# Unit 3 - Engi2800(Section I Engineering Thermodynamics I...

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09/28/09 http://jjl.me.dal.ca/Engi2800 1 J.M. Chuang Dalhousie University Dept. of Mechanical Engineering Last Modified: September 28, 2009 Unit #3 ( Textbook Reference: Ch.3 ) Properties of a Pure Substance Engi2800 (Section I) Engineering Thermodynamics I

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09/28/09 http://jjl.me.dal.ca/Engi2800 2 Contents Introduction The Pure Substance Three Principal Phases Solid Phase Liquid & Gas Phases Vapor-Liquid-Solid Phase Equilibrium Saturation Temperature and Pressure Vapor-Pressure Curve The and Diagrams The Diagram for Different Pressure Quality ( Two-Phase Liquid-Vapor Region ) The Diagram The Diagram Water Phase Diagram Thermodynamic Surface Thermodynamic Tables Water Tables Other Tables State Equation of Ideal Gas Compressibility Factor P - v T - v T - v P - v P - T
09/28/09 http://jjl.me.dal.ca/Engi2800 3 Introduction Three properties of substance: specific volume, pressure and temperature. Pure Substance Phases of substance The number of independent properties Methods of presenting thermodynamic properties Steam Power Plant (Using water as the working substance) High pressure (boiled in steam generator) Low pressure (expansion in turbine) Cooling (in the condenser) High pressure (return to boiler by pump) Refrigerator Substance: boil from liquid to vapor at a low temperature, , absorbing energy from the cold space, keeping it cold. Hot substance is cooled by air flowing around the grille Gas turbine (jet engine) (working substance: gas, no phase change) ¡ 20 o C Thermodynamic Surface: P-v-T

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09/28/09 http://jjl.me.dal.ca/Engi2800 4 Thermodynamic Surfaces The Diagram (Fig. 3.18 & 3.19, Textbook) Substance that expands on freezing Substance that contracts on freezing No distinction Between liquid and vapor P - T - v
09/28/09 http://jjl.me.dal.ca/Engi2800 5 Steam Power Plant Cycle Devices: Stream drum: absorb heat from heat reservoir Turbine: Extract energy from substance Condenser: extract heat from substance Pump: increase pressure to substance Physical Laws: Conservation of mass (Continuity Eqn.) Conservation of energy (1 st Law) Entropy equation (2 nd Law) State of substance Specific volume, Internal energy, Enthalpy, Entropy, Condenser Steam drum Turbine Pump P hi ; T hi P lo ; T hi P lo ; T lo P hi ; T lo W out W in ( P; T ) Reservoir Reservoir T H T L v (m 3 = kg) u (kJ = kg) h (kJ = kg) s (kJ = kg K) Stream table Q H Q L

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09/28/09 http://jjl.me.dal.ca/Engi2800 6 Substance: Refrigerant R-134a, R-410a For R-134a (Table B.5, p. 810) -20 133.7 60 1681.8 30 771.0 -25 107.0 For a give temperature, : If , compressed liquid If , vapor (superheated) Note: heat transfer from to Evaporator Condenser Compressor Expansion valve Reservoir Refrigerated space W in Cold Vapor Warm Vapor Warm Liquid Cold Liquid +Vapor T L Q L Q H T H P > P sat P < P sat T T low T high T ( o C) P sat (kPa) (120 kPa ; ¡ 20 o C) (800 kPa ; 60 o C) (800 kPa ; 30 o C) (120 kPa ; ¡ 25 o C) Vapor-Compression Refrigeration Cycle Desired output Required input COP R = Desired Output Required Input
09/28/09 http://jjl.me.dal.ca/Engi2800 7

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