ENGR 224 – Thermodynamics
Test #2 – Outline
Spring 2011
Chapter 6 – The Second Law of Thermodynamics
 Introduction to the 2nd Law
 1st Law and spontaneity
 Thermal Reservoirs
 Thermodynamic Cycles
o Heat engines: thermal efficiency
o Refrigerators: coefficient of performance
o Heat Pumps: coefficient of performance
o th , COPR, COPHP = fxns(QH, QC)
 The 2nd Law
o Clausius Statement and Kelvin-Planck Statement
o Perpetual motion machines
 Reversibility and Irreversibility
o Sources of irreversibility
 Friction
 Rapid compression or expansion
 Heat transfer through a finite temperature difference
 Others
o Internal and external irreversibility
 The Carnot Cycle
o A reversible heat engine can be reversed to become a refrigerator or heat pump
o PV Diagrams for Carnot Cycles
o Equipment that can be used to carry out a Carnot Cycle
o 1st and 2nd Carnot Principles – latest expression of the 2nd law
 Thermodynamic Temperature Scales
o Kelvin Relationship
o Kelvin temperature scale is identical to the ideal gas temperature scale
o Carnot (reversible) cycle efficiency and COP = fxns(TH and TC) ONLY.
o Plot th , COPR, COPHP as fxns of TH and/or TC.
Chapter 7 – Entropy
 Clausius Inequality
o Reversible and irreversible cycles
 Definition of Entropy
o Apply the definition to thermal reservoirs: S = Q / Tres
 Entropy Data
o Thermodynamic tables
o TS Diagrams
 Areas under internally reversible process paths are Q
 Area enclosed by a Carnot Cycle is W
 Entropy Generation
o Sgen definition and Suniv
 Qirrev < Area on a TS Diagram
 The 1st and 2nd Gibbs Equations

o Special Cases
 Solids and incompressible liquids
 Ideal Gases – Shomate Equation
 Ideal Gas Entropy Function: So(T)
 Constant heat capacities
Polytropic Processes
o Special Cases: Isobaric, isochoric, isothermal, isentropic
o Special P, V, T relationships
o Wb for polytropic processes
o PV and TS Diagrams of polytropic processes
o Isentropic Processes
 Relative properties and how to use them
Chapter 8 –Thermodynamics of Flow Processes
 Entropy Balances on Closed Systems
 Entropy Balances on Open Systems
o Transient and steady-state
o SISO and MIMO
 Mechanical Energy Balance Equation
o Internally reversible, steady-state, SISO
o Combination of 1st Law the definition of entropy
o Special Cases of MEBE
 Bernoulli – no shaft work

ˆ 
W
S
Pout
 Vˆ dP
- no shaft work and Epot = Ekin = 0
Pin




 WS on PV Diagrams
 WS for polytropic processes
Isentropic Efficiency
o Turbines, compressors, pumps and nozzles
o Accessible States
o HS Diagrams
Two-Stage Compression with Intercooling
o Reduced work to accomplish the same compression
o Ideal Gas with Constant Heat Capacities
 Optimal design: Px  Pin Pout and Wb easy to calculate
Lost Work
o
WS,lost  WS,rev  WS,act
o
WS,lost  Tsurr Sgen
 This applies for internal, external and total Sgen and WS,lost.
 Equations were derived for internal, external and total Sgen and WS,lost
o Equations for the lost work for cycles were derived
Second Law Efficiency
o Only defined for processes that produce or consume work
o A more reasonable measure of performance than the isentropic efficiency
o Ratio of actual and reversible work