Experimental Analysis of Inclined orientation Plate Fin Heat Sinks

Transcription

1 e-issn Volume 2 Issue 5, May 216 pp Scientific Journal Impact Factor : Experimental Analysis of Inclined orientation Plate Fin Heat Sinks D.D.Palande 1, Dr. A. M. Mahalle 2 1,2 Laxminarayan Institute of Technology, Nagpur, India Abstract Steady state natural convection from heat sink with vertical base rectangular plate-fin heat sinks having parallel arrangement mounted on inclined base was experimentally investigated. Aluminum heat sink of 2mm length was modeled. Rectangular base was inclined for angle from to 9 keeping upward facing fins. The effects of orientation of inclination on plate fin heat sinks were studied. It was observed that at small inclinations from vertical as well as horizontal the convection heat transfer rate is not change significantly. Keywords plate fin heat sink, Natural convection, Angle of Inclination I. INTRODUCTION Heat sinks are extensively used in air craft engine refrigerators, cooling of computer processors and other electronic devices. Due to rapid development of electronic technology electronic devices are often found in our daily life. Experimental work on vertical and horizontal fin arrays was studied by many authors. Starner and McManus [1] calculated natural heat transfer coefficients for four different fin arrays and three base types (vertical, horizontal, and 45 ) were investigated. Parameters that were varied in their study were the fin spacing and the height, respectively. It was found that the variations in inclination angle have effect on heat transfer coefficient. They found that for the vertical orientation the coefficient is maximum, which may reduce with the increase of fin height. Heat transfer rates for vertical orientation were generally lower than the values those of similarly spaced parallel plates. For the inclined orientation (45 ), heat transfer rates were 5 to 2 percent below from the values taken at vertical position. Vliet [2] investigate the experimental local heat transfer results for natural convection over constant heat flux inclined surfaces using water and air as the test fluids. The data was for Rayleigh numbers up to 1 16 and inclination angles from vertical to 3 degrees from the horizontal, and included results for laminar, transitional, and turbulent flow regions. The effect of the leading, trailing and sides edges of the plate on the local heat transfer and flow regions was not investigated as false walls were attached to each side of the heated plate. In the laminar flow region the data was found to correlate well with vertical plate equations when the gravitational component parallel to the surface was used. Harahap and Mcmanus Jr. [3] investigated the flow field associated with the natural convection from the fin arrays and used as model to find parameters to generalize the data. Two series of horizontal rectangular fin arrays having the same spacing and height were compared. The fin array having shorter fin length showed considerable higher average convection coefficients. This indicates that the fin length is an important factor to be considered in fin design. Yazicioglu and Yuncu [4] performed experiments over thirty different fin configurations with 25 mm and 34 mm fin length. Optimum fin spacing of aluminum rectangular fins on vertical base was examined. The range of base-to-ambient temperature was kept quiet wide from 3 to 15 C for fin height and fin spacing from 5 to 25mm and 4.5 to 85.5 mm, respectively. It was found that optimum fin spacing varies for each fin height which is between 1 and 12 mm. They concluded that geometrical parameter affects the convective heat transfer. It was higher for vertical orientation. Naidu et.al [5] studied effect of inclination of base of heat sink on heat transfer. Experimental study was conducted. Five different inclination angles, 3, 45, 6,9 were selected. Fin length was kept at 153 mm, width at 1 mm. fin thickness was selected as 3 mm. Fin height was varied for 2 mm and 4 mm. Fin spacing was varied for 7, 19, 47 mm. It was observed that the convection All rights Reserved 35

2 transfer rates were increasing from, decreasing from 3 to 45 and again increasing from 45 to 6 and 6 to 9 inclination for orientation of vertical base with vertical fins.tari and Mehrtash [6] investigated steady state natural convection from heat sink of rectangular fins on a vertical base. The effects of geometric parameters and base-to-ambient temperature difference on the heat transfer performance of fin arrays were observed and the optimum fin separation values were determined. 3 fin configurations were tested. Two sets were prepared of fin length 25 mm and 34 mm. By keeping these fin length, width and thickness constant fin heights was varied as 5 mm, 15 mm and 25 mm. Fin spacing was also varied from 5 mm to 85.5 mm. Heat input was varied from 25 W to 125 W. It was observed that convective heat transfer increases as fin spacing increases, reaches to maximum at a certain fin spacing value, termed as optimum fin spacing and beyond that further increase in fin spacing leads to decrease in heat transfer rate. Also, it was found that the optimum fin spacing varied between 1 mm to 12 mm for a proposed range of fin length, width, height. Tari and Mehrtash [7] has tested heat sink for wide range of angle of inclination with upward and downward orientations. By modifying Grashof number with cosine of inclination angle, they suggest the modified correlation, which is best suited for inclination angle interval of -6 θ +8. Steadystate natural convection from heat sinks with parallel arrangement of rectangular cross section vertical plate fins on a vertical base are numerically investigated in order to obtain a validated model that is used for investigating inclined orientations of a heat sink. It was also observed that the flow separation inside the fin channels of the heat sink is an important phenomenon. For upward facing inclinations, they observed that the flow separation location plays an important role. Also, they found that the optimum fin spacing does not significantly change with inclinations suggesting the value as mm. It was concluded that maximum convective heat transfer rate was obtained for vertical orientation. U. V. Awasarmol, A. T. Pise [8] analyzed comparative effect of rate of heat transfer with solid and permeable fins and the effect of angle of inclination of fins. It was found that using permeable fins, heat transfer rate is improved and convective heat transfer coefficient increases by about 2% as compared to solid fins with reduction of cost of the material 3%. The sink was made incline with, 15, 3, 45, 6, 75, and 9 from horizontal. II. EXPERIMENTAL SETUP AND METHODOLOGY The experimental set-up primarily consists of an aerated concrete base and supporting frame on which the concrete is mounted and various instruments for measuring the ambient temperature, baseplate temperature and the power input for the heater. Whole frame is mounted on single shaft which has bearing at the support. The front surface of the frame is covered with acrylic sheet, which has arrangement to replace fin arrays. At one end of the shaft, protractor is kept in-built so as to measure inclination of the heat sink. The schematic view of angle of inclination is as shown in fig.1.the schematic view of experimental setup is as shown in fig.2. The test section was kept in controlled room to establish free convection over fin arrays. The aerated concrete block has 5 mm depth to fit heater plate into All rights Reserved 36

3 Fig 1 side view and angle of inclination Fig.2 Schematic view of experimental setup The base plate of the heat sink was heated using nicrome wire heater which is sandwiched in Mica sheets. The base plate temperatures of heat sink were measured at five points using copperconstantan thermocouples and ambient temperature was measured by thermocouple number six. The heat sink blocks were placed in the enclosure. Tests were conducted over a range of 1 W to 5 W. A calibrated dimmer stat was used to vary the heat input in steps of 1W. After attaining steady state, temperatures were measured to analyze the heat transfer rate though fins by adjusting it with different angles such as:, 3, 45, 6, 9. For angle of the heat sink are vertical and for 9 the heat sink are in horizontal position III. DATA REDUCTION In order to find Nu and Ra, the flow properties must be obtained. Therefore the film temperature is - T f = (1) Ra =.(2) Ra<1x 1 9 flow is Laminar. Heat loss by radiation (Q r ) Q r = ɛ σ A s (T w 4 T 4 ) (3) h = (4) Nu exp =... (5) Where L is the characteristics length (length of fin array) IV. RESULTS AND DISCUSSION The experimental data obtained vertical rectangular plate finned heat sink at various angles is presented. These all results are useful to reveal the effect of geometric parameters, orientation of heat sink and heat input on the steady state heat dissipation from finned surfaces. 4.1 Optimum fin spacing The experimentation for heat sink length 2mm and various fin height from 5mm to 25mm for different fin spacing was carried out to optimize fin spacing.fig 3 shows the variation of convective heat transfer rate with base to ambient temperature difference at height All rights Reserved 37

4 Qc( W) Qc(W) International Journal of Current Trends in Engineering & Research (IJCTER) Qc Vs s S(mm) H= 5mm ΔT = 31K ΔT= 338K ΔT = 364K ΔT = 385K ΔT = 45K Fig.3 Variation of convective heat transfer rate with base to ambient temperature difference at fin height of H=5mm The convection heat transfer rate from an array increases with fin spacing, and after reaching its maximum point, it starts decreasing at a given fin height, fin length and base-to-ambient temperature difference. The corresponding fin spacing value of the maximum convection heat transfer rate point is called optimum fin spacing, Sopt. It is observed that the optimum fin spacing varies between 9.5 mm and 1.5mm. This conclusion reveals that the optimum fin spacing is sensitive to the variations in fin height, fin length and base-to-ambient temperature difference parameters. The variation of optimum fin spacing s with fin height and base-to-ambient temperature difference 4.2 Effect of temperature difference on heat transfer rate for different fin height Figure 4 shows the effect of temperature difference on rate of heat transfer for vertical orientation Qc vs ΔT ΔT 5mm 1mm 15mm 2mm 25mm Flat Plate Fig. 4 Variation of Convection Heat Transfer Rate with Fin Height at a Fin Spacing of s=7mm The convection heat transfer rates from fin heat sink and the vertical flat plate are plotted as a function of base-to-ambient temperature difference for fin spacing s, s = 7 It is observed from fig.4 that the Qc of heat sink depends on fin height fin spacing and base to ambient temperature of heat sink. Same trends are observed for other spacing. It is also observed that the convective heat transfer rates from the rectangular plate fin heat sink increases with fin height and base-to-ambient temperature difference. The heat transfer rates from all fin heights are close to each other at low temperature differences while at high temperature differences it diverge with the variation in fin height. 4.3 Effect of angle of inclination on heat transfer rate for different fin height The effect of fin height on convection heat transfer rate at different angle of inclination can be observed in Figures All rights Reserved 38

5 Tw(degree celcius) Qc(W) International Journal of Current Trends in Engineering & Research (IJCTER) S=9.5 Q=2W Angle(degrees) H=5mm H=1mm H=15mm H=2mm H-25mm Fig.5 Variation of Convection Heat Transfer rate with respect to angle of inclination for various fin height and Heat input Q in =2W. 15 S=9.5 Q=2W Angle (degrees) H=5mm H=1mm H=15mm H=2mm h=25mm Fig 6.Variation of surface temperature with respect to angle of inclination for various fin height As observed in Figure 5 and 6, convection heat transfer rate increases with increase in fin height. For each Fin height, convection heat transfer rate decreases with angle of inclination. As fin height increases, angle dependence of Tw and Qc decrease. V. CONCLUSIONS An experimental result shows that the larger fin height results in higher heat transfer rate at constant fin spacing and fin length. It is concluded that decrement in heat transfer rate is more for large fin height, as compared smaller height as fin array inclined from vertical ( ) to horizontal (9 ) position. For vertically inclined fin array when fin base made to inclined from vertical to horizontal, it was observed that heat dissipation rate decreases for given fin length. Finally, slight change in heat transfer rate is observed for inclined fin heat sink from vertical position to 3 inclination and from horizontal position to 3 inclination. It is because an air flow characteristic seems quiet identical for slightly inclined fin base from either vertical or horizontal position. REFERENCES [1] K.E. Starner, H.N. McManus, An experimental investigation of free convection heat transfer from rectangular fin arrays, J. Heat Transfer 85 (1963) [2] Vliet, G.C., "Natural convection local heat transfer on constant-heat-flux inclined surfaces", Journal of heat transferasme, vol. 91, no. 4(1969) [3] Harahap F. and McManus H.N., Natural Convection Heat Transfer from Horizontal Rectangular Fin Arrays, Journal of Heat Transfer, 32-38, All rights Reserved 39

6 [4] Yazicioglu, B. and Yuncu, H., Optimum fin spacing of rectangular fins on a vertical base in free convection heat transfer, Journal of heat and mass transfer, 27, 44, pp [5] Naidu, S. V., Rao V. D., Rao, B. G., Sombabu, A., Sreenivasulu, B., Natural 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, 21, 5 (9) [6] Tari, I. and Mehrtash, M., Natural convection heat transfer from inclined plate-fin heat sinks, International Journal of Heat and Mass Transfer213, 56, pp [7] Tari, I. and Mehrtash, M., A correlation for natural convection heat transfer from inclined plate-finned heat sinks, Applied Thermal Engineering, 213, 51, pp [8] U.V.Awasarmol, A T.Pise, Experimental Study of Effect of Angle of Inclination of Fins on Natural Convection Heat Transfer through Permeable Fins, Proceedings on International Conference on Thermal Energy and Environment All rights Reserved 31