Industrial Refrigeration Flashcards
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 1kg 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?
- Evaporator
- Compression,
- Condenser,
- Metering device (expansion chamber)
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 is the compressors function?
It is a vapour pump, and is the prime mover of the refrigerant
What is the condensers primary function?
To reject the heat from the circuit.
What are the three (3) types of condensers?
- Air cooled
- Water cooled
- Evaporative condenser.
Out of the three (3) condensers which is the most effective?
Water Cooled Condencer.
What are the two types of water cooled condensers?
- Waste Water System
- Recirculated System.
NOTE: 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.
NOTE: 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.
* 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 get it warmer.
What is moisture in a refrigeration system?
It is a contaminant. It will freeze inside the system.
What lubricates 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?
They are used on 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?
It flows into a low pressure, or low side receiver.
Because you can not have fluids flow into the compressor.
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 or Hot Gas.
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?
- Chilled water circuit
- Cooling tower circuit
- Refrigerant water circuit
Where is the compressor in an absorption refrigeration circuit?
“There is no compressor”
NOTE: 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.
