Calculate Velocity with the Help of Pressure

Let the outlet water flow into a measured container of volume V (V in cm³).

Carefully measure the time T it takes to fill the container (T in seconds).

Determine the area A of the outlet pipe (A in cm²).

Divide the volume of the container by the area of the pipe and the time, this will give you the average speed in cm/sec of the outlet water.

S_avg = V/(A×T).

Dear Mr. vkturki,

Use Bernoulli's Equation, you can calculate the velocity.

DHAYANANDHAN.S

The OP has provided insufficient data to calculate velocity via Bernoulli's equation (or any other for that matter).

Dear Members,

Thanks for the reply. I am adding picture to make my question more clear. As you can see in the inlet I have pressure 6 kg/ cm2. Size of inlet is 1.5 inch and out let is 1.25 inch . I have checked outlet flow.

I had cooler , I could check this physically.

My question: if this project is on drawing board and want to know what will be the velocity of water flowing through the cooler at the inlet. How it will be calculated.

V = √2gh . but it give too high velocity which doesn't match to actual water flow collected.

I passed water through cooler @ 6 bar and flow came out to be 17.2 m3 / hr. and calculated velocity is coming 6 m/s

You need to use the Dynamic Pressure if you want to work out the inlet or outlet velocity. The pressure gauge will normally give you the sum of Static + Dynamic pressure.

'....I passed water through cooler @ 6 bar and flow came out to be 17.2 m3 / hr. and calculated velocity is coming 6 m/s....'

Well there is some useful information. Assuming you are taking pressure measurement for this situation and the only slightly different 6 kg/cm^2 (5.88 bar) as the difference in inlet and outlet pressure, you can make a decent estimate estimate of both velocity and volumetric flow at 6 kg/cm^2 (5.88 bar).

Based on your numbers I'd estimate volumetric flow would be about 17.03m^3/hr and velocity to be about 5.94 m/s

Yes , that calculation is correct. I have also mentioned it in my last post. But my question is how to calculate velocity using pipe size and pressure.

'...But my question is how to calculate velocity using pipe size and pressure.....'

Using only pipe diameter and difference in pressure? You don't have enough information.

.

You can measure flow of a certain section for a given difference in pressure and estimate what is will be at other measurements of difference in pressure.

Dear Members,

Thanks for the reply. I am adding picture to make my question more clear. As you can see in the inlet I have pressure 6 kg/ cm2. Size of inlet is 1.5 inch and out let is 1.25 inch . I have checked outlet flow.

I had cooler , I could check this physically.

My question: if this project is on drawing board and want to know what will be the velocity of water flowing through the cooler at the inlet. How it will be calculated.

V = √2gh . but it give too high velocity which doesn't match to actual water flow collected.

I passed water through cooler @ 6 bar and flow came out to be 17.2 m3 / hr. and calculated velocity is coming 6 m/s

OK. It seems that you need some clarifications:

1- Giving the inlet pressure only, is not sufficient to work out the Flow.

For example, if you blocked the outlet, and measured the inlet pressure, you might have a static pressure of ~ 7 or 8 kg/cm2. BUT you will have no flow (=0 m/sec etc).

2- You need more information: What is the pressure drop in your tubing ?

The installed pump is capable of developing a static pressure (No flow), and, depending on the installation (Tubings etc), will try to drive a certain volume of fluid through. This will cause a back-pressure which will depend on the volume and shape/characteristics of the installation. Hence, a pressure drop.

3- The more resistance the installation exhibits to the flow, the more backpressure there will be, and the less the volume of the flow... and vis-versa.

If you look at any pump chart, you will see that the maximum static pressure will give zero flow, and as the static/backpressure is droped, the flow increases.

In Conclusion: You need to get the differential pressure between inlet and outlet, or at least, since using a specific pump, either look at the chart, or obtain the maximum static pressure developped by the pump, by closing the outlet. Then obtain the running pressure when the outlet is opened. Use the difference in calculating the flow.

BUT THIS IS USELESS TO YOU since you want to calculate the result on the drawing board, right? then use the chart of the pump if you can assure the inlet pressure is allways going to be known (???) at the design stage!!!

Thanks for the reply Mr LAA LUCKE.

I fully agree with your explination.

But here the case is different. i am using a pump which 100mt away from the use point. The pressur 6 bar which i am talking about at the point of use. I think pump curve won't work.

Let me put this question in this way :

We need to calculate the flow of water through pipe.

only known data is pressure of water and size of pipe through which it flow. Is it possible to calculate :

velocity of water through pipe

& flow of water through the pipe

presure is 6 kg/cm2

pipe size at inlet is 1.5" and at the outlet is 1.25"