IntermediateTopic 61 of 105Thermodynamics & Fluids
Minor losses
Valves, bends and fittings add loss coefficients.
In depth
Valves, bends, tees, entrances and exits cause losses h_m=K V²/2g with loss coefficient K (90° elbow ≈0.9, fully open gate valve ≈0.2, sharp entrance 0.5, exit 1.0). Often expressed as equivalent length. Sum with friction loss in energy equation.
Key points
- Loss coefficients from tables
- Smooth transitions reduce K
- Throttle valves add controllable loss
ExampleTen elbows in a system can cost more than metres of straight pipe.
Minor losses from valves, bends and fittings can be as large as pipe friction in short systems, so they must be included in pump calculations.
What is Minor losses?
Valves, bends and fittings add loss coefficients.
Why is it important to understand minor losses?
Minor losses from valves, bends and fittings can be as large as pipe friction in short systems, so they must be included in pump calculations.
What is a loss coefficient?
A dimensionless number K that multiplies the velocity head to give the loss through a fitting, which is typically found from tables.
Why are they called minor losses?
They are usually small compared with friction in long pipes, but they can dominate in short or heavily fitted systems.
How is Minor losses used in practice?
Typical applications include estimating the loss through a gate valve in a pump circuit, adding the losses of several elbows and a tee in a short pipe run and sizing a pump for a process system with many fittings.
What should I learn before Minor losses?
Study "Moody chart" first (topic 60 of 105 in Thermodynamics & Fluids). It covers the groundwork this topic builds on.
What are the key points of Minor losses?
Loss coefficients from tables. Smooth transitions reduce K. Throttle valves add controllable loss.
Can you give an example of Minor losses?
Ten elbows in a system can cost more than metres of straight pipe.
What comes after Minor losses?
The next topic is "Pipe networks", which builds directly on this one.
How difficult is Minor losses?
It is classed as Intermediate in Thermodynamics & Fluids (topic 61 of 105). It is an intermediate topic. Work through the beginner topics in Thermodynamics & Fluids first.