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Fluid Mechanics
Flow Through Pipes
GATE 2011
Hard

Two liquids (P and Q) having same viscosity flow through a double pipe heat exchanger — P through the annulus, Q through the inner pipe. Densities of P and Q are 1000 and 800 kg/m³. Average velocities are 1 and 2.5 m/s. Inner diameters of the pipes are 0.31 and 0.1m. Both pipes are 5mm thick. The ratio of the Reynolds numbers ReP to ReQ is

  • A2.5
  • B1.55
  • 1
  • D4

Explanation

Inner pipe OD=0.1+2×0.005=0.11m. Annulus hydraulic diameter Dh,P=Do−Di=0.31−0.11=0.20m. ReP=ρP·VP·Dh,P/μ=1000×1×0.20/μ=200/μ. ReQ=ρQ·VQ·DQ/μ=800×2.5×0.1/μ=200/μ. Ratio ReP/ReQ=1.

Source: GATE CH 2011 (2011)

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