Heat Engines

[MedPR]

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Hi, last section in my physics class 😀 This is totally conceptual and thus will help you with MCAT.

So the area under a PV curve is the amount of work done during the cycle. Obviously a perfect heat engine is impossible since some of the heat is always lost to the cold sink rather than being converted to work. This all makes sense to me. Graphically, however, it seems like if you maximized the heat extracted (which is what is causing your engine to be imperfect in the first place) all the way down to the x-axis, the area under the curve would increase, which indicates that the amount of work increases.

However, that's completely contradictory because that says "maximize heat extraction == maximize work."

What am I missing?

 

[milski]

Heat extracted is heat that was taken away from the system - that's the heat that was converted to work, not the one that went to the cold reservoir. What's in the CR is the heat left in the system, represented by the bottom line. Pushing that line down decreases the temp in the CR and increases the efficiency and extracted heat.