I was reading about Newcomen’s engine where the introduction of water to the cylinder makes the steam go into liquid, and they refer to it as “partial vaccuum” creation. How come?
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Because it is the most intuitive way to understand physical forces in the engine.
Total vacuum does’t really exist. Even in space, the odd particle flies by randomly.
“Vacuum” is a comparative description of differential pressure, where pressure on one side of the system approaches 0.
Steam is hot gaseous water vapour. Hot vapourous gases occupy far more volume at a given pressure than when in their liquid state.
By cooling steam, you turn it back into a liquid which occupies negligible volume compared to steam. Whatever pressure the steam exerted on the cylinder suddenly becomes negligible.
When a sudden reduction in gas pressure occurs relative to atmospheric pressure, it makes sense that atmospheric pressure will try to force itself into the space left by the cantracting gas. Because this phenomenon resembles what occurs when you evacuate the cylinder, describing it as a partial vacuum is intuitively accurate.
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