As already brought out, Refrigeration has two main uses- one is air conditioning and other is food preservation.
Here we are going to study the refrigeration in very details.
The Refrigerator is the cooling household appliance system where removing the heat from the system to surrounding by the heat pump
so that the inside of the fridge is cooled to a temperature below the ambient temperature of the room.
Main Parts or Component of Refrigerator:
It consists of the 4 main components or Parts:
In most of the common refrigerators, evaporator coils are wound around the freezer cabinet.
Sometimes they are placed between two seats to form a freezer cabinet.
The coil has no fins due to the frosting that collects on it over a period and due to low draft by natural convection.
In frost-free refrigerators, the evaporated is finned and the air is circulated over it by the fan.
The Frost on the evaporator is melted by a very low capacity heating element.
During the cyclical cut off period of the refrigerator, the electric heater switch on the defrost the evaporator. It is switched off before the restart of the compressor.
In this refrigerators, there is forced air circulation due to a finned evaporator and independent compartments.
It is hermetically sealed unit with the reciprocating compressor as the most common type of compressor.
In some large refrigerators, use of rotary or screw compressor is possible. But the use is limited due to the high cost.
The compressor unit is mounted on the rear side of the refrigerator.
The compressor motor capacity ranges from 1/8 to 1/4 HP depending upon the size of the refrigerator.
The starting relay also has overload protection to protect the compressor motor against higher current due to low voltage or tripling of the power supply.
In normal refrigerators, a condenser is installed on the rear side. The air circulation is by natural convection.
In the Frost free refrigerators, the condenser tube is on the inside of the outer cabinet of the refrigerator.
This arrangement prevents condensation on the outer cabinet in humid condition. It also allows placing the refrigerated close to the wall.
4. Expansion device:
In this system, the capillary tube is used as an expansion device.
The capillary is long due to the large difference between condenser pressure and evaporator pressure.
The capillary is sometimes soldered on the outside of the suction line and insulated to provide liquid-suction heat exchanger.
There is a dryer strainer before the capillary tube.
This is the application of food preservation at the end user level. A refrigerator is an insulated box in which low temperature is maintained to facilitate salt or medium-term storage of food.
The refrigerator is usually specified as per volumetric capacity on the inside.
It is available in the capacity of 65 liters, 100 liters, 165 liters, 275 liters, to double door refrigerator of capacity as large as 1000 liters.
Large size refrigerator comes with independent compartments as per food categories.
So you get freezer cabinet, vegetable pulls out compartment and so on.
Most of the refrigerator comes with painting Stell sheet cabinet on the outside with strong industrial plastic inner cabinet for rust proofing shown in the figure.
In early refrigerators, cork expanded polystyrene ( Thermocol ) sheets or granules were used for insulations.
But nowadays polyurethane foam is the most common insulation used in in the refrigerator.
The door of the cabinet is provided with a neoprene rubber gasket to prevent leakage of air from the cabinet.
The inner cabinet and the inner panel of the door are suitably formed to provide trays for different categories of food.
Small refrigerator 165 liters the circulation of air for cooling is by natural convection.
This allows a range of temperature from -20 degree Celsius in the freezer cabinet at the top to about 5 degree Celsius in the vegetable tray located at the bottom.
The trays are not solid to allow air flow through the trays for circulation of air.
The temperature is maintained within a range by cyclic control.
The compressor cuts off at lower end i.e cut off temperature and restarts at Higher end i.e cut in temperature.
Advantages, Disadvantages, Application of Refrigerator:
Refrigerators are used mainly in keeping the refrigeration space cold.
By keeping the refrigeration space cold, the presence of micro-organisms such as Bacteria, Fungi is slowed down. They are not able to multiply fast enough to damage cells present in our foods and drinks.
Therefore, our food and drinks could be preserved over a long duration.
In the System, the bacteria and fungi become inactive under extremely lower temperatures.
Refrigerators are also used for medical and scientific purposes for the same reason.
For medical use, items such as blood and vaccines are stored in it for preservation.
For Scientific use, experimental samples are stores in it.
Used for making ice and ice-creams apart from storage of food.
Many drugs which are to be kept away from direct sunlight and heat like insulin are also stored in refrigerators for longevity.
- Cold storages
- Fish and meat processing
- Concrete cooling
- Paint cooling
- Chemical formulation
- Pharma industries
Some Precaution during uses of Refrigerator:
The refrigerator should be placed at least 15 cm from the wall. This ensures an adequate circulation of atmospheric air over the condenser tubes.
Clean surface of condenser ensures that condenser temperature does not increase due to inadequate heat transfer.
The refrigerator should not be located in hot rooms like a kitchen. The highest temperature would raise the condensing temperature and reduced cooling capacity of the coil.
Hot food should not be placed in the refrigerator. Hot food in the refrigerator raises the evaporated temperature causing overloading of the compressor.
During the opening of the refrigerator, cold air leaks out at the bottom and warm air enters at the top. A frequent opening could raise cabinet temperature and evaporated temperature.
This would overload the compressor. This also causes greater frosting on evaporator due to moisture in warm air.
The dishes/container should not be kept open as they would lose moisture. This moisture would also increase frosting on the evaporator.
Stabilized electrical supply is necessary to avoid overloading of the compressor motor due to a large current drawn during low voltage.
The refrigerated should be labeled to ensure that magnetic rubber gasket on the door, seals the refrigerator.