The natural tendency of heat is to flow from high temperature to low temperature reservoir. Refrigeration is the process of transferring heat from low temperature reservoir to the high temperature reservoir. This is against the natural flow of heat hence power is required to enable this transfer. Refrigeration is also defined as science that deals with the process of reducing and maintaining the temperature of a space or material below the temperature of the surroundings.
The process of refrigeration helps you to chill water, make ice and delicious ice cream. It helps you preserve your fruits, vegetables and other food items. The food items get damaged at atmospheric temperature because bacteria can easily survive in these conditions. At temperatures below 4 degree Celsius, the bacteria cease to exist and hence the food items remain safe and fresh. You can also keep your medicines safe in refrigeration. There are number of other applications of refrigeration.
The refrigeration system comprises of various components like Freon gas, compressor, condenser, evaporator, thermostat etc, which are all enclosed in a casing. The most commonly used refrigeration machines are the household refrigerator and deep freezer, though these machines are available in many other forms.
Household refrigerators are available in various forms and sizes. The size of the refrigerator is defined in terms of the total internal volume of the refrigerator. The volume of the typical household refrigerator can be 10, 14, 16, 18, 20 square feet and even more. These refrigerators can have single door, double door, or side doors.
The larger the size of the refrigerator, the more food items that can be kept in the refrigerator. Accordingly the amount of heat that is to be removed from the refrigerator to maintain the desired temperature also increases. The rate at which this heat must be removed from the refrigerated space is called refrigeration load, cooling load or heating load.
In the freezer section of the refrigerator, temperature below zero degrees Celsius is maintained, hence water and other food items get frozen when kept here. In the main body of the refrigerator, temperatures ranging from 0 to 4 degree Celsius are maintained depending upon the distance of the compartment from the freezer section.
Since the temperature inside the refrigerator compartment is maintained below the atmospheric temperature, the heat flows naturally from atmosphere into the refrigerator compartment. To avoid this and keep the food frozen and fresh, the refrigerators are covered with the insulating materials. The most commonly used insulating material is PUF (Polyurethane foam).