Pressure Drop in Compressed Air Line

dear viewers

also i want to know

how can i calculate cost of pressure drop in terms of drop in pressure and hp rating of compressor and cost of electricity and operating hour/year

pls help me

rahul

That one is easy. It's roughly the pressure drop multiplied by the flowrate, divided by the overall system efficiency, mutiplied by the time that the equipment runs per year, then multiplied by the price per unit energy received.

It isn't often done that way, though. As a rule-of-thumb, the economic size of pipe is one where the velocity of the gas inside it is no more than 10m/s. If it is higher, then the pipe is too small.

dear sir,

what you mean by overall system efficiency how can i find it.the available datas are i allready given for cost calculation.

regards

rahul

Call it 15%.

The easiest way to calculate the pressure drop in any line is to look at pressure gauges each end of it, and subtract the lower reading from the higher one.

dear sir

thank you for your answer

sorry i want to calculate and compare actual with the standard (say as per Is 6206

its my requirement cau you help me in formula

pls its urgent

regards

rahul

So the standard wants something like no more than 0.5 bar pressure drop. Are you designing this system? Otherwise it was just to measure it, calculated the difference and then compare to the requirements in the standard.

If in doubt take the calculation from the standard as it is written and get on with the job.

Those ones that tell you a different story need to explain why they do not adhere to the standard!

In the discussion you will learn a lot about air systems and calculations and probably can teach all of us here how it being done and why!

Good luck!

There's a lot of data missing

What units for each of the inputs?

Is Q measured at standard, normal, or actual conditions, or what?

Is p (and P) gauge or absolute?

Rather than rely on an arbitrary-looking formula I prefer to use the standard approach with Reynolds number etc and calculate friction factor. It's come up on this forum more than once, if memory serves.

But for the hell of it I tried an example, 100Nm³/h, 40mm dia, 100m length, and 6 bar absolute. My way I got pressure drop 59 mbar. Put same figures (ie same units) in your formula (1) and to my surprise got 62 mbar which is excellent agreement.

So with those units it looks like formula (1) is right. With different units formula (2) could be right. Eg if one had d in cm, the other in m, that would account for the 10^-10 factor (100^5 = 10^10) but it doesn't work if (1) has d in mm.

dear sir,

thanks a lot for expert opinion and i really sorry for missing data

i prefer to take all measurement in metric unit ie

dp = pressure drop (kg/cm²)

q= Air flow quantity (FAD) (m³/min)

L = length of pipe (m)

d = inside diameter of pipe (mm)

p=initial abs. pressure (kg/cm²)/bar

actually sir i am person having instrumentation back ground

basically we are looking to place some instruments in our old compressor plant by replacing mechanical type so please suggest me more about to pressure drop and air leakage measurement principles for better instrumentation also give me a equation for manual pressure drop calculation based on above data

your suggestions are very valid for us

regards

rahul

dear sir

how can i calculate air velocity of compressed air through a pipe

and how can i maintain a particular air velocity with out pressure drop

pls help me

rahul

<...maintain a particular air velocity without pressure drop...>

It is not possible for any fluid to pass through a pipe without pressure drop occurring.

Welcome to the world of fluid friction and of momentum transfer.

Sir,

I would like to know about compressed air pressure drop calculation from air leak. In our compressed air system in a leakage test it found that there is a leak of 4.375 m3/minute. Then how can I find pressure drop from this leak. We have no instrumentations for pressure in compressed air line ,please help me is any rela tion or equation of pressure drop calculations from leak

It's very urgent waiting for your replay.

Compressor details are

• Compressor capacity (m3/minute) = 35 (1236.01 CFM)or 2100 m3/hour

• Cut in pressure, kg/cm2 = 6.8

• Cut out pressure, kg/cm2 = 7.5

• Load kW drawn = 188 kW

• Unload kW drawn= 54 kW

• Average 'Load' time =1.5 min

• Average 'Unload' time = 10.5 min

• Pipe diameter - 100 NB (4inch, 101.60mm)

• Length of the pipe - 320m

You're asking a different question now. Originally it was about pressure drop in a pipe at a fixed air flow. Subject to comments made, your (1) appears to be fairly close.

New question is about pressure loss due to a leak. You need to know system volume, area of leak, initial pressure etc. Presumably leaking to atmosphere, and flow will be sonic till pressure falls to about 2 bara. Leakage rate falls as the pressure falls, so it's quite a complicated calculation involving iteration. It's not a simple formula. I think you need to study compressible flow through orifices to tackle it, or find somebody in your organisation who knows.

<...urgent...>

Tell the forum this procedure isn't being used to evaluate different line sizes and make a selection!

dear sir

thank you for your replay

actually sir i really dont get you sorry for my poor knowledge

our compressed air line having line sizes about 100nb for distribution lines and 150 nb for header compressor having capacity of 800 cfm .

replay expected

regards

rahul

What is the consumption rate of this air?

dear sir,

thank you for your replay

compressed air flow rate is 17 cubic_meters_per_minute

pls give me idea about pressure drop calculation and energy loss due to pressure drop

rahul

All the numbers can now drop into the equations in the original post.

The velocity is 20m/s or so, which is on the high side. Consider increasing the size of the main header pipe, duplicating it, or turning it into a ring.

_{<unsubscribes>}

Been away or would have replied before. Do you mean the flow q (or Q) in the formulas is in m3/min? If so I can't find any combination of units for the other inputs that gives anywhere near agreement with my estimate.

I noticed that my ΔP in #6 was based on elevated temperature (~ 120°C, haven't got it to hand). Your formula doesn't have temp but it should, as for a given mass flow ΔP varies as absolute temp. Your formula must be based on an assumed temp, and if that is ambient, say 20°C agreement is not so good, but still in right area based on my assumption re units..

Sir,

I would like to know about compressed air pressure drop calculation from air leak. In our compressed air system in a leakage test it found that there is a leak of 4.375 m3/minute. Then how can I find pressure drop from this leak. We have no instrumentations for pressure in compressed air line ,please help me is any rela tion or equation of pressure drop calculations from leak

It's very urgent waiting for your replay.

Compressor details are

• Compressor capacity (m3/minute) = 35 (1236.01 CFM)or 2100 m3/hour

• Cut in pressure, kg/cm2 = 6.8

• Cut out pressure, kg/cm2 = 7.5

• Load kW drawn = 188 kW

• Unload kW drawn= 54 kW

• Average 'Load' time =1.5 min

• Average 'Unload' time = 10.5 min

• Pipe diameter - 100 NB (4inch, 101.60mm)

• Length of the pipe - 320m

Your 2 equations are the same except for the power of 10. What are the units of measure in both equations?