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International Journal of Mechanical Engineering and Technology (IJMET) Volume 6, Issue 9, Sep 2015, pp. 73-93, Article ID: IJMET_06_09_008
Available online at
http://www.iaeme.com/IJMET/issues.asp?JTypeIJMET&VType=6&IType=9
ISSN Print: 0976-6340 and ISSN Online: 0976-6359
© IAEME Publication
EXPERIMENTAL AND NUMERICAL STUDY
TO ENHANCE HEAT TRANSFER ON A
HEAT EXCHANGER AL2O3/WATER
NANOFLUID USING AN AIR FLOW WITH
WATER DROPLETS
Yasameen H. Abed
M.Sc. Mechanical Engineering Department,
University of Technology, Baghdad, Iraq
Abdulhassan A.Karamallah
Professor, Mechanical Engineering Department,
University of Technology, Baghdad, Iraq
Adel Mahmoud Saleh
Assistance Professor, Mechanical Engineering Department,
University of Technology, Baghdad, Iraq
ABSTRACT
A experimental and numerical study has been carried out on the
enhancement of the heat exchanged on a tube and fin heat exchanger cooled
by an air flow containing water droplets by using nozzle system. A numerical
model representing the heat transfer has been presented and validated using
the experimental data. The cooling of air due to water evaporation upstream
in a channel to the exchanger (condenser fed with hot water with different
temperature) and the supplementary evaporation of droplets while impacting
or crossing the exchanger leads to enhance heat exchange. As additional to
enhance heat exchange, adding a nanoparticle (Al2O3) to the water of the heat
exchanger and studying the effect of the nanofluid with two volume
concentrations (0.5 & 2 %). All the tests were carried out with working fluid
flow rate (4, 6 and 8 L/min) and with temperature (40, 45 and 50 oC).The
results obtained maximum Nusselt number ratio (��� / ���,���� ����)
was (1.235) which occurred at nanofluid concentration 2% with using sprayed
air. The heat transfer coefficient ratio (�� / ��,���� ����) increases when
using nanofluid and by increasing the volume concentration and the maximum
enhancement ratio was (1.45) which occurred at nanofluid concentration 2%
and with using sprayed air to cool the heat exchanger. The average Nusselt
number with Reynolds number correlated for working fluid. The numerical
Yasameen H. Abed, Abdulhassan A.Karamallah and Adel Mahmoud Saleh
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analysis was based on finite volume numerical techniques to solve the
governing partial differential equations in three dimensions, using ANSYS
FLUENT commercial CFD software, to study the effect of using spray water,
air temperature and velocity, working fluid flow and temperature on the heat
transfer enhancement. The comparison between the experimental and
numerical results shows a good agreement, and the maximum error was with
maximum deviation (11%).
Key words: Enhanced, Heat Transfer, Condenser, Water Spray Air, Nanofluid
Cite this Article: Yasameen H. Abed, Abdulhassan A. Karamallah and Adel
Mahmoud Saleh, Experimental and Numerical Study to Enhance Heat
Transfer on A Heat Exchanger Al2o3/Water Nanofluid Using an Air Flow
with Water Droplets. International Journal of Mechanical Engineering and
Technology, 6(9), 2015, pp. 73-93.
http://www.iaeme.com/currentissue.asp?JType=IJMET&VType=6&IType=9
1. INTRODUCTION
Decreasing energy consumption and increasing efficiency is one of the most
important points in our area. Becoming a matter of primary importance in air
conditioning, industrial and commercial cooling applications, supermarket cooling,
blast freezing and process cooling applications, energy efficiency affects design of
chillers (and its equipment such as condensers, compressors etc.) and urges
manufacturers to develop high performance, energy-efficient, environment friendly,
and economic and long life products. The air cooled condensers (fin and tube heat
exchangers) are the most widespread category for low and average refrigeration
capacities because the cooling medium (air) is a natural and free source. However, as
air is not an efficient cooling medium, it implies high air flow and significant
exchanger area. Adding a spray of a controlled and small quantity of fine water
droplets at the air inlet seems to be a potential solution that deserves to be investigated
and analyzed, it is expects to be widely applied and several experimental and
numerical studies investigate in this realm to develop and design more efficient
system. R. Sureshkumar, et al. 2008 [1], showed experimentally that for a specific
water flow rate, the smaller nozzle at higher pressure produced more cooling than a
larger nozzle at lower pressure and they provided accurate with consistent data that
can be used for comparison with other experiments and simulations. They founded in
hot and dry conditions, a cooling up to 14 oC was attainable in both parallel and
counter flow configurations.
R. Faramarzi, et al. 2010 [2] , studied variations in net cooling capacity, total
power consumption, energy efficiency ratio (EER), and water consumption across the
tested climatic conditions, and compared the performance of the unit with the
performance of air-cooled condenser type Air Conditioner (A/C) systems. A
numerical study by K.A. Jahangeer, et al. 2011 [3], investigated the heat transfer
characteristics by using a spray water or droplets in air cooled condenser. K.T.
Chan,et al.2011[4] , used mist evaporation to improve the coefficient of performance
(COP) of air-cooled chillers with variable condensing set point temperature control.
Experimental and numerical study of the enhancement of the heat exchanged on a
tube and fin exchanger (a simple exchanger) using an air flow containing water
droplets sprayed with several varying conditions (several nozzles, set temperature
and humidity conditions, various air flows, etc.) by J. Tissot, et al. 2012, [5] and P.
Boulet et al. 2013, [6]. S.M. Peyghambarzadeh et.al. 2011, [7], studies
Experimental and Numerical Study to Enhance Heat Transfer on A Heat Exchanger
Al2o3/Water Nanofluid Using An Air Flow with Water Droplets
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experimentally forced convective heat transfer in a water based nanofluid and
compared to that of pure water in an automobile radiator with Five different
concentrations of nanofluids in the range of 0, 0.1, 0.3, 0.5, 0.7, and 1 vol.%. M.M.
Heyhat et.al. 2012, [8], investigated experimentally the convective heat transfer and
friction factor of Al2O3 nanofluids with diameters of 40 nm and dispersed in distilled
water with volume concentrations of 0.1–2 vol.%, the results showed that the heat
transfer coefficient of nanofluid increased by 23% at 2 vol.% compared with that of
pure water with increasing the particle concentrations.
The present work submits an experimental work and numerical analysis in order
to study the effect of many parameters of spray conditions on air flow and on the heat
transfer characteristics of the heat exchanger. That are including: the types of fine
spray nozzles, location and directions of nozzle (either co-current or counter-current
directions of the air), and using a nanoparticles with the based fluid of the heat
exchanger which is a water.
2. THE EXPERIMANTAL PILOT
The test rig based on an instrumented air duct with a stabilized airflow in which
droplets are injected using suitable types of fine spray nozzles and the air-droplet flow
is directed in a channel toward a heat exchanger. Various characteristics (flow rate,
velocity, temperature & humidity) are determined experimentally through dedicated
measurement devices. The airflow is pre-heated at the inlet and sucked through a
square duct by a blower. A flow meter allows the measurement of the inlet flow rate.
Honeycomb grids are located after the blower in order to provide a settled and
stationary flow. The air is then entering in the channel section devoted to study the
interactions between the airflow and the droplets. Droplets are injected with a spray
nozzle and the air-droplet flow is directed toward the heat exchanger where the
finned-tube condenser is located. Hygrometers and thermocouples allow the
characterization of the air properties. Flow meter and thermocouples may also be used
for the evaluation of the heat exchanged at the exchanger by characterizing the
properties of the fluid inside the exchanger (water for the present work).
Figure 1 The pilot
Beak
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The pilot experiment shown in Figure.1 in a room where the temperature and the
humidity are controlled and in Figure.2 the sketch of the pilot. Table.1 gives the
characteristics main parts of the test rig, Table.2 gives the characteristics of
condenser, and Table.3 views the used measuring apparatus. The parameters and
measurement rang is shown in Table.4.
Figure 2 The schematic diagram of experiment set up
Table 1 (characteristics of main parts of the test rig)
Parts Characteristics
1. Square duct length= (1.2)m with cross sectional area ( 0.2 x0.2 )m2
2. Cone duct length= (0.5)m with cross sectional area ( 0.2 x0.2 )m
2 and
(0.38x0.28) m2
3. Rectangular
duct width x high x length=(0.38x0.28x1.85) m
3
4. Heat exchanger width x high x length=(0.36x0.26x0.18) m3
5. Heater Power = 3 kW
6. Axial fan Model FAD25-2/ (840) m3/h ,max power =35 W
7. Honey cone width x high x thickness = (0.36 x0.26x0.005) m3
8. Heater Power = 3 kW
9. Mist pumps Diaphragm pump HF-9050 & TYP-2000
10. Thermoregulater Power=7 kW, minimum water pressure=0.2bar
11. Water pump Type KF/0 Qmax= 30L/min, H. max =24 m, r.p.m=2820min
-
1
Table.2 (Details of fin and tube condenser)
Length of tube 360 mm Fin width 18 mm
High of
condenser 250 mm No. of fins 360 / (2.15) = 167.44 ≈167
No. of tube 10 outer diameter of
tube 3′′/8 (10 mm)
Spaced fin 2 mm Tube/ thermal
conductivity 360 W /m.K
Fin thickness 0.15 mm Fin thermal
conductivity
203 W /m.K
Experimental and Numerical Study to Enhance Heat Transfer on A Heat Exchanger
Al2o3/Water Nanofluid Using An Air Flow with Water Droplets
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Table 3 (Apparatuses involved in the measurement chain).
Parameter Measuring device Range of
application Resolution Accuracy
Air flow rate Air flow/ Air velocity
(Anemometer AM-4206)
0.4-25 m/s
0-50 oC
0.1 m/s
0.1 oC
± 2%
0.8 oC
Water flow rate Water flow meter (glass type
K-5012 )
2-20 L/min
35-50 oC
---- ± 2.5%
water
temperature Thermocouples type T ˗ 50
to 400
oC 0.1
oC ± (0.4% +1
oC)
Temperature
recorder
Data logger meter
( BTM- 4208SD)
Operating temp.
0-50 oC
> 85 %RH
0.1 oC ----
Humidity and
temperature
Hygrometer (humidity and
temperature meter) RS232
0 ~ 100%RH -20 -60
oC
0.1%RH
0.1 oC
±2.5%RH ±0.7
oC
Humidity /
temperature
Humidity and temperature
monitor (MHT-381SD)
10 - 90 %RH
0-50 oC
0.1%RH oC
± 4%
± 0.1 oC
Weight scale type EA 15 DEC-L 0- 15 kg ---- ± 1 g
Table.4 (Parameters and Measurement rang).
Parameters Measurement rang
Air flow rat 0.14, 0.18 & 0.22 m3/s
Air temperature 25, 30 & 35
oC
Spray water flow rate 0.6 , 1.5 & 1.7 L/h
Nozzle distance from the condenser 20,40 ,60 &80 cm
Water flow rate in tubes 4, 6, 8 L/min (240,360,480 L/h)
Water temperature in tubes of H.E 40, 45 & 50 oC
Figure.3 Diagram the Relative Humidity and Temperature of the air points placed upstream
and downstream of the heat exchanger in the plane perpendicular to flow of the air.
3. EXPERIMENTAL WORK PROCEDURE
3.1 Experimental parameters
Each experimental test was take the following parameters have been considered:
1. Ambient temperature and humidity.
36 cm
26 cm
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2. Air velocity and temperature in the duct before injection.
3. Air temperature and humidity toward the heat exchanger.
4. Location of the nozzle.
5. Direction of droplets injection (co or counter-current).
6. spray water flow rate.
7. Heat exchanger water flow rate and temperatures at inlet and outlet.
3.2. The steps of experimental test
The following are the steps which must be done to complete the test:
1. Controlled the temperature and the humidity of ambient air.
2. Measured the air velocity and temperature in the duct before injection.
3. Select the location and the direction of droplets injection.
4. Measured the spray water flow rate.
5. Measured the water flow rate and the temperatures at inlet and outlet of the heat
exchanger.
6. Measured the air temperature and humidity before and after the heat exchanger.
3.3. Preparation of Al2O3 nanofluid
In general, there are two methodologies used to produce nanofluids, namely the
single-step method, where nanoparticles are produced and dispersed simultaneously
into the base fluid, and the two-step method, where the two aforementioned processes
are accomplished separately. To produce an even and stable suspension several
techniques are applied, such as use of ultrasonic equipment, pH control or addition of
stabilizers. The material of nanoparticles is chosen as Al2O3 because it is chemically
more stable and its cost is less than their metallic counterparts and also it is easily
available. Al2O3-water nanofluid is prepared by two step method. Adding a specific
grams of the Al2O3 in to the water and the mixture was mixed slowly in the sonicator
about 20 min to break up any particle aggregates and prepared two volume
concentration of nanofluid 0.5 % & 2.0 %.
Thermo physical properties of nanoparticles and base fluid (water) at 25 oC are
shown in the Table 5, and for the water-nanofluid properties are shown in the Table 6
using equations as in M.M. Heyhat 2012 [7].
Table 5 Thermophysical properties of nanoparticles and base fluid (water) at 25 oC .
Property Water Nanofluid Unit
Density ρ�=1000 ρ�=3900 kg/m3
specific heat capacity ���=4.1796 ���=0.880 kj/kg.K
thermal conductivity k�=0.6 k�=42.34 w/m.K
dynamic viscosity μ�=1.003 μ�= --- g /m.s
Nanofluid particles --- D p=30-60 nm
Experimental and Numerical Study to Enhance Heat Transfer on A Heat Exchanger
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Table 6 (Thermophysical water-nanofluid Properties for two concentration 0.5& 2 %).
Water-Nanofluid
Properties Equation
Nanofluid volume
concentration Unit
0.5% 2.0 %
Density ρ� = (1 − φ)ρ� + φρ� 1014.5 1058 kg/m3
specific heat
capacity ��! = "(# ��)$ + (1 − ")(# ��)%
(1 − ")#% + "#$ 4.136 3.966 kj/kg.K
thermal
conductivity &! = &%(1 + 8.733") 0.626 0.705 w/m.K
dynamic viscosity +! = +%(exp / 5.989"0.278 − "4) 0.0003 0.0013 kg /m.s
3.5. Experimental Internal Convection Coefficient
To obtain heat transfer coefficient and corresponding Nusselt number, the following
procedure has been performed. According to Newton’s cooling law,
Peyghambarzadeh 2011 [7]:
Q = h78� A: (T< − T�=>>) (1)
Heat transfer rate can calculated as follows:
Q = m @ Cp (TB� − T:CD) (2)
Regarding the equality of Q in the above equations:
Nu=G = HIJK.LMN = O@ P� (QRST QUVW) LM
N XU (QYT QZ[\\) (3)
Nu=G is average Nusselt number for the whole heat exchanger , m @ is mass flow
rate which is the product of density and volume flow rate of fluid, Cp is fluid specific
heat capacity, A: is peripheral area of the tubes, k is fluid thermal conductivity
and DH is hydraulic diameter of the tube. TB� and T:CD are inlet and outlet
temperatures, T< is bulk temperature which was assumed to be the average values of
inlet and outlet temperature of the fluid moving through the heat exchanger, and T�=>> is tube wall temperature which is the mean value by two surface thermocouples,
Peyghambarzadeh 2011 [7]
4. MATHEMATICAL TREATMENT AND NUMERICAL
SIMULATION
The spray injected into the flow of air at different position in the duct. The air cooled
by evaporation of the spray takes place between the point of injection of the spray and
the heat exchanger (condenser). The first zone of the duct consists of the controlled
misted air and the second zone corresponds to the heat exchanger where the exchange
takes place between the air and the fluid circulating inside the condenser. Analysis
steps for FLUENT software package were used to develop the Computational Fluid
Dynamics (CFD) model of cooling a hot air stream by water injection using species
transport and discrete phase models of ANSYS FLUENT 14.5 and model of heat
transfer between the air-mist water and the heat exchanger. Conservation of mass
equations, energy equation and momentum equation- model RANS (Reynolds
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Averaged Navier-Stokes) can express mathematically for an incompressible fluid as
Collin 2007 [9] and J. Tissot 2011[10]:
^^8_
`ρaUcd e = 0 (4)
^ ^8_
`ρaUcdTa e = ^^8_
f/ρaαD + hiPKi
4 ^Qi^8_
j (5)
^^8_
`ρaUcB Ucd e = ^^8_
f(μa + μD ) ^kcR^8_
j + ^^8_
l(μa + μD ) ^kc_^8R
m − ^^8R
lPr + pq ρakam + S�CB (6)
4.1. Numerical Simulation
The geometry used to perform the simulations corresponds to that of the rectangular
duct which is situated upstream from the exchanger of the experimental pilot.
Improved cooling through increased heat exchange and mass between the drops and
the air. Thus, several parameters are studied including the direction of injection of the
spray with respect to the flow (co-current and countercurrent) to assess the relative
influence of the increase in the exchange surface between the drops and the air and
the spatial dispersion of the spray in the air flow.
Figure 4 Computational domain includes mesh display and boundary conditions.
Figure 5 Computational domain includes mesh display for heat exchanger.
Air inlet as velocity
inlet
Air outlet as
pressure outlet
Interior domain
Wall
260
mm
360
mm
1000
mm
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5. RESULTS AND DISCUSSION
5.1. Influence of distance on air cooling
Evaporation of a spray in an air flow occurs throughout its length. This evaporation
depends on the residence time of the spray and the corresponding increase humidity in
the air. We therefore sought in this section to determine the distance downstream and
upstream of injection of the spray, from which the cooling air is great. For This
distance, measures the temperature of the air are carried out on sections the vein of
experimental pilot between 20 and 80 cm downstream of the injection point spray.
The Figures (4) show the humidity and the temperature distribution of the air flow in
transverse section Z=20,40,60,80cm for nozzle type 10 and the direction of injection
of spray with the air (co- current) with inlet air temperature is 25 oC . The Figures (5)
show the humidity and the temperature distribution with counter-current flow. It seem
that the reduction temperature is not uniform over the entire cross section and is
greater at the center of the vein, in the zone where the spray is most dense. However,
this heterogeneity decreases away from the injection point. The Figures (6) & (7)
presents the evolution of the humidity and the temperature of the air in function of the
distance between the measurement surface and the injection point of the spray.
Indeed, the difference between the average temperature and the minimum temperature
decreases with increase the distance from the injection point. A co-current,
evaporation of the spray and the reduction in temperature is more important the center
of the section, because the water fraction in the air is most important. The reason for
this concentration in the injection configuration is the low spatial dispersion of drops
in space. Therefore, the cooled surface is greater and the reduction in temperature
locally less important. In the counter-current flow, the temperatures obtained the
entire section are more homogeneous and lower average than co-current in the small
distance. For the purposes of misting on a condenser that allows position nozzles near
the condenser and thus limit the drive by spray gusts of wind in the case of a
condenser placed outdoors.
(a) Humidity
Z=80 cm T amb=24.4 C RH=53.7 % T inlet= 25.0 C RH inlet=50.6 %RH min=56 % RHmax=87.6%RH med=60.6 % RH Aver=64.14%
Z=60 cm T amb=25.0 C RH=50.6% T inlet= 25.0 C RH inlet=50.1 %RH min=52.5 % RHmax=85.4 %RH med=62 % RH Aver=63.1 %
Z=40 cm T amb=24.6 C RH=48.6 % T inlet= 25.0 C RH inlet=42.1 %RH min=53.5 % RHmax=80 %RH med=57.2 % RH Aver=61.97 %
Z=20 cm T amb=25.0 C RH=42.8 % T inlet= 25.0 C RH inlet=42.4 %RH min=41.1 % RHmax=87 %RH med=42.5 % RH Aver=46.7 %
0 3 6 9 12 15 18 21 24 27 30 33 36
X
0
2
4
6
8
10
12
14
16
18
20
22
24
26
Y
35
37.5
40
42.5
45
47.5
50
52.5
55
57.5
60
62.5
65
67.5
70
72.5
75
77.5
80
85
0 3 6 9 12 15 18 21 24 27 30 33 36
X
0
2
4
6
8
10
12
14
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18
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26
Y
0 3 6 9 12 15 18 21 24 27 30 33 36
X
0
2
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Y
0 3 6 9 12 15 18 21 24 27 30 33 36
X
0
2
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6
8
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20
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24
26
Y
35
37.5
40
42.5
45
47.5
50
52.5
55
57.5
60
62.5
65
67.5
70
72.5
75
77.5
80
35
37.5
40
42.5
45
47.5
50
52.5
55
57.5
60
62.5
65
67.5
70
72.5
75
77.5
80
85
35
37.5
40
42.5
45
47.5
50
52.5
55
57.5
60
62.5
65
67.5
70
72.5
75
77.5
80
co-current Tinlet =25 C Nozzle=10 , spray flow=0.6 L/h, air velocity=2.4 m/s
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(b) Temperature distribution
Figure 4 (a) Humidity distribution & (b) Temperature distribution in the transverse Z=20, 40,
60&80cm using nozzle type10 with a co-current (Tinlet =25 oC)
(a) Humidity distribution
counter-current Tinlet =25 C Nozzle=10 , spray flow=0.6 L/h, air velocity=2.4 m/s
Z=80 cm T amb=23.5 C RH=52.3 % T inlet= 25.0 C RH inlet= 50.6 %RH min=60.2 % RHmax=65.7 %RH med=63.2 % RH Aver=62.97 %
Z=60 cm T amb=25.0 C RH=50.6 % T inlet= 25.0 C RH inlet= 50.0 %RH min=57.5 % RHmax=64.1 %RH med=60.5 % RH Aver=60.7 %
Z=40 cm T amb=24.8 C RH=50.9 % T inlet= 25.0 C RH inlet= 42.1 %RH min=49.4 % RHmax=66.7 %RH med=53.2 % RH Aver=54 %
Z=20 cm T amb=24.8 C RH=50.1 % T inlet= 25.0 C RH inlet= 42.0%RH min=44.2 % RHmax=84.7 %RH med=60.3 % RH Aver=62.1%
0 3 6 9 12 15 18 21 24 27 30 33 36
X
0
2
4
6
8
10
12
14
16
18
20
22
24
26
Y
35
37.5
40
42.5
45
47.5
50
52.5
55
57.5
60
62.5
63.75
65
67.5
68.75
70
72.5
73.75
75
77.5
80
0 3 6 9 12 15 18 21 24 27 30 33 36
X
0
2
4
6
8
10
12
14
16
18
20
22
24
26
Y
35
37.5
40
42.5
45
47.5
50
52.5
55
57.5
60
61.25
62.5
65
67.5
70
72.5
75
77.5
80
0 3 6 9 12 15 18 21 24 27 30 33 36
X
0
2
4
6
8
10
12
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20
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Y
35
37.5
40
42.5
45
47.5
50
52.5
55
57.5
60
62.5
65
67.5
70
72.5
75
77.5
80
0 3 6 9 12 15 18 21 24 27 30 33 36
X
0
2
4
6
8
10
12
14
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18
20
22
24
26
Y
35
37.5
40
42.5
45
47.5
50
52.5
55
57.5
60
62.5
65
67.5
70
72.5
75
77.5
80
85
x=80 cm T amb=24.4 C RH=53.7 % T inlet= 25.0 C RH inlet=50.6 %T min=20 C T max=24.5 CT med=23.3 C T Aver=23 C
0 3 6 9 12 15 18 21 24 27 30 33 36
Z
0
3
6
9
12
15
18
21
24
Y
19
20
21
22
23
24
25
0 3 6 9 12 15 18 21 24 27 30 33 36
Z
0
3
6
9
12
15
18
21
24
Y
19
20
21
22
23
24
25
x=60 cm T amb=25.0 C RH=50.6% T inlet= 25.0 C RH inlet=50.1 %T min=21.4 C T max=24.6 CT mid=23.5 C T Aver=23.6 C
0 3 6 9 12 15 18 21 24 27 30 33 36
Z
0
2
4
6
8
10
12
14
16
18
20
22
24
26
Y
x=40 cm T amb=24.6 C RH=48.6 % T inlet= 25.0 C RH inlet=42.1 %T min=19.4 C T max=24.9 CT med=23.8 C T Aver=23.2 C
19
20
21
22
23
24
25
0 3 6 9 12 15 18 21 24 27 30 33 36
Z
0
2
4
6
8
10
12
14
16
18
20
22
24
26
Y
x=20 cm T amb=25.0 C RH=42.8 % T inlet= 25.0 C RH inlet=42.4 %T min=19.6 C T max=24.9 CT med=24.8 C TAver=24.4 C
19
20
21
22
23
24
25
co-current Tinlet =25 C Nozzle=10 , spray flow=0.6 L/h, air velocity=2.4 m/s
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(b) Temperature distribution
Figure 5 (a) Humidity distribution & (b) Temperature distribution in the transverse Z=20, 4
0, 60&80cm using nozzle type 10 with a counter-current (T inlet =25 oC)
a- T air=25oC b-T air=30
oC
Figure 6 Average humidity in the transverse Z=20,40,60&80cm using nozzle type 10 with a
co & counter-current current air velocity 2.4 m/s (a)T inlet =25 oC & (b) T inlet =30
oC.
a- T air=25oC b-T air=30
oC
Figure 7 Average temperature in the transverse Z=20,40,60&80cm using nozzle type 10 with
a co & counter-current air velocity 2.4 m/s (a)T inlet =25 oC & (b) T inlet =30
oC.
x=80 cm T amb=23.5 C RH=52.3 % T inlet= 25.0 C RH inlet= 50.6 %T min=22.6 C T max=23.6 CT med=23.1 C T Aver=23.14 C
x=60 cm T amb=25.0 C RH=50.6 % T inlet= 25.0 C RH inlet= 50.0 %T min=23.2 C T max=23.9 CT mid=23.5 C T Aver=23.6 C
x=40 cm T amb=24.8 C RH=50.9 % T inlet= 25.0 C RH inlet= 42.1 %T min=21.4 C T max=24.5 CT med=23.5C T Aver=23.4 C
x=20 cm T amb=24.8 C RH=50.1 % T inlet= 25.0 C RH inlet= 42.0%T min=20.8 C T max=24.9 CT med=23.6 C TAver=23.45 C
0 3 6 9 12 15 18 21 24 27 30 33 36
Z
0
2
4
6
8
10
12
14
16
18
20
22
24
26
Y
21.4
21.8
22.1
22.4
22.6
22.8
23
23.2
23.4
23.6
24
24.4
0 3 6 9 12 15 18 21 24 27 30 33 36
Z
0
2
4
6
8
10
12
14
16
18
20
22
24
26
Y
23.2
23.3
23.4
23.5
23.6
23.7
23.8
0 3 6 9 12 15 18 21 24 27 30 33 36
Z
0
2
4
6
8
10
12
14
16
18
20
22
24
26
Y
21.4
21.8
22.2
22.6
23
23.4
23.8
24.2
0 3 6 9 12 15 18 21 24 27 30 33 36
Z
0
2
4
6
8
10
12
14
16
18
20
22
24
26
Y
20.8
21.2
21.6
22
22.4
22.8
23.2
23.6
24
24.4
24.8
counter-current Tinlet =25 C Nozzle=10 , spray flow=0.6 L/h, air velocity=2.4 m/s
Yasameen H. Abed, Abdulhassan A.Karamallah and Adel Mahmoud Saleh
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4.2. Influence of air flow on air cooling
The same measurements were performed for cooling air flow rates of 0.14, 0.187
& 0.225 m3/s corresponding to speeds of 1.5, 2.0 & 2.4 m/s. The results includes
these measurements of air velocity with the direction of injection of spray (counter-
current) where inlet air temperature is 30 oC. Comparison of the results obtained for
the airflows studied shows that the humidity increases significantly with increasing air
flow and the temperature decreasing for counter current flow, as shown in Figure (8).
In fact, increasing the velocity of the air has the effect more rapidly cause the spray
thereby reducing the residence time and dispersion of droplets in the flow. The
fraction of evaporated water is then directly reflected in diminished.
(a) Humidity distribution (b) Temperature distribution
Figure 8 Humidity and temperature distribution in the transverse Z=40 and 60 cm using
nozzle type 10 with a counter-current and inlet air temperature 30 oC for air velocity 2.4, 2.0
and 1.5 m/s.
4.3. Influence using spray system on heat exchanger
Figure (9) shows the temperature of water out of heat exchanger without and with
using spray system nozzle type 10 at Z=40 cm with a counter-current flow and air
velocity 2.4 and 1.5 m/s, for inlet air temperature 30 and 35 oC. It found that the
counter-current Tinlet =30.0 C Nozzle=10 air velocity=2.4 m/s
counter-current Tinlet =30.0 C Nozzle=10 air velocity=2.0 m/sZ=60 cm T amb=25.0 C RH=39.1 % T inlet= 30.0 C RH inlet= 32.2 %RH min=49.2 % RHmax=70.7 %RH med=58.6 % RH Aver=66.35 %
Z=40 cm T amb=25 C RH=38.6% T inlet= 30.0 C RH inlet=31.2 %RH min=42.3 % RHmax=72.4 %RH med=53.1 % RH Aver=63.8 %
Z=40 cm T amb= 25.0 C RH amb=40.3%T inlet=30.0 C RH inlet=35.1%RH min=38.7 % RH max= 68.6 %RH med=48.2 % RH Aver=50.4 %
0 3 6 9 12 15 18 21 24 27 30 33 36
X
0
2
4
6
8
10
12
14
16
18
20
22
24
26
Y
35
37.5
40
42.5
45
47.5
50
52.5
55
57.5
60
62.5
65
67.5
70
72.5
75
77.5
80
Z=60 cm T amb= 25.5 C RH amb=40.9%T inlet=30.0 C RH inlet=35.8%RH min=47.1 % RH max= 58.1 %RH med=53.7 % RH Aver=52.78 %
0 3 6 9 12 15 18 21 24 27 30 33 36
X
0
2
4
6
8
10
12
14
16
18
20
22
24
26
Y
35
37.5
40
42.5
45
47.5
50
52.5
55
57.5
60
62.5
65
67.5
70
72.5
75
77.5
80
counter-current Tinlet =30.0 C Nozzle=10 air velocity=1.5 m/s
0 3 6 9 12 15 18 21 24 27 30 33 36
X
0
2
4
6
8
10
12
14
16
18
20
22
24
26
Y
0 3 6 9 12 15 18 21 24 27 30 33 36
X
0
2
4
6
8
10
12
14
16
18
20
22
24
26
Y
0 3 6 9 12 15 18 21 24 27 30 33 36
X
0
2
4
6
8
10
12
14
16
18
20
22
24
26
Y
Z=60 cm T amb=24.0 C RH=38 % T inlet= 30.0 C RH inlet= 27 %RH min=50 % RHmax=78.1 %RH med=62.3 % RH Aver=74.75 %
0 3 6 9 12 15 18 21 24 27 30 33 36
X
0
2
4
6
8
10
12
14
16
18
20
22
24
26
Y
Z=40 cm T amb=25.3 C RH=39.3 % T inlet= 30.0 C RH inlet= 33.1 %RH min=45.6 % RHmax=76.8 %RH med=61.5 % RH Aver=73.16 %
35
37.5
40
42.5
45
47.5
50
52.5
55
57.5
60
62.5
65
67.5
70
72.5
75
77.5
80
35
37.5
40
42.5
45
47.5
50
52.5
55
57.5
60
62.5
65
67.5
70
72.5
75
77.5
80
35
37.5
40
42.5
45
47.5
50
52.5
55
57.5
60
62.5
65
67.5
70
72.5
75
77.5
80
35
37.5
40
42.5
45
47.5
50
52.5
55
57.5
60
62.5
65
67.5
70
72.5
75
77.5
80
counter-current Tinlet =30.0 C Nozzle=10 air velocity=2.4 m/s
counter-current Tinlet =30.0 C Nozzle=10 air velocity=2.0 m/s
Z=60 cm T amb=25.0 C RH=39.1 % T inlet= 30.0 C RH inlet= 32.2 %T min=25.7 C T max= 27.0 CT med=26.8 C T Aver=26.7C
Z=40 cm T amb=25.0 C RH=38.6% T inlet= 30.0 C RH inlet=31.2 %T min=23.6 C T max= 27.7 CT med=26.2 C T Aver=26.4 C
counter-current Tinlet =30.0 C Nozzle=10 air velocity=1.5 m/sZ=60 cm T amb=24.0 C RH=38 % T inlet= 30.0 C RH inlet= 27 %T min=24.7 C T max=26.2 CT med=25.7 C T Aver=25.6 C
Z=40 cm T amb=25.3 C RH=39.3 % T inlet= 30.0 C RH inlet= 33.1 %T min=23.8 C T max=27.6 CT med=26.5 C T Aver=26.2 C
Z=40 cm T amb= 25.0 C RH amb=40.3 %T inlet=30.0 C RH inlet=35.1 CT min=23.4 C T max= 28.1 CT med=27.3 C T Aver=26.7 C
Z=60 cm T amb= 25.5 C RH amb=40.9 %T inlet=30.0 C RH inlet=35.8 CT min=26.5 C T max= 27.5 CT med=27.2 C T Aver=27.14 C
0 3 6 9 12 15 18 21 24 27 30 33 36
X
0
2
4
6
8
10
12
14
16
18
20
22
24
26
Y
20
20.5
21
21.5
22
22.5
23
23.5
24
24.5
25
25.5
26
26.5
27
27.5
28
28.5
29
29.5
30
0 3 6 9 12 15 18 21 24 27 30 33 36
X
6
8
10
12
14
16
18
20
22
24
26
Y
20
20.5
21
21.5
22
22.5
23
23.5
24
24.5
25
25.5
26
26.5
27
27.5
28
28.5
29
29.5
30
0 3 6 9 12 15 18 21 24 27 30 33 36
X
0
2
4
6
8
10
12
14
16
18
20
22
24
26
Y
2020.52121.52222.52323.52424.52525.525.752626.2526.526.752727.2527.52828.52929.530
0 3 6 9 12 15 18 21 24 27 30 33 36
X
0
2
4
6
8
10
12
14
16
18
20
22
24
26
Y
20
20.5
21
21.5
22
22.5
23
23.5
24
24.5
25
25.5
26
26.5
27
27.5
28
28.5
29
29.5
30
0 3 6 9 12 15 18 21 24 27 30 33 36
X
0
2
4
6
8
10
12
14
16
18
20
22
24
26
Y
20
20.5
21
21.5
22
22.5
23
23.5
24
24.5
25
25.5
26
26.5
27
27.5
28
28.5
29
29.5
30
0 3 6 9 12 15 18 21 24 27 30 33 36
X
0
2
4
6
8
10
12
14
16
18
20
22
24
26
Y
20
20.5
21
21.5
22
22.5
23
23.5
24
24.5
25
25.5
26
26.5
27
27.5
28
28.5
29
29.5
30
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temperature of the outlet water decreasing with reducing the flow rate and with using
spray system. The temperature of outlet water from heat exchanger decreased when
the inlet air velocity increased, the temperature gradient is dependent on the rate at
which the fluid carries the heat away, and a high velocity produces a large
temperature gradient.
(a) Inlet air temperature 30 oC
(b) Inlet air temperature 35 oC
Figure 9 Comparison the temperature of water out of heat exchanger without and with using
spray system nozzle type 10 at Z=40 with a counter-current flow and air velocity 2.4 m/s,
temperature water inlet the H.E=45 oC, inlet air temperature 30 and 35
oC.
4.4. Effect using the nanofluid flow on heat exchanger cooling
Figure (10) shows the comparison of the heat exchanger cooling performance when
using nanofluid with and without using spray system at inlet air temperature 30oC and
velocity 2.4 m/s for inlet fluid temperature 40, 45 and 50 oC. One can clearly observe
that working fluid outlet temperature has decreased with the augmentation of
nanofluid volume concentration and with used spray system. It is important to
mention that from a practical viewpoint for cooling system; at equal mass flow rate
40.5
41
41.5
42
42.5
43
43.5
44
44.5
4 6 8
tem
pe
ratu
re w
ate
r o
utl
et
th
e H
.E (
oC
)
Volume flow rate( L/min)
air velocity =1.5 m/s air velocity=1.5 m/s
air velocity= 2.4 m/s air velocity= 2.4 m/s
without using spray with using spray
40.5
41
41.5
42
42.5
43
43.5
44
44.5
4 6 8tem
pe
ratu
re w
ate
r o
utl
et
th
e H
.E (
oC
)
Volume flow rate( L/min)
air velocity=1.5 m/s air velocity=1.5 m/s
air velocity= 2.4 m/s air velocity= 2.4 m/s
without using spray with using spray
Yasameen H. Abed, Abdulhassan A.Karamallah and Adel Mahmoud Saleh
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the more reduction in working fluid temperature indicates a better thermal
performance of the cooling system.
(a) 40 oC (b) 45
oC
c) 50 oC
Figure 10 Comparison of the H.E cooling performance of the working fluid with and without
using spray system, inlet air temperature 30oC and air velocity 2.4 m/s for inlet working fluid
temperature in H.E 40, 45 and 50 oC.
4.5 Comparison the average temperature and relative humidity for air
before and after heat exchanger
Figure (11) shows the average temperature and relative humidity of air, with counter
flow before and after the heat exchanger without and with using mist system at Z=40
cm from injection point. When applying mist, temperature of the air decreased from
about 3 oC and the relative humidity of 38% then passed to 50% when the inlet air
temperature 30oC with velocity 2.4 and the flow rate in H.E is 8 L/min with inlet
water temperature 40o
C . Upon passing through the condenser, the temperature of the
36.5
37
37.5
38
38.5
39
4 6 8
Te
mp
. o
f w
ork
ing
flu
id o
utl
et
the
H.E
(oC
)
Vol. flow rat in H.E (L/min)
40.5
41
41.5
42
42.5
43
43.5
44
4 6 8
Te
mp
. o
f w
ork
ing
flu
id o
utl
et
the
H.E
(oC
)
Vol. flow rat in H.E (L/min)
45.5
46
46.5
47
47.5
48
4 6 8
Te
mp
. of
wo
rkin
g f
luid
ou
tle
t th
e H
.E (
oC
)
Vol. flow rat in H.E (L/min)
Experimental and Numerical Study to Enhance Heat Transfer on A Heat Exchanger
Al2o3/Water Nanofluid Using An Air Flow with Water Droplets
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air increases and humidity decreases because of the heat exchange between the humid
air and the heat exchanger.
(a) Average temperature
(b) Average relative humidity
Figure 11 Average temperature and humidity of air with counter flow before and after the
heat exchanger as a function of time, without and with using misting system at Z=40 cm, inlet
air temperature Tair=30oC, inlet fluid temperature in H.E 45
oC with flow 8 L/min.
4.6. Nusselt Numbers
Figure (12) shows the heat transfer enhancement obtained due to the replacement of
water with nanofluids in the heat exchanger, which cooled by air with temperature
30oC and velocity 2.4 m/s with and without spray system. Dispersion of the
nanoparticles into the distilled water increases the thermal conductivity and viscosity
of the nanofluid, this augmentation increases with the increase in particle
concentrations. As can be seen in these figures, Nu number in all the concentrations
has increased by increase in the flow rate of the fluid and consequently Reynolds
25
27
29
31
33
35
37
39
41
43
45
0
10
20
30
40
50
60
70
80
90
10
0
11
0
12
0
Av
era
g t
em
pe
ratu
re o
f a
ir (
oC
)
after H.E after H.E
before H.E before H.E
without using spray with using spray
Time ( s)
10
15
20
25
30
35
40
45
50
55
60
65
0
10
20
30
40
50
60
70
80
90
10
0
11
0
12
0
Av
era
g h
um
idit
y o
f a
ir (
% )
after H.E after H.E
before H.E before H.E
without using spray with using spray
Time (s)
Yasameen H. Abed, Abdulhassan A.Karamallah and Adel Mahmoud Saleh
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number and by increasing inlet fluid temperature. Figure (13) compares the results for
fluid at different inlet temperatures in order to analyze the effect of spray system on
heat transfer performance of the heat exchanger. It is clear from figures that when
using spray system, a slightly improves in Nusselt number. In general, the Nusselt
number increases as volume flow rate (or equally Reynolds number), nanofluid
volume concentration and fluid inlet temperature increase.
The enhancement in the heat transfer is explained by using Nusselt number
ratio (stu / st%,%vwxyzw {$|}~), as shown in (figure 14). It is clear that the Nusselt
number ratio increases when using nanofluid also the ratio increases by increasing the
volume concentration. The effect of using spray system on Nusselt ratio (stu / st%,%vwxyzw {$|}~) can be seen in (figure 15). The Nusselt number ratio increases
when using a sprayed air, due to decrease the temperature of air passing on the heat
exchanger the enhancement in heat transfer coefficient when using nanofluid is
attributed to the effective thermal conductivity of nanofluid solution.
(a) Without using spray (b) With using spray
Figure 12 Effect of fluid inlet temperature on Nusselt numbers for inlet air temperature 30 oC
and velocity 2.4 m/s, without and with using spray.
(a) Water (b) Nanofluid 0.5% (c) Nanofluid 2%
Figure 13 Effect of using spray system on Nusselt numbers at different inlet temperature of working fluid
in heat exchanger (inlet air temperature 30 oC and velocity 2.4 m/s), for water and nanofluid volume
concentration 0.5 and 2 %).
60
80
100
120
140
160
180
10000 20000 30000 40000
Nu
Re
Tin=50 C, ⱷ=2% Tin=45 C, ⱷ=2%
Tin=40 C, ⱷ=2% Tin=50 C, ⱷ=0.5%
Tin=45 C, ⱷ=0.5% Tin=40 C, ⱷ=0.5%
60
80
100
120
140
160
180
10000 20000 30000 40000
Nu
Re
Twin= 40 C Twin= 40 C
Twin=45 C Twin=45 C
Twin= 50 C Twin= 50 C
without using spray with using spray
60
80
100
120
140
160
180
10000 20000 30000 40000
Nu
Re
T in= 40 C T in=40 C
T in=45 C T in= 45 C
T in= 50 C T in= 50 C
without using spray with using spray
60
80
100
120
140
160
180
10000 20000 30000 40000
Nu
Re
T in= 40 C T in=40 C
T in=45 C T in= 45 C
T in= 50 C T in= 50 C
without using spray with using spray
60
80
100
120
140
160
180
10000 20000 30000 40000
Nu
Re
Tin=50 C, ⱷ=2% Tin=45 C, ⱷ=2%
Tin=40 C, ⱷ=2% Tin=50 C, ⱷ=0.5%
Tin=45 C, ⱷ=0.5% Tin=40 C, ⱷ=0.5%
Experimental and Numerical Study to Enhance Heat Transfer on A Heat Exchanger
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(a) Without using spray (b) With using spray
Figure 14 Effect of using nanofluid at different inlet temperature on Nusselt ratio (stu / st%,%vwxyzw {$|}~) for inlet air temperature 30
oC and velocity 2.4 m/s, without and with
using spray.
(a) 40 oC (b) 45
oC
(c) 50 oC
Figure 15 Effect of using spray system on Nusselt ratio (stu / st%,%vwxyzw {$|}~) , inlet air
temperature 30 oC and velocity 2.4 m/s and inlet fluid temperature 40, 45 and 50
oC.
0.90
0.95
1.00
1.05
1.10
1.15
1.20
1.25
1.30
2 4 6 8 10
Nu
f /
Nu
w,
wit
ho
ut
spra
y
Volume flow rate (L/min)
Tin=50 C, ⱷ=0% Tin=45 C, ⱷ=0%Tin=40 C, ⱷ=0% Tin=50 C, ⱷ=0.5%
Tin=45 C, ⱷ=0.5% Tin=40 C, ⱷ=0.5%
Tin=50 C, ⱷ=2% Tin=45 C, ⱷ=2%
Tin=40 C, ⱷ=2%
0.90
0.95
1.00
1.05
1.10
1.15
1.20
1.25
1.30
2 4 6 8 10
Nu
f/
Nu
w,
wit
ho
ut
spra
y
Volume flow rate (L/min)
Tin=50 C, ⱷ=0% Tin=45 C, ⱷ=0%Tin=40 C, ⱷ=0% Tin=50 C, ⱷ=0.5%Tin=45 C, ⱷ=0.5% Tin=40 C, ⱷ=0.5%Tin=50 C, ⱷ=2% Tin=45 C, ⱷ=2%Tin=40 C, ⱷ=2%
0.8
0.9
1.0
1.1
1.2
1.3
1.4
10000 20000 30000
Nu
f /
Nu
w,
wit
ho
ut
spra
y
Re f
water water
ⱷ=0.5 % ⱷ=0.5 %
ⱷ=2.0 % ⱷ=2.0 %
without spray with spray
0.8
0.9
1.0
1.1
1.2
1.3
1.4
10000 20000 30000
Nu
f/
Nu
w,
wit
ho
ut
spra
y
Re f
water water
ⱷ=0.5 % ⱷ=0.5 %
ⱷ=2.0 % ⱷ=2.0 %
without spray with spray
0.8
0.9
1.0
1.1
1.2
1.3
1.4
10000 20000 30000 40000
Nu
f /
Nu
w,
wit
ho
ut
spra
y
Re f
water water
ⱷ=0.5 % ⱷ=0.5 %
ⱷ=2.0 % ⱷ=2.0 %
without spray with spray
Yasameen H. Abed, Abdulhassan A.Karamallah and Adel Mahmoud Saleh
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6. COMPARISON THE NUMERICAL AND EXPERIMENTAL
WORK
6.1. Mist Part
In this section, we will compare the experimental results with the numerical results
obtained in the same conditions. Recall that to perform these simulations, the
computer code needs input data. These data correspond mainly parameters of
instructions experiments:
• The flow rate and temperature of the air at the inlet of the duct
• The flow rate and the water temperature at the inlet of the exchanger
• The flow of mist
• The temperature of the air upstream of the exchanger.
The (figures 16) showed a good agreement between the experimental and
numerical temperature of air using nozzle type 10 in the distance Z=20,40,60&80cm
with air velocity 2.4 m/s for inlet air temperature 25,30&35 oC.
6.2. Heat Exchanger Part
The comparison between the experimental and numerical result for average Nuselt
number are shown in (figure 17) for the working fluids (water and nanofluid) without
and with the sprayed air. Notice a good agreement between the results with maximum
deviation (11%).
6.3. Comparison with the Published Work
Figure (18) Compere temperature of air for the experimental and numerical present
work with the experimental work of J.Tissot 2012 [5] using nozzle type 10 in the
distance Z=40 and 60cm and inlet air temperature 25 oC with air velocity 1.0 m/s for
counter-current and there is a good agreement.
The present heat transfer results of test facility for average inner Nusselt number
(for three inlet working fluid temperatures) are in good agreement with the empirical
correlation of Dittus –Boelter and Pak & Cho as shown in (figures 19).
(a) 25 oC (b) 30
oC
22
23
24
25
26
27
28
29
30
20 40 60 80
Av
era
ge
te
mp
. o
f a
ir f
low
( o
C )
The distance after injection ( cm)
experimental
numerical
22
23
24
25
26
27
28
29
30
20 40 60 80
Av
era
ge
te
mp
. o
f a
ir f
low
( o
C )
The distance after injection ( cm)
numerical
experimental
Experimental and Numerical Study to Enhance Heat Transfer on A Heat Exchanger
Al2o3/Water Nanofluid Using An Air Flow with Water Droplets
http://www.iaeme.com/IJMET/index.asp 91 [email protected]
(c) 35 oC
Figure 16 The experimental and numerical average air temperature with using spray system
(nozzle type 10) in the distance Z=20, 40 ,60 & 80 cm and inlet air temperature 25, 30 , 35 oC with air velocity 2.4 m/s for counter-current flow.
(a) Without the sprayed air
(b) With the sprayed air
Figure 17 Comparison the experimental results of average inner Nusselt number with CFD
results for air temperature 30oC and velocity 2.4 m/s at state (a) without the sprayed air (b)
with the sprayed air
40
90
140
190
10000 20000 30000 40000
Nu
av
Re
ⱷ=2.0 %, exp.
ⱷ=0.5 %, exp.
ⱷ=0 %, exp.
ⱷ=2.0 %, nu.
40
60
80
100
120
140
160
180
200
220
10000 20000 30000 40000
Nu
av
Re
ⱷ=2.0 %, exp.
ⱷ=0.5 %, exp.
ⱷ=0 %, exp.
ⱷ=2.0 %, nu.
22
24
26
28
30
32
34
20 40 60 80
Av
era
ge
te
mp
. o
f a
ir f
low
( o
C )
The distance after injection ( cm)
experimental
numerical
Yasameen H. Abed, Abdulhassan A.Karamallah and Adel Mahmoud Saleh
http://www.iaeme.com/IJMET/index.asp 92 [email protected]
Figure 18 Compere temperature of air for the experimental work of J. Tissot 2012 [ ] with the
experimental and numerical present work using nozzle type 10 in the distance Z=40 & 60
cm and inlet air temperature 25 oC with air velocity 1.0 m/s for counter-current.
(a) without the sprayed air (b) with the sprayed air
Figure 19 Comparison the experimental results of average inner Nusselt number with the
Dittus-Boelter and Pak & Cho equations inlet air temperature 30oC and velocity 2.4m/s at
state (a) without the sprayed air (b) with the sprayed air.
5. CONCLUSIONS
This study showed experimentally and numerically the influence of the cooling of
spray system and the direction of injection thereof into the air then flow toward the
heat exchanger, and in other hand showed the influence of using nanofluid at two
concentrations (0.5 and 2%) on enhance the heat transfer for the heat exchanger. The
results have clearly shown:
• It was demonstrated that the mist against the current is an advantageous
compromise compared to a co-current injection to combine a large exchange
surface and a wide dispersion of spray.
• The measurement results and for calculating distances of 20 to 80 cm are
presented and the temperatures are almost identical between the numerical and
experimental. In both the average temperature for 20, 40, 60 and 80 cm decreases
about ≈ 0.1 to 3 oC. It confirms numerically that evaporation takes place mainly
in the area of the spray back flow. We conclude that the code calculation and is
suitable for our predictive application.
21
21.2
21.4
21.6
21.8
22
22.2
22.4
22.6
40 60
Av
era
ge
te
mp
. o
f a
ir f
low
( o
C )
The distance after injection ( cm)
numerical
experimental
ex. J.Tissot 2012
40
60
80
100
120
140
160
180
200
220
10000 20000 30000 40000
Nu
av
Re
Pak and Cho
Dittus-Boelter
Present experimental data
ⱷ=2.0 %
ⱷ=0.5 %
ⱷ=0 % (water)
40
60
80
100
120
140
160
180
200
220
10000 20000 30000 40000
Nu
av
Re
Pak and ChoDittus-BoelterPresent experimental dataⱷ=2.0 %ⱷ=0.5 %ⱷ=0 % (water)
Experimental and Numerical Study to Enhance Heat Transfer on A Heat Exchanger
Al2o3/Water Nanofluid Using An Air Flow with Water Droplets
http://www.iaeme.com/IJMET/index.asp 93 [email protected]
• The Nusselt number has increased by increase in the flow rate of the fluid and
consequently Reynolds number and by increasing inlet fluid temperature and by
increased nanofluid volume concentration. When using spray system, a slightly
improves in Nusselt number compered without using spray system.
• The maximum enhancement in the heat transfer explained by using Nusselt
number ratio (stu / st%,%vwxyzw {$|}~), was (1.235) which occurred at nanofluid
concentration 2% with using sprayed air.
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