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PRACTICE / Critical speed and flow regimes

State the flow criterion first

For a circular pipe, adopt Re = ρvD/η and a transition criterion Re = 2000. The fluid has density 1000 kg/m³ and dynamic viscosity 0.001 Pa·s. The pipe diameter is 4.0 mm.

Find the mean speed at the adopted threshold.

Organize the givens & assumptions
  • Re = 2000
  • ρ = 1000 kg/m³
  • η = 0.001 Pa·s
  • D = 0.004 m

Newtonian fluid; v is the mean pipe speed and D the full diameter. The supplied threshold is a modelling criterion, not a universal sharp transition.

  1. A0.50 m/s0.50\ \mathrm{m/s}
  2. B1.0 m/s1.0\ \mathrm{m/s}
  3. C0.00050 m/s0.00050\ \mathrm{m/s}
  4. D2.0 m/s2.0\ \mathrm{m/s}

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