Calculate Pipe Sized Based on Pressure Differential and Flow Rate

In summary, the inside diameter of pipe needed to maintain a flow velocity of 300 ft/s is 0.729 meters.
  • #1
SonnyBoy
8
0
Hi, everyone. This is my first post so I figured I'd introduce myself very quickly before I get to the problem. My name is Matt and I'm a first year engineering student at Oregon State University. I've read quite a few topics here, but this is the first time I've really joined in on anything. I'm hoping to make that a more regular occurance as my knowledge grows.

Homework Statement


With a given flow rate of 26 CFM of air and a pressure differential of 1.5 inches of Mercury between the start and end of the pipe, what is the inside diameter of pipe is necessary to maintain a flow velocity of 300 feet per second, assuming there are no losses along the length of the pipe.


Homework Equations


This is the part I need help with. I'm not sure where to start.


The Attempt at a Solution


I will attempt it as soon as I know which equation(s) to use.
 
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  • #2
Problems states the volumetric flow rate is 26 CFM. What is the formula for volumetric flow rate?
 
  • #3
I'm afraid I don't have a formula for the flow rate, it's a given value for the equation along with the pressure differential and air velocity.
 
  • #4
Volumetric flow rate is 26 ft^3/minute. What two common flow parameters must be multiplied together to arrive at ft^3/minute? That tells you the formula to use.
 
  • #5
It's just Q = v * A? The pressure differential doesn't matter?
 
  • #6
I think it was a confusion factor. Volumetric flow rate is indeed velocity times area. You are given the velocity and the volumetric flow rate. Therefore you can compute the area once you make the units uniform.

Actually, I do not see how there is a pressure drop without friction unless the pipeline is going uphill or unless there is heat transfer or unless there is an area change.
 
  • #7
The question was academic, so I suspect that you are correct in your friction statement. For the purposes of this problem, an air pump was "sucking" the air through the pipe and the low pressure generated by the pump was 1.5" of Hg.
 
  • #8
You'll be studying Fanno and Rayleigh flow in the future. Fanno flow is flow considering frictional effects while Rayleigh flow is flow considers heat transfer effects. In the real world, you have them simultaneously.

Good fortune with your studies.
 
  • #9
Thanks very much for the help!
 

1. How do I calculate the required pipe size based on pressure differential and flow rate?

To calculate the required pipe size, you will need to know the flow rate (in gallons per minute or cubic meters per hour) and the pressure differential (in pounds per square inch or kilopascals) of the fluid running through the pipe. You can then use a pipe sizing calculator or consult a pipe sizing chart to determine the appropriate pipe size for your specific application.

2. Why is it important to calculate pipe size based on pressure differential and flow rate?

Calculating the pipe size based on pressure differential and flow rate is important because it ensures that the fluid can flow through the pipe at the desired rate without causing excessive pressure or friction. This is crucial for the proper functioning and efficiency of any system that relies on fluid flow, such as plumbing, irrigation, or industrial processes.

3. Are there any other factors that should be considered when determining pipe size?

Yes, in addition to pressure differential and flow rate, there are other factors that should be considered when determining pipe size. These include the type of fluid being transported, the temperature and viscosity of the fluid, the length and elevation of the pipe, and the desired velocity of the fluid. These factors may affect the required pipe size and should be taken into account for accurate calculations.

4. What happens if the pipe size is too small?

If the pipe size is too small, it can cause excessive pressure drop, which can lead to reduced flow rates, system inefficiency, and potential damage to the pipe or equipment. This can also result in increased energy costs and maintenance expenses. In extreme cases, a small pipe size can cause the system to fail completely.

5. Can pipe size be changed after installation?

While it is possible to change the pipe size after installation, it can be a costly and time-consuming process. It is best to carefully calculate and select the appropriate pipe size before installation to avoid any potential issues or added expenses in the future. If changes need to be made, it is recommended to consult a professional to ensure the new pipe size will meet the system's requirements.

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