SStudy of Heat Pipes
INTRODUCTION
The
heat pipe is a highly effective passive device for transmitting heat at high
rates over considerable distances with extremely small temperature drops,
exceptional flexibility, simple construction, and easy control with no external
pumping power. Engineers, scientists and graduate students interested in heat
pipe science often times struggle and spend considerable time poring through archival
publications or the contents of heat pipe books in order to understand and
predict a heat pipe system.
The
subject of heat pipe science has immense importance in a large variety of
traditional engineering disciplines. The sub-discipline of heat pipe science
has its foundation in several classical fields, such as fluid mechanics, heat
transfer, thermodynamics and solid mechanics. Heat pipe science also provides
an opportunity for scientists and engineers to apply a variety of complex
physical phenomena and fundamental laws in the thermal-fluids area to a
relatively simple system, such as the heat pipe. This includes the steady and
unsteady forced laminar and turbulent convective heat and mass transfer, compressible
vapor effects, phase-change phenomena, boiling, condensation/evaporation,
two-phase flow, rotating flows, thin film flows, liquid flow in porous media,
rarefied gases, interfacial heat and mass transfer, magneto-hydrodynamic flows,
and conjugate heat transfer effects. [3]
Nowadays
heat pipes are used in several applications, where one has limited space and
the necessity of a high heat flux. Of course it is still in use in space
applications, but it is also used in heat transfer systems, cooling of
computers, cell phones and cooling of solar collectors.[1]
What is a Heat pipe?
A
heat pipe is a simple device that can quickly transfer heat from one Point to
another. By means of evaporation & condensation of fluid in a sealed system
they are often referred to as the "superconductors" of heat as they
possess an extra ordinary heat transfer capacity & rate with almost no heat
loss. It consists of a sealed aluminum or copper container whose inner surface
have a capillary wicking material. The working fluid is placed inside it & it
is highly evacuated. Because of that the working fluid is virtually in a state
of liquid-vapor equilibrium. consequently, a slight increase in temperature
will cause it to boil &evaporate The central portion of it is heavily
insulated on the outside. One end of pipe is known as heating end (evaporator)
where heat is absorbed & the other end is known as cooling end (condenser)
where heat is given out.
A
heat pipe is similar to a thermo-syphon. It differs from a thermo-syphon by
Virtue obits ability to transport heat against gravity by an evaporation
–condensation cycle with the help of porous capillaries that form the wick. The
wick provides the capillary driving force to return the condensate to the
evaporator. The quality and type of wick usually determines the performance of
the heat pipe, for this is the heart of the product. different types of wicks
are used depending on the application for which the heat pipes being used.
Fig:1.
Heat pipe model
HISTORICAL DEVELOPMENT OF HEAT PIPES
The
predecessor of the heat pipe, the Perkins tube, was introduced by the Perkins
family from the mid-nineteenth to the twentieth century through a series of
patents in the United Kingdom. Most of the Perkins tubes were wickless
gravity-assisted heat pipes (thermosyphons), in which heat transfer was
achieved by a change of phase (latent heat of evaporation). The Perkins tube
design closest to the present heat pipe was patented by Jacob Perkins (1836).
This design was a closed tube containing a small quantity of water operating as
a two-phase cycle. The introduction of the heat pipe was first conceived by
Gaugler (1944) of the General Motors Corporation in the U.S. Patent No. 2350348.
Gaugler, who was working on refrigeration problems at that time, envisioned a
device which would evaporate a liquid at a point above the place where
condensation would occur without requiring any additional work to move the
liquid to the higher elevation. His device consisted of a closed tube in which
the liquid would absorb heat at one location causing the liquid to evaporate.
The vapor would then travel down the length of the tube, where it would
recondense and release its latent heat. It would then travel back up the tube
via capillary pressure to start the process over. In order to move the liquid
back up to a higher point, Gaugler suggested the use of a capillary structure
consisting of a sintered iron wick. A refrigeration unit proposed by Gaugler
used a heat pipe to transfer the heat from the interior of a compartment to a
pan of crushed ice below. His idea, however, was not used by General Motors for
the refrigeration problem.
In
1962, Trefethen (1962) resurrected the idea of a heat pipe in connection with
the space program. Serious development started in 1964 when the heat pipe was
independently reinvented and a patent application was filed by Grover at Los
Alamos National Laboratory in New Mexico. Grover et al. (1964) and Grover
(1966) built several prototype heat pipes, the first of which used water as a
working fluid, and was soon followed by a sodium heat pipe which operated at
1100 K. Grover and his co-workers also demonstrated the effectiveness of heat
pipes as a high performance heat transmission device and proposed several
applications for their use. In a U.S. patent application filed by Grover on
behalf of the U.S. Atomic Energy Commission, Grover (1966) coined the phrase
“heat pipe” and described a device almost exactly the same as Gaugler’s,
stating, “with certain limitations on the manner of use, a heat pipe may be
regarded as a synergistic engineering structure which is equivalent to a
material having a thermal conductivity greatly exceeding that of any known
metal.” In the patent application, Grover (1966) gave a very limited
theoretical analysis of heat pipes, but presented experimental results obtained
from stainless steel heat pipes that incorporated a screen wick with sodium,
silver and lithium as working fluids.
The
recognition of the heat pipe as a reliable thermal device was initially due to
the preliminary theoretical results and design tools that were reported in the
first publication on heat pipe analysis by Cotter (1965). Following this
publication, research began worldwide. The United Kingdom Atomic Energy
Laboratory at Harwell started experimenting with sodium heat pipes to use as
thermionic diode converters. In addition, scientists started conducting similar
work at the Joint Nuclear Research Center in Italy, which soon became the most
active research center outside the U.S. Shortly thereafter, other countries
such as Germany, France, and the former USSR initiated efforts in this regard.
The
early development of terrestrial applications of heat pipes proceeded at a slow
pace. Due to capillary action, heat pipes can operate in micro gravitational
fields without any external force field or pump. Because of this, most early
efforts were directed toward space applications. However, due to the high cost
of energy, especially in Japan and Europe, the industrial community began to
appreciate the significance of heat pipes and thermosyphons in energy savings applications.
Today, all developed countries have been actively involved in research,
development, and commercialization of heat pipes.
Within
the last decade, a major transformation regarding heat pipe technology and
application has occurred due to the critical need of electronic cooling and
energy systems, as well as the invention of new heat pipes. Several million
heat pipes per month are now being manufactured since all modern laptop
computers use heat pipe technology to transfer heat away from the processor.
Furthermore, research and development for new heat pipes such as loop heat
pipes, micro and miniature heat pipes, and pulsating heat pipes, has matured enough
for use in various applications.
A significant amount
of basic and applied research & development has been performed since 1985
in the area of heat pipes due to the great potential use of this technology for
various applications. [3]
WORKING PRINCIPLE
The
operation of a heat pipe is easily understood by using a cylindrical geometry, However,
heat pipes can be of any size or shape. The components of a heat pipe are a
sealed container (pipe wall and end caps), a wick structure, and a small amount
of working fluid which is in equilibrium with its own vapor. Different types of
working fluids such as water, acetone, methanol, ammonia or sodium can be used
in heat pipes based on the required operating temperature. The length of a heat
pipe is divided into three parts: the evaporator section, adiabatic (transport)
section and condenser section. A heat pipe may have multiple heat sources or
sinks with or without adiabatic sections depending on specific applications and
design. Heat applied externally to the evaporator section is conducted through
the pipe wall and wick structure, where it vaporizes the working fluid. The
resulting vapor pressure drives the vapor through the adiabatic section to the
condenser, where the vapor condenses, releasing its latent heat of vaporization
to the provided heat sink. The capillary pressure created by the menisci in the
wick pumps the condensed fluid back to the evaporator section. Therefore, the
heat pipe can continuously transport the latent heat of vaporization from the evaporator
to the condenser section. This process will continue as long as there is a
sufficient capillary pressure to drive the condensate back to the evaporator.
Fig:2.
Schematic diagram of a heat pipe.
EXPERIMENTAL SETUP
The experimental setup of heat pipe was
developed and tested in the laboratory. All the experimentations are carried
out at controlled conditions. The setup consists of a Heat pipe, temperature
recorder, power supply unit, and water tank cooling system for condenser. Both
the evaporation and adiabatic sections were well thermally insulated by the
proper insulation materials. The heat pipe consisting of 10 turns, is made of
copper capillary tube having inner diameter is 2.0 mm; the outer diameter is
3.6 mm. The pitch distance between tubes was maintained 15 mm. The heat pipe consists
of evaporation, adiabatic and condensation sections with the height of 50 mm
for each section. The heating power is provided by a carefully designed power
supply unit. Heating was done by oil bath and cooling by water tank. The power
meter measures the AC voltage, the current and the corresponding power
simultaneously. The Filling Ratio was maintained at 50%. The heating
configuration was bottom heat orientation (+900). Ten K-type thermocouples were
attached to the wall of the heat pipe. Flow meter was also recorded the mass
flow rate of the cooling water.(we can use different size of heat pipe) [4]
Fig:3. Experimental setup
COMPONENTS OF A HEAT PIPE
The
three basic components of a heat pipe are:
1.
The container
2.
The working fluid
3. The wick or
capillary structure
Fig:4. Components of heat pipe
The choice of each component has marked effect
on the working Performance of heat pipe and therefore proper selection of each Component
is very important in design of heat pipe. Following explanation is given below
Container
The
function of the container is to isolate the working fluid from the outside
environment. It has to therefore be leak-proof, maintain the pressure differential
across its walls, and enable transfer of heat to take place from and into the
working fluid.
Selection
of the container material depends on many factors. These are as follows:
·
Compatibility (both with working fluid
and external environment)
·
Strength to weight ratio
- Thermal conductivity
- Ease of fabrication, including welding, machine ability and ductility
- Porosity
- Wettability
Working fluid
A
first consideration in the identification of a suitable working fluid is the
operating vapor temperature range. Within the approximate temperature band,
several possible working fluids may exist, and a variety of characteristics
must be examined in order to determine the most acceptable of these fluids for
the application considered.
The prime requirements are:
- · compatibility with wick and wall materials
- · good thermal stability
- · wet ability of wick and wall materials
- · vapor pressure not too high or low over the
- · operating temperature range
- · high latent heat
- · high thermal conductivity
- · low liquid and vapor viscosities
- · high surface tension
- Acceptable freezing or pour point
The selection of the working fluid must also be
based on thermodynamic considerations which are concerned with the various
limitations to heat flow occurring within the heat pipe like, viscous, sonic,
capillary, entrainment and nucleate boiling levels. In heat pipe design, a high
value of surface tension is desirable in order to enable the heat pipe to
operate against gravity and to generate a high capillary driving force. In
addition to high surface tension, it is necessary for the working fluid to wet the
wick and the container material i.e. contact angle should be zero or very
small. The vapor pressure over the operating temperature range must be sufficiently
great to avoid high vapor velocities, which tend to setup large temperature gradient
and cause flow instabilities. A high latent heat of vaporization is desirable
in order to transfer large amounts of heat with minimum fluid flow, and hence
to maintain low pressure drops within the heat pipe. The thermal conductivity
of the working fluid should preferably be high in order to minimize the radial
temperature gradient and to reduce the possibility of nucleate boiling at the wick
or wall surface. The resistance to fluid flow will be minimized by choosing
fluids with low values of vapor and liquid viscosities.
|
WORKING FLUID
|
COMPATIBLE MATERIAL
|
INCOMPATIBLE MATERIAL
|
|
|
Water
|
Stainless steel,
Copper, Silica, Nickel, Titanium
|
Aluminum, Inconel
|
|
|
Ammonia
|
Aluminum, Stainless
steel, Cold rolled steel, Iron, Nickel
|
|
|
|
Methanol
|
Stainless steel,
Copper, silica, Nickel, Iron, Brass
|
Aluminum
|
|
|
Acetone
|
Aluminum, Stainless
steel, Copper, Brass, Silica
|
|
|
|
Freon-21
|
Aluminum, Iron
|
|
|
|
Heptane
|
Aluminum
|
|
|
|
Dowtherm
|
Stainless Steel,
Copper, Silica
|
|
|
|
Lithium
|
Tungsten, Tantalum,
Molybdenum, Niobium
|
Stainless Steel,
Nickel, Inconel, Titanium
|
|
|
Sodium
|
Stainless Steel,
Nickel, Inconel, Niobium
|
Titanium
|
|
|
Cesium
|
Titanium, Niobium,
Stainless Steel, Nickel based super alloys
|
|
|
|
Mercury
|
Stainless steel
|
Tantalum,
Molybdenum,Niobium, Nickel, Inconel, Titanium
|
|
|
Lead
|
Tungsten, Tantalum
|
Stainless Steel,
Nickel, Inconel, Titanium, Niobium
|
|
|
Silver
|
Tungsten, Tantalum
|
Rhenium
|
Table:1.
Materials
compatibility relative to working fluid.
|
MEDIUM
|
MELTING POINT ( ̊C )
|
BOILING POINT AT ATMOSPHERIC PRESSURE ( ̊C )
|
USEFUL RANGE ( ̊C )
|
|
Helium
|
-271
|
-261
|
-271 to -269
|
|
Nitrogen
|
-210
|
-196
|
-203 to -160
|
|
Ammonia
|
-78
|
-33
|
-60 to 100
|
|
Acetone
|
-95
|
57
|
0 to 120
|
|
Methanol
|
-98
|
64
|
10 to 130
|
|
Flutec PP2
|
-50
|
76
|
10 to 160
|
|
Ethanol
|
-112
|
78
|
0 to 130
|
|
Water
|
0
|
100
|
30 to 200
|
|
Toluene
|
-95
|
110
|
50 to 200
|
|
Mercury
|
-39
|
361
|
250 to 650
|
|
Sodium
|
98
|
892
|
600 to 1200
|
|
Lithium
|
179
|
1340
|
1000 to 1800
|
|
Silver
|
960
|
2212
|
1800 to 2300
|
Table:2. fluids and their
temperature range
Wick or Capillary structure
It is a porous structure made of materials like
steel, aluminium, nickel or copper in various ranges of pore sizes. The prime
purpose of the wick is to generate capillary pressure to transport the working fluid
from the condenser to the evaporator. It must also be able to distribute the
liquid around the evaporator section to any area where heat is likely to be
received by the heat pipe. Often these two functions require wicks of different
forms. The selection of the wick for a heat pipe depends on many factors, several
of which are closely linked to the properties of the working fluid. The maximum
capillary head generated by a wick increases with decrease in pore size. The
wick permeability increases with increasing pore size. Another feature of the
wick, which must be optimized, is its thickness. The heat transport capability
of the heat pipe is raised by increasing the wick thickness. The overall
thermal resistance at the evaporator also depends on the conductivity of the
working fluid in the wick. Other necessary properties of the wick are
compatibility with the working fluid and wet ability. [5]
Various
wicks structures:
- · screen mesh
- · sintered metal powder grooves
- · sintered metal powders
- · sintered metal powder grooves (fine grooves)
- · clockwise-axial grooves
- sintered slabs
Fig:5. Various wicks structures
(1.screen mesh 2. sintered metal powder grooves 3. sintered metal powders 4. sintered metal powder grooves 5. clockwise-axial
grooves 6. sintered slabs)
The most common types
of wicks that are used are as follows:
Sintered
Metal Powder:
This process will provide high power handling,
low temperature gradients and high capillary forces for anti-gravity
applications. The photograph shows a complex sintered wick with several vapor
channels and small arteries to increase the liquid flow rate. Very tight bends
in the heat pipe can be achieved with this type of structure.
Grooved Tube:
The
small capillary driving force generated by the axial grooves is adequate for
low power heat pipes when operated horizontally, or with gravity assistance.
The tube can be readily bent. When used in conjunction with screen mesh the
performance can be considerably enhanced.
Screen Mesh:
This type of wick is used in the majority of the
products and provides readily variable characteristics in terms of power
transport and orientation sensitivity, according to the number of layers and
mesh counts used. [2]
OPERATING LIMITATION
Since the heat pipe
benefits from the phase change of the working fluid, the thermodynamics of the
process are critical. The operation of the heat pipe is limited by several
operating phenomena. The main limitations are
- · Capillary Limit
- · Boiling Limit
- · Sonic Limit
- · Entrainment Limit
- · Flooding Limit
Capillary limit
The wick structure of the heat pipe generates a
capillary pressure, which is dependent on the pore radius of the wick and the
surface tension of the working fluid. The capillary pressure generated by the
wick must be greater than the sum of the gravitational losses, liquid flow
losses through the wick, and vapor flow losses. The liquid and vapor pressure
drops area function of the heat pipe and wick structure geometry and the fluid properties. A critical heat
flux exists that balances the capillary pressure with the pressure drop
associated with the fluid and vapor circulation. For horizontal or against
gravity, the capillary limit is the heat pipe limit. For gravity-aided
orientations, the capillary limitation may be neglected, and the flooding limit
may be used if the heat pipe can have an excess fluid charge.
Boiling Limit
As more heat is
applied to the heat pipe at the evaporator, bubbles may be formed in the
evaporator wick. The formation of vapor bubbles in the wick is undesirable
because they can cause hot spots and obstruct the circulation of the liquid. As
the heat flux is increased, more bubbles are formed. At a certain heat flux
limit, the bubble formation completely blocks the liquid flow. This limitation
is associated to a radial heat flux. The boiling limitation is typically a high
temperature phenomenon. Heat flux limitations for various wick structures should
be used for design criteria. Sintered powder metal wick structures have
significantly more surface area, and can therefore handle higher heat fluxes.
Conservative values are 50 W/cm2 for powder metal wicks,10 W/cm2 for screen
wicks, 5 W/cm2 for bare wall thermo syphons.
. Sonic Limit
In a heat pipe of constant vapor space diameter, the vapor flow accelerates and decelerates because of the vapor addition in the evaporator and the vapor removal in the condenser. The changes in vapor flow also change the pressures along the heat pipe. As more heat Is applied to the heat pipe, the vapor velocities generally increase. A choked flow condition will eventually arise, where the flow becomes sonic. At this point, the vapor velocities can not increase and a maximum heat transport limitation is achieved. The heat flux that results in choked flow is considered the sonic limit. The addition of more heat will result in an un proportional increase in the heat pipe temperature delta by an increase in the evaporation temperature. This phenomenon is self-correcting as the heat pipe warms up. An additional benefit of the high vapor velocities is the very quick response to heat input.Entrainment Limit
Since
the vapor and the liquid move in opposite directions in a heat pipe, a shear
force exists at the liquid-vapor interface. If the vapor velocity is
sufficiently high, a limit can be reached at which the liquid will be torn from
the pores of the wick and entrained in the vapor. When enough fluid is
entrained in the vapor that the condensate flow is stopped, abrupt dry-out of
the wick at the evaporator results. The corresponding heat flux that results in
this phenomenon is called the Entrainment Limit. The Entrainment Limit is
typically not the bounding value.
Flooding Limit
The flooding limit is only applicable to gravity aided orientations with excess fluid. The wick structure is saturated and the excess fluid results in a “puddle” flow on the surface of the wick structure. The flooding limit, similar to the entrainment, occurs when high vapor velocities preclude the fluid that is flowing on the surface of the wick to return to the evaporator. The vapor shear hold up prevents the condensate from returning to the evaporator and leads to a flooding condition in the condenser section. This causes a partial dry-out of the evaporator, which results in wall temperature excursions or in limiting the operation of the system. [1]
Fig:6.
Heat pipe limitations
THE SPECIAL FEATURES OF HEAT PIPES
A. Very High Thermal
Conductivity
Heat pipe utilizes
latent heat of evaporation of the working fluid to
transfer heat from the evaporator
to
condenser of the heat pipe. This mode results a
very
high thermal conductivity. The effective
thermal
conductivity is several orders of
magnitudes
greater than that of the best solid
conductor
B.
Low Relative Weight
The
heat pipe is not a solid metal piece. The weight can be significantly reduced.
C.
Reliable in Operation
Heat
pipes do not have moving parts; they are extremely reliable. The main cause of
failure is non-condensable gas generation in the heat pipe. By proper chosen of
container and working fluid combination, this problem can be eliminated.
D.
Flexible
The
heat pipes can be made in various forms. Circular heat pipe is the most popular
from, since it is easy fabrication and low cost. There exist flat plate and
double casing heat pipes, rigid and flexible heat pipes, as well as large and
micro heat pipes.
E.
The Temperature Operating Range
Heat
pipe can be designed to operate over a wide range of temperature from cryogenic
applications using helium or nitrogen as the working fluid to high temperature
applications using silver. The type of working fluid and the operating pressure
inside the heat pipe depend on the operating temperature. The operating
temperature, in general, should be above the triple point temperature and below
the critical temperature of the working fluid. [5]
APPLICATIONS OF HEAT PIPE
Heat
pipe heat sink has been frequently used to remove the heat from power
transistors, Thyristors , and individual chips. Currently, a popular application
to use heat pipes is cooling Intel’s Pentium processors in notebook computers. Perhaps
the best way to demonstrate the heat pipes application to electronics cooling
is to present a few of the more common examples.
A.
Cooling of Laptop Computer.
B.
Cooling of High Power Electronics.
C.
HEAT PIPES for Dehumidification and Heat
A. Heat pipes keep laptops cool
ICs
in today's laptop computers generate about 50 W/cm2 of heat. To prevent overheating, a fan, often a noisy one, blows heat down onto a
copper heat sink on the bottom of
the computer, which can really warm
up the users lap.
As chips get stacked
and circuits are downsized, next-generation ICs might produce 100 W/cm2, the heat
levels produced by a light bulb and enough to damage the chips. This could
cause some real discomfort. Heat pipes are one possible solution being studied
at Sandia National Laboratory. Self powered with no moving parts, they can
direct heat to specific areas where it can be safely, and comfortably,
dispersed. Heat pipes can also easily retrofit into existing laptop designs. In
the heat pipe, heat converts liquid methanol into vapor, which travels the
length of the pipe. At the cool end, which can be made cooler by using a small external
fan if necessary, the vapour condenses to a liquid and is wicked back to the
hot end. Wicks in this design are finely etched lines about as deep as fingerprints.
Methanol travels up the wick using capillary action and defying gravity if
necessary.
Fig:7. Heat pipe used in laptop
B. Cooling of High Power Electronics.
In
addition, other high power electronics including Silicon Controlled Rectifiers
(SCR's), Insulated Gate Bipolar Transistors (IGBT's) and Thyristors , often
utilize heat pipe heat sinks. Heat pipe, are capable of cooling several devices
with total heat loads up to 5 kW. These heat sinks are also available in
electrically isolated versions where the fin stack can be at ground potential
with the evaporator operating at the device potentials of upto 10 kV. Typical
thermal resistances for the high power heat sinks range from 0.05 to
0.1°C/watt. Again, the resistance is predominately controlled by the available
fin volume and air flow.
Fig:8.
Multi-Kilowatt heat pipe assembly
C. Cold energy storage for agricultural products
Heat pipe will collect
cold energy in the winter season and storing underground to create a permafrost
system for storage of agricultural products throughout the year. The whole cold
energy system is passive, ie. there are no moving parts, there is no electrical
consumption and it is reliable and maintenance free. [5]
ADVANTAGES
- · Rate of heat transfer is very high than the solid material.
- · It has no moving parts hence maintains is not required
- · It can transmit heat over the appreciable distance without loss of the heat (i. e isothermal). And thus permitting separation of the heat source and sink
- · It require no power source to accomplish this function
- · It can transfer the heat where a very low temperature difference is available in between source and sink.
- · It is ideal device for removing the heat from a concentrated heat source such as thermo core.
- · It is rugged like any piece of pipe or tube and has no any wearing part hence it has long life.
- · The absence of the gravity does not affect the operation of the heat pipe determinately liquid flow does not depend upon gravity
DISADVANTAGES
Like
any other practical devices, heat pipe has also disadvantages as listed below:
- · Undesired increase in point-to-point temperature differential along the heat pipe can lead to damage to evaporator section
- · Length of heat pipe is limited
- · Design is complicated
- · The cost of a given heat pipe will tend to reach a minimum in the temperature range of 70 ̊ C to 120 ̊ C. But above &below this range, total cost of heat pipe will be more.
CONCLUSION
Heat pipes are very efficient heat transport elements
which can be described as light weight devices with high thermal conductance.
They allow the transportation of high fluxes with small temperature difference
with no change in operating temperature. They can operate at zero gravity
environments. In addition there is no moving mechanical parts in heat pipes,
and special sets of them can be used for temperature control, as thermal diodes
and thermal switches. . It is presently
used in space technology, thermal power stations, home applications etc has. It
has very bright future.
REFERENCE:
[1] Heat
pipes and its applications Fabian Korn, Dept. of Energy Sciences, Faculty of
Engineering,Lund University, Box 118, 22100 Lund, Sweden.
[2] Heat
Pipe for Aerospace Applications—An Overview, K. N. Shukla ,PRERANA CGHS Ltd.,
Gurgaon, India.
[3] HEAT
PIPES: REVIEW, OPPORTUNITIES AND CHALLENGES, Amir Faghri, Department of
Mechanical Engineering, University of Connecticut, Storrs, CT 06269, U.S.A.
[4] THERMAL
PERFORMANCE OF CLOSED LOOP PULSATING HEAT PIPE USING PURE AND BINARY WORKING
FLUIDS, Pramod R. Pachgharea, Assistant Professor, Department of Mechanical
Engineering, Government College of Engineering, Amravati-444 604, India. Ashish
M. Mahalleb, Associate Professor, Department of General Engineering, Laxinarayan
Institute of Technology, Nagpur-444 001, India
[5] A
Review Paper on Role of Heat Pipes in Cooling, vishnu Agarwal ,Dr. Sudhir Jain,
Keerti Vyas,Ginni Jain
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