Transcript FG-Ch03.ppt

Brief Summary of
Fay & Golomb Ch3
2/12/13
Chapter in Brief
• Objective: To present a brief yet comprehensive
overview of thermodynamic principles applied to
energy systems
• Forms of Energy
• Work and Heat
• First and Second Laws
• Thermodynamic Properties and Functions
• Heat Transfer
• Thermodynamic Cycles
• Energy Processing
Heat Engines
• A heat engine is a system that by
operating in a cycle on a working medium
transforms heat into work
• A thermopower plant is a heat engine that
transfers the work produced to an
external agent
• A refrigerating plant is a heat engine that
consumes heat provided by an external
agent
Thermopower Plants
• Key components
– Working Medium Carries out Expansion and
Produces Work
• Turbine (in in turbine engines)
• Cylinder/Piston (Expansion stroke in IC engines)
• Propelling Nozzle (in jet engines)
– Working Medium Undergoes Compression under
the influence of External Work
• Compressor (in turbine and jet engines)
• Cylinder/Piston (Compression Stroke in IC engines)
Thermodynamics of Heat Engines
• The principles of thermodynamics allow
the quantitative analysis of the energy
conversion efficiency of heat engines
• Representation of cycles in a p-V diagram
• Representation of cycles in a T-S diagram
Forms of Energy
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Mechanical Energy (Kinetic and Potential)
Internal Energy
Chemical Energy
Electric and Magnetic Energy
Nuclear Energy
Total Energy
Work and Heat
• Types of Work
– Due to force on a particle
– Due to pressure on a gas
– Due to electric potential on a charge
– Due to a torque on a rotating body
• Types of Heat
– Sensible heat
– Latent heat
Laws of Thermodynamics
• First Law:
– Energy is conserved
– Heat Input minus Work Done equal to Internal
Energy Change
• Second Law:
– The Entropy of the universe never decreases
Thermodynamic Properties
and Functions
• Intensive properties: e.g. p and T
• Extensive properties: e.g. V, Internal
Energy
• Specific properties: Extensive/mass
• Enthalpy H and Specific Heat Cp
• Gibbs Free Energy F
• Systems with Steady Flow ( h = q – w)
• Heat Transfer (Q = U T)
Thermodynamic Cycles
• Systems starts and ends in the same state
• Carnot
– Two isotherms+Two adiabats
– Efficiency = (Th-Tc)/Th
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Rankine
Otto
Brayton
Combined Cycles
Refrigeration Cycles
Energy Processing
• Schematic representation of energy processing
devices operating under steady flow conditions
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Inputs of mass, enthalpy, Gibbs free energy
Outputs of mass, enthalpy, Gibbs free energy
Heat Input
Work Done
• Conversion Constraint: w <= fin - fout
• Concept of Adiabatic Combustion Temperature
and Fuel Heating Value