Mech Theory 4 Flashcards
What are the energy statements for boiling liquids
As pressure increases, volume decreases and more energy is needed to boil a liquid
As pressure decreases, volume increases and less energy is required to boil a liquid
Three ways heat can be transferred
Convection
Conduction
Radiation
Sensible heat
Heat required to change temperature but not state
Latent heat
Heat required to change the state but not temperature
Super heat
When the temperature goes above the boiling point
Every degree of temperature above then gains 1 degree of superheat
For example 101c = 1c of superheat
Define sub cooling
When a substance cools and condences into liquid and drops below its boiling point it is sub cooled, for every degree below its boilling point it gains one degree of super cooling
Name the four components in the 4 part refrigiration cycle
Compressor
Condensor
Thermal expansion valve (TEV)
Evaporator
TEV?
Thermal expansion valve
What does the compressor do
Pumps the refrigerant around the system and raises the temperature
What does the condenser do
Uses sea water to cool the refrigirant to change its state from a gas into a liquid
What does the thermal expansion valve do
Used to slow the rate of the refrigerant flow and lowers the pressure and temperature of the liquid
What does the evaporator do
Very cold liquid enters the evaporator and changes the liquid into a gas
What are the uses of water
- Drinking
- Washing
- Cooking
- Cleaning
What are the methods of defrosting
Natural defrosting
Hot gas defrosting
Electrical heating coils
What are the methods of leak detection
Oil slicks IRLDS (Infra red leak detection) Spectrolyne dye and UV lamp Snoop Halogen leak detector
3 types of fridges
Freezers
Walk in veg stores
Ready to use fridge
Montreal summit
To reduce ozone damaging gases
CFC
HCFC
Halon
Kyoto summit
To reduce green house gases
HFC
PFC
CO2
Hydroscopic?
Absorbs water from the atmosphere
Three types of refrigerant oil
OM70
Suniso 3GS
SW 68
Methods of topping up oil
Sump filling plug
Hand pump
Dazing pot
What colour is the fresh water hose and what should you do before connecting it to the ship
BLUE
clean the hose by flushing it out with fresh water
When are chlorine leaks checked
Daily
Before embarking
Why must chlorine be added to the water tank and NOT during reverse osmosis procedure
Because it can cause irreversible damage to the membrane
Types of filters
Panel filters Supply filters Grease filters Lint filters Dust filters Flameproof gauzes
Special areas with ventilation requirements
Galleys Store rooms Auxiliary machinery spaces Sewage treatment spaces Magazines
ATU? And what are the % of air it runs at
Air Treatment Unit
33% fresh air
67% Re-Circulated air
Before entering the refrigeration machinery room you must
Inform the rating in charge
No smoking
Breathing apparatus available
Exhaust fans running
3 parts of the AFU
Pre particulate filter
Particulate filter
Gas filter
Pre particulate filter
Paper filter which removes course particles
Particulate filter
Glass fibre filter made to remove bacteria by entrapment
Gas filter
To remove all known chemical warfare agents
When will phosgene gas be created
If it is exposed to high temperatures
What is given off if fruit and veg decomposes
CO2
What are the procedures for entering refrigeration compartments
- Exhaust fans running
- No smoking
- Inform a senior rate
- Tag in and out
1 major difference of refrigeration and chilled water plant
refrigeration has a chiller instead of a evaporator
What are the uses of ventilation
- electronic equipment
- galley ventilation
Condition of refrigerant as it flows through each compartment
HOT-WARM-VERY COLD- COOL
HIGH PRESSURE X2-LOW PRESSURE X2
GAS-LIQUID-LIQUID-GAS
4 refrigeration hazards
- Heavier than air, so it displaces oxygen
- Phosgene gas
- Frost bite
- Decomposing fruit and veg (CO2)
Types of oil used
OX30 RED
OX40 GREEN
OM33 YELLOW/ORANGE
Desirable properties of hydraulic oil
- Incompressible
- Good lubrication
- Good sealing properties
What does Demulsibility mean
When the water can be separated from a fluid
Why are anti oxidants added to oil
To stop sludge and gum
List 6 hydraulic pumps
- Integral gearwheel
- External gearwheel
- Vane
- Lobe
- Radial piston
- Axial piston
Purpose of a drain leg
Returns oil that has been used for lubrication, sealing and cooling
What does an actuator do
Converts hydraulic energy into mechanical motion
4 advantages of a hydraulic system over an electric system
- Easily reversible
- Infinite speed range
- High torque low speed
- Reliable
State 4 types of filters
- Panel
- Supply
- Lint
- Dust
When would a bleed valve be operated
If the pressure is more than 2 WG
What is a citadel
Whole ship shelters from chemical, nuclear and biological warfare and makes it air type
Parts of the desalination
- SW inlet
- Membrane
- O seal
- Permeable water
- Concentrate
Type of filter
Bag filter 60 MICRONS
CCV - concentration control valve
Controls the back pressure and of what quality
Fresh water tests
- CHEMets
- Visual
- Taste
What system is hydroscopic referring to
Refrigerant oils
Refrigerant oils
- OM70
- Suniso 3GS
- SW 68
Hydraulic oils
- OM30 Red Sub
- OM33 Yellow T42s
- OX40 Green T45s
