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
1401-1402
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
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 aluminium alloy and pure copper. *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) Experimental 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 (rectangular , 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 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 embedded in a thermally stratified high porosity medium. It is observed that for certain values of the ambient stratification parameters, the skin friction vanishes and the direction of the heat transfer changes. R.Roslan et al. [8] studied the problem of unsteady natural convection induced by a temperature difference between a cold outer square enclosure and a hot inner circular cylinder and obtained that the maximum heat transfer augmentation for frequency between 25π and 30π for a high amplitude and moderate source radius. Bae and Hun [9] carried out a study on air cooling in an unsteady laminar natural convection in a vertical rectangular 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 electronic equipment projects. Madhavan and Sastri [10] developed a parametric study of natural convection in a set of boards inside an enclosure. Each board has heat sources. This layout has direct application 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 ra1
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 constant heat flux inner cylinder while the outer cylinder 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 investigated the heat transfer rates from horizontal cylinder surface of an internally heated tube under constant heat flux conditions and the effect of conduction–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 slender body is higher than from the blunt body. There are no available literatures concerning the heat transfer by natural convection over a circular cylinder for different orientations. The present study covers this lack and gives a clear view to actual physical behavior in the heat transfer process by natural convection. EXPERIMENTAL APPARATUS The apparatus consist of wooden box with aluminum 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. 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 carefully by fine grain paper. The insulation material glass wool was placed in between the holder and cylinder.
a) The inclination angle of the cylinder was adjusted as required. b) The electrical heater was switched on and the heater input power then adjusted to give the required heat flux at particular angle c) The apparatus was left at least two hours to establish steady state condition .the thermocouple readings were measured every half an hour by means of the digital electronic thermometer until the reading became constant ,a final reading of temperature d) Now whole rectangular box is tilted to required angle and wait for half an hour to establish steady state condition and the note down readings .then again change the angles with respective vertical and note down the readings, e) The input power to the heater could be increased 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 cylinder 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 degrees > The readings of thermocouples in degrees centigrade > The heater current in amperes.
Fig. 1 Aluminium alloy hollow Cylinder when Ø = 00
All thermocouples are fixed with the help of studs. The distance between these thermocouples are varied constantly from bottom to top for both the aluminum alloy and copper hollow cylinders. The experimental 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 procedure was followed:
Fig. 2 coppper hollow Cylinder when Ø = 00
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Fig.3 Aluminium alloy hollow Cylinder when Ø = 300
Fig. 6 coppper hollow Cylinder when Ø = 450
Fig. 4 coppper hollow cylinder when Ø = 300
Fig. 7 Aluminium alloy hollow Cylinder when Ø = 600
Fig. 5 Aluminium alloy hollow Cylinder when Ø = 450
Fig. 8 coppper hollow Cylinder when Ø = 600
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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
Fig. 9 Aluminium alloy hollow Cylinder when Ø = 900
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 surface temperatures increases with increase of heat flux for both the hollow cylinders. It was also observed 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 temperature 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
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/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
The variations of average heat transfer coefficient over uniformly heated cylinder models made of Copper 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 observed that average heat transfer coefficient 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 of the heat transfer coefficient along the cylindrical surfaces for particular 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 aluminum alloy From the plots 35 and 36 it was observed that the experimental average heat transfer coefficient increases with increase of heat flux for both the hollow cylinders. It was also observed that average heat transfer coefficient for hollow cylinders made of aluminum alloy was better than copper cylinder for different heat fluxes and angle of inclinations (moves from horizontal to vertical)
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C.Local Heat Transfer Coefficient Variation From figures15-22 it shows the variation of local heat transfer coefficient with distance between thermocouples from the bottom at different voltages and again drawn for different angles respectively It tells that as the distance increases from the bottom, local heat transfer coefficient decreases. From the plots it was observed that local heat transfer coefficient of copper is better than the aluminium alloy D.Average Nusselt Number Variation From figures 27-34 it shows the variation of local nusselt number with distance between thermocouples from the bottom at different voltages and again drawn for different angles respectively . It tells that as the distance increases from the bottom ,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 aluminium alloy. Local nusselt number is directly proportional to distance 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 ,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 established 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 orientations. > The experimental average heat transfer coefficient 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 coefficient 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 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 Engineers" McGraw-Hill,'Tokyo,4th Edition 1984. [3].OAtayilmaz,Ismail Teke "Experimental and numerical 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, “Natural convection heat transfer in a inclined circular cylinder”, Journal of Engg., vol. 17, pp. 659-673, 2011. [5].A.M Akeel, "Natural convection heat transfer 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 thermal 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 “natural convection in an enclosure containing a sinusoidally heated cylindrical source” Int.J. Of Heat and Mass Transfer, 70,119-127, 2014. [9].J.H. Bae and J.M. Hun “Time dependent buoyant 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 sources mounted on a substrate placed inside an eclosure: 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” Desalination publications, 30,89-97,2011. 5
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[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 convection 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 thermal radition with laminar natural convection from a horizontal cylinder in air” Warme And Stoffubertragung,26, 654-69,1991. [15].M.A.Hossain, M.A.Alim, D.A.S.Rees “Effect of thermal radiation on natural convection over cylinders of elliptic cross section” Acta mechanica, 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 13 variation of average heat transfer coefficient w.r.t particular voltage (80 V) for different orientations of aluminiumalloy hollow cylinder
Fig 14 variation of average heat transfer coefficient w.r.t particular voltage (80V) for different orientations 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 Fig. 12 variation of average heat transfer coefficient w.r.t voltage for different orientations of copper hollow cylinder
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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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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 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 distance from the bottom at =00 at different voltages for aluminium alloyhollow cylinder
Fig 24 variation of average surface temperature w.r.t voltage for different orientations of copper hollow cylinder Fig 28 variation of local Nusselt number w.r.t distance from the bottom at =00 at different voltages for copper hollow cylinder
Fig 25 variation of average surface temperature w.r.t voltage for different orientations of aluminium alloy hollow cylinder 8
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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 32 variation of local Nusselt number w.r.t distance from the bottom at =450 at different voltages for copper 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.33 variation of local Nusselt number w.r.t distance from the bottom at =600 at different voltages for aluminiumalloy 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 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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Author
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
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
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