The Refrigeration Cycle

The word cycle, as applied here, means a series of operation in which heat is first absorbed by the refrigerant, changing it from liquid to a gas, then the gas is compressed by the circulating air, thus bringing the refrigerant back to its original or liquid state. The cycle of operation onsists of the following steps:

1. The compressor pumps refrigerant through the entire system. It draws cool refrigerant gas in through the suction line from the evaporator freezer coils. At the same time, it compresses the gas and pumps it into the discharge line. The compressed gas sharply rises in temperature and enters the condenser.
2. The condenser performs a function similar to that of the radiator in an automobile, that is, the condenser is the cooling coil for the hot refrigerant gas. In the condenser, the heat is expelled into the room air outside the cabinet. During this process, the refrigerant gas gives up the heat it removed from inside the cabinet and changes into a liquid state.
3. As the hot refrigerant liquid leaves the condenser to enter the capillary tube, a drier - strainer removes any moisture or impurities.
4. The capillary tube is carefully calibrated in length and inside diameter to meter the exact amount of liquid refrigerant flow required for each unit. A predetermined length of the capillary tube is usually soldered along the exterior of the suction line, forming a heat exchanger which helps to cool the hot liquid refrigerant in the capillary tube. The capillary tube then connects to the larger diameter tubing of the evaporator.
5. As the refrigerant leaves the capillary tube and enters the larger tubing of the humid plate and evaporator, the sudden increase in tubing diameter forms a low pressure area, and the temperature of the refrigerant drops rapidly as it changes to a mixture of liquid and gas. In the process of passing through the evaporator, the refrigerant absorbs heat from the storage area and is gradually changed from a liquid and gas mixture to a gas.
6. The low pressure refrigerant gas leaving the evaporator coil now enters the accumulator. The accumulator is a large cylinder designed to trap any refrigerant liquid which may not have changed to gas in the evaporator. Since it is impossible to compress a liquid, the accumulator prevents any liquid from returning to the compressor.
7. As the refrigerant gas leaving the accumulator, it returns to the compressor through the suction line which is part of the heat exchanger, thus completing the cycle.

Heat Transmission

                           In refrigeration, the trasmission of heat may be accomplished in three ways;

1. By Conduction

2. By Convection

3. By Radiation

                                                      Conduction

                           This is the transference of heat by molecular impact from one particle to another in contact. For instance, if the end of a bar of iron is heated in the fire, some of the heat will pass through the bar to the cooler portion. Heat trevelling in a body, or from one body to another where the  two are in intimate contact, is termed conduction. Metal are usually splendid heat conductors. Each and every material has a conduction value, some good like the metals, other mediocre, and a few very poor. For instance, heat will quickly pass through a piece of copper but will have consideration difficulty in passing through a piece of cork. The material that have very low heat conductivities are termed heat insulators. Even the very poorest conductors, or insulation material, allow a certain amount of heat to pass through. There is no material which offers a perfect barrier or resistance to the passage of heat.

                                                      Convection

                              Convection is the principle used in hot-air heating. Air that is free to circulate, such as in any air body of appreciable size, will be set into motion where a difference of temperature occurs, for it will be absorb heat from the warmer wall, become heated, expand and become lighter The heated portion of the air eventually moves over to the colder wall, and the heat flows from the air to the colder object. Thus, any body of air capable of motion will transmit heat by convection. Hot-air and hot-water heating system work on the convection principle. They convey heat by bodily moving the heated substances from one place to another.

                                                      Radiation

                                Heat energy transmitted through air in the same way light is sent out by a lighted lamp, a radiant heater, or the sun, is called radiated energy. Large cold storage, warehouse, auditoriums, theaters, and homes are built with consideration of the heat evolved through radiant energy of the sun. Small household appliance rarely have to consider any radiant heat factor, for they are used in existing structures without any change in building design and are sheltered from direct heat.