上海交通大学：《制冷原理与装置》课程教学资源（课件讲义，双语版）Basic Principle of Heat Transfer

Summer Conditions Basic Principle of Heat Transfer Hot 72F 田田田 Summer Conditions Summer Conditions emperature Finned-Tube heat exchanger Indoor coil Refrigera Indoor Air

1 Basic Principle of Heat Transfer Hot Cold Summer Conditions 90 F 72 F Summer Conditions Heat flow Indoor air temperature Summer Conditions Heat flow Indoor air temperature Remove heat from indoor air Finned-Tube Heat Exchanger (Indoor coil) Indoor Air Refrigerant Indoor Coil 72 F 55 F

Heat transferred from the air to the Refrigerant refrigera nt The fluid used for energy exchanges in ar Usually the refrigerant absorbs heat while undergoing a liquid to vapor (evaporation) and releases heat while undergoing a vapor to liquid phase change Evaporation ondensation Indoor coil System Components (E System Pressures and Temperatures Refrigerant flow 0000

2 Warm indoor air (72 F) Cold refrigerant (40 F) Heat transferred from the air to the refrigerant Refrigerant The fluid used for energy exchanges in an air conditioning, refrigeration or heat pump system. Usually the refrigerant absorbs heat while undergoing a liquid to vapor phase change (evaporation) and releases heat while undergoing a vapor to liquid phase change (condensation). Heat Evaporation liquid vapor Heat Condensation Refrigerant liquid Refrigerant vapor Indoor Coil (Evaporator) System Components Outdoor coil Expansion valve Compressor Indoor coil Reversing valve High pressure & temperature Low pressure & temperature System Pressures and Temperatures Outdoor coil Expansion valve Compressor Indoor coil Refrigerant flow

Outdoor coil Air Conditioning Cycle (Condenser) Refrigerant OutdoorAir Residential Air-Conditioning System System Performance Outdoor coil valve Maximum COP for an Air-Conditioning Cycle as Coefficient of Performance a Function of Outdoor Air Temperature COP Desired heat transfer effect(units) Work required (units) COP =Heat transfer rate FROM indoor air- input to the compr Indoor air temperature 72 F 日30.0 Energy Efficiency Ratio EER= 9095100105110 Outdoor air temperature(F)

3 Outdoor coil (Condenser) Outdoor Air Refrigerant vapor Refrigerant liquid Air Conditioning Cycle Outdoor air 72 F 55 F 90 F low temperature high temperature Indoor air 110 F Residential Air-Conditioning System Outdoor Unit • Outdoor coil • Compressor • Fan Indoor Unit • Indoor coil • Valve • Fan System Performance Work Heat Heat Coefficient of Performance Energy Efficiency Ratio COP = Desired heat transfer effect (units) Work required (units) COP = Heat transfer rate FROM indoor air Power input to the compressor and fans EER = Heat transfer rate (Btu/hr) Electrical power (Watts) 0.0 10.0 20.0 30.0 40.0 50.0 60.0 70.0 80 85 90 95 100 105 110 115 Outdoor air temperature (F) COP (dimensionless) Indoor air temperature = 72 F Maximum COP for an Air-Conditioning Cycle as a Function of Outdoor Air Temperature

Winter Conditions Winter Conditions 25F 72 72 由由田 Winter conditions Beware of the snowman 72 Reverse the operation of the air Direction of refrigerant flow is reversed in conditioning system all components except the compressor. 00

4 Winter Conditions 25 F 72 F Winter Conditions 25 F 72 F Indoor air temperature Winter Conditions 25 F 72 F Add heat to the indoor air Indoor air temperature Beware of the snowman Reverse the operation of the air conditioning system Low pressure & temperature High pressure & temperature Outdoor coil Expansion valve Compressor Indoor coil Direction of refrigerant flow is reversed in all components except the compressor

Compare to the air conditioning cycle Heat Pump Cycle 0000 System Performance Coefficient of Performance Desired heat transfer effect(units Work required(units) COP= Heat transfer rate To indoor air Power input to pressor and fans Energy Efficiency Ratio Heat transfer rate(Btu/hr) EER= Maximum COP for a Heat-Pump Cycle as a Function of Outdoor Air Temperature Heat Pumps Outdoor air temperature(F)

5 Compare to the air conditioning cycle. Heat Pump Cycle Outdoor air 20 F 10 F 72 F low temperature high temperature Indoor air 90 F System Performance Work Heat Heat Coefficient of Performance Energy Efficiency Ratio COP = Desired heat transfer effect (units) Work required (units) COP = Heat transfer rate TO indoor air Power input to the compressor and fans EER = Heat transfer rate (Btu/hr) Electrical power (Watts) 0.0 10.0 20.0 30.0 40.0 50.0 -10 0 10 20 30 40 50 60 Outdoor air temperature (F) COP (dimensionless) Indoor air temperature = 72 F Maximum COP for a Heat-Pump Cycle as a Function of Outdoor Air Temperature Geothermal Heat Pumps

Power meter Energy Systems 2.0 Determining the performance parameters of refrigeration and heat pump system CoP= Heat transfer rate TO/FROM indoor air Heat transter rate(Btu/ Calculate the heat transfer rate to/from the air Atmospheric Air Nitrogen Argon(0.93>Dry air Water vapor Carbon dioxide (0.03) other gases Calculating the heat transfer rate to the air Calculating the heat transfer rate from the air mperature of the increases while water Depending on the temperature of the coil, water vapor ent of the air stream The air is cooled and dehumidified Only sensible heat transfer is present. In this case both sensible and latent heat transfer

6 Determining the performance parameters of a refrigeration and heat pump system. COP = Heat transfer rate TO/FROM indoor air Power input to the compressor and fans EER = Heat transfer rate (Btu/hr) Electrical power (Watts) •Measure the electrical power. •Calculate the heat transfer rate to/from the air. Energy Systems 2.0 Outdoor coil Indoor coil Compressor Digital thermometer Power meter Exp. valve Rev. valve Duct 4-inch Nozzle Atmospheric Air Nitrogen (78.08) Oxygen (20.95) Argon (0.93) Carbon dioxide (0.03) other gases (0.01) Dry air + Water vapor Moist air Ideal gas mixture Calculating the heat transfer rate to the air. Tin Tout Temperature of the moist air increases while water vapor content of the air remains constant. Only sensible heat transfer is present. Duct Heating coil Calculating the heat transfer rate from the air. Tin Tout Depending on the temperature of the coil, water vapor condenses on the coil surface and is removed from the air stream. The air is cooled and dehumidified. In this case both sensible and latent heat transfer effects are present. Duct Cooling coil Condensate removed

Ideal Gas Calculate the heat transfer rates assuming DRY AIR(no water vapor is present) RT P= atmospheric pressure q R= gas constant for air v=specific volume R=5352f-b 1b -R Q=volume flow rate T=air temperature(R) Calculating the volume flow rate of ai Assignment Write a 3-6 page technical paper discussing the Q=VA(ft/min) should include V=average velocity(ft/min) A summary A= cross sectional area(ft) A diagram of the system The basic principles involved a clear discussion of how the system works Velocity probe is used to How you determined the performance parameters Your experimental results

7 Calculate the heat transfer rates assuming DRY AIR (no water vapor is present). ( ) Q volume flow rate c specific heat specific volume c T T Q q p p out in = = = = −    v v Ideal Gas T air temperature (R) lb R ft lb R 53.352 R gas constant for air P atmospheric pressure P R T m f a a a = − − = = = v = Duct 4-inch Nozzle Calculating the volume flow rate of air. A cross sectional area (ft ) V average velocity (ft/min) Q VA (ft / min) 2 3 = = =  V Velocity probe is used to measure the air velocity • A summary. • A diagram of the system. • The basic principles involved. • A clear discussion of how the system works. • How you determined the performance parameters. • Your experimental results. • Your calculations of the performance parameters. Assignment Write a 3-6 page technical paper discussing the refrigeration unit and your experiment. This report should include: