Working of Domestic Refrigerators: Chapter 2
Freezers
In this module, we will learn freezer configurations and types. We’ll also discuss their applications. Skip to quiz!
Freezer Configuration
Recall that refrigerators are classified based on their arrangement as freestanding, built-in, or integrated. Refrigerators are also classified according to the placement of the freezers inside them. This includes:
Top mount freezers, and
Bottom mount freezers.
As the name implies, a top-mount freezer has its freezer placed above the fridge. A bottom-mount freezer will have its freezer positioned below the fridge.
As discussed earlier, single-door and two-door refrigerators have a freezer compartment at the top. Two-door refrigerator variants are also available with a freezer at the bottom. Recall that all types of French door refrigerators have a freezer at the bottom.
Most of these top and bottom freezer units have refrigerator cabinets with single swing doors. The bottom freezer compartment can have a drawer or a swing door. Meanwhile, the freezer compartment of a top-mount is always a swing door.
Bottom-mount freezers with a swing-door or a pull-drawer have organizing baskets. This will help you organize and access your frozen goods more easily than top-mount refrigerators.
A freezer’s configuration will affect its daily use. Since we tend to open the fridge compartment more often than the freezer, having the fridge at eye level will make it easier to use. We don't have to bend down each time to reach something inside the fridge.
Freezer Types
With a modern fridge, we require a lot of room to accommodate the refrigerator system. But without the freezer, a refrigerator system can be small and fit into the tiniest of spaces.
Recall that the temperature in a freezer is below 0℉, so we can store food items longer. In a freezerless refrigerator, there will be no freezer compartment. This is why they’re used in small shops to keep drinks or snacks for a limited time.
Apart from a freezerless refrigerator, we might also need a machine whose sole purpose is to store frozen food. For extra or long-term frozen food storage, there are dedicated freezers. These include:
Chest freezers, and
Upright freezers.
Chest freezers are laid out horizontally with their doors opening at the top. They either come with a solid hinged-top door or a sliding glass door. Chest freezers are commonly used in ice cream parlors, utility rooms, and house basements.
Upright freezers stand vertically – they look a lot like regular refrigerators except that they don’t have a fresh-food compartment. Compared to wide and bulky chest freezers, it’s just a slim and tall freezer compartment. Upright freezers are used in smaller garages or basements to save space.
Upright freezers are easier to organize because of the built-in shelves than chest freezers. Upright freezers are also easier to reach, as the compartments are shallow. Meanwhile, a chest freezer only has one deep compartment for everything.
A top-mount freezer has its freezer placed above the fridge. A bottom-mount will have its freezer positioned below the fridge.
In a freezerless refrigerator, as the name implies, there will be no freezer compartment. Chest freezers and upright freezers are dedicated freezers to store frozen food.
Refrigeration Cycle
In this module, we will recall the refrigeration cycle used in refrigeration systems. We’ll also discuss the components of refrigerators. Skip to quiz!
Refrigeration Cycle
A refrigerator removes heat from a closed space by using the basic refrigeration cycle. Recall that the four main components of the basic refrigeration cycle are:
Compressor,
Condenser,
A metering device, and
Evaporator.
Recall that a refrigerator works by transferring heat from the space inside to the outside. It uses refrigerant to do this. Refrigerant is fluid used in refrigeration systems to transfer heat.
Recall that ODP is the capacity of refrigerant to damage the ozone layer. Recall that GWP is the capacity of refrigerant to cause global warming. These factors measure the environmental impact of refrigerant.
Earlier generations of refrigerators used R-134a refrigerant. A majority of modern domestic refrigerators use R-600a refrigerant. This is because R-600a has a lower ODP and GWP than R-314a.
The molecules of vapor refrigerant are pressed closer together to increase the pressure. As pressure increases, temperature also increases. Then high-pressure, high-temperature vapor refrigerant enters the condenser.
Heat is removed from the vapor refrigerant by the flow of relatively cool air over the condenser. As high-temperature vapor refrigerant transfers its heat to the cool air, it changes from vapor to liquid. Liquid refrigerant is then sent to an expansion device.
When refrigerant enters the throttling valve, it expands and releases pressure. Consequently, the temperature drops at this stage, as pressure and temperature are related. Liquid refrigerant is then circulated through an evaporator.
In the evaporator, the refrigerant absorbs heat from the closed inside space of the refrigerator. Let’s discuss each of these components in detail.
Compressors
Recall that a compressor’s main job is to increase the pressure of refrigerant. We see the following types of compressors in a refrigerator:
Reciprocating compressors,
Scroll compressors, and
Screw compressors.
These are categorized based on how they work.
Recall that a motor drives reciprocating compressors. They have a piston and cylinder, just like a car engine.
Domestic refrigerators usually have air-tight, hermetically sealed reciprocating compressors. Recall that the motor and the compressor are contained and sealed inside a single shell in hermetic compressors. They are also relatively quiet, which makes them ideal for household use.
Recall that scroll compressors consist of two matching scrolls, one stationary and the other rotating around the first. One scroll rotates around the other in a circular motion to compress refrigerant.
Screw compressors also use a circular motion to compress refrigerant. That’s why they’re sometimes called rotary screw compressors.
Condensers
Recall that a condenser’s main job is to cool down refrigerant. The main types of condensers in refrigerators are:
Wire and tube type, and
Plate surface condenser.
These condensers are classified based on their structure.
A wire and tube condenser is similar to a fin and tube condenser. The difference is, there are no plate-like fins in wire and tube condensers. In their place, thin wires are used. The wires act as fins to increase the heat transfer area.
The reason they use wires in place of plate fins is that the condenser can be seen outside the refrigerator. If we use plate fins, it may cut someone's hand. So we use wires that can be made relatively more safe.
Plate surface condensers are flat, as shown in this image. The refrigerant carrying tubes are attached to the outer walls of a refrigerator. Unlike fin tube condensers, the whole body of the refrigerator acts like a fin and no separate fins are provided.
Metering Devices
Recall that a metering device’s job is to decrease the pressure of refrigerant. Refrigerators mainly use two main types of metering devices:
Capillary tube, and
Thermal expansion valve (TXV).
We’ll discuss how these metering devices work in refrigerators in detail.
Capillary tubes have a small diameter, which reduces the amount of refrigerant that can flow through at any given time. This decreases the pressure of refrigerant.
Refrigerant in a tube starts off with very high pressure. As it flows through this long thin capillary tube, refrigerant loses its pressure, and we only get a slow stream of water at the end.
Capillary tubes are more susceptible to clogging and damage. That’s why modern refrigerators use thermostatic expansion valves. TXVs control the amount of refrigerant that flows into an evaporator based on the evaporator outlet temperature.
Evaporators
Recall that an evaporator’s job is to absorb heat from the space inside a refrigerator. Refrigerators mainly use two main types of evaporators:
Bare tube, and
Plate surface evaporators.
Bare tube evaporators are the most simple type of evaporator. These evaporators are generally just refrigerant tubes that are made of either copper or aluminum. There is refrigerant inside the refrigerant tube, which changes from liquid to vapor by absorbing heat from the air.
Plate surface evaporators are flat, as shown in this image. These evaporators are made up of two plates that are joined together. Usually the two plates are made of aluminum because it conducts heat well.
Liquid refrigerant flows through a tube made between the two plates. This tube carrying refrigerant is the raised part of the plate that we can see in this image.
Plate surface evaporators are an improvement over bare tube evaporators. This is because they have a higher surface area for air to flow over them. The higher the surface area, the more heat can be transferred into refrigerant.
In plate surface evaporators, food can be placed directly on the plate for more effective cooling. This improves heat transfer even more.
Unlike bare tube evaporators, there are no tubes in plate surface evaporators. This makes them easy to clean and defrost.
Plate surface evaporators are less likely to leak refrigerant and safer to handle. This is because plates are stronger than tubes. As there are no fins, there is no danger of cutting our hands. This makes them suitable for refrigerators.
We see the following types of compressors in refrigerators:
Reciprocating compressors,
Scroll compressors, and
Screw compressors.
We mainly use two types of condensers in refrigerators:
Wire and tube condenser, and
Plate type condenser.
The two main types of metering devices used in refrigerators are:
Capillary tube, and
Thermal expansion valve.
Refrigerators mainly use the two main types of evaporators:
Bare tube, and
Plate surface evaporators.
Secondary Components
In this module, we will learn the secondary components used in a refrigerator. We’ll also discuss their function. Skip to quiz!
Airflow Systems
Recall that condensers cool down refrigerant by exchanging heat with the air around it. The air can be circulated around the condenser coils by using either of the following systems:
Natural draft, and
Forced draft airflow system.
Recall that natural draft airflow is airflow without the use of fans. Natural airflow depends on the principle that hot air naturally rises and cool air sinks.
If a bottle surface is heated, the air inside the bottle rises. Similarly, hot refrigerant in condenser coils transfers heat to the air around it. This air becomes warm and starts to rise above the condensing unit.
Cold air from the surroundings moves into the place of the warmer air, because cold air sinks. As a condenser runs, this process repeats and can be summarized as:
Hot air keeps rising, and
Cool air sinks to take hot air’s place.
This cycle repeats to create a natural flow of air.
Because the natural airflow system depends on air to move naturally, we can't control how fast it cools. It's like waiting for a cool breeze on a hot summer day. That’s why we find this type of system in older refrigerators.
To overcome the flaws in natural draft airflow, forced draft airflow was invented. Both induced and forced draft airflow use fans to direct the flow of air. As fans turn on and go faster or slower, we can better control the amount of air flowing over a condenser.
Blower Fans
Most modern refrigerators use a fan to blow air over the coils. There are two blower fans used in refrigerators. These include:
Condenser fan, and
Evaporator fan.
Condenser fans are located under refrigerators. They’re used to force air over compressors and condenser coils to cool them.
Evaporator fans are located inside refrigerators. Unlike natural air circulation, the fan moves air around the cool evaporator coils inside a refrigerator. This cooled air is then distributed inside the refrigerator to cool the food stored inside.
Filter Driers
The presence of moisture inside a system can damage it. We use a filter drier to remove moisture from and filter refrigerant. It removes small particles of dirt, water, and debris from refrigerant.
Filter driers are placed after a condenser and before an expansion device.
Filter driers consist of two parts; the shell and the core. The core is in the inner part, which absorbs moisture. Whereas, the shell is the outer metal covering.
When liquid refrigerant moves inside a drier, it will pass through the core. The core of a drier absorbs moisture and dirt particles. This cleans refrigerant coming out of a drier.
Liquid Line Receiver Tanks
A liquid line receiver tank is a storage tank that stores excess liquid refrigerant. There is a large amount of liquid refrigerant flowing in the refrigerant circuit of a refrigerator. We need a container to store this.
A receiver tank is installed in the refrigerant line, as close as possible to the outlet of the condenser. With a receiver, a system can have liquid refrigerant back up if the refrigerant level in the condenser drops due to leaks.
Accumulator Tanks
Recall that liquid refrigerant can cause the failure of a compressor. We use accumulator tanks to prevent liquid refrigerant from entering compressors. They’re placed between the evaporator outlet and the compressor suction line.
If liquid refrigerant does not boil off completely in an evaporator, it can enter the compressor. An accumulator placed at the compressor suction line ensures that only vapor refrigerant enters the compressor.
Most modern refrigerators use fans to blow air over condensers and evaporator coils. We use filter driers to remove moisture from and filter refrigerant. A liquid line receiver tank is a storage tank that stores excess liquid refrigerant.
Question #1: A top-mount freezer has its freezer positioned below the fridge.
True
False
Scroll down for the answer...
Answer: False
False. A top-mount freezer has its freezer placed above the fridge. A bottom-mount freezer will have its freezer positioned below the fridge.
Question #2: What is the door type of a bottom freezer compartment? (Select all that apply)
Slide down type
Pull-drawer style
Slide up type
Swing-door style
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Answer: Pull-drawer style
Swing-door style
The compartment of a bottom freezer type can be either a pull-drawer or swing-door.
Question #3: How many freezers are present in a freezerless refrigerator?
Two
One
Zero
More than two
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Answer: Zero
In a freezerless refrigerator, as the name implies, there will be no freezer compartment.
Question #4: Which type of freezer requires more horizontal space?
Chest freezer
Bottom mount freezer
Top mount freezer
Upright freezer
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Answer: Chest freezer
Chest freezers are wide and bulky, thus require more horizontal space compared to other freezers.
Question #5: Upright freezers are easier to organize compared to chest freezers.
True
False
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Answer: True
True. Upright freezers are easier to organize compared to chest freezers. They are also easier to reach into, as the compartments are shallow.
Question #6: After the metering device, which component does the refrigerant travel to next in the refrigeration cycle?
Condenser
Compressor
Metering Device
Evaporator
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Answer: Evaporator
After the metering device, refrigerant goes to the evaporator.
Question #7: Which refrigerant is used in most modern domestic refrigerators?
R-717
R-20
R-600a
R-134a
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Answer: R-600a
Earlier generations of refrigerators ran on R134A, tetrafluoromethane. The majority of modern domestic refrigerators run on R600A, isobutane.
Question #8: Which types of compressors are used in domestic refrigerators? (Select all that apply)
Reciprocating Compressor
Scroll Compressor
Screw Compressor
Centrifugal Compressor
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Answer: Reciprocating Compressor
Scroll Compressor
Screw Compressor
We see the following types of compressors in refrigerators:
Reciprocating compressors,
Scroll compressors, and
Screw compressors.
Question #9: How do wire and tube type condensers used in refrigerators differ from finned tube condensers found in air conditioners?
They have fins in place of wires
They have wires in place of fins
They are same
They have both fins and wires
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Answer: They have wires in place of fins
Unlike finned tube condensers, wire and tube condensers have thin wires in place of fins.
Question #10: Which type of metering device do we prefer in modern refrigerators?
Electronic expansion valve
Capillary tube
Thermostatic expansion valve
Nozzle
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Answer: Thermostatic expansion valve
Modern refrigerators use thermostatic expansion valves to control the amount of refrigerant.
Question #11: In which type of evaporator can food be placed directly on the evaporator plate for more effective cooling?
Finned Tube Evaporators
Plate surface evaporator
Bare tube evaporator
Shell and Tube Evaporators
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Answer: Plate surface evaporator
In plate surface evaporators, food can be placed directly on the plate for more effective cooling.
Question #12: Why do we prefer plate-type evaporators in domestic refrigerators? (Select all that apply)
They are safe to handle
They are easy to clean
They have single plate
They are less likely to leak
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Answer: They are safe to handle
They are easy to clean
They are less likely to leak
Plate surface evaporators are easy to clean and defrost. They are less likely to leak refrigerant and safer to handle.
Question #13: What is the principle that natural airflow depends on?
Conservation of airflow
Hot air sinks, cold air rises
Hot air rises, cold air sinks
All of these
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Answer: Hot air rises, cold air sinks
Hot air rises, and cold air sinks. Since natural airflow does not use fans, it relies on the standard principle that moves air.
Question #14: Which of the following airflow systems uses fans to direct the flow of air? (Select all that apply)
Natural airflow system
Induced draft airflow system
Forced draft airflow system
Cold air rise airflow system
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Answer: Induced draft airflow system
Forced draft airflow system
Both induced and forced draft airflow use fans to direct the flow of air.
Question #15: Condenser fans and evaporator fans work on the principle of the natural airflow system.
True
False
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Answer: False
False. Unlike natural air circulation, condenser and evaporator fans move air around the coils of a refrigerator.
Question #16: Filter driers add moisture to refrigerant.
True
False
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Answer: False
False. Filter driers are used to remove moisture from and filter refrigerant.
Question #17: Where are liquid line receiver tanks located?
Inlet of the condenser
Outlet of condenser
Inlet of evaporator
Inlet of compressor
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Answer: Outlet of condenser
A receiver tank is installed in the refrigerant line, as close as possible to the outlet of the condenser.
Question #18: Which of the following components is used to prevent liquid refrigerant from entering the compressor?
Filter drier
Accumulator tank
Liquid line receiver tank
Dehumidifier
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Answer: Accumulator tank
An accumulator tank is used to prevent liquid refrigerant from entering the compressor.