Some Studies on the Performance of Automotive Radiator at Higher

Transcription

Journal of Basic and Applied Engineering Research
Print ISSN: 2350-0077; Online ISSN: 2350-0255; Volume 1, Number 3; October, 2014 pp. 41-46
© Krishi Sanskriti Publications
http://www.krishisanskriti.org/jbaer.html
Some Studies on the Performance of Automotive
Radiator at Higher Coolant Temperature
Devendra Vashist1, Sunny Bhatia2, Ashish Kalra3
1,2,3
Automobile Engineering Department, Manav Rachna International University
Abstract: Automotive engine cooling system takes care of excess
heat produced during engine operation. It regulates engine surface
temperature for engine optimum efficiency. Recent advancement in
engine for power forced engine cooling system to develop new
strategies to improve its performance efficiency. Also to reduce fuel
consumption along with controlling engine emission to mitigate
environmental pollution norms. This paper throws light on
parameters which influence radiator performance at high coolant
temperature that is 105o C and its effect on the effectiveness at
variable fan speed. A literature review has been done and ways
were identified how to enhance radiator performance
Keywords: Automotive engine cooling system, Performance,
Radiator
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 use
of Computational Fluid Dynamics (CFD) modeling simulation
of mass flow rate of air passing across the tubes of an
automotive radiator was carried out [1]. Studies on the use of
nano fluids in compact heat exchangers were carried out by
P.Gunnasegaran et.al. [2]. Some studies to increase the rate of
heat transfer were carried using twisted tape [3]. numerical
study of heat transfer and pressure drop in a heat exchanger
that is designed with different shape pin fins were carried out
by Hamid Nabati [5]. Some studies were also carried out for
Improving Radiator Efficiency by Air Flow Optimization by
Salvio Chacko et.al [6]. Studies on the effect of blockage of
dirt on engine radiator in the engine cooling system was
carried out by S. D. Oduro [10]. Much of the work is going on
to increase the value of convective heat transfer coefficient on
the similar patters this work is being directed on increasing the
value of h by adjusting the rpm of the fan with the help of
electrical regulator/ changing the windings of the motor. Some
studies were made on effects of variable mass flow rate of the
coolant in the radiator, the rate of flow is controlled by the
water body pump. A test rig was developed which creates the
same conditions of air flow as for a moving vehicle with
variable air flow rate.
2. OBJECTIVE
Performance of engine cooling system is influenced by factors
like air and coolant mass flow rate, air inlet temperature,
coolant fluid, fin type, fin pitch, tube type and tube pitch etc.
While designing cooling system main aim remains that the
size of the cooling system should be less but three factors does
not allow the size to decrease. The factors are
1.
High altitude: At high altitude, air density becomes low
and hence affects air mass flow rate.
2.
Summer conditions: During summer surrounding air is
hot i.e. air inlet temperature is more.
3.
Maximum power: Engine condition producing maximum
power like when vehicle is climbing uphill, maximum
heat rejection is required during this condition.
To compensate all these factors radiator core size required
may be large. In this study approach has been made to
increase the value of air flow rate which in turn takes care of
the size of the radiator.
3. MATERIAL AND METHOD
The radiator (Fig 1) used in the study is of Maruti 800
standard type. Material of the radiator is aluminium that is
why it is light in weight and less prone to corrosion.
42
Devendra Vashist, Sunny Bhatia, Ashish Kalra
Fig. 6 Diameter Reducer Fig. 7 Heating Element
Fig. 1 Radiator Fig. 2 Coolant Tank
Anchor company switches (fig 5) are used and wooden box is
used to enclose the electrical panel and heavy duty wires are
used in this system to prevent the system from the failure.
Diameter reducer (fig 6) is used in this system to maintain the
mass flow rate of the system. The heating element (fig 7) used
in the system is of the capacity 3 KW of coil shape.
Thermocouples (fig 8) are used in the system for measuring
the temperature of the system. The thermometer used for
measuring air temperature is of the analogue type while the
thermocouple having range 40oC – 120°C is used for
measuring coolant temperature. A motor of 0.25HP (fig 9) is
used in the system to run the water body pump.
Fig. 3 Pipes
The material used for the fabrication of the coolant tank (fig 2)
is steel sheet as it can bear high temperature and its weight is
moderate but less than cast iron. The operating range of the
tank is 0oC to 150°C. The pipes (fig 3) used in the system
should be able to bear high temperature that’s why plastic
pipes and the rubber hose pipes are used in the system. Cast
iron coolant pump (fig 4) is used that can operate at high
temperatures and can bear thermal stresses. The pump is
driven from the belt system arrangement.
Fig. 4 Water Pump Fig. 5 Electrical Switches
Fig. 8 Thermocouples Fig. 9 Motor
The system used for transmitting the power from motor to
water body pump is belt drive system (Fig 10) .
Fig. 10 Belt Drive System
Journal of Basic and Applied Engineering Research (JBAER)
Print ISSN: 2350-0077; Online ISSN: 2350-0255; Volume 1, Number 3; October, 2014
Some Studies on the Performance of Automotive Radiator at Higher Coolant Temperature
The complete set up is shown in the figure 11.
43
5. EXPERIMENTAL PROCEDURE
PROCEDU
The radiator of the engine was 320 mm in length by 350 mm
in breath as showed in Fig. 1, and had a total number of 33
tubes. All the 33 tubes were in a single row and each tube was
2 mm thick. The fins were made of aluminum alloy with a
thickness of 0.8 mm, height of 20 mm and spaced 1.9 mm
apart as shown in figure 1. The radiator was thoroughly
thoro
cleaned of all dust and debris before the experiments were
carried.
6. ASSUMPTIONS
In order to carry out the studies following assumptions were
made;
Fig. 11 Complete set up
4. DESCRIPTION OF EQUIPMENT
Thermocouples are used for measuring the inlet and out let
temperatures of the coolant that is coming out of the radiator.
The details of the radiator are given in the Table 1
A mixture of glycerol (Fig 12) and water was used as the
coolant having a boiling point of 110C with 40% glycerol in
water by volume. Data about the additive used is given below:
Formula: C3H8O3
Boiling point: 290 °C(pure)
Density: 1.26 g/cm³
Melting point: 17.8 °C
Molar mass: 92.09382 g/mol
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
ra
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.The thermal
conductivity of the
he radiator material was considered to be
constant 8.There were no heat sources and sinks within the
radiator 9.There was no fluid stratification, losses and flow
misdistribution. The heat transfer process in the radiator was
studied as a forced convective heat transfer operation.
Table 1. Specification of Experimental Setup
Pipe diameter inlet / outlet
26 mm
Thickness of 1 fin
0.8 mm
Width of fin
20 mm
Diameter of cooling pipe
2 mm
Radiator core height (aluminum part only)
320mm
Radiator core length (aluminum part only)
350mm
Number of fins in single column
180
Number of fin columns
34
Total number of fins
6120
Total number of pipes
33
Distance between 2 pipes
7.5 mm
Distance between 2 fins
1.9 mm
Diameter of fan
0.27 m
Fig. 12 Glycerol-3D-balls
balls structure
Print ISSN: 2350-0077;
0077; Online ISSN: 2350
2350-0255; Volume 1, Number 3; October, 2014
44
variation of temperature along the length of Heat Exchanger
for the two different speeds of motor.
Variation of temperature for water and
air along the length of Radiator at 1200
rpm
120
Temperature
100
80
60
40
20
0
Figure 13 Line Diagram
length of HE
7. OBSERVATIONS
Table 2 shows the observations made when the air was passed
through the radiator at variable fan motor speed. Table 3
shows the different formulas used for calculations. The speed
of the fan was made variable by changing the number of
windings in the fan of the motor. Figure 13 and 14 shows the
air inlet and outlet temperature
water inlet and out let
Fig. 14 Variation of temperature along length of radiator at 1200
rpm
Table 2 Observations from the test rig
Fan
Motor
speed
Air inlet
Air outlet
temperature temperature
Water inlet Water outlet
temperature temperature
Water
Mass flow
rate
Air Mass
flow rate
Effectiv
eness
(є)
Cooling
Capacity
kW
1200 rpm
25
42
105
61
0.06kg/sec
0.201kg/sec
0.6875
11
1830 rpm
25
50
105
55
0.06kg/sec
0.306kg/sec
0.62
12.5
120
Variation of temperature of water and air along the length of Radiator at 1830
rpm
Temperature
100
80
Air inlet and outlet
temperature
60
40
20
Water inlet and
outlet temperature
0
Length of Heat Exchanger
Fig. 15 Variation of temperature along length of radiator at 1830 rpm
Some Studies on the Performance of Automotive Radiator at Higher Coolant Temperature
45
A graph (fig 16) is plotted showing the variation of effectiveness and cooling capacity with the variation of air flow rate at
different rpm by keeping mass flow rate of coolant constant. Air flow rate has been plotted on X- Axis and the effectiveness on y
axis. The temperature of inlet air has been maintained at 25o C. By the graphs plotted it is observed that effectiveness remains
same with increase in air flow rate but cooling capacity increases by 12 % with an increase in air flow rate by 52.52 % keeping the
mass flow rate of the coolant constant.
14
12
10
8
Cooling capacity at
different fan rpm
6
4
Effectiveness
2
0
1200
1830
Fig 16: Variation of effectiveness and cooling capacity with the variation of air flow rate
Table 3
Maximaum heat transfer =

At 1 LPM mc =
Cpc = 4.18 kJ/kg K.
#&##"/
&##"/
Effectiveness of radiator (є) =
o–
o–
/UR (for water)
Cpa = 1.005 kJ/kg K.
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
st
nd
ma = 0.201 (for 1 case) ma = 0.306 (for 2 case)
st
Where mc = mass flow rate of coolant in kg/sec.
nd
mc = 0.06 (for 1 case) mc = 0.06 (for 2 case)
8. FUTURE SCOPE
8.1 Use of nano fluids
Nano particles can be dispensed in conventional heat transfer
fluid such as water ethylene glycol, engine oil. It produces a
new class of high efficient heat exchange fluids called Nanofluids [2, 7, 12]. Many experimental and theoretical analyses
are carried and found these new heat exchanger coolants are
excellent.
8.2 Fins Shape
Many studies have showed that the fin shape affects the
characteristics of the radiator [5, 12]. The fin angle effect,
guide wing effect, fin width effect, fin length effect, and fin
tco = output temperature of coolant
tai = input temperature of air.
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.
46
8.3 Increasing turbulence of coolants
The effectiveness of the radiator can be increased by
employing turbulence promoters [12].
[2]
8.4 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 [12].
[3]
[4]
[5]
9. CONCLUSION
A set of numerical data on automotive radiator using coolant
operating at high temperature has been presented in the study.
By the literature survey a number of recommendations have
been provided for the development of a more effective and
compact radiator. The same is elaborated in the section, future
scope. In the performance evaluation of the radiator, a radiator
is installed into a test set up and parameter of mass flow rate
of air is varied its effect on the effectiveness and cooling
capacity is studied. The same parameters were presented
graphically and the inferences made.
[6]
[7]
[8]
[9]
[10]
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