Vapour Cycle

Environmental Systems Environmental Systems And And

IntegrationIntegration

Roger CoatesRoger Coates

Vapour Cycle Vapour Cycle SystemSystem

Aircraft Air ConditioningAircraft Air Conditioning

Basic Vapour CycleBasic Vapour Cycle

High Pressure Side• High side includes

– Discharge side of Compressor– High Pressure vapor lines to condenser– Condenser– High Pressure liquid lines to orifice valve– Inlet side of orifice Valve

Low Pressure Side• Includes:

– Orifice

– Low Pressure Liquid lines

– Evaporator

– Low Pressure Vapor Lines

– Suction side of Compressor

– Outlet side of orifice valve

Receiver DrierReceiver Drier

Expansion ValveExpansion Valve

Evaporator

• Function is opposite of condenser

• Evaporator coils remove heat and humidity from the air being circulated in passenger compartment.

• When liquid refrigerant absorbs heat, it again becomes a vapor under low pressure

• Has a tray to collect moisture from fins

EvaporatorEvaporator

CompressorCompressor

Condenser

• Located in front of radiator

• Compressor pumps high pressure vapor into condenser where ram air passing over coils carries off heat

• The heat loss causes the refrigerant to become a high-pressure liquid.

Expansion Valve or Fixed Orifice Tube

• Provides a restriction in refrigerant flow which the compressor can build up a pressure in the condenser.

• Compressor suction lowers pressure in the evaporator

• Regulates pressure differential between the high and low sides.

• Keeps evaporation and expansion of refrigerant and most efficient level.

CondenserCondenser

Service ValvesService Valves

SERVICE VALVES

SERVICE VALVES

A/C Service Connectors

SERVICE VALVES

Schrader ValvesSchrader Valves

Indirect Liquid CoolingIndirect Liquid Cooling and and

Properties of RefrigerantsProperties of Refrigerants

Basic OperationBasic Operation

Basic OperationBasic Operation

Properties of Properties of RefrigerantsRefrigerants1. Boiling point at atmospheric pressure as close

as possible to the degree of refrigerant required.

2. A low specific heat in liquid form.3. A high specific heat in vapour form.4. A high latent heat.5. Non-Flammable.6. Non-Toxic.7. Non-Corrosive.8. No undesirable action with oil.9. Leaks easily detected and controlled.10. Low cost.

Group Definition

1 Gases or vapours which, in concentrations of the order of ½ to 1 % for durations of exposure of the order of five minutes, are lethal or produce serious injury. (Example: Sulphur Dioxide)

2 Gases or vapours which, in concentrations of the order of ½ to 1 % for durations of exposure of the order of ½ hour, are lethal or produce serious injury. (Example: Ammonia)

3 Gases or vapours which, in concentrations of the order of 2 to 2½ % for durations of exposure of the order of one hour, are lethal or produce serious injury. (Example: Methyl Formate)

4 Gases or vapours which, in concentrations of the order of 2 to 2½ % for durations of exposure of the order of two hours, are lethal or produce serious injury. (Example: Methyl Chloride)

Hazards of Gases and VapoursHazards of Gases and Vapours

Group Definition

Between 4 & 5

Gases or vapours which appear to classify as somewhat less toxic than group 4. (Example: Methyl Chloride)

Gases or vapours which are much less toxic than group 4, but somewhat more toxic than group 5. (Example: Refrigerant 113)

5a Gases or vapours which are much less toxic than group 4 but are more toxic than group 6.

(Example: Refrigerant 11, Refrigerant 22, Carbon dioxide, Refrigerant 500

5b Gases or vapours which, available data indicate, would classify as either group 5a or 6

6 Gases or vapours which, when in concentrations up to at least about 20% by volume for durations of exposure of the order of two hours, do not appear to produce injury.

(example: Refrigerant 12, Refrigerant 114)

Hazards of Gases and VapoursHazards of Gases and Vapours

Types of RefrigerantsTypes of RefrigerantsAmmonia• Not generally used as a refrigerant in aircraft.• Oldest known refrigerant.• Consists of Nitrogen, chemically combined with

hydrogen.• Highest latent heat of any of the common

refrigerants.• Corrosive to copper in the presence of oxygen.• Vapour considered flammable, explosive and

toxic.• Sharp penetrating odour, leaks quickly detected.• Not oil miscible.• Will not dilute the oil in the compressor.

Types of RefrigerantsTypes of RefrigerantsSulphur Dioxide• Not generally used as a refrigerant in aircraft.• Produced from the combustion of sulphur.• Most sulphur dioxide installations have been

replaced by Methyl Chloride or Fluorocarbon type refrigerants.

• Highest latent heat of any of the common refrigerants.

• Highly toxic.• Non-flammable and non-explosive.• Not oil miscible.• Heavier than oil.

Types of RefrigerantsTypes of Refrigerants

Methyl Chloride• Classified as a Halocarbon type refrigerant.• Considered to be non-toxic.• In large concentrations, has an effect similar to

chloroform.• Moderately flammable.• Explosive when mixed with air.• When used with usual caution, these factors are not

considered limiting.


Carbon Dioxide• Used in small commercial systems.• Liquefiable only under high pressure, therefore not

suitable for small refrigeration units.• Considered to be non-toxic.• Colourless• Odourless.• Leaks must be detected using limewater• Or with the use of an odorous oil (peppermint,

cloves, etc).


Refrigerant 11• Trichloromonofluoromethane.• Non-toxic.• Non-flammable.• Design pressures are very low and require small

pressure differentials of 15 to 20psi.• Suitable for applications at sub-zero temperatures.• Faint ethereal odour.• Leaks readily detected with a halide leak detector.• Miscible with oil in all proportions.


Refrigerant 12• Most commonly used refrigerant in air

conditioning.• Dichlorodifluoromethane.• Practically odourless• Non-toxic, harmless to breath except in extremely

concentrated form..• Non-flammable.• Miscible with oil in all proportions.• May be used with all ferrous and non-ferrous

metals.

Types of RefrigerantsTypes of RefrigerantsRefrigerant 22• Monochlorodifluoromethane.• Characteristics similar to Refrigerant 12.• Non-toxic.• Non-flammable.• May be used with all ferrous and non-ferrous

metals.• Miscible with oil in all proportions at normal

condensing temperatures.• Relatively low solubility for oil at evaporator

temperatures• Designed for refrigeration installations with a very

low-temperature cooling unit.

Types of RefrigerantsTypes of RefrigerantsRefrigerant 114• Dichlorotetrafluoromethane.• Can be used in centrifugal, rotary or reciprocating

compressors.• Generally used for centrifugal applications because the

compressor displacement required is very low.• The volume of vapour circulated per ton is about three

times that for Refrigerant R12.• Low toxicity.• Non-flammable.• Chemically stable.

Types of RefrigerantsTypes of RefrigerantsRefrigerant 114 (Cont.)• Faint ethereal odour.• Miscible with oil in all proportions at normal

condensing temperatures.• At lower temperatures there is only partial solubility

and two liquid layers are formed.• Designed for refrigeration installations with a very

low-temperature cooling unit.

Physical Properties of Physical Properties of RefrigerantsRefrigerants

Refrigerant HandlingRefrigerant Handling

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Vapour Cycle