B1-8 Vapour Compression Refrigeration; Absorption Refrigeration Flashcards
Most modern refrigeration systems make use of the principle of absorbing heat by:
A) condensing refrigerant at a low pressure
B) passing refrigerant vapour through tubes in contact with a cooled product
C) evaporating a liquid, then discarding the heat from the vapour to the atmosphere
D) evaporating brine and then raising its pressure
E) using a refrigerant such as calcium chloride to cool a product
C) evaporating a liquid, then discarding the heat from the vapour to the atmosphere
The temperature at which a refrigerant boils is dependant upon the: A) absolute volume B) boiling index C) total evaporator heating surface D) heat content E) pressure acting on the surface
E) pressure acting on the surface
A group A1 refrigerant which has low toxicity and is nonflammable, with a -29.8*C boiling temperature at atmospheric pressure is: A) ammonia B) freon 12 C) butane D) sulphur dioxide E) propane
B) freon 12
In the standard refrigeration cycle, condensation takes place at a temperature of: A) 12* C B) 30*C C) -15*C D) -12*C E) -7*C
B) 30*C
Ammonia refrigerant:
A) will not mix with water
B) will dilute the oil in the crankcase
C) is miscible only with hot lubricating oil
D) is very miscible with refrigerant lubricating oil
E) is not miscible with refrigerant lubricating oil
E) is not miscible with refrigerant lubricating oil
The low pressure side of a refrigeration system refers to the:
A) condenser outlet, receiver and upstream side of regulating valve
B) receiver outlet, regulating valve and evaporator
C) compressor discharge, condenser and receiver
D) downstream side of regulating valve, evaporator and compressor suction
E) compressor discharge and the condenser
D) downstream side of regulating valve, evaporator and compressor suction
A refrigeration system which circulates brine to cooling coils in the cold rooms is said to be: A) wet B) direct C) indirect D) flooded E) dry expansion
C) indirect
In a rotating sliding vane refrigeration compressor, a good seal is maintained between the vanes and the cylinder by: A) a gear mechanism B) an eccentric mechanism C) centrifugal force D) low suction pressure E) high pressure refrigerant vapour
C) centrifugal force
The theoretical mass of a refrigerant moved by a compressor is 8.28 kg/min. If the volumetric efficiency is 75%, the actual mass moved is: A) 33.12 kg/min B) 6.21 kg/min C) 2.07 kg/min D) 11.04 kg/min E) 8.28 kg/min
B) 6.21 kg/min
The refrigeration condenser used most extensively in ammonia installations is the: A) air cooled condenser B) shell and tube condenser C) atmospheric condenser D) shell and coil condenser E) double pipe condenser
B) shell and tube condenser
Refrigerant condensers:
A) are always water cooled
B) remove the latent heat from the gas
C) remove only the sensible heat from the gas
D) cool the liquid refrigerant leaving the compressor
E) keep the refrigerant from flooding the compressor
B) remove the latent heat from the gas
In a compression refrigeration system, the high pressure safety cutout shuts down the compressor in the event of: A) high compressor discharge pressure B) high refrigerant receiver pressure C) high condenser temperature D) high evaporator pressure E) high compressor suction pressure
A) high compressor discharge pressure
A refrigerant flow control that employs a hygroscopic sensing element is a: A) purge flow regulator B) flooded evaporator level regulator C) pressurestat D) thermostat E) humidistat
E) humidistat
The amount of refrigerant charge is critical in a system equipped with a: A) high pressure float valve B) automatic expansion valve C) low pressure float valve D) hand expansion valve E) thermostatic expansion valve
A) high pressure float valve
A compressor capacity control that results in no reduction in power consumption and may cause compressor overheating is the: A) evaporator damper method B) cylinder bypass method C) cylinder unloader method D) hot gas bypass method E) speed control method
D) hot gas bypass method
Hand operated expansion valves are used in modern refrigeration systems:
A) as a shutoff valve upstream of a thermostatic expansion valve
B) as a primary control when the evaporator is large
C) never
D) as a shutoff valve upstream of a low pressure float valve
E) in bypass lines around an automatic control valve
E) in bypass lines around an automatic control valve
Noise transmission is reduced in refrigeration piping systems by the use of:
A) vibration absorbers
B) mufflers in the compressor suction pipe
C) insulated enclosures around the evaporators
D) expansion bends
E) PVC piping
A) vibration absorbers
A construction material that should not be used in an ammonia refrigeration piping system either on its own or in alloys is: A) silver B) chromium C) copper D) steel E) molybdenum
C) copper
Direct expansion evaporators with more than one refrigerant circuit should be equipped with: A) an accumulator B) a fusible plug C) an emergency discharge valve D) a liquid distributor E) a high pressure cutoff device
D) a liquid distributor
Prior to performing a leak test on a newly installed refrigeration system, it is important to:
A) ensure cooling water is turned on to the compressor
B) start the compressor and run it on air for a few hours
C) purge air from the system using natural gas
D) remove or isolate controls and relief valves
E) ensure all instruments have been tested and operate as specified
D) remove or isolate controls and relief valves
An automatic purger for a large ammonia refrigeration system returns refrigerant to the system by employing a: A) heating element B) hot gas coil C) chilling coil D) liquid knockout drum E) relief valve
C) chilling coil
When conducting a pressure test on a newly installed refrigeration system, a suitable test medium is: A) oxygen B) ammonia C) hydrogen D) nitrogen E) odour iced natural gas
D) nitrogen
In the event the refrigeration compressor fails to start, the problem could be:
A) a lack of refrigerant
B) a dirty suction strainer
C) an open control circuit
D) the thermostat is set too low
E) low pressure controller differential is set too close
C) an open control circuit
When starting up a reciprocating refrigeration system that has been shut down for a short period, it is important to:
A) wear safety goggles
B) manually lift all relief valves
C) ensure the oil sump heater is energized to drive off refrigerant
D) first ensure the inspecting power engineer has been advised
E) ensure cooling water is not turned on until the compressor oil is up to temperature
C) ensure the oil sump heater is energized to drive off refrigerant
Abnormally low head pressure in a compression refrigeration system may be caused by:
A) excessive opening of the expansion valve
B) inadequate refrigerant charge in the system
C) noncondensables in the system
D) dirty condenser tubes
E) high refrigerant level in the condenser/receiver
B) inadequate refrigerant charge in the system
In an ammonia absorption system, the components that are operated under relatively high pressures are:
A) absorber, evaporator and liquid receiver
B) condenser and generator
C) evaporator, condenser and heat exchanger
D) absorber and evaporator
E) generator and absorber
B) condenser and generator
In order to lower the boiling point of the refrigerant, it is important that the system maintains: A) high absorbent circulation B) very fast refrigerant flow C) an extremely high vacuum D) very high pressure E) a pressure near atmospheric pressure
C) an extremely high vacuum
Ammonia systems are seldom used for air conditioning purposes in large buildings mainly because:
A) ammonia systems require a separate power supply not available in most large buildings
B) ammonia does not provide sufficient cooling power for large building operations
C) ammonia systems require too much maintenance
D) ammonia is too toxic
E) ammonia systems are too expensive
D) ammonia is too toxic
Select the statement about lithium bromide systems that is false:
A) system efficiency is increased by forcing water through a spray header
B) the operating cycle in the system is continuous
C) the evaporator is operated under vacuum which lowers the boiling point of water
D) lithium bromide solution has the ability to absorb water vapour
E) when water vapour is absorbed by lithium bromide, the pressure increase
E) when water vapour is absorbed by lithium bromide, the pressure increases
Compared to a compression system, absorption units:
A) require more electrical power
B) require more cooling water
C) are not damaged by carryover of evaporator liquids
D) require more space for equipment
E) require fewer pieces of equipment
D) require more space for equipment
In a lithium bromide absorption refrigeration system, the change of concentration of lithium bromide takes place:
A) in the condenser
B) when water vapour is absorbed in the absorber
C) none of the above
D) in the evaporator
E) when going through the generator pump
B) when water vapour is absorbed in the absorber
To prevent crystallization when shutting down an absorption unit, the unit is run through a: A) delayed stop cycle B) dilution cycle C) reclaim cycle D) heating cycle E) purge cycle
B) dilution cycle
The intermediate lithium bromide solution:
A) comes from the sump of the absorber
B) is a result of mixing concentrated lithium bromide solution with water
C) is drawn by the absorber pump and delivered to the spray header in the absorber
D) is delivered by the generator pump from the absorber to the generator
E) does not exist in the lithium bromide absorption refrigeration system
D) is delivered by the generator pump from the absorber to the generator
In an absorption refrigeration system, cooling of saturated lithium bromide solution will result in: A) reduced salt concentration B) crystallization C) increased solubility of the salt D) corrosion of the concentrator tubes E) vaporization of the water
B) crystallization
The pumps of an absorption refrigeration unit must:
A) be equipped with water cooled motors
B) have a discharge relief valve to prevent over pressure
C) have stainless steel motor windings to protect against corrosion
D) be of a hermetic design
E) be of a reciprocating design
D) be of a hermetic design
Superheated refrigerant is refrigerant at saturation pressure, whose temperature is above the: A) conduction temperature B) compressor suction temperature C) sensible temperature D) saturation temperature E) fusion temperature
D) saturation temperature
Most modern refrigeration systems make use of the principle of absorbing heat by:
A) condensing refrigerant at a low pressure
B) evaporating brine and then raising its pressure
C) using a refrigerant such as calcium chloride to cool a product
D) passing refrigerant vapour through tubes in contact with a cooled product
E) evaporating a liquid, the discarding the heat from the vapour to atmosphere
E) evaporating a liquid, the discarding the heat from the vapour to atmosphere
Refrigerants are identified by:
A) saturation pressure, refrigerant number, weight, colour
B) trade name, refrigerant number, chemical formula, density
C) chemical composition, specific gravity, trade name, freezing point
D) chemical formula, trade name, refrigerant number, chemical name
E) density, chemical formula, common names weight
D) chemical formula, trade name, refrigerant number, chemical name
A desirable quality of a refrigerant is:
A) a high boiling point at atmospheric pressure
B) a high latent heat capacity
C) highly flammable for use in absorption systems
D) a high condensing pressure
E) an offensive odour to easily detect leaks
B) a high latent heat capacity
Ammonia refrigerant:
A) is miscible only with hot lubricating oil
B) will not mix with water
C) will dilute the oil in the crankcase
D) is very miscible with refrigerant lubricating oil
E) is not miscible with refrigerant lubricating oil
E) is not miscible with refrigerant lubricating oil
Refrigeration compressors:
A) determine the degree of superheat of the refrigerant leaving the evaporator
B) must have water jackets
C) raise the refrigerant vapour temperature above the condensing water temperature
D) must be placed outside the building
E) raise the vapour pressure on discharge side of the evaporator
C) raise the refrigerant vapour temperature above the condensing water temperature
A secondary refrigerant commonly employed in the cooling coils beneath an arena's ice surface is: A) ammonia B) ammonium chloride C) water D) calcium chloride brine E) freon 12
D) calcium chloride brine
High velocity of the vapour inside centrifugal refrigeration compressor is converted to pressure by:
A) directing the vapour through specially shaped passages of increasing cross sectional area
B) increasing the temperature of the vapour
C) increasing the density of the vapour
D) using rotary screws
E) trapping the vapour in a octet and reducing its volume
A) directing the vapour through specially shaped passages of increasing cross sectional area
Calculate the piston displacement in cubic metres per minute for the following single stage, single acting reciprocating compressor. Stroke = 12 cm Diameter = 10 cm Speed = 1100 rev/min A) 1.037 cu m/min B) 1.027 cu m/min C) 1.017 cu m/min D) 0.937 cu m/min E) 0.654 cu m/min
A) 1.037 cu m/min
In a refrigeration system, the evaporator:
A) removes water that may be absorbed by the refrigerant
B) removes the heat of compression from the refrigerant
C) stores the liquid refrigerant for future use
D) cools the room in which it is placed
E) keeps the refrigerant from flooding the compressor
D) cools the room in which it is placed
The purpose of a condenser in a refrigeration system is to:
A) store the liquid refrigerant for future use
B) keep the refrigerant from flooding the compressor
C) cool the room in which it is placed
D) remove water that may be absorbed by the refrigerant
E) cool the hot gases to a liquid phase
E) cool the hot gases to a liquid phase
A refrigerant flow control that employs a hygroscopic sensing element is a: A) purge flow regulator B) thermostat C) pressurestat D) humidistat E) flooded evaporator level regulator
D) humidistat
Temperature actuated refrigeration system controls may be of the:
A) limiting or non limiting type
B) actuating or non actuating type
C) direct or indirect type
D) operational or safety type
E) indirect pressure or direct temperature type
C) direct or indirect type
A refrigerant condenser cooling water regulating valve operates by sensing:
A) compressor discharge pressure
B) cooling water temperature leaving the condenser
C) liquid refrigerant flow entering the evaporator
D) refrigerant vapour flow entering the condenser
E) cooling water temperature entering the condenser
A) compressor discharge pressure
The thermostatic expansion valve controls refrigerant by:
A) evaporator pressure
B) a temperature sensor at the evaporator inlet
C) a temperature sensor at the evaporator outlet
D) liquid level in the receiver
E) liquid level in the evaporator
C) a temperature sensor at the evaporator outlet
Methods used to regulate the output capacity of continuous operation refrigeration compressors include: 1) on off control 2) cylinder unloaders 3) evaporator dampers 4) cylinder bypass 5) speed control 6) throttle governing A) 2,4 and 5 only B) 1,2,4 and 5 only C) 1,2,3 and 4 only D) 2 and 3 only E) 1,4 and 6 only
A) 2,4 and 5 only
Low pressure float valves are used to regulate refrigerant flow in: A) flooded evaporators B) liquid receivers C) dry expansion evaporators D) evaporative condensers E) multiple effect evaporators
A) flooded evaporators
A construction material that should not be used in an ammonia refrigeration piping system on its own or in alloys is: A) silver B) molybdenum C) chromium D) copper E) steel
D) copper
The main function of a refrigerant strainer drier is:
A) removal of moisture from liquid refrigerant
B) to prevent vapour bubbles from entering the expansion valve
C) removal of oil from the liquid refrigerant
D) to prevent desiccant from entering the expansion valve
E) removal of ice from the liquid refrigerant
A) removal of moisture from liquid refrigerant
That gauge glass of a refrigerant receiver should be equipped with:
A) safety type self sealing valves
B) an accumulator column to dampen pulsations
C) coloured glass for ease of viewing
D) an electric lighting system
E) a remote valve closing mechanism
A) safety type self sealing valves
Using a burning sulphur candle , a refrigerant leak is detected by the appearance of: A) dark black smoke B) yellow fumes C) bright red smoke D) a strong sulphur odour E) dense white smoke
E) dense white smoke
A refrigeration system is purged to remove: A) noncondensable gases B) ammonia vapours C) excess refrigerant D) water vapour E) used compressor oil
A) noncondensable gases
When handling refrigerants, it is important to:
A) ensure the inspecting power engineer has been advised
B) wear self contained breathing apparatus
C) check the last inspection date on the refrigerant cylinder
D) ensure a fire extinguisher is readily available
E) wear safety goggles
E) wear safety goggles
In the event the refrigeration compressor fails to start, the problem could be:
A) a lack of refrigerant
B) a dirty suction strainer
C) an open control circuit
D) low pressure controller differential is set too close
E) the thermostat is set too low
C) an open control circuit
Abnormally low head pressure in a compression refrigeration system may be caused by:
A) excessive opening of the expansion valve
B) high refrigerant level in the condenser/receiver
C) dirty condenser tubes
D) non condensables in the system
E) inadequate refrigerant charge in the system
E) inadequate refrigerant charge in the system
When starting up a reciprocating refrigeration system that has been shut down for a short period, it is important to:
A) check the operation of interlocks
B) wear self contained breathing apparatus
C) ensure cooling water is not turned on until the compressor oil is up to temperature
D) manually lift all relief valves
E) wear safety goggles
A) check the operation of interlocks
The design temperature for the chilled water return from cooling coils entering the lithium bromide absorption chiller is: A) 12-13*C B) 7-10*C C) 4-7*C D) 4*C E) 2*C
A) 12-13*C
In order to lower the boiling point of the refrigerant, it is important that the system maintains: A) very high pressure B) a pressure near atmospheric pressure C) an extremely high vacuum D) high absorbent circulation E) very fast refrigerant flow
C) an extremely high vacuum
The hermetic principle on absorption units involves:
A) equipping the unit with a purge system
B) installing special seals on the solution pumps
C) constructing the unit in a cylindrical shape
D) completely seal welding the components which are subject to vacuum
E) separating the high pressure side and the low pressure side into two cylindrical casings
D) completely seal welding the components which are subject to vacuum
The design pressure in the absorber and the evaporator of a lithium bromide absorption system is about: A) 0.61-1.7 kPa B) 0.84-1.0 kPa C) 0.84-1.7 kPa D) 0.61-1.0 kPa E) 0.61-0.84 kPa
B) 0.84-1.0 kPa
In the basic absorption system, the refrigeration compressor is replaced by the:
A) absorber, condenser and oil separator
B) absorber, expansion valve and liquid receiver
C) absorber, generator and liquid receiver
D) generator, absorber and pump
E) condenser and absorber
D) generator, absorber and pump
When the temperature of the lithium bromide solution is raised, the molecular movement of the water vapour: A) increases B) decreases C) stays constant D) decreases rapidly E) has no effect whatsoever
A) increases
The cooling load of a lithium bromide absorption chiller is controlled by:
A) starting and stopping of the evaporator pump
B) regulating flow rate of chilled water through the chiller
C) starting and stopping the condenser water fan
D) regulating steam or hot water flow to the generator
E) starting and stopping the absorber pump
D) regulating steam or hot water flow to the generator
Crystallization occurs when:
A) the solute in a solution exceeds its maximum solubility at a given temperature
B) different kinds of solute are introduced into an unsaturated solution
C) there is an increase in the temperature of a saturated solution
D) the solvent in the solution is increased
A) the solute in a solution exceeds its maximum solubility at a given temperature
In an absorption chiller, when water in the condenser is passed through the orifice into the evaporator, it’s temperature decreases because:
A) it takes its own latent heat which is used as sensible heat to convert some of the water vapour into liquid water
B) it takes its own sensible heat which is used as latent heat to convert some of the liquid water into vapour
C) the temperature in the evaporator is lower
D) the pressure in the evaporator is higher
E) the heat is carried away by the chilled water
B) it takes its own sensible heat which is used as latent heat to convert some of the liquid water into vapour
In a lithium bromide chiller, crystallization following startup could be the result of: 1) condenser tubes fouled 2) faulty purging 3) too much octyl alcohol on the system 4) noncondensables in the machine 5) condenser cooling water too cold A) 3 and 5 only B) 2,4 and 5 only C) 1,2,3 and 4 only D) 1,3 and 5 only
B) 2,4 and 5 only
