AutoQuiz is edited by Joel Don, ISA’s social media community manager.

 

Today’s automation industry quiz question comes from the ISA Certified Automation Professional certification program. ISA CAP certification provides a non-biased, third-party, objective assessment and confirmation of an automation professional’s skills. The CAP exam is focused on direction, definition, design, development/application, deployment, documentation, and support of systems, software, and equipment used in control systems, manufacturing information systems, systems integration, and operational consulting. Click this link for more information about the CAP program.

What is the term used for phenomenon in liquid flow where falling static pressure causes the formation of vapor bubbles that subsequently collapse back into the all-liquid state as the fluid static pressure is recovered?

a) cavitation
b) pressure piling
c) saturation
d) vortex shedding
e) none of the above

   

Click Here to Reveal the Answer

 

Answer B is not correct. Pressure Piling is a condition that results from the ignition of pre-compressed gases in compartments or subdivisions other than those in which ignition was initiated.

Answer C is not correct. Saturation is a device characteristic exhibited when a further change in an input causes no further change in the output.

Answer D is not correct. Vortex Shedding is the phenomenon that occurs when fluid flows past an obstruction. The shear layer near the obstruction has a high velocity gradient, which makes it inherently unstable. At some point downstream of the immediate vicinity of the obstruction, the shear layer breaks down into well-defined vortices.

The correct answer is A, Cavitation. Cavitation is a two-stage phenomenon of liquid flow. The first stage is the formation of vapor bubbles within the liquid system because of the fluid’s static pressure falling below the fluid vapor pressure  The second stage is the collapse or implosion of these cavities back into an all-liquid state as the fluid decelerates and static pressure is recovered.

Reference: The Automation, Systems, and Instrumentation Dictionary, Fourth Edition, ISA.

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