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

• 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

• Rankine• Otto• Brayton• Combined Cycles• Refrigeration Cycles

Energy Processing

• Schematic representation of energy processing devices operating under steady flow conditions– 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