Experiments were carried out to investigate natural convection heat transfer over uniformly heated hollow cylinder models made of aluminium alloy and pure copper. The effect of surface temperature, heat transfer coefficient and Nusselt’s number with respect to different heat fluxes and different orientations of two hollow cylinders. In the current study the heat fluxes range covers from 124w/m2 to 621 w/m2 . Whereas, the different orientations consider for the present investigation are 00(vertical), 300, 450, 600, 900(horizontal) respectively for conducting experiments on both hollow cylinders. Based on the experimental result (surface temperature) the following parameters such as theoretical heat transfer coefficient, experimental heat transfer coefficient and Nusselt number are evaluated and depicted graphically for both hollow cylinders made of aluminium alloy and pure copper.

1. 1
International Journal of Research and Innovation (IJRI)
International Journal of Research and Innovation (IJRI)
Experimental Investigation on Heat Transfer By Natural
Convection Over A Cylinder for Different Orientations
S. Madhava rao1
, D. Santha rao2
, Dr.S. Rajesh3
1 P.G student, Department Of Mechanical Engineering, B.V.C. Engineering College, Odalarevu-533210, India.
2 Associate professor , Department Of Mechanical Engineering, B.V.C. Engineering College, Odalarevu-533210, India.
3 Assistant professor , Department Of Mechanical Engineering, S.R.K.R. Engineering College, Bhimavaram-534204, India
*Corresponding Author:
S. Madhava rao ,
P.G Student, Department Of Mechanical Engineering,
B.V.C. Engineering College,
Odalarevu, India.
Published: December 16, 2014
Review Type: peer reviewed
Volume: I, Issue : I
Citation: S. Madhava rao, P.G student (2014) Experimen-
tal Investigation on Heat Transfer By Natural Convection
Over A Cylinder for Different Orientations
INTRODUCTION
The problem of natural convection heat transfer
across a channel of various cross section (rectan-
gular , circular , concentric annulus and parallel
plates) has received considerable attention in view
of its fundamental importance germane to numer-
ous engineering application such as electronic sys-
tems , chemical process equipments , combustion
chambers , environmental control system chemi-
cal catalytic reactors, fiber and granular insulation
,packed beds ,petroleum reservoirs ,nuclear waste
repositories ,boiler design ,air cooling systems in air
conditioners and so on [1-2] .Atayilmaz and Teke
[3] studied natural convection heat transfer from a
horizontal cylinder experimentally and numerically
and concluded that Nusselt numbers increases with
increasing Rayliegh numbers. Akeel et al. [4] car-
ried out experiments to investigate natural convec-
tion heat transfer in an inclined uniformly heated
circular cylinder and deduced an empirical equa-
tion of average nusselt number as a function of ray-
liegh number. Akeel [5] carried out experiments to
study the local and average heat transfer by natural
convection in a vertical concentric cylinder annu-
lus and deduced an empirical equation of average
nusselt number as a function of rayliegh number.
Reymond et al. [6] investigated natural convection
heat transfer from a single horizontal cylinder and
a pair of vertically aligned horizontal cylinders and
concluded that spectral analysis of surface heat
transfer signals has established the influence of the
plume oscillations on the heat transfer H.S.Takhar
et al. [7] studied the laminar natural convection
boundary layer flow on an isothermal vertical thin
cylinder
embedded in a thermally stratified high porosity
medium. It is observed that for certain values of
the ambient stratification parameters, the skin fric-
tion vanishes and the direction of the heat transfer
changes. R.Roslan et al. [8] studied the problem of
unsteady natural convection induced by a tempera-
ture difference between a cold outer square enclo-
sure and a hot inner circular cylinder and obtained
that the maximum heat transfer augmentation for
frequency between 25π and 30π for a high ampli-
tude and moderate source radius. Bae and Hun [9]
carried out a study on air cooling in an unsteady
laminar natural convection in a vertical rectangu-
lar channel with three flush mounted heat sources
on one vertical wall .The results show the effects of
the thermal conditions of the lowest source on the
downstream sources . The study emphasizes that
the transient temperatures may exceed average
values in time This is important for designing elec-
tronic equipment projects. Madhavan and Sastri
[10] developed a parametric study of natural con-
vection in a set of boards inside an enclosure. Each
board has heat sources. This layout has direct ap-
plication on electronic equipment cooling. It’s noted
that the Rayliegh and the Prandtl numbers as well
as the boundary conditions strongly affect the fluid
flow and heat transfer features. M.M.Molla et al.
[11] investigated the effect of radiation on natural
convection flow from an isothermal circular cylinder
numerically and concluded that the effect of the ra-
Abstract
Experiments were carried out to investigate natural convection heat transfer over uniformly heated hollow cylinder mod-
els made of aluminium alloy and pure copper. The effect of surface temperature, heat transfer coefficient and Nusselt’s
number with respect to different heat fluxes and different orientations of two hollow cylinders. In the current study the
heat fluxes range covers from 124w/m2 to 621 w/m2 . Whereas, the different orientations consider for the present in-
vestigation are 00(vertical), 300, 450, 600, 900(horizontal) respectively for conducting experiments on both hollow cylin-
ders. Based on the experimental result (surface temperature) the following parameters such as theoretical heat transfer
coefficient, experimental heat transfer coefficient and Nusselt number are evaluated and depicted graphically for both
hollow cylinders made of aluminium alloy and pure copper.
1401-1402

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International Journal of Research and Innovation (IJRI)
diation the skin–friction coefficients as well as the
rate of heat transfer increased. Vande Sande and
Hamer [12] and Aitsaada et.al.[13]] have obtained
empirical correlations for natural convection heat
transfer in concentric and eccentric annuli of con-
stant heat flux inner cylinder while the outer cylin-
der was subjected to the ambient temperature. An
empirical equation of average Nusselt number as
a function of Rayliegh number was deduced. P.K.
Sarma et.al.[14] and M.A.Hossain et.al.[15] have in-
vestigated the heat transfer rates from horizontal
cylinder surface of an internally heated tube under
constant heat flux conditions and the effect of con-
duction–radiation on natural convection flow of an
optically dense viscous incompressible fluid along
an isothermal cylinder of ellipitical cross section. it
is found that the rate of heat transfer from the slen-
der body is higher than from the blunt body. There
are no available literatures concerning the heat
transfer by natural convection over a circular cylin-
der for different orientations. The present study cov-
ers this lack and gives a clear view to actual physi-
cal behavior in the heat transfer process by natural
convection.
EXPERIMENTAL APPARATUS
The apparatus consist of wooden box with alu-
minum alloy and copper hollow cylinders as a test
section mounted on a heating coil, analog ammeter
(0-2A), analog voltmeter (0-300v), digital tempera-
ture indicator (0-4000c), thermocouples, AC con-
troller (220/240v) & rotary switch. Aluminum al-
loy and copper hollow cylinder pipe with finite wall
thickness is exposed to a ambient medium Of air
at a constant wall temperature. The thermal con-
ditions at a inner wall corresponds to the case of
constant heat flux. The test section consist of an
aluminium hallow cylinder with a wall thickness
of10mm ,inner diameter 40mm,outer diameter
50mm and length of cylinder is 450mm.The cylin-
der was heated electrically using an electrical heater
which consist of 250kw .It is used to heat external
surface with a constant heat. The cylinder surface
temperature was measured by 8 thermocouples
arranged along the cylinder. Thermocouples were
fixed by drilling 8 holes of 0.5mm thickness along
the cylinder. The excess material was cleaned care-
fully by fine
grain paper. The insulation material glass wool was
placed in between the holder and cylinder.
All thermocouples are fixed with the help of studs.
The distance between these thermocouples are var-
ied constantly from bottom to top for both the alu-
minum alloy and copper hollow cylinders. The ex-
perimental set up developed for the current work for
various orientations of cylinder was depicted in the
Fig.1 to Fig 10.
EXPERIMENTAL PROCEDURE
To carry out the experiments the following proce-
dure was followed:
a) The inclination angle of the cylinder was ad-
justed as required.
b) The electrical heater was switched on and
the heater input power then adjusted to give the re-
quired heat flux at particular angle
c) The apparatus was left at least two hours
to establish steady state condition .the thermocou-
ple readings were measured every half an hour by
means of the digital electronic thermometer until
the reading became constant ,a final reading of tem-
perature
d) Now whole rectangular box is tilted to re-
quired angle and wait for half an hour to establish
steady state condition and the note down readings
.then again change the angles with respective verti-
cal and note down the readings,
e) The input power to the heater could be in-
creased to cover another run in a shorter period of
time and to obtain steady state condition s for next
heat flux .subsequent runs for other ranges of cyl-
inder inclination angles were performed in the same
previous procedure.
f) during each test run ,the following readings
were recorded:
> The angle of inclination of the cylinder in de-
grees
> The readings of thermocouples in degrees
centigrade
> The heater current in amperes.
Fig. 1 Aluminium alloy hollow Cylinder when Ø = 00
Fig. 2 coppper hollow Cylinder when Ø = 00

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International Journal of Research and Innovation (IJRI)
Fig.3 Aluminium alloy hollow Cylinder when Ø = 300
Fig. 4 coppper hollow cylinder when Ø = 300
Fig. 5 Aluminium alloy hollow Cylinder when Ø =
450
Fig. 6 coppper hollow Cylinder when Ø = 450
Fig. 7 Aluminium alloy hollow Cylinder when Ø =
600
Fig. 8 coppper hollow Cylinder when Ø = 600

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International Journal of Research and Innovation (IJRI)
Fig. 9 Aluminium alloy hollow Cylinder when Ø =
900
Fig. 10 coppper hollow Cylinder when Ø = 900
Data Analysis
Simplified steps were used to analyze the heat
transfer process for the air flow in a cylinder when
it surface was subjected to a uniform heat flux. The
total input power supplied to the cylinder can be
calculated
Total heat transfer Q = V×I (watt ) (1)
Average heat transfer coefficient can be obtained as
h = Q / (A*(Ts-T∞)) ( w/m2
k) (2)
where
Ts = average heat transfer coefficient obtained from
table (0c)
T∞ = ambient temperature ( 0c)
A = surface area of cylinder ( m2
)
h value from empirical correlation taken from heat
&mass transfer data book
A. For vertical cylinder
Nu = 0.59(GrlPr)0.25 for constant heat flux or con-
stant wall temperature, When GrlPr < 109
(3)
B. For inclined cylinder
NuL =[0.60-0.488(sinθ)1.03](GrLcPr)Z for constant
heat flux,
When GrLcPr < 2 ×108 and
Z=0.25+0.083(sinθ)1.75 (4)
C. For horizontal cylinder
Nu = C×(Grd Pr)m for constant wall temperature
Grd Pr = 104 to 107 where C = 0.48 m = 0.25
(5)
Results and Discussion
A. Average Temperature Variation
The variations of average surface temperature over
uniformly heated hollow cylinder models made of
Copper and Aluminium alloy at different heat fluxes
and angle of inclinations 00
(vertical),300
,450
,600
,
900
(horizontal)) was studied on the corresponding
graphs are plotted and depicted in figures 23&24.
From the plots it was observed that the average sur-
face temperatures increases with increase of heat
flux for both the hollow cylinders. It was also ob-
served that average surface temperatures for hollow
cylinders made of copper was better than aluminum
alloy cylinder for different heat fluxes and angle of
inclinations(moves from vertical to horizontal)
The effect of angle of inclinations on the tem-
perature distribution along the cylindrical surfaces
for particular voltage (100v) is plotted. From the
plots are show in figures 25&26. it was observed
that average surface temperature of copper is better
than the aluminum alloy
B.Average Heat Transfer Coefficient Variation
The variations of average heat transfer coefficient
over uniformly heated cylinder models made of Cop-
per and Aluminum alloy at different heat fluxes and
angle of inclinations(00
(vertical),300
,450
,600
,900
(hor
izontal)) was studied on the corresponding graphs
are plotted and depicated in figures 11&12.
From the plots it was observed that the average heat
transfer coefficient increases with increase of heat
flux for both the hollow cylinders. It was also ob-
served that average heat transfer coefficient for hol-
low cylinders made of copper was better than alu-
minum alloy cylinder for different heat fluxes and
angle of inclinations (moves from vertical to hori-
zontal)
The effect of angle of inclinations of the heat trans-
fer coefficient along the cylindrical surfaces for par-
ticular voltage (100v) is plotted. From the plots are
shown in figures13&14. it was observed that heat
transfer coefficient of copper is better than the alu-
minum alloy
From the plots 35 and 36 it was observed that the
experimental average heat transfer coefficient in-
creases with increase of heat flux for both the hol-
low cylinders. It was also observed that average heat
transfer coefficient for hollow cylinders made of alu-
minum alloy was better than copper cylinder for dif-
ferent heat fluxes and angle of inclinations (moves
from horizontal to vertical)

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International Journal of Research and Innovation (IJRI)
C.Local Heat Transfer Coefficient Variation
From figures15-22 it shows the variation of local
heat transfer coefficient with distance between ther-
mocouples from the bottom at different voltages and
again drawn for different angles respectively
It tells that as the distance increases from the bot-
tom, local heat transfer coefficient decreases.
From the plots it was observed that local heat trans-
fer coefficient of copper is better than the alumini-
um alloy
D.Average Nusselt Number Variation
From figures 27-34 it shows the variation of local
nusselt number with distance between thermocou-
ples from the bottom at different voltages and again
drawn for different angles respectively .
It tells that as the distance increases from the bot-
tom ,local nusselt number also increases.
Nux = (h*x)/ k
From the plots it was observed that the average
nusselt number of copper is better than the alu-
minium alloy.
Local nusselt number is directly proportional to dis-
tance between thermocouples from the bottom.
CONCLUSION
Natural convection heat transfer experiments were
conducted on two hollow cylindrical models made
of aluminium alloy and copper in order to study the
various theoretical heat transfer coefficient ,experi-
mental heat transfer coefficient and nusselt number
for different heat fluxes and orientations .Based on
the experimental observation the following conclu-
sions were observed.
> Experimental setup was successfully estab-
lished for analysing the heat transfer over a hollow
cylinder for different orientations..
> From the results , it is concluded that the
average surface temperature of hollow cylinders
made of copper is better than the aluminium alloy
for different heat fluxes and orientations .Hence, the
copper was obtained higher value at the horizontal
position (Ø = 900
) when compared with other orien-
tations.
> The experimental average heat transfer coef-
ficient of aluminium alloy is better than copper at
different orientations. Average heat transfer coeffi-
cient of aluminium alloy is better in vertical position
(Ø = 00
) compared with other orientations .The heat
flux increase with increase of average heat transfer
coefficient.
> The theoretical average heat transfer coeffi-
cient of copper alloy is better than aluminium alloy
at different orientations. Average heat transfer coef-
ficient of copper alloy is better in horizontal position
(Ø = 900
) compared with other orientations.
> The local heat transfer coefficient of cylin-
ders made of aluminium alloy is better than copper
at different orientations. Local heat transfer coeffi-
cient of aluminium alloy was better vertical posi-
tion (Ø = 00
) compared with the other orientations at
distance between thermocouples top to bottom. The
local heat transfer coefficient increases when hollow
cylinder moves from horizontal to vertical position
> The local nusselt number of hollow cylin-
ders made of copper is better than aluminium alloy
at different orientations. The local nusselt number
of copper was better vertical position (Ø = 00
) com-
pared with the other orientations. The local nusselt
number increases with increase of distance between
thermocouples bottom to top. The nusselt number
increases when hollow cylinder moves from vertical
to horizontal position.
> The average nusselt number of hollow cyl-
inder made of copper is better than aluminium al-
loy at different orientations. The heat flux increases
with increase of average nusselt number. The cop-
per has obtained the higher value of average nus-
selt number at vertical position. Hence, the average
nusselt number is better in vertical position.
REFERENCES
[1].J.Grimson “Advance Fluid dynamic and heat
transfer “McGraw-Hill.,England,1971.
[2].J.P.Holman"Experimental Method For Engi-
neers" McGraw-Hill,'Tokyo,4th Edition 1984.
[3].OAtayilmaz,Ismail Teke "Experimental and nu-
merical study of the natural convection from a heat-
ed horizontal cylinder”, Int.Com in Heat and mass
Transfer,36,731-738,2009.
[4].A.M. Akeel, A.M. Mahmood and S.A. Raad, “Nat-
ural convection heat transfer in a inclined circular
cylinder”, Journal of Engg., vol. 17, pp. 659-673,
2011.
[5].A.M Akeel, "Natural convection heat trans-
fer in a vertical concentric annulus” ,journal of
Engg.,vol.13,pp1417-1423,2007.
[6].Olivier Reymond, Darina B.Murray, Tadhg
S.O’Donovan, “ Natural convection heat transfer
from two horizontal cylinders” Experimental ther-
mal and fluid science,32,1702-1709,2008.
[7].H.S.Takhar, A.J.Chamkhar, G.Nath “Natural
convection on a vertical cylinder embedded in a
thermally stratified high-porosity medium” Int. J.
Therm. Sci.41,83-93,2002.
[8].R.Rosian, H.Saleh, I.Hashim, A.S.Bataineh “nat-
ural convection in an enclosure containing a sinu-
soidally heated cylindrical source” Int.J. Of Heat
and Mass Transfer, 70,119-127, 2014.
[9].J.H. Bae and J.M. Hun “Time dependent buoy-
ant convection in an enclosure with discrete heat
sources”, Int. J. Therm. Sci., 2003.
[10].P.N. Madhavan and V.M.K. Sastri, “Conjucate
natural convection colling of protruding heat sourc-
es mounted on a substrate placed inside an eclo-
sure: a parametric study”, Comp. Methods Appl.
Mech. Engg., vol. 188, pp. 187-202, 2003.
[11].M.M.Molla, S.C.Saha, M.A.I.Khan, M.A.Hossain
“Radiation effects on natural convection laminar
flow from a horizontal circular cylinder” Desalina-
tion publications, 30,89-97,2011.

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International Journal of Research and Innovation (IJRI)
[12].E. Vande Sarde and B.J.G. Hamer, “Study and
transient natural convection in enclosure between
horizontal circular cylinders (constant heat flux)”,
Int. J. Heat mass Transfer, vol. 22, pp. 361-370,
1979.
[13].M. Ait Saada, S. Chikh, A. Campo “Natural con-
vection around a horizontal solid cylinder wrapped
with a layer of fibrous or porous material” Inter. J.
of Heat and Fluid Flow 28, 483–495,2007.
[14].P.K.Sarma , P.V.Sunitha “Interaction of ther-
mal radition with laminar natural convection from a
horizontal cylinder in air” Warme And Stoffubertra-
gung,26, 654-69,1991.
[15].M.A.Hossain, M.A.Alim, D.A.S.Rees “Effect of
thermal radiation on natural convection over cyl-
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129,177-186, 1998.
Fig. 11 variation of average heat transfer coefficient
w.r.t voltage for different orientations of aluminium
alloy hollow cylinder
Fig. 12 variation of average heat transfer coefficient
w.r.t voltage for different orientations of copper hol-
low cylinder
Fig 13 variation of average heat transfer coefficient
w.r.t particular voltage (80 V) for different orienta-
tions of aluminiumalloy hollow cylinder
Fig 14 variation of average heat transfer coefficient
w.r.t particular voltage (80V) for different orienta-
tions of copper hollow cylinder
Fig 15 variation of local heat transfer coefficient
w.r.t distance from the bottom at = 00
at different
voltages for aluminium alloy hollow cylinder

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International Journal of Research and Innovation (IJRI)
Fig 16 variation of local heat transfer coefficient
w.r.t distance from the bottom at = 00
at different
voltages for copper hollow cylinder
Fig. 17 variation of local heat transfer coefficient
w.r.t distance from the bottom at =300
at different
voltages for aluminium alloy hollow cylinder
Fig. 18 variation of local heat transfer coefficient
w.r.t distance from the bottom at =300
at different
voltages for copper hollow cylinder
Fig.19 variation of local heat transfer coefficient
w.r.t distance from the bottom at =450
at different
voltages for aluminium alloy hollow cylinder
Fig.20 variation of local heat transfer coefficient
w.r.t distance from the bottom at =450
at different
voltages for copper hollow cylinder
Fig.21 variation of local heat transfer coefficient
w.r.t distance from the bottom at =600
at different
voltages for aluminium alloy hollow cylinder

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International Journal of Research and Innovation (IJRI)
Fig.22 variation of local heat transfer coefficient w.r.t distance
from the bottom at =600
at different voltages for copper hollow
cylinder
Fig 23 variation of average surface temperature
w.r.t voltage for different orientations of aluminium
alloy hollow cylinder
Fig 24 variation of average surface temperature
w.r.t voltage for different orientations of copper
hollow cylinder
Fig 25 variation of average surface temperature
w.r.t voltage for different orientations of aluminium
alloy hollow cylinder
Fig 26 variation of average surface temperature
w.r.t voltage for different orientations of copper
hollow cylinder
Fig 27 variation of local Nusselt number w.r.t dis-
tance from the bottom at =00
at different voltages
for aluminium alloyhollow cylinder
Fig 28 variation of local Nusselt number w.r.t
distance from the bottom at =00
at different voltages
for copper hollow cylinder

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International Journal of Research and Innovation (IJRI)
Fig 29 variation of local Nusselt number w.r.to
distance from the bottom at =300
at different
voltages for aluminium alloy hollow cylinder
Fig 30 variation of local Nusselt number w.r.t
distance from the bottom at =300
at different
voltages for copper hollow cylinder
Fig 31 variation of local Nusselt number w.r.t
distance from the bottom at=450
at different voltages
for aluminium alloy hollow cylinder
Fig 32 variation of local Nusselt number w.r.t distance from
the bottom at =450
at different voltages for copper hollow
cylinder
Fig.33 variation of local Nusselt number w.r.t dis-
tance from the bottom at =600
at different voltages
for aluminiumalloy hollow cylinder
Fig 34 variation of local Nusselt number w.r.t distance
from the bottom at =600
at different voltages for copper hollow
cylinder

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International Journal of Research and Innovation (IJRI)
Fig 35 variation of therritical and experimental
heat transfer coefficient w.r.t voltage for different
orientations of aluminium alloy hollow cylinder
Fig.36 variation of therritical and experimental
heat transfer coefficient w.r.t voltage for different
orientations of copper hollow cylinder
Author
S. Madhava rao,
P.G Student,
Department Of Mechanical Engineering,
B.V.C. Engineering College,
Odalarevu, India.
madhava690@gmail.com
9494622010
D. Santha rao
Associate professor
Mechanical dept.
Experience 14 YEARS.
B.V.C. Engineering College
Odalarevu-533210, India
dsantharao@gmail.com
Dr.S. Rajesh
Mechanical Engineering
Assistant professor(9years)
S.R.K.R. Engineering College
Bhimavaram-534204, India
dr.rajesh.mech@gmail.com