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# MCQs on Types of Flow in Channels

The flow characteristics of a channel does not change with time at any point. What type of flow is it?

a) Steady flow

b) Uniform flow

c) Laminar flow

d) Turbulent flow

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a

Explanation: The flow characteristics unchanged with time is a steady flow, characteristics unchanged with space is a uniform flow. Laminar and turbulent flows are classified with reference to Reynolds number.

The Reynolds number for a flow in a channel is 1000. What type of flow is it?

a) Laminar

b) Turbulent

c) Transition

d) Steady

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c

Explanation: Reynolds number – 500 to 600 – Laminar flow

Reynolds number – 500 to 2000 – Transition

Reynolds number – > 2000 – Turbulent flow.

The ratio of inertia force and gravitational force is called as ______

a) Reynolds number

b) Stokes number

c) Froude’s number

d) Euler’s number

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c

Explanation: Froude’s number is the ratio of inertia forces and gravitational forces. Froude’s number is used to classify the flow into critical, sub critical and super critical.

The Froude’s number for a flow in a channel section is 1. What type of flow is it?

a) Sub Critical

b) Critical

c) Super critical

d) Tranquil

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b

Explanation: Froude’s number = 1 – Critical flow

Froude’s number < 1 – Sub Critical flow Froude’s number > – Super Critical flow.

What is the Froude’s number for a channel having mean velocity 4.34 m/s and mean hydraulic depth of 3m?

a) 0.4m

b) 0.6m

c) 0.7m

d) 0.8m

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d

Explanation: Froude’s number (Fr) = V/ (gD2)

= 4.34/ (9.81) (32)

= 0.8m.

Calculate the mean hydraulic radius for a channel having 20m2 cross sectional area and 50m of wetted perimeter.

a) 0.4m

b) 0.5m

c) 0.6m

d) 0.7m

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a

Explanation: Hydraulic Radius(R) = A/P

= 20/50

= 0.4m.

Calculate the mean hydraulic depth of a channel having top width of 7m and cross sectional area of 35m2.

a) 4m

b) 5m

c) 6m

d) 7m

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b

Explanation: Hydraulic depth (D) = A/T

= 35/7

= 5m.

Estimate the section factor for a channel section having cross sectional area of 40m2 and hydraulic depth of 6m.

a) 94.3

b) 95.6

c) 97.9

d) 100

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c

Explanation: Section factor (Z) = A√D

= 40√6

= 97.9.

Calculate the Froude’s number for a channel having discharge of 261.03m3/s, cross sectional area of 42m2 and the top width being 6m.

a) 0.65

b) 0.72

c) 0.38

d) 0.75

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d

Explanation: Fr= V⁄√gD

V = Q/A

V = 261.03/42 = 6.215 m/s

D = A/T = 42/6 = 7m

Fr = 0.75 (Subcritical).

Calculate the aspect ratio having channel width of 6m and depth of 8m.

a) 0.75m

b) 1.33m

c) 1.50m

d) 1.68m

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b

Explanation: Aspect ratio = Depth / width

= 8/6 = 1.33m.

Estimate the type of flow in a channel having cross sectional area of 50m2 and top of the channel is 5m. The mean velocity of flow is 0.1m/s and the absolute viscosity of water is 0.625 N-s/m2.

a) Laminar

b) Turbulent

c) Transition

d) Steady

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c

Explanation: Reynolds number (Re)=1000VD/µ

Re = 1000(0.1) (D)/ 0.625

D = A/T = 50/5 = 10 m

Re = 1000(0.1) (10)/ 0.625

= 1600

Transition flow (500 – 2000).