What is the maximum CFM through a pipe in the rock drilling industry?

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    Cfm Maximum Pipe
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Discussion Overview

The discussion revolves around calculating the maximum cubic feet per minute (CFM) that can be achieved through a pipe in the rock drilling industry, specifically considering factors such as pipe diameter, compressor specifications, and system conditions. The conversation includes theoretical considerations and practical implications related to airflow in piping systems.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Exploratory

Main Points Raised

  • One participant seeks a formula to determine the actual CFM at the end of a pipe given specific parameters, such as pipe diameter and compressor output.
  • Another participant notes that the actual CFM depends on various factors, including the length of the pipe and whether the quoted CFM is at the intake or discharge of the compressor.
  • Some participants argue that while the compressor may deliver a constant CFM, the output can vary based on the working fluid, pipe length, and roughness.
  • There is a discussion about the impact of aftercoolers on the actual CFM, as they can change temperature and moisture content, affecting the flow rate.
  • One participant mentions the importance of understanding what "600 CFM" means in the context of the compressor's specifications and suggests consulting manufacturer resources for clarification.
  • Another participant acknowledges the complexity of mass flow rates versus volumetric flow rates, indicating that the latter can change with pipe length.

Areas of Agreement / Disagreement

Participants express differing views on whether the mass flow rate remains constant and how various factors influence the actual CFM. There is no consensus on a definitive formula or method for calculating the maximum CFM through the pipe.

Contextual Notes

Participants highlight that assumptions about compressor type, conditions at intake, and the presence of components like aftercoolers can significantly affect calculations. The discussion does not resolve these complexities.

tc114
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I am in he rock drilling industry and I am looking for a formula to be able to calculate what the maximum CFM is through a pipe. For example I have a 0.5” dia. pipe, 600CFM @ 150psi compressor. What is going to be the actual CFM that I will get at the end of a pipe?
Any help will be greatly appreciated.
 
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It depends on how long the pipe is, and other details. Also, note that it depends on just what the "600 cfm" is...Is it at the intake of the compressor, or at the discharge? Is there an aftercooler? etc. The best thing for you to do is go to the compressor manufacturer's website (ingersol-rand, or atlas copco are big ones) and see if they don't have tech info pages. All this used to be in their catalogs, so I'm sure they have it on line by now. Another source is the Crane "Flow of Fluids..." book. Another excellent source of advice is http://www.eng-tips.com/

Good Luck
 
gmax137 said:
It depends on how long the pipe is

Surely, if the compressor is delivering a particular CFM (which may or may not be the 600 quoted), this is what you'll get out of the pipe? You will have changes in density and pressure, but the overall mass flow rate has to stay constant, no?

Apologies if I've missed something!
 
I agree with Owen, depending on the type of compressor, it should deliver a constant CFM. Now what's coming out of the pipe will vary depending on the working fluid, length of the pipe, roughness of pipe, etc.

but the overall mass flow rate has to stay constant, no?

Not necessarily, it depends on what kind of pump and what the conditions are for its intake. If its intake is constant temp, and pressure, then yes mass flow rate will be constant. However if this is more of like an impeller kind of air pump, then things got a lot more complicated.
 
He didn't tell us what kind of compressor he has (but you're right, it is likely a recip or screw, ie, positive displacement machine). Which would lead you to believe that the mass flow is constant down the line. But, if it has an aftercooler, (they reduce the temp and take out a lot of the water) that affects the "actual cfm" too. I still would go to the I-R or atlas site to see how they explain things (like, what exactly the "600 cfm" nameplate means). EDIT
And IIRC, actual CFM is the volumetric flow at the line pressure, so the ACFM may change with length of the pipe (since the pressure drops along the length).
 
My mistake, too many years spent dealing with mass flow rates! Of course the volume flow rate will change with pipe length!
 

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