Thermodynamics ME 3322
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This 0 page Class Notes was uploaded by Chloe Reilly on Monday November 2, 2015. The Class Notes belongs to ME 3322 at Georgia Institute of Technology - Main Campus taught by Nader Sadegh in Fall. Since its upload, it has received 56 views. For similar materials see /class/234242/me-3322-georgia-institute-of-technology-main-campus in Mechanical Engineering at Georgia Institute of Technology - Main Campus.
Reviews for Thermodynamics
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Date Created: 11/02/15
Review of Thermodynamics 1St and 2nd Law Applications Conservation of Energy The 1 Law of Thermodynamics Change in Net amount of amount of energy energ transferred in contained within across the the system 39 system during some boundary by time interval heat transfer during the time interval Net amount of energy transferred out across the system boundary by work during the time interval Alternative Forms of the Energy Balance Differential Form Time Rate Form First law for Cycles First law for an arbitrary system AEQW For a cycle AEcycle0 since it begins and ends at the same state Thus Power Cycle A Power system receives heat Qin from a hot reservoir and rejects heat Qout to a cold reservoir Net cycle heat QcycleQinQout Thus chcleQin39Qout Thermal ef ciency Refrigeration Cycle A Refrigeration cycle extracts heat from a cold reservoir and rejects heat Qout to a hot reservoir Net cycle heat QcycleQinQout Thus chcleQcycleO Coef cient of Performance COP Heat Pump Cycle Heat pump is similar to refrigeratior except that Qout is the output of interest Coef cient of Performance COP Summary of Cycle Analysis AEcycle Qcycle W cycle Power Cycles Refrigeration amp Heat Pump Cycles Chapter 3 Evaluating Prop 2quot erties n Engineering Thermodynamics Property Relations I The State Principle Two independent intensive thermodynamic properties are required to x the state of a simple compressible system For example P and v T and u and h intensive thermodynamic properties h specific u specific internal x quality s specific entropy enthalpy energy isteam oniyi P absolme T absoiute v specific Less used pressure temperature volume q r Gibbs in energy PvT Relation Note the location of the following Single phase regions TWO phase regions Saturation states Triple line v Critical Point V i 5 mm 1 mm W M wquot V Wm Tv diagram gt 39 u Cnucn V j Saunalion Slates Phase Transition LiquiIHGn imuramd mr Dame r Diamam cuunes uHeW M Seiizman 2mm Linear Interpolation Between values in the tables m k 1mm 02275 100T 020M IE 2 215 140 71 C Subscripts L Value in table at lower end H Va ue in table at upper end None value ofinterest Quality For use in Tables A2 and A3 For Saturated Mixture LiquidVapor Region 7 Quality X an intensive x property X gives fraction that is m f m vapor gas 1X gives Moisture Content x D a Saturated Liquid subscript 1 x 1 a Saturated Vapor subscript 9 f9 A 9 Quality Relations LET b ANY INTENSIVE PROPERTY b v u h 5 etc Chapter 4 Control Volume Analysis Using Energy Conservation of Mass for a Control Volume Lime rate of charge of quot time rate of flowquot Lime rate of ow quot the control volume or me tj Lmle t or me t J Lextte or me t J Conservation of Energy for a ControILV me mum atwhtch tame mm of mm mm atwhtch m e exgy u m e cant at am the central mum at byhzattxansfex m r mum of may Special Cases Steady State Flow Steady State 1D Flow Q V Wchh 7h92 7V922gz 7290 m Steady State 1D Flow negligible PE and K5 QCV7WCVI77I7 0 Chapter 5 The 2nd Law of Thermodynamics m mu hp envme pm 5 mm auva An Introduction Statements of the 2nd Law Clausius Statement It is impossible for any system to operate in such a way that the sole result would be an energy transfer by heat from a cooler to a hotter body KelvinPlanck Statement It is impossible for any system to operate in a thermodynamic cycle and deliver a net amount of energy by work to its surroundings while receiving energy from a single thermal reservoir Carnot Corollaries The thermal ef ciency ofan irreversible power cycle is always less than that of a reversible one when each operates between the same two reservoirs All reversible power cycles between the same two thermal reservoirs have the same thermal ef ciency There are similar corollaries for refrigeration and heat pump cycles Maximum Performance Heat Engines Refrigerators amp Heat Pumps TC max TH TC 10 b TH x 7 a 05 max E T H T C 0 a 298 1000 2000 3000 TH K Clausius Inequality V Tb Inequality chcle so 39 it cyclic integral over the boundary and cycle Qiquotiirf V Eili fi isPfes i t wit ihtheWidth Unlike energy entropy in the presence of irreversibilities is always produced Defining Entropy The Clausius inequality statest at for an internally reversible cycle 55 3 0 This implies that If is indepergdent ofthej path from state 1 to 2 quot Therefore LZW can be considered a prc39iperty change This integral is defined to be the entropy at state 2 relative to 1 2 SO 52 51 l Finding Entropy Data For Water and Refrigerants Motivation Application ofthe 2quotd Law ofThermodynamics frequently requires nding speci c entropy data Using Tables A2 A18 Use Table A 4 For example Saturation Data Liquid Data In the absence of tables use the Compressed Liguid Rule Graphical Entropy Data T dS Equations MS 2 dU PdV Per Unit Mass Tds duPdv TdSde VdP Tds dh vdP Ideal Gases Ideal gas law Internal energy and enthalpy entropy Properties for Ideal Gases Requirements Z w 1 P D PC T D TC Ew The Ideal Gas Model Tables A22E and A23 E When specific heats are assumed constant Table A20E Finding Entropy Data For Ideal Gases Motivation Application of the 2 d Law of Thermodynamics frequently requires finding specific entropy data du CVT dh CPT PvRT For an Ideal Gas Using these relations with the Tds equations yields Ideal Gases with Constant Speci c Heats Use Specific heat data in Tables A20 For example Isentropic Processes Showing isentropic processes is rapid on Ts or hs diagrams However tabular data may still be used as well Isentropic Processes with Ideal Gases Constant Specific Heats For air Table A22 only Air Table A22 man a raw Gus Plvpm w m l JD97 Hus 1mm m m g7 H9 an 7 mm 220 z 997 liblz l u 2 215m m 23m mm mm 4 2mm mu 3 s a 927 mm 121952 1 ma 7 w 1 279m 2 199M 9 2 sum 1 35531 7 39m 6 s m l pMIA39ruinrm mlll q hmunuwwuy Table A22 i n dirfkllkgr39ls7lk xi Win A v n 1 35199 mm max new 12507 mus ma 29m man meal 90770 mu man 299034 mm 09135 szm man mun mm m7 mm in nle x39 mm mu umx mw 3mm mi mm mas All It pm 9979 mm Han izsul 91557 mm I 127 9 um um taunt 951m am m l32493 95395 39iZHS mi mass man um um mm mm mm mm 72 mm Tum4A4 m mm u Kninn my Km L m l blu wit quotmm M Finding Entropy Data For Incompress39ble Substances lncompIessibe substance model is generally used with liquids and solids only and assumes constant specific volume C Specific Heat or Heat Capacity Entrop Balance Closed Systems Entropy Entropy Entropy Change Transfer Production Since 0 measures the effect of irreversibilities present within the system during a process its value depends on the nature of the process and thus is NOT a property Other comm the entropy balance Rate basis Uniform Boundary Temperature Increase in Entropy Principle Closed Systems The summation of the entropy changes of surroundings AND system must always increase or remain the same Entropy Rate Balance Control Volumes Rate of Rate 0f Rates of entropy transfer entropy change production lnte ral Form At Stead State Special Case SISO The entropy balance for a Single Inlet Single Outlet Q Z ms sec395 02 CV 1 Q g Se sm7j m lfthe system is adiabatic no heat transfer then Special Cases Heat Transfer and W Imemzm musuhle Stmwstme mm mwa 0 lnlunzlw rmmhm sum751m lncnrmmsshle quotum A wewa he spwmmuwaa MWnamigaswedPamadjacenfm the Syracuse Wme campus m Sracuse Nv Boiler Rankine Cycle Turbine39 Pump mm oudcmcr I 3 Overall Performance u condenser 1 Side Rankine Idealizations Processes 12 34 Isentropic Processes 23 41 Isobaric Saturated liquid at State 3 Reversible Pump Work Equation For Incompressible Fluids Only Principal Device Analysis Principal Device Analysis Qin Boiler I hI r I l I Couliug Wale Condenser Improving Cycle Performance Supemeat and Reheat protect the turbine and increase TH Improving Cycle Performance Adding an Open Feedwater Heater with pump Um urn Improving Cycle Performance Adding a Closed Feedwater Heater 25 PistonCylinder Engines gtS39xnk plug it nitx Humor 4 Stroke Engine Process lntake Stroke my in AIMJLA IKH nllimu Compression Stroke 7min Power Stroke Expansion mill Exhaust Stroke Bmumv dmd cmim k vim For Spark Ignition engines intake is 0 an airfuel mixture For Diesel engines intake is air on Cycle Analysis 4 Internally Reversible Processes lse Co tropic Compression stant Volume Heat Addition lsentropic Expansion Constant Volume Heat Rejection n n Sign Conventions Work in negative etc are sometimes changed for cycle applications Analysis amp Performance Parameters Air Standard Analysis Cold Air Standard Analysis Mean Effective Pressure mep mep is the mean pressure acting on the piston during the cycle Mep is the ratio of the net work per cycle and displacement volume chcleVdis Vdis nNLB24 Bbore diameter Ldistance between the TDC and BBC Nnumber of cylinders Power12chclexengine speed revsec Engine torqueWCycle4n Diesel Cycles Cycle Analysis 4 Internally Reversible Processes lsentropic Compression Constant Pressure Heat Addition lsentropic Expansion Constant Volume Heat Rejection 5 Internally Reversible Processes lsentropic Compression Constant Volume Heat Addition Constant Pressure Heat Addition lsentropic Expansion Constant Volume Heat Rejection
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