74 Questions
What is the function of a refrigerant compressor in a refrigeration system?
To compress the refrigerant and raise its pressure
Where does the evaporator operate in a refrigeration system?
Low pressure side
What is the main function of an evaporator in a refrigeration system?
To absorb heat and change liquid refrigerant into vapor
Where is the condenser located in a refrigeration system?
High pressure side
What is the purpose of the expansion device in a refrigeration system?
To divide the high and low pressure sides
Why must the temperature of the boiling refrigerant in the evaporator be lower than that of the surrounding medium?
To prevent heat flow to the refrigerant
Which type of compressor is best suited for refrigerants with moderate or low condensing pressures like R-21 and R-114?
Reciprocating compressor
What type of compressor is recommended for refrigerants that require a large displacement and operate at low condensing pressure?
Centrifugal compressor
What defines the ratio of the clearance volume to the swept volume in reciprocating compressors?
Clearance factor
Which component in a reciprocating compressor expands from discharge pressure to suction pressure, filling part of the cylinder space before suction begins?
Clearance space
What is the primary motion involved in compressing the vapour refrigerant in reciprocating compressors?
Back-and-forth motion
Which type of compressor is commonly used in domestic refrigerators?
Rotary compressor
What type of refrigerants are reciprocating and screw compressors best suited for?
$R-12$ and $R-22$
What is the volume that remains in the cylinder during the operation cycle of a reciprocating compressor?
$Vc$
Which factor is normally around 5% and represents the effect of clearance on reducing the volume of sucked vapour in reciprocating compressors?
$0.005L + 0.5$
In a reciprocating compressor, when does the discharge valve open?
At position 2 when cylinder pressure equals discharge pressure
What happens to the volumetric efficiency of a reciprocating compressor as suction pressure decreases?
Decreases
What effect does wire-drawing at the valves have on the overall volumetric efficiency of a compressor?
Decreases efficiency
Which method is NOT mentioned as a way to improve the volumetric efficiency of a reciprocating compressor?
Increasing pressure drops at the valves
What role does the diffuser play in a single-stage centrifugal compressor?
Convert kinetic energy into pressure energy
Which material is commonly used for making the impeller of a centrifugal compressor?
Alloy (chrome-nickel) steels
What is the effect of a large clearance volume on the volumetric efficiency of a reciprocating compressor?
Decreases efficiency
How does the pressure drop across suction and discharge valves affect their operation in a compressor?
Open when there is a pressure drop
What happens to the refrigerating capacity of a reciprocating compressor with decreasing evaporator pressure?
Becomes zero
What is the main reason for the effect of clearance volume on the work of compression in a reciprocating compressor?
Expansion and contraction of clearance gas like a spring
What is the purpose of an inlet casing in a single-stage centrifugal compressor?
Accelerate the fluid to the impeller inlet
What is the purpose of a condenser in a refrigeration system?
To desuperheat the gas
How does a rotary screw compressor function?
By injecting oil to seal leakage paths
What is the primary advantage of a screw compressor over reciprocating compressors?
Avoids surging issues
What function does the slide valve serve in a screw compressor?
Controls capacity
How do air-cooled condensers differ from water-cooled condensers?
Use air as the cooling medium instead of water
Why are high pressure refrigerants like R-22 and ammonia used in screw compressors?
To increase the compressor's capacity
How many basic continuous phases are involved in the working cycle of a screw compressor?
3
What type of rotors does a rotary screw compressor have?
Four-lobe male and five-gully female
What eliminates leakage in a screw compressor?
Injecting oil to seal the leakage paths
Why is oil injected into a screw compressor?
To cool, lubricate, and seal leakage paths
What is the main limitation of a natural convection condenser?
Cannot reject heat rapidly
Which material is generally used for the condenser tubes in small refrigeration units?
Steel
What purpose do the wires welded to the condenser tubes serve?
Increase mechanical strength
Why are fins in forced-air circulation condensers closely spaced?
To prevent dirt and lint accumulation
In a water cooled condenser, what issue can arise due to impurities present in water?
Formation of scale on the tube surface
What is the purpose of the shell in a shell-and-coil condenser?
To contain the refrigerant
Why are intermediate tube supports provided in a shell-and-tube condenser?
To enhance mechanical stability
How does the liquid flow from the accumulator to the evaporator coil?
By gravity
What prevents the carry-over of liquid particles from the accumulator to the suction line?
Liquid eliminators at the accumulator top
In a 'liquid-overfeed system', how is the refrigerant circulated from the accumulator to the evaporator coil?
By liquid pump
What is the purpose of a liquid- suction heat exchanger on the suction line?
To superheat the suction vapour
In what way does 'dry expansion' differ from 'flooded' in refrigeration systems?
In the manner of feeding refrigerant into the evaporator
What describes 'natural convection' in cooling/circulating a fluid around the evaporator?
Colder layer rises up, warmer layer falls down
What phenomenon in centrifugal compressors occurs when the load decreases to below 35 per cent of the rated capacity?
Surging
What is one of the methods mentioned to control the capacity of centrifugal compressors?
Variable inlet whirl vanes
What is the purpose of a speed-reduction gear in centrifugal compressors?
Control the compressor speed
In a rolling piston type rotary compressor, what role does the spring play?
Maintains contact between roller and blade
Why are rotary compressors preferred for low-temperature applications in chemical and industrial processing?
High volumetric efficiencies
What contributes to achieving high tip speeds in centrifugal compressors?
Large diameter impeller
What causes surging in centrifugal compressors?
Load decreasing to below 35 per cent of rated capacity
How does capacity control vary in rotary compressors as compared to centrifugal compressors?
By maintaining contact between the roller and blade
Which component in rotary compressors ensures the seal between high-pressure and low-pressure sides?
Oil film surrounding rotor and vanes
In a water-cooled condenser, how is the overall resistance calculated?
By adding all the resistances in series
What is the purpose of the expansion valve in a dry expansion evaporator?
To control the rate of flow of refrigerant to the evaporator
Why is a flooded evaporator more efficient in terms of heat transfer?
Because it maintains a constant liquid level inside
How is the refrigerant supplied to a dry expansion evaporator?
By an expansion valve
What distinguishes a dry expansion evaporator from a flooded evaporator?
The liquid level maintained inside
Which component contributes to maintaining a constant liquid level in a flooded evaporator?
'Accumulators'
What happens to the refrigerant in a direct expansion evaporator as it passes through?
It turns into a mix of liquid and vapor
What does the cooling process involve in an evaporator?
Vaporizing the refrigerant to remove heat
Which factor determines the heat-transfer efficiency of a flooded evaporator?
'Liquid level' maintained inside
Why is an expansion device crucial in a refrigeration system?
To regulate the flow of refrigerant into the evaporator
What type of tubes are used in ammonia condensers to prevent the effects of ammonia on copper?
Steel tubes
What is the purpose of the small grooves in the holes of the tube sheets?
To prevent tubes from getting loose at the ends
Why are removable water boxes provided at the ends of the condenser?
To facilitate brushing of the water tubes
What is the purpose of extra rows of water tubes provided at the lower end of some condensers?
Sub-cooling the liquid below the condensing temperature
Why is it important not to overcharge the refrigeration system with refrigerant?
To prevent excessive head pressure and condensing temperature
What safety feature is fixed on the shell of the condenser to protect against excessive pressures?
Fusible plug
Test your knowledge on the equipment used in a refrigeration system such as compressor, condenser, evaporator, and expansion devices. Learn about the functions of each equipment in the system.
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