WEIRS -NOTCHES SHORT QUESTION ANSWERS CLASS NOTES

 

WEIRS-NOTCHES 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 rate of flow of water in a river	It is to measure the rate of flow of water in a small channel Or 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 = (ρv²l / 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 multi-phase 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

2. 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

4. Write any one equation for head loss due to friction in a turbulent liquid flow in a pipe.

Darcy Welsbach equation is for frictional a pressure drop in a turbulent liquid flow in a pipe. It is given below:

Δh_f =4f l v² / 2gd

Where

Δh_f =head loss due to friction

f= friction factor = 0.06 to 0.006 for Re> 4000

l= Pipe length

v= velocity of fluid in pipe

d= diameter of the pipe

5. Explain major and minor losses in a pipe flow. State under what conditions the minor losses are negligible?

Major losses: Loss of pressure due to friction in a straight length of a pipe. It is significant. It is given by Darcy equation.

(Δh_f)_major =4f l v² / 2gd

Minor losses:  Due to change in velocity by a sudden enlargement, contraction, valves, bends and tees. All these are function of the larger velocity.

(Δh_f)_minor

sudden enlargement,  (Δh_f)_minor= (v1 – v2)²/ 2g,      v1 is bigger velocity.

sudden contraction, (Δh_f)_minor= 0.5v²/2g, v is the bigger velocity

entrance of a pipe        (Δh_f)_minor   = 0.5v²/2g, v is the bigger velocity

exit of a pipe         (Δh_f)_minor          = v²/2g, v is the bigger velocity

In a pipe fitting         (Δh_f)_minor   = k v²/2g

Q. list and explain the two most commonly used pipe joints.

A.

(i)  Socket and spigot joint

(ii) Flanged pipe joint

Socket and spigot joint: It is used in cast iron pipes. Every pipe has two ends. One end is straight called the spigot end. The other end is bigger in diameter and is called the socket end. The spigot end of one pipe goes into the socket end of the other pipe. The annular empty space between the socket and spigot is filled with jute thread flowed by molten lead. Lead on solidification forms a leak proof joint. Mostly these are used in underground pipes. It is a permanent joint.

Flanged pipe joint: These are used in pipes above the ground for water, wastewater, air and oil flow. Flanges to the pipe may be integral in the pipe or connected by a screwed joint, welded joint. These flanges use even number of bolts with a gasket in between to make the joint leak proof. It is a temporary joint and has easiness in cleaning, inspection, modification, repair, servicing and replacement.