Energy grade lines in pipe flow – position of the Total Energy Line (TEL) The total energy line lies above the pipe centre line by an amount equal to:

Introduction:
Two reference lines describe energy in pipe flow: the Hydraulic Grade Line (HGL) and the Total Energy Line (TEL). Understanding their vertical positions relative to the pipe center line helps visualize pressure and kinetic energy distribution.

Given Data / Assumptions:

• Steady incompressible flow in a pipe of constant elevation reference.
• Centre line chosen as z = 0 for convenience.
• No pump/turbine between the two nearby sections considered.

Concept / Approach:
Bernoulli's equation per unit weight is H = z + p/gamma + V^2/(2g). The HGL represents z + p/gamma, while the TEL represents the full H. If the centre line is the elevation datum (z = 0), the TEL is above it by p/gamma + V^2/(2g).

Step-by-Step Solution:
1) Write H at the section: H = 0 + p/gamma + V^2/(2g).2) The vertical distance from centre line to TEL is H.3) Therefore, the distance equals pressure head plus velocity head.

Verification / Alternative check:
HGL sits below TEL by exactly the velocity head. Observing piezometer level (HGL) and total head (Pitot, TEL) in experiments confirms this spacing.

Why Other Options Are Wrong:

• Pressure head: misses the velocity head contribution.
• Velocity head: misses the pressure head contribution.
• Pressure head − velocity head: not consistent with Bernoulli representation.

Common Pitfalls:
Confusing HGL with TEL; forgetting that selecting the pipe centre line as datum sets z = 0, not removing other head terms.

Final Answer:
pressure head + velocity head