Refrigerators are a part of modern-day life that they are almost taken for granted. Although this is the case, the scientific laws that enable the development and manufacture of household refrigerators are remarkable. It is worth getting to know how your fridge keeps your brewskies cold.
Compressor fridges work in the following steps
- Cold gas is passed through the evaporator coils.
- The heat in the fridge transfers to the gas.
- The gas is compressed and sent through the condenser.
- The coils dissipate the gas.
- The gas enters a low-pressure area where it liquifies and cools.
Fridges use fantastic technology which has the effect of removing heat from within the fridge compartment. The science has been understood for over 250 years; however, it is only in the last 90 years that it has become commercially viable to manufacture fridges for private home use.
Fridges Work In The Following Manner
Fridges do not work by cooling the air inside them. It seems a strange statement; however, fridges do not cool the air but instead remove the heat within the fridges compartment. As the heat energy is released, the molecules in the air slow down, causing the temperature to reduce.
There are varying types of refrigeration technology used in different fridges, which include
- Compressor refrigerators are the most used technology.
- Absorption refrigerators use heat to drive the evaporation process to absorb heat into the coolant.
- Peltier effect refrigerators use a heat pump to transfer heat from one side of the device to the other.
- Ultra-low temperature refrigerators employ two stages of cooling to reach as low as −196 °C
Compressor refrigerators are the most effective, low-cost way most modern refrigerators have the low temperatures needed to preserve food.
In summary, compressor fridges take the heat inside the compartment and transfer it into the outside atmosphere, which in most cases is the kitchen.
The actual process involves the following steps.
Step 1 – The Evaporator Coils
Refrigerators have a curved pipe, called an evaporator coil, installed within the refrigerator walls.
Refrigerant is placed in the evaporator coils.
The refrigerant in the coils is in a cooled gaseous state.
A pump attached to the coil sucks the cold gaseous refrigerant from the pipes and the coils installed in the fridge walls. The Evaporator coils directly contact the air in the food compartment.
The evaporator coils absorb heat from the fridge into the low pressure, cool refrigerant gas.
Transferring the heat from the inside of the refrigerator heats the refrigerant gas.
Step 2 – The Refrigerant Is Compressed
Heated-up gas is pumped into a compressor and is pushed into condenser coils installed at the back of the fridge.
As the gas is compressed, its pressure and temperature are raised, making the condenser coils act as heat exchangers, which cause the refrigerant to dissipate its heat.
The heat is transferred into the atmosphere.
It explains why the condenser coils at the back of the fridge are hot.
The effect of this is to cool the refrigerant gas.
Step 3 – Refrigerant Is Sent to the Expansion Valve
As the refrigerant gas cools, it returns to a liquid state.
The now liquid refrigerant is passed through the condenser coils to an expansion valve, changing the pressure from high to low.
This change in pressure makes the refrigerant liquid expand and evaporate (causing it to change into a gaseous state). As the refrigerant expands, it draws the energy from its surroundings and the temperature of the refrigerant gas drops.
It is similar to a person with a sweaty body standing in the wind. The sweat absorbs the heat and evaporates, causing it to become cold.
As the gas refrigerant is cooled, it creates the capacity to absorb more heat.
Step 4 – The Cycle Continues
The refrigerant gas returns to the evaporator coils, where the whole cycle is repeated.
How Refrigeration works has evolved over time
To better understand how fridges work, we can take a look at their history.
For centuries many societies have been aware of the benefits of storing perishable foodstuff in colder environments to preserve the items for future consumption.
As early as 1.000 BC, Chinese people harvested ice from rivers and lakes and used it in various containers to store food.
Hebrews, Greeks, and Romans all used snow shoveled into pits covered with grass, chaff, or tree branches and were used to store food.
Ancient Egyptians and Indians used a primitive form of heat transfer by moistening the outside of glass containers causing the subsequent evaporation to cool the inside of the glass.
Persians (modern-day Iranians) developed Yakhchal’s, which were ice pits or underground caverns used to store food. These areas were outfitted with special devices designed to draw cool air in.
In the 1800s, servants of the English nobility were expected to collect ice and store it in icehouses, which were used to preserve food. They maintained the ice with salt in these structures, wrapped in material, and held it underground to keep them frozen until the summer.
Frederic Tudor, an American businessman and merchant started harvesting ice in New England and shipping it to the Caribbean islands, Europe, India, and Hong Kong.
In 1748 William Cullen studying at the University of Glasgow demonstrated the first example of artificial cooling. He cooled the air by letting ethyl ether boil into a partial vacuum. This experiment could not be monetized as the method was not practically viable.
In 1805 an American inventor designed the first viable artificial cooling system.
The Advent Of Commercially Available Refrigerators
Alexander C. Twinning developed the first commercially available system in 1856
The early systems used ammonia as the refrigerant, which smelt terrible and was also toxic.
Some early systems involved a significant installation process, including installing various mechanical components and electric motor and compressor in a separate room. The actual icebox was connected to these devices and installed in the kitchen.
It wasn’t until 1926 that scientists developed a synthetic refrigerant called Freon. It was the first genuine commercial application of modern private refrigerators.
Technology has advanced and includes automatic defrosting and automatic ice making, greater efficiency, environmentally safe refrigerant, but the basic principles still drive modern refrigerators.
Next time you open your refrigerator door, have a quick thought about the level of science that allows it to keep perishable food useable. These fantastic appliances run year after year, often enduring much abuse, yet they keep on trucking along.
We have discussed how to deal with fruit flies in your fridge here.
Of course, when the refrigerator at home fails, it is all panic station because the valuable foodstuff stored inside stands a real risk of perishing. Imagine what life would be like if the technology driving refrigerators didn’t exist.
If you want to learn even more, we have discussed how a thermistor works in a fridge here.