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Study on Performance Evaluation of Automotive Radiator

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  • School of Management Sciences,Technical Campus, Lucknow
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Study on Performance Evaluation of Automotive Radiator

Abstract and Figures

A complete set of numerical parametric studies on automotive radiator has been presented in detail in this study. The modeling of radiator has been described by two methods, one is finite difference method and the other is thermal resistance concept. In the performance evaluation, a radiator is installed into a test-setup and the various parameters including mass flow rate of coolant, inlet coolant temperature; etc. are varied. A comparative analysis between different coolants is also shown. One coolant as water and other as mixture of water in propylene glycol in a ratio of 40:60 is used. It is observed that that the water is still the best coolant but its limitation is that it is corrosive and contains dissolved salts that degrade the coolant flow passage.
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Study on Performance Evaluation of Automotive Radiator
JP Yadav1* and Bharat Raj Singh2
ABSTRACT
A complete set of numerical parametric studies on automotive radiator has been presented in detail in this study.
The modeling of radiator has been described by two methods, one is finite difference method and the other is
thermal resistance concept. In the performance evaluation, a radiator is installed into a test-setup and the
various parameters including mass flow rate of coolant, inlet coolant temperature; etc. are varied. A comparative
analysis between different coolants is also shown. One coolant as water and other as mixture of water in
propylene glycol in a ratio of 40:60 is used. It is observed that that the water is still the best coolant but its
limitation is that it is corrosive and contains dissolved salts that degrade the coolant flow passage.
Keywords: Radiator, coolant, thermal resistance, nano-fluids, carbon-foam fins.
1*. JP Yadav, Associate Professor, Chandra Shekhar Azad University of Agriculture & Technology, Campus-Etawah (U.P.), India, e-mail:
jpyadav_caet@yahoo.com
2. Bharat Raj Singh, Professor and Associate Director, SMS Institute of Technology, Kashimpur, Lucknow-227125, (U.P), India, e-mail:
brsinghlko@yahoo.com
1. INTRODUCTION
he demand for more powerful engines in smaller
hood spaces has created a problem of insufficient rates
of heat dissipation in automotive radiators. Upwards
of 33% of the energy generated by the engine through
combustion is lost in heat. Insufficient heat dissipation
can result in the overheating of the engine, which leads
to the breakdown of lubricating oil, metal weakening
of engine parts, and significant wear between engine
parts. To minimize the stress on the engine as a result
of heat generation, automotive radiators must be
redesigned to be more compact while still maintaining
high levels of heat transfer performance.
In an automobile, fuel and air produce power
within the engine through combustion. Only a portion
of the total generated power actually supplied to the
automobile with power, the rest is wasted in the form
of exhaust and heat. If this excess heat is not removed,
the engine temperature becomes too high which results
in overheating and viscosity breakdown of the
lubricating oil, metal weakening of the overheated
engine parts, and stress between engine parts resulting
in quicker wear, among the related moving posts . A
cooling system is used to remove this excessive heat.
Most automotive cooling systems consist of the
following components: radiator, water pump, electric
cooling fan, radiator pressure cap, and thermostat.
Of these components, the radiator is the most
prominent part of the system because it transfers heat.
As coolant travels through the engine’s cylinder block,
it accumulates heat. Once the coolant temperature
increases above a certain threshold value, the vehicle’s
thermostat triggers a valve which forces the coolant
to flow through the radiator. As the coolant flows
through the tubes of the radiator, heat is transferred
through the fins and tube walls to the air by conduction
and convection.
2. AUTOMOTIVE RADIATOR
A radiator is a type of heat exchanger. It is
designed to transfer heat from the hot coolant that
flows through it to the air blown through it by the fan.
Most modern cars use aluminum radiators. These
radiators are made by brazing thin aluminum fins to
flattened aluminum tubes. The coolant flows from the
inlet to the outlet through many tubes mounted in a
parallel arrangement. The fins conduct the heat from
T
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Study on Performance Evaluation of Automotive Radiator
the tubes and transfer it to the air flowing through the
radiator. The tubes sometimes have a type of fin
inserted into them called a turbulator, which increases
the turbulence of the fluid flowing through the tubes.
If the fluid flows very smoothly through the tubes, only
the fluid actually touching the tubes would be cooled
directly. The amount of heat transferred to the tubes
from the fluid running through them depends on the
difference in temperature between the tube and the
fluid touching it. So if the fluid that is in contact with
the tube cools down quickly, less heat will be
transferred. By creating turbulence inside the tube, all
of the fluid mixes together, keeping the temperature
of the fluid touching the tubes up so that more heat
can be extracted, and all of the fluid inside the tube is
used effectively. Radiators usually have a tank on each
side, and inside the tank is a transmission cooler. From
fig. 1 the inlet and outlet shown where the oil from the
transmission enters the cooler. The transmission cooler
is like a radiator within a radiator, except instead of
exchanging heat with the air, the oil exchanges heat
with the coolant in the radiator.
2.1 Working of Radiator
The pump sends the fluid into the engine block,
where it makes its way through passages in the engine
around the cylinders. Then it returns through the
cylinder head of the engine. The thermostat is located
where the fluid leaves the engine. The plumbing around
the thermostat sends the fluid back to the pump
directly if the thermostat is closed. If it is open, the
fluid goes through the radiator first and then back to
the pump [1].
Fig. 1: Parts of cooling system
Fig. 2: Working of Radiator
There is also a separate circuit for the heating
system. This circuit takes fluid from the cylinder head
and passes it through a heater core and then back to
the pump. On cars with automatic transmissions, there
is normally also a separate circuit for cooling the
transmission fluid built into the radiator. The oil from
the transmission is pumped by the transmission through
a second heat exchanger inside the radiator, as shown
in fig.2.
2.2 Cooling System and Antifreeze
An automobile’s cooling system is the collection
of parts and substances (coolants) that work together
to maintain the engine’s temperature at optimal levels.
Comprising many different components such as water
pump, coolant, a thermostat, etc, the system enables
smooth and efficient functioning of the engine at the
same time protecting it from damage. While it’s
running, an automobile’s engine generates enormous
amounts of heat. Each combustion cycle entails
thousands of controlled explosions taking place every
minute inside the engine. If the automobile races on
and the heat generated within isn’t dissipated, it would
cause the engine to self-destruct. Hence, it is
imperative to concurrently remove the waste heat.
While the waste heat is also dissipated through the
intake of cool air and exit of hot exhaust gases, the
engine’s cooling system is explicitly meant to keep
the temperature within limits. The cooling system
essentially comprises passages inside the engine block
and heads, a pump to circulate the coolant, a
thermostat to control the flow of the coolant, a radiator
to cool the coolant and a radiator cap controls the
pressure within the system. In order to achieve the
cooling action, the system circulates the liquid coolant
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JP Yadav and Bharat Raj Singh
through passages in the engine block and heads. As it
runs through, the coolant absorbs heat before returning
to the radiator, to be cooled itself. Next, the cooled
down coolant is re-circulated and the cycle continues
to maintain the engine’s temperature at the right levels.
2.3 Automotive use of antifreeze
The term engine coolant is widely used in the
automotive industry, which covers its primary function
of convective heat transfer. When used in an
automotive context, corrosion inhibitors are also
added to help protect vehiclescooling systems, which
often contain a range of electrochemically incompatible
metals (aluminum, cast iron, copper, lead solder, etc).
Antifreeze was developed to overcome the
shortcomings of water as a heat transfer fluid. In most
engines, freeze plugs are placed in the engine block
which could protect the engine if no antifreeze was in
the cooling system or if the ambient temperature
dropped below the freezing point of the antifreeze. If
the engine coolant gets too hot, it might boil while
inside the engine, causing voids (pockets of steam)
leading to the catastrophic failure of the engine. Using
proper engine coolant and a pressurized coolant
system can help alleviate both problems. Some
antifreeze can prevent freezing till - 870C.
3. ANTIFREEZE AGENTS
3.1 Methanol
Methanol, also known as methyl alcohol, carbinol,
wood alcohol, wood naphtha or wood spirits, is a
chemical compound with chemical formula CH3OH
(often abbreviated MeOH). It is the simplest alcohol,
and is a light, volatile, colourless, flammable, poisonous
liquid with a distinctive odor that is somewhat milder
and sweeter than ethanol (ethyl alcohol). At room
temperature it is a polar liquid and is used as an
antifreeze, solvent, fuel, and as a denaturant for ethyl
alcohol. It is not very popular for machinery, but it
can be found in automotive windshield washer fluid,
de-icers, and gasoline additives to name a few.
3.2 Ethylene glycol
Ethylene glycol (IUPAC name: ethane-1, 2-diol)
is an organic compound widely used as an automotive
antifreeze and a precursor to polymers. In its pure
form, it is an odorless, colorless, syrupy, sweet tasting
Fig. 3: Ethylene glycol
liquid. However, ethylene glycol is toxic, and ingestion
can result in death.
Ethylene glycol solutions became available in 1926
and were marketed as “permanent antifreeze,since
the higher boiling points provided advantages for
summertime use as well as during cold weather. They
are still used today for a wide variety of applications,
including automobiles. Being ubiquitous, ethylene
glycol has been ingested on occasion, causing ethylene
glycol poisoning. Coolant containing ethylene glycol
should not be disposed of in a way that will result in it
being ingested by animals, because of its toxicity.
Many animals like its sweet taste. As little as a
teaspoonful can be fatal to a cat, and four teaspoonfuls
can be dangerous to a dog. In some places it is
permitted to pour moderate amounts down the toilet,
but there are also places where it can be taken for
processing.
3.3 Propylene glycol
Propylene glycol, on the other hand, is
considerably less toxic and may be labeled as “non-
toxic antifreeze”. It is used as antifreeze where ethylene
glycol would be inappropriate, such as in food-
processing systems or in water pipes in homes, as
well as numerous other settings. It is also used in food,
medicines, and cosmetics, often as a binding agent.
Propylene glycol is fig. 4 is “generally recognized as
safe” by the Food and Drug Administration (FDA)
for use in food. However, propylene glycol-based
antifreeze should not be considered safe for
consumption. In the event of accidental ingestion,
emergency medical services should be contacted
immediately.
Fig. 4: Propylene glycol
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Propylene glycol oxidizes when exposed to air and
heat. When this occurs lactic acid is formed. [5]. If
not properly inhibited, this fluid can be very corrosive.
Protodin is added to propylene glycol to act as a buffer,
preventing low pH attack on the system metals. It
forms a protective skin inside the tank and pipelines
which helps to prevent acid attack that cause
corrosion. Besides cooling system breakdown,
biological fouling also occurs. Once the bacterial slime
starts, the corrosion rate of the system increases. In
systems where a glycol solution is maintained on a
continuous basis, regular monitoring of freeze
protection, pH, specific gravity, inhibitor level, color
and biological contamination should be checked
routinely. Propylene glycol should be replaced when
it turns reddish in color.
4. FUNCTIONS OF ANTIFREEZE
Engine antifreeze and additive mixture for
automobile radiator are meant to:
4.1 Reduce cooling system corrosion
Every automotive cooling system will corrode
eventually, but this mixture of antifreeze and additive
will make the overall process of corrosion slow
therefore, increasing the life of cooling system.
4.2 Reduce cavitation
In large diesel engines, air or tiny bubbles in the
coolant can cause serious problems or engine
overheating. So, for a diesel vehicle, it is highly
recommended that a cavitation reducing engine coolant
must be used.
4.3 Buffer the acidity of your engine coolant
The more acidic an engine coolant, the more quickly
it can corrode and damage the cooling system and
automobile radiator.
4.4 Raise the boiling point of the engine coolant
A higher boiling temperature means that the coolant
can cool better as the engine gets hotter. It also reduces
the chance of blowing a head gasket.
5. TESTING SETUP OF AUTOMOTIVE
RADIATOR
In the performance evaluation of radiator a test
apparatus is prepared in as shown test diagram fig.5
& test model fig. 6 which a radiator, fan, flow meter,
heating element, pump, two thermocouples, digital
meters for conversion of thermal emf into digital form
are used.
Fig. 5: Schematic diagram of test setup
Fig. 6: Testing model of project
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The various components used are described below.
Reservoir with heating element: In the test
apparatus the hot water acting as the coolant taking
heat from the engine block is provided here the
help of a heating element fixed into the reservoir
container. In this container the water is heated up
to the range of 65-75OC
Pump: The water pump uses centrifugal force to
send fluid to the outside while it spins, causing fluid
to be drawn from the center continuously. The inlet
to the pump is located near the center so that fluid
returning from the radiator hits the pump vanes.
The pump vanes fling the fluid to the outside of the
pump. After this the flow rate is measured with the
help of a flow meter.
Rotameter: A rotameter is a constant pressure
drop, variable area flow meter. It consists of a
tapered metering glass tube inside of which located
a rotor or active element (float) of the meter. The
tube is provided with inlet and outlet connections.
The specific gravity of the float or bob material is
higher than that of the fluid to be metered. On a
part of a float spherical slots are cut which cause it
(float) to rotate slowly about the axis of the tube
and keep it centered. Owing to this spinning
accumulation of any sediment on the top sides of
float is checked. However, the stability of the bob
may also be insured by using guide along which
the float winds slight. When the rate of flow
increases the float rise in the tube and consequently
there is an increase in the annular area between
the float and the tube. Thus, the float rides higher
or lowers depending on the rate of flow.
Thermocouples: The most common electrical
method of temperature measurement uses the
thermocouple. It is based upon see-back effect
i.e. when two dissimilar metals are jointed, these
forms two junctions and if these junctions are
maintained at different temperatures than an emf
is produced and this emf depends on the
temperature difference. Therefore in thermocouple
emf plays thermometric property, the property
which helps in holding in finding out the temperature
is named as the thermometric property.
Radiator: The radiator is a type of heat exchanger
in which the coolant looses heat by convection and
conduction phenomenon occurring in the tubes of
radiator. The radiator is generally made up of
aluminum metal because of its light weight and high
thermal conductivity.
Fan: A fan is installed just behind the radiator so
as to increase the cooling capacity of the radiator.
When the temperature of the coolant increases
because of constant acceleration the fan starts
operating, sucking in the air through the fins of the
radiator. This fan is controlled by an ECU (Engine
Control Unit). In the apparatus the fan runs
continuously to give an effect of a moving vehicle.
Coolant bottle: The coolant bottle serves here
an important function of controlling the coolant
from overflowing. When the fluid in the cooling
system heats up, it expands, causing the pressure
to build up. The cap is the only place where this
pressure can escape, so the setting of the spring
on the cap determines the maximum pressure in
the cooling system. The cap is actually a pressure
release valve, and on cars it is usually set to 15
psi. When the pressure reaches 15 psi, the pressure
pushes the valve open, allowing coolant to escape
from the cooling system. This coolant flows through
the overflow tube into the cooling bottle. This
arrangement keeps air out of the system. When
the radiator cools back down, a vacuum is created
in the cooling system that pulls open another spring
loaded valve, sucking water back in from the
cooling bottle to replace the water that was
expelled.
5.1 Testing procedure
In the test apparatus the heating element will be
acting as a source of heat which will act just like an
engine in an automobile. This heating element will heat
JP Yadav and Bharat Raj Singh
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up the coolant to a temperature range of 80OC -
120OC. After heating, the hot water is pumped with
the help of a pump in to the radiator. At the outlet of
the pump a rotameter is installed to measure the mass
flow rate of the hot coolant. The flow to rotameter is
controlled by a controlling valve, which helps in
obtaining different mass flow rate of the hot coolant.
Then the inlet temperature to radiator is calculated by
installing one thermocouple at inlet and is digitalized
by one digital meter. The hot water then flows through
the radiator core. Here with the help of a fan cold air
is sucked in, which helps in decreasing the temperature
of the coolant flowing through the radiator. Then, the
temperature at outlet is measured by a second
thermocouple. After this the coolant from outlet is
returned to the reservoir where it again becomes hot
by the action of heating element and is re-circulated
in the flow circuit to maintain the continuity of flow.
During testing, firstly water is taken as a coolant. It is
circulated at a mass flow rate of 5 LPM (liter per
minute). The fan is rotated at a speed of 6000 rpm.
After this the temperature of hot coolant at the outlet
is recorded at particular inlet coolant temperatures.
These readings are taken twice, at the first time by
rotating the fan at 6000 rpm and at the second time
by stopping the fan. After this first round of data
recording the coolant is changed. This time water is
replaced with a mixture containing 60% propylene
glycol and 40% water. Here the mass flow rate is
maintained at the same level as before and the fan is
also circulated with the same speed of 6000 rpm.
The temperature of the hot coolant at the inlet is also
maintained at the previous values and the
corresponding temperature values of the hot coolant
at the outlet are recorded. After the process of this
initial data recording the mass flow rate is varied by
keeping the temperature of the hot coolant at inlet
fixed at 80OC. The different mass flow rate values
include values from 5.0 LPM, 5.5 LPM, 6.0 LPM to
8.5 LPM. At these varying mass flow rates the
corresponding outlet temperature values of the hot
coolant is recorded. The above readings are taken
with water as well as with mixture of 60% propylene
glycol and 40% water one by one acting as coolants.
5.2 Assumptions
The results obtained are based on the following
assumptions:
a) Velocity and temperature at the entrance of the
radiator core on both air and coolant sides are
uniform.
b) There are no phase changes (condensation or
boiling) in all fluid streams.
c) Fluid flow rate is uniformly distributed through the
core in each pass on each fluid side. No stratification,
flow bypassing, or flow leakages occur in any
stream. The flow condition is characterized by
the bulk speed at any cross section.
d) The temperature of each fluid is uniform over every
flow cross section, so that a single bulk
temperature applies to each stream at a given
cross section.
e) The heat transfer coefficient between the fluid and
tube material is uniform over the inner and outside
tube surface for a constant fluid mass flow rate.
f) For the extended fin of the radiator, the surface
effectiveness is considered uniform and constant.
g) Heat transfer area is distributed uniformly on each
side
h) Both the inner dimension and the outer dimension
of the tube are assumed constant.
i) The thermal conductivity of the tube material is
constant in the axial direction.
j) No internal source exists for thermal-energy
generation.
k) There is no heat loss or gain external to the radiator
and no axial heat conduction in the radiator.
l) Thermal conduction parallel to the flow direction
of both the wall and the fluids are equal to zero.
m) Humidity is 71%.
n) Wind velocity is 4 km/hr.
o) Room temperature is 30OC.
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Where, mc = mass flow rate of coolant in kg/s
ma= mass flow rate of air in kg/s
Cpc= specific heat capacity of coolant at constant
pressure in kJ/kg K.
Cpa= specific heat capacity of air at constant
pressure in kJ/kg K.
tci = input temperature of coolant.
tco = output temperature of coolant.
tai = input temperature of air.
5.4 Influence of coolant mass flow
A graph is plotted graph showing the variation of
effectiveness and cooling capacity by the variation of
coolant flow rate. Coolant flow rate has been plotted
on X-axis and the effectiveness and cooling capacity
has been plotted at the primary and secondary Y-
axis. The temperature of inlet coolant has been
maintained at 80OC. By the graphs plotted it is
observed that effectiveness and the cooling capacity
of the radiator has direct relation with the coolant flow
rate. With an increase in the value of inlet cooling flow
rate there is corresponding increase in the value of
the effectiveness and cooling capacity.
One thing which needs to be noted is that the graph
of water is above the graph when mixture has been
used as the coolant. This is because the specific heat
capacity of the water is very much greater than the
mixture. So, if it is required to increase the cooling
capacity with the mixture then its mass flow rate is to
5.3 Mathematical Relations
In the test the following mathematical equation has been used.
At 1LPM mc = 601000
1
m³/s = 601000
1000
(for water)
= 601000
1062
kg/s (for water + propylene glycol)
Cpc = 4.18 kJ/kg K (for water) = 3.39 kJ/kg K (for 40% water + 60% propylene glycol)
Cpa = 1.005 kJ/kg K
ma = 1.49 kg/sc
The radiator fan rotates with 6000 rpm and its radius is 14 cm and effective pitch is 8 inches and it has
2735.28 CFM (cubic fit per minute)
1 CFM = min1 )1(
min1 )1( 33 ftft sm
sft
m
60
3048.0
60
min1
1
)3048.0( 3
3
  4-79 x 10-4 m3 s-1
be increased. Same is true with the plot of effectiveness
against the coolant mass flow rate.
5.5 Influence of coolant inlet temperature
In the following graphs the variation of the variation
in the cooling capacity and outlet temperature of hot
coolant is plotted against the inlet temperature of hot
coolant. On the X-axis inlet temperature of hot coolant
is plotted. The cooling capacity and the outlet
Fig. 7: Effectiveness and Cooling Capacity Versus
Coolant Flow of Radiator
Effectiveness of radiator () = ferheat trans Maximaum Transferheat Actual
tai)l (tci Cpa ma tco)- (tci Cpc mc )/tt(C ma
)t(tC mc
aicipa
cocipc
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Study on Performance Evaluation of Automotive Radiator
Fig.8 : Cooling Capacity and Output Temperature versus
Inlet temperature of Radiator with Fan
temperature are plotted on primary and secondary
Y-axis. The first graph is plotted when the fan is
rotating at a speed of 6000 rpm and the second graph
is plotted by considering it to be stationary. After
observing the first graph it is found that with the
increase in the inlet temperature of the coolant the
cooling capacity of the radiator increases. Also, with
the increase in the inlet temperature of the coolant the
temperature range of operation increases rapidly i.e.
at higher ranges of temperature operation the
difference between the inlet and the outlet temperature
of coolant increases rapidly. This happens because
the heat transfer between ambient and radiator surface
takes place by two phenomenon’s one is conduction
and the other is convection. In both these process the
heat transfer is directly proportional to the temperature
difference i.e. higher the temperature difference
between two medium higher will be the heat transfer.
The second graph has been plotted by considering
the fan to be stationary. As expected with the increase
in the value of inlet coolant temperature the cooling
capacity of the radiator increases. This is due to the
fact that the specific heat capacity of the water is very
much greater than the mixture. This fact can also be
seen by a sharp difference in the reading at the
corresponding values of coolant inlet temperature. In
the case of variation of outlet temperature with the
inlet temperature of coolant, there is not so much
difference since the effect of forced convection is
negligible. Hence the two graphs are almost
coincident.
Fig. 9: Cooling Capacity and Output Temperature versus
Input Temperature of Radiator without Fan
6. CONCLUSION
A complete set of numerical parametric studies on
automotive radiator has been presented in detail in
this study. The modeling of radiator has been
described by two methods, one is finite difference
method & the other is thermal resistance concept. By
a detailed literature survey a number of
recommendations have been provided for the
development of a more effective & compact radiator.
All these recommendations are listed in the future
scope section. These recommendations demand
changes from the range of the geometrical parameters
to the extent of coolant composition. In the
performance evaluation of the radiator, a radiator is
installed into a test-setup and the various parameters
including mass flow rate of coolant, inlet coolant
temperature etc. are varied. Then the corresponding
value of the effectiveness and outlet coolant
temperature are reversed. These values are then
plotted in the 3-axis graphs and their behavior is
studied.
In the testing, a comparative analysis between
different coolants has also been shown. Here, one of
the coolants is used as water and other as mixture of
water in propylene glycol in a ratio of 40:60. Here a
big difference in the cooling capacity of the radiator is
seen when the flowing coolant from water is changed
to mixture. This is on the account of a very high value
of specific heat of water in comparison to the mixture.
It therefore can be concluded that the water is still the
best coolant but its limitation are that it is corrosive
and contains dissolved salts that degrade the coolant
flow passage. By making a mixture with ethylene glycol
its specific heat is decreased but its other properties
are enhanced. It also increases the boiling temperature
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JP Yadav and Bharat Raj Singh
of water and decreases freezing temperature also. But
if the mixture is to be as effective as that of the water
then its mass flow rate should be increased.
All the formulas used in the calculation are listed in
the testing results and discussion section. Hence on
the basis of the study it is concluded that:-
The cooling capacity and the effectiveness are in
direct relation with the inlet temperature of hot
coolant i.e. with an increase in the value of inlet
coolant temperature the cooling capacity & the
effectiveness of the radiator increases respectively.
The cooling capacity and the effectiveness are also
in direct relation to the mass flow rate of the
coolant.
All these results have been calculated by taking
the fan speed at 6000rpm.
During our testing we have taken the maximum
fluid inlet temperature at 80OC. So, the values of
effectiveness are lower at this low temperature.
Whereas in actual the inlet coolant temperature to the
radiator is very much higher than experimented.
Therefore, the nature of the graph needs to be
concentrated on and not the specific values. Same is
true for the other plots also
7. FUTURE SCOPE
7.1 Use of nano-fluids
A three-dimensional laminar flow and heat transfer
with two different nano-fluids, Al2O3 and CuO, in an
ethylene glycol and water mixture circulating through
the flat tubes of an automobile radiator can also be
numerically studied to evaluate their superiority over
the base fluid. In radiators, which are vital component
in the control of the engine temperature in automobiles,
a liquid (commonly water – glycol mixture) is to be
cooled by air. The liquid flows in flat tubes while the
air flows in channels setup by fin surfaces. With recent
developments in Nanotechnology has been widely
used in traditional industries because materials with
grain size of nanometers posses unique optical,
electrical and thermal properties etc. Recently, nano-
particles can be dispersed in conventional heat transfer
fluids such as water, Ethylene glycol, Engine oil. It
produces a new class of high efficient heat exchange
fluids called Nano-fluids [4]. Many experimental and
theoretical analyses are carried and found these new
heat exchanger coolants are excellent. Nusselt number
in turbulent and laminar flows of different nano-fluids
(Al2O3 + H2O, Cu + H2O; etc) have been found,
showing that these fluids possess very high thermal
properties than conventional coolants.
7.2 S-shaped fins
Numerical studies have showed that the fin shape
affects the thermal-hydraulic characteristics of the
radiator with S-shaped fins. The fin angle effect, guide
wing effect, fin width effect, fin length effect, and fin
roundness effect were studied. The guide wing effect
was studied while changing the radial position and
circumferential fin arc length. Narrower fins produce
more heat transfer area per unit volume but worsen
the fin efficiency more than the wider fins. In the S-
shaped fin model, the narrowest fins showed the
largest heat transfer rate. A longer fin length reduces
the stream bend and pressure drop that occurs because
of the stream bend. The fin length effect was less than
the other fin effects if uniform flow was realized in the
channel. Fin roundness at the head and tail edge of
the fins minimally affect the heat transfer performance
but greatly affect the pressure drop performance.
From the real fin shape manufactured by chemical
etching, the pressure drop is increased by about 30%.
Lesser fin roundness is preferred to reduce the
pressure drop.
7.3 Increasing turbulence of coolants
The effectiveness of the radiator can be increased
by employing turbulence promoters. First the heat
transfer in plain fin arrangements was investigated to
determine the influence of corner radii of bent metal
sheets of the ribs. The Reynolds number range
extended from 500 to 3000, and a transition from
laminar to turbulent flow was observed at about
Re=2000. The ducts with the smallest radii resulted
in the highest Nusselt number for a given Reynolds
number, Nu exceeding that of ducts with the largest
radii by about 15%. However, a comparison of the
investigated geometries in terms of the volume
56 copyright samriddhi, 2011
S-JPSET : ISSN : 2229-7111, Vol. 2, Issue 2
goodness factors showed that the ducts with the
greatest radii were most advantageous.
Second, the influence of circular segment shaped
turbulence promoters in staggered, non staggered and
inclined arrangements was examined, the
determination of average Nusselt number showed that
the non staggered geometries deliver the highest heat
transfer rates. The best volume goodness factor was
achieved with the staggered arrangement.
7.4 Use of carbon-foam fins
One more modification which can be employed is
to replace aluminum fins with carbon foam channels.
Due to the thermal properties of carbon foam (k =
175-180 W/mK for carbon foam with 70% porosity),
along with increasing the amount of heat rejected, we
will be able to reduce the overall size of the radiator
while simultaneously increasing the surface area
exposed to the air, thus reducing the air side resistance.
Figure below shows our new design concept.
Study on Performance Evaluation of Automotive Radiator
Fig. 10: Flow pattern in non staggered arrangement
Fig. 11: Flow pattern in staggered arrangement
Fig. 12: Flow pattern in aligned arrangement
Fig.13: Carbon foam films
The carbon foam has channels in a corrugated
pattern. This corrugation channels air into the slots
and forces the air through the carbon foam. Also, there
are many tubes which are arranged in a parallel design.
They provide support for the carbon foam as well as
contain the necessary volume of coolant. The end caps
are made out of aluminum and also provide structural
support and mounting locations. Overall, this design
concept is a simple design which will meet most of
our customer requirements, including dissipating 147
kW of heat with an inlet fluid temperature of 85°C,
decreasing the overall volume.
REFERENCES
[1] F. G. Tenkel, “Computer Simulation of Automotive
Cooling Systems,” SAE Paper 740087, 1974 in page
no. 19.
[2] J.C. Corbel, “An Original Simulation Method for Car
Engine Cooling Systems: A Modular System,” SAE
Paper 870713, 1987 in page no. 27.
[3] W. Eichlseder, G. Raab, J. Hager and M. Raup, “Quasi-
Steady Calculation of Cooling Systems with Forecast
on Unsteady Calculations,” SAE Paper 954042, 1995
in page no. 29.
[4] S.U.S. Choi, “effect of nanolayer thickness on thermal
conductivity at the tube surface”, 1995 in page no.
42.
[5] M. Gollin, D. Bjork, Comparative performance of
ethylene glycol/ water and propylene glycol/water
coolants in automobile radiators, SAE Technical Paper
Series SP-1175, 960372, 1996 in page no. 21.
[6] J. A. Sidders and D. G. Tilley, “Optimizing Cooling
System Performance Using Computer Simulation,”
SAE Paper 971802, 1997 in page no. 16.
[7] C. Lin, J. Saunders, S. Watkins, The effect of changes
in ambient and coolant radiator inlet temperatures
and coolant flow rate on specific dissipation, SAE
Technical Paper Series (2000-01-0579), 2000, P.No.12.
[8] J. Burke and J. Haws, “Vehicle Thermal Systems
Modeling Using FLOWMASTER2,” SAE Paper 2001-
01-16, P.No.24.
[9] H. Cho, D. Jung and D. N. Assanis, “Control Strategy
of Electric Coolant Pumps for Fuel Economy
Improvement,” International Journal of Automotive
Technology, Vol. 6, No. 3, pp 269-275, 2005 in page
no. 30.
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Quasi-Steady Calculation of Cooling Systems with Forecast on Unsteady Calculations
  • W Eichlseder
  • G Raab
  • J Hager
  • M Raup
W. Eichlseder, G. Raab, J. Hager and M. Raup, "Quasi-Steady Calculation of Cooling Systems with Forecast on Unsteady Calculations," SAE Paper 954042, 1995 in page no. 29.
effect of nanolayer thickness on thermal conductivity at the tube surface
  • S U S Choi
S.U.S. Choi, "effect of nanolayer thickness on thermal conductivity at the tube surface", 1995 in page no. 42.
The effect of changes in ambient and coolant radiator inlet temperatures and coolant flow rate on specific dissipation, SAE Technical Paper Series Vehicle Thermal Systems Modeling Using FLOWMASTER2
  • C Lin
  • J Saunders
  • S Watkins
  • J Burke
  • J Haws
C. Lin, J. Saunders, S. Watkins, The effect of changes in ambient and coolant radiator inlet temperatures and coolant flow rate on specific dissipation, SAE Technical Paper Series (2000-01-0579), 2000, P.No.12. [8] J. Burke and J. Haws, " Vehicle Thermal Systems Modeling Using FLOWMASTER2, " SAE Paper 2001- 01-16, P.No.24. [9]