大连理工大学：《工程热力学》课程教学资源（PPT课件）6 热力循环 Thermodynamic Cycles

6. Thermodynamic CyclesObjective.Classification of Thermodynamics CyclesAnalysis & Calculation of Power CyclesCarnot Vapor Cycle,Rankie Cycle, RegenerationRankieCycle,ReheatRankieCycle·Cogeneration· Gas Refrigeration Cycle.Vapor-Compression Refrigeration Cycle·Refrigerant: Other Refrigeration Cycles

6. Thermodynamic Cycles Objective •Classification of Thermodynamics Cycles •Analysis & Calculation of Power Cycles Carnot Vapor Cycle, Rankie Cycle, Regeneration Rankie Cycle,Reheat Rankie Cycle • Cogeneration • Gas Refrigeration Cycle • Vapor-Compression Refrigeration Cycle • Refrigerant • Other Refrigeration Cycles

6.1ClassificationofThermodynamicsCyclesPowerCycle (+)Heat EnergyMechanical EnergyHeatPumpCycle(一)Refrigeration Cycle: keep low temperature of heat source with lowtemperature Heat Pump Cycle: keep high temperature of heat source with high temperatureWorking FluidGas Cycle: no phase-change of working fluid during cycleVapor Cycle: phase-change of working fluid during cycleCombustion formInnerCombustionOuterCombustionCombustion occurs in systemCombustionoccursoutofsystemThe heat is transferred to workingGas is also the working fluidfluid throughheat exchanger

6.1 Classification of Thermodynamics Cycles Heat Energy Mechanical Energy Power Cycle (+) Heat Pump Cycle (－) Refrigeration Cycle: keep low temperature of heat source with low temperature Heat Pump Cycle: keep high temperature of heat source with high temperature Working Fluid Gas Cycle: no phase-change of working fluid during cycle Vapor Cycle: phase-change of working fluid during cycle Combustion form Inner Combustion Outer Combustion Combustion occurs in system Combustion occurs out of system Gas is also the working fluid. The heat is transferred to working fluid through heat exchanger

6.2 Carnot Vapor CycleBoilerTurbCompWnetCondenserQLAllprocesses areS(a)totallyreversibleSeveralimpracticalitiesareassociatedwiththiscycle:1.Itis impractical todesigna compressorthatwill handletwophasesforisentropiccompressionprocess(4-1)2.Thequalityofsteamdecreaseduringisentropicexpansionprocess(2-3)whichdoharmtoturbineblades

6.2 Carnot Vapor Cycle Several impracticalities are associated with this cycle: 1. It is impractical to design a compressor that will handle two phases for isentropic compression process(4-1). 2. The quality of steam decrease during isentropic expansion process(2-3) which do harm to turbine blades

6.2 Carnot Vapor CycleBoilerTurbCompWnetCondenser具QLAll processes are5(a)totallyreversible3.The critical point limitsthe maximumtemperature used in the cyclewhich also limits thethermal efficiency.4.The specific volume of steamis muchhigherthanthatofwaterwhichneedsbigequipmentsandlargeamountofworkinput

3. The critical point limits the maximum temperature used in the cycle which also limits the thermal efficiency. 4. The specific volume of steam is much higher than that of water which needs big equipments and large amount of work input. 6.2 Carnot Vapor Cycle

6.2 Carnot Vapor Cycle

6.2 Carnot Vapor Cycle

6.3Rankine Vapor CyclePrinciple4in4-6Constantpressureheatadditionin a boilerBoiler6-1 to Superheat VaporWurb,out21-2 Isentropicexpansion inTurbineWpump.ina turbinePump22-3 ConstantpressureheatHoutrejectionin a condenserCondenser33-4Isentropiccompressioninapump

6.3 Rankine Vapor Cycle 4-6 Constant pressure heat addition in a boiler 6-1 to Superheat Vapor 1-2 Isentropic expansion in a turbine 2-3 Constant pressure heat rejection in a condenser 3-4 Isentropic compression in a pump S 4 6 1 2 3 Principle

6.3Rankine Vapor CycleSimpleSteamPowerPlantStack1ACombustiongasestostackEketrieTrbinetBodlerCvolingtiowerFuelCandemerPAir小小WamwaterPanpCoolodwaterMakeupwaterFeedwaterpump

6.3 Rankine Vapor Cycle

6.3Rankine Vapor Cyclepp1qin165BoilerP232Wqurb,outRTurbineWpump.inPump2AoutCondenserWturb.out35qin6?3qoutpump.in

S 4 6 1 2 3 T s 1 6 5 4 3 2 p v 1 5 6 4 3 2 p1 p2 6.3 Rankine Vapor Cycle

6.3Rankine Vapor CycleEfficiency4-5-6-1 Constant pressure heat addition in a boilerqi = h, -hy1-2 lsentropic expansion in a turbineWr =h, -h,2-3 Constant pressure heat rejection in a condenserq2 = h, -h;3-4 lsentropic compression in a pumpWip = hy - h3

4-5-6-1 Constant pressure heat addition in a boiler 1 1 4 q h h = − 1-2 Isentropic expansion in a turbine w h h tT 1 2 = − 2-3 Constant pressure heat rejection in a condenser 2 2 3 q h h = − 3-4 Isentropic compression in a pump w h h tP 4 3 = − 6.3 Rankine Vapor Cycle Efficiency

6.3Rankine Vapor CycleBecause of uncompressibility of waterWip = V(p4 P3)< WiTh, ~hsE,=0,E,=0-Wtp = qi - qz ~ h, - h, = WWTh, -hzW0nth, -h3q1

Because of uncompressibility of water ( ) w v p p w tP 4 3 tT = − 4 3 h h  o tT tP 1 2 1 2 s o 1 2 t 1 1 3 w w w q q h h w w h h q h h  = − = −  − = − =  − 0, 0 E E k p = = 6.3 Rankine Vapor Cycle