The Refrigeration Cycle

Refrigeration allows food to stay fresher longer, extends shelf life in homes, and is essential for transporting temperature-sensitive products. It has also sparked new settlement patterns by allowing people to live farther away from natural food sources.

The refrigerator door is usually the warmest area, so use it for items that can handle warmer temps like condiments, salad dressing, and butter. Milk and eggs belong in the coldest part of the fridge. Click here at to learn more.

refrigerationRefrigeration Cycle

The Refrigeration Cycle is the process by which the refrigerant passes through all of the components of a refrigeration system – Compressor, Condenser, Expansion Valve, and Evaporator in a cyclic manner to achieve cooling effects. It is also referred to as the heat pump cycle or absorption cycle. Refrigeration cycles are based on the thermodynamic principle that the transmission of heat flow from one place at a lower temperature to another at a higher temperature involves continuously circulating, evaporating, and condensing a fixed quantity of refrigerant in a closed loop.

The refrigeration cycle begins with the compressor, which takes in liquid refrigerant and pumps it into a pressurized gas state. As the pressure increases, so does the temperature. The ideal state for changing from liquid to gas is a point known as the boiling point. It requires a lot of energy to induce the change from liquid to gas, and from gas back to a liquid. This is why the energy required to maintain a certain refrigeration temperature is proportional to the square of the pressure.

As the refrigerant enters the condenser it starts to decompress. As a result, it moves to a higher temperature and lower pressure. This is where the latent heat of vaporization is released. The vapor then goes to the evaporator where it changes its phase again from gas to a low-pressure liquid. The liquid now absorbs heat from the surrounding air which is blowing over it through a fan and as a result, it expands and releases the latent heat of vaporization.

Once it is a hot low-pressure liquid, it moves to the expansion valve where it is restricted and lowered in pressure by the resistance of the valve. The low-pressure liquid now moves to the evaporator and starts to evaporate again as it absorbs heat from the adjacent cooling coil. Its final state is a cold low-pressure vapor that is delivered to the customer’s premises for cooling.

There are many different types of compressors ranging from the reciprocating to the screw or centrifugal type. Each has a specific function but the core of the system is always the same. The same can be said for the evaporator and the expansion valve/metering device. There are also various designs of evaporators, from the simple bare pipe design to finned or even with fans passing over them.


The compressor is the heart of any refrigeration system based on a vapor compression cycle. The compressor takes the refrigerant in liquid form and converts it into a gas by spinning it through an impeller that increases its speed as it spins. As the speed of the refrigerant increases, it gains kinetic energy, which is then converted into pressure by sensors inside the compressor. Once the pressure reaches a set point, the system will then pump the high-pressure refrigerant gas over to the condenser to start a new cycle of cooling.

There are different types of compressors used in refrigeration and air conditioning. They can be split into two groups – positive-displacement (piston, rotary) and non-positive-displacement (centrifugal). In addition to this, compressors are also classified based on their mechanism for fluid compression. Piston compressors use pistons and cylinders to provide the compressive force, whereas rotary compressors use one or more rotating vanes to increase volume.

Once the system is running, a power source or electric motor will turn on and operate the compressor’s crank. This will cause the piston to start moving up and down in the cylinder, gradually increasing the pressure of the trapped R22 refrigerant. As the piston reaches the bottom of the cylinder (point A), it will stop moving because the LP valve has closed and the LP pressure equilibrates with the inlet pressure.

Many compressors are designed to be staged, meaning that the fluid is compressed in several steps or stages, each with a higher discharge pressure. This can be done to improve efficiency and reduce noise levels, as well as make it possible to store the compressed gas at a lower temperature.

Some systems use hermetic compressors, which are complete with a casing that covers both the compressor and drive motor, protecting them from the elements. However, this can make them harder to repair and is not suitable for certain refrigeration applications. Rotary-screw and rotary-vane compressors, on the other hand, are easier to get into for repairs. They are usually hermetic but can be semi-hermetic, depending on the design.


The condenser is another heat exchanger, but it’s a little different than the compressor. Its function is to cool the refrigerant gas so it can be converted back into a liquid state. Its ability to do so allows it to reject any superheated vapor that might have made its way from the compressor (it’s important to remember that a compressor acts like a pump, but pumps move liquids, not gases). This prevents any of that liquid from making it back into the compressor and doing some serious damage.

A common analogy to explain this is to think of steam condensing into water. As the tiny molecules of water get closer together they slow down and lose their heat energy. Once they do that, they coalesce and turn into water. Likewise, when the refrigerant gas is cooled enough it will convert back to a liquid state.

In a refrigeration system, the condenser is one of two heat exchangers that make up the evaporator/condenser cycle and is also one of the most important parts of any air conditioning or refrigerator system. It’s located on the back of your refrigerator and is likely covered in a thick layer of dust that needs to be cleaned occasionally with a feather duster.

Your refrigerator’s condenser is essentially a heat exchanger that does its work in the air of your home. It does so by using a series of coils to remove heat from the blowing air that passes over it. These coils can be either finned tube or flat panel types depending on the type of refrigerator you have.

When it comes to keeping your refrigerator in top condition, the most important step is regular maintenance by a professional. You should not attempt to do this yourself since it is likely to cause some damage to the components. Also, it’s best to avoid running your fridge when it’s raining outside since this could cause moisture to enter the condenser and lead to damage over time. Your professional will look at both your evaporator coil and condenser to ensure they are in good shape, have no signs of damage, and are functioning properly.


The evaporator is an important part of the refrigeration cycle. It is where the liquid refrigerant evaporates into a gas, similar to what happens when you boil water and it changes to steam. It also acts as a heat exchanger that transfers heat from the substance being cooled to the evaporating refrigerant.

The liquid refrigerant exits the condenser at high pressure and enters the evaporator at low pressure. The evaporator is either forced convection or natural convection. Forced convection uses a fan to move the liquid being cooled over the evaporator, while natural convection simply flows to the evaporator due to differences in density between the cool and warm liquids. There are also different types of evaporator construction including bare tube, plate surface, and capillary tube. Bare tube and plate surface evaporators have the entire evaporator in contact with the evaporating refrigerant while capillary tube evaporators have a special tube that is in contact with the evaporating refrigerant.

Once the sub-cooled liquid refrigerant enters the evaporator at a low temperature it will expand through the expansion valve. This causes the liquid to form flash gas which quickly vaporizes. The vapor absorbs heat from the warmer secondary fluid and the vapor begins to rise. When the vapor reaches saturation at full evaporation the system is at the desired temperature.

A proper evaporator design is important for the entire refrigeration process. If the evaporator has poor heat transfer or not enough space for the vapor to reach saturation then little refrigeration will be achieved. Insufficient heat transfer is usually caused by dirty or iced-up evaporator coils, inoperable fan motors, improper airflow, or a defective metering device.

If the metering device is not functioning correctly it may not supply enough or too much refrigerant to the evaporator coil causing improper superheat values. Generally, a low-temperature application will require 4deg to 6deg of superheat and a medium-temperature system will require 6deg to 8deg of superheat. This is why a good maintenance plan is so important for a successful refrigeration system.