61- 71 Al-Khwarizmi Engineering Journal,Vol. 12, No. 3, P.P. 6 Experimental Simulation of Finned Vertical Department of Mechanical Engineering / (Received 20 Dec ___________________________________________________________________________ Abstract In this work an experimental simulation along heated finned vertical base plate Two types of fin arrays namely vertical fin heights and spaces. The influence of inc parameters such as fin height and fin spacing and average Nusselt number have been between average Nusselt number versus Rayleigh number that the configuration of V-fins array coefficient about 20% greater compare present work are compared with a previous works Keywords: Natural-convection, experimental _______________________________________________________________________ 1. Introduction The configurations of fins and inclinations play an important role in natural-convective transfer. Fins and fin arrays are extended surfaces used to enhance and increase heat transfer rate and heat dissipation from heated surfaces to the surroundings in electronic devices and engineering applications. Many configurations of fin arrays like vertical fins, tri trapezoidal fins, tree-shaped fins , pin fins ,V shaped and V-shaped with bottom spacing. arrays on vertical base plates of various shapes are of great importance in industrial applications as cooling of the electronic and micro equipments , high voltage power transformers motors, high power chips, nuclear reactor cores , compact heat exchangers , radiators the houses , energy storage system and collectors . Churchill and Chu [1] deduced correlation to predict the Nusselt number Khwarizmi Engineering Journal,Vol. 12, No. 3, P.P. 61- 71 (2016) Simulation of Natural Heat Convection Vertical Plate with Different Inclinations Saad Najeeb Shehab Engineering / College of Engineering /Al-Mustansiriayah E-mail: saad_najeeb16@ yahoo.com eceived 20 December 2015; accepted 14 April 2016) ___________________________________________________________________________ simulation is made to predict the performance of steady-state plate to ambient air with different inclination angles and config vertical fins array and V-fins array on heated vertical base pl of inclination angle of the plate , configuration of fins spacing on the temperature distribution, base convection have been plotted and discussed. The experimental data are correlated to a formula versus Rayleigh number for vertical plate and vertical fins array gave best natural-convection heat transfer performance compared with vertical fins array. Experimental simulation data and correlations previous works shows good agreement. xperimental simulation, finned plate, fins array. _______________________________________________________________________ configurations of fins and inclinations convective heat Fins and fin arrays are extended surfaces used to enhance and increase heat transfer rate and heat dissipation from heated surfaces to the surroundings in electronic devices and engineering applications. Many configurations of triangular fins, shaped fins , pin fins ,V- shaped with bottom spacing. Fin s of various shapes are applications such and micro- electronic high voltage power transformers , nuclear reactor cores , radiators, heating of , energy storage system and solar deduced an empirical Nusselt number for steady-state free-convection heat transfer from vertically heated base plate turbulent flow conditions Baudoin [2] obtained th convection heat transfer and inclined flat plate after several experiments They measured the temperatures by u (IR) thermography. The results show that the increase in convection heat transfer coefficient about 10% when roughness elements used than flat surfaces. Rao et al. numerically the combined free radiation heat transfer from vertical plate with fins array. They solved the governing equations Alternate Direct Implicit (ADI) method. noted that the convection heat transfer rate increasing with fin spacing decreases and fin length increases. Abid [4] the effects of fin shape on convection. He used vertical and pin fins array and developed empirical correlation fins and pin fins array in laminar condition Sable et al. [5] investigated Al-Khwarizmi Engineering Journal (2016) Convection from Inclinations Mustansiriayah University _______________________________________________________________________________________ state natural heat convection configurations of fin array. late are used with different array and fin geometrical convection heat transfer coefficient data are correlated to a formula for vertical plate and vertical fins array. The results indicate performance as base heat transfer data and correlations of the ____________________________________________________________________________________ convection heat transfer from plate in a laminar and conditions .Vermeulen and the experimental free- convection heat transfer correlations for vertical and inclined flat plate after several experiments. the temperatures by using infrared (IR) thermography. The results show that the increase in convection heat transfer coefficient of about 10% when roughness elements (fins) are Rao et al. [3] investigated numerically the combined free-convection and radiation heat transfer from vertical plate with fins governing equations using Direct Implicit (ADI) method. They noted that the convection heat transfer rate increasing with fin spacing decreases and fin ] studied experimentally fin shape on laminar natural vertical and pin fins array and developed empirical correlations for vertical and pin fins array in laminar condition flow. ] investigated enhancement of free- Saad Najeeb Shehab Al-Khwarizmi Engineering Journal, Vol. 12, No. 3, P.P. 61- 71 (2016) 62 convection heat transfer on heated vertical plate by multiple V-fins array. The results show that the V-fins array gave better heat transfer performance than vertical fins array and V-fins with bottom spacing array. Naidu et al. [6] studied the problem of natural convection experimentally and numerically by using Alternate Direct Implicit (ADI) method from fin arrays with different inclination angles of two geometric orientations, vertical and horizontal fins array. The results show that the convection heat transfer rate of vertical fins array is great than horizontal fins array for the same inclinations angles. Fahiminia et al. [7] presented computational analysis of the natural-convection on extended vertical base surfaces by using finite volume method (FVM). They concluded that the heat convection rates increases with increasing fin space reaches to optimum spacing . More et al. [8] presented review study of natural-convection from heated plate with different configurations of the fin arrays and inclinations. The results of study show that the all configurations of fin arrays are improved thermal design and heat dissipation rate of the heated surfaces with different percentages. Hireholi et al. [9] investigated experimentally and theoretically the heat transfer by free-convection of heat sink used for cooling of the electronic chips. They found the optimum fin spacing. They compared that the experimentally measured temperatures of heat sink with theoretically predicted temperatures using two-dimensional model and show a very good agreement. Tiwari and Malhotra [10] studied heat transfer of laminar natural-convection over a flat plate bounded by enclosures with effects of the surface roughness , ambient temperature , flow velocity and surface inclinations on the convection heat transfer coefficient at different heat source input. They noted that the increase in heat source input increases the heat transfer rates and the increase in surface inclination decreases the heat transfer coefficient. The present work concentrates experimentally on the effects of configuration of fins array, base plate inclinations (ϕ), fin height (H) and fin spacing (S) on performance of natural-convection heat transfer over a heated vertical base plate. This is assist to predict of the temperatures distribution along a vertical heated base plate and to calculate convection heat transfer coefficient with and without fin arrays to choose the best configuration and design of fins array. 2. Experimental Work 2.1. Experimental Rig The experimental test rig and it’s components shown in Fig. 1 consists of an aluminum square base plate of 200 mm side has thickness 2.0 mm. Vertical plate and two configurations of fin arrays vertical fins and V-fins are joined on the base plate are tested as shown in Fig. 2 with different fin height (H) and fin spacing (S) having thickness 2.0 mm. The vertical base plate is heated from backside using an electrical heater wire is coiled around mica sheet and then is sandwiched between two symmetrical square sheets of mica with same dimensions of the base plate and thickness of 0.5 mm to obtain homogeneous heating of the base plate and ensured the electrical insulation of heater wire. It’s fixed on the backside of base plate by thermal super glue. The backside of base plate assembly is a good insulation using polyurethane foam layer with 60 mm thickness to minimize the conduction heat loss. Also the sides are framed by plywood frame. The whole assembly of base plate is fixed in a vertical position with an adjustable support allowing different angles of inclination in a square enclosure constructed of cast acrylic sheet of thickness 6 mm, with dimensions (500 mm length × 500 mm width × 600 mm height) opened from upper and lower ends under guaranteed a good free-convection heat transfer conditions. The inclination angles of base plate are measured with vertical position by a fixed Protractor. The heating element is supplied up to 300 W with stabilized alternating current (AC) and voltage of 220 V through a contact type voltage regulator with digital reader type SAKO-TDGC2 to control on the electrical heat input and digital multi-meter type VICTOR-VC890C+ to measure voltage and current. Twelve K-type calibrated thermo-couples are embedded at different suitable locations in back surface of the vertical base plate to measure surface temperatures. They are matrix form distributed (4 rows × 3 columns) with equal distances. The thermocouples are connected to twelve channels digital temperature recorder type BTM-4208SD. Another two same K-type calibrated thermocouples are joined in digital multi-meter to record temperatures difference to evaluate the conduction heat loss from the backside of heated base plate. Additional two separate K-type digital calibrated thermocouples are used to measure the ambient temperature inside the enclosure. Saad Najeeb Shehab Al-Khwarizmi Engineering Journal, Vol. 12, No. 3, P.P. 61- 71 (2016) 63 a. Front photo b. Side photo 1. Opened enclosure 2. Finned plate assembly. 3. Digital temperature recorder. 4. Thermocouple wires. 5. Adjustable support. 6. Protractor. 7. Voltage regulator. 8. Digital multi-meter. Fig. 1. Photos of the experimental rig. a. Vertical plate b. Vertical fins array c. V-fins array Fig. 2. Tested vertical plate and fin arrays configurations. 2.2. Experimental Procedure and Calculations Three cases are studied , vertical base plate , vertical base plate with vertical fins array and vertical base plate with V-fins array. Three angles of inclination with respect to vertical position are used (ϕ= 15o , 30o and 45o). Cases of fin arrays is carried out for different fin height (H= 15 , 30 and 45 mm) and fin spacing (S= 14.5 , 20 , 31 and 64 mm) depending on numbers of fins as Table 1. Multi- range of the electrical heater input Wattage namely 25 , 50 , 75 , 100 , 125 and 150 W are used. All readings of the temperatures are recorded under steady-state conditions every 45 minutes approximately and when varying of the temperature readings less than 0.5 oC. Table 1, Number of fins against fin spacing in fins array. Number of fins, N 4 7 10 13 Fin spacing (S), mm 64 31 20 14.5 The electrical heat input (Qin) to the heating element is : ��� = � � …(1) It's transferred to the ambient mainly by natural- convection (QC) in addition to radiation (QR) and conduction (QCd) heat transfer losses. Then, the rate of natural-convection heat transfe (QC) can be evaluated as : � = � � − �� − � � … (2) The radiation heat transfer rate (QR) is [11] : �� = �����(����� − ���) …(3) The conduction heat transfer rate (QCd) is calculated by Fourier’s equation as [11,12] : Saad Najeeb Shehab Al-Khwarizmi Engineering Journal, Vol. 12, No. 3, P.P. 61- 71 (2016) 64 � � = � ��� ∆� …(4) The radiation heat transfer (QR) from the heated base plate and fins array is small because the emissivity (ε) of bright rolled aluminum used in manufacturing the base plate and fins is 0.04 and it’s found to be less than 5% of electrical heat input (Qin) for all cases. The loss by heat conduction (QCd) is minimized using a thick layer of polyurethane foam with very low of thermal conductivity about 0.028 W/m.K . It’s found to be approximately 2% of heat input (Qin) . According to Newton’s law of cooling, the net heat transfer from the base heated plate by natural-convection is expressed as [11] : � = ℎ���(���� − ����) …(5) Hence, the base convection heat transfer coefficient (hb) is : ℎ� = � � − (�� + � �)��(���� − ����) …(6) and the average convection heat transfer coefficient (hav) can be evaluated as follows : ℎ�� = � � − (�� + � �)�&(���� − ����) …(7) The total surface area of free-convection heat transfer (At) for vertical fins array is : �& = (�� –*+,- + 2*.+ …(8) and for V-fins array is : �& = (�� –, ∑ +1� 2�34 - + 2. ∑ +1�2�34 …(9) where , LV is the length of V-fin. The average Nusselt number (Nu89) at the heated plate is computed by [11,12]: Nu89 = h89L׳) . The squared correlation coefficients (R2= 99%) , the absolute percentage relative of error between suggested correlation and experimental data is (e < 3.5%). The relative error between the suggested correlation of vertical plate with other correlations is (e < 10%). The agreement of present work is very good especially with McAdam’s correlation (e < 5.5%), also the relative error between the suggested correlation of vertical fins array with Abid correlation is (e < 15%) at same conditions according to the Figures (13) and (14) . Fig. 3. Base convection heat-transfer coefficient versus average surface temperature for vertical plate and vertical fins array. Saad Najeeb Shehab Al-Khwarizmi Engineering Journal, Vol. 12, No. 3, P.P. 61- 71 (2016) 66 Fig. 4. Base heat transfer coefficient versus average surface temperature for vertical plate and V-fins array. Fig. 5. Base heat transfer coefficient versus inclination angle for vertical plate. Fig. 6. Base heat transfer coefficient versus inclination angle for vertical fins array. Fig. 7. Base heat transfer coefficient versus inclination angle for V-fins array. Saad Najeeb Shehab Al-Khwarizmi Engineering Journal, Vol. 12, No. 3, P.P. 61- 71 (2016) 67 Fig. 8. Base heat transfer coefficient versus fin spacing for vertical fins array. Fig. 9. Base heat transfer coefficient versus fin spacing for V-fins array. Fig. 10. Average surface temperature versus fin spacing for vertical fins array. Fig. 11. Average surface temperature versus fin spacing for V-fins array. Saad Najeeb Shehab Al-Khwarizmi Engineering Journal, Vol. 12, No. 3, P.P. 61- 71 (2016) 68 Fig. 12. Analysis of the experimental simulation data of present work for vertical base plate to the power function fits. Fig. 13. Comparison of average Nusselt numbers ( Nuav ) for vertical base plate with available empirical correlations . Fig. 14. Experimental simulation data of present work for vertical fins array compared with Abid correlation. Saad Najeeb Shehab Al-Khwarizmi Engineering Journal, Vol. 12, No. 3, P.P. 61- 71 (2016) 69 4. Conclusions Natural-convective heat transfer from the heated vertical base plate, vertical fins array and V-shaped fins array are studied experimentally and focused on the determination of the geometrical configuration giving the best natural- convection heat transfer performance. The following conclusions can be drawn: 1- The type of V-fins array gave better convection heat transfer performance in term of base convection heat transfer coefficient about 20% bigger compared than vertical fins array. 2- As the height of fin increased, the average surface temperature decreased and the base convection heat transfer coefficient increased. 3- The base convection heat transfer coefficient decreases with inclinations increasing and heat input decreasing. 4- The optimum value of fin spacing is about 20 mm for vertical fins and V-fins arrays when maximizing base convection heat transfer coefficient. 5- Experimental correlations are suggested to predict the average Nusselt number for vertical plate and vertical fins array. Nomenclature Ab Base area, (m 2) AS Surface area of heat transfer, (m 2) At Total surface area of convection heat transfer from fin-arrays, (m2) F Radiation shape factor, (--) g Gravitational acceleration, (m/s2) Gr Grashof number, (--) h Convection heat-transfer coefficient, (W/m2.K) H Fin height, (m) I Input current intensity, (A) k Thermal conductivity of material, (W/m.K) L Length / Height of vertical plate or fins array, (m) LC The characteristics length of geometry, (m) N Number of fins, (--) Nu Nusselt number, (--) Pr Prandtl number, (--) QC Convection heat transfer rate, (W) Ra Rayleigh number, (--) Ra׳ modified Rayleigh number, (--) S Fin spacing, (m) t Fin thickness, (m) TA Ambient temperature, ( oC) TS Surface temperature, ( oC) ∆T Temperature difference, (oC) V Voltage supplied, (V) X Thickness, (m) Greek Letters β Volumetric coefficient of thermal expansion, (1/K) ε Emissivity of the surface, (--) ϑ Kinematic viscosity of the air, (m2/s) σ Stefan-Boltzmann constant , (σ = 5.67 × 10-8 W/ m2.K4) ϕ Inclination angle of the plate with vertical position, (deg) Subscript Symbols av Average b Base 5. References [1] Churchill, S.W. and Chu, H. H. S. “Correlating Equation for Laminar and Turbulent Free Convection from a Vertical Plate “ , International Journal of Heat and Mass Transfer , Vol. 18 , pp. 1323-1329 , 1975 . [2] Vermeulen, J.P. and Baudoin , P. “ Study of Free Convection by Infrared Thermography over a Constant Heat-Flux Heated Plate “ , Eurotherm Series 27-EETI Edition , Paris, 1992 . [3] Rao, V.D. , Naidu , S.V. , Roa. B.G. and Sharma , K.V. “Combined Convection and Radiation Heat Transfer from a Fin Array with a Vertical Base and Horizontal Fins”, Proceedings of the World Congress on Engineering and Computer Science WCECS , San Francisco, USA, October 2007 . [4] Abid , W. M. “Study of Fins Shape Efects on Natural Thermal Convection “, Journal of Al- Qadisyia for Engineering Sciences, Vol. 2, No. 2 , 2009 . [5] Sable, M.J., Jagtap, S.J. , Patil, P.S., Baviskar , P.R. and Barve , S.B. ”Enhancement of Natural Convection Heat Transfer on Vertical Heated Plate by Multiple V- Fin Array” , IJRRAS , Vol. 5 (No. 2) , Nov. 2010 . [6] Naidu, S.V., Rao, V.D., Roa, B.G., Sombabu, A. and Sreenivasulu, B. “ Natural Saad Najeeb Shehab Al-Khwarizmi Engineering Journal, Vol. 12, No. 3, P.P. 61- 71 (2016) 70 Convection Heat Transfer from Fin Arrays - Experimental and Theoretical Study on Effect of Inclination of Base on Heat Transfer “, ARPN Journal of Engineering and Applied Sciences , Vol. 5 , No. 9 , Sep. 2010 . [7] Fahiminia, M. , Naserian, M.M. , Goshyeshi, H.R. and Majidian, D. “Investigation of Natural Convection Heat Transfer Coefficient on Extended Vertical Base Plates “ , J. of Energy and Power Engineering, Vol. 3, pp. 174-180 , 2011 . [8] More, R.S. , Mehta, R.I. and Kakade, V.A. “ Review Study of Natural Convection Heat Transfer on Heated Plate by Different Types of Fin Array “ , International Journal of Engineering Sciences and Research Technology , 2 (12) , Dec. 2013. [9] Hireholi, S. , Shekhar , K.S.S. and Milton , G.S. “ Experimental and Theoretical Study of Heat Transfer by Natural Convection of a Heat Sink Used for Cooling of Electronic Chip “ , International Journal of Engineering Inventions ,Vol. 2, Issue 2, pp. 01-09 , Jan. 2013. [10] Tiwari, P. and Malhotra, V. “Natural Convection Over a Flat Plate from Side to Side Enclosures “ , International Journal of Application or Innovation in Engineering and Management, Vol. 3 , Issue 2 , Feb. 2014 . [11] Lienhard, J.H. “A Heat Transfer Textbook“ , Phlogiston Press, 3rd Edition , USA, 2008. [12] Long, C. and Sayma, N. “Heat Transfer”, Ventus Publishing , 1st Edition , London, 2009. 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