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