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Vacuum Demonstrations

One of the most important concepts in understanding the operation of the early steam engines is the creation of vacuum by condensation. These demonstrations provide simple illustrations using a soft drink bottle and boiling water.

The important thing to recognize is that condensation can pull a vacuum. The vacuum can be substantial if all the air is removed from the vessel before condensation. If air is completely removed and the vapor is condensed, the final pressure will be the vapor pressure of water. At 25C, this is 0.032 bar, 24 mm Hg, or 29.0 inches of vacuum!

Experiment Setup

The setup consists of a pot of colored water on the left. The pot is not heated. The pan on the right holds colored water that is boiling during experiments where the bottle is heated.

Demo using dry bottle without heating. Click the image to watch the demo.

This demo shows an inverted bottle being submerged in colored water. The air keeps the colored water from entering the inverted bottle and verifies that water will not spontaneously enter. You may want to skip this one if you understand that concept.

Demo using dry bottle. Click the image to load the movie.

Demo using water in bottle. Click the image to watch the movie.

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Updated 9/22/21 ,Copyright 2021, Carl T. Lira, lira@egr.msu.edu All rights reserved.
Prepared as a supplement to Introductory Chemical Engineering Thermodynamics.