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Kartik Jujare et al Int. Journal of Engineering Research and Applications
ISSN : 2248-9622, Vol. 4, Issue 1( Version 1), January 2014, pp.256-260

RESEARCH ARTICLE

www.ijera.com

OPEN ACCESS

Experimental Investigation of Jet Impingement Cooling On a
Ribbed Surface with Holes
Kartik Jujare1, Shashank Kumat, Akash Thawkar
(Department of Mechanical Engineering, MIT Academy of Engineering Alandi (D), Pune University - 412105)

ABSTRACT
Jet impingement has found applications in many processes where there is a need for higher heat transfer The
paper reports the results of experimental investigations of the flow and heat transfer from a triangular ribbed
heated plate with holes, impinged by a round jet in a confined case built around the plate. The parameters varied
are heat flux, ratio of the distance of the nozzle from the plate to the diameter of the nozzle and flow rate of air.
These values are further processed to calculate the Reynolds number, heat transfer coefficients and consequently
the Nusselt numbers for each combination.
Keywords – Jet impingement, Reynolds number, Triangular Ribbed surface.

I.

Introduction

The jet impingement configuration is
applied to many processes, especially where there is a
need for high transfer of the heat generated such as in
applications concerning electronic cooling. Prior
studies have focused their attention on a variety of
parameters i.e. variation in the nozzle geometry,
Reynolds number, angle of incidence and the
geometry configuration. Narayanan et. al. [1] studied
the mechanics of an impinging slot jet flow
concluding that the mean and RMS – averaged
fluctuating surface pressure, and local heat transfer
coefficient peaked at the impinging region and
decreased monotonically in the wall bounded flow
past impingement . The study also tabulates prior
important studies and their variation parameters.
Shyy woei et.al [2] studied the heat transfer
characteristics of impinging a jet onto concave and
convex dimpled surfaces with effusion. Among other
geometries studied, Yan and Mei [3] examined the
angled rib effects by considering both continuous and
broken V-shaped configurations with different exit
flow orientations.
Katti and Prabhu [4] in their pursuit to
understand and enhance the heat transfer in the
detached rib configuration found, contrary to results
of the smooth surface, that there is a continuous
increase in the heat transfer coefficient from the
stagnation point in the stagnation region.
Rallabandi et. al. [5] studied the heat
transfer characteristics of both jet impingement and
channel flow conditions. The range of the Reynolds
number for the flow was 5000 to 40000. The study
was also made on the heat transfer characteristics of
inline and staggered ribs.

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In yet another study, Duda et al. [6] concluded that
when a cylindrical pedestal is placed the flow quickly
separates over the pedestal edge leading to three
distinct regions of the wall jet. There is a
recirculation region at the base of the pedestal, a
separation zone where flow detaches from the
pedestal surface and does not reattach downstream
(for low H/d spacing), and a region of separated flow
which reattaches after the pedestal boundary and
forms the wall jet.
Donovana and Murray [7] in their work
studied the effects of rotational motion provided to
the Al-foam which was being studied for heat
transfer.
In view of these studies, geometry with
triangular ribs in parallel orientation was
manufactured, with holes drilled between the ribs.
The aim was to understand the effect of holes on the
air flow patterns and heat transfer characteristics in
the enclosure.

II.

Experimental setup

The impinging air jet is issued from a
blower system which can deliver a maximum air flow
of 50 cfm. The nozzle is constructed from a solid
nylon pipe. It is made convergent and curved
smoothly which allows rapid acceleration of fluid
without the occurrence of flow separation. Therefore,
uniform velocity profile associated with relatively
low turbulence intensity across the nozzle width at
the exit is obtained. The jet velocity is measured with
a calibrated Orifice meter. The flow can be regulated
by a flow regulator on the blower or a dimmerstat.
The manual regulator is kept fully open throughout
the experiment. The measurement of the velocity is in
congruence with the method followed generally.
Vorifice = Cv. 2𝑔ℎmano
(1)
256 | P a g e

2

Kartik Jujare et al Int. Journal of Engineering Research and Applications
ISSN : 2248-9622, Vol. 4, Issue 1( Version 1), January 2014, pp.256-260
Aorifice x Vorifice = Anozzle x Vnozzle
(2)
Diameter of nozzle exit is 26.7 mm and
length being 80 mm.

www.ijera.com

reduced. The enclosure dimension is made slightly
larger than the target plate. The enclosure supports a
collapsible roof which has the nozzle fixed to it. The
space between the enclosure and the internally sliding
roof is made air tight with the help of rubber sheets.

Figure 1 Schematic of Target plate
The schematic of the target plate is shown in
Fig. 1. It is 10 cm wide and 18 cm long. There are
three 10mm high and a base of 20 mm triangular rib
elements. The target plate consists of 8 holes which
act as the sole exit route for the spent air. It houses a
3 mm thin heater pad, a 5 mm thin Asbestos sheet
and another 5 mm steel plate is fastened to the target
plate with the help of bolts to minimize the heat loss.
The eight holes extend through the heater, asbestos
sheet and the MS plate. The heater wires (nichrome)
are placed carefully so as to avoid being exposed
directly to air. The target plate can be heated by
passing electric current through the wires cased in a
pad. All the ribs are equally spaced. To account for
the additional radiation heat loss directly from the
asbestos sheet, the total heat loss to the surroundings
is estimated by assuming the heat transfer co-efficient
as 10.
Qgenerated = V.I
(3)
Qloss= hbottom x Abottom x (Tbottom – Tambient)
(4)
To ensure that the heater pad is heated
uniformly, the entire heater wires inside the heater is
arranged in circular fashion. With the desired voltage
V and current I passing through the thin heater pad,
the heat flux along the surface can be calculated and
is equal to VI/A, where A is the area of the top
surface of the target plate excluding the holes. The
local heat Transfer coefficients were determined with
the following equations:
Qactual= Qtotal – Qloss
(5)
qactual= Qactual/ Atop
(6)
qactual
hactual=
(7)
Tsurface −Tinlet
The enclosure of the setup, which houses the
target plate and the collapsible roof, is made up of
two materials. Polycarbonate sheet (k = 0.19 W/mK)
has been used on two sides to provide visibility inside
the enclosure and plywood (k = 0.13 W/mK) on the
other two sides. The enclosure is insulated at the
bottom of the vertical walls with neoprene rubber
sheets (k = 0.19 W/mK) which is glued so that the
heat loss from the vertical walls of the target plate is
www.ijera.com

Figure 2 Enclosure assembly
The target plate is mounted on an MS plate
which has its central portion cut in a rectangular
fashion just enough to support the target plate as well
as to allow for the spent air to pass out to the
atmosphere (different from the one used to bolt the
heater assembly). It is 5 mm thick and saves the user
from having to handle the hot target plate. This also
serves the purpose of varying the height by moving it
along 4 rods which are bolted to the stand.
The plastic pipe which delivers the air is not
glued to the L-joint as seen in Fig 2 to allow for
flexibility while changing the height of the enclosure.
Power is supplied from a regulated AC
power supply. The voltage and current across the
heater is measured by a digital voltmeter ammeter.
All the temperature signals are acquired with a help
of a temperature detector. The temperature is
measured using Fe-K thermocouples positioned at
five locations- (I) to measure the inlet air temperature
(II) placed directly below the exit hole. (III) To
measure surface temp the first rib of the plate. (IV)
Placed below the heater assembly to calculate the
heat loss (V) to measure the atmospheric
temperature. The thermocouple wires are extricated
carefully from slots made into the rubber sheets.
The Nusselt number for the heat transfer
was calculated by
𝑁𝑢 =

ℎ𝑑

(6)

𝑘

III.

Observations

The observations were made by varying
three parameters, namely, Heat flux, H/d ratio,
Reynolds’s number. Table 1 shows the values for
varying H/d ratio and flux for constant Reynolds
number of 18300.
257 | P a g e

3

Kartik Jujare et al Int. Journal of Engineering Research and Applications
ISSN : 2248-9622, Vol. 4, Issue 1( Version 1), January 2014, pp.256-260
Table 1The range of values of parameters
Sl.
Parameters
Range of values
no.
studied
1.
Reynolds
13700, 15900, 18300
number
2.
H/d ratio
4.02, 8.02, 11.02
3.
Flux (W/m2)
2812.25,3696.88,4802.119,
5956.68, 7286.54

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Various non-dimensional and dimensional parameters
were calculated, including heat transfer coefficient and
Nusselt number.

Table 2
Results obtained for Reynolds number of 18300
Sl. no. H/d ratio V(volts)
I(amp)
Flux(W/m2)
1.
4.02
130.99
0.7467
2812.25

Tatmo
28

Tinlet
34

Texit
40

Tbottom
56

Tsurface
45

2.

150.12

0.8565

3696.88

28

36

40

59

47

3.

170.725

0.9783

4802.19

28

36

41

62

50

4.

190.75

1.0861

5956.68

28

36

43

67

53

5.

211.7

1.1971

7286.54

28

37

45

73

56

130.99

0.7467

2812.25

28

36

41

55

47

7.

150.12

0.8565

3696.88

28

35

44

63

50

8.

170.725

0.9783

4802.19

28

35

47

70

54

9.

190.75

1.0861

5956.68

28

34

46

80

56

10.

211.7

1.1971

7286.54

28

34

48

90

62

130.99

0.7467

2812.25

28

36

41

54

46

12.

150.12

0.8565

3696.88

28

36

41

59

49

13.

170.725

0.9783

4802.19

28

37

43

67

53

14.

190.75

1.0861

5956.68

28

37

45

73

57

15.

211.7

1.1971

7286.54

28

37

46

91

65

6

8.02

11.

11.02

The procedure to note down readings was as
follows: The heater and the blower were switched on
at the right voltage and was allowed to run till steady
state is reached. The readings of the temperature
indicator were noted once it reached the steady state
position. While evaluating the observations following
data were considered,
Table 3
Values of parameters considered for calculation
Sl. no.
Parameter
Value
1.
Density of air
1.225 kg/m3
2.
Dynamic viscosity of air
17.89 x 10-6
kg/ms
3.
Thermal conductivity of
0.0242
air
W/mk
4.
Coefficient of velocity
0.92
5.
Atop for qactual
0.02 m2
6.
Abottom for qloss
0.01478 m2

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IV.

Calculations

The methodology to calculate the heat transfer
coefficient and Nusselt number is shown in
Appendix-I. Table 4 shows the values of HTC and
Nusselt number against the flux and H/d ratio
provided. The heat transfer coefficient for the loss
was assumed to be 10 W/m2K.

V.

Analysis

In the present study, the parametric variation
of the heat transfer coefficient shows an increasing
trend with the increase in the Reynolds number.
Similarly the Nusselt number can generally be seen
to be increasing with the corresponding increase in
the Reynolds number and the heat flux evident from
Fig 3, 4 and 5.
The effect of the variation of the H/d is as
follows.
The higher H/d ratio causes high entrailment
compared to lower H/d ratios.

258 | P a g e

4

Kartik Jujare et al Int. Journal of Engineering Research and Applications
ISSN : 2248-9622, Vol. 4, Issue 1( Version 1), January 2014, pp.256-260
Table 4
Nusselt number for Reynolds number of 18300.
Sl. H/d
Flux
Heat
Nusselt
no. ratio
(W/m2) transfer
number
coefficient
(W/m2K)
1.
4.02
2812.25
425.7811
469.76671
2.
3696.88
563.6181
621.8431
3.
4802.19
578.5538
638.32177
4.
5956.68
592.3805
653.57685
5.
7286.54
649.4081
716.49569
6.
8.02
2812.25
426.4529
470.50793
7.
3696.88
411.3493
453.84403
8.
4802.19
423.1912
466.90933
9.
5956.68
453.3818
500.21872
10.
7286.54
436.183
481.24321
11. 11.02 2812.25
469.8372
518.37406
12.
3696.88
476.9076
526.17493
13.
4802.19
503.9252
555.9836
14.
5956.68
501.3064
553.09429
15.
7286.54
435.9191
480.95201

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700
650
600
550
500
450
400

f 2812
f 3697
f 4802
f 5957
H/d
4.02

H/d
8.02

H/d
11.02

f 7287

Figure 4 Values of Nusselt number for Reynolds
number 15900
The incoherence in the readings can be attributed to
the instabilities arising because of the interaction
between natural and forced convection.

f 2812
f 3697

f 2812

600

f 3697

500

550
500
450
400
350
300
250

700

f 4802

400

f 5957
H/d
4.02

H/d
8.02

H/d
11.02

f 7287

f 4802
f 5957
H/d
4.02

H/d
8.02

H/d
11.02

f 7287

Figure 5 Values of Nusselt number for Reynolds
number 18300

VI.
Figure 3 Values of Nusselt number for Reynolds
number 13700
For higher H/d ratios the momentum
exchange observed between impinging and quiescent
fluid implies that the impinging jet becomes broader
and spreads over more surface area which also causes
possible vortex formation. However in case of less
H/d ratio same amount of fluid spreads over less
surface area thus causing higher heat transfer rate.
The oddity to understand would be the
increase in the inlet temperature of air. This increase
could be attributed in a small way to the heat gain
from the blower but majorly because of the rise of
hot air from the enclosure towards the inlet
thermocouple.
Secondly, we observe that the heat transfer
coefficients remain more or less the same because of
the simple reason that the assembly is housed inside
an enclosure which allows the air to exit in only one
way that is through the holes in the target plate.

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Conclusion

In this work effect of Reynolds number, heat
flux, and H/d ratio on the local Nusselt number is
investigated. It was carried out on a triangularly
ribbed target plate with holes. As the bottom grill is
the only exit, there is an increase in the heat transfer
coefficient.
The following can be concluded from the study
 That there is an increase in the heat transfer
as the H/d ratio decreases.
 With a general increase in the heat flux
there is a general rise in the heat transfer
rate.
 An increase in the Reynolds number also
increases the heat transfer rate for constant
heat flux and H/d ratio

VII.

Acknowledgement

The authors would like to thank Dr. Mayur
Bhoite for his support and MIT Academy of
Engineering, Alandi for providing us with the
opportunity and space to conduct the study. We also
thank Ms. Sayali Wable for her help in putting
together the Experimental setup.

259 | P a g e

5

Kartik Jujare et al Int. Journal of Engineering Research and Applications
ISSN : 2248-9622, Vol. 4, Issue 1( Version 1), January 2014, pp.256-260
References
[1]

[2]

[3]

[4]

[5]

[6]

[7]

V. Narayanan, J. Seyed-Yagoobi, R.H. Page, An
experimental study of fluid mechanics and heat
transfer in an impinging slot jet flow,
International Journal of Heat and Mass Transfer
47 (2004) 1827–1845.
Shyy Woei Changa, Hsin-Feng Liou ,Heat
transfer of impinging jet-array onto concave- and
convex-dimpled
surfaces
with
effusion,
International Journal of Heat and Mass Transfer
52 (2009) 4484–4499.
W.M. Yan, S.C. Mei, Measurement of detailed
heat transfer along rib-roughened surface under
arrays of impinging elliptic jets, International
Journal of Heat and Mass Transfer 47 (2004)
5235–5245.
Vadiraj Katti, S.V. Prabhu, Heat transfer
enhancement on a flat surface with axisymmetric
detached ribs by normal impingement of circular
air jet, International Journal of Heat and Fluid
Flow 29 (2008) 1279–1294
Akhilesh P. Rallabandi, Dong-Ho Rhee, Zhihong
Gao, Je-Chin Han, Heat transfer enhancement in
rectangular channels with axial ribs or porous
foam under through flow and impinging jet
conditions, International Journal of Heat and
Mass Transfer 53 (2010) 4663–4671
John C. Duda, Francis D. Lagor, Amy S.
Fleischer, A flow visualization study of the
development of vortex structures in a round jet
impinging on a flat plate and a cylindrical
pedestal, Experimental Thermal and Fluid
Science 32 (2008) 1754–1758
Tadhg S. O’Donovana, Darina B. Murray,
Fluctuating fluid flow and heat transfer of an
obliquely impinging air jet, International Journal
of Heat and Mass Transfer 51 (2008) 6169–6179

Nomenclature
Vorifice
Cv
H/d ratio

g
Hmano
Abottom
Aorifice
Anozzle
Vnozzle
Qgenerated
Qloss
qactual

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Velocity at orifice
Coefficient of velocity
The ratio of the height
between nozzle and
plate to the diameter of
nozzle.
Gravitational constant
Height observed in
manometer
Area of heater assembly
exposed to air for qactual
Area of orifice opening
Area of nozzle opening
Velocity at nozzle
opening
Total heat generated
from the heater
Total heat lost from the
bottom exposure to air
Heat actually carried
away by jet
impingement per unit

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area
Heat transfer coefficient
for bottom surface
Actual heat transfer
coefficient
Temperature obtained
on the bottom surface of
target plate
Atmospheric
temperature

hbottom
hactual
Tbottom
Tatmo

Appendix I
Sample calculation:
Atop = 0.02 m2
Abottom = 0.01478 m 2
Qtotal = (V x I) = 97.81W
𝑄𝑡𝑜𝑡𝑎𝑙
Flux =
= 2812.25 W/m2
(Abottom +Atop )

Qloss = hbottom x Abottom (Tbottom – Tatmo)
= 10 * 0.01478 *(40-28)
= 4.1384 W
hbottom = 10 W/m2K (assumed)
Qactual= Qtotal – Qloss = (97.81-4.1384)
= 93.6716 W
qactual = Qactual/ Atop = 93.6716 /0.02
= 4683.5917 W/m2
qactual = hactual*(Tsurface – Tinlet)
hactual = qactual/(T4 – T1)
=4683.5917 /(45-34)
= 425.78 W/m2 k
Reynold’s number calculation
V1 = Cv (2𝑔ℎmano) = 1.1085 m/s
Cv = 0.92
From Continuity equation: A1V1= A2V2
V2 = 10 m/s
Re = (ρair V2 D)/ϑ
= (1.225*7.5*0.0267)/(1.79E-05)
= 18272
Nusselt Number calculation
Nu = (h x L) / K
= (425.78 *0.0267)/(0.0242)
= 469.76

260 | P a g e

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  • 1. Kartik Jujare et al Int. Journal of Engineering Research and Applications ISSN : 2248-9622, Vol. 4, Issue 1( Version 1), January 2014, pp.256-260 RESEARCH ARTICLE www.ijera.com OPEN ACCESS Experimental Investigation of Jet Impingement Cooling On a Ribbed Surface with Holes Kartik Jujare1, Shashank Kumat, Akash Thawkar (Department of Mechanical Engineering, MIT Academy of Engineering Alandi (D), Pune University - 412105) ABSTRACT Jet impingement has found applications in many processes where there is a need for higher heat transfer The paper reports the results of experimental investigations of the flow and heat transfer from a triangular ribbed heated plate with holes, impinged by a round jet in a confined case built around the plate. The parameters varied are heat flux, ratio of the distance of the nozzle from the plate to the diameter of the nozzle and flow rate of air. These values are further processed to calculate the Reynolds number, heat transfer coefficients and consequently the Nusselt numbers for each combination. Keywords – Jet impingement, Reynolds number, Triangular Ribbed surface. I. Introduction The jet impingement configuration is applied to many processes, especially where there is a need for high transfer of the heat generated such as in applications concerning electronic cooling. Prior studies have focused their attention on a variety of parameters i.e. variation in the nozzle geometry, Reynolds number, angle of incidence and the geometry configuration. Narayanan et. al. [1] studied the mechanics of an impinging slot jet flow concluding that the mean and RMS – averaged fluctuating surface pressure, and local heat transfer coefficient peaked at the impinging region and decreased monotonically in the wall bounded flow past impingement . The study also tabulates prior important studies and their variation parameters. Shyy woei et.al [2] studied the heat transfer characteristics of impinging a jet onto concave and convex dimpled surfaces with effusion. Among other geometries studied, Yan and Mei [3] examined the angled rib effects by considering both continuous and broken V-shaped configurations with different exit flow orientations. Katti and Prabhu [4] in their pursuit to understand and enhance the heat transfer in the detached rib configuration found, contrary to results of the smooth surface, that there is a continuous increase in the heat transfer coefficient from the stagnation point in the stagnation region. Rallabandi et. al. [5] studied the heat transfer characteristics of both jet impingement and channel flow conditions. The range of the Reynolds number for the flow was 5000 to 40000. The study was also made on the heat transfer characteristics of inline and staggered ribs. www.ijera.com In yet another study, Duda et al. [6] concluded that when a cylindrical pedestal is placed the flow quickly separates over the pedestal edge leading to three distinct regions of the wall jet. There is a recirculation region at the base of the pedestal, a separation zone where flow detaches from the pedestal surface and does not reattach downstream (for low H/d spacing), and a region of separated flow which reattaches after the pedestal boundary and forms the wall jet. Donovana and Murray [7] in their work studied the effects of rotational motion provided to the Al-foam which was being studied for heat transfer. In view of these studies, geometry with triangular ribs in parallel orientation was manufactured, with holes drilled between the ribs. The aim was to understand the effect of holes on the air flow patterns and heat transfer characteristics in the enclosure. II. Experimental setup The impinging air jet is issued from a blower system which can deliver a maximum air flow of 50 cfm. The nozzle is constructed from a solid nylon pipe. It is made convergent and curved smoothly which allows rapid acceleration of fluid without the occurrence of flow separation. Therefore, uniform velocity profile associated with relatively low turbulence intensity across the nozzle width at the exit is obtained. The jet velocity is measured with a calibrated Orifice meter. The flow can be regulated by a flow regulator on the blower or a dimmerstat. The manual regulator is kept fully open throughout the experiment. The measurement of the velocity is in congruence with the method followed generally. Vorifice = Cv. 2𝑔ℎmano (1) 256 | P a g e
  • 2. Kartik Jujare et al Int. Journal of Engineering Research and Applications ISSN : 2248-9622, Vol. 4, Issue 1( Version 1), January 2014, pp.256-260 Aorifice x Vorifice = Anozzle x Vnozzle (2) Diameter of nozzle exit is 26.7 mm and length being 80 mm. www.ijera.com reduced. The enclosure dimension is made slightly larger than the target plate. The enclosure supports a collapsible roof which has the nozzle fixed to it. The space between the enclosure and the internally sliding roof is made air tight with the help of rubber sheets. Figure 1 Schematic of Target plate The schematic of the target plate is shown in Fig. 1. It is 10 cm wide and 18 cm long. There are three 10mm high and a base of 20 mm triangular rib elements. The target plate consists of 8 holes which act as the sole exit route for the spent air. It houses a 3 mm thin heater pad, a 5 mm thin Asbestos sheet and another 5 mm steel plate is fastened to the target plate with the help of bolts to minimize the heat loss. The eight holes extend through the heater, asbestos sheet and the MS plate. The heater wires (nichrome) are placed carefully so as to avoid being exposed directly to air. The target plate can be heated by passing electric current through the wires cased in a pad. All the ribs are equally spaced. To account for the additional radiation heat loss directly from the asbestos sheet, the total heat loss to the surroundings is estimated by assuming the heat transfer co-efficient as 10. Qgenerated = V.I (3) Qloss= hbottom x Abottom x (Tbottom – Tambient) (4) To ensure that the heater pad is heated uniformly, the entire heater wires inside the heater is arranged in circular fashion. With the desired voltage V and current I passing through the thin heater pad, the heat flux along the surface can be calculated and is equal to VI/A, where A is the area of the top surface of the target plate excluding the holes. The local heat Transfer coefficients were determined with the following equations: Qactual= Qtotal – Qloss (5) qactual= Qactual/ Atop (6) qactual hactual= (7) Tsurface −Tinlet The enclosure of the setup, which houses the target plate and the collapsible roof, is made up of two materials. Polycarbonate sheet (k = 0.19 W/mK) has been used on two sides to provide visibility inside the enclosure and plywood (k = 0.13 W/mK) on the other two sides. The enclosure is insulated at the bottom of the vertical walls with neoprene rubber sheets (k = 0.19 W/mK) which is glued so that the heat loss from the vertical walls of the target plate is www.ijera.com Figure 2 Enclosure assembly The target plate is mounted on an MS plate which has its central portion cut in a rectangular fashion just enough to support the target plate as well as to allow for the spent air to pass out to the atmosphere (different from the one used to bolt the heater assembly). It is 5 mm thick and saves the user from having to handle the hot target plate. This also serves the purpose of varying the height by moving it along 4 rods which are bolted to the stand. The plastic pipe which delivers the air is not glued to the L-joint as seen in Fig 2 to allow for flexibility while changing the height of the enclosure. Power is supplied from a regulated AC power supply. The voltage and current across the heater is measured by a digital voltmeter ammeter. All the temperature signals are acquired with a help of a temperature detector. The temperature is measured using Fe-K thermocouples positioned at five locations- (I) to measure the inlet air temperature (II) placed directly below the exit hole. (III) To measure surface temp the first rib of the plate. (IV) Placed below the heater assembly to calculate the heat loss (V) to measure the atmospheric temperature. The thermocouple wires are extricated carefully from slots made into the rubber sheets. The Nusselt number for the heat transfer was calculated by 𝑁𝑢 = ℎ𝑑 (6) 𝑘 III. Observations The observations were made by varying three parameters, namely, Heat flux, H/d ratio, Reynolds’s number. Table 1 shows the values for varying H/d ratio and flux for constant Reynolds number of 18300. 257 | P a g e
  • 3. Kartik Jujare et al Int. Journal of Engineering Research and Applications ISSN : 2248-9622, Vol. 4, Issue 1( Version 1), January 2014, pp.256-260 Table 1The range of values of parameters Sl. Parameters Range of values no. studied 1. Reynolds 13700, 15900, 18300 number 2. H/d ratio 4.02, 8.02, 11.02 3. Flux (W/m2) 2812.25,3696.88,4802.119, 5956.68, 7286.54 www.ijera.com Various non-dimensional and dimensional parameters were calculated, including heat transfer coefficient and Nusselt number. Table 2 Results obtained for Reynolds number of 18300 Sl. no. H/d ratio V(volts) I(amp) Flux(W/m2) 1. 4.02 130.99 0.7467 2812.25 Tatmo 28 Tinlet 34 Texit 40 Tbottom 56 Tsurface 45 2. 150.12 0.8565 3696.88 28 36 40 59 47 3. 170.725 0.9783 4802.19 28 36 41 62 50 4. 190.75 1.0861 5956.68 28 36 43 67 53 5. 211.7 1.1971 7286.54 28 37 45 73 56 130.99 0.7467 2812.25 28 36 41 55 47 7. 150.12 0.8565 3696.88 28 35 44 63 50 8. 170.725 0.9783 4802.19 28 35 47 70 54 9. 190.75 1.0861 5956.68 28 34 46 80 56 10. 211.7 1.1971 7286.54 28 34 48 90 62 130.99 0.7467 2812.25 28 36 41 54 46 12. 150.12 0.8565 3696.88 28 36 41 59 49 13. 170.725 0.9783 4802.19 28 37 43 67 53 14. 190.75 1.0861 5956.68 28 37 45 73 57 15. 211.7 1.1971 7286.54 28 37 46 91 65 6 8.02 11. 11.02 The procedure to note down readings was as follows: The heater and the blower were switched on at the right voltage and was allowed to run till steady state is reached. The readings of the temperature indicator were noted once it reached the steady state position. While evaluating the observations following data were considered, Table 3 Values of parameters considered for calculation Sl. no. Parameter Value 1. Density of air 1.225 kg/m3 2. Dynamic viscosity of air 17.89 x 10-6 kg/ms 3. Thermal conductivity of 0.0242 air W/mk 4. Coefficient of velocity 0.92 5. Atop for qactual 0.02 m2 6. Abottom for qloss 0.01478 m2 www.ijera.com IV. Calculations The methodology to calculate the heat transfer coefficient and Nusselt number is shown in Appendix-I. Table 4 shows the values of HTC and Nusselt number against the flux and H/d ratio provided. The heat transfer coefficient for the loss was assumed to be 10 W/m2K. V. Analysis In the present study, the parametric variation of the heat transfer coefficient shows an increasing trend with the increase in the Reynolds number. Similarly the Nusselt number can generally be seen to be increasing with the corresponding increase in the Reynolds number and the heat flux evident from Fig 3, 4 and 5. The effect of the variation of the H/d is as follows. The higher H/d ratio causes high entrailment compared to lower H/d ratios. 258 | P a g e
  • 4. Kartik Jujare et al Int. Journal of Engineering Research and Applications ISSN : 2248-9622, Vol. 4, Issue 1( Version 1), January 2014, pp.256-260 Table 4 Nusselt number for Reynolds number of 18300. Sl. H/d Flux Heat Nusselt no. ratio (W/m2) transfer number coefficient (W/m2K) 1. 4.02 2812.25 425.7811 469.76671 2. 3696.88 563.6181 621.8431 3. 4802.19 578.5538 638.32177 4. 5956.68 592.3805 653.57685 5. 7286.54 649.4081 716.49569 6. 8.02 2812.25 426.4529 470.50793 7. 3696.88 411.3493 453.84403 8. 4802.19 423.1912 466.90933 9. 5956.68 453.3818 500.21872 10. 7286.54 436.183 481.24321 11. 11.02 2812.25 469.8372 518.37406 12. 3696.88 476.9076 526.17493 13. 4802.19 503.9252 555.9836 14. 5956.68 501.3064 553.09429 15. 7286.54 435.9191 480.95201 www.ijera.com 700 650 600 550 500 450 400 f 2812 f 3697 f 4802 f 5957 H/d 4.02 H/d 8.02 H/d 11.02 f 7287 Figure 4 Values of Nusselt number for Reynolds number 15900 The incoherence in the readings can be attributed to the instabilities arising because of the interaction between natural and forced convection. f 2812 f 3697 f 2812 600 f 3697 500 550 500 450 400 350 300 250 700 f 4802 400 f 5957 H/d 4.02 H/d 8.02 H/d 11.02 f 7287 f 4802 f 5957 H/d 4.02 H/d 8.02 H/d 11.02 f 7287 Figure 5 Values of Nusselt number for Reynolds number 18300 VI. Figure 3 Values of Nusselt number for Reynolds number 13700 For higher H/d ratios the momentum exchange observed between impinging and quiescent fluid implies that the impinging jet becomes broader and spreads over more surface area which also causes possible vortex formation. However in case of less H/d ratio same amount of fluid spreads over less surface area thus causing higher heat transfer rate. The oddity to understand would be the increase in the inlet temperature of air. This increase could be attributed in a small way to the heat gain from the blower but majorly because of the rise of hot air from the enclosure towards the inlet thermocouple. Secondly, we observe that the heat transfer coefficients remain more or less the same because of the simple reason that the assembly is housed inside an enclosure which allows the air to exit in only one way that is through the holes in the target plate. www.ijera.com Conclusion In this work effect of Reynolds number, heat flux, and H/d ratio on the local Nusselt number is investigated. It was carried out on a triangularly ribbed target plate with holes. As the bottom grill is the only exit, there is an increase in the heat transfer coefficient. The following can be concluded from the study  That there is an increase in the heat transfer as the H/d ratio decreases.  With a general increase in the heat flux there is a general rise in the heat transfer rate.  An increase in the Reynolds number also increases the heat transfer rate for constant heat flux and H/d ratio VII. Acknowledgement The authors would like to thank Dr. Mayur Bhoite for his support and MIT Academy of Engineering, Alandi for providing us with the opportunity and space to conduct the study. We also thank Ms. Sayali Wable for her help in putting together the Experimental setup. 259 | P a g e
  • 5. Kartik Jujare et al Int. Journal of Engineering Research and Applications ISSN : 2248-9622, Vol. 4, Issue 1( Version 1), January 2014, pp.256-260 References [1] [2] [3] [4] [5] [6] [7] V. Narayanan, J. Seyed-Yagoobi, R.H. Page, An experimental study of fluid mechanics and heat transfer in an impinging slot jet flow, International Journal of Heat and Mass Transfer 47 (2004) 1827–1845. Shyy Woei Changa, Hsin-Feng Liou ,Heat transfer of impinging jet-array onto concave- and convex-dimpled surfaces with effusion, International Journal of Heat and Mass Transfer 52 (2009) 4484–4499. W.M. Yan, S.C. Mei, Measurement of detailed heat transfer along rib-roughened surface under arrays of impinging elliptic jets, International Journal of Heat and Mass Transfer 47 (2004) 5235–5245. Vadiraj Katti, S.V. Prabhu, Heat transfer enhancement on a flat surface with axisymmetric detached ribs by normal impingement of circular air jet, International Journal of Heat and Fluid Flow 29 (2008) 1279–1294 Akhilesh P. Rallabandi, Dong-Ho Rhee, Zhihong Gao, Je-Chin Han, Heat transfer enhancement in rectangular channels with axial ribs or porous foam under through flow and impinging jet conditions, International Journal of Heat and Mass Transfer 53 (2010) 4663–4671 John C. Duda, Francis D. Lagor, Amy S. Fleischer, A flow visualization study of the development of vortex structures in a round jet impinging on a flat plate and a cylindrical pedestal, Experimental Thermal and Fluid Science 32 (2008) 1754–1758 Tadhg S. O’Donovana, Darina B. Murray, Fluctuating fluid flow and heat transfer of an obliquely impinging air jet, International Journal of Heat and Mass Transfer 51 (2008) 6169–6179 Nomenclature Vorifice Cv H/d ratio g Hmano Abottom Aorifice Anozzle Vnozzle Qgenerated Qloss qactual www.ijera.com Velocity at orifice Coefficient of velocity The ratio of the height between nozzle and plate to the diameter of nozzle. Gravitational constant Height observed in manometer Area of heater assembly exposed to air for qactual Area of orifice opening Area of nozzle opening Velocity at nozzle opening Total heat generated from the heater Total heat lost from the bottom exposure to air Heat actually carried away by jet impingement per unit www.ijera.com area Heat transfer coefficient for bottom surface Actual heat transfer coefficient Temperature obtained on the bottom surface of target plate Atmospheric temperature hbottom hactual Tbottom Tatmo Appendix I Sample calculation: Atop = 0.02 m2 Abottom = 0.01478 m 2 Qtotal = (V x I) = 97.81W 𝑄𝑡𝑜𝑡𝑎𝑙 Flux = = 2812.25 W/m2 (Abottom +Atop ) Qloss = hbottom x Abottom (Tbottom – Tatmo) = 10 * 0.01478 *(40-28) = 4.1384 W hbottom = 10 W/m2K (assumed) Qactual= Qtotal – Qloss = (97.81-4.1384) = 93.6716 W qactual = Qactual/ Atop = 93.6716 /0.02 = 4683.5917 W/m2 qactual = hactual*(Tsurface – Tinlet) hactual = qactual/(T4 – T1) =4683.5917 /(45-34) = 425.78 W/m2 k Reynold’s number calculation V1 = Cv (2𝑔ℎmano) = 1.1085 m/s Cv = 0.92 From Continuity equation: A1V1= A2V2 V2 = 10 m/s Re = (ρair V2 D)/ϑ = (1.225*7.5*0.0267)/(1.79E-05) = 18272 Nusselt Number calculation Nu = (h x L) / K = (425.78 *0.0267)/(0.0242) = 469.76 260 | P a g e