10. How much work can be extracted from heat? Hot source of energy Cold sink of energy heat energy delivered from source heat energy delivered to sink externally delivered work: conservation of energy Q T h Q h Q c W = Q h – Q c T c efficiency = = W work done Q h heat supplied
11. Let’s crank up the efficiency Let’s extract a lot of work, and deliver very little heat to the sink In fact, let’s demand 100% efficiency by sending no heat to the sink: all converted to useful work T h Q h Q c W = Q h – Q c T c efficiency = = W work done Q h heat supplied
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15. Example efficiencies of power plants Power plants these days (almost all of which are heat-engines) typically get no better than 33% overall efficiency
20. Heat Pumps and Refrigerators: Thermodynamics W = Q h – Q c Hot entity (indoor air) Cold entity (outside air or refrigerator) heat energy delivered heat energy extracted delivered work: conservation of energy Just a heat engine run backwards… T h Q h Q c T c efficiency = = W work done Q h heat delivered (heat pump) efficiency = = W work done Q c heat extracted (refrigerator)