid Flow ChE 202. The short answer is that these two variables; Pressure (P) and Velocity (v) and let me also add in a 3rd one which is Height (Z) when added together will always be a constant. This is a form of Energy balance, if you will. Simple way of looking at it : If your increase one of these variables then one or two of the others will drop. This is the layman's answer to your question. By and large, you will always be dealing with a balanced system. Each of the 3 variables represents a type/class of energy. They are more or less interchangeable and can be converted from one form into another. This is done in such away so that the total of the 3 remains constant.

For a more decent answer, I would refer you to Bernoulli's Equation which explains this phenomenon precisely. Good approach to such basics is to always look it up on Wikipedia and store the answer in a Folder on your PC. E.g. see Bernoulli's Principle on Wiki. All in all, I prefer the practical explanation above.

Do let us know how you fare on this one.

Nit...

Considering your "fluid flowing through a pipe" example....

If the fluid is a liquid, then the pressure drops as it flows along the pipe due to the internal friction developed at the pipe wall. Because liquids are incompressible, the fluid velocitity stays the same.

If the fluid is a gas moving through a pipe, more interesting things can happen.

Gasses are compresible, and as the flow moves along the pipe, pressure will drop, but the gas properties will also change. This change in gas properties affects the calculated velocity.

Special things happen when you reach the Mach number for a gas flow problem.

Suggest that you purchase ( yes, purchase...do not steal) a copy of Crane Technical Manual #410. Read it and report back.

Are you an engineer ? Do you have a degree ?

Bernoulli,

How Velocity will Decrease when Pressure increased.???? Talking about pipe?

No change in the cross section?

Bernouillis equation is true only along a line of current ( might not be the right term in english). It is about conservation of energy. It is the equivalent of mv2+ mgh= C for a rigid body. I understand that the concept you are talking about is ambiguous because consider a bottle of water with a small hole in it, Of course if you apply more pressure, flow will get out faster. But for a particule of water going from inside the bottle to outside, a pressure decrease will be felt as it will be accelerated. Hope it helps. Alwayz take spoken facts in their right context.

Nithin,

Have you read the literature or the basics? Please do so. You will find that your level of discussion will lift up once you have put in the effort to read up. See links given above. We all had to do this at some stage. I find it odd that you say above that you do not know the difference between Pressure and Velocity.

Some members may feel that this discussion may be way too basic for this Forumn. But nevertheless, those people that are in fields other than Mechanical or Process engineering might want to benefit from this. However, I am not even sure as to what really is your question. For clarity, what is your technical backgound? Are you a student or graduate? This should give us an idea as to who we are having this discussion with.

Nithin,

Here is a very basic little low-cost experiment you may try. Take a piece of paper
say about 10 cm x 10 cm or thereabouts. Hold it with both hands at one end close to your mouth and let it dangle down away from your mouth. Now blow over the top of this paper (away from you). Notice what happens to the paper. It will lift. Ask yourself : why?

The explanation : Velocity at the top of the paper is roughly equal to the speed of the air you are blowing. Velocity at the bottom is zero (as there is not movement of air below). Hence the Velocity forces above are greater than the velocity forces below. Height of the paper above and below are much the same.

Hence, for conservation of energy we will have a compensation happening. This compensation will be that the pressure above will be lower than the pressure below the paper. The net result is that the paper will lift. This is in fact precisely what keeps an aeroplane in the air. The wings are shaped in such a way so as to force this type of action to occur. Again, an application of good old Bernoulli's Equation.

Much the same with your pipe system ! As for your question : How can Pressure be altered? In your piping arrangement you may have an assortment of different devices and fittings that do just this [e.g. Expansion Joints, Pressure Regulators, Flow Control Devices, a rise in pipe Height]. Also unexpected events may occur [blocked pipe, incorrect opening of valves, etc.] While one is dealing with a closed system, the same rule of thumb will apply. Increase the one then the other will decrease. Remember, there are actually 3 variables (at least) in such a system. [Velocity, Pressure as well as Height]. When operating a plant you sometimes want pressure and other times you ant velocity in the pipe. You a free to chop and change as you so require. This assumes that you are only using control devices & fittings to achieve this and not changing the energy into the system e.g. by putting in another pump.

Hope I have helped a bit. Always ready to assist.