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International Journal of Automotive Engineering Vol. 2, Number 3, July 2012
Assessing the Effect of Blockage of Dirt on Engine Radiator
in the Engine Cooling System
S. D. Oduro1
1Lecturer , Design and Technology Department, University of Education Winneba, Kumasi Campus, Ghana
sethodurod@yahoo.co.uk
Abstract
This thesis looked at the effect of clay and silt soil blocking the heat transfer area of the radiator and its
effect on the engine coolant through the conduct of experiments and a mathematical model developed. The
results indicated that the percentage area covered resulted in a proportional increase of the inlet and outlet
temperatures of the coolant in the radiator. The mathematically model developed also predicted the
experimental data very well. Regression analysis pointed out that every 10% increase area of the radiator
covered with silt soil resulted in an increase of about 17 oC of the outlet temperature of the radiator coolant.
Similarly, using clay as a cover material, 10% of the area covered of the radiator resulted in an increase of
about 20 oC of the outlet temperature of the radiator coolant. Statistical analysis pointed to the fact that the
result obtained for clay, silt and the mathematical model were not significantly different. Thus, irrespective
of the type of material that blocks the radiator surface area, the coolant rises with proportion of the radiator
covered.
Keywords: Radiator, Silt, Clay, Temperature, Coolant.
1. INTRODUCTION
The radiator plays a very important role in an
automobile. It dissipates the waste heat generated
after the combustion process and useful work has
been done. The effectiveness with which waste heat is
transferred from the engine walls to the surrounding
is crucial in preserving the material integrity of the
engine and enhancing the performance of the engine.
Various studies have been carried out on engine
radiators focusing primarily on optimizing their
performance. The effect of pin fin on heat transfer
enhancement in a radiator was conducted to find out
the fin groove influence [1]. The study concluded that
an optimum angle of grooves and number of threads
per inch exist where the heat loss to the environment
is maximum. The effect of mass flow, inlet
temperature and coolant fluid thermal properties have
been extensively investigated by Oliet et al [2]. The
study also covered the effect of fin pitch, louver angle
and the importance of coolant flow lay-out on the
radiator. The paper concludes that the overall heat
transfer coefficient is essentially dependent on the
coolant flow regime and not the air side inlet
temperature.
The effect of electric field on the heat transfer
performance of a radiator at low frontal air velocity
has also been investigated by Vithayasai et al [3].
The paper concluded that an electric field can
enhance heat transfer when the frontal velocity is
below 1.6m/s. However, no significant effect on the
radiator was noticed when the frontal velocity was
above 1.6m/s. In addition, a correlation was observed
between the degree of heat transfer and the voltage
supplied. Other studies on the use of Computational
Fluid Dynamics (CFD) and the Effectiveness-Number
of Heat Transfer Units (e-NTU) to model and
optimize the heat transfer process of the radiator has
been carried out by Lin et al, [4]; Dittus and Boelter
[5] and Colburn [6].
Over the years, vehicles that are used in the Ghana
are imported from Europe, North America and other
Asian countries. The vehicles are manufactured
without taking into consideration the nature of the
roads in Ghana. When these cars are brought into the
country, they encounter numerous problems such as
engine breakdown, cylinder head gasket burnt and
S. D. Oduro 164
International Journal of Automotive Engineering Vol. 2, Number 3, July 2012
overheating. As the cars move on the untarred
roads, dust and mud get in contact with the radiator
fins. This dust and mud block the fins and impede the
flow of air through the radiator which eventually
settle on the engine and the radiator. As a result the
temperature of the coolant in the engine rises and
significantly affects the engine performance.
In Ghana, vehicles in cities, towns and villages
encounter these problems since most of the roads
these vehicles ply on are untarred roads. For example,
only 23% of roads in Kumasi city are tarred [7].
These dust and mud accumulate on the fins of radiator
and other component of the cooling system affect the
radiator performance. The accumulation narrows the
heat dissipation air passage area. The greater soils on
the road are mainly clay and silt which predominately
are found on Ghanaian roads.
There has been little or no research conducted on
the effects of soil blocking radiator fins and its effect
on the cooling system in Ghana. Little is known on
the quantification of dirt on the radiator fins and its
effect on the engine performance. These studies take a
critical looks at the effect of dirt blocking the radiator
fins and its effect on the coolant temperature
.
2. Material and Methods
2.1 Experimental Setup
This paper which formed part of a whole project
work has the experimental setup comprised of a four
cylinder petrol engine as shown in Fig. 1. The engine
is a water-cooled with a radiator tank capacity of 5.5
liters and the compression ratio is 9.8 to 1. The
radiator consists of fins, tubes, upper and lower hose
and the outer frontal surface area which was covered
using clay and silt soil during the experiment. The
radiator outer surface area was divided into 10 equal
parts each representing 10% of the surface area
covered. It was then covered with clay or silt from
each ends at 5% from the outer surface area of the
radiator as shown in figure 1.
2.2 Description of Equipment and Engine
The engine was fitted with two Cola-Parma model
8110-10 thermocouple with an accuracy of ± 0.10 oC
to read the inlet and outlet temperature of the water
into and out of the radiator. Details of the
specification of the engine and radiator used for the
experiment are given in Table 1.
K-type Thermocouple Radiator surface area covered with Clay or Silt
Fig1. The K-type of t hermocouple fitted to both the outlet and i nlet radiator hose
2.3 Experimental procedure
The radiator of the engine was 65 mm in length by
35 mm in breath as showed in Fig. 1, and had a total
number of 66 tubes. All the 66 tubes were in a single
row and each tube was 2 mm thick. The fins were
made of copper with a thickness of 0.5 mm, height of
16 mm and spaced 3 mm apart as shown in figure 1.
The radiator was thoroughly cleaned of all dust and
debris before the experiments were carried.
165 Assessing the Effect of Blockage of…..
International Journal of Automotive Engineering Vol. 2, Number 3, July 2012
Table 1: Shows the specifications of Engine and Radiator Used
for the Experiment
Year 1996
Manufacturer Nissan
Model range Primera
Engine Capacit y 1597cc
Engine Type GA 16
Number of cylinders 4/DOHC
Engine Firing Order 1-3-4-2
Compression Rati o 9.8:1
Cooling System capacity 5.5 litres of water
Thermostat opening 76.5c
Radiator Pressure 0.78-0.98 bar
Ignition timing basic BTDC Engine/rpm 10+2/62 5
Idling Speed 750+50 rpm
The radiator effective heat transfer surface area as
showed in Fig. 1 was divided into ten (10) equal
parts, each representing 10% of the effective heat
transfer area. The outer part of the radiator heat
transfer area was covered whiles the engine cooling
fan mounted in the inner surface area was used to
draw air through the radiator as each percentage of
outer surface area covered. The fan speed was held
constant throughout the experiment. Part of the outer
effective heat transfer area was then covered with
either clay or silt soil to the required percentage
before running the engine. The engine was run for
about fifteen (15) minutes to attain stable conditions
before readings were taken. For each set-up, three
readings were taken at intervals of two minutes. The
rotational speeds of the engine and the fan speed were
held constant throughout the experiment. Also, the
load on the engine was not increased, throughout the
experiment, the engine was idling. At the end of each
experiment, the radiator is thoroughly cleaned; it is
then covered with silt or clay soil which is the major
soil on our roads and selected for the experiment to
the required percentage. The K-thermometer used was
to connect both the lower and upper radiator hose
where readings were taken simultaneously from the
coolant entering in and out of the engine. The
readings were taken at two minutes interval by the K -
thermometer. When the engine was running, coolant
flows into the block and through the water jacket
surrounding the cylinder. It then flows through the
upper radiator hose as shown in Fig.2. As the coolant
flows through the radiator, the fan draws air through
the heat transfer surface area of the r adiator and
pumps it into the engine by the water pump.
A mathematical model was develop based on the
Effectiveness – Number of Heat Transfer Units
(ɛ-NTU) method was used to validate the
experimental result. In modeling the radiator, the ɛ-
NTU was used because, the focus of this paper was
on the outlet and inlet temperature of the water after
the effective heat transfer area was partially covered
with either clay or silt soil to the required percentage
before running the engine. When the inlet or outlet
temperatures are to be estimated, the ɛ-NTU method
comes in handy.
Fig2. Experimental set-up showing K-type t hermocouple and radiator outer surface area covered
S. D. Oduro 166
International Journal of Automotive Engineering Vol. 2, Number 3, July 2012
3. Mathematical Equation Used
The model was developed to predict the outlet
temperature of the coolant from the radiator given the
dimensions of the radiator, the flow rates of the fluids
and the cooling load. In order to solve the analytical
model, the following assumptions were made;
1.Constant coolant flow rate and fluid
temperatures at both the inlet and outlet temperatures,
that the system operated at steady state
2.There were no phase changes in the coolant
3.Heat conduction through the walls of the coolant
tube was negligible
4.Heat loss by coolant was only transferred to the
cooling air, thus no other heat transfer mode such as
radiation was considered
5.Coolant fluid flow was in a fully developed
condition in each tube
6.All dimensions were uniform throughout the
radiator and the heat transfer of surface area was
consistent and distributed uniformly
7.Pure water was used as the coolant
8.The thermal conductivity of the radiator material
was considered to be constant
9.There were no heat sources and sinks within the
radiator
10.There was no fluid stratification, losses and
flow misdistribution.
The heat transfer process in the radiator was modelled
as a forced convective heat transfer operation. The
equations for the model were taken from Lin et al [4].
The parameters for calculating the heat transfer area
are given in Table 2 below. The relevant equations
are given from equation 1 to 25
Table 1.Parameters for the radiator heat transfer area
Core height B
H
Core width B
W
Core thickness
B
T
Number of coolant tubes in core depth dimension N
r
Number of coolant tubes in one row N
ct
Number of profiles N
p
Number of fins in one meter N
f/m
Louvre pitch L
p
Louvre length L
l
Fin thickness
F
t
Fin height F
h
Fin pitch F
p
Fin end radius R
f
Angle of fin α
f
Coolant tube length Y
l
Coolant tube cross section length Y
cl
Coolant tube cross section width
Y
cw
Coolant tube thickness Y
t
Coolant tube pitch Y
p
Coolant tube end radius R
t
The fin length, Fl is given by;
ܨ= ߨR+ିଶୖ
ୡ୭ୱ (1)
The radiator core frontal area, Afr is given by;
ܣ = ܤுܤ௪ (2)
Coolant tube frontal area, Afr,t is given by;
ܣ.௧ = ܻ௪ܻܰ௧ (3)
Fin heat transfer area, Af, is given by;
ܣ=2.ܤ்ܨ்ܻܰܰ (4)
The total heat transfer area on air side, Aa is given
by;
ܣ= ܣ+2ܰ௧ܻܰ[ሺܻ −2ܴ௧ሻ+ሺ2ߨܴ௧ሻ] (5)
167 Assessing the Effect of Blockage of…..
International Journal of Automotive Engineering Vol. 2, Number 3, July 2012
The total heat transfer area on coolant side, Ac is
given by;
The total coolant pass area, Ap,c is given by;
ܣ, = [ߨሺܴ௧−ܻ௧ሻଶ+ሺܻ௪ − 2ܻ௧ሻሺܻ −
2ܴ௧ሻ]ܰ௧ܰ (7)
The following dimensionless groups for
convective heat transfer were used;
Reynolds number – which may be defined as ratio
of flow momentum rate (inertia force) to viscous
force for a particular geometry. It is given by;
ܴ݁ = ఘ
ఓ (8)
Nusselt number – which is defined as the ratio of
the convective heat transfer coefficient (h) to the pure
molecular thermal conductance (k/L), thus,
ܰݑ =
(9)
Prandtl number – defined as the ratio of
momentum heat diffusivity to thermal diffusivity of
the fluid. It is solely a fluid property modulus
ܲݎ = ௩
ఈ=ఓ
. (10)
Where ρ = density of the fluid, kg/m3
V = velocity of the fluid, m/s
L = length of tube, m
k = thermal conductivity of the fluid, W/m.k
Cp = Specific heat capacity of the fluid,
kJ/kg.K
h = heat transfer coefficient, J/m2.K
α = thermal diffusivity of the fluid, m2/s
µ = viscosity of the fluid, centipoise
υ = kinematic viscosity of the fluid, m2/s
3.1OVERALLHEATTRANSFER COEFFICIENT
The overall heat transfer resistance for radiators
can be considered to be due to;
Wall conductance
Fouling on the air side
Air side convection
Fouling on the coolant side
Coolant-side convection
Mathematically, it can be defined as;
ଵ
=ଵ
ሺ୬୦ሻ+Rୟ +∆୶
ሺ୩ሻ౭+ଵ
ሺ୬୦ሻౙ (11)
Where U = the overall heat transfer coefficient
h = heat transfer coefficient
no = total surface efficiency of an extended
fin surface
Rf = fouling factor
Subscript a, c and w refer to air side, coolant
side and coolant wall respectively.
For purposes of simplicity, the fouling factor on
both the air side and the coolant side was assumed to
be negligible. Also, the thermal resistance due to the
coolant wall was assumed to be negligible as
compared with the other terms because the coolant
tube is most often made with either copper or
aluminium both of which have large thermal
conductivities whilst the thickness of the tube is
usually small. The total surface efficiency of the fin
was also assumed t o be unity for purpose of
simplicity.
When all these assumption are taken into effect
the corrected equation becomes;
ଵ
౨,౨ =ଵ
୦+ଵ
୦ౙౙ (12)
Where Afr,r = radiator core frontal area
Aa = total heat transfer area on air side
Ac = total heat transfer area on coolant side
ha = heat transfer coefficient on air side
hc = heat transfer coefficient on coolant side
The air side heat transfer coefficient was taken
from Davenport [8] and is given by;
hୟ= 0.249Re୪
ି.ସଶL୦
୭.ଷଷ ቀ
ቁଵ.ଵ F୦
.ଶ൨େ౦,
౨
మయ
ൗ (13)
Where Lh = louver height
Ll = louver length
Fh = Fin height
Other parameters retain their meaning as already
defined above.
The coolant side Nusselt number was taken from
Holman [9] is given by;
Nuୡ= 3.66 + .଼൬ీ,ౙ
ౕభ൰ୖୣ୰
ଵା.ସ൬ీ,ౙ
ౕభ൰ୖୣ୰൨మయ
ൗ (14)
This equation was employed because of the
laminar nature of the fluid flow in our radiator. Other
correlations may be applicable depending on the
nature of fluid flow – transition or turbulent.
Where Dh = hydraulic diameter
Yl = coolant tube length
3.2 THE Ɛ-NTU METHOD
The heat transfer rate in the radiator is given by;
Q = εC୫୧୬ሺTୡ୧ −Tୟ୧ሻ (15)
ܣ
=
[
2
ߨ
ሺ
ܴ
௧
−
ܻ
௧
ሻ
+
2
ሺ
ܻ
−
2
ܴ
௧
ሻ
]
ܻ
ܰ
௧
ܰ
ሺ6ሻ
S. D. Oduro 168
International Journal of Automotive Engineering Vol. 2, Number 3, July 2012
Where Cmin = minimum heat capacity rate
The radiator thermal efficiency (ɛ) is defined as
the ratio of the actual transfer rate from the hot fluid
(coolant) to the cold fluid (air) in a given radiator to
the maximum possible heat transfer rate. It is
expressed as;
The actual heat transfer balance equation at steady
state which is defined in terms of energy lost on
coolant side and energy gained on the air side is given
by;
Where Ca = heat capacity of air
Cc = heat capacity of coolant
Tci = Coolant inlet temperature
Tco = Coolant outlet temperature
Tao = Air outlet temperature
Tai = Air inlet temperature
The heat capacity ratio is defined as the product of
the mass flow rate and the specific heat of the fluid;
For air: ܥ= ݉ݔܥ, = ܣߩܸܥ, (18)
For coolant:
ܥ= ݉ݔܥ, = ܣߩܸܥ, (19)
The heat capacity ratio is defined as the ratio of
the smaller to the larger capacity rate for the two fluid
streams and is expressed as;
Where Cmin is the smaller of Ca and Cc. According
to SAE JI393 [10], the minimum capacity rate Cmin is
always on the air side. Hence
Cmin = Ca and Cmax = Cc. (21)
It follows therefore that the heat transfer rate is
given by;
The number of heat transfer units (NTU) is the
ratio of overall conductance UA to the smaller
capacity rate Cmin;
The radiator effectiveness is defined as a function of
both the NTU and the Cr by Kays and London [11]
and is given by;
The model equations were developed to predict
the outlet temperature (T1) of the coolant from the
radiator given the dimensions of the radiator, the flow
rates of the fluids and the cooling load. The following
equations were generated and based on the equation
outlined below, the model was developed using
MATLAB and run with an algorithm.
The final result obtained was used to validate the
experimental results.
4. Results and Discussions
As shown in Fig.3 when the result of the
mathematical model was compared to the results
obtained from experiment the experiment using clay
and silt soil, it was observed that the mathematical
model predicted the heat transfer phenomenon quite
well. In spite of the many assumptions, it was
observed that the temperature of the coolant from the
radiator was comparable to results obtained for the
experiments. The model predicted closely, the results
obtained when clay was the covering material better
than silt. This is perhaps due to the fact that clay was
a better coverage material than silt that clay stuck
better on the radiator surface than silt. This is also in
line with literature because Davenport [8] performed
visualization studies on radiator and concluded that as
the effective heat transfer area of a radiator deceases
the total heat transfer through the radiator also
decrease and vice versa. It was generally observed
that as the area of the radiator covered was increased,
the temperature of the coolant from the radiator also
increased considerably. This can be explained by the
fact that the effective heat transfer area was reduced,
thereby limiting the quantity of air admitted through
the radiator for purposes of cooling the coolant. In all
cases this trend of increasing outlet temperature of the
coolant from the radiator was observed. As shown in
the fig. 3, the temperature of the ambient air was
found to be relatively constant. This therefore did not
significantly affect the rate of heat transfer because
the air mass was almost constant just as the thermal
properties of the air.
Comparing the temperature of the coolant into the
radiator for three scenarios – the model, clay and silt
covering, it can be observed in Fig.4, that the results
obtained were similar. The model was able to predict
the heat transfer process quite well. In all the three
cases the temperature of the coolant into the radiator
increased as the area of the radiator covered also
ߝ
=
ொ
ொ
ೌೣ
(16)
ܳ
=
ܥ
ሺ
ܶ
−
ܶ
ሻ
=
ܥ
ሺ
ܶ
−
ܶ
ሻ
(17)
ܥ
=
ೌೣ
(20
)
ܳ
=
ߝ
ܥ
ሺ
ܶ
−
ܶ
ሻ
(22
)
ܷܰܶ
=
ೝ
,
ೝ
=
ଵ
ܷ
.
݀
ܣ
,
(23
)
ߝ
=
1
−
݁ݔ
ቄ
ே்
బ
.
మమ
ೝ
[
݁ݔ
ሺ
−
ܥ
.
ܷܰܶ
.
଼
ሻ
−
1
]
ቅ
(24)
T1=T2
-
Qc/ሺe*Ca_w
ሻ
ሺ
25
ሻ
169 Assessing the Effect of Blockage of….
International Journal of Automotive Engineering Vol. 2, Number 3, July 2012
Increased. This is due to the fact that when the
surface area of the radiator is reduced by covering,
less heat is taken out of the coolant, thus increasing
the outlet temperature of the coolant from the radiator
as observed above. Since the coolant is not well
cooled, it picks up heat from the engine which
increases its temperature higher than expected before
entering the radiator. During the experiment it was
also noticed that the engine stopped running after a
short time when the radiator was completely covered.
This was as a result of the inability of the coolant
from taking away enough heat from the walls of the
engine thereby causing poor idling and rough running
and subsequently forcing the engine to stop running
in order to prevent substantial damage to the engine.
As given in the table 2, the regression
relationships between the radiator coolant outlet
temperatures and the proportion of the radiator
surface area covered with clay, silt and Matlab
simulation respectively. As expected it can be seen
that as the percentage of the radiator surface covered
increases the outlet temperature of the radiator
coolant increases. The regression models used to
predict the outlet temperatures of radiator coolant
from the percentage of area covered of the radiator.
Fig3. Comparison of model results of temperature of water out of the radiator with result s obtained with silt and clay
Fig4. Comparison of result s of inlet temperature of water into t he radiator for the model with that of silt and clay
S. D. Oduro 170
International Journal of Automotive Engineering Vol. 2, Number 3, July 2012
The Matlab model was a simulated model to
evaluate the validity of the silt and clay models. All
the three models predicted well and were statistically
significant at a 1% probability level. The coefficient
of determination (R2) of the three models ranged
from 0.98 to 0.99. At least 99% of the variation in the
outlet coolant temperatures was explained by the
percentage of the area covered of the radiator. For the
silt model, for every 10% increase or decrease of the
area covered of the radiator resulted in an average
increase or decrease of about 17 degree Celsius of the
outlet temperature of the radiator coolant. In the case
of the clay model, a 10% increase or decrease of the
area covered of the radiator resulted in about 21
degree Celsius of the outlet temperature of the
radiator coolant (Table 3). In the Matlab model, a
change in 10% of the area covered of the radiator
resulted in a change of about 20 degree Celsius of the
outlet temperature of the radiator coolant.
The Analysis of Variance (ANOVA) which was
conducted to find out if there were statistically
significant differences among the three models
namely clay, silt and the Matlab (Table 4). The Table
3 given clearly showed that, there were no statistically
significant differences among the three models. This
indicates that the Matlab model predicted the
experimental result quit well. It can also be said when
the same amount of clay or silt covers the same area
of a radiator the same temperature rise of the radiator
coolant will obtained.
Table 3: Models to predict outlet temperature (°C) of coolant from the Area covered of the radiator (%).
Model Regression equation R
2
T – Test (Two-tailed) P-value
Silt T=0.1652 A+40.29 0.9858 78.558 <0.0001
Clay T=0.2072A+41.6 99 0.9792 70.039 <0.0001
Mat lab T=0.20A+42.323 0.999 905.980 <0.0001
Table 4: Analysis Of Variance (ANOVA) for comparison outlet temperatures based on the silt, clay and Matlab models
Sum of squares
Df
Mean Square
F
-
Value
p
-
value
Between Groups 106,246 2 53,123 1.425 0.255
Within Groups 1230,285 33 37,283
Total 1336,531 35
5. Conclusions
Experiments were successfully conducted on the
radiator of four cylinder petrol engine at base load.
Two different soil types, namely silt and clay, were
used as covering material to cover the heat transfer
area of the radiator to determine the heat transfer
process during the running of the engine. It was
observed that the inlet temperature of the coolant in
the radiator increased as the percentage area of the
radiator covered increased. It was also observed that
The outlet temperature of the coolant from the
radiator increased monotonically with increases in
the percentage area of the radiator covered. In both
cases, at 80% coverage of the heat transfer area of the
radiator the engine vibrated excessively and the idling
was not stable. It can be concluded that dirt on the
surface of a radiator decreased the performance of the
radiator which could affect the engine in the long run.
It is recommended that, future studies should consider
a long real live engine testing for a longer period of
time. This will give us a long term effect on the
engine due to part of the radiator being covered with
silt or clay as is the case in most African countries.
171 Assessing the Effect of Blockage of….
International Journal of Automotive Engineering Vol. 2, Number 3, July 2012
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