In this blog post, we’ll take an easy-to-understand look at the historical background of refrigerators, changes in the state of matter, and how refrigerators work using refrigerant circulation. We’ll also explore the significance of modern refrigeration technology and its future direction.

History and Background

In prehistoric times, people did not have a great need to store food for long periods, so temporarily storing it in clay pots or similar containers was sufficient. However, as agriculture developed and people began to settle in one place, the need to preserve food for longer periods grew, leading to the development of various storage technologies.
In Korea, facilities for storing ice appeared after the Three Kingdoms Period, with the stone ice house being a prime example. A stone ice house is a storage facility made of stone, designed to store ice harvested in winter for use through the summer. These storage facilities were primarily built in underground spaces or designed to take advantage of the terrain to minimize the influence of external temperatures.
Underground spaces are relatively less affected by changes in external temperature, allowing the internal temperature to remain relatively constant. In fact, if you enter a lava cave such as Manjang Cave on Jeju Island, you can experience a cool environment even in the height of summer and notice that temperature fluctuations are minimal even in winter. These naturally cool environments were also effectively utilized for food storage.
However, as cities developed and populations became more densely concentrated, relying solely on storage methods that utilized natural terrain became insufficient to meet the growing demand for food preservation. As technology advanced to overcome these limitations, modern refrigerators were developed, and today they have become essential household appliances in nearly every home and industrial setting.

States of Matter and the Basic Principles of Cooling

Matter generally exists in three states: solid, liquid, and gas. These phase changes are closely linked to the process of absorbing or releasing heat, and refrigerators also operate using these physical principles.
For example, when you wipe your skin with an alcohol swab before getting an injection, it feels instantly cold. This is because the liquid alcohol absorbs heat from its surroundings as it evaporates into a gas. The phenomenon of heat being removed during evaporation is called the heat of vaporization, and refrigerators actively utilize this principle as well.
The Second Law of Thermodynamics states that in an isolated system, entropy either increases or remains constant; in everyday terms, this can be understood as “heat naturally flows from a higher temperature to a lower temperature.” A classic example of this is the phenomenon where, when hot water and cold water are mixed, their temperatures eventually become similar over time.
Matter is composed of molecules, and its state changes depending on the arrangement and kinetic energy of these molecules. When molecules are packed very tightly together, they form a solid; when they move with a certain degree of freedom, they form a liquid; and when the distance between molecules increases significantly and their motion becomes more vigorous, they form a gas. When a substance absorbs heat, the motion of its molecules becomes more vigorous, causing a phase change from solid to liquid or from liquid to gas; conversely, when it releases heat, it changes from gas to liquid or from liquid to solid.

Components and Operating Principles of a Refrigerator

The core of a modern refrigerator is the vapor-compression refrigeration cycle, which uses a refrigerant. In this process, the refrigerant repeatedly cycles between liquid and gas states, transferring heat from inside the refrigerator to the outside. The main components consist of a compressor, a condenser, an expansion device (capillary tube or expansion valve), and an evaporator.
First, the compressor compresses the gaseous refrigerant to high pressure, bringing it to a high-temperature, high-pressure state. During compression, the refrigerant’s temperature rises significantly, and this heated refrigerant moves to the condenser.
In the condenser, the refrigerant releases heat to the outside air.
As the refrigerant loses heat, it condenses from a gas to a liquid; this is why the back or sides of the refrigerator may feel warm or hot. This indicates that heat drawn from inside the refrigerator is being released to the outside.
The high-pressure liquid refrigerant that has passed through the condenser experiences a sharp drop in pressure as it passes through the capillary tube or expansion valve. This process is driven not simply by Bernoulli’s principle, but rather by the pressure reduction that occurs as the refrigerant passes through the expansion device. The refrigerant, now at a lower pressure, is in a state where it can easily evaporate even at low temperatures.
The refrigerant then moves to the evaporator, where it evaporates from a liquid to a gas. During this process, the refrigerant absorbs the heat required for evaporation from the air inside the refrigerator, resulting in a lower internal temperature. The cooled air circulates throughout the refrigerator and freezer compartments, keeping food fresh.
Once the evaporation process is complete, the refrigerant returns to the compressor in its gaseous state, and the cycle repeats. Because this refrigerant cycle continues, the refrigerator is able to maintain a constant low temperature inside.

Summary and Significance

Refrigerators have evolved from ancient natural storage techniques into sophisticated cooling devices that utilize modern refrigerant circulation technology. The combination of refrigerant circulation—which harnesses the absorption and release of heat resulting from changes in the state of matter, as well as changes in pressure—has made it possible to keep food fresh for extended periods.
Today, refrigerators have become indispensable household appliances, playing a crucial role in enhancing food safety and distribution efficiency. Recently, to improve energy efficiency and reduce environmental impact, there has been ongoing development of eco-friendly refrigerants with low global warming potential (GWP), high-efficiency compressors, and artificial intelligence (AI)-based temperature control technologies. In the future, refrigeration technology will continue to evolve toward greater efficiency and environmental sustainability, and these technological innovations will serve as a vital foundation for making our lives more convenient and sustainable.