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Fluid Mechanics - Engineering

Q1:

Pick out the wrong statement about cavitation.

A Sudden reduction of pressure in a fluid flow system caused by flow separation, vortex formation or abrupt closing of valve leads to cavitation.

B Cavitation may be caused due to boiling of liquid by decreasing the pressure resulting in formation & collapse of vapor cavities.

C Cavitation begins at higher static pressure and lower velocity in larger diameter pipelines resulting in audible noise.

D Large scale cavitation can not damage pipeline, restrict fluid flow and damage steam turbine blades.

ANS:D - Large scale cavitation can not damage pipeline, restrict fluid flow and damage steam turbine blades.

The wrong statement about cavitation is: Large scale cavitation can not damage pipeline, restrict fluid flow and damage steam turbine blades. Here’s why this statement is incorrect:

  • Impact of Cavitation: Cavitation can indeed cause significant damage and operational issues in fluid systems:
    1. Damage to Pipeline: Cavitation can erode and damage the internal surfaces of pipelines, especially at areas where it occurs intensely. This erosion can weaken the pipeline over time.
    2. Fluid Flow Restriction: The formation and collapse of vapor cavities (bubbles) during cavitation can create turbulence and pressure fluctuations, which may lead to flow restriction and inefficient operation of the system.
    3. Damage to Turbine Blades: In steam turbines or other rotating equipment, cavitation can lead to erosion and pitting on the surfaces of turbine blades or other components exposed to the cavitation zone. This can degrade the efficiency and lifespan of the equipment.
  • Cavitation Characteristics: Cavitation typically starts at regions of lower pressure and higher velocity, not higher static pressure and lower velocity in larger diameter pipelines as stated in the incorrect option.
In summary, large scale cavitation can indeed cause damage to pipelines, restrict fluid flow, and damage turbine blades, making the statement incorrect.