Electrical, Refrigeration and AC Systems and controls Flashcards
(30 cards)
What is the boiling point of liquid raised by?
Increasing the pressure of the refrigerant
What is the name of the heat transfer process that ice undergoes in an icebox?
Latent heat
What are some correct values of refrigeration?
-335 000 kj per 24 hours
-13 958 kj/h
-3.88 kj/s
What are the refrigerant safety classification?
-Higher Flammability
-A3, B3
-Lower Flammability
-A2, B2
-Lower Flammability (with a max burning velocity of 10 cm/s
-A2L, B2L
-No Flame Propagation
-A1, B1
What are the factors that affect the leakage tendency of a refrigerant ?
-Operating pressure
-Density
-Molecular mass
What is the use of oil-miscible refrigerants?
-Dissolve most of the oil in the system components
-Return the oil to the compressor
-Avoid problems due to oil blockage
What are some of the major components of the basic mechanical refrigeration system?
-evaporator
-condenser
-compressor
-receiver
-expansion valve
-drier
-King valve
What brine temperature is used when cooling an ice surface?
-11C (12F)
What compressor type requires the use of a shaft seal?
Open type
What are some designs of a rotary compressor ?
-Helical rotor
-stationary single blade
-rotating vane
What are packing gland seals made up of?
Semi metallic material impregnated with graphite
What are types of condensers?
-Air cooled
-water cooled
-evaporative
Where are evaporative condensers favored in locations where it is necessary to conserve on?
Space
Roughly how many gauges are used in a refrigeration system?
2
The diffuser on the emergency release line is placed not less than __________ away from any windows or other openings?
7.6 m (24.93 ft)
How many sets of motorized dampers are there on a conventional air handling unit?
3 dampers
What equipment is part of a unit ventilator ?
-fan
-Heating/cooling coil
-Manually adjustable duct connection
What does the automatic expansion valve strive to control?
Compressor and suction pressure
What are the 3 controlling pressures in a thermostatic expansion valve?
-Thermal element
-Spring
-Evaporator pressure
What is the purpose of the “weighted valve pin” used within a high pressure float valve?
To reduce the amount of line frosting after the float valve
What are the various methods to control the compressor output?
-Intermittent operation
-Compressor unloader
-Cylinder bypass
-Hot gas bypass
-Compressor speed control
-Suction throttling
-Variable inlet guide vanes
What are the distinct classes of refrigeration controls?
-Operating or Primary controls
-Actuating or Secondary controls
-Limiting and Safety controls
In the event of a low oil pressure condition, the oil pressure failure switch will do what?
Shut down the compressor
Why shouldn’t oxygen be used to pressurize a system for leak checking purpose?
It could result in a explosion
