WEIRS NOTCHES SHORT QUESTION ANSWERS CLASS NOTES
WEIRSNOTCHES SHORT
QUESTION ANSWERS
CLASS NOTES
Question answers help to increase
knowledge. It increases clarity and
depth of understanding. Then basic
principles are applied in practical
applications.
1. Define a Weir. State the difference between a notch and a weir.
A weir is a concrete or masonry structure. It is constructed across a river to raise the water level & measure the rate of water flow.
Or
It is a series of enclosures placed in a stream to catch fish.
State the Differences between a weir and a notch
Sr. No. 
Weir 
Notch 
1. 
It measures the rateof flow of water in a river 
It is to measure the rate of flowof water in a small channelOr in a small tank. 
2. 
Weirs are across big rivers and hence are big in size. 
Notches are smaller in sizes. 
3. 
A Weir is made of masonry or of concrete. 
A notch is metallic. 
Q2. What is a Weber number? State its significance.
Weber number (We) is a square root of the ratio of inertia force to surface tension. It is a dimensionless number. Mathematically
We = (ρv^{2}l / σ)^{0.5}
OR
The dimensionless Weber number (W) is ratio
( disturbing hydrodynamic inertia force/ surface tension force)^{0.5}
Significance
It is applied in solving fluid flows
(i) when there is an interface between two different fluids
(ii) for multiphase fluid flow with strong curved surfaces
(iii) same phase having different chemical properties
(iv) flow of oil and water
(v)involving thin film flows with formation of droplets & bubbles.
Practical examples
Examples of multiphase flow are
(i) simultaneous flow of oil, water and gas in the oil industry
(ii) mud slides
(iii) rain fall
(iv) snowfall
(v) fog phenomenon
(vi) avalanches
(vii) sediment transport
(viii) debris flows in nature

Give the values of Reynolds number
(i) for laminar and turbulent flows in a pipe
(ii) Flows over a flat plate.
Table: Values of Reynolds Number
Flow in a pipe Flow over a flat plate 

Laminar 
Turbulent 
Laminar 
Turbulent 
≤ 2100 
≥ 4000 
≤ 500000 
≥ 700000 