Vapor Pressure Phenomenon in Physics; Cavitation Problem

There are different kinds of phenomena about pure substances in thermodynamics and fluid mechanics. One of the phenomena is the vapor pressure of liquids. It is very important to understand this phenomenon for a designer or engineer. Because it affects the different kinds of systems in engineering.

So, you can find information about this pressure and cavitation problem in fluid mechanics and engineering.

Cavitation erosions.
Cavitation erosion on boat impeller(Image Source: Britannica).

What is the Vapor Pressure?

The vapor pressure of a substance is the pressure that it exerts at the phase equilibrium with its liquid. For pure substances, the vapor pressure is equal to the saturation pressure. At the saturation pressure of a pure substance, evaporation starts at a given temperature.

Partial Pressure

Also, this is a very important physical thing to be understood. The partial pressures of liquids are not the same as the vapor pressure for a given temperature.

The partial pressure is the pressure of a gas in a gas mixture. For example, atmospheric pressure is 101,325 Pa and the partial pressure of the vapor in this pressure is 2,300 Pa at room temperature.

But if we think about the vapor pressure of the water at room temperature of 2,340 Pa.

As you see above, there is a slight difference between the partial pressure of the water vapor and this pressure

Evaporation Process of Water

Because of this pressure difference between this pressure and the partial pressure of water, evaporation takes place. Once the partial pressure of vapor in that environment becomes equal to the vapor pressure of water, evaporation of water stops. This is the main mechanism behind the evaporation of water that has a temperature lower than the boiling point.

Cavitation Problem in Engineering

In the engineering systems such as impellers, pumps, and turbines, they need to make designs with consideration of cavitation problems.

In these systems, the pressure of the flowing fluid can decrease below the vapor pressure in some regions of the impellers or turbines. This may lead to unwanted vaporization in these sections. This phenomenon is called cavitation. And the bubbles are the cavitation bubbles.

These cavitation bubbles can lead to serious pressure waves and ripples on the impeller wings. Because of this, the performance and efficiency of machinery can drop. Also, massive corrosion on the mechanical elements takes place in the cavitation problem.

We can hear the cavitation sounds during the working of pumps and fluid machinery. Check the video below.


These are the general explanations of this phenomenon and the cavitation problems in engineering systems. You need to be aware of this phenomenon while you are designing your systems.

In conclusion, do not forget to leave your comments and questions below about this topic and cavitation.

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