Have you ever felt the back of the refrigerator? Or the gasket that lines it? If you have, you would know how warm it is to touch. But why would a piece of equipment designed to keep your food fresh and cold heat up?
An interesting fact about the refrigerator is that it does not produce cold air. Instead, it collects warm air and gets rid of it. If you are wondering how that works, it works on certain fascinating scientific principles which this article aims to elaborate upon.
After reading this, you will gain an insight into the mechanism that governs the working of a refrigerator and the different components of a refrigerator. You can enhance your knowledge about the various refrigerant gases used and the shift in the types of refrigerants that have occurred over the years.
Some of the recent innovations that improve the efficiency of the refrigerator will also be discussed. You will also learn why it is advisable to occasionally defrost your freezer and how it impacts the durability of the refrigerator.
A basic model of refrigerator has been considered. However, the principles apply to all the models.
What Does a Refrigerator Do?
Food cannot stay longer without getting spoilt when kept at room temperature. It is the ideal temperature for the micro-organisms to multiply rapidly and bring about spoilage of food. The low temperature inside a refrigerator provides an environment in which the bacteria cannot thrive. It is mostly in the case of food items containing moisture and cooked food.
In addition to preventing spoilage and wastage of leftovers, refrigeration also slows down the aging or ripening of many fruits and vegetables caused by the enzymes naturally present in the food. Freezing is also a method of preservation. Frozen food and other food items stored in a deep freezer can last for months.
Refrigeration renders the food safe for consumption by preventing the micro-organisms from secreting harmful toxins into the food.
What is a refrigerant?
A refrigerant means a fluid that is capable of turning itself into a gaseous state on boiling and a liquid state on being condensed. Water is also fluid, but it is not efficient enough to carry out its functions continuously in a repetitive cycle. Hence, the refrigerants commonly used in refrigerators and air conditioners are gases that are legally prescribed and do not have a detrimental effect on the environment.
Until the late 1900s, chlorofluorocarbons were in use. However, it had a negative impact on the environment and contributed significantly to ozone gas depletion. In recent times, these toxic gases have been replaced with cold gases such as HFCs, a mixture of hydrogen, fluorine, and carbon, comparatively a much better and sustainable option.
Today a range of gases are used, such as Tetrafluoroethene, Freon, and Butane.
How Does a Refrigerant Work?
Refrigerant is the backbone of the refrigerating cycle. It is the agent who conducts the whole process. It is a gas that is converted into a liquid state as it passes through various compartments and finally obtains its gaseous state as it completes an entire cycle. It, in turn, is responsible for transferring the internal heat to an outer material and keeping the interiors cold.
Components of a refrigerator
A compressor works like a pump that aids the flow of the refrigerant. It is done by bringing about a change in the pressure and temperature of the refrigerant. It increases the pressure of the refrigerant before it enters the condenser. After completing a whole cycle, the refrigerant in its vaporized form again enters the compressor, and the exact mechanism is repeated. It forms a crucial part of the refrigeration cycle.
Reciprocating, Rotary, and Centrifugal are the different types of compressors that are generally used in refrigerators meant for domestic purposes.
Just like the name suggests, the primary function of the condenser is to change gas to liquid. In this case, it is to change the refrigerant gas to liquid form. The refrigerant flows through the condenser, transferring the heat to the air in the process.
This way, it gets rid of the heat inside the refrigerator and keeps the interior cool.
The evaporator is located right behind the freezer. Contrary to the condenser, the evaporator turns liquid into gas. While a condenser helps in getting rid of the heat, the evaporator helps in trapping this heat that needs to be gotten rid of, ultimately keeping the food items cold. Both the condenser and evaporator are primarily responsible for cooling.
There are two types of evaporators that are used-
- Forced Convection Evaporator
The liquid is cooled down by the action of force. A fan or a pump can be used to achieve the same.
- Natural Convection Evaporator
It works on the principle that there is a difference between the density of cold and hot water. Hence, the liquid gets cooled down naturally without the use of force.
It is a coiled copper tube. It is used as a throttling device, which means it controls the flow of the refrigerant. There is a change in pressure as the refrigerant moves from the condenser to the capillary tube and then further. Its primary function is to prevent load on the compressor. When the system stops for some reason, the capillary ensures uniform pressure on both the ends of the coil and the compressor. It allows the compressor to start re-functioning without taking many loads due to high pressure.
A Thermostat is used to control the temperature, also known as a cold control. The thermostat either supplies current to the compressor or cuts off the current supply depending on the internal temperature.
They are also known as cooling fans since they provide an outlet for hot air. To ensure proper airflow within the refrigerator, a ventilation system is needed. The ventilation in a refrigerator also works quite similarly to a ventilation hood or fan in a kitchen. It helps to keep the internal temperature of the refrigerator low so that the system can work smoothly without consuming too much power.
It acts as a passage as the refrigerant traverses from a high-pressure area to a low-pressure area. It regulates the pressure of the refrigerant to enable the refrigerant to expand and get converted to a gaseous state from a liquid state. When the pressure is low, the liquid refrigerant is cold. In this state, it moves towards the evaporator, where it is vaporized.
Mechanism of a refrigerator
Refrigerator works on an elementary principle. Think of a cup of tea left on the kitchen counter. Eventually, it cools down, but that would be from a layman’s perspective. In reality, the cup transfers the heat to a different medium, such as the table or the air around. A refrigerator also functions similarly. The fridge does not emit cool air to keep the food cold, but instead, gets rid of the heat. The mechanism has been discussed in the subsequent paragraphs.
When a liquid evaporates, it absorbs heat. When a liquid condenses, it releases heat.
Throughout the whole process, a cold liquid known as the refrigerant moves around and takes away the heat. Refrigerant is a high-pressure liquid.
A refrigerator makes use of a throttling device known as the capillary tube. When the refrigerant enters the capillary tube, it witnesses a pressure drop. Along with the pressure, the temperature also falls from 45°C to -20°C. This is necessary to bring down the boiling point of the liquid. The refrigerant liquid then expands, cools, and starts evaporating while passing through a body that absorbs heat until it is fully converted to vapor. Evaporators are fitted with fans to be able to maintain different temperature levels.
Now, for the cycle to repeat itself, the pressure of the refrigerant has to be increased. For this purpose, a compressor is used. The compressor along with increasing the pressure of the refrigerant also compresses gas which causes a temperature rise.
The refrigerant is now a high-pressure vapor that needs to be converted back to its liquid state.
A condenser condenses the liquid and results in a drop in the temperature of the refrigerant. It is a heat exchanger which is located outside the refrigerator, enabling it to liberate the heat to the surrounding air.
Once the refrigerant has assumed its former state, of a high-pressure liquid, it is ready to repeat the cycle.
In theory, this might seem very smooth and efficient but practically a lot of issues could develop during the cycle. For instance, when the moist air that is circulated comes in contact with the cold evaporation coil, there is frost formation around the coil. In such a case, it is advisable to defrost the refrigerator. Otherwise, it could prevent heat transfer, making the refrigerator inefficient.
The refrigerator also has a “command center” known as a thermostat. It is responsible for maintaining uniformity in temperature. The thermostat first gauges the temperature of the air inside the refrigerator and then controls the flow of current to the compressor. It then performs other functions and helps in maintaining the desired temperature. If the inside air is too warm, the thermostat supports the flow of current, which would further indicate the same to the compressor. On the other hand, if the inside temperature is desirably low, the thermostat cuts off the current to the compressor.
Previously, single-speed technology compressors were used. Such a compressor turns off immediately after the inside temperature reaches an optimum level. It restarts only when the temperature rises above a certain level. However, these days digital inverter compressors are used. They control temperature efficiently and are durable.
To conclude, that was a comprehensive account of the mechanism of a refrigerator.
Next time when your refrigerator acts up, you can troubleshoot. It will enable you to have a better understanding of the problem. When your mechanic gives you a list of parts to be replaced, you can compare various alternatives and make an intelligent purchase. A responsible consumer always makes informed choices. While buying a refrigerator or any other electronic appliance, always go for the one that is sustainable in the long run.