Refrigerants flow patterns - Open Loop , Closed Loop & Vapour absorption system

Concept of refrigeration

Refrigeration is a process in which work is done to move heat from one location to another. The work of heat transport is traditionally driven by mechanical work, but can also be driven by heat, magnetism, electricity, laser, or other means.

Transporting perishable cargo has always required special thought, equipment and care. Refrigeration is required to prevent natural decomposition. A common agent of decomposition in chemistry is heat, which can reduce both inorganic and organic compounds to their natural constituents. Refrigeration is applied to goods to minimize this process. In the case of fruit cargo (living cargo), the cooling process is used to reduce the metabolic processes that would normally lead to ripening. Advances in technology have now led to reefer carriage in “inert atmospheres”, commonly known as Controlled Atmosphere (CA) carriage.

Below are details of most commonly used refrigerants flow pattern in a refrigeration process

open loop system

When water is kept in an open container, heat is lost to the ambient air through evaporation and cooling. In humans, sweating is a means of temperature regulation. Evaporation of sweat from the surface of the skin has a cooling effect due to the latent heat of evaporation of water. It could be said that human sweat is acting as a refrigerant.

In tropical countries where refrigerated trucks are not frequently used, ice may be used to cover baskets of seafood that are transported by rail over short distances. The ice acts as a refrigerant, protecting and preserving the seafood for a short time by preventing direct contact with atmospheric heat. As the ice melts, the water flows off and finally evaporates. This is known as an open loop system, where the refrigerant is used only once. Water and dry ice are commonly used as refrigerants in open loop systems.

Closed Loop System

Ice is inexpensive, easy to manufacture and does not damage the environment. However, not all refrigerants are like this. Some of them are expensive, not easily available and may harm the environment, so they are not released into the atmosphere but are recycled, returning them to their original state and so restoring their original heat absorbing properties. This is known as a closed loop system. Most refrigeration installations used today are closed loop system.

Vapour Absorption and Vapour Compression Systems

There are two types of refrigeration systems: the vapour absorption type and the vapour compression type.

Vapour Absorption Systems

This technology was invented in the middle of the nineteenth century by the Carré brothers. During the years of cheap electricity this technology was not used but it has made a comeback as electricity costs have risen. Vapour absorption systems are not used onboard ships, but are commonly found onshore in places such as hotels where there is a limit to the maximum demand a consumer can draw from the power grid at any one time. These systems limit the effect of the momentary peaks in power consumption caused by the high starting current required by heavy machinery. It is more suitable for air conditioning than refrigeration. A unit using this technology is called a Vapour Absorption Machine (VAM).

Learn more on vapour compression cycle

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Reefer cargo
Why refrigerate?
We choose to refrigerate commodities such as fruits and vegetables because we want to prolong their “practical shelf life” – the time from harvest until the product loses its commercial value.

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