Refrigeration

Graphical illustration of refrigeration process

Refrigeration is defined as the process of removing heat to reduce the temperature of a certain space.  This is based on the idea that when heat is not present in any place or any substance, what is left is only its "absence," which is known as “cold.”

Yes, cooling effect produced by any refrigerating equipment is a result of the absence of heat.   In other words, to produce low temperature in a particular place, heat must be removed rather than adding any low temperature substance on it.

Removing heat is not as easy as removing water from a certain surface when it spills. This is due to the fact that heat is something that is not tangible. In fact, the art of handling heat to be able to remove it involves some principles and complex processes. This is the main concern and field of study in refrigeration technology.

Technically, refrigeration is the process of heat absorption and extraction, where heat is being absorbed from the place where it is not wanted, and extracted to the place where it can do no harm. Heat is always present everywhere, it may be useful for some reasons, at the same time, it can also create undesirable effect if not controlled.

Water absorption

The basic idea to understand refrigeration is to imagine a portion of water that spills into the floor and makes the floor wet. To make the floor dry, we need to use any material that is water absorbent since no body can hold water with bare hands. This is called "absorbing medium" so that we can take that water out from the floor and purge it into some container or throw  to the place where it can do no harm.

In the above mentioned scenario, water plays the role of heat that is subject for absorption and extraction. When not removed, it may cause some danger or any unwanted effect.  The condition of having a wet floor may be similar to the presence of heat in a substance. When the floor becomes dry, or no more presence of water on it, the condition of being dry can represent the absence of heat in a substance where cooling takes place.

This is totally similar to how heat is being removed by heat absorption and extraction process. The only difference is that, water is visible while heat is not.

In refrigeration and air conditioning, heat may not be totally removed from a certain place. It is only controlled to attain required amount for some purposes. To be able to accomplish the heat absorption and extraction process, a certain amount of work must take place. This is done by mechanical processes or by the use of different mechanical components driven by electrical energy. This comprises the whole refrigeration and air conditioning systems in many different applications today.

Mechanical Refrigeration

As mentioned above, mechanical refrigeration is widely used today in all air conditioning and refrigeration systems.  The process of heat absorption and extraction is done by employing mechanical processes that does the work beyond human intervention. By the use of a fluid or substance that is highly heat absorbent, plus the effect of work done by mechanical components, heat are being handled properly and transferred from one place to another. This is further explained on the subject principles of refrigeration.

Refrigeration System

The term refrigeration system refers to the whole bunch of mechanical and electrical components that are put together to make the whole system works for the purpose of heat absorption and extraction.  From the term itself, system or unit means, composed of many sub-parts that are dependent from each other to do its role.

Mechanically, refrigeration system is just a loop of tubes, which is made of copper or any metals that withstands varying amount of pressure and temperature.  In that series of tubes, a heat absorbing agent called refrigerant is constantly circulating. This circulation of refrigerant as the heat absorption and extraction occurs is known as refrigeration cycle.

In that cycle, the refrigerant, which is a kind of fluid that has a boiling point lower than water undergoes constant chemical reaction as a result of presence and absence of heat. This changes its phase from vapor to liquid and vice versa, as it circulates in the system. The chemical change occurred on refrigerant can also be more understood on the subject 2 kinds of heat in this website.

To understand this process, we to need recall on some laws of gasses and the second thermodynamic principle that talks about how heat moves and its effect on fluids or any substance. These laws are the fundamental principles of refrigeration, which if not fully understood, will create confusion and difficulty in the field of servicing and maintenance of those systems.

4 Basic Parts of Mechanical Refrigeration System

Refrigeration and air conditioning systems in various designs and applications may be too complex to imagine if we take a look on the actual unit. But basically, there are only  four parts of the system that perform the whole process of heat absorption and extraction. These are the compressor, condenser, refrigerant flow control device, also known as metering device and evaporator.

Compressor - is a mechanical device driven by an internal electric motor that compresses vapor refrigerant from low pressure into high pressure. The compression effect also increases the temperature of the vapor refrigerant as it leaves the compression chamber via discharge line.

The increase in temperature of the vapor refrigerant creates temperature difference between that body and the outside air. This makes the heat from the compressed vapor leaves and move into colder body, which is the outside space.

Condenser – The word condenser originates from the word “condense,” which means, the change of phase of any gaseous substance into liquid. This is a result of the absence of heat that holds the vapor body. When heat leaves, any vapor substance will undergo chemical reaction and changes its state into liquid, called condensation process.

Inside the condenser, vapor refrigerant changes to liquid as the heat leaves the vapor body and move into the outside air. This is where the heat extraction process takes place as a result of mandatory heat transfer whenever there is a temperature difference between two bodies. Condenser is located after the discharge line of the compressor and is visible outside of any refrigerating and air conditioning equipment, directly exposed to the outside air.

Refrigerant Flow Control Device -   This part of the system is the key player for producing cooling effect. While the compressor compresses vapor refrigerant for the purpose of heat extraction,   this device, which is also known as metering device, controls the flow of liquid refrigerant for the purpose of heat absorption.

This is done by allowing the liquid refrigerant from the condenser to undergo a sudden low pressure by controlling its flow and subjecting it to sudden increase in volume. The small amount of liquid refrigerant that is being throttled by the metering device will occupy a larger space from where it previously flows. The decrease in pressure also decreases the temperature of the liquid refrigerant on that particular place in the system.

The decrease in temperature creates a temperature difference between the liquid refrigerant throttled by the metering device and the outside space of the tube. This allows the heat to flow from the outside surface of the tube to the liquid refrigerant inside the tube. The principle behind the  flow of heat from outer surface of the  tube to the refrigerant is explained on the second thermodynamic principle.

Evaporator – If in the condenser the liquid refrigerant changes its phase from vapor to liquid as a result of absence of heat, the complete reverse process occurs in the evaporator. Evaporator is part of the system where liquid refrigerant changes its phase into vapor as a result of the presence of heat. The presence of heat is a result of heat transfer that occurred between the outside space and the refrigerant.

As the heat leaves the surrounding air and moves into the inner part of the evaporator tube, heat absorption takes place and produces cooling on the outside space where evaporator is located. To make this process effective, evaporator must be confined and no other external source of heat must be allowed to enter into the evaporator room. This is the reason why refrigerator cabinets are thick enough and properly insulated to avoid heat transfer from outside.

Uses of Refrigeration

The idea of producing artificial cooling effect by the use or refrigeration process has a wide range of uses and applications.  Therefore, refrigeration  systems  are designed according to how it is being applied. This results to have variations of units designs from smaller to larger units. The following are the major uses of refrigeration that identifies  its unit design.

1. Food Preservation

Transport refrigeration units

Under food preservation, here comes transport refrigeration, or the use of refrigeration system for transporting perishable products.  This involves container van refrigeration and vessel refrigeration systems.

Container refrigeration could be either land based or sea based units. For land based container units, here comes reefer trucks and land based reefer vans.

Other forms of refrigeration units for food preservation purposes are those that are used in cold storage, commercial refrigeration units and domestic refrigeration systems.

2.    Air Conditioning

Air conditioning is sometimes misunderstood that is something totally independent from the field of refrigeration. This is due to some misconception about the term itself that could mean as something that is related only to refrigerators and freezers. Therefore, air conditioning may appear to be outside of its scope. To correct the misconception, it is important to understand that air conditioning is just one application of refrigeration.

If refrigeration is the process of removing heat in a certain space or place, in the field of air conditioning, the focus of removing heat are is the "air" or rooms, where people stay such as residential rooms, offices, hotels, malls and many other places where heat causes discomfort to human being. The main purpose is to provide human comfort by reducing  the amount of heat and by purifying the air.

3. Beverage Cooling

In many bottling companies, where products must be kept in a certain temperature for preservation,  refrigeration is the only way possible to control temperature on their storage rooms. Even when those bottled products are already distributed to retailers, the need for refrigerating equipment is still very important to maintain the lifespan of those products, until sold to consumers.

For the consumers, before drinking whatever beverage it might be, it could be  a beer, soft-drinks, a juice or just a bottled water,  it is always good if it is being cooled from any refrigerating equipment.

4. Ice Manufacturing

Ice skating

Ice could be used in many different purposes. From small gathering with drinking sessions, for making fruit shakes, fish preservation in some fishing boats, to ice skating in some malls.

In countries where temperature stays above zero during winter, ice must be produced artificially by the used of refrigeration.

Related Page: Air Conditioning