705 AC & Refrigeration Plants
Transcript of 705 AC & Refrigeration Plants
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Refrigeration
andAir Conditioning
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References Introduction to Naval Engineering,
Chapter 19, pp. 341-351
Principles of Naval Engineering,
Chapter 22, pp. 22-1 -
22-17
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AC &RObjectives Basic operation
Principle components
Safety considerations
Thermodynamic principles
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Uses of AC&R Systems Cooling of stores and cargo
Cooling of electronic spaces and equipment
CIC (computers and consoles)
Radio (communications gear)
Radars
Cooling of magazines
Air conditioning for crew comfort
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Definition Review Specific heat (Cp)
Amount of heat required to raise the
temperature of 1 pound of substance 1F
(water is 1 Btu/lb F) Sensible heat - add energy and temp rises
Latent heat of vaporization - liquid to vapor
BTU (British Thermal Unit) Refrigeration - Cooling of an object and the
maintenance of its temp below that of
surroundings
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Generic Cycle
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Thermodynamic Cycle
Evaporator
Condenser
CompressorTXV
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Vapor-Compression
Refrigeration Cycle Refrigerant
Receiver
Thermostatic expansion valve (TXV)
Evaporator
Compressor Condenser
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RefrigerationCycle
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Refrigerant
Must have the following properties
High latent heat of vaporization - max cooling
Non-toxicity - not a health hazard
Desirable saturation temperature - for operating
pressures
Stability - nonflammable/nonexplosive
Ease of leak detection
Low cost
Readily available
R-12, R-114
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Expansion
Liquid Freon enters the expansion valve at
high pressure
Refrigerant leaves TXV at a much lower
pressure
As pressure drops, vapor formation begins
as Freon enters saturation region
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Evaporation
From TXV - Freon is a saturated mixture of
liquid and vapor
Cooling coil acts as a heat exchanger
Absorbs its latent heat of vaporization from
the surroundings
Slightly superheated (10F) - ensures no
liquid goes to compressor
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Compression
Low pressure, superheated Freon vapor
enters the suction side of the compressor
Refrigerant is compressed from a lowpressure vapor to a high pressure vapor
Increase in energy provides the driving
force to allow the Freon to flow through thesystem
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Condensation
Refrigerant returned to starting point as a
high pressure/temperature subcooled liquid
Latent heat of condensation (LHC)
Sea water heat exchanger is used to absorb
the LHC and discharge it overboard
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Receiver
Temporary storage space and surge tank for
the sub-cooled refrigerant
Serves as a vapor seal to prevent vapor fromentering the expansion valve
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Air Conditioning
Principles of Operation Air Conditioning
Maintaining the atmosphere of an enclosedspace at a required temp, humidity and purity
Cools / Dehumidifies air via cooling coils
within ventilation system
Heaters in ventilation system
Humidification units may be present
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Air Conditioning
Systems Refrigerant circulating system
Directly cools cooling coils
Chilled water circulating system
Refrigeration system cools chill water, which
cools cooling coils
Self-Contained System Added on to ships which originally did not
have AC plants
Not located in ventilation system (window unit)
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Basic AC System
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Safety Associated
AC&R Phosgene gas hazard (created when
refrigerant is exposed to high temperatures)
Handling procedures: Wear goggles and
gloves to avoid eye irritation and frostbite
Asphyxiation hazard in non-ventilatedspaces (bilges since heavier than air)
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Summary