# Fluid Mechanics Questions and Answers – Types of Flow in Channels

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This set of Fluid Mechanics Multiple Choice Questions & Answers (MCQs) focuses on “Types of Flow in Channels”.

1. The flow characteristics of a channel does not change with time at any point. What type of flow is it?
b) Uniform flow
c) Laminar flow
d) Turbulent flow

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.

2. The Reynolds number for a flow in a channel is 1000. What type of flow is it?
a) Laminar
b) Turbulent
c) Transition

Explanation: Reynolds number – 500 to 600 – Laminar flow
Reynolds number – 500 to 2000 – Transition
Reynolds number – > 2000 – Turbulent flow.

3. 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

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.
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4. 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

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

5. 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

Explanation: Froude’s number (Fr) = V/ (gD2)
= 4.34/ (9.81) (32)
= 0.8m.

6. 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

= 20/50
= 0.4m.

7. 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

Explanation: Hydraulic depth (D) = A/T
= 35/7
= 5m.

8. 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

Explanation: Section factor (Z) = A√D
= 40√6
= 97.9.

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

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).

10. 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

Explanation: Aspect ratio = Depth / width
= 8/6 = 1.33m.

11. 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

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).

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