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# Review of Basic Principle of Thermodynamics 1

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Review of Basic Principle of Thermodynamics 1
1. Properties of Pure Substances 2. Heat and Work st Law for Closed Systems st Law for Control Volumes nd Law of Thermodynamics 6. Entropy Assoc.Prof.Sommai Priprem, PhD. Faculty of Engineering Khon Kaen University รศ.ดร.สมหมาย ปรีเปรม

T-v diagram of a pure substance
P2 >P1 Critical Point Tc Superheated Vapour Region Saturated Liquid-Vapour Region Compressed Liquid Region Saturated Liquid Line Saturated Vapour Line T-v diagram of a pure substance Sommai Priprem รศ.ดร.สมหมาย ปรีเปรม

P-v diagram of a pure substance
T2 >T1 Critical Point Superheated Vapour Region Saturated Liquid-Vapour Region Compressed Liquid Region Saturated Liquid Line Saturated Vapour Line P-v diagram of a pure substance รศ.ดร.สมหมาย ปรีเปรม

Thermodynamics Table Properties Relationship are too COMPLEX
Not simple EQUATIONS can be represented Therefore, TABLEs are more convenion Each substance; more than one table, Each table for each REGION ie.; Compressed Liquid Saturated Liquid and Saturated Vapour (2 = T table & P table) Superheated Vapour No table for Mixture  Calculate using Saturated Table + x รศ.ดร.สมหมาย ปรีเปรม

Critical Constants Table Compressed Liquid Table
Superheated Vapor Table T Compressed Liquid Table Saturated Table Saturated Liquid Line Saturated Vapour Line v Sommai Priprem รศ.ดร.สมหมาย ปรีเปรม

Saturated Liquid-Vapor Mixture
During vaporization (or Condenzation) process a substance exist both saturated Liquid and saturated Vapor. To analyze the mixture we need to know the QUALITY, x x = mvapor mtotal P or T v Critical Point Superheated Vapour Region Saturated Liquid-Vapour Region Compressed Liquid Region Saturated Liquid Line Saturated Vapour Line mass Piston Liquid Vapour Note < x < 1.0 vavg = vf + xvfg uavg = uf + xufg havg = hf + xhfg savg = sf + xsfg รศ.ดร.สมหมาย ปรีเปรม

Compressed Liquid or Subcooled Liquid
When saturated liquid is subjected to higher pressure it will not Saturated any more but will becomes Compressed Liquid P or T Critical Point Superheated Vapor Region Saturated Vapour Line Compressed Liquid Region On the other hand if saturated liquid is cooled it cannot stays Saturated but will becomes Subcooled Liquid Saturated Liquid Line Saturated Liquid-Vapour Region v Data for compressed liquid is limited. In absence of Table, a property, y (i.e. v,u,s), can be approximate as y = Tsat except: h = รศ.ดร.สมหมาย ปรีเปรม

Critical Constants Table Compressed Liquid Table
Ideal Gas Critical Constants Table Superheated Vapor Table T Compressed Liquid Table Saturated Table Saturated Liquid Line Saturated Vapour Line v รศ.ดร.สมหมาย ปรีเปรม

Ideal Gas Pv =RT ideal gas equation of state R = Ru/M kJ/kg-K
Ru = Universal gas constant = kJ/kmol-K = Btu/lbmol-R = 1545 ft-lbf/lbmol-R M = Molecular weight of the gas, kg/kMol m = nM n = number of mole of the gas รศ.ดร.สมหมาย ปรีเปรม

Pv = RT …...........(1) V=mv  PV = mRT ...............(2)
m=nM, R = Ru/M  PV = (nM)(Ru/M)T PV = nRuT (3) For a fixed mass; Eq (2) P1V1 = mRT1 and P2V2 = mRT2 P1V1 /T1 = P2V2/T2 รศ.ดร.สมหมาย ปรีเปรม

Generalized Compressibility Chart
Z = Pv/RT Pr = P/Pcr รศ.ดร.สมหมาย ปรีเปรม

Compressibility Factor, Z – A measure of Deviation from Ideal-Gas Behavior
Z = Pv/RT Pr = P/Pcr = reduced pressure Tr = T/Tcr = reduced temperature Conclusion from the chart at low P; Pr << 1; good to assume ideal gas regardless of T at high T; Tr > 2 ; good to assume ideal gas (except when Pr >> 1) Near Critcal Point ; Greatest deviation from ideal gas behavior รศ.ดร.สมหมาย ปรีเปรม

Moving Boundary Work P 1 2 v v1 v2 P P รศ.ดร.สมหมาย ปรีเปรม
Process path dv P 2 v1 v2 P รศ.ดร.สมหมาย ปรีเปรม

Work is a PATH function Amount of work involved depends not only on the initial and final state of the working fluid but also on the PROCESS as well. In this example, the beginning and final states are the same but WA>WB>WC v P 1 C B A 2 v1 v2 P รศ.ดร.สมหมาย ปรีเปรม

Specific Heat is defined as “the energy required to raise the temperature of a unit mass of a substance by one degree.” For fluids there are two different specific heat: Specific heat at constant volume, Specific heat at constant pressure, รศ.ดร.สมหมาย ปรีเปรม

Internal Energy, Enthalpy, and Specific Heat of Ideal Gases
v; du = CvdT p; dh = CpdT รศ.ดร.สมหมาย ปรีเปรม

To determine Δu and Δh of Ideal Gases
3- Ways Δu = u2 – u1 (Table) Δu = Cv,avΔT Δh  similar ways รศ.ดร.สมหมาย ปรีเปรม

Conclusion of Importance Equations of Chapter 3
Boundary Work; w =∫ Pdv (1) 1st Law general ΣEin - ΣEout = ΔE (2) Closed System; Q – W = ΔU + ΔKE + ΔPE (3) Enthalpy (defined) h = u + Pv (4) Specific Heat: du = CvdT (5) dh = CpdT (6) for Ideal gases: Cp = Cv + R (7) k = Cp/Cv (8) รศ.ดร.สมหมาย ปรีเปรม

The First Law of Thermodynamics : The Principle of Energy Conservation
Between State 1 Begining State 2 Final 1 unit of Energy E1 + ΣEin = E2 + ΣEout ΣEin - ΣEout = E2- E1 = ΔE รศ.ดร.สมหมาย ปรีเปรม

1st Law Equations (General)
Control Volume m2 m1 e +Q Q + ∑Eflow-in = W + ∑Eflow-out+(E2-E1) Subscripts: i = at inlet, e = at exit = at time start, 2 = at time end รศ.ดร.สมหมาย ปรีเปรม

Total Energy of Fluid for non-flow  mass inside control volume (cv)
enonflow = u + ke + pe kJ/kg Enonflow = m(u + ½ V2 + zg) J for flowing fluid  mass flowing in/out of cv. eflow = enonflow+ flow work eflow = u + Pv + ke + pe defined: h = u + Pv eflow = h + ke + pe kJ/kg Eflow = m(h + ½ V2 + zg) J รศ.ดร.สมหมาย ปรีเปรม

Sign Convention of HEAT and WORK
Heat Engine System Model Add heat to system, Qin System gives WORK, Wout +Q +W รศ.ดร.สมหมาย ปรีเปรม

1st Law Equations for cycles
Control Volume m1 m2 +Q i e Q + ∑Eflow-in = W + ∑Eflow-out+(E2-E1) Qnet = Wnet รศ.ดร.สมหมาย ปรีเปรม

1st Law Equations for Closed Systems
Control Volume m1 m2 +Q i e Q + ∑Eflow-in = W + ∑Eflow-out+(E2-E1) Q1-2 = W1-2 + (U2 – U1) +∆KE + ∆PE รศ.ดร.สมหมาย ปรีเปรม

1st Law Equations for SSSF Systems
Control Volume m1 m2 +Q i e Q + ∑Eflow-in = W + ∑Eflow-out+(E2-E1) รศ.ดร.สมหมาย ปรีเปรม

SSSF 1-inlet and 1-exit +W +Q i e Control Surface Control Volume
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Chapter 5 2nd Law of Thermodynamics
Assoc.Prof.Sommai Priprem, PhD. Department of Mechanical Engineering Khon Kaen University รศ.ดร.สมหมาย ปรีเปรม

Summary Processes occur in a certain direction, not in any direction.
A process will not occur unless it satisfy both 1st and 2nd law. Importance Definitions: Thermal Reservoir; Source, Sink Thermal Efficiency and Heat Engine Coefficient of Performance and Heat Pump Reversible Process and Irreversible Process Carnot cycle and Carnot Principles รศ.ดร.สมหมาย ปรีเปรม

Thermal Efficiency Performance = desired output (5.1) required input
Heat engine: Thermal efficiency = net work output (5.2) total heat input th = Wnet (5.3) Qin th = 1- QL (5.4) QH QL and QH are magnitude (amount) of heat, their direction are already accounted for in the equation. Heat Engine Source, TH Sink, TL Wnet QH QL รศ.ดร.สมหมาย ปรีเปรม

The Second Law of Thermodynamics: Kelvin-Planck Statement
It is impossible for any device that operates on a cycle to receive heat from a single reservoir and produce a net amount of work Source, TH Sink, TL Source, TH meaning: QL > 0 from th = Wnet = 1- QL QH QH No heat engine can have a thermal efficiency of 100 % Wnet QH QL Wnet QH QL = 0 Heat Engine Heat Engine Impossible Possible รศ.ดร.สมหมาย ปรีเปรม

The Second Law of Thermodynamics: Clausuis Statement
It is impossible to construct a device that operates in a cycle and produces no effect other than the transfer of heat from a lower-temperature body to a higher-temperature body. meaning: W > 0 from COP = Q W No heat pump can have a COP of  High-Temp. Body, TH High-Temp. Body, TH QH QL Q Heat Pump W Low-Temp. Body, TL Low-Temp. Body, TL Impossible Possible รศ.ดร.สมหมาย ปรีเปรม

High-temp. reservoir, TH
The Carnot Principles The efficiency of an irreversible heat engine is always less than the efficiency of a reversible one operating between the same two reservoirs. The efficiency of all reversible heat engines operating between the same two reservoirs are the same. High-temp. reservoir, TH Low-temp. reservoir, TL 1 Irrev. HE 2 rev. HE 3 rev. HE th,1 < th,2 th,2 = th,3 รศ.ดร.สมหมาย ปรีเปรม

Heat Engine Source, TH Sink, TL Wnet QH QL Reversible Cycle QH/QL = TH/TL (5.7) The Carnot Efficiency Heat Engine: th = 1- QL  th,rev = TL (5.9) QH TH Refrigerator COPR =  COPR,rev = (5.10) QH /QL – TH /TL – 1 Heat Pump COPHP =  COPHP,rev = (5.11) 1 – QL/QH TL/TH รศ.ดร.สมหมาย ปรีเปรม

Chapter 6 ENTROPY รศ.ดร.สมหมาย ปรีเปรม

Inequality of CLAUSIUS
Heat Engine Source, TH Sink, TL Wrev QH QL รศ.ดร.สมหมาย ปรีเปรม

ENTROPY: A Property of a System
Consider Two Reversible Cycles A-B and A-C A 1 2 C B รศ.ดร.สมหมาย ปรีเปรม

Two Important Thermodynamics Relations
Consider a internally reversible CLOSED system; 1st Law δQ = dU + δW TdS = dU +PdV T ds = du + Pdv (6.4) but h = u + Pv  dh = du + d(Pv) dh = du + Pdv + vdP substitute in (6.4) Tds = dh – vdP (6.5) รศ.ดร.สมหมาย ปรีเปรม

Principle of Increase of Entropy
Surroundings, temperature = T0 Q W System, temperature = T รศ.ดร.สมหมาย ปรีเปรม

Entropy Change of a Solid or Liquid
Solid & Liquid  Specific Heat = Constant ΔV very small  Δh~Δu ~ q ds = (Q/T)rev  du/T  CdT/T s2-s1  C ln(T2/T1) รศ.ดร.สมหมาย ปรีเปรม

Entropy Change of an Ideal Gas
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Isentropic Process of Ideal Gases
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Reversible Polytropic Process of Ideal Gases
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Second Law Efficiency รศ.ดร.สมหมาย ปรีเปรม

END รศ.ดร.สมหมาย ปรีเปรม

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