Refrigeration System Equipment Quiz
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Questions and Answers

What is the main function of a refrigerant compressor in a refrigeration system?

  • To cool down the refrigerant
  • To remove heat from the evaporator
  • To raise the refrigerant pressure (correct)
  • To boil the refrigerant
  • Where does the evaporator fit in a refrigeration system?

  • Between the receiver and the evaporator
  • Low pressure side (correct)
  • High pressure side
  • Connected to the condenser
  • What is the primary purpose of an evaporator in a refrigeration system?

  • To connect the high pressure side and low pressure side
  • To raise the pressure of the refrigerant
  • To absorb heat from the surroundings (correct)
  • To remove heat from the surroundings
  • Why must the temperature of the boiling refrigerant in the evaporator be lower than that of the surrounding medium?

    <p>To ensure heat flows into the refrigerant</p> Signup and view all the answers

    Where is the expansion device located in a refrigeration system?

    <p>Between the compressor and condenser</p> Signup and view all the answers

    What kind of knowledge is required to understand a refrigeration system according to the text?

    <p>Individual knowledge of each equipment in the system</p> Signup and view all the answers

    What is the main function of a reciprocating compressor?

    <p>To compress vapour refrigerants using a back and forth motion of the piston</p> Signup and view all the answers

    Which compressor type is most suited for pumping refrigerants with moderate or low condensing pressures?

    <p>Rotary compressor</p> Signup and view all the answers

    What is the main difference between reciprocating and centrifugal compressors?

    <p>Reciprocating compressors handle smaller displacements at high pressure, while centrifugal compressors handle larger displacements at low pressure</p> Signup and view all the answers

    Which refrigerant is best suited for use with screw compressors?

    <p>R-22</p> Signup and view all the answers

    Why is a clearance volume necessary in reciprocating compressors?

    <p>To provide for thermal expansion and machining tolerances</p> Signup and view all the answers

    What is the main factor contributing to reducing the volume of the sucked vapour in reciprocating compressors?

    <p>Clearance volume</p> Signup and view all the answers

    Which compressor type operates at low condensing pressure?

    <p>Centrifugal compressor</p> Signup and view all the answers

    What mechanism is used to compress vapour refrigerants in centrifugal compressors?

    <p>Rotary motion</p> Signup and view all the answers

    What does the volumetric efficiency of a reciprocating compressor account for?

    <p>Difference between displacement in-built in the compressor and actual suction vapour volume pumped</p> Signup and view all the answers

    What is the ratio of clearance volume to swept volume called in reciprocating compressors?

    <p>Clearance factor C</p> Signup and view all the answers

    What happens to the refrigerating capacity of a reciprocating compressor as the evaporator pressure decreases?

    <p>It tends to zero</p> Signup and view all the answers

    How does the suction volume and volumetric efficiency vary with decreasing suction pressure for a reciprocating compressor?

    <p>They both decrease</p> Signup and view all the answers

    What is the effect of pressure drops at the valves on the indicator diagram of a compressor?

    <p>Causes the pressure inside the cylinder to rise</p> Signup and view all the answers

    What is one method suggested for improving the volumetric efficiency of a reciprocating compressor?

    <p>Maintaining a low pressure ratio</p> Signup and view all the answers

    What is the impact of a large clearance volume on the work of compression?

    <p>Leads to low volumetric efficiency and increased friction</p> Signup and view all the answers

    Which component of a single-stage centrifugal compressor is responsible for accelerating the fluid to the impeller inlet?

    <p>Inlet casing</p> Signup and view all the answers

    What is the function of a diffuser in a centrifugal compressor?

    <p>Convert kinetic energy into pressure energy</p> Signup and view all the answers

    What material is typically used for making the impeller of a centrifugal compressor?

    <p>Alloy (chrome-nickel) steels</p> Signup and view all the answers

    What are the three basic continuous phases of the working cycle in a screw compressor?

    <p>Suction, compression, discharge</p> Signup and view all the answers

    What is the purpose of injecting oil in a screw compressor?

    <p>To cool and lubricate the rotors</p> Signup and view all the answers

    What type of refrigerants are typically used in screw compressors?

    <p>High-pressure refrigerants</p> Signup and view all the answers

    How does a slide valve function in a screw compressor for capacity control?

    <p>By controlling the flow passage</p> Signup and view all the answers

    What is one advantage of a screw compressor compared to reciprocating compressors?

    <p>No residual gas remaining in rotors</p> Signup and view all the answers

    What type of movement is responsible for air-cooling in natural convection condensers?

    <p>Natural convection</p> Signup and view all the answers

    Which condenser type uses both water and air as cooling mediums?

    <p>Evaporative condenser</p> Signup and view all the answers

    What is the main function of the condenser in a refrigeration system?

    <p>To cool down the refrigerant gas</p> Signup and view all the answers

    What mechanism is used for capacity control in a screw compressor?

    <p>Slide valve</p> Signup and view all the answers

    Which component of a screw compressor serves the purpose of cooling and lubricating?

    <p>Oil injection system</p> Signup and view all the answers

    What is the phenomenon of reversal of flow in centrifugal compressors called?

    <p>Surging</p> Signup and view all the answers

    Why is it important to have reasonable width shrouds in a centrifugal compressor?

    <p>To minimize friction and achieve high efficiency</p> Signup and view all the answers

    How is the capacity of centrifugal compressors controlled through variable inlet whirl vanes?

    <p>By altering the angle at which the gas enters the impeller</p> Signup and view all the answers

    Which type of compressor is known for its high volumetric efficiencies due to negligible clearance?

    <p>Rotary compressor</p> Signup and view all the answers

    At what percentage of rated capacity does surging typically occur in centrifugal compressors?

    <p>~25%</p> Signup and view all the answers

    What shifts the point of operation from point A to point B in a centrifugal compressor?

    <p>Decreasing refrigeration load</p> Signup and view all the answers

    What type of material forms the seal between the high-pressure and low-pressure sides in rotary compressors?

    <p>Oil film</p> Signup and view all the answers

    What is one method used to control the capacity of centrifugal compressors by varying the compressor speed?

    <p>Speed-reduction gear</p> Signup and view all the answers

    How do large diameter impellers or high RPM contribute to achieving high tip speeds in centrifugal compressors?

    <p>They elevate tip speeds</p> Signup and view all the answers

    In a rotary compressor, what happens when the compressor stops regarding high/low pressure sides?

    <p>The pressure remains constant on both sides</p> Signup and view all the answers

    What type of condenser requires a relatively large surface area due to slow air movement by natural convection?

    <p>Plate-type Condenser</p> Signup and view all the answers

    How are fins arranged in a forced-air circulation condenser to optimize heat transfer?

    <p>Closely spaced (8-17 fins per inch)</p> Signup and view all the answers

    In a water-cooled tube-in-tube condenser, what forms on the water-side of the tube causing impediment to heat transfer?

    <p>Scale</p> Signup and view all the answers

    Which type of condenser involves a coil of finned tubing where water flows through the coil and refrigerant is in the shell?

    <p>Shell-and-Coil Condenser</p> Signup and view all the answers

    What is the main purpose of using widely-spaced fins in a condenser design?

    <p>Improve natural convection air currents</p> Signup and view all the answers

    Why is it challenging to clean the water-side of tubes in a tube-in-tube system?

    <p>The scale formation on the tubes</p> Signup and view all the answers

    Which type of condenser employs a fan or blower to circulate air over the condenser coil?

    <p>Forced-air Circulation Condenser</p> Signup and view all the answers

    What is the function of wires welded to the condenser tubes in a small unit design?

    <p>Increase mechanical strength</p> Signup and view all the answers

    What design feature of a plate-type condenser allows for better natural convection air currents?

    <p>A small gap between cabinet and plate</p> Signup and view all the answers

    How does the arrangement of tubes in a shell-and-tube condenser differ from that of a flooded chiller?

    <p>Tubes are straight with integral fins stacked inside a cylindrical shell</p> Signup and view all the answers

    Why are steel tubes used for ammonia condensers instead of copper?

    <p>Ammonia reacts with copper</p> Signup and view all the answers

    What is the purpose of the grooves in the holes of the tube sheets in water-cooled condensers?

    <p>To anchor the tube ends and prevent movement</p> Signup and view all the answers

    Why are removable water boxes provided at the ends of the condenser?

    <p>To facilitate brushing of the water tubes</p> Signup and view all the answers

    How does an evaporative condenser differ from a water-cooled condenser?

    <p>It combines functions of a water-cooled condenser and a cooling tower</p> Signup and view all the answers

    What is the source of heat for vaporizing the water in an evaporative condenser?

    <p>Refrigerant</p> Signup and view all the answers

    Why is it challenging to keep the surface of the condenser coil clean in an evaporative condenser?

    <p>The surface is constantly wet and hot</p> Signup and view all the answers

    Why is it important not to overcharge a refrigeration system with refrigerant?

    <p>It can lead to excessive hydraulic pressures</p> Signup and view all the answers

    What role does a fusible plug or safety pressure relief valve play in a refrigeration system?

    <p>Protect against excessive pressures</p> Signup and view all the answers

    What happens if too much liquid accumulates in the condenser of a refrigeration system?

    <p>It increases hydraulic pressure</p> Signup and view all the answers

    In what scenario would a receiver of adequate capacity need to be added to a refrigeration system?

    <p>For ice-plants and cold-storage jobs</p> Signup and view all the answers

    How is the liquid flow from the accumulator to the evaporator coil primarily achieved?

    <p>By natural convection</p> Signup and view all the answers

    What is the purpose of a liquid eliminator located in the accumulator top?

    <p>To prevent carry-over of liquid particles to the suction line</p> Signup and view all the answers

    In a 'liquid-overfeed system', how is the refrigerant liquid circulated from the accumulator to the evaporator coil?

    <p>By refrigerant liquid pump</p> Signup and view all the answers

    In a refrigeration system, what do the terms 'dry expansion' and 'flooded' refer to?

    <p>The manner in which the liquid refrigerant is fed into the evaporator</p> Signup and view all the answers

    What is the main difference between 'natural convection' and 'forced convection' in a refrigeration system?

    <p>'Natural convection' involves movement in a fluid due to temperature differences while 'forced convection' uses fans or pumps to circulate fluid.</p> Signup and view all the answers

    What is the function of a 'liquid-suction heat exchanger' used on the suction line in a refrigeration system?

    <p>To cool down the liquid refrigerant before entering the evaporator coil</p> Signup and view all the answers

    In a water-cooled condenser, what does the overall heat transfer coefficient (U) depend on?

    <p>Surface area A and outside refrigerant film coefficient h0</p> Signup and view all the answers

    Which component contributes to the overall heat-transfer resistance in a water-cooled condenser according to the text?

    <p>Metal wall</p> Signup and view all the answers

    What is the main difference between a 'dry expansion' evaporator and a 'flooded' evaporator?

    <p>The liquid refrigerant level</p> Signup and view all the answers

    How does a direct expansion evaporator differ from a dry expansion evaporator?

    <p>Proportion of liquid to vapor in the evaporator length</p> Signup and view all the answers

    What is the role of a float valve in a flooded-type evaporator?

    <p>Maintaining a constant liquid level</p> Signup and view all the answers

    Which factor contributes to making a flooded evaporator more efficient than other types?

    <p>Liquid refrigerant contact with entire surface</p> Signup and view all the answers

    What distinguishes a direct expansion evaporator from a flooded evaporator?

    <p>'Dry' state at outlet</p> Signup and view all the answers

    Which type of evaporator maintains a varying proportion of liquid and vapour along its length?

    <p>'Direct expansion' evaporator</p> Signup and view all the answers

    What determines the refrigerant liquid level in a flooded-type evaporator?

    <p>Heat supplied by substance to be cooled</p> Signup and view all the answers

    What contributes to maintaining a constant refrigerant liquid level in a flooded-type evaporator?

    <p>Float valve operation</p> Signup and view all the answers

    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

    • 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.

    • The compressor is a machine used to compress the refrigerant from the evaporator and raise its pressure.

    • 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.

    • The evaporator is used in the low-pressure side of a refrigeration system to absorb heat from the surrounding location or medium being cooled.

    • 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.

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