This question is from Fundamentals of Engineering Thermodynamics, Moran Shapiro,

Question

This question is from Fundamentals of Engineering Thermodynamics, Moran Shapiro, 7th Ed. (Ch 5, #77)

"A quantity of water within a piston-cylinder assembly executes a Carnot power cycle. During isothermal expansion, the water is heated from saturated liquid at 50 bar until it is a saturated vapor. The vapor then expands adiabatically to a pressure of 5 bar while doing 364.31 kJ/kg of work."

I do not understand the wording. How can something be heated during isothermal expansion, and do work while expanding adiabatically?

Explanation / Answer

1) During an isothermal process, the temperature does not change. This is not the same as not adding heat.

2) During an adiabatic process, no heat is exchanged with the environment. This does not mean no work is done. In fact, work must be done, because the vapor expanded and dW = p*dV, dV isn't 0 and p isn't 0 either -> dW isn't 0.

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