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Advanced Thermodynamics

by: Laverne Langosh

Advanced Thermodynamics ME 3345

Laverne Langosh
Baylor University
GPA 3.79

Jeffrey Castleberry

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Jeffrey Castleberry
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This 141 page Class Notes was uploaded by Laverne Langosh on Saturday October 3, 2015. The Class Notes belongs to ME 3345 at Baylor University taught by Jeffrey Castleberry in Fall. Since its upload, it has received 30 views. For similar materials see /class/217945/me-3345-baylor-university in Mechanical Engineering at Baylor University.

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Date Created: 10/03/15
Thermodynamics Review and Fundamentals 10 January 2011 Steam Engines OttQ Vn Guericke 16505 Papin 1690 Practical Efficiency COAL combustion The heat required raise the temperature of 1 pound of water from 595 F to 605 F is 1 British Thermal Unit 1Btu Work Performed Work Force Distance 1 tquottbf QH W Work Rate Horsepower Caloric Theory of Heat Caloric an imponderable fluid invisible and weightless Selfrepulsive elastic attracted to ordinary matter Density of caloric is temperature Conserved property Dimensions and Units Dimensional Homogeneity Convert terms to a system of consistent units Perform algebra on the scalar values Assign correct units to the results Dimensional Analysis Units treated as algebraic entities Identity unit conversions Temperature Units Kelvin K absolute zero 0K triple point of water 27316K Celcius C water freezes at1 atm 0 C water boils at1 atm 100 C Fahrenheit F water freezes at1 atm 32 F water boils at1 atm 212 F Rankine R Absolute zero 0R Same magnitude as Fahrenheit Boundary System Surroundings System the quantity being studied Boundary simple closed surface that encloses the system fixed or movable Surroundings Outside the boundary unchanged by the processes going on in the system N1NNOUTA N NDESTROYEDNCREATED dN N IN N OUT dt N DESTROYED N CREATED Control Volumes Surroundings Transfer Out 0 O 0 Boundary System 3 destruction generation A change Transfer in Notation V Velocity ms or fts 1 71 Volume m3 orft3 v Specific Volume kag or ft3Ibm 2mi22k g3k g4k g l s s s Zmezlk gH e s s Work and Heat Heat Energy transfer into the system Positive heat energy transfer in Q EIN Negative heat energy transfer out Work Energy transfer out of the system Positive work energy transfer out E Negative work energy transfer In W OUT Sign conventions when transporting conserved properties across CV boundanes Units dimensional homogeneity and dimensional analysis Temperature units relative and absolute State Properties T P v u h s 4 g a State postulate state of a simple compressible system is completely specified by two independent intensive properties State Property Sources General substances Phases solid liquid gas During a phase change T and P are not independent Properties are tabulated lncompressible liquids and solids Properties are independent of pressure Gasses Real gasses properties are tabulated Equations of state Ideal gas law Van der Waals Virial Psycnrometncs Psychrometric Chart and Air Conditioning 4 April 2011 State Postulate Simpe Compressible Substance State defined by two independent properties Convenient to plot state on a 2D chart Psychrometric mixture State defined by three independent properties Cannot be plotted on a 2D chart But if one property was a constant Remaining two independent properties could be ploueo on a zu cnart Constant Total Pressure Vaid Assumption for v w Applications Air conditioning Humidification In general oosatT P a t0622 Ps T sa PPsatT But with constant pressure oosatT Saturation Absolute Humidity ssure 47 sia Satuvatiun pvessuve equatiun due in Hyiand and Wexiey Dyy Euib Tempevatuve Famenm iy Pounds Water Found Dry Air Him Relative Humidity Relative humidity P Absolute Humidity p At a given pressure amp i wT a 0622 P IiatT Relative Humidity r 47 sia Saiuiaiiun pvessuve menuquot We in Hyiand and Wexiei Dyy Euib Tempevaiuve Famenmi iy Pounds Waisr Found Dry Air Him Enthalpy Not a function of pressure h CWT ahfg CWT For a given h 03T h CPaT a hfg CP VT Enthalpy Samvatmn pvessuve Equauun m m Hy and and Wex ev Dyy Bum Tempevamve Fahvenhen Hummw Pounds Wam F mmd Dry Av Wet Bulb Isotherms 9 4 7 sia Samvatmn pvessuve Equauun m m Hy and and Wex ev Dyy Bum Tempevamve Fahvenhen Hummw Pounds Wam F mmd Dry Av Psychrometric Chart Example Given Humid Air Dry Bulb Temperature 80 F Pressure 147 psia Relative Humidity 30 Determine Absolute humidity Enthalpy Dew point temperature Wet bulb temperature Psyohrometric Chart 9 Pressure 147 sia Saiuiaiiun pvessuve Equaiiun m in Hyiand and Wexiev Given Tdb80 F 30 Determine Absolute humidity Answer 03 00065 Dyy Euib Tempevaiuve Famenm yipnunus Water F mmd Dry Air Hum Psyohrometric Chart Pressure 147 sia Samvatmn pvessuve equauun m m Hy and and Wex ev Given Tdb80 F 30 Determine Enthalpy Dyy Bum Tempevamve Fahvenhen Pounds Wam F mmd Dry Av Hum Psyohrometric Chart Pressure 147 sia Samvatmn pvessuve Equauun m m Hy and and Wex ev Given Tdb80 F 30 Determine Dew Point Temp Answer po 458 F Dyy Bum Tempevamve Fahvenhen Pounds Wam F mmd Dry Av Hum Psyohrometric Chart Pressure 147 sia 53mmquot pvessuve equauun m m Hy and and Wex ev Given Tdb80 F 30 Determine Wet Bulb Temp Answer wa 602 F Dyy an Tempevamve Fahvenhen Pounds Wam F nund Dry Av Hum Pschrometric Chart Processes Simple Heating cooling Humidifying with steam Evaporative Cooling Adsorption Dehumidifying by cooling Adiabatic Mixing Simple Heating amp Cooling No water added to or removed from the air gt gt Humid Air gt gt Flow gt gt H ating Element gt gt Humid Air gt gt Flow gt gt I I l C oling Coils Psyohrometric Chart 9 Pressure 147 sia Satuiatiun mm Equatiun m in Hyiand and Wexiei Heating amp cooling absolute humidity constant Diy Euib Tempeiatuie Fammii yipnunus Water F nund Dry Air Hum Steam Humidification Steam injected into humid air Psyohrometric Chart Pressure 147 sia Saiuraiiun pressure Equaiiun m in Hyiand and Wexier Steam Humidification Temperature increases El D28 W n ma Absolute humidity increases aw A1 9 n n24 9w Am 9 El D22 Dry Euib Temperature Fahrenheit Hurridiiy Pounds Water F mmd Dry Air Evaporative Cooling Liquid water in contac quotit uiu w Psyohrometric Chart Pressure 147 sia Samarmn pressure menuquot m m Hyrana and Wex er Izvaporatlve cooling Temperature decreases w A Wet Buleemperature constant 3w quot 9N m 9 Dry Burr Temperamre Fahrenhert Humduy Pounds Waer F mmd Dry Arr Adsorption Humid air moves through pacnw WV V desiccant material Psyohrometric Chart Pressure 147 sia Saiuraiiun pressure Equaiiun m in Hyiand and Wexier Adsorption Temperature increases Absolute humidity decreases Pounds Water F mmd Dry in i2 Dry Euib Temperature Fahrenheit Dehumidifying by cooling Humid air coolw bowquot dequot M temperature liquid water condensed out of the humid air Humid Air gt gt Flow gt gt 0 O 6 0 cocoofoo Psyohrometric Chart Pressure 147 sia Saluvaliun massqu Equaliun m in Hyland and Wexlev Dehumidifying by cooling First cooling with no change in humidity EIEIZE v9 EIqu Then coolinV I rocess follows My A1 um I VFW 59 saturation curve B Buzz Dyy Bull Tempevaluve Famenm Hummiy Pounds Waler F nund Dry Air Adiabatic Mixing Psyohrometric Chart Pressure 147 sia Saiuiaiiun pvessuve equaiiun m in Hyiand and Wexiev Adiabatic Mixing Mixed state lies between 1 and 2 Dyy Euib Tempevaiuve Famenmi yipnunus Waisr F mmd Dry Air Hum Psyohrometric Chart Pressure 147 sia Satuvatmn pvessuve Equatmn m m Hy and and Wex ev Indoor UOmTOfT Range 72 F lt Tdb lt 80 F 40 lt lt 60 Dyy Bum Tempevamve Fahvenhen Pounds Wam F mmd Dry Av Hum Gas Power Cycles Enhanced Otto Cycles and Atkinson Cycles 26 January 2011 Knock Ignition spark timing critical to engine performance andlongev y Combined high temperature and pressure can cause fuelair mixture to spontaneously combust too soon Rising piston collides with exploding charge Shock causes engine to ring at natural frequencies distinctive knocking or pinging sound Knock sensors tuned to detect vibrations at natural frequencies ECM responds by retarding spark timing leaning AF mixture Octane Number lsooctane has an octane number of 100 nheptane has an octane number of O 90 isooctane 10 nheptane 90 Equivalent octane number for gasoline determined in a variable compression ratio engine run at constant load speed and temperature RON Research Octane Number MON Motor Octane Number Difference between RON and MON is the fuel sensitivty Gas stations advertise the PON pump octane number PON is the average of MON and RON Price per gallon All taxes included MINIMUM OCTANE RATING FHM I 2 ME rHOD 8 Price per gallon All taxes included MINIMUM OCTANE RATING Hm I 2 METHOD MINIMUM OCTANE RATING RM I 2 METHOD 93 Otto Cycle Shortcomings Volume ratio same in compression and expansion At the end of expansion stroke the gas is still at high temperature and pressure exergy available Piston can t continue to expand gas exergy is lost in isometric cooling exhaust stroke in 4 stroke engine Otto Cycle Improvements Use exergy wasted at end of expansion Turbocharger PressureWave Supercharger Turbocharger Atkinson Cycle 12 Isentropic compression 23 Isometric Heating 34 Isentropic expansion 45 Isometric Cooling 51 Isobaric Cooling compression ratio it rC V2 V2 expansion ratio Atkinson Cycle Pi Pressure isometric cooHng net work out isentropic expansion isentropic compression isometric cooHng isoba c coolingcomp V Volume Gas Power Cycles Jet Engines 14 February 2011 Jet Engines Exhaust from turbine not expanded to ambient pressure Turbine powers compressor mainly plus small accessories generator fuel pump Turbine exhaust expands to ambient pressure in a nozzle velocity increases In flight intake air pressure rises in a diffuser velocity decreases P p u P r WP Fthrust Vaircraft Vexit Vinlet Vaircraft Diffusers amp Nozzles Adiabatic No shaft work Energy Balance 1 1 dE min hin Vi2n m0ut hout ViutE h and ke must be dimensionally similar Convert units EVEN IN SI Afterburners AF mixture in combustor is leaner than the stoichiometric ratio limited by turbine inlet temperature Bypass some of the air from the compressor goes around the combustor and the turbine Excess oxygen in exhaust can be used to burn more fuel raise nozzle inlet temperature higher exit velocity Ram Jet At higher speeds pressure recovery in inlet diffuser increases At supersonic speeds 2ltMlt6 pressure recovery in diffuser makes compressor and turbine uneccesary Inlet gtCombustor gtNozzle Ramjet Subsonic flow through combustor Scramjet Supersonic flow through combustor Thermodynamics Entropy and the 2nd Law of Thermodynamics 12 January 2011 Control Volume Analysis Generic Form N 1N N OUT 2 A N N DESTROYED N CREATED 1st Law of Thermodynamics N Energy ElN EOUTZAE 2nd Law of Thermodynamics N Entropy SIN SOUTZASSCREATED Energy Transfer o Work positive for energy going out boundary work changing the size of the CV fow work done by mass entering or exiting other shaft work electrical work etc o Heat positive for energy going in aways due to a temperature difference o Advection energy of mass entering or exiting Entropy Transfer SINZTQIJ Heat transfer direction of entropy transfer is the same as the heat heat in transfers entropy in Advection entropy of mass entering or exiting Calculating Entropy Change General form C 81 C 5p ds PdT dP v T 8T P ds T dT 6T va v Ideal Gas 2 2 2 2 CP CV 0117 s SI dTR szslTdTRP 21JT v Ideal Gas w constant specific heats T P T v sz slszln 2 Rln 2 Sz SIZCVPIH 2 Rln 2 T1 P1 1 v1 Calculating Entropy Change Ideal Gas w variable specific heats 0 0 0 0 P2 S2S1 P2 S2 S1 S2 S1 R1n 32 s1 Rln lncompressible liquids and solids T sz slCln T 2 1 Entropy Generation Sgen gt O possible Sgen O theroretical limit of what is possible Sgen lt O impossible Psyohrometry Evaporative Cooling Adiabatic Saturation and Wet Bulb Temperature 30 March 2011 Enthalpy Humid Air per mass of dry air h ijarmthfg CP3VT h 024 Btu Ta10609g t0435 Btu T 1me 1me Temperature in F h 21005kgiKT w25009kg K182 T Temperature in C kgK Liquid Water per mass of water hw 101th Temperature in F hw 41868kgLKT Temperature in C Evaporative Cooling Mass Balance Humid Humid mv1 m2 mv3 Liquid mz ma 3 wl water Energy Balance mall11 mzhz moth3 h1a3 a1h2 Adiabatic Saturation Saturated Humld Humid Air Air in out Air out is saturated 3 100 03 0622M P PSATZ Makeup water Makeup water in at temperature of air out Wet Bulb Temperature Thermometer cooled by evaporation Water soaked wick Airflow over wick Thermal boundary layer Massdiffusion boundary layer Different phenomena than adiabatic sat For waterair mixtures normal range of temperatures Wet Bulb Partial Pressure of vapor at We su aw Absolute humidity at WB surface vab wwb 0622 P vwb Absolute humidity of ambient air a Cpa wa Tdb wwb CpvabJ hfg Cpgdeb Vapor Cycles Vapor Compression Refrigeration 23 February 2011 Heat Engines amp Refrigerators Heat Engines Producedzw Consumed QH Refrigerators Produced QL Consumed W COPref QL Reversible Refrigerator COP for a refrigerator COPref QL W COP for a reversible refrigerator COP TLTH TL rev ref Second law efficiency of a refrigerator 1 COP COP ref rev ref Exergy Heat Engines Ein EoutZA Edest Em ZQn 1 QH 1 TL QL 1 E0152 WoutW EdestzQH 1 5 W TH Exergy Refrigerators Ein EoutZA Edest TO Ein ZQn T QL1 0 QH1T O L 0 Eut Z Wut W TO EdestZQL Vapor Compression Refrigeration Sat Liqid Exxap riamr SatVapor Gas Power Cycles Second Law Analysis of Gas Power and Otto Cycles 24 January 2011 Heat Engines Pressure Temperature 8 Volume Entropy Clockwise path area inside the loop is the net work output or net heat input Basic Processes Pressure ll isometric isobaric a L 3 A 4 1 V Q isothermal isobaric 8 Isothermal E a I isentropic Isometric r Entropy S Volume Totally Reversible Processes Internally Heat Externally Totally Reversible Transfer Reversible Reversible lsochoric Yes Yes No No HeatingCooling lsobaric Yes Yes No No ExpansionCompression Isothermal Yes Yes Yes Yes ExpansionCompression Adiabatic Yes No Yes Yes ExpansionCompression If the temperature difference between the system and the reservoir is infinitessimal Carnot Cycle Pressure l isentropic isothermal net work out isentropic isothermal Volume Temperature isothermal isentropic isothermal net heat in isentropic Entropy v The Otto Cycle Nikolaus August Otto German machine builder Invented carburetor and twostroke engine 1861 Invented and patented four stroke engine in 1876 Patent revoked in 1886 Otto Cycle named in his honor Otto Cycle Implementation Quasiturbine Reciprocating Piston Wankel Rotary mimic Am ltm 00 Oltom OO OltOm Imgt mmLmOjOZ Ii OOltummmmOZ Imgt gtUUOZ mxugtzmOZ OOltummmmOZ mxugtzmOZ mX1gtcm ZgtAm OOltwcmOZ LmNOAm mZQZm Ideal Otto Cycle Pressure isentropic expansion net work out isentropic isometric compression cooling 7 Volume Temperature isentropic isometric hea ng GD E net heat in g isentropic 5 expansion E 8 GD isometric cooHng v Entropy Dual Cycle Pressure isoba c heatingexpansion isometric hea ng C net work out isentropic expansion isentropic compression 1 isometric cooHng gt Vdume Vapor Cycles The Rankine Cycle 21 February 2011 Working Fluids Gasses noncondensing Ideal gasses constant C calculated properties Real gasses tabulated properties Vapors liquid and gas phases Tabulated properties Mixtures of Gasses Gas Vapor Mixtures psychrometry Reacting Mixtures combustion Pv Diagram for Water it spongy liquid Critical Point P CR 777777777777777777777777777777777777777777777777777777777 w I 9 a e 2 393 gas 9 3 a 3 50m 5 liquidvapor mixture e Triple Line PTP solidvapor mixture Specific Volume Processes Pressure isometric A V Isobaric Isothermal isentropic Vdume v P isometric g isobaric 3 V w isothermal L D i Isentropic V Vdume Singlephase Gas Multiphase LiquidVapor Rankine Cycle Isobaric Heating Steam Generator Adiabatic Expansion Turbine Isobaric Cooling Condenser Adiabatic Compression Pump Compressed Liquid Approximations An alternative to the Compressed Liquid Tables WWWm N SW SW hmle hflTlVflTlP P satlTl For calculating Changes in enthalpy and entropy both states CL 172 1736 T2 T1v P2P1 52 Slmcln T2 1 kJ Btu Cwater 41868kg K 1O Pump Calculations using compressed liquid tables state T C PkPa vm3kg hkJkg skJkg 1 5397 15 0001014 22594 07549 isentropic 23 L 40 30000 0000995 19390 05646 2s 21249 07549 1 23 H 60 30000 0001004 26726 08156 efficiency 2 L 60 30000 0001004 26726 08156 2 6021 30000 0001004 27712 08181 2 H 80 30000 0001016 35886 10564 Pump Calculations using compressed liquid quot1 hZ hl approximations state T C PkPa Vm3kg hkJkg skJkg 1 5397 15 0001014 22594 07549 P P v2 v1 h22h1v1P2 P1 UP T2 s2s1cln V 2 5881 30000 0001014 27661 08164 Gas Mixtures NonReacting Mixtures of Ideal Gasses 21 March 2011 Quantity n number of moles n N NA N number of molecules NA Avogadro s Number 6022 x 1023 39 m mass m M n M molecular weight Molecular Weight Atomic Weight appears on periodic table Mass in grams of NA 6022 x 10 atoms Molecular Weight sum of Atomic weights of all the atoms in the molecules Units mass per number kmole 1000 moles lbmole 4536 moles M has the same value in units of gmol kgkmol or lbmlbmol gmol kgkmol lbmlbmol H 455545 55555555 42 5455555 45 5 C 42 5457 raj 44 55quot Be AI Mg 255545555 454 24 55555 25 55555 V53 555555 H a h 555555555 551 M H 5555 31 5455 mm 5 5555 25 5 27 quot5 55557 x 5 55 5555455 25 S 22 25 24 MI 25 C 25 25 55 54 52 c5 5 T v c r5 quot Ni Cu 2 Ga 65 5 44555542 4 54555545 5 55555455 H mm 4557554 47557447 55544541 55555455 4 55545525 55555452 555455 555527 557254 725455 V57 5 57 m nmhmm mnmum cadmium 57x 39 55555 5554 55455555555 555455 v54555 5455 5555 5 5455444 544 55 44 45 45 55 v 45 m 42 45 44 m 45 47 Ed 45 55 54 527 I 54 s z Mo T R le Ag I 5 SI T5 5 m 5 X5 5555555 5255555 5 5 45255555 4 442444 W5 42 55447 57524 5422452 55454 575572454 75 455424 45755242 4445455 44574575 554 425555 454252 97 2 Q7 W7 47 anuhmv gum 5 39 555 54455 73 5555 55455 55555 55455 54445 E 5555 54455 455 555 554wquot me mm 5774 2 T 74 75 75 77 75 I 55 54 52 55 554 55 55 5 an Hf 41 w R5 05 Ir P 1959mm Hg Tl Pl 3 P 4 RH 45752707 4754552 4555454 455257454552554522475 45555455 392uutm nmm3jm 25724 255555454255 241 2535 574 2225475 2 47 A 4 7555 H hnmmm n I V 39 39 39 y 55 454 455 455 5457 455 455 5445 444 442 445 444 445 445 447 445 DI 51 m H5 M n y U Uuq Llllp um Us Him 225 25 255 25 25 4444155542454 2545247 255 4544555 4555 5724455 5724555 2551 255 3952 254 255quot 45m 5555 5 5 5 5 54 55555 555 555555 554m 55555 555555 75555 5555 45455 55555 4555quot 57 55 55 54 52 55 54 55 55 57 5395 55 75 7394 5 Eu Gd 11 By H5 Er Tm v1 Lu 4553552 454 454 457425 4555254552 45255541 4545555252745725555 4555442442 471549 47455744 5m 5 515mm ilemmz alE m 39 mummy 5 i i Propane 391 1 39 CsHs 99 9 9 9 Atomic weights GB GB GD Carbon 12011 gmol Hydrogen 10079 gmol Molar mass Propane moles 3 0110 12011 g m0 epropane mOICCarbon 8mleSHyd gen 10079 g m0 ePropane m0 eHydrogen MPropane 44097 gmol 44097 kgkmol 44097 IbmIbmol Mole and Mass Fraction Mole fraction ratio of moles of a single component to the total number of moles in the mixture yininniZni Zyi1 Mass fraction ratio of mass of a single component to the total mass of the mixture mfimimmiZmi mei1 M y EMM mfnz Apparent Molar Mass Molar mass of a pure substance Mass of a substance per mole Apparent or average molar mass of a mixture Mass of a mixture per mole of mixture 1 mm Mm mZyiMi mfi N i Mixtures of Gasses Component A Component B Mixture has T P Dalton Model Partial Pressures Component A Component B Properties of Components GibbsDalton Law for ideal gasses Each component behaves as if it were alone Properties evaluated at T v Pi Partial pressure for each component is proportional to mole fraction PiyiP Properties of Mixtures U22 UFZmiul HZHiZmihi SZSiZmisi EfZZE ZZmie Uum thm Ssm Efefm uZZ mfiui 112 mfihl 52 mfisl efZmeie C1322 mfiCRi CVmeiCV7i Psych rometrics Gas Vapor Mixtures 23 March 2011 Water Vapor The thermodynamic behavior of the water vapor constituent in humid air is as if the water vapor was alone at the temperature of the humid air mixture and the partial pressure of the water vapor in the humid air mixture TV T Pv Yi P Conventions Dry air constituent of the humid air mixture behaves as an ideal gas The dry air constituent is conserved The dry air subscript is a Water vapor is at very low reduced pressure also behaves as an ideal gas The water vapor is condensable Water vapor is added to removed from mixture Water vapor subscript is v Limitations Water vapor at very low reduced pressure also behaves as an ideal gas Temperature limit Less than122 F 50 C Pressure limit Less than 178 psia 123 kPa In most atmospheric and air conditioning applications these limits are not exceeded Absolute Humidity Mass fraction of water vapor Mass of water vapor per m mass of humid air mixture m Absolute humidity indicates Mass of water vapor per mass of dry air m Partial Pressure Water vapor and dry air constituents Both are at the same temperature Both occupy the same volume Both behave as ideal gasses wzmvz z izo z Pv ma MaNa 2897 Pa P PV wP aO622 PV R P P 0622a Relative Humidity Relative humidity is the ratio of the water vapor partial pressure to the water vapor saturation pressure at the mixture temperature i i PsatT wmax Relative humidity is not the ratio of the absolute humidity to the maximum absolute humidity Saturation TemperaturePressure CIayperonClausius Equation In E zh ii P1 R T1 T2 1n P 217138 m psia T Temperature in R 1nkij 1890 5290398 K Pa Temperature in K State Postulate The state of a simple compressible system is completely specified by two independent intensive properties For a mixture of two gasses like humid air specifying the state requires three intensive properties T P o T P 1 T P po Name Brayton Cycle Analysis Working Fluid air properties 1243 059172 059172 2025 070858 0192792 2112 071868 060182 8167 0968798 5047 093205 3149 081519 081519 0300568 3623 084956 085327 Process dQdt dWdt d Ein dt d Eout dt d Edest dt Btumin Btumin Btumin Btumin Btumin 12 Compressor 0 4346 0 263 263 23 Combustor 14676 0 17048 13212 3836 34 Turbine 0 7118 13212 12318 894 41 Heat Rejection 11904 0 5200 0 5200 2772 2772 10193 Edest dt 066321 0 84341 477 50471 51861 093891 Gas Power Cycles Diesel HotAir and Stirling Cycles 31 January 2011 Compression Ignition Engines Intake and Compression strokes just air Fuel injected directly into combustion chamber Higher compression ratios guarantee temperatures sufficient for spontaneous combustion of fuel air mixture No spark plugs needed ignition timing controlled by fuel injector timing Less refined fueloils can be used InjectionCombustion process takes longer to finish well into the power stroke Diesel Cycle 1 gt2 Adiabatic compression 2 gt3 Isobaric heating 3 gt4 Adiabatic expansion 4 gt1 Constant volume cooling Rudolph Christian Carl Diesel 18581913 Diesel Cycle isobanc k heatin expansion isobanc hea ng P isentropic D expansion network out 3 w 0 isentropic compression isometric cooHng 7 Volume V1 v1 Compressnon ratio r 2 V2 Ti 5 net heat in 9 g isentropic 3 g 5 expansion Q g E a 1 8r GD E t CD isometric cooHng Entropy S V3 v3 Cutoffratlo r CV2 V2 Stirling Engine Rev Dr Robert Stirling Patented 1816 Stirling Cycle 1e2 Isothermal compression 2 Isometric heating w heat from regenerator 3e4 Isothermal expansion 4e1 Isometric cooling w heat to regenerator Hot Air amp Stirling Cycles Pressure i ometric heating isothermal expansion net work out isothermal isometric compression cooling 7 Volume Temperature net heat in isometric isothermal exansio n hea ng quot Isometric cooHng isothermal compression Entropy S PsyChrometrlcs Dew Point Temperature and Psychrometric Properties 28 March 2011 0 0 0 I oo 3 o O 0 Partial Pressure ofWater Vapor psia F3 F3 F3 F3 lt3 N A L 0391 C c Saturation Temperature F o ln P j17138 m psza lnk11 2189052908 K v a 1 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100 How much Water is in Humid Air Pounds of water vapor per pound of dry air Moisture content P m a V 0622 Aka Absolute humidity m PP a V Partial I ressure of the water val or relative to the saturation pressure at the air temperature Relative humidity Usually expressed in Pv RH RAT Maximum Water in Humid Air The partial pressure of the water vapor cannot exceed the saturation pressure for water at the temperature of the air Saturated Humid Air 100 RH Saturated Humid Air DryAir HumidAir 0 lt R lt MT R 114T Pv P T Z 0 100 PW T max PM T P PsatT 8 o a 0622 v mm 0622 P P P PWXT V Dew Point Temperature State of Humid Air defined b three inde endent intensive state properties typically T mixture temperature P mixture pressure some measure of how much water vapor is in the air mv PV Absolute Humidity 0 0622 ma V Relative Humidity V Psat Dew Point Temperature TDP TZW Enthalpy of Humid Air Mixture of ideal gasses H22Hl HaHV Air component base state H0O at T0 0 F or 0 C Ha Ha Ha0 maCPaT Tol Water vapor component base state H0O for saturated liquid at T0 Hv Hv Hv0 mvvzjfg CPVT 7 hfg accounts for enthalpy change from liquid to vapor Specific Enthalpy of Humid Air Specific enthalpy per mass of mixture h CPaTT0 hfg CPVTT0 m m Specific enthalpy per mass of dm air hiCPaTT0 hfgCPVT YB ma ma ma T T0 T in Fahrenheit or Celcius h CWT wihfg CPWT Specific Enthalpy of Humid Air Specific per mass of dry air Using constant specific heats and latent heat values at 59 F fl 2 024 a10609 j 0435 1me 1me Temperature in F ih 21005 KT w25009182 i kgK l l Temperature in C Liquid Water Enthalpy Same base state as for humid air h00 for liquid at TO F or TO C hw hoyw C water T T0i hw 10 If T T in degrees Fahrenheit hw 41868T T in degrees Celsius Specific Volume 0 Humid Air GibbsDalton Law All components of the mixture occupy the same volume 1 1 Va 2v IH Specific per mass of mixture 20 2 1 0 mg m 10 m 10 Exergy Useful Work Potential Exergy Transfer and Exergy Balance 19 January 2011 Second Law of Thermodynamics KelvinPlank Statement A cyclic heat engine cannot OH operate while receiving heat from a single thermal energy reservoir and producing work Exergy amp Useful Work Exergy quantifies the potential of a system to do useful work Potential not in thermodynamic equilibrium with the environment dead state Useful work Useful work i Energy Useful work 6 Work Shaft work useful work Flow work useful work Boundary work useful work Surroundings Work SLUT WW Wu If the system does boundary work not all of the work done by the system is usefull W actual work done by the system WSW Work to displace the surroundings WU useful work left over Specific Exergy Specific exergy for closed systems eu u0P0v vO T0s SOkepe Specific exergy for flow streams efh hO T0s SOkepe Exergy is not a property of the fluid exergy depends on the state of the environment Exegry Analysis Generic Control Volume Analysis N inN outZA N Ndestroyed N created Exergy Balance N Exergy Ein Eout A E Edestroyed Exergy Transfer Exergy transfer by heat To Follows sign convention Q is positive in E l T Q Q in results in exergy transfer into CV 1 Q out results in exergy transfer out of CV Exergy transfer by heat Follows sign convention W is positive out Eout W PO A V W out results in exergy transfer out of CV W in results in exergy transfer into CV Exergy transfer by advection for open systems e Ein Eoutzz mefi Ze mef l Exergy Destruction Exergy is not a conserved property Exergy is the potential to do usefull work an opportunity that can be wasted The exergy in a CV can decrease without any exergy being transferred out of the CV Exergy destroyed proportional to entropy generated Exergy destroyed also called Irreversibility Edest TOSgen I Edest gt 0 real processes 0 reversible processes lt 0 imposible


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