A pipe has a porous section of length L as shown in the figure. Velocity at the start of this section of V0. If fluid leaks into the pipe through the porous section at a volumetric rate per unit area q(x/L)2, what will be axial velocity in the pipe at any „x‟? Assume incompressible one dimensional flow i.e., no gradients in the radial direction ?

Correct answer: D. VX = V0 + (4/3) q (x3/L2D)

  • A. VX = V0 + q (x3/L2D)
  • B. VX = V0 + ⅓q (x3/L2)
  • C. VX = V0 + 2q (x2/LD)
  • D. VX = V0 + (4/3) q (x3/L2D)

Explanation

Continuity gives dV/dx = [q(x/L)²]P/A, and for a circular pipe P/A = 4/D. Integrating from 0 to x gives Vx = V0 + 4qx³/(3L²D), which is option d.

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