Performance Analysis of Automobile Radiator

Abstract

An automobile radiator is a component of an automotive cooling system which plays a major role in transferring the heat from the engine parts to the environment through its complex system and working. It is a type of cross flow heat exchanger which is designed to transfer the heat from the hot coolant coming from the engine to the air blown through it by the fan. A small segment of the radiator is analyzed for the various speed of the air striking the radiator as the vehicle moves from its rest position to a certain speed. The heat transfer processes takes place from the coolant to the tubes then from the tubes to the air through the fins. After the analysis is carried out, the heat transfer coefficient of air and ethylene glycol is estimated and further overall heat transfer coefficient is calculated.

Full text

International Journal on Recent Technologies in Mechanical and Electrical Engineering (IJRMEE) ISSN: 2349-7947
Volume: 3 Issue: 5 35 - 38
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Performance Analysis of Automobile Radiator
P. Mounika1, Rajesh K Sharma2
Students
Department of mechanical engineering
Andhra university college of engineering
Visakhapatnam, India
email: mounikasklm@gmail.com1
email: stayne.rockey0059@gmail.com2
P. S. Kishore3
Professor
Department of mechanical engineering
Andhra university college of engineering
Visakhapatnam, India
email: srinivaskishore_p@yahoo.com3
Abstract:-An automobile radiator is a component of an automotive cooling system which plays a major role in transferring the heat from the
engine parts to the environment through its complex system and working. It is a type of cross flow heat exchanger which is designed to transfer
the heat from the hot coolant coming from the engine to the air blown through it by the fan. A small segment of the radiator is analyzed for the
various speed of the air striking the radiator as the vehicle moves from its rest position to a certain speed. The heat transfer processes takes place
from the coolant to the tubes then from the tubes to the air through the fins. After the analysis is carried out, the heat transfer coefficient of air
and ethylene glycol is estimated and further overall heat transfer coefficient is calculated.
Keywords: Automobile radiator, velocity, convection, fins, heat transfer coefficients.
__________________________________________________*****_________________________________________________
1. INTRODUCTION:
An automobile travels at various ranges of velocities. The
faster it travels, the more power engine needs to generate
and hence the better the cooling process has to be. The
coolant(ethylene glycol) coming from the engine passes
through the tubes of the radiator where the heat transfer
from the coolant to the surrounding takes place through heat
transfer processes, mainly conduction and convection. Thus,
the velocity of the air striking the radiator becomes a crucial
parameter during the cooling phenomenon through the fins.
Oliet et al. [1], studied different factors which influence
radiator performance. It includes air and coolant flow, fin
density and air inlet temperature. Yadav and Singh [2], in
their studies also presented parametric study on automotive
radiator. The various parameters including mass flow rate of
coolant, inlet coolant temperature; etc. are varied. Mazen Al-
Amayreh[3],in his study, tested the thermal conductivities of
ethylene glycol + water, diethylene glycol + water and
triethylene glycol + water mixtures, measured at
temperatures ranging from 25°C to 40°C and concentrations
ranging from 25 wt. % glycol to 75 wt.% glycol. Trivedi
and Vasava [4], illustrated the effect of Tube pitch for best
configured radiator for optimum performance. Heat transfer
increases as the surface area of the radiator assembly is
increased. Chavan and Tasgaonkar [5], explained
conventional radiator size is rectangular which is difficult for
circular fan to cover whole surface area. It creates lower
velocity zones at corners giving less heat transfer.Leong et
all [6],described use of nanofluid based coolant in engine
cooling system and its effect on cooling capacity. It is found
that nano-fluid having higher thermal conductivity than base
coolant like 50%/50% water and ethylene glycol. John
Vetrovec [7], carried work on engine cooling system with
heat load averaging capacity using passive heat load
accumulator. Salah et all [8], discussed about hydraulic
actuated cooling system. Actuators can improve temperature
tracking and reduce parasitic losses. Cengel [9], said that the
common definition for cross flow heat exchanger is where
both hot and cold fluid travel perpendicular to each other.
Kishore [10], in his thesis dealt with enhancement of heat
transfer for both laminar and turbulent flow conditions and
derived the equations for Nusselt number and friction factor.
Sarma et al. [11] in their article discussed the momentum
effects and heat transfer induced effects in evaluating the
correlations for heat transfer and friction factor. They said
that the turbulence introduces the need for evaluating the
momentum and thermal eddy diffusivities. K.Balanna and
P.S.Kishore in their paper written about the evaluation of
heat transfer and friction factor on wavy fin of an automotive
radiator.
2. DESCRIPTION AND WORKING OF THE
RADIATOR:
LINE DIAGRAM OF HEAT TRANSFER THROUGH
COOLING SYSTEM
The radiator is part of the cooling system of the
engine Automobile radiators utilize mostly a cross flow heat
exchanger. The two working fluids are generally air and
coolant. As the air flows through the radiator, the heat is
transferred from the coolant to the air. The purpose of the air
is to remove heat from the coolant, which causes the coolant
to exit the radiator at a lower temperature than it entered at.
Coolant is passed through engine, where it is absorb heat.
The hot coolant is then feed into tank of the radiator. From
tank of radiator, it is distributed across the radiator core
through tubes to another tank on opposite side of the
radiator. As the coolant passes through the radiator tubes on

International Journal on Recent Technologies in Mechanical and Electrical Engineering (IJRMEE) ISSN: 2349-7947
Volume: 3 Issue: 5 35 - 38
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its way to the opposite tank, it transfers much of its heat to
the tubes which, in turn, transfer the heat to the fins that are
lodged between each row of tubes. The radiator acts as a
       
coolant fluid into the air. The radiator is composed of tubes

pressure valve and a tank on each side to catch the coolant
fluid overflow. In addition, the tubes carrying the coolant
fluid usually contain a turbulator, which agitates the fluid
inside. This way, the coolant fluid is mixed together, cooling
all the fluid evenly, and not just cooling the fluid that
touches the sides of the tubes. By creating turbulence inside
the tubes, the fluid can be used more effectively.
RADIATOR CORE GEOMETRY
1) Tube
Radiator consists of circular tubes whose diameter is 0.59
cm (air side) and 0.56 cm (coolant side), number of tubes
are arranged in parallel as shown in Fig.1. The fluid
circulates through the tubes which take out the heat from the
engine cylinder.
2) Wavy Fin
Continuous fins of thickness, made of aluminum is taken
3) Upper and Lower Cover
The upper and lower radiator covers are surrounded
on top and bottom of radiator
3. THERMAL ANALYSIS OF THE PROBLEM:
The performance parameters like heat transfer coefficient
and efficiency are to be analyzed for different set of values
of velocity of the automobile (i.e., velocity of air)
3.1 ASSUMPTIONS:
Heat transfer analysis of a radiator in an automobile radiator
in an automobile engine is done by considering the
following assumptions.
1. The radiator operates under steady-state conditions that is
constant flow rate and coolant temperatures at the inlet and
within the radiator are independent of time.
2. There are no thermal energy sources and sinks in radiator
walls or coolant.
3. Either there are no phase changes in the coolant stream
flowing through the exchanger.
4. The specific heats of ethylene glycol and air are constant
throughout the radiator.
5. The fluid flow rate is uniformly distributed through the
radiator on each fluid side in each pass. No flow
stratification, flow bypassing or flow leakages occur in any
stream.
6. Kinetic energy and potential energy changes are
negligible.
3.2 HYDRAULIC DIAMETER:
The hydraulic diameter must be used because it is a non-
circular cross section. The hydraulic diameter can then be
used to estimate the Reynolds number. The equation for the
hydraulic diameter calls for the wetted perimeter of the
tubes. However, the difference in the outer and inner tube
dimensions is so negligible that the outer perimeter is used
for convenience.
Hydraulic diameter,
Dhyd =4Atube
Ptube (1)
Where,
Atube = Area of the radiator tube
Ptube = Perimeter of the radiator tube
3.3 NUSSELT NUMBER
The Nusselt number was found for a rectangular cross
section for fully developed laminar flow. The ratio of width
over height of the tube is used.
Nueg = 0.023 ×Reeg
0.8 ×Preg
0.4 (2)
Where,
Reg = Dhyd ×× v

Reeg = Reynolds number of ethylene glycol
Preg = Prandtl number of ethylene glycol
EXTERNAL FLOW OF AIR
The air flows from the fan across the radiator tubes and
through the fins utilizing convective heat transfer. In reality,
the flow of air over the tubes will be slightly different due to
the fluid flowing around the first tube before reaching the
second tube, so calculating the heat transfer coefficient
would be very difficult. To simplify the calculations, the
flow is assumed to be the same over both tubes. Also,
because the height to width ratio of the tubes is so small, the
air will be assumed to be flowing on both sides of a flat
plate.
3.4 VELOCITY
Vair =Qair
Aradiator Ntube Htube Lradiator  (3)
Here,
Qair = Total air volumetric flow rate
Aradiator = Area of the radiator
Ntube = Number of tubes
Htube = Height of the tube
Lradiator = Length of the radiator
3.5 REYNOLDS NUMBER
Reair =Vair Wfin
vair (4)
Here,
Vair = Velocity of air
Wfin = Width of the fin
air = Kinematic viscosity of air

International Journal on Recent Technologies in Mechanical and Electrical Engineering (IJRMEE) ISSN: 2349-7947
Volume: 3 Issue: 5 35 - 38
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3.6 NUSSELT NUMBER
Looking at the geometry of the tubes, it can be assumed that
the flow of air is similar to parallel flow over a flat plate.
Since the flow never reaches the critical Reynolds number
for a flat plate, Re = 0.5x10, it is said to be laminar for the
entire process.
Nuair = .664Reair
1
2Prair
1
3 (5)
Where,
Reair = Reynolds number of air
Prair = Prandtl number of air
3.7 CONVECTIVE HEAT TRANSFER COEFFICIENT
FOR AIR FLOW hair =Nu air ×kair
Wtube
(6)
Where,
Nuair = Nusselt number of air
kair = Thermal conductivity of air
Wtube = Width of the tube
3.8 FIN DIMENSIONS AND EFFICIENCY
The geometry of the fins on the radiator is sinusoidal. The
troughs of the fins touch the lower adjacent tube and the
peaks of the fins touch the upper adjacent tube. The heat
from the tubes emanates through the fins. The fins and tubes
are then cooled by the air from the fan, which is traveling
across the radiator. To simplify the geometry for the ease of
calculations, the fins are assumed to be straight instead of
sinusoidal. This is a minor transition in geometry since the
shape and position of the actual fins are so close to the
straight configuration. The following formulas are given
below to calculate the fin efficiency.
fin =tanh (mL c)
mL c (7)
Where,
Lc = Characterstic length of the fin
4. RESULTS AND DISCUSSIONS:
Graphs are drawn between different parameters from the
values that we derive from the calculations.
4.1 NUSSELT NUMBER OF AIR vs REYNOLDS
NUMBER OF THE AIR
The graph is plotted between Nusselt number on Y-axis and
Reynolds number of air on X-axis. The graph clearly shows
that as the Reynolds number of the air increases the Nusselt
number also increases.
4.2 HEAT TRANSFER COEFFICIENT OF AIR vs
VELOCITY OF AIR
In the graph, Heat transfer coefficient of air (W/m2k) is
plotted against velocity of air(kmph).
4.3 EFFICIENCY OF THE FINS vs. REYNOLDS
NUMBER OF THE AIR
The graph shows the variation of efficiency of the fins with
the Reynolds number of the air that strikes the radiator at
different velocities. When an automobile travels at a very
faster rate, huge amount of heat is generated in the engine
and its parts. The fins used in the radiator play a crucial role
in helping the radiator to dissipate the heat. As we can see
from the graph with increase in Reynolds number the
efficiency of the fins decreases, but the decrement is very
small and it is still very useful for the cooling of the radiator.
4.4 OVERALL HEAT TRANSFER COEFFICIENT vs
REYNOLDS NUMBER OF AIR
0
50
100
150
200
050000 100000
Nusselt number of
air
Reynolds number of air
0
50
100
150
200
050 100
Heat trasnfer coefficient of
air
Velocity of air
88
90
92
94
96
020000 40000 60000 80000
Efficiency of fin
Reynolds number
0
50
100
150
020000 40000 60000 80000
Overall heat transfer
coeffecient
Reynolds number of air

International Journal on Recent Technologies in Mechanical and Electrical Engineering (IJRMEE) ISSN: 2349-7947
Volume: 3 Issue: 5 35 - 38
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A graph is plotted between overall heat transfer coefficient
and Reynolds number on. From the graph, it is seen clearly
that the value of overall heat transfer coefficient increases as
the Reynolds number increases. Overall heat transfer
coefficient depends upon the heat transfer coefficient of the
air and the coolant used (ethylene glycol).
5. CONCLUSIONS
Heat transfer analysis of an automobile radiator is done for
the range of 15 kmph to 75 kmph speed of the air striking
the radiator with ethylene glycol as coolant and conclusions
obtained are as follows:
1. Nusselt number of the air is calculated, as the Reynolds
number of the air increases, the value of Nusselt number
increases from 69 % to 125 %.
2. The heat transfer coefficient values are increased by 125
% when the velocity of the air striking the radiator changes.
3. It is also observed that, at higher velocity of air striking
the radiator, the Reynolds number is higher and as a result
of it the efficiency of the fins is reduced slightly. Efficiency
of the fins reduces by 6.1% when the Reynolds number
changes from 14000 to 71000.
4. Overall heat transfer coefficient is the function of the heat
transfer coefficient of the air as well as the coolant used (
ethylene glycol ). As the Reynolds number increases from
14000 to 71000, there is 91 % increase in the overall heat
transfer coefficient.
5. When engines run at high values of rpm to increase the
speed of the vehicle, the heat generated in the parts of the
engine also increases drastically. Hence, at higher speed the
cooling process should also be effective in order to dissipate
the heat to the atmosphere. It can concluded by this analysis
that, even at higher speed the given dimensioned radiator
with given number of fins attached to it works properly with
slight compromise in the decrease in efficiency of the fins
used in the radiator.
6. NOMENCLATURE
L Lemgth, m
H Height, m
W Width, m
D Diameter, m
A Cross-sectional area, m2
P Perimeter, m
V Velocity, m/s
Q Volumetric flow rate, m3/s
N Number
Re Reynolds number
h Convective heat transfer coefficient ,
W/m2-K
Nu Nusselt number
k Thermal conductivity, W/m-K
Pr Prandtl number
m Coefficient for calculating efficiency
UA Overall heat transfer coefficient
6.1 GREEK SYMBOLS

 Kinematic viscosity
 Efficiency
6.2 SUFFIXES
eg Ethylene glycol
f Fin
b Base
hyd Hydraulic
rad Radiator
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