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# Fluid Mechanics MCQ – Hydraulic Gradient and Total Energy Line

Energy gradient line takes into consideration

a) potential and kinetic heads only

b) potential and pressure heads only

c) kinetic and pressure heads only

d) potential, kinetic and pressure heads

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Answer: d

Explanation: EGL is obtained by plotting total head at various points along the axis of the pipe.

where H is the total head, P / γ is the pressure head, z is the potential head and v^{2} / 2g is the velocity head. Hence, EGL is also called Total Energy Line (TEL).

Hydraulic gradient line takes into consideration

a) potential and kinetic heads only

b) potential and pressure heads only

c) kinetic and pressure heads only

d) potential, kinetic and pressure heads

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Answer: b

Explanation: HGL is obtained by plotting piezometric head at various points along the axis of the pipe.

Hp = P ⁄ γ + z

where Hp is the piezometric head, P ⁄ γ is the pressure head and z is the potential head.

Which of the following is true?

a) EGL always drops in the direction of c

b) EGL always rises in the direction of flow

c) EGL always remains constant in the direction of flow

d) EGL may or may not in the direction of flow

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Answer: a

Explanation: EGL is obtained by plotting total head at various points along the axis of the pipe. Since the total head decreases in the direction of flow, EGL will always drop in that direction.

Which of the following is true?

a) HGL always drops in the direction of flow

b) HGL always rises in the direction of flow

c) HGL always remains constant in the direction of flow

d) HGL may or may not in the direction of flow

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Answer: d

Explanation: HGL is obtained by plotting piezometric head at various points along the axis of the pipe. Since pressure may either rise or fall in the direction of flow, HGL may or may not change in that direction.

Which of the following is true?

a) HGL will never be above EGL

b) HGL will never be under EGL

c) HGL will never coincide with EGL

d) HGL will may or may not be above EGL

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Answer: a

Explanation: EGL is obtained by plotting total head and HGL is obtained by plotting piezometric head at various points along the axis of the pipe.

H_{p} = P ⁄ γ + z

where H is the total head, P ⁄ γ is the pressure head, z is the potential head, H_{p} is the piezometric head, and v^{2} / 2g is the velocity head.

H = Hp + v^{2} / 2g Since Hp < H, HGL can never be above EGL.

The vertical intercept between EGL and HGL is equal to

a) pressure head

b) potential head

c) kinetic head

d) Piezometric head

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Answer: c

Explanation: EGL is obtained by plotting total head and HGL is obtained by plotting piezometric head at various points along the axis of the pipe.

H_{p} = P ⁄ γ + z

where H is the total head, P ⁄ γ is the pressure head, z is the potential head, H_{p} is the piezometric head, and v^{2} / 2g is the velocity head.

H – Hp = v^{2} / 2g, the vertical intercept between EGL and HGL is equal to the kinetic head.

The slope of HGL will be

a) greater than that of EGL for a pipe of uniform cross-section

b) smaller than that of EGL for a pipe of uniform cross-section

c) equal than that of EGL for a pipe of uniform cross-section

d) independent of that of EGL for a pipe of uniform cross-section

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Answer: c

Explanation: The vertical intercept between EGL and HGL is equal to the kinetic head. For a pipe of uniform cross-section, there will be no change in the velocity of flow across the pipe. Since the kinetic head remian constant, the slope of HGL will be equal than that of EGL.

For a nozzle, the vertical intercept between EGL and HGL

a) increases

b) decreases

c) remains constant

d) may increase or decrease

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Answer: a

Explanation: The vertical intercept between EGL and HGL is equal to the kinetic head. For a nozzle, the cross-sectional area decreases in the direction of flow leading to an increase in the velocity of flow across the pipe. Since the kinetic head increases, the vertical intercept between EGL and HGL will increase.

For a diffuser, the vertical intercept between EGL and HGL

a) increases

b) decreases

c) remains constant

d) may increase or decrease

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Answer: b

Explanation: The vertical intercept between EGL and HGL is equal to the kinetic head. For a diffuser, the cross-sectional area increases in the direction of flow leading to a decrease in the velocity of flow across the pipe. Since the kinetic head decreases, the vertical intercept between EGL and HGL will decrease.

Which of the following is true?

a) the slope of EGL will always be greater than that of the axis of the pipe

b) the slope of EGL will always be smaller than that of the axis of the pipe

c) the slope of EGL will always be equal to that of the axis of the pipe

d) the slope of EGL will always be independent of that of the axis of the pipe

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Answer: d

Explanation: EGL is obtained by plotting total head at various points along the axis of the pipe.

where H is the total head, P ⁄ γ is the pressure head, z is the potential head, , and v^{2} / 2g is the velocity head.

Hence, there is no relation whatsoever between the slope of EGL and that of the axis of the pipe.