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Last time we introduced the phenomenon of cavitation, which simply stated is the rapid formation and collapse of vapor bubbles within liquids. It’s a destructive force that eats away at the metal parts of water pumps, used in power plants and other industrial settings. To understand how cavitation comes into play, we’ll explore a branch of engineering known as thermodynamics. Cavitation doesn’t occur in a glass of water resting on a counter, but bring that water to a boil and the cavitation process will begin. That’s because cavitation is initiated when liquids change form from one physical state to another, in this case from a liquid to a vapor we commonly call steam. All liquids exist in three states, namely solid, liquid, and vapor, but in our thermodynamic analysis we’ll only consider two, liquid and vapor, because cavitation can’t occur in solids.
Thermodynamic Properties of Water and Cavitation
At normal atmospheric pressure of 15 pounds per square inch (PSI) which exists in the average kitchen, water remains in a liquid state between the temperatures of 32ºF and 212ºF. Above 212ºF water begins to boil, transforming into steam vapor. The state in which water exists depends on two thermodynamic properties, namely temperature and pressure. Change one of these variables and it affects the other, and thereby the conditions under which cavitation will occur. We’ll take an in-depth look at this next time when we revisit the topics of pressurization and vacuums. opyright 2018 – Philip J. O’Keefe, PE Engineering Expert Witness Blog ____________________________________ |
