Noise Calculations for Pipe Flow 2

[sammars]

thread124-43781

thread378-18736

Hi Guys,

Can anyone help me to calculate the noise level from a 16" pipe of Nitrogen gas at pressure of 20 barg, temp 250 oC and the flowrate is 50,000 kg/hr.

Steps to calculate or formulae

Cheers,
Sam

 

[LittleInch]

You need to do some work first.

1) figure out the actual velocity in the pipe.
2) Is this just a pipe or does it have an open end or an orifice.

Pipe per se generally makes little noise unless you're really shifting. the noise comes from fittings like tees, control valves or orifices, especially where they are critical flow and hence the flow has exceeded sonic velocity.

Those posts you have listed show some evidence of calculations.

what have you considered so far?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[sammars]

Hi LittleInch,

Thanks for your advise.

But actual process is as below,

Nitrogen gas passes through pipe and at outlet of pipe has relief valve where conditions are changed to flowrate is 50,000 kg/hr, pressure 2 Barg and Temp. 250 Deg C. Outlet size of valve is flange 16"

So how I can calculate noise level at that point.

Could you help me to calculate or advise me formulas.

I have gone through earlier thread but couldn't get required information.

Thanks,
Sam

 

[LittleInch]

Ok, More info = better answer.

try this

http://frame.leser.com/engineering/file/EHB_en_file_6.5.4-Calculation-of-the-Noise-Emission.pdf

or this

http://www.iomosaic.com/diersweb/docs/PVCMC-0296-US_tcm106-35825.pdf

Or better still ask the vendor of the relief valve. At that pressure drop you will be at sonic velocity

Be prepared for a very high number. I can't quite grasp what 50,000 kg/hr is in reality, but at 14 kg/sec, you're going to hear that valve about 5 miles away..... - Ever stood behind a raw jet engine? That's what this thing is going to sound like.

I think you're going to need a silencer of some sort.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[georgeverghese]

At 2barg with this flow, you've got approx 57m/sec line velocity in this 16inch line - which doesnt seem to be a cause for worry on a PSV exit line. Does this help with using these spreadsheets referred to in the earlier threads ?

 

[sammars]

Hi LittleInch,

Thank you very much for your all details.

Your answer given me solution for Noise calculations. I will check with vendor for sonic velocity.

But last sentence got me a another question now. How I will get silencer for sort out or another way to reduce noise.

I have referred earlier thread but could not get answer for my queries. Will really spreadsheets will give me answer for another question.

Hi george,

Line size correctly designed for given flow and pressure. Could you advise me how these velocity is calculated?

Thanks,
Sam

 

[LittleInch]

That's a different question.

There are many different types of silencer design - search this site and generally for silencer design.

You'll probably need to wrap the valve in acoustic cladding then have some sort of lining or design on the vent pipe to absorb the noise and reduce velocities.

I would be interested to know what sound level you come up with or that the vendor advises.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[mechswa]

Most of companies use silencer after valve for such high flow.

U need to design silencer as below,

1) Inlet diffuser - which reduces pressure and changes flow. As pressure is low diffuser noise reduction will be done here also.

2) In this part noise generated will be absorb by some absorbing material.


Yes LittleInch previous mention threads will help in understanding of design. It will give you idea for designing important points is as per spreadsheets answer will be there if it is still available. I have gone for earlier threads but unable to get spreadsheets or other files.

You can try and may be someone who has spreadsheets will share it.

Good Luck,
Mechs

 

[georgeverghese]

Line velocity is calculated as follows:

N2 density at 200kpag, 250+273 = 523degK, R = 8.314 kJ/kgmole / degK, MW = 28 for N2, and approximating Z=1.0 gives

rho = MW. P / (ZRT) = 28 * (200+101) / (1.0 *8.314*523) = 1.94 kg/m3

Line csa = 0.7854*(0.4^2) = 0.126m2

line velocity = mass rate / pipe csa / rho = 50 000 / 0.126 / 1.94 = 204549 m /hr = 57m/sec

 

[sammars]

Hi george,

Thanks for detail calculation. It is will easy to understand now.

Hi LittleInch,

I have asked by vendor to provide calculation and I will try to calculate my self as per files provided and give you result.

Hi Mechs,

Could you advise me how both part will be designed. Design part by manually looks complicated. Hopes to receive spreadsheets.

 

[georgeverghese]

Do you really need a silencer on this PSV exit at 57m/sec which would be rarely in operation ?. What is the noise limit for very infrequent operating cases?

 

[LittleInch]

I don't think it's the exit that's the issue so much, but the sonic velocity in the relief valve and a big relief valve at that.

The fact that the relief exit pressure is 2 barg, says to me there's a long vent pipe involved here which we haven't been told about, but which could radiate a lot of noise from the valve.

Not sure if this is a new valve or existing.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[sammars]

Hi george,

vendor has come up with noise level around 150 db approximate and valve will be used in operation at time of exhaust

Hi LittleInch,

client says will not be worry about pipe length and they will use cladding for piping. But they ate forcing for noise reduction at exhaust of PSV and it will has some serious high noise level.

This is new plant design and client has started for installation in new plant for available equipment. It is just expansion of there plant.

Also they have another client asked for silencer for 138,000 kg/hr flow rate of steam with 60 Barg valve inlet and 6 Barg valve outlet pressure considering 400 deg c temp.

 

[LittleInch]

I told you it might be quite high....

150dB -

http://www.industrialnoisecontrol.com/comparative-noise-examples.htm

Silencers or more correctly mufflers (nothing will "silence" this) are a different thing altogether. There was recent post -

http://www.eng-tips.com/viewthread.cfm?qid=403742

and others about on the subject.

It's a difficult subject to look at alone - a good vendor is worth finding.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[georgeverghese]

57m/sec on a flare or RV exit line is very low, and I've not come across cases where noise was this high at these low velocities - maybe ask for a 2nd opinion or run a manual calc if you can.

 

[sammars]

Thanks George and LittleInch.

sorry I was out of town for few days.

we are looking doing design at our end as we could not have budget. Looking for some sort of design sheet

http://rapidshare.com/files/17227580/flow_noise.zip.html

which is uploaded in earlier thread. Currently download is unavailable.

 

[EmmanuelTop]

You can easily generate your own spreadsheet, by using the link (Lesser-ISO 4126) LittleInch provided in his second post or by using other methods, e.g.

http://www.peutz.de/pdf/Pipe_noise.pdf

or others. There is plenty of resources. Equations are fairly simply and easy to incorporate into Excel.

Dejan IVANOVIC
Process Engineer, MSChE

 

[sammars]

Hi Dejan,

Thank you very much for file. But could we get design sheet or file which shows how to design silencer.

Thanks,
SAM