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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



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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


voltage for different orientations of copper hollow

cylinder


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.

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,IsmailTeke "Experimental and nu-

merical study of the natural convection from a

heated horizontal cylinder”, Int.Com in Heat and

mass Transfer,36,731-738,2009.

[4].A.M. Akeel, A.M. Mahmood and S.A. Raad,

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[5].A.M Akeel, "Natural convection heat transfer

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[6].Olivier Reymond, Darina B.Murray,

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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.

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INTERNATIONAL JOURNAL OF RESEARCH AND INNOVATIONijripublishers.com/Articals/Volume-1/Issue-1/IJRI-01-003/EXPERIMENTA… · "Experimental Investigation on Heat Transfer By Natural