Theory 4 Flashcards
What are the Pressure, Volume, Energy statement for boiling liquids?
As Pressure Increases, Volume Decreases and More Energy is required to boil a liquid
As Pressure Decreases, Volume Increases and Less Energy is required to boil a liquid
What direction does heat transfer?
Heat always travels from hot to cold
What are the three ways in which heat can be transferred?
- Conduction: Heat transfer through a Solid
- Convection: Heat transfer through a Fluid
- Radiation: Heat transfer through a Space
What is sensible heat?
This is the heat required to change Temperature, not change the State of a substance
What is latent heat?
This is the Heat required to Change the State of a substance without any change in its Temperature
What is superheat?
When a substance goes above its Boiling Point it is superheated. For every degree it goes above its boiling point it gains one degree of superheat.
What is subcooling?
When a substance cools and condenses into liquid and then drops below its boiling point it is Sub-cooled. For every degree below its boiling point it gains one degree of Sub-cooling.
What are the four components of the refrigeration cycle and their function?
- Compressor – Pumps the refrigerant around the system
- Condenser – Uses sea water to cool the refrigerant changing its state from a Gas into a Liquid.
- TEV (Thermal Expansion Valve) – Controls the flowrate of refrigerant through the system. Increasing or decreasing the flow depending on the temperature of the refrigerant leaving the Evaporator.
- Evaporator – The refrigerant flowing through the Evaporator removes heat from the refrigerator / cold room. This action changes the state of the refrigerant from a Liquid into a Gas.
What is the condition of the refrigerant as it flows through each component?
- Compressor to Condenser – Hot, High Pressure, Gas
- Condenser to TEV – Warm, High Pressure, Liquid (Sub-cooled)
- TEV to Evaporator – Very Cold, Low Pressure, Liquid
- Evaporator to Compressor – Cool, Low Pressure, Gas (Super-Heated)
Refrigeration procedures -defrosting:
Required when ice builds-up on the Evaporator coils – methods of defrosting are:
• Natural Defrost - carried out every 3 to 6 months
• Hot Gas Defrosting – This is done for a maximum of 1 hour in 24 in 15 minute slots
• Electrical Heating Coils – This is also done for a maximum of 1 hour in 24
Refrigeration procedures-leak detection
Refrigerant leaks are harmful to the environment and reduce refrigerant plant efficiency
Methods of Leak Detection are:
• Oil slicks – where oil is leaking there will also be refrigerant leaking
• IRLDS Infra-red leak detection system
• Spectrolyne Dye and UV Lamp
• Snoop
• Halogen Leak Detector
Refrigeration procedures- lubrication:
The Compressor requires lubricating with special lubricants – E.g. OM70 and SW68
These lubricants are HYGROSCOPIC (Absorb moisture from the atmosphere)
Only new, unopened cans to be used
What is the Montreal protocol?
Agreement to phase out harmful ozone depleting substances / refrigerants such as:
• CFCs
• HCFC
• Halons
What is the Kyoto summit?
Agreement to reduce all Greenhouse gases: • Greenhouse Gases o CO² o HFC o PFC
What are the four refrigeration hazards?
They are heavier than air and will displace Oxygen
If exposed to high temperatures they can produce PHOSGENE GAS
Can produce Cold Burns on exposed skin (Frost Bite)
Decomposing Fruit and Veg can produce CO²
Health and safety procedures when working on refrigeration
If refrigerant gets into eyes they need flushing with running water and then require medical treatment.
Refrigerant on the skin requires washing off immediately
What are the procedures for entering refrigeration compartments?
- The Rating in charge of the watch is to be informed that personnel are entering the compartment, and informed when the compartment is vacated
- Breathing Apparatus is available at the machinery space access
- The high and low exhaust fans are running
- No smoking at any time in the refrigeration area. Any hot work is to be very tightly controlled
- The Infra-Red Leak Detections System (IRLDS) is working correctly and indicating safe
- The personnel trapped warning lamps are in working order
- Any rating entering the room is to be accompanied by another rating who remains outside the room as a safety number
- The internal door opening mechanism is in correct working order
What is chilled water used for?
Chilled Water is used to provide cooling for: • Weapons Systems • Radars • Ships Computer Systems • Air Treatment Units (ATUs)
What is the one major difference in the components of a refrigeration and a chilled water plant?
The chilled water plant has a CHILLER in place of the EVAPORATOR
What provides cooling for the condenser and motors
Sea water
What are the uses of ventilation?
- Cooling of Electronic Equipment
- CBRN
- Habitability
- Main Machinery Space Cooling
- Galley Ventilation
Where is fan supply and fan exhaust used?
Machinery spaces, Galleys, Laundries, WCs and Bathrooms
Used to remove large quantities of wild heat, moisture or toxic fumes
Where is fan supply and natural exhaust used?
Store rooms and Workshops
Supply of fresh air to compartments is primary objective
Where is natural supply and fan exhaust used?
Paint stores, Spirit rooms, Inflame stores
Removal noxious gasses and flammable vapours is primary objective
Where is natural supply and natural exhaust used?
This is only used in minor unoccupied compartments and lobbies
What are the 6 common filters?
Panel filter Supply filter Grease filters Lint filters Dust filters Flameproof gauzes
What are the five special requirements?
- Galleys – Have Fire Flaps fitted to their exhaust trunking
- Store Rooms - subject to the build-up of toxic fumes
- Auxiliary Machinery Spaces - . To prevent any build-up of gas
- Sewage Treatment Spaces - These spaces require 15 air changes per hour
- Magazines - fitted with their own air conditioning system
What are ATU systems?
under normal conditions use 33% Fresh air and 67% Re-circulated
AFU(air filtration unit)
Used in CBRNDC state 1
AFUs consist of three sections:
1. Pre-Particulate Filter – A paper filter which removes coarse particulate matter including radio-active fall-out
2. Particulate Filter – Made of glass fibre; designed to remove particulate such as bacteria by entrapment
3. Gas Filter – Designed to remove all known chemical warfare agents in the form of gases or vapours from the airstream by absorption in the activated charcoal filling
What is the citadel?
- As a whole ship chemical, biological and nuclear shelter
- Formed by closing the ship down to an increased gas tight state
- The Citadel works by increasing the atmospheric pressure within the ship above external pressure using air filtered by AFU units
What are the 5 citadel tests?
- Annually
- Prior to DED
- During Harbour Acceptance Trials (HATS)
- During Sea Acceptance Trials (SATS)
- during FOST Work-up
What is crash stop?
A crash stop facility is built into the ventilation system to allow all fans to be stopped in case of an emergency
RESTART of VENT SYSTEMS
vent intakes should be checked they are clear of Smoke, Welding fumes and Debris.
What is fluid definition?
- It is a substance that will readily take the shape of its container
- It is capable of transmitting power
- It can be a liquid or gas
What are the advantages of hydraulics?
- reliable
- easy to understand
- Infinite speed range
- Easily reversed
- Ability to withstand overload
- No spark risks
- High torque at low speeds
- 1/12 size of equivalent electric motor
What are the disadvantages of hydraulics?
- Fire risk with mineral oil systems
- Noise
- Risk of contamination
- Less efficient (85-95%)
Health and safety on hydraulics
Denso steel working mastic and PVC self-adhesive tapes give off toxic gases when ignited
O rings are made from Fluorocarbon elastomers which as 300C and above gives off gases like hydrogen fluoride
What PPE must you wear when working with fluorocarbon elastomers?
- PVC gauntlets
- Rubber boots
- PVC coveralls
- Full-face visor
What are the two types of hydraulic fluid?
Petroleum based
Synthetic based
What oils are used with hydraulics?
OX30-RED
OM33-Yellow/Orange
OX40-Green
Rust veto
Requirements of a hydraulic fluid:
- transmission of power
- The fluid must flow easily through lines
- It must be as incompressible
- Lubrication
- Sealing
- Cooling .
What are the common causes of contamination in hydraulic oil?
- Airborne particles and moisture
- Construction dirt
- Dirt in new fluid
- Dirt produced by wearing in new system
- Dirt from human sources
Methods of reducing contamination are:
- Good system design
- Filtration and filter maintenance
- Operation of filter and clogging indicators
- Good working practices
- Use of Guardian filter pack
- Caps should be fitted to open pipework
- Clean working area
Positive displacement pumps are used for hydraulic systems. Different types are:
- Internal gearwheel type
- External gearwheel type
- Vane type
- Lobe type
- Radial piston type
- Axial Piston Pump
Axial piston pumps are used on:
- Stabiliser systems
- CPP systems
- Steering systems
What are actuators?
Actuators convert hydraulic energy (system pressure) into mechanical motion.
There are two types to consider, Linear and Rotary.
Linear actuators can be either Single or Double Acting.
What are accumulators?
store energy and to smooth out pulsations. They are used as a surge or pulsation dampener or absorber.
Uses of fresh water?
- Drinking
- Washing
- Cooking
- Cleaning
The services provided by the fresh water system include:
- The laundry
- The galley
- Showers and sinks
- Water heaters
- Medical use
- Bridge window washers
- Fresh water hose reals
- Machinery cooling
What is osmosis?
Is the transfer of pure water through a semi-permeable membrane into salt water
What is reverse osmosis?
Is the transfer of water from salt water through a semi-permeable membrane into pure water
TDS-measure of water purity
- The TDS of sea water is approximately 34,000ppm
- The TDS of the water after desalination is between 250 & 300ppm
- Approximately 80% of the supplied sea water is ejected
- The desalinated water is called “Permeate” and is sometimes referred to as “Made Water”
- The waste water after desalination is called “Concentrate”
The reverse osmosis plant
Has two filtration stages- first stage is a bag filter that filters down to 60 microns
Second stage is a cartridge filter that filters down to 10 microns
The RO plant has a High Pressure, 3 Piston Positive Displacement Pump. This provides pressure up to 65bar
The concentration control valve
This controls the Back Pressure of the sea water acting on the Membrane Cushions. By Closing the valve, the back pressure is Increased and the amount of Permeate is Increased. Therefore, Opening the valve Reduces the back pressure and the amount of Permeate is Reduced.
Chlorine and Chlorination
Chlorine levels, in fresh water tanks, are checked Daily and before Embarkation. It is maintained at 0.2ppm.
Health and safety in water production
Desalination should not continue if the source of water is likely to be contaminated. Harbour water and Estuary waters being prime examples.
The Section Head will authorise and supervise any addition of chlorine to the fresh water.
What are the three fresh water tests and when are they carried out?
Fresh water testing is carried out daily and prior to embarkation.
- CHEMets
- Visual
- Taste
What is used to heat water on a ship?
Calorifiers
What is a air eliminator?
One symptom of air in the fresh water system is known as “water hammer” which is a loud and repetitive banging noise inside the pipes
How do we bring on fresh water?
Fresh Water hoses are Blue in colour – they should be flushed with fresh water before use
How do we add oil to a compressor?
- Via Sump Filler Plug
- By a Hand Pump
- Through the use of a Dosing Pot
