Methods of Refrigeration.pdf

Removing undesirable heat from one item, substance, or area and transferring it to another is known as refrigeration, sometimes known as chilling. The temperature can be reduced by removing heat, which can be accomplished by the use of ice, snow, cooled water, or mechanical refrigeration.

1. Methods of Refrigeration
May 9, 2023admin
Refrigeration
Removing undesirable heat from one item, substance, or area and
transferring it to another is known as refrigeration, sometimes known as chilling.
The temperature can be reduced by removing heat, which can be
accomplished by the use of ice, snow, cooled water, or mechanical
refrigeration.
Methods of Refrigeration
There are three types of refrigeration techniques: thermoelectric, cyclic, and
non-cyclic.
Non-cyclic refrigeration
These techniques allow for the sublimation of dry ice or the melting of ice to
achieve refrigeration. These methods are utilised in laboratories and
workplaces for small-scale refrigeration or portable coolers.
Due to its constant melting point of 0 °C (32 °F), ice is a powerful cooling
agent. Ice requires 333.55 kJ/kg (or around 144 Btu/lb.) of heat to melt. Foods
kept at this temperature or a little higher have a longer shelf life. Dry ice, or
solid carbon dioxide, is another type of refrigerant. At a temperature of -78.5
°C (-109.3 °F), it sublimes directly from the solid to vapor phase since it has
no liquid phase at normal atmospheric pressure. For keeping items at low
temperatures throughout the sublimation process, dry ice works well.
Cyclic refrigeration
This consists of the thermodynamic power cycle and the refrigeration cycle,
where heat is transferred from a low-temperature area or source and rejected
to a high-temperature sink with the aid of external effort. Heat is given to the
engine during the power cycle from a high-temperature source, with some of
the heat being utilized to generate work and the remainder being rejected to a
low-temperature sink. This complies with the second rule of thermodynamics.
A refrigeration cycle explains the alterations that the refrigerant experiences
as it travels through a refrigerator, alternately absorbing and rejecting heat. It
is used to describe the “process” of refrigerant flow through an HVACR unit,
whether it be a packaged or split system, when it comes to HVACR work.

2. Naturally, heat moves from hot to cold. Heat is transferred from a lower
temperature heat source to a higher temperature heat sink in order to chill a
dwelling area or storage area. Insulation is utilized to lessen the effort and
energy needed to lower the temperature in the cooled room and keep it there.
Said Carnot mathematically outlined the refrigeration cycle’s operation as a
heat engine in 1824. Although absorption heat pumps are employed in a small
number of applications, the reverse-Rankine vapor-compression refrigeration
cycle is the most used form of refrigeration system.
The following categories apply to cyclic refrigeration:
1. Vapor cycle
2. Gas cycle
The following categories apply to cyclic refrigeration:
1. Vapor compression refrigeration
2. Vapor absorption refrigeration
Vapor-compression cycle
Most home refrigerators as well as several huge commercial and industrial
refrigeration systems employ the vapor-compression cycle.

An analysis of the cycle’s thermodynamics may be done using the diagram. A
circulating refrigerant, such Freon, enters the compressor during this cycle as
a vapor. The vapor is compressed at constant entropy from point to another

3. point , and it leaves the compressor superheated. The superheated vapor
goes via the condenser, which first cools and eliminates the superheat before
condensing the vapor into a liquid by removing more heat at constant
pressure and temperature from point through and on to another point . The
expansion valve, also known for the throttle valve, is where the liquid
refrigerant travels between points . Here, its pressure suddenly drops,
triggering flash evaporation and auto-refrigeration of, generally, less than half
of the liquid refrigerant.
The chilly air (from the refrigerated compartment) is then blasted by a fan
through the evaporator coil or tubes, where the cold liquid-vapor combination
subsequently passes before being totally vaporized. The thermodynamic cycle
is finished when the refrigerant vapor that results goes back to point at the
compressor inlet. The reasoning above is based on a perfect vapor-
compression refrigeration cycle and ignores phenomena that may occur in
practice, such as frictional pressure loss in the system, a small amount of
thermodynamic irreversibility during the compression of the refrigerant vapor,
or (if any) less-than-ideal gas behavior.
The venerable “Perry’s Chemical Engineers’ Handbook” provides more details
on the construction and operation of vapor-compression refrigeration systems.
Vapor absorption cycle
The vapor absorption cycle using water-ammonia systems was well-liked and
widely used in the early years of the 20th century, but after the invention of the
vapor compression cycle, it lost a lot of significance due to its low coefficient
of performance (which was only about one fifth that of the vapor compression
cycle). Nowadays, the vapor absorption cycle is only employed when waste
heat, solar heat, or a lack of energy are all available.

4. The mechanism used to increase the pressure of the refrigerant vapor differs
between the absorption cycle and the compression cycle. The compressor is
replaced in the absorption system by an absorber that disperses the
refrigerant in a suitable liquid, a liquid pump that increases pressure, and a
generator that, upon the addition of heat, pushes the refrigerant vapor from
the high-pressure liquid. The liquid pump has some work to do, but for a given
amount of refrigerant, it is far less than what the compressor has to do during
the vapor compression cycle. A proper blend of refrigerant and absorbent is
utilized in an absorption refrigerator. The most popular combinations are water
(absorbent) and lithium bromide (refrigerant), as well as ammonia (refrigerant)
and water (absorbent).
Gas cycle
The refrigeration cycle is known as a gas cycle when the working fluid is a gas
that is compressed and expanded but does not change phase. Most
frequently, this working fluid is air. The hot and cold gas-to-gas heat
exchangers in gas cycles are equivalent to the condenser and evaporator in a
vapor compression cycle since condensation and evaporation are not
envisaged in gas cycles.
Because the gas cycle uses the reverse Brayton cycle rather than the reverse
Rankine cycle, it is less effective than the vapor compression cycle. Due to
this, the working fluid does not absorb and emit heat at a steady rate. The
cooling effect in the gas cycle is equal to the product of the gas’s specific heat
and its temperature increase at the low temperature side. Therefore, a gas

5. refrigeration cycle would need a high mass flow rate and be bulky for the
same cooling load. Air cycle coolers are no longer often employed in
terrestrial cooling equipment due to their reduced efficiency and greater mass.
On gas turbine-powered jet aircraft, however, the air cycle machine is
particularly prevalent because compressed air is easily accessible from the
compressor portions of the engines. The cooling and ventilation systems on
these jet aircraft also pressurize the cabin.
Thermoelectric refrigeration
The Peltier effect is used in thermoelectric cooling to produce a heat flux at
the intersection of two types of materials. This effect is frequently used to cool
electrical parts and tiny instruments, as well as in portable coolers for
camping.
Magnetic refrigeration
A cooling method based on the magnetocaloric effect, a characteristic of
magnetic materials, is known as magnetic refrigeration, sometimes known as
adiabatic demagnetization. A paramagnetic salt, such as cerium magnesium
nitrate, is frequently used as the refrigerant. The electron shells of the
paramagnetic atoms serve as the case’s active magnetic dipoles. The
refrigerant is exposed to a high magnetic field, which causes the refrigerant’s
numerous magnetic dipoles to align and lowers the entropy of these degrees
of freedom. The heat generated by the refrigerant as a result of its loss of
entropy is subsequently absorbed by a heat sink. The magnetic field is
subsequently turned off and thermal contact with the heat sink is severed,
insulating the system. As a result, the refrigerant’s temperature drops below
that of the heat sink. This enhances the heat capacity of the refrigerant.
Applications have thus far been restricted to cryogenics and research since
few materials have the necessary characteristics at ambient temperature.
Other methods
Air cycle machines used in aero planes, vortex tubes used for spot cooling
when compressed air is available, and thermoacoustic refrigeration, which
uses sound waves in a pressurized gas to promote heat transfer and heat
exchange, are further ways of refrigeration.
Unit of refrigeration

6. The cooling capacity of residential and commercial refrigerators may be
expressed in kJ/s or Btu/h. In the US, commercial refrigerators are often rated
in tones of refrigeration, although elsewhere they are measured in kW. One
short tone of water may be frozen at 0 °C (32 °F) in 24 hours using one tone
of refrigeration capacity. Considering that
Heat of fusion, or latent heat of ice, is equal to 333.55 kJ/kg 144 Btu/lb.
A short tone weighs 2000 pounds.
Heat extracted is equal to 2000(144)/24 hours, 288000 BTUs, 12000 BTUs
each hour, and 200 BTUs every minute.
200 Btu/min refrigeration is 3.517 kJ/s or 3.517 kW.
The rate of heat removal necessary to freeze a metric tone (i.e., 1000 kg) of
water at 0 °C in a 24-hour period is 1 tone of refrigeration, which is a
considerably less frequent term. A tone of refrigeration requires 13,898 kJ/h or
3.861 kW based on the heat of fusion being 333.55 kJ/kg. One tone of
refrigeration is 10% greater than one tone of refrigeration, as can be shown.
The majority of household air conditioning units have a 1 to 5 tone refrigerated
capacity range.
The 4 Main Refrigeration Cycle Components
All of us have been there. You are happily greeted by a wall of chilly air as
soon as you enter on a hot day. For that break, you may thank the
refrigeration cycle. Although there are many different ways to heat and cool
things, the fundamental purpose is still the same and is utilized in some way
by numerous different processes and businesses. The purpose of a
refrigeration cycle is to absorb and reject heat, to put it simply. You can only
remove heat, as any HVAC instructor would forcefully point out, thus you can’t
create cold. By directing heat away from the region you wish to chill, the
refrigeration cycle—also referred to as a heat pump cycle—can be used to
achieve that goal. This is done by cycling through a cycle of compression and
expansion to alter the pressure of the working refrigerant (air, water, synthetic
refrigerants, etc.).
Of course, that’s not the whole image, but it conveys the general notion. Let’s
now discuss the tools used to carry out that task. There are undoubtedly other
aspects in the majority of loops, but most people concur that a basic cycle
consists of the following four core components:
 The compressor

7.  The condenser
 The expansion device
 The evaporator
The compressor
Compression is the first step of refrigeration, and a compressor is the piece of
equipment used to increase the working gas’s pressure. Low-pressure, low-
temperature refrigerant enters the compressor and exits as high-pressure,
high-temperature gas.
Types of compressors
Due to the variety of mechanical methods that may be employed to create
compression, a variety of compressor designs are now used in HVAC and
refrigeration systems. There are other instances, but a few well-liked options
include:
 Reciprocating compressors
 Scroll compressors
 Rotary compressors
The condenser
The condenser, sometimes referred to as the condenser coil, is one of the two
different types of heat exchangers utilized in a basic refrigeration loop. High-
temperature, high-pressure, vaporized refrigerant from the compressor is
used to fuel this component. Until it condenses into a saturated liquid state,
also known as condensation, the condenser removes heat from the heated
refrigerant vapor gas vapor.
When the refrigerant condenses, it becomes a high-pressure, low-temperature
liquid, at which time it is directed towards the expansion device of the loop.
The expansion device
There are several distinct designs for these parts. Fixed orifices, thermostatic
expansion valves (TXV) or thermal expansion valves , and the more
sophisticated electronic expansion valves (EEVs) are common layouts.
However, regardless of arrangement, an expansion device’s duty is to lower
pressure once the refrigerant exits the condenser. Some of the refrigerant will
start to boil fast as a result of the pressure reduction, resulting in a two-phase
mixture.

8. Flashing is the name for this abrupt phase shift, which sets up the evaporator,
the next piece of machinery in the circuit, to carry out its intended purpose.
The evaporator
The evaporator, like the condenser, is called for its primary purpose and is the
second heat exchanger in a typical refrigeration circuit. It serves as the
“business end” of a refrigeration cycle since it absorbs heat in a similar
manner to how air conditioning works. This happens when air is forced
through the evaporator’s fins by a fan. The refrigerant, which enters the
evaporator as a low temperature liquid at low pressure, absorbs the heat from
the room in question and cools the air as a result.
The process then resumes when the refrigerant is returned to the compressor.
And that’s basically how a refrigeration loop operates. Give us a call if you
have any questions concerning the refrigeration cycle or any of its parts,
including how they function. Since over a century ago, we have been assisting
clients in maximizing the performance of their HVAC and refrigeration
equipment.
Home and consumer use

Safer refrigerators for residential and consumer use became feasible with the
development of synthetic refrigeration systems, which are primarily based on
the chemical chlorofluorocarbon (CFC). These CFC refrigerants, as well as
subsequent hydrochlorofluorocarbon (HCFC) and hydrofluorocarbon (HFC),
are referred to as “Freon,” a trademark of the DuPont Corporation. These
refrigerants, which were created in the late 1920s, were thought to be safer
than the routinely employed refrigerants of the time, such as methyl format,

9. ammonia, methyl chloride, and Sulphur dioxide. The goal was to supply
residential refrigeration equipment while protecting the tenants’ life. These
CFC refrigerants provided the solution.
Reference
 https://www.newworldencyclopedia.org/entry/Refrigeration
 https://www.britannica.com/technology/refrigeration