studying of convective heat transfer over an aluminum flat plate...

International Journal of Mechanical & Mechatronics Engineering IJMME-IJENS Vol:17 No:06 1

170206-3434-IJMME-IJENS © December 2017 IJENS I J E N S

Studying of Convective Heat Transfer Over an

Aluminum Flat Plate Based on Twin Jets

Impingement Mechanism for Different Reynolds

Number Mahir Faris Abdullah*, Rozli Zulkifli*, Zambri Harun, Shahrir Abdullah,

Wan Aizon W.Ghopa

Department of Mechanical Engineering and Materials, Universiti Kebangsaan Malaysia, 43600 Bangi, Selangor

*Corresponding Author [email protected], [email protected]

Abstract-- The impact of Reynolds number, jet-to-plate spacing,

and jet-to-jet distance on the distribution of local heat transfer to

impinging circular air jet in an aluminium flat surface is studied

through an experimental investigation. For several decades, this

has been an active research topic, Based on nozzle exit condition,

the Reynolds number is 17,000, 13,000 and 10,000, nozzle-to-

nozzle spacing 1-3 cm and jet-to-plate distance is 1, 6 and 11 cm.

Graphtec GL820 multichannel data logger was used to collect

thermal data, while an infrared thermal imaging technique

employing Fluke Ti25 was used to obtain thermal images for

capturing the temperature distribution in front of the aluminium

foil. The analysis of distributions of local heat transfer is based on

theoretical foretelling and experimental results of the fluid flow

characteristics in different places of jet impingement. The heat

flux of the jet impinging on a flat plate surface was measured

through an experimental setup by employing a heat flux micro-

sensor placed away at radial positions of 0–14 cm from the

stagnation point. The heat flux measurement was considered for

the calculation of local Nusselt (Nu) number for air jet

impingement as well as the local heat-transfer coefficient. Based

on the results, calculation of the local Nusselt number was done at

all mensuration points. Moreover, in a steady jet, with increase in

the Re number, the Nu number also increases. On analysing the

connection between the outcomes, it was observed that higher

Reynolds number led to higher localised heat flux in the air jet that

was steadily heated, which was impinged on the flat surface of the

plate. Also, the best heat-transfer coefficient was found at the

region near to the aluminium plate and nozzles as well on the

distance between the nozzles when be close, particularly at the

plate’s first points, which decreased gradually with increase in the

distance from the centre of the aluminium plate for all Reynolds

numbers employed.

Index Term-- Local Nusselt number; enhancement heat transfer;

twin jets impingement; Reynolds number, heat flux;

INTRODUCTION

An important factor that has resulted in high usage of

impingement jets is the high convective heat transfer

coefficient, which also enhances the overall efficiency of many

applications [1-4]. Many industrial applications employ jet

impingement as it allows producing high heat transfer rates. It

is employed in film cooling, turbine blade cooling, bearing

cooling, automobile windshield de-icing/defogging, electronics

cooling, glass tempering and drying of paper [5-8]. Many

studies have been published on enhancement heat transfer by

impingement jet, both in terms of experimental and numerical

aspects [9-11]. Most of the information that is available focuses

on impinging jets’ heat transfer characteristics for normal jet

impingement on a flat surface.

The impact of different velocities of twin jets on the heat

transfer rate number is studied through an experimental

investigation by employing the twin jet impingement

technique. Impinging jets have a broad range of industrial

applications and are crucial in the industry for cooling and

heating applications. In several applications, to achieve

efficient heat transfer rates, the fluids’ thermal conductivity

needs to be enhanced [12, 13]. The wide popularity of jet

impingement heat transfer technique in research studies is

attributed to its ability to produce high heat transfer coefficients

via forced convection action. In many industrial applications,

impinging jets are employed in a broad range of configurations

and disciplines, such as in the food industry, textile drying,

electronic chip cooling, turbine blade cooling, metal annealing

and glass tempering. Comprehensive research has been done to

study how applying twin impinging steady jets can affect the

heat transfer and flow characteristics. Most studies are based on

enhancing heat transfer by employing single and twin

impingement jets [14-16].

Zulkifli and Sopian [17] conducted many experimental studies

on mechanism of jet impingement heat transfer and presented

the results. Three Re numbers were used for measurements,

namely 16,000, 23,300 and 32,000. The recorded value of the

heat flux was referred to calculate the local Nusselt number of

the twin air jet impinging on a plate. A heat flux sensor was

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employed to measure the heat flux. Their results showed higher

values of the calculated local Nu numbers for all radial

locations, even those away from the stagnation point. A high

Nu number at localised radial positions can be achieved through

high instantaneous velocity, as demonstrated by the velocity

profile plotted in the experiment’s first part.

The local Nu numbers of the pulsating and steady jets were

compared by Zulkifli et al. [18] with different jet velocities,

frequencies, and radial locations away from the stagnation

point. The steady-state heating of a surface plate measured

patterned was evaluated by Dobbertean and Rahman [19]under

free liquid jet impingement. The cooled plate was applied with

a constant heat flux. Re numbers were calculated, which ranged

from 500 to 1,000 with different depths. The local heat-transfer

coefficient decreased with increasing Re number.

The heat-transfer characteristics were studied by Wang et al.

[20] via impingement jet at high-temperature surface plate

measured to determine the effect of surface plate temperature,

jet velocity and water temperature on heat transfer

characteristics for different engineering applications. Water

temperature, Jet velocity and surface temperature were found to

influence heat flux maximum.

High-velocity small-slot jet impingement was considered for

experimentally studying heat-transfer characteristics [21],

which was boiled on Nano scale modification flat in an effort

to increase the heat flux of critical. This also allowed

investigating the quantitative effects as well as surface-

distinguishing parameters’ effect mechanism. Moreover, the jet

impingement heat transfer have been investigated by authors in

[22] at a concave surface of the wing leading edge (correlation

development and experimental study). At the stagnation point,

heat-transfer increases with the Reynolds and <alpha>

numbers, and at the stagnation point, the preferable heat-

transfer efficiency that conforms to specific operating

parameters is achieved by maintaining an optimal nozzle–plate

distance (H/D).

The authors in [9] studied the characteristics of transient heat-

transfer on a surface plate by employing air-jet impingement

circular. While the air jet started its impingement, the local

Nusselt number increased rapidly. However, the increase in Nu

speed gradually decelerated with cooling down of the

impinging jet at the fifty to eighty s region. Moreover, the heat

transfer and fluid flow were studied by the authors in [23] for a

slot impingement jet with a little nozzle-to-plate surface

spacing, which showed a secondary peak in the Nusselt

number. Based on the findings, it was observed that in the

stagnation point, the mean velocity profile deviated from the

standard law of the wall. The Nusselt number was better when

compared to the condition where there were no perturbations,

and near to the location of the secondary Nu number peak,

large-scale vertical structures were spotted. The impact of

nozzle-to-plate surface distance on the fluid flow and heat

transfer of the submerged jet impingement was studied by [24].

Based on the results, the Nu number and pressure were found

to be divided into three zones. In zone I, there was a drastic

increase in the pressure and Nusselt number with decrease in

nozzle-to-plate distance. In zone II, it was observed that there

was negligible impact of the nozzle-to-plate distance on the

pressure and Nusselt number, in zone III, the pressure and

Nusselt number were observed to monotonically decrease with

rise in nozzle-to-plate surface spacing. The impact of

frequency, amplitude and pulse shape on time-averaged and

instantaneous convective heat transfer was theoretically

examined by Mladin and Zumbrunnen [25] in a planar

stagnation area by employing a detailed boundary layer style.

In their study, they recorded the presence of a threshold

Strouhal number, St>0.26, below which there would be no

enhancement of heat transfer effects significantly.

Moreover, comprehensive data still remain limited regarding

the impact of jet impingement on local heat-transfer profiles,

which are placed at radial positions at plate from the stagnation

point towards the plate surface end, and additional investigation

is required. The main objective of the current study is to

examine the twin circular jet heat transfer characteristics for

various Reynolds number as well as put emphasis on the Nu

number and local heat transfer coefficient. Moreover, the

Nusselt numbers on the radial distance are compared for the

aluminium flat plate impingement jet heat transfer. On the

stagnation point, the local Nusselt number is considered to be

radially symmetrical.

EXPERIMENTAL SETUP

To guarantee a flat impingement surface, the aluminium foil

was firmly held. A heat flux-temperature sensor and a square

aluminium foil of 30×30×0.4 cm dimension were settled on the

surface measured of the aluminium foil by employing a high-

conductivity heat sink complex and the impact of air gaps,

between the sensors and aluminium surface, was minimised by

applying Kapton tape.

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Fig. 1. The positions of thermocouples and thermal flux sensor on an aluminium measured surface

Figure 1 displays the positions of thermocouples and the heat

flux (thermal flux) sensor on an aluminium plate surface. For

all models, the nozzles’ arrangement is presented in Figure 2.

A square aluminium foil with surface dimensions and thickness

(L) has been employed as a jet impingement objective.

Fig. 2. Arrangement of 9 models of nozzles

During this article, two K-type thermocouples have been

employed, which were kept 120 mm apart and were linked to

an aluminium plate to keep an eye on the plate temperature. The

comet model H7331 was employed to collect the data from all

sensors, which include static pressure (pitot tube), temperature,

chamber humidity, due point and atmospheric pressure [26].

Uniform distribution of temperature throughout the foil

thickness was achieved due to small thickness of the aluminium

foil and high-thermal conductivity (k) to ensure accurate

temperature measurement at the surface [18]. The Graphtec

GL820 multichannel data logger was used to collect thermal

data. The temperature distribution at the aluminium foil was

captured through a Fluke Ti25 Infrared thermal imager, which

is appropriated for various kinds of thermocouples (i.e. J, B, S,

K, T, E and R types) [18].

Figure 3 shows TJIM with the aluminium foil objective

employed in our work in real life.



Fig. 3. Twin jet impingement mechanism

EXPERIMENTAL EXECUTION AND METHODOLOGY

A graphical drawing of the experimental instruments setup is

presented in Figure 4. The main compressor was used to supply

compressed air of 4 psi (0.275 bar). The steps of the

experimental procedures are as follows. First, we set the air

flow for each jet to achieve Renumbers of 17,000, 13,000 and

10,000 by employing a pitot tube to measure the twin jet centre

point’s velocity at the nozzle exit. Second, in the TJIM, we

installed a digital airflow meter to determine the velocity and

flow rate of the steady jet flow by maintaining a constant

temperature of 100°C. In this experimental setup, the flow

meter anemometer employed was take up from Dantec

Dynamics. Flow meter device was positioned between the

TJIM pipes passing the twin jets and the refrigerated air dryer.

Meanwhile, the velocity acquired from the pitot tube was

employed to run the twin impingement jets, and a flow meter

was used to confirm this velocity. Then, the highest Re

number=17,000 obtained along with 13,000 and 10,000 was

considered for capturing the heat transfer from the data logger

per unit time (q) as well as to measure the convective heat-

transfer coefficient (h) in terms of units (W/(m²K)).

An air reservoir would store the compressed air, which was

controlled by a ball valve. A refrigerated air dryer was

employed to remove moisture from the compressed air. To

evade fluctuation from the cyclic on/off of the central

compressor as well as control air pressure, a regulator and a

pressure gauge were installed, respectively. On the contrary, a

digital air flow meter (VA 420, CS Apparatus) was employed

to measure the air flow rate. Through the installed two identical

pipe lines, the air would be passed to the twin jet impingement

mechanism (TJIM). A ball valve would control each line to

guarantee similar flow characteristics for the twin jets.



Fig. 4. A schematic diagram of thermal imaging setup and heat-transfer experiment for twin jets impingement

Subsequently, for the 15 points, we then calculated the localised

Nu number at a measured radial distance surface from the

stagnation point. Thirdly, the pressure difference was created

through the differential pressure as an analogue that was used

as input for data acquisition Ni 6008, which is transformed to a

signal and subsequently transformed to a value in the form of

Scilab code to carry out the results. This setting up of

differential pressure was carried out between the Ni 6008 data

acquisition and the pitot tube. Fourth, we place the aluminium

foil at 1-11 cm away from the nozzle exit towards the measured

surface, where the space amongst the twin nozzles was 1-3 cm.

This meant that the experimental test required developing of

nine models. This preparation was done for determining the

surface temperature and the heat flux on the impingement

surface. Fifth, the temperature distribution and the thermal

images at the surface were captured simultaneously by the

Fluke Ti25 Infrared thermal imager until a steady state was

reached by the heat transfer. The steady heat transfer would

occur only when there was an equilibrium between the heat lost

by natural convection and heat inlet to the aluminium foil by

the jets. To reduce the experimental error, a total of 675 samples

were recorded during the heat flux–temperature sensor

mensuration, and figure 5 presents the average value.

Fig. 5. Twin jets impingement impact



Before these experiments, we kept constant various parameters related to the thermal imager and TJIM as showed in Table 1.

Table I

constant value parameters

Constant parameter Value

Nozzle-to-plate distance 1 to 11 cm

Nozzle-to-nozzle spacing 1 to 3 cm

Reynolds number

17,000,13,000,

10,000

Ambient temperature 24oC

Aluminium plate temperature 100oC

Emissivity of foil aluminium 0.97

Background temperature 25oC

Transmission 100%

We need to consider fluid mechanics and heat-transfer to

address jet impingement heat transfer problems. Consequently,

dimensionless numbers that are related also have to

be specified.

The computation of Re number (the velocity) of the twin air jet,

which also correlates to the inertial forces because of viscous

forces, is given as follows [19]:

Revd

(1)

when μ represents the fluid’s dynamic viscosity (Pa·s or kg/(s)

or N·s/m2), ν signifies the fluid velocity x (m/s) and ρ denotes

the fluid density (kg/m3).

Forced convection is dominated during the jet impingement

heat transfer. The Newton’s law equation can be employed to

determine the heat-transfer coefficient (h), i.e.[27]

( )s jQ h T T , which gives:

s j

qh

T T

(2)

When sT represents the surface temperature,

jT signifies the

air jet temperature and q denotes the amount of heat flux

(W/m2).

The Nu number equation can be used to calculate the ratio of

convective to conductive heat transfer as follows [28]:

hdNu

k (3)

When h indicates the convective heat-transfer coefficient, d

represents the pipe diameter and k signifies the fluid’s thermal

conductivity.

RESULT AND DISCUSSION

As presented in Figures 6–14, to obtain the Nu numbers, heat-

transfer enhancement tests were performed with defined the

distance between nozzle and surface plate (H/d=1 to 11 cm) and

nozzle-to-nozzle spacing (S/d=1,2 and 3cm). These results

verify that the use of the TJIM improved Nu number. Further,

employing the nine models with different velocities resulted in

steady jets giving different Nu numbers.

https://en.wikipedia.org/wiki/Mu_(letter)

https://en.wikipedia.org/wiki/Fluid

https://en.wikipedia.org/wiki/Dynamic_viscosity

https://en.wikipedia.org/wiki/Nu_(letter)

https://en.wikipedia.org/wiki/Rho_(letter)

https://en.wikipedia.org/wiki/Density

https://en.wikipedia.org/wiki/Heat_flux

https://en.wikipedia.org/wiki/Convective

https://en.wikipedia.org/wiki/Heat_transfer_coefficient

https://en.wikipedia.org/wiki/Hydraulic_diameter

https://en.wikipedia.org/wiki/Thermal_conductivity

https://en.wikipedia.org/wiki/Thermal_conductivity



Fig. 6. Values of Nusselt number at H/d=1 and S/d=1 (Model 1)

As per Figure 6, the first model included a distance of H/d=1

cm between the aluminium plate surface and the nozzles and

spacing of S/d=1 cm between nozzles. In the first point, the

heat-transfer enhancement reduced gradually with the moving

away of the heat flux sensor towards the end of the surface flat

plate until it reached almost 44.3 at Re=17,000, 41.6 at

Re=13,000 and 35.3 at Re=10,000 while the maximum Nusselt

numbers were 136.6 at Re=17,000, 122.7 at Re=13,000 and

116.4 at Re= 10,000.

Fig. 7. Nusselt number values at H/d=6 and S/d=1 (Model 2)



Figure 7 shows the second model with spacing of S/d=1 cm

between nozzles and a distance of H/d=6 cm between the

aluminium plate surface and the nozzles. In the first four points,

the heat-transfer enhancement reduced gradually with opposite

movement of the twin jets in a horizontal direction towards the

end of the plate surface until it arrived near to 48.3 when

Re=17,000, 44.7 when Re=13,000, and 38 when Re=10,000,

with the maximum Nu numbers at almost 136.4 at Re=17,000,

127.6 at Re=13,000 and 118.9 at Re=10,000.


Figure 8 above shows values of the Nusselt number where the

spacing was S/d = 1 cm between nozzles and the distance was

H/d=11 cm between the aluminium plate surface and the

nozzles. In the first points, the heat-transfer enhancement

reduced gradually with movement away from the heat flux

sensor towards the end of the aluminium plate until it arrived

almost 48.3 at Re=17,000, 41.4 at Re=13,000 and 35.5 at

Re=10,000, while the maximum Nu numbers were near to

149.4 at Re=17,000, 136.8 at Re=13,000 and 120.8 at

Re=10,000.




Figure 9 shows the spacing was S/d = 2 cm between nozzles

and the distance was H/d = 1 cm between the aluminium plate

surface and nozzles (fourth model). In the first 4 points, the

heat-transfer enhancement reduced gradually with the

movement away from the twin impingement jets in the opposite

horizontal direction towards the end of the flat plate surface

until it arrived 48.9 at Re=17,000, 42 at Re=13,000 and 36.3

when Re=10,000 and the maximum Nu numbers were almost

156.8 at Re=17,000, 135.3 at Re=13,000 and 119.4 at

Re=10,000.


Figure 10 above shows the Nu values when the spacing was

S/d=2 cm amongst nozzles and the distance was H/d=6 cm

between the aluminium plate surface and the nozzles. In the

first 4 points, the heat-transfer enhancement reduced gradually

with the movement of the air twin jets in the opposite horizontal

direction towards the end of the flat plate surface until it reached

almost 52.1 at Re=17,000, 46.2 at Re=13,000 and 39.7 at



Re=10,000 and the maximum Nu numbers were 143.7 at

Re=17,000, 131.3 at Re=13,000 and 117.09 at Re=10,000.


Moreover, in the first 4 points, at a radial distance of flat surface from the stagnation point, through the TJIM, the maximum Nu numbers were approximately

152.6 at Re=17,000, 136.8 at Re=13,000 and 127.1 at Re= 10,000, which reduced gradually towards the end of the aluminium flat plate surface until it reached

almost 48.5 at Re=17,000, 42.6 at Re=13,000 and 37.6 at Re= 10,000 towards the end of the aluminium plate, when the S/d=2 cm amongst nozzles and the distance was H/d=11 cm between the aluminium plate surface and the nozzles (Figure 11).

Fig. 12. Nusselt number values at H/d=1 and S/d=3 (Model 7)



Figure 12 shows the spacing was S/d=3 cm amongst nozzles

and the distance was H/d=1 cm (seventh model) between the

aluminium plate surface and the nozzles. In the first 4 or 5

points, the enhancement of heat transfer reduced gradually with

the movement of the air twin jets in the opposite horizontal

direction towards the end of the measured surface until it

arrived almost 48.5 at Re=17,000, 42.8 at Re=13,000 and 41.2

at Re=10,000, where the maximum Nu numbers were 151.5 at

Re=17,000, 133.7 at Re=13,000 and 119.5 at Re=10,000.


Figure 13 shows the spacing was S/d=3 cm amongst nozzles

and the distance was H/d=6 cm between the aluminium plate

surface and the nozzles (eighth model). In the first points, the

heat-transfer enhancement increased gradually. When the heat

flux sensor moved away towards the end of the aluminium flat

plate, it started decreasing until it reached almost 52.9 at

Re=17,000, 48.1 at Re=13,000 and 41.8 at Re=10,000, while

the maximum Nu numbers were around 144.8 at Re=17,000,

129.7 at Re=13,000 and 119.8 at Re=10,000.




Lastly, the ninth model had the maximum Nusselt numbers

where the spacing was S/d=3 cm amongst nozzles and the

distance was H/d=11 cm between the aluminium plate surface

and the nozzles; it was almost 150.5 when Re=17,000, 133.4

when Re=13,000 and 117.09 when Re=10,000. In the first 5

points, this was obtained by the TJIM with an approximate

radial distance of plate surface from the stagnation point, which

gradually reduced towards the end of the aluminium plate

surface until it arrived less than 50 at Re=17,000, 43.9 at

Re=13,000 and 39.7 at Re=10,000 towards the end of the

aluminium plate. Figure 14 displays the Nu numbers when the

spacing was S/d=3cm amongst nozzles and the distance was

H/d=11 cm between the aluminium plate surface and the

nozzles.

In outline, we can conclude that the values of Nusselt number

exhibited a reasonable change with increase in Reynolds

number values [18, 29-31]. These results looks more logically

clear on comparing with other research works that reflect the

Nu number’s behaviour qualitatively and quantitatively, when

steady or where impinging air twin jets on a hot plate surface

near the interference zone’s centre line passing to all the twin

jets’ holes towards the end of the surface plate [31]. This section

presents the results from the experimental data. Figures 15, 16

and 17 demonstrate the effect of TJIM on the surface

temperature as measured through a heat flux-temperature

sensor placed on the front of flat plate surface and the thermal

image on the surface. At the first 4 or 5 points, there is an

increase in surface temperature on the plate surface, which then

starts decreasing gradually after the 5-point distance on the

aluminium surface plate measured.

It is important to show how TJIM can impact the Nusselt

number in the midpoint or centre between the air twin jets

passing to the end of the interference zone near the terminal

aluminium plate surface. The figures demonstrate how Nu

numbers are influenced based on measurements through micro

foil sensors. The recorded Nu number was found to decrease

with increase in distance from the centre of the aluminium plate

surface towards the terminal of the surface (low rates at distant

points away from the flat plate surface centre). This result was

logical as, in this experiment, the increase in heat-transfer rate

occurred until the twin jets were close to the flat plate surface

and when under direct impact experienced by the heat flux

sensor under the twin jets air flow on the surface. There was a

gradual decrease as the distance from the centre of the

interference zone increased on Comparing to other researchers

[18, 29-31]

Figures 15, 16 and 17 present the images that were captured

through a thermal imager. These thermo images show how

TJIM affected and distributed on the plate surface measured of

the impinged target. The images are labelled with the centre of

the temperature values. The presented steady jet cases below

are for the nine models. Moreover, 18 pictures were captured

for all models, with one picture for each model at Re=17000,

13000 and 10000. In these images, some observations can be

clearly made. First, the hottest spots could be clearly seen,

which was due to the impact of twin jets impingement. Then,

after the midlevel point of temperature, an elliptical

temperature distribution can be seen. Further, higher

temperature rates were achieved through the steady jet case as

a result of high flow rates for the jets. In contrast, in TJIM, due



to its duty principles, the lower flow rate was supplied. In

addition, Figure 15 displaying the higher centre temperature of

165.8°C when H/d=1 and S/d=2 (Fourth Model). Also, twin jets

had the highest temperature due to high sensitivity of the

thermal imager that can detect even the minimal temperature

changes between both jets. Refer Figure 15 given below.

Fig. 15. Thermographic distribution on aluminium flat plate Model (1) to (9) at Re=17,000

Figure 16 shows the thermal distributions and the heat-transfer

behaviour for the steady jet case. Nine pictures were captured

for the all different models. Some monitoring can be clearly

made in these images. First, the hottest spots can be seen

viewed, which is a result of the effect of twin jets impingement.

Then, after the midlevel point of temperature, an elliptical

temperature distribution can be seen. Higher temperature rates

were achieved by the steady jet case due to jets’ high flow rates.

In contrast, in TJIM, due to its duty principles, a lower flow rate

was supplied. As seen in Figure 16, the fourth model produced

higher centre temperature of 164.4°C when H/d=1 and 6 and

S/d=2.




Figure 17 shows the thermal distributions and the heat-transfer

behaviour for the steady jet case. Nine pictures were captured

for all different models. Some surveillances can be clearly made

in these images. First, the hottest spots can be seen viewed,

which is a result of the effect of twin jets impingement. Then,

after the midlevel point of temperature, an elliptical

temperature distribution can be seen. Higher temperature rates

were achieved by the steady jet case due to jets’ high flow rates.

In contrast, in TJIM, due to its duty principles, a lower flow rate

was supplied. As seen in Figure 16, the eighth model produced

higher centre temperature of 163.1°C when H/d=6 and 6 and

S/d= 3.




CONCLUSION

This paper presents a study to enhance heat transfer by

employing twin jet impingement technique as well as to

examine the effect of different velocities on the localised

Nusselt number. This investigation is based on IR thermal

imaging and measurements of heat flux–temperature micro foil

sensor. The results show significant improvement in localised

Nu number of the steady flow at a radial distance on the

aluminium with measured flat plate surface of 0–4 cm when Re

numbers were 17,000, 13,000 and 10000, which gradually

reduced as the distance increased from the centre of the

interference zone. thereafter, on the aluminium foil flat target

surface, we conduct the thermography capturing process while

different Re on the impinged plate surface of the target were

employed to collect the heat flux–temperature data for the all

different nine models. For all parameters, the results presented

logical behaviour under consideration. The performance of the

air twin jets system confirms the identical effect of air twin jets,

which was designed to produce identical two jets. Furthermore,

for the current problem, the optimal condition to achieve higher

heat-transfer rates was based on the distance between twin

nozzles and the spacing between nozzles and the plate surface.

In conclusion, the different results presented here could explain

the effect of the nine different models on TJIM’s heat-transfer

characteristics, which could contribute to enhancement of the

performance for several engineering and industrial

applications.

ACKNOWLEDGEMENTS

We are thankful to the National university of Malaysia

FRGS/1/2013/TK01/UKM/02/3 and Arus Perdana AP-2015-

003 for providing the financial supports and Prof. Dr. Faris

Abdullah Aljanaby.

REFERENCES [1] Arik, M., Local heat transfer coefficients of a high-frequency

synthetic jet during impingement cooling over flat surfaces. Heat

Transfer Engineering, 2008. 29(9): p. 763-773.

[2] Kandlikar, S.G. and A.V. Bapat, Evaluation of jet impingement,

spray and microchannel chip cooling options for high heat flux

removal. Heat Transfer Engineering, 2007. 28(11): p. 911-923.

[3] Sharif, M. and A. Banerjee, Numerical analysis of heat transfer due to confined slot-jet impingement on a moving plate. Applied

Thermal Engineering, 2009. 29(2): p. 532-540.

[4] Chinige Sampath Kumara, S.M., Martin Geierb, Arvind Pattamatta, Numerical investigations on convective heat transfer enhancement

in jet impingement due to the presence of porous media using

Cascaded Lattice Boltzmann method. International Journal of Thermal Sciences, 2017. 122: p. 201-217.

[5] Ibuki, K., et al., Heat transfer characteristics of a planar water jet

impinging normally or obliquely on a flat surface at relatively low Reynolds numbers. Experimental thermal and fluid science, 2009.

33(8): p. 1226-1234.



[6] Baffigi, F. and C. Bartoli, Heat transfer enhancement in natural

convection between vertical and downward inclined wall and air by pulsating jets. Experimental Thermal and Fluid Science, 2010.

34(7): p. 943-953.

[7] Attalla, M. and M. Salem, Experimental investigation of heat transfer for a jet impinging obliquely on a flat surface. Experimental

Heat Transfer, 2015. 28(4): p. 378-391.

[8] Harinaldia, D.R. and R. Defriadic, Flow and Heat Transfer Characteristics of an Impinging Synthetic Air Jet under Sinusoidal

and Triangular Wave Forcing.

[9] Guo, Q., Z. Wen, and R. Dou, Experimental and numerical study on the transient heat-transfer characteristics of circular air-jet

impingement on a flat plate. International Journal of Heat and Mass

Transfer, 2017. 104: p. 1177-1188. [10] Roy, S. and P. Patel, Study of heat transfer for a pair of rectangular

jets impinging on an inclined surface. International Journal of Heat

and Mass Transfer, 2003. 46(3): p. 411-425. [11] O’donovan, T.S. and D.B. Murray, Fluctuating fluid flow and heat

transfer of an obliquely impinging air jet. International Journal of

Heat and Mass Transfer, 2008. 51(25): p. 6169-6179.

[12] Tawfika, M.M., Experimental studies of nanofluid thermal

conductivity enhancement and applications: A review. 2016.

[13] Attalla, M., H.M. Maghrabie, and E. Specht, Effect of inclination angle of a pair of air jets on heat transfer into the flat surface.

Experimental Thermal and Fluid Science, 2017. 85: p. 85-94.

[14] Gitan, A.A., et al., Twin Pulsating Jets Impingement Heat Transfer for Fuel Preheating in Automotives. Applied Mechanics and

Materials, 2014. 663: p. 322-328.

[15] Kondjoyan, A., F. Péneau, and H.-C. Boisson, Effect of high free stream turbulence on heat transfer between plates and air flows: a

review of existing experimental results. International journal of

thermal sciences, 2002. 41(1): p. 1-16. [16] Chaniotis, A., D. Poulikakos, and Y. Ventikos, Dual pulsating or

steady slot jet cooling of a constant heat flux surface. Journal of heat

transfer, 2003. 125(4): p. 575-586. [17] Sopian, R.Z.a.K., studies on pulse jet impingement heat transfer:

flow profile and effect of pulse frequencies on heat transfer.

International Journal of Engineering and Technology, 2007 International Journal of Engineering and Technology. 4.

[18] Rozli Zulkifli, K.S., Shahrir Abdullah and Mohd Sobri Takriff, Comparison of Local Nusselt Number Between Steady and

Pulsating Jet at Different Jet Reynolds Number. WSEAS

TRANSACTIONS on ENVIRONMENT and DEVELOPMENT, 2009. 5(5).

[19] Dobbertean, M.M. and M.M. Rahman, Numerical analysis of steady

state heat transfer for jet impingement on patterned surfaces. Applied Thermal Engineering, 2016. 103: p. 481-490.

[20] Wang, B., et al., Heat transfer characteristics during jet

impingement on a high-temperature plate surface. Applied Thermal Engineering, 2016. 100: p. 902-910.

[21] Wang, X.-J., Z.-H. Liu, and Y.-Y. Li, Experimental study of heat

transfer characteristics of high-velocity small slot jet impingement boiling on nanoscale modification surfaces. International Journal of

Heat and Mass Transfer, 2016. 103: p. 1042-1052.

[22] Bu, X., et al., Jet impingement heat transfer on a concave surface in a wing leading edge: Experimental study and correlation

development. Experimental Thermal and Fluid Science, 2016. 78: p.

199-207. [23] Dutta, R., A. Dewan, and B. Srinivasan, Large Eddy Simulation of

Turbulent Slot Jet Impingement Heat Transfer at Small Nozzle-to-

Plate Spacing. Heat Transfer Engineering, 2016. 37(15): p. 1242-1251.

[24] Choo, K., et al., The influence of nozzle-to-plate spacing on heat

transfer and fluid flow of submerged jet impingement. International Journal of Heat and Mass Transfer, 2016. 97: p. 66-69.

[25] Mladin, E.-C. and D.A. Zumbrunnen, Alterations to coherent flow

structures and heat transfer due to pulsations in an impinging air-jet. International Journal of Thermal Sciences, 2000. 39(2): p. 236-

248.

[26] Ghazalia, I., et al., THE DEVELOPMENT OF A MULTI-PURPOSE WIND TUNNEL.

[27] Bergman, T.L., et al., Fundamentals of heat and mass transfer.

2011: John Wiley & Sons.

[28] Incropera, F.P., et al., Fundamentals of heat and mass transfer.

2007: Wiley.

[29] Sailor, D.J., D.J. Rohli, and Q. Fu, Effect of variable duty cycle flow pulsations on heat transfer enhancement for an impinging air jet.

International Journal of Heat and Fluid Flow, 1999. 20(6): p. 574-

580. [30] Azevedo, L., B. Webb, and M. Queiroz, Pulsed air jet impingement

heat transfer. Experimental Thermal and Fluid Science, 1994. 8(3):

p. 206-213. [31] Mahir Faris Abdullah, R.Z., Zambri Harun, Shahrir Abdullah, Wan

Aizon W.Ghopa, Ashraf Amer Abbas, Experimental Investigation

on Comparison of Local Nusselt Number Using Twin Jet Impingement Mechanism. Vol. 17. 2017: International Journal of

Mechanical & Mechatronics Engineering IJMME-IJENS.

studying of convective heat transfer over an aluminum flat plate...

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