٠٠٩ :. (Heat sinks).. (Dissipated).. (31%)..(0.1%) : STUDY OF FINS SHAPES' EFFECT ON NATURAL THERMAL CONVECTION Waleed Mohammad Abid Engineering College Anbar University ٧٩
٠٠٩ Abstract: In many electric circuit boards thermally induced buoyancy effects are not always sufficient to adequately cool high density electronic packages found in modern circuit boards. Instances thermal enhancement techniques, such as heat sinks, must be used to increase the effective surface area for heat transfer so lower the thermal resistance between sources and sink. Both vertical rectangular and pin finned surfaces were studied to show the shape effect and natural convection heat transfer coefficient. The thermal dissipated from vertical rectangular finned surfaces greater than pins finned surfaces. The overall thermal resistance of the pins finned surfaces greater (31%) compared with vertical rectangular finned surfaces. An empirical equation was predicted to calculate average natural convection heat transfer coefficient from vertical rectangular and pin fins. The results show an excellent convince with the Literature review where the overall error was about (0.1%). : (m) (W) ( ) سمك الزعنفة (m) عرض الصفيحة المزعنفة (m) Gr N P Pr Q * T t W (m ) (m). (m) (W/m ºC) (m) (W/mºC) (W/mºC) (m /s) As b C net D F h H k k f m g conv. rad. total s (1/K) (m /s) - (kg/m 3 ) η β ν σ ρ ٨٠
٠٠٩ ٨١ (Extended surface). (Fins).(Heat sinks) (Horizontal (Vertical fins) ( ).(Pins) fins).[1] ( ).[] = 1 4 35 * * 1 e 0.75 :[3] (Elenbass) (1).(Modified ) ( * ) [4] (Van de pol and Tiemey) ( ).(0.6< <100) [5] (Welling and Wooldridge) [6] (Jones and Smith)..( ) ( 10 < <6 10 5 ) (Boundary layer) [7] (Garg and Velusamy). (Blasius equation) [8] (Culham et. al). (META) (10 3 < <10 10 ) (Karagiozis) (META) [9] (Yovanovichet et. al).(9%)
٠٠٩ " (Developing).. ( ) ( ) (heater).(85ºc) (100ºC). (Thermocouple). (Digital thermometer)... : : (100mm 110mm) (Finned Plate) ( ) ( ) (Vertical fins) (L=100mm, (k=01w/mºc) ٨
٠٠٩ (1-18 W).H=66.5mm, t=1.5mm). (T ) (Ts) :[] Q rad. 4 4 = As F σ (Ts T ) () : :[9] :F Cnet F = (3) H ( b + L ) :. :C net. :[1] () 3 g β ( Ts T ) b b = Gr Pr = Pr (4) ν * Modify ).(b=10mm) (b) : :[9] (yliegh mber b = b (5) L :.(b/l=0.1). (b/l) : b Q = conv. b k As (Ts T ) (6) f :.(As=LH(N-1)) :As. (N=9) :N :[1] ٨٣
٠٠٩ k f H H t tanh b ( + 1 ) k b t L η fin = (7) k f H H t b ( + 1 ) k b t L b total = η fin rad. Q = Q + Q b conv. (8). b * (9) : : (Pins plat) ( ) ( ) (100mm 110mm) (Staggered) (D=13 mm, H=67 mm). (1-18 W) (digital thermometer) (Ts).(T ) : Q rad. 4 4 = Asσ F (Ts T ) (10) () 3 g β (Ts T ) D = Gr.Pr = Pr (11) D ν :.(Pr) (Tf =(Ts+T )/) : ( D ) Qconv. D D = As (Ts T )k (1) As = f π ( WL ( N D )) + N DL π : : :As.[1] ٨٤
٠٠٩ ( mh ) tanh η = (13) mh m = 4 D D k Q + f k total = Qrad. Qconv. (15) (14) : ( ) ٨٥.. T Q conv. = 1 has = R th (31%) : (16).. ( ) (1W) (0.7ºC) ( ).(18W) (6.ºC) ( ). : (Statistics V5.5) 0.75 D = 0.008 D (17) ( ). (0.18%) (R = 95%).. : (Statistics V5.5) ( ) 0. 75 b = 0.045 b (18) (0.08%) (R =98%)
٠٠٩. ( ) = 1 4 37.3 * * 1 e 0.75 : [3] (Elenbass) (19) (0.31%).(0.1%) ( ) : 1. Cengel Y. A. 'HEAT TRANSFER A PRACTICAL APPROACH' McGraw-Hill, Int. 001.. Lienhard IV J. H. and Lienhard V J. H. 'A HEAT TRANSFER TEXTBOOK' Third ed. Cambridge, MA: Phlogiston Press, 006. 3. Elenbass W. 'HEAT DISSIPATION OF PARALLEL PLATES BY FREE CONVECTION' Physical, Vol. 9, No.1,194. 4. Van de pol D. W. and Tiemey J. K. ' FREE CONVECTION NUSSELT NUMBER FOR VERTICAL U-SHAPED CHAMELS' J. of Heat Transfer, Vol. 95, 1973. 5. Welling J. R. and Wooldridge C. B. ' FREE CONVECTION HEAT TRANSFER COEFFICIENTS FROM RECTANGULAR VERTICAL FINS' J. of Heat Transfer, Vol. 87, 1965. 6. Jones C. D. and Smith L.F. 'OPTIMUM ARRANGEMENT OF RECTANGULAR FINS ON HORIZONTAL SURFACES FOR FREE CONVECTION HEAT TRANSFER' J. of Heat Transfer, Vol. 9, 1970. 7. Garg V. K. and Velusamy K. ' HEAT TRANSFER CHARACTERISTICS FOR A PLATE FIN ' J. of Heat Transfer, Vol. 108, 1986. 8. Culham J. R., Yovanovich M. M. and Lee S. 'THERMAL MODELLING OF ISOTHERMAL CUBOIDS AND RECTANGULAR HEAT SINKS COOLED BY NATURAL CONVECTION' IEEE Transaction on components, Packaging, and Manufacturing Technology-part A, Vol. 18, 1995. 9. Yovanovich M. M., Teertstra P., and Culham J. R. ' NATURAL CONVECTION MODELLING OF HEAT TRANSFER SINKS USING WEB-BASED TOOLS. www.electronics-coollingcom/html/000-sep-a4.html,004. ٨٦
٠٠٩. ( ). ( ) ٨٧
٠٠٩ W H D L. ( ) 35 30 فرق درجة الحرارة ) (Ts-T 5 0 15 10 5 0 0 3 6 9 1 15 18 1 (W). ( ) ٨٨
٠٠٩ 6 5 =0.008 ^0.75 4 3 1 0 1000 000 3000 4000 5000 6000 7000. (5) 3.5 = 0.045 ^0.75 1.5 1 0.5 0 0 50 100 150 00 50. ( ) ٨٩
٠٠٩ 4 3 Elenabass 1 0 0 50 100 150 00 50 300. ( ) ٩٠