Insulation/refrigeration Flashcards
What is another application for insulation?
Sound proofing
What three ways can heat be transferred?
Conduction, convection, radiation
What are some purposes of insulation?
Keeps thing warm, or cool, which increases efficiency. It also protects damage due to exposure due to heat, or corrosive atmospheres. Another common application is to prevent water condensation on cold surfaces.
What are the three insulation categories?
Cryogenic (below -10 1°C)
Thermal (between -10 1°C to 815°C)
Refractory (above 815°C)
What is cryogenic insulation?
It is used in the temperature range of -101 down to absolute zero. Cryogenics often is used to keep liquified gasses in the liquid state.
How are containers for cryogenics constructed?
In an insulated material to withstand extremely low temperatures without losing their strength. Usually a container inside a container similar to a thermos
What is cellular glass?
It is a common cryogenic range insulation. It is light weight rigid material made up of millions of completely sealed glass cells and each one in an isolated space. It is extremely abrasive.
What is super insulation?
The term applied to insulating blankets developed for spaceflight. The blanket consists of approximately 50 to 100 layers per inch of aluminized mylar separated by thin air spaces
Describe thermal insulation.
Most common type of insulation, there are three subcategories of thermal insulation- low temp, intermediate temp, high temp
Typical materials are fibreglass, rock wool, foamed plastics
What is effectively used in insulating building materials?
Small air pockets in the material greatly increase its insulation
What are the three thermal insulation categories?
Fibrous
Cellular
Granular
Describe fibrous insulation
Made from long small diameter fibers that divide the air into many tiny compartments. Fiberglass and mineral wool are commonly used
Describes cellular insulation
Use the principle of dividing the air pockets into tiny compartments. Foamed in plastics such as polystyrene and polyurethane are common
What is granular insulation
It is a loose horrible material such as vermiculite. Did commonly is used to fill the void inside hollow brick walls.
Define Refractory insulation
Typical applications are steel foundries and cement and lime kilns. The different forms of refracture he insulation available are: castable refractories, standard and specially shaped bricks, gunnite mixes, ramming mixes
What is a castable refractory
Made of minerals that withstand high temperature in the way they form ceramic, glass, or crystalline bond with manufactured.
What are refractory bricks?
They are used to line the surface of a kiln. The bricks are non conducting, and thick enough to keep the steel shell from becoming red hot and warping
What is gunnite?
It is mixed to a specific consistency, similar to mixing concrete, and is then sprayed onto the surface
What is a ramming mix?
Has the consistency of thick plasticine. These mixes are used mainly for patching and for filling in small areas where it is too difficult to cut bricks to match
What things are considered when selecting insulation
Thermal properties, mechanical properties, and chemical properties
What is temperature conductivity?
Thermal conductivity is similar to thermal conductance except that conductivity is rated on a 1 inch thick section of insulation. It is known as the K value. The lower the number the better the K factor is
What is thermal resistance?
It is the resistance to flow through a unit of area. It is known as the R value, and the higher the number, the better
Define insulation
Any material that is a poor conductor of heat or electricity that is used to stop or slow down the flow of heat or electricity
Another use for insulation other than stopping heat transfer
Noise control
Prolonged noise over ___db is not considered safe
70
What are some methods of sound control
Moveable curtains can reduce noise by 25db
Curtains with core acoustic insulation
What is cladding?
Also called jacketing. Protects the insulation from moisture and in some cases UV rays
What are some materials for cladding?
Aluminum sheeting, stainless steel for sheeting, pvc, woven tape, cloth sheets, plastic, foil laminates, roofing felt
As much as 98% of insulation problems are related to_____
Moisture
What is the purpose of a moisture barrier?
Prevents condensation from getting into the insulation. It is always put on the warm side of the insulation
How do most refrigeration systems produce cold?
The vapour compression cycle.
What is energy?
It is the capacity to do work, and can exist as potential energy, or as kinetic energy.
Explain energy conversion
In a refrigeration cycle, electrical energy is brought in, which is converted to mechanical energy through a motor then produces heat energy as it is running.
When one form of energy disappears, what happens?
Another form of energy appears. Energy can not be created or destroyed.
What is latent heat of vaporization?
The quantity of heat required to completely vaporize one kg of a liquid. The reverse process is called latent heat of condensation
How does a pressure increase change the boiling point of a liquid?
As the pressure increases, a higher temperature is required
Compressing a vapour does what ?
It increases its pressure, and temperature.
What are the boiling points of propane, and ammonia?
Propane boils at -42°C
Ammonia boils at -33°C
At atmospheric pressure
What components are on the high pressure side and low pressure side?
The low pressure side starts from the outlet of the metering device and continues as the refrigerant flows to the inlet of the compressor through the evaporator. high-pressure side starts on the inlet of the compressor through the condenser and back to the inlet of the metering device
What is the vapour compression cycle?
Compression,condenser, metering device (expansion chamber), evaporator
What is superheating
The addition of heat to a vapour, which elevates the temperature higher than the boiling point
What is sub cooling?
The removal of heat from a saturated liquid
What must be available for a liquid to vaporize?
Heat
What are the components, in order, of the vapour compression refrigeration cycle
Compressor
Condenser
Metering device(expansion)
Evaporator
What is the compressors function?
It is a vapour pump, and is the prime mover of the refrigerant
What is s condensers primary function?
To reject the heat from the circuit
What are the three types of condensers, and which is most effective?
Air cooled, water cooled, evaporative condenser.
What are the two types of water cooled condensers?
Waste water system, recirculated system. If a recirculated system is used, a cooling tower must be used.
What is an evaporative condenser?
Much like a cooling tower., it uses both water and air to cool the refrigerant
What are the components, in order, of the vapour compression refrigeration cycle
Compressor
Condenser
Metering device(expansion)
Evaporator
What is the compressors function?
It is a vapour pump, and is the prime mover of the refrigerant
What is s condensers primary function?
To reject the heat from the circuit
What are the three types of condensers, and which is most effective?
Air cooled, water cooled, evaporative condenser.
What are the two types of water cooled condensers?
Waste water system, recirculated system. If a recirculated system is used, a cooling tower must be used.
What is an evaporative condenser?
Much like a cooling tower., it uses both water and air to cool the refrigerant
What is the metering device?
It is used as a pressure reducer. They are basically an adjustable flow restrictor
What are the different types evaporators?
Frosting or non frosting, liquid type or air type. These are decided by what they cool (air or liquid)
What is the designation for copper piping used for refrigeration system
ACR tubing, and it is sized by the ID
What systems cannot use copper tubing?
Ammonia and propane systems
What is the metering device?
It is used as a pressure reducer. They are basically an adjustable flow restrictor
What are the different types evaporators?
Frosting or non frosting, liquid type or air type. These are decided by what they cool (air or liquid)
What is the designation for copper piping used for refrigeration system
ACR tubing, and it is sized by the ID
What systems cannot use copper tubing?
Ammonia and propane systems
What are the typical applications for ammonia and propane systems
Propane is used in natural gas processes, and ammonia is used in larger buildings
If liquid ammonia is splashed on your skin or clothing, what is the procedure?
Do not remove clothing, but try to hold it away from your skin. Gradually flush area with cool water slowly getting warmer.
What is moisture in a refrigeration system?
It is a contaminant. It will freeze inside the system
What lubricated the compressor?
There is a small amount of oil that is in the refrigeration circuit.
Where are oil separator always used?
Always in ammonia systems, because oil and ammonia are not mixable
What is the primary function of a chilled water circuit?
Larger air conditioning systems
What is a centrifugal compressor vulnerable to in a chilled water circuit?
It is vulnerable to surging
What refrigerant is used typically in a chilled water circuit?
R-22 or R-134a
What is a liquid over feed system?
It is where more refrigerant is pumped into the system than is needed. At the exit over the evaporator, some of the refrigerant is still a liquid
If some of the refrigerant is still a liquid after the evaporator, where does it go?
Because you can not have fluids flow into the compressor, it flows into a low pressure, or low side receiver
What is the benefit of the liquid over feed system?
It ensures all heat transfer is latent transfer, it reacts quickly to high demand changes, it is easily modified, putting more evaporators in the circuit, or removing them quickly
How is defrosting of the evaporators done in a liquid over feed system?
Sometimes they use electric heaters, ,but because plenty of hot vapours are available they sometimes use those hot vapours
Describe a flooded refrigeration system
It is the type that is used in hockey arenas. It has two separate systems, one for the refrigerant and one for the brine
Why do they call it a flooded refrigeration system?
Because the brine is completely immersed or flooded in the refrigerant. It uses a shell and tube system for the two solutions
What must a flooded refrigeration system have to prevent fluids from entering the compressor?
They must have a surge tank
What is the primary system and what is the secondary system of a flooded refrigeration system?
Primary system-ammonia
Secondary system- brine
What are two safety systems or features to keep public safe using this system?
The brine tank is vented so if any ammonia gets in there, it will go out the vent. If there is a fire, a button can be pushed to vent the pressurized ammonia out the top of the building, from the sealed ammonia compressor room
What is an absorption refrigeration circuit also known as?
Lithium bromide system
Where are absorption circuits used?
They were used in high volumes buildings such as hospitals. They are seldom used now
How many separate circuits are in a absorption circuit?
Three
Chilled water circuit
Cooling tower circuit
Refrigerant water circuit
Where is the compressor in an absorption refrigeration circuit?
There is no compressor, heat energy is used instead. The lithium bromide absorbs the moisture, and when it becomes saturated, it goes through a steam generator to charge it again
Why is the absorption method tough to maintain?
Because the entire absorption system must be kept gas tight
What must a flooded refrigeration system have to prevent fluids from entering the compressor?
They must have a surge tank
What is the primary system and what is the secondary system of a flooded refrigeration system?
Primary system-ammonia
Secondary system- brine
