Lesson 6 - Principles of Fluid Mechanics 3
This lesson considers the factors which contribute to pressure loss when fluid follows through a pipe or duct system. It will examine in detail, the factors which contribute to frictional pressure losses and also losses due to the presence of fittings in the pipeline.
Design Flow Rates and Frictional Pressure Drops
In practice, the velocity and hence flow rate, and frictional pressure drops which transport fluids down pipes and ducts are not arrived at, or chosen, by chance. They are chosen based on either the perceived sensitivity of the fluid to transport or an attempt to reduce pumping costs of more robust fluids. Let us consider some typical values for the latter category of robust fluids, such as utilities fluids, water, steam, air, and CO₂ etc.
Typical fluid velocities and allowable pressure drops, which can be used to estimate pipe sizes, are given below.
Table: Typical fluid mean velocities and frictional pressure drops
|
|
Mean velocity (m/s) |
∆Pf |
|
Liquids, pumped (not viscous) |
1-3 |
0.5 kPa/m run |
|
Liquids, gravity flow |
- |
0.05 kPa/m run
|
|
Gases and vapours |
15-30 |
0.02% of line pressure |
|
High pressure steam (> 8 bar) |
30-60 |
- |