How does pipe diameter affect pressure in fluid flow?

Click For Summary

Discussion Overview

The discussion revolves around how changes in pipe diameter affect pressure in fluid flow, specifically focusing on a scenario involving ethylene flowing from a 6" pipe into a 1" pipe at 400 psi. Participants explore the relationship between pressure and velocity, as well as the factors contributing to pressure changes, including friction losses and fittings.

Discussion Character

  • Exploratory, Technical explanation, Debate/contested

Main Points Raised

  • One participant suggests that pressure decreases and velocity increases when fluid flows from a larger diameter pipe to a smaller one, but seeks clarification on how pressure decreases and whether this decrease is linear.
  • Another participant emphasizes that they are not interested in calculating pressure loss across the length of the pipe, indicating a focus on understanding the nature of pressure changes rather than numerical calculations.
  • A different participant notes that pressure change is influenced by both velocity change and friction losses, suggesting that if the initial velocity is low, the pressure change may be negligible.
  • Minor losses due to fittings, such as reducers, are mentioned as factors that can affect pressure change, with a reference provided for further exploration of minor loss coefficients.

Areas of Agreement / Disagreement

Participants express differing views on the specifics of how pressure changes with diameter reduction, indicating that the discussion remains unresolved with multiple competing perspectives on the nature of pressure loss.

Contextual Notes

Participants acknowledge the complexity of pressure changes, including the roles of velocity and friction losses, but do not reach a consensus on the exact nature of these changes or their calculations.

DinjiP
Messages
7
Reaction score
0
How does change in pipe diameter affect pressure? For example, ethylene in a 6" pipe at 400 psi, enters a 1" pipe. How does the pressure change?

I am fairly sure that pressure decreases and velocity increases. However, I need to know how pressure decreases? At what rate? Is it linear?
 
Engineering news on Phys.org
I should point out, I do know how to calculate pressure loss across the length of a pipe. That is not what I am interested in.
 
DinjiP said:
I should point out, I do know how to calculate pressure loss across the length of a pipe. That is not what I am interested in.
Pipe friction is termed major losses, pressure drop due to fittings like valves, tees, or in your case a reducer (specifically a 6" to 1" reducer) are termed minor losses and are even easier to calculate. You can find an overview here:
http://www.engineeringtoolbox.com/minor-loss-coefficients-pipes-d_626.html
You'll have to do some more searching to find the minor loss coefficient for your specific fitting.
 
Pressure change, both due to velocity change and due to friction losses is a function of velocity. Since your starting pressure is high, if your velocity happens to be low, the pressure change may well be negligible.
 

Similar threads

  • · Replies 38 ·
2
Replies
38
Views
4K
  • · Replies 9 ·
Replies
9
Views
2K
  • · Replies 2 ·
Replies
2
Views
4K
  • · Replies 5 ·
Replies
5
Views
2K
  • · Replies 11 ·
Replies
11
Views
4K
  • · Replies 4 ·
Replies
4
Views
4K
  • · Replies 7 ·
Replies
7
Views
2K
  • · Replies 31 ·
2
Replies
31
Views
5K
  • · Replies 3 ·
Replies
3
Views
2K
Replies
0
Views
2K