Question

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

I got this question in unit test.

Question is from Hydraulic Gradient and Total Energy Line topic in chapter Flow Through Pipes of Fluid Mechanics

Answer 1

Correct answer is (a) HGL will never be above EGL

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

Hp = P ⁄ γ + z

where H is the total head, P ⁄ γ  is the pressure head, z is the potential head, Hp 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.