Refrigeration System Equipment Quiz

Study Flashcards Play Quiz

Questions and Answers

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

To raise the refrigerant pressure

Where does the evaporator fit in a refrigeration system?

Low pressure side

What is the primary purpose of an evaporator in a refrigeration system?

To absorb heat from the surroundings

Why must the temperature of the boiling refrigerant in the evaporator be lower than that of the surrounding medium?

To ensure heat flows into the refrigerant Signup and view all the answers

Where is the expansion device located in a refrigeration system?

Between the compressor and condenser Signup and view all the answers

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

Individual knowledge of each equipment in the system Signup and view all the answers

What is the main function of a reciprocating compressor?

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

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

Rotary compressor Signup and view all the answers

What is the main difference between reciprocating and centrifugal compressors?

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

Which refrigerant is best suited for use with screw compressors?

R-22 Signup and view all the answers

Why is a clearance volume necessary in reciprocating compressors?

To provide for thermal expansion and machining tolerances Signup and view all the answers

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

Clearance volume Signup and view all the answers

Which compressor type operates at low condensing pressure?

Centrifugal compressor Signup and view all the answers

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

Rotary motion Signup and view all the answers

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

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

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

Clearance factor C Signup and view all the answers

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

It tends to zero Signup and view all the answers

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

They both decrease Signup and view all the answers

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

Causes the pressure inside the cylinder to rise Signup and view all the answers

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

Maintaining a low pressure ratio Signup and view all the answers

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

Leads to low volumetric efficiency and increased friction Signup and view all the answers

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

Inlet casing Signup and view all the answers

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

Convert kinetic energy into pressure energy Signup and view all the answers

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

Alloy (chrome-nickel) steels Signup and view all the answers

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

Suction, compression, discharge Signup and view all the answers

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

To cool and lubricate the rotors Signup and view all the answers

What type of refrigerants are typically used in screw compressors?

High-pressure refrigerants Signup and view all the answers

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

By controlling the flow passage Signup and view all the answers

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

No residual gas remaining in rotors Signup and view all the answers

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

Natural convection Signup and view all the answers

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

Evaporative condenser Signup and view all the answers

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

To cool down the refrigerant gas Signup and view all the answers

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

Slide valve Signup and view all the answers

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

Oil injection system Signup and view all the answers

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

Surging Signup and view all the answers

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

To minimize friction and achieve high efficiency Signup and view all the answers

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

By altering the angle at which the gas enters the impeller Signup and view all the answers

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

Rotary compressor Signup and view all the answers

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

~25% Signup and view all the answers

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

Decreasing refrigeration load Signup and view all the answers

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

Oil film Signup and view all the answers

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

Speed-reduction gear Signup and view all the answers

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

They elevate tip speeds Signup and view all the answers

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

The pressure remains constant on both sides Signup and view all the answers

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

Plate-type Condenser Signup and view all the answers

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

Closely spaced (8-17 fins per inch) 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?

Scale 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?

Shell-and-Coil Condenser Signup and view all the answers

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

Improve natural convection air currents Signup and view all the answers

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

The scale formation on the tubes Signup and view all the answers

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

Forced-air Circulation Condenser Signup and view all the answers

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

Increase mechanical strength Signup and view all the answers

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

A small gap between cabinet and plate 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?

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

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

Ammonia reacts with copper Signup and view all the answers

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

To anchor the tube ends and prevent movement Signup and view all the answers

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

To facilitate brushing of the water tubes Signup and view all the answers

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

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

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

Refrigerant Signup and view all the answers

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

The surface is constantly wet and hot Signup and view all the answers

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

It can lead to excessive hydraulic pressures Signup and view all the answers

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

Protect against excessive pressures Signup and view all the answers

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

It increases hydraulic pressure Signup and view all the answers

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

For ice-plants and cold-storage jobs Signup and view all the answers

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

By natural convection Signup and view all the answers

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

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

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

By refrigerant liquid pump Signup and view all the answers

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

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

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

'Natural convection' involves movement in a fluid due to temperature differences while 'forced convection' uses fans or pumps to circulate fluid. 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?

To cool down the liquid refrigerant before entering the evaporator coil Signup and view all the answers

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

Surface area A and outside refrigerant film coefficient h0 Signup and view all the answers

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

Metal wall Signup and view all the answers

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

The liquid refrigerant level Signup and view all the answers

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

Proportion of liquid to vapor in the evaporator length Signup and view all the answers

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

Maintaining a constant liquid level Signup and view all the answers

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

Liquid refrigerant contact with entire surface Signup and view all the answers

What distinguishes a direct expansion evaporator from a flooded evaporator?

'Dry' state at outlet Signup and view all the answers

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

'Direct expansion' evaporator Signup and view all the answers

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

Heat supplied by substance to be cooled Signup and view all the answers

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

Float valve operation 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.

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.