Flow In Real Systems Flashcards
What are ‘minor’ losses in fluid flow systems?
‘Minor’ losses are additional sources of pressure loss in fluid flow systems, resulting from components that change flow direction, speed, or obstruct flow (bends, expansions, and contractions)
Minor losses are contrasted with major losses, which are primarily due to friction.
What are the two classifications of losses in fluid flow systems?
- Major losses
- Minor losses
What happens during a sudden expansion in a pipe?
The fluid must spread and slow down, creating areas of lower pressure and leading to the formation of eddies.
Define ‘eddies’ in the context of fluid flow.
Eddies are regions of swirling and recirculating flow that form flow separation, contributing to pressure loss.
What is a ‘vena contracta’?
A ‘vena contracta’ is the narrowest point of flow in a pipe contraction where fluid velocity is highest.
How can ‘diffusers’ help reduce pressure losses?
Diffusers gradually increase the diameter of the system to minimize flow separation.
What is the optimal diffuser angle to minimize losses?
Approximately 6-7°.
What effect do rounded corners have on pressure loss in pipes?
Rounded corners reduce pressure loss, especially when the radius of curvature is greater than 0.14 times the downstream pipe diameter.
How does a pipe bend affect fluid flow?
A pipe bend generates a force where the flow impacts the outer wall, creating pressure gradients and leading to the formation of eddies.
What is the relationship between the radius of curvature and pressure loss in bends?
The magnitude of pressure loss increases with sharper bends.
What are loss coefficients used for in calculating minor losses?
Loss coefficients are applied to compute overall pressure loss, often using head loss coefficients (K).
What is a check valve?
A check valve is a non-return valve that allows flow in only one direction.
What are control valves used for?
Control valves are used to stop/start flow, limit flow rate, or direct fluid in multiple directions.
Describe a spool valve.
A spool valve features seals along the surface of pistons that shift to direct fluid flow within a hydraulic system.
What is the flow coefficient (CQ) used for?
The flow coefficient (CQ) is used to calculate theoretical flow based on mean fluid velocity and restricted cross-sectional area.
Fill in the blank: The theoretical flow can be calculated as the product of the mean fluid velocity and _______.
[restricted cross-sectional area (A)]
True or False: Minor losses have a negligible effect on pressure loss in fluid systems.
False
What factors influence the magnitude of minor pressure losses?
- Properties of the fluid
- Properties of the flow
- Geometry of the system
How can minor losses be determined experimentally?
Head loss coefficients (K) are determined experimentally for different types of losses, with typical values found in textbooks.
What happens to flow through a contraction in a pipe?
The flow narrows and accelerates, forming pressure gradients and leading to flow separation and eddies.
What is the effect of fluid momentum in a pipe contraction?
Fluid momentum creates smaller regions of recirculating flow downstream, contributing to pressure loss.
In what context is Bernoulli’s equation applied while calculating flow through restrictors?
Bernoulli’s equation is used to calculate mean velocity as a function of pressure differential across the orifice.
