Understanding Refrigerators: Principles and Applications
Understanding Refrigerators
A refrigerator is any device capable of lowering the temperature of a particular object or place to make it lower than its surroundings.
Top-Operation
To explain its operation, it’s necessary to understand that there is a relationship between work and heat consumed or vice versa. Whenever the final state of the system is equal to the initial state, heat cannot transfer spontaneously from a colder body to a hotter one.
The cold produced by evaporation of a fluid is due to a refrigerant substance that changes state by condensation or evaporation at certain pressures and temperatures.
Fluids used include water, methyl and ethyl chlorides, ammonia, propane, butane, and fluorinated and chlorinated hydrocarbons.
Constitution of a Refrigeration System
- The refrigerant fluid is compressed in the compressor, where energy is added.
- It is then liquefied by cooling in the condenser.
- Next, it undergoes expansion in the expansion system, which reduces the fluid pressure to reach the evaporator.
- In the evaporator, the fluid evaporates, taking heat from the surroundings and causing cooling.
- Finally, the fluid returns to the initial conditions and passes through the compressor for a new cycle.
General Outline of a Refrigerator System
The mission of the compressor is twofold: it compresses the refrigerant fluid in a vapor state and facilitates the movement of fluid over the cycle. The compressor is driven by a motor that consumes energy from the system. The refrigerant enters the condenser where liquefaction occurs via airflow or water. In this phase, it releases heat and reduces its volume at constant pressure. The accumulator stores fluid from the condenser and feeds the evaporator through the expansion valve. The fluid volume expands in the evaporator, originating the processing of fluid into steam, which takes a lot of heat from the environment and causes cooling. The fluid exiting the evaporator is in the initial refrigerant conditions.
Applications of Refrigeration
- Alimentary industry
- Distribution of perishable items
- Air conditioning
- Refrigerators and freezers for domestic and medical use
Heat Pumps
A heat pump is a refrigerator that can take the heat transferred to the capacitor for a given space. The principle of operation is equal to the refrigerator. The difference is that the refrigerator is intended to produce a cooling effect in the evaporator, while the heat pump is designed to produce a heating effect in the condenser.
Types of Heat Pumps
- Water-Water Heat Pump: Cold water with a temperature between 13 and 15 degrees Celsius is used. A hydraulic pump moves the water in the evaporator, where the refrigerant fluid evaporates, taking heat. The water temperature drops by about 5 degrees Celsius. The water then enters the condenser circuit, taking calories as the refrigerant fluid condenses. The exit water is hot, with a temperature of about 50 degrees Celsius.
- Air-Air Heat Pump: Cold air is collected by a fan and goes to the evaporator, where the refrigerant fluid takes a certain amount of heat and evaporates. The exit air is colder. The condenser uses air as a heat source, driven by another fan. The refrigerant fluid releases heat to liquefy, and the exit air is at a temperature of 50 degrees Celsius.
- Single-Source Heat Pumps: Sun-air-water heat pumps use the sun as the cold source and work like reversible devices, heating in winter or cooling in summer.