Theory Flashcards
What is the approach & the range when talking about cooling towers?
The measure of performance.
How do you calculate the approach?
Water Outlet of cooling tower - wet bulb temperature
how do you calculate the range?
Water In - Water out
One example of a type of non-evaporative water-cooled condenser?
Dry Cooler
What is the difference between an indirect and a direct cooling tower?
A direct cooling tower is open to atmosphere. An indirect cooling tower is a closed loop system (not exposed, in a tube) that uses multiple cooling sources
What is the difference between an evaporative condenser and a indirect cooling tower?
An evaporative condenser’s tubes are filled with high pressure refrigerant. An indirect cooling towers tubes are filled with water or glycol
What applications are evaporative condensers used and why?
Ammonia (R-717) because evaporation is great at removing heat and ammonia has a high discharge temperature.
Waste Water Condensing systems reject the heat absorbed by the water where?
Floor Drain
In a waste water condensing system what valve regulates discharge pressure?
A direct acting water regulating valve
Dry Coolers use evaporation, true or false?
False
What is the purpose of the fill in a cooling tower?
Increase the surface area of the water.
What is the job of spray headers or distrubtuion throughs?
keep the fill wetted for optimal heat exchange
What is the job of a drift eliminator in a cooling tower/evaporative condenser?
Stop water from leaving the equiptment
What is the difference between forced draft and induced draft cooling towers
Forced draft has a fan at the bottom of the tower that mechanically pushes ambient air through the tower. Induced draft pulls air through the tower rather than pushing it. The fan is located at the top.
What is the calulation for finding a cooling towers efficency?
=Range/Range + Approach
A lower wet bulb temperature will effect the capacity of the cooling tower how?
Increase in capacity with dry air
Tower Bypass is a type of wat for cooling towers?
Capacity Control
Explain what a tower bypass does?
Maintains a minimum condenser water return temperature in low ambient conditions to prevent freeze up
What is the advantage of an induced draft cooling tower?
Losses less water to drift
Three types of evaporators are?
Dry Expansion, Flooded, & Liquid Recirculation (Liquid overfeed)
In a Dry Expansion Evaporator where is the refrigerant?
In the tubes
Tube and Shell is a type of flooded evaporator, true or fale?
True
Liquid overfeed is used in what type of application?
Multiple evaporator installations. Large cold storage operations. Industrial
How is the refrigerant circulated through the evaporator in a liquid overfeed system?
Liquid refrigerant pump
How much superheat is expected in a flooded evaporator?
No Superheat - Vapour leaving the evaporator is at Saturation Temperature
Three types of air cooling evaporators?
Bare Tube, Finned Tube, Plate Type
What are the purpose of the fins in a Finned Tube evaporator?
Increase surface area.
What determines the fin spacing?
Coil operating temperature (To accommodate frost)
What happens to the relative humidity if the Temperature Difference increase?
Decreases
Counter flow decreases heat transfer efficency? True of False?
False. It increases heat transfer.
Which forced convection evaporator has a better throw, Draw through or Blow Through?
Draw Through
Which forced convection evaporator has a better humidification, Draw through or Blow Through?
Blow through (Due to lower air velocity)
What is the primary and secondary surfaces of a Fine and Tube Evaporator?
Primary = Tubes
Secondary = Fins
A thicker slab evaporator will have a greater or lesser dehumidification ability
Greater
When is a defrost cycle required?
Evaporator SST is below freezing point of water.
6 Methods of Defrost
Manuel, off-cycle, hot gas, spray, electric, “Cool” gas
Off-Cycle defrosts often use this temperature sensing device..
Constant Cut-In
What is the purpose of a re-evaporator coil in a hot gas defrost?
adds heat from the ambient air to the hot gas defrost cycle to aid in defrost of the coil.
What is the difference between boiling and evaporation?
Boiling requires heat and evaporation does not
Why don’t we use H20 as a refrigerant?
1) Because it freezes at 32 F
2) It rejects oil
3) Its corrosive
In a lithium bromide absorber refrigeration system, what is the refrigerant?
Water
In a lithium bromide absorber refrigeration system, what is the absorber?
Lithium Bromide
Liquid evaporation stops when …?
Wet Bulb = Dry Bulb
In an ammonia absorbtion system, what is the refrigerant?
Ammonia
In an ammonia absorption system, what is the absorber?
Water
Why is it called a propane refrigration system?
Because Propane is the heat source that is needed
What does a postive displacement compressor do?
Increases the pressure by decreasing the volume (Squeezes)
What does a non-positive displacement compressor do?
Increases the pressure of a refrigerant vapour by accelerating low pressure & low velocity refrigerant via motor impeller
3 Compressor Categories
1) Open
2) Hermetic
3) Semi-Hermetic
How do we use capacity control for centrifigual compressors?
Guiding Vanes (act like shutters to open/close access to the impeller)
What device is used in screw compressors for capacity control?
Slide Valve
