Railways Technical Ability Fluid Mechanics and Machinery Question Bank Fluid Mechanics

  • question_answer While water passes through a given pipe at a mean velocity 'V, the flow is found to change from laminar to turbulent. If another fluid of specific gravity 0.8 and coefficient of viscosity 20% of that of water, is passed through the same pipe, the transition of flow from laminar to turbulent is expected if the flow velocity is:

    A) 2V                               

    B) V

    C) V/2                              

    D) V/4

    Correct Answer: D

    Solution :

    Re \[=\frac{vd}{v}\] \[v=\frac{\mu }{\rho },\] \[{{v}_{2}}=\frac{0.2\mu }{0.8\rho }=\frac{\mu }{4\rho }=\frac{v}{4}\] \[\frac{vd}{v}=\frac{4{{v}_{2}}d}{v}\] \[{{v}_{2}}=\frac{v}{4}\]

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