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Questions and Answers
What is the main function of a refrigerant compressor in a refrigeration system?
What is the main function of a refrigerant compressor in a refrigeration system?
Where does the evaporator fit in a refrigeration system?
Where does the evaporator fit in a refrigeration system?
What is the primary purpose of an evaporator in a refrigeration system?
What is the primary purpose of an evaporator in a refrigeration system?
Why must the temperature of the boiling refrigerant in the evaporator be lower than that of the surrounding medium?
Why must the temperature of the boiling refrigerant in the evaporator be lower than that of the surrounding medium?
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Where is the expansion device located in a refrigeration system?
Where is the expansion device located in a refrigeration system?
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What kind of knowledge is required to understand a refrigeration system according to the text?
What kind of knowledge is required to understand a refrigeration system according to the text?
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What is the main function of a reciprocating compressor?
What is the main function of a reciprocating compressor?
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Which compressor type is most suited for pumping refrigerants with moderate or low condensing pressures?
Which compressor type is most suited for pumping refrigerants with moderate or low condensing pressures?
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What is the main difference between reciprocating and centrifugal compressors?
What is the main difference between reciprocating and centrifugal compressors?
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Which refrigerant is best suited for use with screw compressors?
Which refrigerant is best suited for use with screw compressors?
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Why is a clearance volume necessary in reciprocating compressors?
Why is a clearance volume necessary in reciprocating compressors?
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What is the main factor contributing to reducing the volume of the sucked vapour in reciprocating compressors?
What is the main factor contributing to reducing the volume of the sucked vapour in reciprocating compressors?
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Which compressor type operates at low condensing pressure?
Which compressor type operates at low condensing pressure?
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What mechanism is used to compress vapour refrigerants in centrifugal compressors?
What mechanism is used to compress vapour refrigerants in centrifugal compressors?
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What does the volumetric efficiency of a reciprocating compressor account for?
What does the volumetric efficiency of a reciprocating compressor account for?
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What is the ratio of clearance volume to swept volume called in reciprocating compressors?
What is the ratio of clearance volume to swept volume called in reciprocating compressors?
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What happens to the refrigerating capacity of a reciprocating compressor as the evaporator pressure decreases?
What happens to the refrigerating capacity of a reciprocating compressor as the evaporator pressure decreases?
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How does the suction volume and volumetric efficiency vary with decreasing suction pressure for a reciprocating compressor?
How does the suction volume and volumetric efficiency vary with decreasing suction pressure for a reciprocating compressor?
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What is the effect of pressure drops at the valves on the indicator diagram of a compressor?
What is the effect of pressure drops at the valves on the indicator diagram of a compressor?
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What is one method suggested for improving the volumetric efficiency of a reciprocating compressor?
What is one method suggested for improving the volumetric efficiency of a reciprocating compressor?
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What is the impact of a large clearance volume on the work of compression?
What is the impact of a large clearance volume on the work of compression?
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Which component of a single-stage centrifugal compressor is responsible for accelerating the fluid to the impeller inlet?
Which component of a single-stage centrifugal compressor is responsible for accelerating the fluid to the impeller inlet?
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What is the function of a diffuser in a centrifugal compressor?
What is the function of a diffuser in a centrifugal compressor?
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What material is typically used for making the impeller of a centrifugal compressor?
What material is typically used for making the impeller of a centrifugal compressor?
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What are the three basic continuous phases of the working cycle in a screw compressor?
What are the three basic continuous phases of the working cycle in a screw compressor?
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What is the purpose of injecting oil in a screw compressor?
What is the purpose of injecting oil in a screw compressor?
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What type of refrigerants are typically used in screw compressors?
What type of refrigerants are typically used in screw compressors?
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How does a slide valve function in a screw compressor for capacity control?
How does a slide valve function in a screw compressor for capacity control?
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What is one advantage of a screw compressor compared to reciprocating compressors?
What is one advantage of a screw compressor compared to reciprocating compressors?
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What type of movement is responsible for air-cooling in natural convection condensers?
What type of movement is responsible for air-cooling in natural convection condensers?
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Which condenser type uses both water and air as cooling mediums?
Which condenser type uses both water and air as cooling mediums?
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What is the main function of the condenser in a refrigeration system?
What is the main function of the condenser in a refrigeration system?
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What mechanism is used for capacity control in a screw compressor?
What mechanism is used for capacity control in a screw compressor?
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Which component of a screw compressor serves the purpose of cooling and lubricating?
Which component of a screw compressor serves the purpose of cooling and lubricating?
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What is the phenomenon of reversal of flow in centrifugal compressors called?
What is the phenomenon of reversal of flow in centrifugal compressors called?
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Why is it important to have reasonable width shrouds in a centrifugal compressor?
Why is it important to have reasonable width shrouds in a centrifugal compressor?
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How is the capacity of centrifugal compressors controlled through variable inlet whirl vanes?
How is the capacity of centrifugal compressors controlled through variable inlet whirl vanes?
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Which type of compressor is known for its high volumetric efficiencies due to negligible clearance?
Which type of compressor is known for its high volumetric efficiencies due to negligible clearance?
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At what percentage of rated capacity does surging typically occur in centrifugal compressors?
At what percentage of rated capacity does surging typically occur in centrifugal compressors?
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What shifts the point of operation from point A to point B in a centrifugal compressor?
What shifts the point of operation from point A to point B in a centrifugal compressor?
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What type of material forms the seal between the high-pressure and low-pressure sides in rotary compressors?
What type of material forms the seal between the high-pressure and low-pressure sides in rotary compressors?
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What is one method used to control the capacity of centrifugal compressors by varying the compressor speed?
What is one method used to control the capacity of centrifugal compressors by varying the compressor speed?
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How do large diameter impellers or high RPM contribute to achieving high tip speeds in centrifugal compressors?
How do large diameter impellers or high RPM contribute to achieving high tip speeds in centrifugal compressors?
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In a rotary compressor, what happens when the compressor stops regarding high/low pressure sides?
In a rotary compressor, what happens when the compressor stops regarding high/low pressure sides?
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What type of condenser requires a relatively large surface area due to slow air movement by natural convection?
What type of condenser requires a relatively large surface area due to slow air movement by natural convection?
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How are fins arranged in a forced-air circulation condenser to optimize heat transfer?
How are fins arranged in a forced-air circulation condenser to optimize heat transfer?
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In a water-cooled tube-in-tube condenser, what forms on the water-side of the tube causing impediment to heat transfer?
In a water-cooled tube-in-tube condenser, what forms on the water-side of the tube causing impediment to heat transfer?
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Which type of condenser involves a coil of finned tubing where water flows through the coil and refrigerant is in the shell?
Which type of condenser involves a coil of finned tubing where water flows through the coil and refrigerant is in the shell?
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What is the main purpose of using widely-spaced fins in a condenser design?
What is the main purpose of using widely-spaced fins in a condenser design?
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Why is it challenging to clean the water-side of tubes in a tube-in-tube system?
Why is it challenging to clean the water-side of tubes in a tube-in-tube system?
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Which type of condenser employs a fan or blower to circulate air over the condenser coil?
Which type of condenser employs a fan or blower to circulate air over the condenser coil?
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What is the function of wires welded to the condenser tubes in a small unit design?
What is the function of wires welded to the condenser tubes in a small unit design?
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What design feature of a plate-type condenser allows for better natural convection air currents?
What design feature of a plate-type condenser allows for better natural convection air currents?
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How does the arrangement of tubes in a shell-and-tube condenser differ from that of a flooded chiller?
How does the arrangement of tubes in a shell-and-tube condenser differ from that of a flooded chiller?
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Why are steel tubes used for ammonia condensers instead of copper?
Why are steel tubes used for ammonia condensers instead of copper?
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What is the purpose of the grooves in the holes of the tube sheets in water-cooled condensers?
What is the purpose of the grooves in the holes of the tube sheets in water-cooled condensers?
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Why are removable water boxes provided at the ends of the condenser?
Why are removable water boxes provided at the ends of the condenser?
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How does an evaporative condenser differ from a water-cooled condenser?
How does an evaporative condenser differ from a water-cooled condenser?
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What is the source of heat for vaporizing the water in an evaporative condenser?
What is the source of heat for vaporizing the water in an evaporative condenser?
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Why is it challenging to keep the surface of the condenser coil clean in an evaporative condenser?
Why is it challenging to keep the surface of the condenser coil clean in an evaporative condenser?
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Why is it important not to overcharge a refrigeration system with refrigerant?
Why is it important not to overcharge a refrigeration system with refrigerant?
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What role does a fusible plug or safety pressure relief valve play in a refrigeration system?
What role does a fusible plug or safety pressure relief valve play in a refrigeration system?
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What happens if too much liquid accumulates in the condenser of a refrigeration system?
What happens if too much liquid accumulates in the condenser of a refrigeration system?
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In what scenario would a receiver of adequate capacity need to be added to a refrigeration system?
In what scenario would a receiver of adequate capacity need to be added to a refrigeration system?
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How is the liquid flow from the accumulator to the evaporator coil primarily achieved?
How is the liquid flow from the accumulator to the evaporator coil primarily achieved?
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What is the purpose of a liquid eliminator located in the accumulator top?
What is the purpose of a liquid eliminator located in the accumulator top?
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In a 'liquid-overfeed system', how is the refrigerant liquid circulated from the accumulator to the evaporator coil?
In a 'liquid-overfeed system', how is the refrigerant liquid circulated from the accumulator to the evaporator coil?
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In a refrigeration system, what do the terms 'dry expansion' and 'flooded' refer to?
In a refrigeration system, what do the terms 'dry expansion' and 'flooded' refer to?
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What is the main difference between 'natural convection' and 'forced convection' in a refrigeration system?
What is the main difference between 'natural convection' and 'forced convection' in a refrigeration system?
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What is the function of a 'liquid-suction heat exchanger' used on the suction line in a refrigeration system?
What is the function of a 'liquid-suction heat exchanger' used on the suction line in a refrigeration system?
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In a water-cooled condenser, what does the overall heat transfer coefficient (U) depend on?
In a water-cooled condenser, what does the overall heat transfer coefficient (U) depend on?
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Which component contributes to the overall heat-transfer resistance in a water-cooled condenser according to the text?
Which component contributes to the overall heat-transfer resistance in a water-cooled condenser according to the text?
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What is the main difference between a 'dry expansion' evaporator and a 'flooded' evaporator?
What is the main difference between a 'dry expansion' evaporator and a 'flooded' evaporator?
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How does a direct expansion evaporator differ from a dry expansion evaporator?
How does a direct expansion evaporator differ from a dry expansion evaporator?
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What is the role of a float valve in a flooded-type evaporator?
What is the role of a float valve in a flooded-type evaporator?
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Which factor contributes to making a flooded evaporator more efficient than other types?
Which factor contributes to making a flooded evaporator more efficient than other types?
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What distinguishes a direct expansion evaporator from a flooded evaporator?
What distinguishes a direct expansion evaporator from a flooded evaporator?
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Which type of evaporator maintains a varying proportion of liquid and vapour along its length?
Which type of evaporator maintains a varying proportion of liquid and vapour along its length?
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What determines the refrigerant liquid level in a flooded-type evaporator?
What determines the refrigerant liquid level in a flooded-type evaporator?
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What contributes to maintaining a constant refrigerant liquid level in a flooded-type evaporator?
What contributes to maintaining a constant refrigerant liquid level in a flooded-type evaporator?
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Study Notes
Refrigerant Equipments and Classification
- There are different types of compressors used in refrigeration systems, including:
- Reciprocating compressor
- Centrifugal compressor
- Rotary compressor
- Screw compressor
- Scroll compressor
- Each type is suited for use with specific refrigerants and operating conditions.
Reciprocating Compressor
- The reciprocating compressor is best suited for use with refrigerants that require a relatively small displacement and condense at relatively high pressure (e.g., R-12, R-22, Ammonia).
- The compressor compression cycle consists of:
- Suction stroke: piston moves outward, suction valve opens, and vapour is drawn into the cylinder
- Compression stroke: piston moves inward, suction valve closes, and compression begins
- Discharge stroke: piston reaches the end of the inward motion, discharge valve opens, and compressed vapour is released
- Volumetric efficiency is reduced due to clearance volume, which is necessary for thermal expansion and machining tolerances.
Centrifugal Compressor
- A single-stage centrifugal compressor consists of:
- Inlet casing
- Impeller
- Diffuser
- Volute casing
- The impeller transfers energy to the fluid, increasing static pressure and kinetic energy.
- The diffuser converts kinetic energy into static pressure energy.
- The volute casing collects the fluid and further converts kinetic energy into static pressure energy.
Condensers
- Natural Convection Condenser:
- Limited to small units due to low heat transfer rate
- Requires large surface area
- Examples include domestic refrigerators and freezers
- Forced-Air Circulation Condenser:
- Uses a fan or blower to increase air flow over the condenser coil
- Finned tubes are used to increase heat transfer
- Water-Cooled Condenser:
- Tube-in-tube or double pipe condenser
- Shell-and-coil condenser
- Shell-and-tube condenser
- Evaporative Condenser:
- Combines features of air- and water-cooled condensers
- Water is pumped to a spray header and sprayed over the condenser coil
- Air is blown over the coil to enhance heat transfer
Evaporators
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Evaporators are classified into two categories:
- Dry expansion evaporator
- Flooded evaporator
-
Dry Expansion Evaporator:
- Liquid refrigerant is fed by an expansion valve
- Refrigerant is vaporized and superheated by the time it reaches the outlet end
-
Flooded Evaporator:
- Constant refrigerant liquid level is maintained
- Float valve is used as the throttling device
- Liquid level is maintained by admitting more liquid as necessary### Refrigeration System Components
-
A refrigeration system consists of several equipment including compressor, condenser, evaporator, expansion devices, and accumulator.
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The compressor is a machine used to compress the refrigerant from the evaporator and raise its pressure.
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The condenser is an important device used in the high-pressure side of a refrigeration system to remove heat from the hot vapor refrigerant discharged from the compressor.
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The evaporator is used in the low-pressure side of a refrigeration system to absorb heat from the surrounding location or medium being cooled.
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The expansion device divides the high-pressure side and the low-pressure side of a refrigeration system and is connected between the receiver and the evaporator.
Compressor Types
- Screw compressors are positive displacement machines with two helically-grooved rotors that rotate in a housing.
- Screw compressors have no suction and discharge valves, and leakage paths are eliminated by oil injection.
- Screw compressors combine the advantages of both centrifugal and reciprocating compressors and are suitable for large capacity low-temperature applications.
- Rotary compressors are positive displacement, direct-drive machines available in two designs: rolling piston type and rotating vane type.
Condenser
- The condenser functions to desuperheat the high-pressure gas, condense it, and sub-cool the liquid.
- Three types of condensers are: air-cooled, water-cooled, and evaporative.
- Air-cooled condensers use air as the cooling medium, water-cooled condensers use water, and evaporative condensers use both water and air.
Capacity Control
- Capacity control of centrifugal compressors can be achieved by varying the compressor speed through a speed-reduction gear or by using variable inlet whirl vanes.
- Rotary compressors have high volumetric efficiencies due to negligible clearance and are normally used in a single stage up to a capacity of 5 TR with R-114.
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Description
This quiz covers the different equipment used in a refrigeration system such as compressor, condenser, evaporator, and expansion devices. Test your knowledge about the functions and roles of each component in a typical refrigeration setup.