Manual for Refrigeration Servicing Technicians - UNEP - Division of ...

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2 Refrigerants Refrigerant blends Although refrigerants can be one single substance, they can also be a mixture of two or more substances, and these are normally referred to as “blends”. Refrigerant blends have been formulated to provide a match to certain properties and characteristics of the refrigerants originally used (i.e. in the case of retrofit blends), or to achieve a particular set of properties for other reasons. Most commercially available blends have between two and five components. These components may be HCFCs, HFCs and/or HCs and PFCs. The individual component refrigerants in a blended refrigerant do not have identical physical characteristics; they have different densities, different viscosities and different evaporation and condensation temperatures at a given pressure. With most blends, the components within the mixture change their composition in the liquid and vapour phases as the blend boils or condenses; these are known as zeotropes. These have an R-number designation, R4xx. Less commonly, the individual components in certain blends interact such that the vapour phase and liquid phase have the same composition at a given pressure; these blends are called azeotropic mixtures. These have an R-number designation, R5xx. There are two types of blend: Azeotropic 4 Zeotropic 4 46
2 Refrigerants Azeotropic Blends An azeotropic blend is a mixture of usually two substances, which behaves as if it were a pure fluid. When heat is added to or removed from an azeotropic refrigerant blend, the composition (mole fraction) of the vapour and the liquid remain essentially unchanged throughout the complete process. In other words, in a blend of 50% of fluid A and 50% of fluid B, for every molecule of fluid A that vaporises or condenses, a molecule of fluid B does the same. An azeotropic blend behaves like a single refrigerant when condensing or evaporating, i.e., the temperature remains constant at a given pressure, as shown in this figure: TEMPERATURE SINGLE COMPONENT PRESSURE - TEMPERATURE CHART LENGTH OF HEAT EXCHANGER SUBCOOLED SUPERHEATED BOILING EVAPORATING EVAPORATING (CONSTANT PRESSURE) Condensation and evaporation of an azeotropic blend Historically, the commonly used ozone depleting substance (ODS) blends were R500 (mixture of R12 and R152a) and R502 (mixture of R22 and R115). More recently, an azeotropic blend using only HFCs has been found, R507A (mixture of R125 and R143a). Zeotropic blends A zeotropic blend is a mixture of refrigerants whose different volatilities are seen when observing the performance of a refrigeration cycle. For example, a change in the molar composition and/or a change in saturation temperature during boiling or condensation; in this way, it does not behave like a single refrigerant when condensing or evaporating. Two different situations arise, depending upon the type of system. Direct expansion system: • Flow-boiling occurs in the evaporator and flow-condensation in the condenser. Fluid A boils or condenses at a different rate than fluid B, and because the liquid composition of fluid A and fluid B changes, whilst the pressure remains the same, the saturation temperature along the heat exchanger varies. • Flooded system: Pool-boiling occurs in the evaporator and filmcondensation in the condenser. Fluid A boils or condenses at a different rate from fluid B, which results in an accumulation of the most volatile fluid in the condenser and the less volatile fluid in the evaporator. Whilst the phase-change process occurs at a constant temperature, there is essentially a short-circuiting of the refrigerant, which results in a loss in performance. 47
Page 1 and 2: Manual for Refrigeration Servicing
Page 3 and 4: Introduction When to use the manual
Page 5 and 6: Introduction The Factors affecting
Page 7 and 8: Introduction How to assess conditio
Page 9 and 10: Introduction Characteristics of Sel
Page 11 and 12: Introduction Another form of refere
Page 13 and 14: Introduction Choose your chapter Th
Page 15 and 16: 1 Environmental impact of refrigera
Page 17 and 18: 1 Environmental Impact The ozone la
Page 19 and 20: 1 Environmental Impact RADIATION FR
Page 21 and 22: 1 Environmental Impact The ozone la
Page 23 and 24: 1 Environmental Impact Effects of o
Page 25 and 26: 1 Environmental Impact The greenhou
Page 27 and 28: 1 Environmental Impact Timeline act
Page 29 and 30: 1 Environmental Impact Alternative
Page 31 and 32: 1 Environmental Impact The way forw
Page 33 and 34: 2 Refrigerants 2.1. Section objecti
Page 35 and 36: 2 Refrigerants Chemical properties
Page 37 and 38: 2 Refrigerants Safety characteristi
Page 39 and 40: 2 Refrigerants Types of refrigerant
Page 41 and 42: 2 Refrigerants Those with ozone dep
Page 43 and 44: 2 Refrigerants Those with zero ozon
Page 45: 2 Refrigerants Carbon dioxide (CO2,
Page 49 and 50: 2 Refrigerants Using Refrigerant Bl
Page 51 and 52: 2 Refrigerants Lubricants Today, al
Page 53 and 54: 2 Refrigerants Refrigerants and app
Page 55 and 56: 2 Refrigerants Properties of most c
Page 57 and 58: 3 Refrigerants Content Management M
Page 59 and 60: 3 Refrigerant Management The majori
Page 61 and 62: 3 Refrigerant Management Handling o
Page 63 and 64: 3 Refrigerant Management Recovery c
Page 65 and 66: 3 Refrigerant Management Refrigeran
Page 67 and 68: 3 Refrigerant Management Refrigeran
Page 69 and 70: 3 Refrigerant Management Open Refri
Page 71 and 72: 3 Refrigerant Management CHAPITRE 3
Page 73 and 74: 3 Refrigerant Management Recycling
Page 75 and 76: 3 Refrigerant Management equipment
Page 79 and 80: 3 Refrigerant Management PAGE 22 Ex
Page 83 and 84: 3 Refrigerant Management Further re
Page 85 and 86: Summary This section will provide t
Page 87 and 88: 4 Servicing Practices Moisture Mois
Page 89 and 90: 4 Servicing Practices Non-condensab
Page 91 and 92: 4 Servicing Practices Evacuation A
Page 93 and 94: 4 Servicing Practices 7 - For large
Page 95 and 96: 4 Servicing Practices Pressure unit
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CHAPITRE 4 4PAGE 10 LEAK DETECTION
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4 Servicing Practices Detection met
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4 Servicing Practices CHAPITRE 4 PA
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4 Servicing Practices Volumetric ch
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4 Servicing Practices Electronic ch
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4 Servicing Practices Why charge re
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5 Retrofitting Content General retr
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5 Retrofitting • Upon evaluation
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5 Retrofitting General retrofitting
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5 Retrofitting procedures that you
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5 Retrofitting MVAC retrofitting pr
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5 Retrofitting Although, in general
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5 Retrofitting Further reading UNEP
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6 Summary 6.1. Overview of refriger
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6 Safe Refrigerant Handling Oxygen
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6 Safe Refrigerant Handling The com
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6 Safe Refrigerant Handling • Nev
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6 Safe Refrigerant Handling Safe ha
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6 Safe Refrigerant Handling leak de
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6 Safe Refrigerant Handling • Lea
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6 Safe Refrigerant Handling Storage
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6 Safe Refrigerant Handling Recomme
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6 Safe Refrigerant Handling 3 - Sho
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Glossary Glossary Absolute pressure
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Glossary Fossil fuels Carbon-based
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Glossary hole in late 1985, governm
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Glossary Sealed system A refrigerat
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Acknowledgements Acknowledgements I
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Copyright Copyright © United Natio
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