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lecture06 - LECTURE 6 THERMODYNAMICS An Engineering...

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1 LECTURE 6 THERMODYNAMICS An Engineering Approach REFRIGERATION AND HEAT PUMP SYSTEMS THERMODYNAMICS PROPERTY RELATIONS & MIXTURES (Gas Mixtures & Gas-Vapor Mixtures) Dr. MinJun Kim Department of Mechanical Engineering & Mechanics Drexel University Preliminaries condenser evaporator Hot region, T H Cold region, T c 2 1 4 3 compressor turbine t W D c W D IN Q D OUT Q D Carnot Vapor Refrigeration Cycle 1 2 3 4 T s T H T C ba m W m W m Q t C in MAX D D D D D D / / / = β ) )( ( ) ( b a C H b a C s s T T s s T =
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2 Vapor-Compressor Refrigeration condenser evaporator 2 1 4 3 compressor c W D IN Q D OUT Q D expansion valve saturated or superheted vapor 1 2 h h m W c = > > 4 1 h h m Q in = > > 3 2 h h m Q out = ± ± h 4 = h 3 throttling process 1 2 4 1 / / h h h h m W m Q C in = = > > > > β Performance of Vapor-Compression Systems Process 1-2s : Isentropic compression of the refrigerant from state 1 to the condenser pressure at state 2s. Process 2s-3 : Heat transfer from the refrigerant as it flows at constant pressure through the condenser. Process 3-4 : Throttling process from state 3 to a two- phase liquid-vapor mixture at 4. Process 4-1 : Heat transfer to the refrigerant as it flows at constant pressure through the evaporator to complete the cycle. () 1 2 1 2 / / h h h h m W m W s C s C C = = D D D D η T s 1 2 3 4 3’ 2s Temperature of warm region, T H Temperature of cold region, T C
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3 Example (I) Refrigerant 12 is the working fluid in an ideal vapor-compression refrigeration cycle that communicates thermally with a cold region at 20 ° C and a warm region at 40 ° C. Saturated vapor enters the compressor at 20 ° C and saturated liquid leaves the condenser at 40 ° C. The mass flow rate of the refrigerant is 0.008kg/s. Determine (a) the compressor power, in kW. (b) the refrigeration capacity, in tons, (c) the coefficient of performance, and (d) the coefficient of performance of a Carnot refrigeration cycle operating between warm and cold regions at 40 and 20 ° C, respectively. IN Q D condenser evaporator 2s 1 4 3 compressor c W D OUT Q D expansion valve warm region, T H =40 ° C cold region, T C =20 ° C T s 1 2 3 4 2s 40 ° C 20 ° C Heat Pump Systems condenser evaporator Hot region, T H Cold region, T c 2 1 4 3 compressor turbine t W ± c W D IN Q D OUT Q D Carnot Heat Pump Cycle net in out W Q Q D D D + = m W m W m Q t C out D D D D D D / / / max = γ 1 2 3 4 T s T H T C ba ) )( ( ) ( b a C H b a H s s T T s s T =
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4 Vapor-Compression Heat Pump System 1 2 34 condenser evaporator compressor expansion valve outside air inside air OUT Q D IN Q D C W D 1 2 3 2 / / h h h h m W m Q C OUT = = D D D D γ Gas Refrigeration Systems T s 1 2 3 4 p = c p = c 4s 2s Heat exchanger turbine Heat exchanger compressor 1 2 3 4 Hot region, T H Cold region, T c IN Q D OUT Q D T H T C ( ) ( ) 4 3 1 2 4 1 / / / h h h h h h m W m W m Q t C IN = = D D D D D D β 4 3 h h m W t = D D 1 2 h h m W c = D D 2 3 h h m Q in = D D t C cycle W W W D D D =
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5 Example (II)
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lecture06 - LECTURE 6 THERMODYNAMICS An Engineering...

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