What is Frost-Free and Dairy refrigeration?

FROST-FREE REFRIGERATION:

Major components used:

WORKING:

When the evaporator in a refrigerator operates at temperatures below 0°C, it is subjected to ice or frost accumulation.
The formation of ice is due to water vapor in the humid air comes in contact with the freezer coils.
The frost acts as an insulation and decreases heat transfer rate and reduction in the evaporator capacity and system efficiency.
In frost-free refrigerators, the defrosting is done automatically.
A defroster system in the refrigerator has a timer, Heating coil, and Temperature sensor.
In a frost-free system, the evaporator is located in a separate compartment and the cold air is circulated to the food compartment by a fan.
The humidity air is drawn over the evaporator by the fan deposits its condensation on the evaporator and the resulting dry air is circulated to the food compartment, avoiding frost on the food and other cold surfaces.
For a pre-determined time (say eight hours), the timer turns 'ON' the heating coil and switches 'OFF' the compressor and fan.
The heating coil is wrapped among the freezer coils. The heater melts the frost (ice) on the coils.
The water produced from the melting of frost is collected in a trough and fed outside the freezer through a tube.
When defrosting is done, the temperature sensor senses the temperature rising above 0°C and turns 'OFF' the heater and switch 'ON' the compressor and fan.
Now again the cold, dry air is circulated in the food compartment.

ADVANTAGES:

Frost-free refrigerators do not require any manual operations for defrosting. It is handled automatically.
It is better for maintaining consistent temperatures and keeping food fresh for a longer period of time.

DAIRY REFRIGERATION:

Dairy refrigeration is the process in which dairy products are precooled, processed, and preserved for various purposes.
The preservation of milk involves blending, processing, packaging, and distribution.
Before processing, dairy plants pre-cool the milk to 2.5°C for the separation of cream and blending.
It involves a hot and cold milk separation process.
Cold milk separation takes place at a temperature of 4°C.
The milk is sent for pasteurization after separation and blending.
Pasteurization means partial sterilization of a product, such as milk to make it safe for consumption and improve its keeping quality.
Pasteurization of milk is done by heating the milk to a temperature of 65°C and holding it at this temperature for 30 minutes, followed by rapid chilling (cooling) to below 10°C. This temperature is maintained till usage.
Chilling of milk should be carried above -2°C, otherwise, the milk may freeze.
Chilling and pasteurization of the dairy milk are done by a vat-type milk cooler.
Pasteurization of milk kills all pathogenic bacteria.
Refrigeration is also required for cooling the cream before churning and the mechanical separation of butter.
For the storage of butter, a temperature of 0°C to 4°C is sufficient. But for storage for 6 months or more a temperature of -23°C to -18°C must be used.

ADVANTAGES:

COLD STORAGE:

The storage which is used for short-term storage purposes is known as cold storage.
In cold storage, the product is chilled and stored at some temperature above its freezing point.
Depending on the product, short-term storage periods normally range from 1 to 2 days in some cases to a week.

WORKING:

Cold storage is a space to be refrigerated.
The components of the system are housed in a room adjacent to the storage or downstairs.
The refrigerant flowing in the system keeps the evaporator coils cool.
Warm air drawn from the space to be refrigerated is blown over these coils.
It loses heat to the cold refrigerant inside the evaporator coils and gets chilled.
Chilled air is blown into the room or space to be cooled by the blowers through the directing louvers.
Refrigerant liquid after absorbing the heat of warm air evaporates and the vapor is drawn into the compressor.
The compressor compresses the vapor to a higher pressure and delivers it to a condenser where it is condensed into a liquid state.
This high-pressure cold liquid refrigerant is collected in a receiver and throttled to lower pressure by an expansion valve.
A low-pressure cold refrigerant enters the evaporator coil and absorbs the heat of warm air.
Thus the cycle is repeated.

ADVANTAGES: