×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Volume of Gas Through a Line (Again)

Volume of Gas Through a Line (Again)

Volume of Gas Through a Line (Again)

(OP)
My apologies in advance for creating another gas flow thread and I promise not to use any text-speak! It has been 32 years since I took fluid mechanics so there has been a lot of corrosion in my memory and I need some assistance in pigging that portion of my brain. Thanks in advance for any help!

I am designing a process flow control system for sending various sample gases through a heated line and need to create a calculator for the Volumetric Flow Rate based on the following:

Variables
-Input Pressure: 40-60psi
-Line Length: 65-200 feet
-Gas Type: Nitrogen (This varies among 10 different gases and gas mixes so we will change this in the calculator as needed.)

Fixed
-Line ID: 3/8" (0.375")
-Line Material: Teflon
-Coefficient of Kinetic Friction: 0.04
-Outlet: Open to atmosphere
-Inlet Temperature: 75F
-Outlet Temperature: 375F
-Height Delta: 15-65'

If this is not enough information to make the calculator, please let me know what else I need.

Scott

RE: Volume of Gas Through a Line (Again)

This problem really requires knowledge of your goal.
  • If you are trying to heat a fixed size sample to a specified temperature then you need the heat transfer characteristics of the system to know how long the gas must be in the heat to acquire enough heat to reach the desired temperature. That soak time will determine your flow rate--usually the velocity is so slow that the friction is not a significant consideration.
  • If you are trying to get a fixed volume to flow from a process into an analysis then you need some sort of regulator since each gas species will give you a different friction value (and your "coefficient of Kinetic Friction" is kind of meaningless without knowing the gas species and pipe relative roughness)
  • Some other goal
Without knowing the goal, the path is difficult to assess.

David Simpson, PE
MuleShoe Engineering

In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. Galileo Galilei, Italian Physicist

RE: Volume of Gas Through a Line (Again)

(OP)
This is for an emissions analysis system. Currently we flow various dilution gases into a chamber varying distances from our source gases, usually 65' or 100', that mixes with exhaust gas allowing us to measure the makeup of the exhaust gas using an FTIR. The current gas flow is at 40psi through a 3/8" teflon line, wrapped in heat tape, insulated, and is 375F when it enters the chamber at the aforementioned distances. Our objective is 2-fold. First, we want to install a mass flow controller to automate the process gas selection. Second, we want to be able to determine how much we can lower the flow rate to possibly reduce our consumption and therefore cost of process gas. This will also allow us to determine the effect of lower flow on response times. Our IT guys need a volumetric flow rate formula to use in programming the PLC.

RE: Volume of Gas Through a Line (Again)

I don't think you're going to get a simple formula that the PLC will understand.

You have, IMO, too many variables - length of line, type of gas, inlet pressure and variables which change along the pipe, i.e. density caused by reduced pressure and also density changes fro the increase in temperature to get any sort of reliable calculation.

how do you measure flowrate now? Or don't you?

A simple strap on ultrasonic meter would give you volumetric flow when you can determine the ID of the tube and a pressure tapping would allow you to correct this flow to standard conditions.

Just measure the flow and feed it back into the PLC.

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

RE: Volume of Gas Through a Line (Again)


Typically the end use (equipment on the recieving end) defines the flow required.

First you regulate the pressure for the required flow, cool it as necessary, remove any condensibles, and tackle the rest of the design....

RE: Volume of Gas Through a Line (Again)

(OP)
Thanks for the replies! Decided it was easier to pull the line to the top of the office building, turn on the temperature controller, open the regulator, and measure the flow at the outlet line then reverse engineer the formula.

Much appreciated!

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources

eBook - Mastering Tolerances for Machined Parts
When making CNC machined parts, mastering tolerances can be challenging. Are general tolerances good enough? When does it make sense to call out for tighter tolerances? Do you need a better understanding of fits, datums, or GD&T? Learn about these topics and more in Xometry's new e-book. Download Now
eBook – How to Choose the Correct Corrosion Testing Method
When designing a metal component, engineers have to consider how susceptible certain alloys are to corrosion in the final product’s operating environment. In a recent study by NACE (National Association of Corrosion Engineers), it was estimated that the direct and indirect costs of corrosion in the United States is approximately 6.2% of the GDP. In 2016, that cost exceeded $1 trillion dollars for the first time. Download Now

Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close