Which factor causes the greatest friction loss in a pipe?

Which factor causes the greatest friction loss in a pipe?

• A. Increasing the velocity of the fluid
• B. Increasing pipe length
• C. Increasing pipe diameter
• D. Higher fluid temperature

Answer: (A)

Friction losses in a pipe scale strongly with how fast the fluid is moving. The standard relationship shows head loss is proportional to the square of the flow velocity (hf ∝ v^2), along with factors for pipe length and diameter. This means increasing velocity makes friction loss grow very quickly—doubling the velocity makes the loss roughly four times larger, all else equal. If you lengthen the pipe, losses increase, but only linearly with length. Increasing the pipe diameter tends to reduce losses for a given flow because it lowers velocity and changes the L/D term, so it isn’t a factor that increases friction loss. Temperature effects modify viscosity a bit, which has a relatively small impact compared with changing velocity or length. So, the factor that causes the greatest friction loss among the options is increasing the velocity of the fluid, because its effect is squared in the head loss relationship.

Friction losses in a pipe scale strongly with how fast the fluid is moving. The standard relationship shows head loss is proportional to the square of the flow velocity (hf ∝ v^2), along with factors for pipe length and diameter. This means increasing velocity makes friction loss grow very quickly—doubling the velocity makes the loss roughly four times larger, all else equal.

If you lengthen the pipe, losses increase, but only linearly with length. Increasing the pipe diameter tends to reduce losses for a given flow because it lowers velocity and changes the L/D term, so it isn’t a factor that increases friction loss. Temperature effects modify viscosity a bit, which has a relatively small impact compared with changing velocity or length.

So, the factor that causes the greatest friction loss among the options is increasing the velocity of the fluid, because its effect is squared in the head loss relationship.