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Lester Stewart
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8//005 herodynaics ecture Series Entropy uantifyg Energy Degradation Applied Sciences Education Research Group (ASERG) Faculty of Applied Sciences Universiti eknologi MARA eail: drjjlanita@hotail.

y/staff/drjj/ uotes he prcipal goal of education is to create en and woen who are capable of dog new thgs not siply repeatg what other erations have done Jean Piaget What we have to learn to do we

Energies as causes (ats) of change W W Mass 8//005 Copyrights DR JJ ASERG FSG UiM Shah Ala 005 3 Review - First aw Energy Enterg a te - Energy eavg a te Energy Balance Change of te s energy E E E kj

1 8//005 herodynaics ecture Series Entropy uantifyg Energy Degradation Applied Sciences Education Research Group (ASERG) Faculty of Applied Sciences Universiti eknologi MARA eail: uotes he prcipal goal of education is to create en and woen who are capable of dog new thgs not siply repeatg what other erations have done Jean Piaget What we have to learn to do we learn by dog Este 8//005 Copyrights DR JJ ASERG FSG UiM Shah Ala 005 ow to relate changes to the cause Review - First aw Mass Properties will change dicatg change of state Syste E P V o E P V Dynaic Energies as causes (ats) of change W W Mass 8//005 Copyrights DR JJ ASERG FSG UiM Shah Ala Review - First aw Energy Enterg a te - Energy eavg a te Energy Balance Change of te s energy E E E kj or e e e kj/kg or E 8//005 Copyrights DR JJ ASERG FSG UiM Shah Ala E E Review - First aw Mass Enterg a te - Mass eavg a te Mass Balance Change of te s ass kg or 8//005 Copyrights DR JJ ASERG FSG UiM Shah Ala kg / s Energy Balance Control Volue Steady-Flow Steady-flow is a flow all properties with boundary of the te reas constant with tie E 0 kj; e 0 kj/kg V 0 3 ; 0 or kg 0 kg/s Review - First aw 0 or kg/s 8//005 Copyrights DR JJ ASERG FSG UiM Shah Ala Copyrights DR JJ ASERG FSG UiM Shah Ala 005

2 8//005 Mass balance Review - First aw Mass & Energy Balance Steady-Flow: Sgle Strea 0. So kg/s Workg fluid: Water - ω - ω ω net + Second aw igh Res. Furnace Stea Power Plant Purpose: Produce work W ω ω net Energy balance + W W E 0. So E ϑ ϑ + ω ω θ θ kj/kg kj/s 8//005 Copyrights DR JJ ASERG FSG UiM Shah Ala E ω net - ow Res. Water fro river An Energy-Flow diagra for a SPP 8//005 Copyrights DR JJ ASERG FSG UiM Shah Ala Second aw heral Efficiency for stea power plants ω η desired put ω η reuired put net net 8//005 Copyrights DR JJ ASERG FSG UiM Shah Ala Workg fluid: Ref-34a ω - ω ω net - ω net - Second aw igh Res. itchen roo / Outside house Refrigerator/ Air Cond ow eperature Res. Inside fridge or house ω net Purpose: Mata space at low by Reovg An Energy-Flow diagra for a Refrigerator/Air Cond. 8//005 Copyrights DR JJ ASERG FSG UiM Shah Ala Second aw Coefficient of Perforance for a Refrigerator desired put COP R reuired put ω COP R ω net net 8//005 Copyrights DR JJ ASERG FSG UiM Shah Ala 005 Workg fluid: Ref-34a ω net + ω net - Second aw igh eperature Res. Inside house eat Pup Purpose: Mata space at high by supplyg ω net ω net - ow eperature Res. Outside house An Energy-Flow diagra for a eat Pup 8//005 Copyrights DR JJ ASERG FSG UiM Shah Ala 005 Copyrights DR JJ ASERG FSG UiM Shah Ala 005

3 8//005 Second aw Coefficient of Perforance for a eat Pup desired put COP P reuired put ω COP P ω net net 8//005 Copyrights DR JJ ASERG FSG UiM Shah Ala Second aw Energy Degrade What is the axiu perforance of real enges if it can never achieve 00%?? Factors of irreversibilities less heat can be converted to work Friction between ovg surfaces Processes happen too fast Non-isotheral heat transfer 8//005 Copyrights DR JJ ASERG FSG UiM Shah Ala Second aw Drea Enge Carnot Cycle Isotheral expansion Slow addg of resultg work done by te (te expand) W U 0. So W. Pressure drops. Adiabatic expansion 0 W U. Fal U saller than itial U. & P drops. Second aw Drea Enge Carnot Cycle Isotheral copression Work done on the te Slow rejection of - + W U 0. So W. Pressure creases. Adiabatic copression 0 + W U. Fal U higher than itial U. & P creases. 8//005 Copyrights DR JJ ASERG FSG UiM Shah Ala //005 Copyrights DR JJ ASERG FSG UiM Shah Ala Second aw Drea Enge Carnot Cycle Second aw Drea Enge Reverse Carnot Cycle P kpa P - ν diagra for a Carnot (ideal) power plant P kpa P - ν diagra for a Carnot (ideal) refrigerator ν 3 /kg 8//005 Copyrights DR JJ ASERG FSG UiM Shah Ala i n 8//005 Copyrights DR JJ ASERG FSG UiM Shah Ala ν 3 /kg Copyrights DR JJ ASERG FSG UiM Shah Ala 005 3

4 8//005 Second aw Drea Enge Carnot Prciples For heat enges contact with the sae hot and cold reservoir All enges have the sae perforance. Real enges will have lower perforance than the ideal enges. rev () () 8//005 Copyrights DR JJ ASERG FSG UiM Shah Ala Workg fluid: Not a factor P: η η η 3 Second aw igh Res. Furnace Stea Power Plants An Energy-Flow diagra for a Carnot SPPs ω net P: η real < η rev () ηrev () ow Res. Water fro river real 8//005 Copyrights DR JJ ASERG FSG UiM Shah Ala η Workg fluid: Not a factor COP P Second aw igh Res. itchen roo / Outside house Rev. Fridge/ eat Pup COP ω net COPP rev COPR rev rev ow eperature rev COP Res. Inside COPR rev P rev fridge or house An Energy-Flow diagra for Carnot Fridge/eat Pup 8//005 Copyrights DR JJ ASERG FSG UiM Shah Ala 005 R Second aw Will a Process appen Carnot Prciples For heat enges contact with the sae hot and cold reservoir P: η η η 3 (Euality) P: η real < η rev (Ineuality) ηreal η rev Processes satisfyg Carnot Prciples obeys the Second aw of herodynaics 8//005 Copyrights DR JJ ASERG FSG UiM Shah Ala 005 Second aw Will a Process appen Clausius Ineuality : Su of / a cyclic process ust be zero for processes and negative for real processes δ kj δ kj kg δ 0 δ < 0 real δ ipossible > 0 8//005 Copyrights DR JJ ASERG FSG UiM Shah Ala δ Second aw Will a Process appen Source rev Stea Power Plant ω net Sk Processes satisfyg Clausius Ineuality obeys the Second aw of herodynaics Carnot SPP 8//005 Copyrights DR JJ ASERG FSG UiM Shah Ala Copyrights DR JJ ASERG FSG UiM Shah Ala 005 4

5 8//005 Entropy Entropy uantifyg Disorder ds δ t rev Entropy Change a process S S ds Source source + Stea Power Plant Sk ω net δ S S s k + t rev 8//005 Copyrights DR JJ ASERG FSG UiM Shah Ala Entropy uantifyg Disorder Entropy uantitative easure of disorder or chaos Is a te s property just like the others Does not depend on process path as values at every state 8//005 Copyrights DR JJ ASERG FSG UiM Shah Ala Entropy uantifyg Disorder Entropy uantifies lost of energy uality Can be transferred by heat and ass or erated due to irreversibilty factors: Frictional forces between ovg surfaces. Fast expansion & copression. eat transfer at fite teperature difference. 8//005 Copyrights DR JJ ASERG FSG UiM Shah Ala Entropy uantifyg Disorder Increase of Entropy Prciple he entropy of an isolated (closed and adiabatic) te undergog any process will always crease. isolated For pure substance : surr + surr 0 S ( ) (s s ) surr surr Surroundg Syste 8//005 Copyrights DR JJ ASERG FSG UiM Shah Ala So: Entropy uantifyg Disorder Increase of Entropy Prciple Proven Consider the followg cyclic process contag an ir forward path and a return path ir Clausius Ineuality δ δ + Entropy Change t rev δ hen: + S S δ S S 8//005 Copyrights DR JJ ASERG FSG UiM Shah Ala S S δ t rev ds δ Entropy uantifyg Disorder Increase of Entropy Prciple Proven Consider the followg cyclic process contag an ir forward path and a return path hen entropy change for the closed te: ir S S S S 8//005 Copyrights DR JJ ASERG FSG UiM Shah Ala S S > δ δ δ rev. irrev. Copyrights DR JJ ASERG FSG UiM Shah Ala 005 5

6 8//005 Entropy uantifyg Disorder Increase of Entropy Prciple Proven Consider the followg cyclic process contag an ir forward path and a return path hen entropy change for the closed te: ir S S 8//005 Copyrights DR JJ ASERG FSG UiM Shah Ala δ S S δ + S S S Sheat + S Entropy uantifyg Disorder Increase of Entropy Prciple Proven Consider the followg cyclic process contag an ir forward path and a return path hen entropy change for the closed te: S S Sheat + S ir For adiabatic process: Sadiab S S S S 0 + S S 8//005 Copyrights DR JJ ASERG FSG UiM Shah Ala Entropy uantifyg Disorder Increase of Entropy Prciple Proven Consider the followg cyclic process contag an ir forward path and a return path Entropy uantifyg Disorder Increase of Entropy Prciple Proven Consider the followg cyclic process contag an ir forward path and a return path hen entropy change for the closed te: S S Sheat + S ir For adiabatic te: Siso S S S S hen entropy change for the closed te: S S Sheat + S ir For isolated (adiabatic & closed) te iso 0 + S 0 Isentropic or constant entropy process S + surr 0 8//005 Copyrights DR JJ ASERG FSG UiM Shah Ala //005 Copyrights DR JJ ASERG FSG UiM Shah Ala Entropy uantifyg Disorder S diagra Area of curve under P V diagra represents total work done Area of curve under S diagra represents total heat transfer Recall ds δ t rev ence total heat transfer is δ t rev ds hen δ t rev ds Area under - S diagra is aount of heat a process 8//005 Copyrights DR JJ ASERG FSG UiM Shah Ala Entropy uantifyg Disorder s diagra C A da ds he fite area da area of strip ds ds Addg all the area of the strips fro state to state will give the total area under process curve. It represents specific heat received for this process 8//005 Copyrights DR JJ ASERG FSG UiM Shah Ala s kj/kg Copyrights DR JJ ASERG FSG UiM Shah Ala 005 6

7 8//005 Entropy uantifyg Disorder Factors affectg Entropy (disorder) Entropy will change when there is eat transfer (receivg heat creases entropy) Mass transfer (ovg ass changes entropy) Irreversibilities (entropy will always be erated) Entropy uantifyg Disorder Entropy Balance For any te undergog any process Energy ust be conserved (E E E ) Mass ust be conserved ( ) Entropy will always be erated except for processes Entropy balance is (S S + S ) 8//005 Copyrights DR JJ ASERG FSG UiM Shah Ala //005 Copyrights DR JJ ASERG FSG UiM Shah Ala Entropy uantifyg Disorder Entropy Balance Closed te Energy Balance: Entropy Balance: s + ω ω u + ke + pe 8//005 Copyrights DR JJ ASERG FSG UiM Shah Ala s + s s kj kg ( sheat + sass ) ( sheat + sass ) + s s ( s heat + 0 ) ( s heat ) s + s s + 0 ( s s ) + kj kg kj kg Entropy uantifyg Disorder + W W ϑ S S + S 0 hen: S S heat + S ass ϑ So S S 8//005 Copyrights DR JJ ASERG FSG UiM Shah Ala S heat + S ass + s s exit S S let Nozzle: Entropy uantifyg Disorder + W W ( ϑexit ϑlet Assue adiabatic no work done pe ass 0 Entropy Balance In State A << A ( h + ke h ke S + s s Out State S ( s s 8//005 Copyrights DR JJ ASERG FSG UiM Shah Ala let exit urbe: Entropy uantifyg Disorder + W W ( ϑexit ϑlet Assue adiabatic ke ass 0 pe ass 0 Entropy Balance W ( h h 8//005 Copyrights DR JJ ASERG FSG UiM Shah Ala let S + s s S ( s s exit In Out Copyrights DR JJ ASERG FSG UiM Shah Ala 005 7

8 8//005 Entropy uantifyg Disorder eat exchanger: energy balance; cases let Assue ke ass 0 pe ass 0 Case Case + W W ( ϑexit ϑlet 0 4 h4 3 h3 + h h h h 0 h h exit 8//005 Copyrights DR JJ ASERG FSG UiM Shah Ala Entropy uantifyg Disorder eat exchanger: Entropy Balance let exit Case S s4 3 s3 + s s Case S + s s 8//005 Copyrights DR JJ ASERG FSG UiM Shah Ala Entropy uantifyg Disorder Mixg Chaber: + W W let exit ϑ ϑ let 8//005 Copyrights DR JJ ASERG FSG UiM Shah Ala exit + W W 3 h3 h h S + 3 s3 s s 3 Copyrights DR JJ ASERG FSG UiM Shah Ala 005 8

Thermodynamics Lecture Series

Thermodynamics Lecture Series Second Law uality of Energy Applied Sciences Education Research Group (ASERG) Faculty of Applied Sciences Universiti Teknologi MARA email: drjjlanita@hotmail.com http://www.uitm.edu.my/faculties/fsg/drjj.html