1. INTRODUCTION:
Today one cannot refuse the use of refrigeration system in our life, not
only in kitchen but also in shops, industries and commercial purposes.Today’s
compression refrigeration system
has given very
good performance. But refrigerants (Chlorofluorocarbons,
Hydrochloroflorocarbons) used in this systems are hazardous to the environment
and human life, because they react with very useful gas ozone (O3). Thus depletion of ozone layer is the main
problem in front of us.
Thermo-electric refrigeration system can
able to substitute vapor compression refrigeration system for small-scale
applicant and may result as solution of the problem above discussed.
COMPARISION WITH
CONVENTIONAL COOLING SYSTEM:
Thermo-electric cooling is described as
a solid-state method of heat transfer generated primarily through the use of
dissimilar semiconductor materials. To understand the cooling method, it is
first necessary to know how thermoelectric cooling systems differ from their conventional
refrigeration counterparts. Like conventional refrigeration, thermoelectric
obey the basic laws of thermodynamics. Both in result and principle, then,
thermoelectric cooling has much in common with conventional refrigeration
methods - only the actual system for cooling is different.
Perhaps the best way to show the differences in
the two refrigeration methods is to describe the systems themselves. In a
conventional refrigeration system, the main working parts are the evaporator,
condenser, and compressor. The evaporator surface is where the liquid
refrigerant boils, changes to vapor and absorbs heat energy. The compressor
circulates the refrigerant and applies enough pressure to increase the
temperature above ambient level. The condenser helps discharge the absorbed
heat into the ambient air. In thermo-electric
refrigeration, essentially nothing has changed. The refrigerant in both
liquid and vapor form is replaced by two dissimilar conductors. The cold
junction (evaporator surface) becomes cold through absorption of energy by the
electrons as they pass from one semiconductor to another, instead of energy
absorption by the refrigerant as it changes from liquid to vapor. The
compressor is replaced by a DC power source which pumps the electrons from one
semiconductor to another. A heat sink replaces the conventional condenser fins,
discharging the accumulated heat energy from the system. The difference between
the two refrigeration methods, then, is that a thermo-electric cooling system refrigerates without the use of
mechanical devices, except in the auxiliary sense, and without refrigerant.
2. BASICS OF THERMOELECTRIC
REFRIGERATION:
Thermo-electric refrigeration system
is based upon
the principle of thermo-electric
effect, which is observed first by Henrich Lenze in 1938. This effect is based
on different five laws, which are as stated below-
2.1 Seebeck effect:
“When two junctions
of a pair of two dissimilar metals maintained at different temperatures, there
is generation of e.m.f.”
Mr. Seeback conducted a
series of tests by
varying the temperatures of the junctions of various combinations of set
of materials. The e.m.f. Output was found to be:
D E µ D T
D E = µabD T
Where
µab= Seeback coefficient.
2.2 Peltier
effect:
“If direct current is passed
through a pair of dissimilar metals there is heating at one junction, cooling
at other depending upon material combinations.”
Q µ I
Q=pab. I
Where Q = rate of heating or cooling.
I = current passing through the
junction.
p = Peltier coefficient.
Early in the 19th
Century, Jean Peltier discovered that a refrigerating power is obtained by
passing current along a circuit containing dissimilar materials. Heat is absorbed at one junction of the two
materials and heat is released at the other junction. The transfer of heat is caused by the change
in electron energy levels when electrons access the conduction band as defined
by quantum physics. The conduction band
varies with each material which means that conducting electrons in some
materials are at a higher energy level than in other materials. When electrons pass down a circuit of
dissimilar materials, the electrons alternately extract energy or release
energy with each change in conduction band.
The desired refrigerating effect occurs when electrons move to a higher
energy level upon change of material. A
reverse effect also occurs where electricity is generated from a circuit of
dissimilar materials that are exposed to a temperature differential. This is the physical principle that forms the
basis of the thermocouple and is known as the Seebeck effect. The Peltier and Seebeck effects are
complimentary manifestations of the same physical phenomenon. Thermo-electric
power generation is also currently under research as a means of obtaining
electrical energy out of waste heat from steelworks and incineration plants,
automobile exhausts. A schematic diagram
of the electrical circuit that generates the Peltier effect and the electronic
mechanism of refrigeration is shown in Figure 2.
For most electrical conductors, viz. metals, the effect is too weak to
be useful. With metals, a weak Peltier effect
is overwhelmed by strong Ohmic heating and there is no net cooling effect.
2.3 Thomson
effect:
It
is reversible thermoelectric
phenomenon. “When a current passes through a single conductor having
temperature gradient has exhibited.”
2.4 Joulean
effect: “When the electric
current passed through a conductor, there is dissipation of electrical energy
in the form of heat.”
According to Joule it is
related as
qj = I2R
Where I= current
R=
electrical resistance
2.5 Conduction
effect:
“If the
ends of any
element are maintained
at different temperatures, there
is heat transfer
from hot end
to cold end ”
& it is related by
Qcond =
U (Th-Tl)
Where
U =
overall conductance
Th=high
temperature
Tl=low temperature
*Abram Ioffe and
co-workers discovered that some semi-conductors exerted a much stronger
Peltier/Seebeck effect and developed thermo-electric power modules that were
used to generate electricity in remote locations. In 1950, a co-worker of Ioffe, Lazar
Stilbans, developed the first recorded design of thermo-electric refrigerator
using bismuth telluride and related compounds to achieve a cabinet interior
temperature of –2.3 degrees Celsius inside a room temperature of 19 degrees
Celsius.
3.
WORKING OF THERMO-ELECTRIC
REFRIGERATION:
As shown in figure 3 two different materials are
connected by battery in which P-type region is connected to the positive
terminal and N-type to the negative terminal.
If
a current is passed trough them, the cooling is produced at one junction and
heat is produced at other junction. If Th is maintained at ambient
temperature, Tc will be lower at ambient temperature. It also to be
noted that which of the junction or ends will become cold or hot depends on
direction of flow of current.
From the analysis of all the effects it has
been found that coefficient performance
of system is –
COP= qc/energy supplied
= [µab I Tl-I2R/2-U (Th-Tl)]/
[µab (Th-Tl)
I+I2R]
Where µab= Seeback constant
I = Current passed
R= Electrical resistance
U= Overall conductance
Th= High temperature
Tl= Low temperature
Assumptions
made
for COP equation are:
1.
Heat transfer takes place
through the semiconductor at the ends only.
2.
No energy exchange
between the conductors through space separating them.
3.
Properties such as
conductivity resistance are invariant with temperature.
Theory
of Operation
The semiconductor materials are N and P type, and are so named
because either they have more electrons than necessary to complete a perfect
molecular lattice structure (N-type) or not enough electrons to complete a
lattice structure (P-type). The extra electrons in the N-type material and the
holes left in the P-type material are called "carriers" and they are
the agents that move the heat energy from the cold to the hot junction.
Heat absorbed at the cold junction is pumped to
the hot junction at a rate proportional to carrier current passing through the
circuit and the number of couples. Good thermo-electric
semiconductor materials such as bismuth telluride greatly impede
conventional heat conduction from hot to cold areas, yet provide an easy flow
for the carriers. in addition, these materials have carriers with a capacity
for carrying more heat.
Heat Sinks
The design of the heat exchanger is a very
important aspect of a good thermo-electric
system. The upper part of the diagram illustrates the steady-state
temperature profile across a typical thermo-electric
device from the load side to the ambient. If the heat sink is not capable of
rejecting the required Qs from the given system, the temperature of
the entire system will rise and the cold junction temperature will increase. If
the thermo-electric current is
increased to maintain the load temperature, the COP (Coefficient of
Performance) tends to decrease. Thus, a good heat sink contributes to improve
COP. Energy may be transferred to or from the thermo-electric system by three basic modules: conduction,
convection, and radiation. The values of Qc and Q1 may be
easily estimated; their total along with the power input gives Qs,
the energy the hot-junction heat sink must dissipate.
Refrigeration
based on the Peltier effect:
It is obtained by
arranging a series of thermo-electric
cells in a horizontal array which is then encased in plates made of an
electrical insulator. Each thermo-electric cell consists of a pair
of dissimilar semi-conductors which are connected by electrical conductors at
either end. The requisite dissimilarity in semi-conductors is obtained not only
by using dissimilar materials, but also by using different dopants. The tablet shaped component that is produced
by this means is called a module or Peltier module. The passage of electric current through the
module causes one of the plates to become hot and the other to become
cold. When there is adequate cooling to
the heated plate, the opposing plate can reach a low temperature or extra heat on
a continuous basis. Figure 4 shows a
schematic diagram of a Peltier module and how it transfers heat.
The Coefficient of
Performance (COP) of a Peltier module is defined in the same way as for a
conventional refrigeration system, viz.
Coefficient of Performance = Rate of heat
extraction divided by Electrical Power input.
Critical materials parameters to ensure a high COP are a high thermo-electric coefficient to generate
the cooling effect, a high electrical conductivity to suppress Ohmic heating
and a low thermal conductivity to prevent much heat being conducted from the
hot side of the module to the cold side of the module.
Peltier modules are widely used to produce localized
cooling in scientific and technical applications such as laser-chip coolers and
a portable insulin cold-box. The advantages of mechanical simplicity and
suitability for small-scale applications are the principle reasons for
selecting thermo-electric cooling instead of compressor-driven refrigeration
for these applications.
Large
scale cooling applications such as air-conditioning and refrigeration have been
attempted and technically functional systems were developed to cool trains,
helicopters and aircraft. Small volume
applications such as the train driver’s cab where convenience and lack of
moving parts overweighed considerations of power consumption were found to be
appropriate for thermo-electric air
conditioning. A refrigerator (without freezer) was developed for hotel bedrooms
where the air-conditioning prevents over-heating on hot summer days and the
lack of compressor noise is considered a major asset. This thermo-electric
refrigerator is now sold in Japan
The
energy efficiency or coefficient of performance of the thermo-electric refrigerator remains a major consideration. The efficiency of the thermo-electric modules are more sensitive to the temperature
difference between hot and cold sides than a corresponding compressor
system. The efficiency of the thermo-electric refrigerator largely
depends on the heat transfer system used to transfer heat from the refrigerated
cabinet through the comparatively small thermo-electric
module and out to the external atmosphere.
A well-designed thermo-electric
system can offer a higher coefficient of performance than an adsorption
refrigerator.
The
thermo-electric system which only
needs water or brine for efficient functioning has become a potentially
attractive mode of refrigeration. In
this article, the major limitations of current thermo-electric refrigeration systems are discussed together with
proposals for future remedy.
Thermo-electric device manufacturers
report that a single-stage thermo-electric
cooler can achieve temperature differences up to 70°C (126°F) or can
transfer a maximum load of 125 watts (426 Btu/h) when the temperature difference
is zero. By cascading several devices together, multistage coolers increase
cooling capabilities. Greater temperature differences up to 131°C (236°F) can
be achieved in this manner.
However,
there are a number of recent developments that have made the application of thermo-electric cooling and heating more
attractive for commercial products. New applications, materials and technology
have enhanced those commercial potentials significantly. For example, certain
semi-conductors (alloys of tellurium are of particular interest) have thermo-electric properties superior to
conductor materials. These characteristics have allowed several niche
applications to develop.
4.
CURRENT THERMO-ELECTRIC TECHNOLOGY
The simplest system
involves air cooling on both the hot and cold sides; more advanced systems have
water cooling on either the hot or cold sides or else on both faces. The air-air system can be used for
air-conditioning where indoor air to be cooled is blown directly onto the cold
face of the Peltier module while heat is released directly to outdoor air. A commercial cooling system involving
air-cooling on the hot side and heat transfer to a coolant or test fluid on the
cold-side is marketed by several companies.
A system using heat transfer to water on both the cold and hot faces of
the module was developed for use in a refrigerator.
The main advantage of air-cooling is simplicity
since only fins and a fan are required but the major disadvantage is reduced
thermal efficiency. It is found that the
poor thermal conductivity of air causes a high temperature to develop on the
hot face and conversely a very low temperature on the cold face for even a
moderate level of heat transfer. For
example, if the difference in temperature between the interior of refrigerator
and the external atmosphere is 20 degrees Kelvin, then the thermo-electric module would have to operate at approximately 40
degrees Kelvin temperature difference in order for sufficient heat transport to
balance the heat leakage into the cabinet.
Each face of the module would need approximately 10 degrees Kelvin
temperature difference relative to either the refrigerated cabinet or the
external air before there is sufficient heat transfer by convection in
air. This larger temperature difference
causes the coefficient of performance to decline from approximately 1 to 0.5 or
less because of reverse thermal conduction in the module.
A liquid-liquid heat
transfer system for the Peltier module usually involves a liquid coolant which
transfers heat from the module to the air by a radiator. It is also possible to cool a process fluid
directly without using a radiator. This
is a more efficient process but may involve problems of corrosion or blockage
inside the heat exchange tubes. A pump
is required to circulate the coolant and the radiator will probably require a
fan, thus raising the level of mechanical complexity of the system when
compared to direct air cooling. In most
cases, water is used as the coolant because it is readily available,
non-corrosive and an efficient medium for heat transfer. Brine is also used on the cold side of the
module in order to prevent blockage by freezing of the coolant.
The main advantage of
using water-based cooling systems is that the Peltier module can work at a
temperature difference that is far closer to the nominal temperature difference
of the system. This is because the
convective heat transfer coefficient between water and a solid interface is
much higher than air for comparable flow conditions. The Peltier module is then able to work at
close to its optimum thermodynamic efficiency thus reducing electricity
consumption to practicable levels.
Refrigeration is a major source of electricity consumption and there is
little purpose to mitigate ozone destruction if in return, the greenhouse
effect is intensified by an increase in electricity demand. European Union (EU) legislation has imposed
limits on the amount of electricity that can be consumed annually by an
individual refrigerator inside EU countries.
This legislation necessitates either a high coefficient of performance
from the refrigerating system or very efficient thermal insulation on the
refrigerator cabinet.
The maximum temperature
difference between hot and cold side for practical functioning by Peltier modules
is approximately 70 degrees Celsius.
Larger temperature differences can be obtained by stacking the Peltier
modules where the waste heat from the coldest module is conducted to the cold
side of the warmer module. The
disadvantage of this method is the low COP so that it is mostly used for specialized
instrumentation applications.
A valuable feature of thermo-electric refrigeration is the
ease at which fractional power settings (for example, half-power) can be
maintained. The full power of the
thermo-electric system is reserved for cooling the cabinets from ambient
temperature to set temperature while the fractional power setting at steady
state is optimized for maximum COP. A thermo-electric refrigeration system can
be set at a power level sufficient to maintain the set temperature indefinitely
instead of hunting around a set point, as is the case with a compressor
refrigerator. Typically a compressor driven refrigerator is controlled by a thermostat
which only starts up the compressor when the temperature is approximately 3
degrees Kelvin higher than the set-point.
It is possible to reduce this temperature bandwidth but then the
compressor must function at reduced efficiency because of frequent operations
for short periods of time when the compressor is still warm. Thermo-electric
refrigeration enables food to be held within a narrow temperature range
without being exposed to periods of unsuitably high or low temperatures. This control of temperature minimises low
temperature damage (chilling injury) to fruits and vegetables, while
suppressing the growth of pathogenic organisms such as salmonella, in
stored meats. Bacterial growth rates
have an exponential relationship with temperature, which means that even brief
excursions of temperature above the set-point generate a disproportionately
large amount of bacterial growth.
Bacteria can degrade the nutrients within the food and release toxins,
which may cause illness for the consumer of the food.
5. DEVELOPMENT OF MATERIALS:
Since the beginning of the industrial revolution,
humanity has demanded an ever-increasing supply of energy.
TE devices are currently used in automotive seat
coolers/heaters (over 500,000/yr), in portable refrigerators that plug into an
automobile’s cigarette lighter, and in chemical and nuclear generators in
arctic regions and space probes. Increasing the efficiency of TE materials has
been the primary goal of research in the field, and may allow penetration of
the economical and environmentally friendly technology. Thermo-electric might then be coupled to any number of heat sources
to extract electricity from heat that would otherwise have been dissipated into
the environment as waste. Examples of potentially useful heat sources include
fuel cells, the steam generator systems inherent in all large power plants,
solar collectors, the shaded sides of solar cells, and automotive exhaust. A
Japanese collaboration has predicted that gas mileage would be improved by
several miles per gallon if the alternator were replaced by an array of TE
generators. Generators could also be attached to wood stoves to electrify
remote areas. Proposed uses of efficient TE refrigerators include the cooling
of high-temperature superconductor cables that could be used to distribute
electric power without loss and the cooling of microchips to enable faster
computing and more sensitive detectors. The military is considering the use of thermoelectric in wireless IR detectors,
temperature stabilization of optics, cooling of microprocessors and CCDs,
controlling heat signatures, individual man portable micro-climate systems,
remote power sources, and air conditioning and waste heat recovery for ships,
submarines, land vehicles, and aircraft.
TE materials naturally
generate a temperature gradient in the presence of an electromotive force (emf)
and they produce an emf in a temperature gradient. While all materials except
superconductors possess some TE character, only a few systems are efficient
enough to generate interest. These include the lead, bismuth, and antimony
chalcogenides, skutterudites such as cobalt triantimonide, bismuth antimony,
silicon germanium, boron carbides, and more complex compounds and alloys based
on these systems. A TE refrigerator connects two or more pieces of TE material
to of voltage source. A generator can be made from the same device is the
voltage source is replaced by a load (e.g. a battery charger). Nearly all
devices use two different types of materials, one "n-type" and the
other "p-type." These pieces must be connected so that they are
electrically in series, but thermally in parallel. This situation is
illustrated in the figures below.
The figure above is a
simplified schematic of a TE cooler. The voltage source moves electrons and
holes (think of them as bubbles in a sea of electrons) to the right in the n-
and p-type materials, respectively. These charge carriers also carry heat as
they travel, picking it up on the left and dumping it on the right.
Simultaneously, phonons (vibrations in the atoms of a solid) carry some heat
back, detracting from the performance of the device.
Earlier Bismuth and
Antimony were used in thermo-electric
refrigerator. Latter on various semiconductor materials developed. In
today’s status materials like BiTe3/Sb2Te3/Bi2Se3
alloy are being used in Peltier refrigeration.
Further investigations suggest compounds made from elements found in the
lower right corner of the periodic table group IIIB to VIB.
Some materials and their
figure of merits are as shown in chart.
6. ADVANTAGES AND DISADVANTAGES:
Thermo-electric
coolers are small, compact, lightweight, use solid state construction and have
no moving parts, fluids or gases. These characteristics can offer many
advantages compared to other heating/cooling technologies. A fan or pump may be
needed for heat transfer in larger thermoelectric systems; however, proper
choice can limit energy consumption and keep the system quiet. As uses increase
and mass production becomes more of a reality, the prices of these devices are
expected to decrease, making their applications even more attractive.
How
Efficient Are TE's?
The efficiency of a TE device or material is
captured by its figure-of-merit:
ZT=S2 σ T/κ
Where S is the Seebeck coefficient, σ is the
electrical conductivity, It is the absolute temperature, and κ is the
thermal conductivity. The Seebeck coefficient describes the magnitude of the
voltage that develops between the two ends of a device/material held at
different temperatures. Typical materials have figures-of-merit near one which
make them about 10% efficient. Compressor and steam generator systems, in
contrast, operate near 30% efficiency. Researchers have long sought to improve
the efficiency of TE materials. To accomplish this, one must increase the
Seebeck coefficient (large effective masses, unusual band structures), increase
the carrier mobility (covalently bonded solids, quantum wells), and/or decrease
the thermal conductivity (large unit cells, large effective masses, increasing
disorder to decrease mean free path of phonons). However, difficulties in
enhancing ZT arise because these materials properties are not normally
independent—increases in S lead to decreases in s, and increases in s lead to increases in k. New approaches to
improving the figure of merit center around attempts to decouple these
relationships using super lattice structures, segmentation, quantum
confinement, and phonon “rattlers.”
Advantages
1. Absence of moving parts eliminates vibration problem as
well as regular attendance. Therefore, it can
be best suited for system where
vibration is undesirable. It is
lighter in weight per unit mass of refrigeration.
2. It is most suitable or
the production cooling suit.
3. Since no refrigerant is
used, there is no question of toxicity environmental problem and can directly
used for air condition.
4. The load can be easily
controlled by means of adjusting the current to meet the situation.
5. Its design and
manufacture is rather much simpler then the other refrigeration systems.
Disadvantages
The major disadvantage with thermo-electric cooling remains the low efficiency. New materials with
better characteristics need to be developed before thermoelectric cooling can
be used in larger air-conditioning and refrigeration systems. Yet, there are
already many niche applications where this technology is used effectively.
Overall
COP of this system experimentally found to be 0.1 to 0.2.
7. APPLICATIONS:
One application in practical use is that of a drinking water
cooler. Although there may be variations by different manufacturers, the author
has observed and used one thermo-electrically
cooled (and heated) drinking water cooler that dispenses ice water. The
thermoelectric module cools a disk at the bottom of a holding tank well. In
this well, there is a focus beam that shines across the disk to a light sensor.
The 120 volt power supply has a switching circuit that detects the amount of light
across the disk. When ice forms
on the disk and it builds to a thickness that deflects some of the light, the
power supply is switched off. With the current stopped, some of the heat from
the module’s hot side heat exchanger will, warm the disk to free the ice by
conduction. The remainder of the heat is dissipated to the atmosphere with a
small fan. Once the ice breaks free, it will float to the top of the holding
tank, the light sensor will turn the power supply back on, and a new block will
be produced approximately every hour.
Today, thermo-electric
cooling is used in medical and pharmaceutical equipment, spectroscopy
systems, and various types of detectors, electronic equipment, portable
refrigerators, beverage coolers, chilled food and beverage dispensers, and
drinking water coolers. Requiring cooling devices with high reliability that
fit into small spaces, powerful integrated circuits in today's personal
computers also employ thermoelectric coolers. These devices are also used to
provide temperature control in telecommunication systems and have even been
used as a toy in an electronic pen that draws and erases on a
thermally-sensitive writing pad. Using solid state heat pumps that utilize the
Peltier effect, thermo-electric cooling
devices are also under scrutiny for larger spaces such as passenger
compartments of idling aircraft parked at the gate.
Thermo-electric devices manufacturers are
expanding their production lines and are offering custom items designed and
built to precise customer specifications. Cooling assemblies are being made
now, using a coordinated system of heat exchangers, cold plates and even
customer- supplied accessories ready to be plugged into a system by the user.
8.
FUTURE DEVELOPMENTS:
The two main issues in
thermo-electric refrigeration are the development of new materials with
stronger Peltier effects and the application of these materials to real
engineering problems such as refrigeration and control of process heat. The former issue is primarily the domain of
physicists and materials scientists who test a large number of materials
looking for crystalline structures which combine high electrical conductivity
with low thermal conductivity as well as a strong thermo-electric characteristic. The latter issue is of greatest concern to
mechanical engineering where problems such as heat transfer between the module
and cheap manufacture of modules are of concern. For refrigeration, unlike air-conditioning,
the power consumption is relatively small, typically 50 Watts which means that
the number of modules and their cost is also small. This means that the main issue for
refrigeration is heat transfer between the module and its external environment. The level of interest in these engineering
problems is intensifying as the efforts of physicists and materials scientists
produce thermo-electric materials
with usefully high levels of performance.
There has been steady
progress in raising the performance of the materials and construction of thermo-electric
modules since the first application of bismuth telluride in the 1950’s. A purified form of bismuth telluride now
enables the manufacture of thermo-electric modules with a Coefficient of
Performance approximately equal to unity for temperature differences of 29
degrees Kelvin. The standard test
temperature difference for a refrigerator cabinet is 29 degrees Kelvin where
the cabinet interior is set at 3 degrees Celsius and the exterior at 32 degrees
Celsius. The thermo-electric module would operate at a higher temperature
difference than this because of conduction and convection losses in the thermo-electric refrigerating system. A high efficiency of the Peltier module is
obtained when these secondary temperature losses are reduced to very small
values compared to the temperature difference across the Peltier module.
Enhancement of the heat transfer between the hot
and cold faces of
a Peltier module and the working fluid is still
however a major topic of research since the relative power consumption of a
Peltier when used in a refrigeration system remains high. The key factor to improve energy efficiency
is efficient heat transfer. A major
problem is the small size of the Peltier modules compared to their heat output
which means that a generous heat transfer coefficient is needed to prevent a
large temperature difference between the module and the working fluid. It is fortunate that water is an effective
heat transfer since the choice of fluids is greatly limited by considerations
of non-toxicity and non-corrosiveness for a domestic refrigerator. The sensitivity of Peltier module efficiency
to temperature difference between hot and cold face means that even a saving of
1 degree in temperature losses can generate a significant increase in the
overall Coefficient of Performance. A
fundamental problem is that the same pumps and fans which generate vigorous
convective heat transfer and thereby raise the coefficient of performance of
the Peltier module, also consume power to lower the overall system
efficiency. The efficiency of the pumps
and manifolds should be as high as possible with a balanced distribution of
electrical power to the various sub-systems within the refrigerator.
9. CONCLUSION:
From the all above discussion we can predict that the thermo-electric refrigeration is in
experimental stage. Though it is so, today it is being used in surgery for
cooling the instrument used for extracting the crystalline lens out of the eye.
There is problem from testing of thermo-electric
refrigerator that by using the heat pipe, we can achieve heat transfer rate
500 times more than the conventional heat removal aids like fins etc.by
evaporating the heat pipe reverse heat transfer which occurs after the shutoff
power supply can be solved So it has been noticed that use of heat pipe will
lead to improve the performance of the thermo-electric
module and ulmatly the refrigerator.
Thermo-electric
refrigeration is likely to become a significant form of domestic refrigeration
within the medium term because of the need to avoid refrigerating fluids that
are hostile to the environment.
Precise control of temperature for better food
preservation, low noise and a reduced number of moving parts are also
significant benefits of thermo-electric
refrigeration.
The energy consumption of thermo-electric refrigeration can be reduced to moderate levels
with further improvements in the heat transfer between the various stages of
the refrigerating system.
Last but not least, I feel that
though thermo-electric refrigeration
system is at experimental stage and have less application today, in future it
can become popular, convenient, reliable eco-friendly alternative refrigeration
system.