# Energy & Its Impact on Global Society Jerome K. Williams, Ph.D. Saint Leo University Dept. Mathematics & Sciences.

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Energy & Its Impact on Global Society Jerome K. Williams, Ph.D. Saint Leo University Dept. Mathematics & Sciences

Chapter 4: Heat and Work Heat Engines Second Law Thermodynamics Engine Efficiency

Heat Engines Heat engines include all devices that take heat and convert it into useful work. – Automobile engine – Steam Turbine (Electrical Power Plant) Heat flow proceeds through a fluid medium (working fluid) – Gasoline (Automobile) :Water (Steam Turbine)

Heat Engines What energy conversions take place in a car and in an electric generating plant?

Heat Engines Energy Conservation tells us the following relationship is true. Systems can be open or closed in design

Heat Engines Types of Heat Engines (Table 4.3) – Vapor (Rankine) cycle: working fluid changes state – Gas Cycle: working fluid remains in gas phase

Heat Engines A Final Example of Heat Engine Device Ocean Thermal Energy Conversion (OTEC) – Use temperature difference at various depths in Ocean to generate electricity – http://www.youtube.com/watch?v=qGwsvuxuK7g http://www.youtube.com/watch?v=qGwsvuxuK7g

Second Law Thermodynamics Second Law relates to direction a physical process can proceed in by itself. Entropy is a property of a system; it measures the disorder of a system. Nature favors disorder.

Second Law Thermodynamics In an isolated system the entropy change for a spontaneous system can only increase or stay the same. Second Law states that the amount of disorder in the world is continually increasing. “Arrow of Time” shows direction of process

Second Law Thermodynamics Can we go against Mother Nature? Yes, but to increase the order of a system one must supply external work (energy) to make this happen.

Second Law Thermodynamics Statements of Second Law Thermodynamics – 1. Heat flows spontaneously (by itself) from heat source to cold sink. – 2. No engine can be constructed that takes heat from a hot source and converts it entirely to useful work. Some heat must be lost to cold sink.

Engine Efficiency First Law: Work output = Heat input minus Heat transferred out. Remember: Temperatures must be in Kelvin

Engine Efficiency Efficiency of Engine will always be less than 100% due to heat loss that must occur. Perpetual Motion Machines??

Engine Efficiency

Problems 3, 4, 16, 18, 21, 22, 28, 32

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