Fluid flow question through hose

Click For Summary

Discussion Overview

The discussion revolves around calculating pressure drops in hoses of different diameters while maintaining the same flow rate. Participants explore the factors influencing pressure drop and methods for measurement and calculation, focusing on a practical application involving hoses with specific dimensions.

Discussion Character

  • Technical explanation
  • Mathematical reasoning

Main Points Raised

  • One participant seeks to understand how to calculate pressure drops through hoses of different sizes while using the same flow rate.
  • Another participant suggests measuring the pressure difference (delta P) rather than calculating it, emphasizing the need to adjust the pump pressure to achieve equal flow rates.
  • A third participant outlines the factors affecting pressure drop, including fluid density, velocity, hose roughness, length, diameter, and elevation changes, and provides a standard equation for calculating pressure drop.
  • The equation presented includes variables such as fluid density, friction factor, length, velocity, diameter, and elevation change, with a note on the importance of determining the flow regime to find the friction factor.
  • A later reply recommends consulting the Moody chart for additional information on flow regimes and friction factors.

Areas of Agreement / Disagreement

Participants present various approaches to understanding pressure drop, with some focusing on calculation methods and others on measurement techniques. There is no consensus on a single method or approach, and multiple viewpoints remain regarding the best way to address the question.

Contextual Notes

The discussion includes assumptions about fluid properties and flow conditions that may not be explicitly stated, such as the type of fluid and flow regime. The reliance on empirical testing in certain flow conditions is also noted but not resolved.

greydient
Messages
15
Reaction score
0
Here's a silly question.

If I'm comparing two different sizes of hose, using the same flow rate in gpm, how do I calculate the pressure drops through each for comparison?

I'm considering using hoses with interior diameter .438 and .688, each with a length of 5 inches.
 
Engineering news on Phys.org
I am assuming that you want to measure the delta P, not calculate it. Calculating it is basic stuff.

If you are flowing to atmosphere on one end, you will have to adjust the pressure side of the pump you are using to get the flowrates to be equal between the two hose sizes. You can rely on a pressure gauge right at the outlet of the pump to give you the required delta P data.
 
Pressure drop depends on these items. The fluid density, fluid velocity, pipe (or hose) roughness, length of the pipe (or hose), diameter of pipe (or hose), and any elevation changes between the two ends.

A standard equation for pressure drop is given by:

delta p = ((pf*f*L*v^2)/(144*d*2*g)) + ((z*pf)/144)

where,

delta p = pressure drop in lbs/in^2
pf = density of fluid in lbs/ft^3
f = friction factor
L = length in feet
v = velocity of fluid in ft/sec
d = diameter in ft
g = gravitational acceleration in ft/sec^2
z = elevation change in feet

The friction factor, f, is found depending on whether the flow is laminar or turbulent. If you find that the flow is in the critical region (between laminar and turbulent, 2000 > Re < 4000), then emperical testing is more accurate.

Hope this helps...

PS
Make sure your units are the same as shown above!
 
look up Moody chart the rest is standard and described above. (find Re #)
 

Similar threads

Replies
4
Views
4K
Replies
0
Views
2K
  • · Replies 3 ·
Replies
3
Views
2K
  • · Replies 4 ·
Replies
4
Views
2K
  • · Replies 11 ·
Replies
11
Views
4K
  • · Replies 29 ·
Replies
29
Views
7K
  • · Replies 20 ·
Replies
20
Views
11K
  • · Replies 21 ·
Replies
21
Views
2K
  • · Replies 38 ·
2
Replies
38
Views
4K
  • · Replies 5 ·
Replies
5
Views
3K