Refrigeration Cycle Experiment

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Refrigeration Cycle Experiment

• Study of a vapor-compression system
• Martín Peña
• Tamara N. Mejía-Rabell

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Agenda

• Background
• Theory
• Objectives
• Equations
• Procedure
• Sample Calculations
• Results
• Significance of Results
• Questions and Answers

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(No Transcript)
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Capillary Tube
Condenser
Evaporator
Compressor
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Theory

• Coolant (R-12) is like a sponge.
• Background Info.
• Cooling is accomplished by evaporation of a
  liquid refrigerant under reduced pressure and
  temperature.
• The refrigeration cycle is repeated.
• Heat normally flows High ? Low
• Refrigeration Low ? High

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Objectives

• Measure power requirements of the system
• Measure the condenser heat rejection rate and
  evaporator heat absorption rate based on both the
  coolant and the air flow

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Objectives

• Calculate COP (Coefficient of Performance) and
  compare to an ideal cycle (Carnot)
• Determine effect of air flow rate through the
  exchangers on the above

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Equations

• ? density of air
• From Ideal Gas Law
• ? P MW
  
• RT
• Mass Flow Rate
• m A v ?

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Equations Cont.

• Evaporator and Condenser Heat Transfer based on
• Air Flow
• Q ?H m Cp (Texit Troom)
• Coolant Flow
• Qc mcoolant (H1 H4)

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Coefficient of Performance

• Air Flow Method
• COP Qc / ( WT WF )
• Coolant Flow Method
• COP -Qc / (WT WF )

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Coefficient of Performance Carnot Cycle

• Coolant Temperature Basis
• COP Tc / (Th Tc)
• Coolant Enthalpy Basis
• COP (H1 H4) / (H2 H1)

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Procedure

• Record Wattmeter for Fan Power and Total
  Consumption
• Measure average velocity and temperature of air
  for evaporator and condenser.
• Calculate density and mass flow rate with the
• area of the evaporator and condenser.

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Procedure Cont.

• Calculate the heat rejection/absorption rate by
• 1). the flow rate and temperature difference of
  the air.
• 2). the flow rate and enthalpy difference of the
  refrigerant flowing through the condenser.
• Note R-12 using Perrys Chemical Engineering
  Handbook Table 2-301.

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Data
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Data Cont.
Medium Speed
High Speed
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Data Cont.

• Total Power Consumption
• Fan _at_ Medium Speed 965 Watts
• Fan _at_ High Speed 976 Watts
• Fan Power Consumption
• Fan _at_ Medium Speed 162 Watts
• Fan _at_ High Speed 187 Watts
• Refrigerant Flow _at_
• High Speed 1.32 kg/min
• Medium Speed 1.28 kg/min

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Data Constants
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Sample Calculations

• ? P MW 1atm 29g/Mol
  
• R T 8.314J/MolK 306K
• ? 1.12kg/m3
• m A v ?
• m 0.075m2 1.8m/s 1.12kg/m3
• m 0.155kg/s

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• Air Flow
• Q ?H m Cp (Texit Troom)
• Q 0.155kg/s 1.005kJ/kgK (306K 298K)
• Q 1.25Watts
• Coolant Flow
• Qc mcoolant (H1 H4)
• Qc 0.022kg/s (556.87 411.51)kJ/kg (1000)
• Qc 3198J/s

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• Air Flow Method
• COP Qc/( WT WF )
• COP 3198J/s/(976 187)Watts
• COP 4.05
• Coolant Flow Method
• COP -Qc/(WT WF )
• COP -(-3119J/s)/(976 187)Watts
• COP 3.95

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• Ideal COP
• COP Tc/(Th Tc)
• COP 284.11K/(319.67 284.11)K
• COP 7.99
• Coolant Enthalpy Basis
• COP (H1 H4)/(H2 H1)
• COP (556.87 411.51)/(570.78 - 556.87)kJ/kg
• COP 10.45

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Results

• Heat Transfer Coefficient
• Air Flow calculations
• High speed - negative
• Medium speed - positive
• Coolant Flow calculations
• Evaporator - positive
• Condenser - negative

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Results Cont.

• COP
• Air Flow
• Medium - positive
• High - negative
• Coolant Flow
• Medium - positive
• High - positive

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Significance of Results

• Qair does not equal Qcoolant and Qc does not
  equal Qh
• Heat losses in the system
• Lower fan speed gives poorer operation
• Tends to affect Condenser more

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Questions and Answers

• Thank you

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References

• http//filebox.vt.edu/eng/mech/scott/ref.html
• http//www.warmair.com/html/refrigeration_cycle.ht
  m
• http//www.engineeringtoolbox.com/24_156.html
• http//one.drexel.edu/cp/tn/fs?tnmc
• Perry, R.H. and Green, D.W., Chemical Engineerís
  Handbook, 7th Ed., McGraw Hill, New York (1999).