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INTERNATIONAL JOURNAL OF RESEARCH AND INNOVATION
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Subject: Thermal Engineering IJRITE
EXPERIMENTAL INVESTIGATION ON HEAT TRANSFER BY NATURAL
CONVECTION OVER A CYLINDER FOR DIFFERENT ORIENTATIONS
S. Madhava rao1, D. Santha rao2, Dr.S. Rajesh3.
1 Research Scholar, Department of Mechanical Engineering, B.V.C. Engineering College, Odalarevu, India.
2 Associate professor, Department of Mechanical Engineering, B.V.C. Engineering College, Odalarevu,
India.
3 Assistant professor, Department of Mechanical Engineering, S.R.K.R. Engineering College, Bhimavaram,
India.
Abstract
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 aluminum alloy and pure copper.
*Corresponding Author:
S. Madhavarao,
Research Scholar,
Department of Mechanical Engineering,
B.V.C. Engineering College, Odalarevu, India.
Email: [email protected]
Year of publication: 2014
Paper Type: Review paper
Review Type: peer reviewed
Volume: I, Issue: I
*Citation: S.Madhava rao, Research Scholar,
"Experimental Investigation on Heat Transfer By
Natural Convection Over A Cylinder for Different
Orientations" International Journal of Research
and Innovation (IJRI) 1.1 (2014) 13-20.
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
numerous engineering application such as
electronic systems , chemical process equipments
, combustion chambers , environmental control
system chemical 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
INTERNATIONAL JOURNAL OF RESEARCH AND INNOVATION
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numerically and concluded that Nusselt numbers
increases with increasing Rayliegh numbers.
Akeel et al. [4] carried out experiments to
investigate natural convection heat transfer in an
inclined uniformly heated circular cylinder and
deduced an empirical equation of average nusselt
number as a function of rayliegh number. Akeel
[5] carried out experiments to study the local and
average heat transfer by natural convection in a
vertical concentric cylinder annulus 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.
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
temperature indicator (0-4000c), thermocouples,
AC controller (220/240v) & rotary switch.
Aluminum alloy and copper hollow cylinder pipe
with finite wall thickness is exposed to a ambient
medium Of air at a constant wall temperature.
The thermal conditions 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 cylinder was heated
electrically using an electrical heater which
consist of 250kw .It is used to heat external
surface with a constant heat.
EXPERIMENTAL PROCEDURE
Copper hollow Cylinder when Ø = 00
Aluminium alloy hollow Cylinder when Ø = 300
Copper hollow cylinder when Ø = 300
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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/m2k) (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
constant 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×(GrdPr)m for constant wall temperature
GrdPr = 104 to 107 where C = 0.48 m = 0.25 (5)
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Variation of average heat transfer coefficient w.r.t
voltage for different orientations of aluminium alloy hollow cylinder
Variation of average heat transfer coefficient w.r.t
voltage for different orientations of copper hollow
cylinder
Variation of average heat transfer coefficient w.r.t
particular voltage (80 V) for different orientations
of aluminiumalloy hollow cylinder
Variation of local heat transfer coefficient w.r.t
distance from the bottom at = 00 at different
voltages for copper hollow cylinder
variation of local heat transfer coefficient w.r.t
distance from the bottom at =300at different
voltages for aluminium alloy hollow cylinder
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Variation of average surface temperature w.r.t voltage for different orientations of aluminium
alloy hollow cylinder
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Variation of local Nusselt number w.r.t distance
from the bottom at =00 at different voltages for
aluminium alloyhollow cylinder
Variation of local Nusselt number w.r.t distance
from the bottom at=450 at different voltages for aluminium alloy hollow cylinder
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Variation of theoretical and experimental heat
transfer coefficient w.r.t voltage for different
orientations of aluminium alloy hollow cylinder
Variation of theoretical and experimental heat
transfer coefficient w.r.t voltage for different
orientations of copper hollow cylinder
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, experimental heat transfer coefficient
and Nusselt number for different heat fluxes and
orientations .Based on the experimental
observation the following conclusions were
observed.
> Experimental setup was successfully estab-
lished for analyzing 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 orientations.
> The experimental average heat transfer coef-
ficient of aluminium alloy is better than copper at
different orientations. Average heat transfer
coefficient 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 coefficient
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 cylinders
made of aluminium alloy is better than copper
at different orientations. Local heat transfer
coefficient of aluminium alloy was better vertical
position (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 cylinders
made of copper is better than aluminium alloy at
different orientations. The local nusselt number
of copper was better vertical position (Ø = 00)
compared with the other orientations. The local
nusselt number increases with increase of
distance between thermocouples bottom to top.
The nusselt number increases when hollow
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cylinder moves from vertical to horizontal
position.
> The average nusselt number of hollow cylinder
made of copper is better than aluminium alloy at
different orientations. The heat flux increases
with increase of average nusselt number. The
copper has obtained the higher value of average
nusselt number at vertical position. Hence, the
average nusselt number is better in vertical
position.
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AUTHORS
S. Madhavarao,
Research Scholar,
Department of Mechanical Engineering,
B.V.C. Engineering College, Odalarevu, India.
D. Santharao,
Associate professor, Mechanical dept.
Experience 14 YEARS.
B.V.C. Engineering CollegeOdalarevu,India.
Dr.S. Rajesh,
Mechanical Engineering,
Assistant professor(9years),
S.R.K.R. Engineering College,
Bhimavaram-, India.