Question

The minor losses due to sudden contraction is significantly attributed to ____

• A. Flow contraction
• B. Expansion of flow after sudden contraction
• C. Boundary friction
• D. Cavitation

Hint:

Minor losses: \[ \boxed{ \begin{aligned} \text{Sudden Expansion} &\rightarrow \text{Loss due to expansion}\\ \text{Sudden Contraction} &\rightarrow \text{Loss mainly after vena contracta expansion} \end{aligned} } \]

Answer 1

The Correct Option is B

Step 1: Follow the flow right after the contraction.
When a pipe suddenly narrows, the flow can't hug the sharp corner instantly, so the jet keeps squeezing inward for a short distance past the junction, forming a section narrower than the pipe itself known as the vena contracta.
Step 2: Follow what happens right after that.
Beyond the vena contracta, the jet has to spread back out to fill the full width of the smaller pipe, and this sudden re-expansion creates turbulent eddies, exactly the same mechanism that causes losses at a sudden expansion.
Step 3: Compare where most of the energy actually goes.
The contraction itself is a fairly smooth, gradual squeezing, while the re-expansion afterward is abrupt and eddy forming, so the bulk of the head loss is attributed to this expansion of flow after the sudden contraction, not the contraction itself.
\[ \boxed{\text{Expansion of flow after sudden contraction}} \]