The Reynolds number for flow of a certain fluid in circular tube is specified as 2500. What will be the Reynolds number when the pipe diameter is increased by 20% and the fluid velocity is decreased by 40% keeping fluid the same?
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Question

The Reynolds number for flow of a certain fluid in circular tube is specified as 2500. What will be the Reynolds number when the pipe diameter is increased by 20% and the fluid velocity is decreased by 40% keeping fluid the same?

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G1 Physics · Accepted Answer

Step 1: Reynolds number Re=ρvD/η, so for the same fluid Re ∝ vD. Step 2: D increases by 20% and v decreases by 40%, giving Re′=2500×1.2×0.6=1800. Final answer: C.