Elektronik devrelerin soğutulması ve jet püskürtmeli soğutma sistemlerinin analizi
Cooling of electronic circuits and analysis of jet impingement cooling systems
- Tez No: 66844
- Danışmanlar: PROF. DR. MURAT TUNÇ
- Tez Türü: Yüksek Lisans
- Konular: Makine Mühendisliği, Mechanical Engineering
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 1997
- Dil: Türkçe
- Üniversite: İstanbul Teknik Üniversitesi
- Enstitü: Fen Bilimleri Enstitüsü
- Ana Bilim Dalı: Makine Mühendisliği Ana Bilim Dalı
- Bilim Dalı: Belirtilmemiş.
- Sayfa Sayısı: 90
Özet
ÖZET Elektronik devrelerin soğutulması, gün geçtikçe önem kazanmakta ve daha karmaşık bir problem halini almaktadır. Karşılaşılan problem: tipik baskı levhalarda olduğu gibi blok geometrilerin söz konusu olduğu farklı bir ortamın, minimum soğutucu akışkan ile maksimum soğutma sağlayacak şekilde, sistem basınç kayıplarını karşılayarak istenilen hassasiyette sıcaklık kontrolünün sağlanmasıdır. Dolayısı ile bilinen konvansiyonel tip soğutma teknikleri bu noktada yetersiz kalmaktadır. Bu nedenle son yıllarda çeşitli ileri sıcaklık yönetimi teknikleri geliştirilmeye çalışılmıştır. Bu alanda üzerinde durulan en önemli yöntemlerden birisi de Jet Püskürtmeli Soğutma Sistemleridir. Başlıca kare dizilimli, dairesel hava jeti püskürtmeli ve sınırlandırılmış, daldırılmış tek FC-77 sıvı jeti püskürtmeli olmak üzere elektronik devrelerin soğutulmasında pratikte sıkça kullanılan iki sistemin incelendiği bu çalışmada, yapılan deneysel çalışmalar incelenerek ısı transferi; ısı taşınım katsayısına, lüle ve perfore plaka geometrisine ve basınç düşümlerine bağlı olarak nümerik ve ampirik formüllerle ifade edilmiştir. Dört korelasyon denkleminin elde edildiği çalışmada ayrıca iki yeni yaklaşımla konuya, özellikle mühendislik çalışmaları açısından ışık tutulmaya çalışılmıştır. Aşağıdaki bölümlerde problemin detayları, çözüm metotları ve yaklaşımları bulunmaktadır.
Özet (Çeviri)
SUMMARY The rapid advances and miniaturisation in the microelectronics and reductions of the electronic component sizes have been resulted to increase power densities and also amount of heat. The reliability of electronic components is, therefore, getting more critically dependent on the accuracy of heat transfer management. Therefore the cooling of electronic equipment is going to be one of the most important branches of heat transfer investigation. This activity is motivated by reliability considerations, by the desire to decrease the transit time of electronic signals, and by the advent of new electronic equipment configurations. Reliability revolves about the control of the temperature level of critical components. In these situations, the problem is not only dissipation of heat from electronic devices, but also optimisation of the pressure drops Increased heat densities per device have necessitated the search for innovative techniques of heat dissipation. On the other hand, in recent decades, component heating and cooling through the use of high velocity perpendicularly impingement jets to heat transfer surfaces have found considerable industrial applications, like painting and drying of textiles and papers, tempering of glass and cooling of engines and turbines. Recently jet impingement has been managed for use in cooling of electronic components. Surface heat transfer coefficients generated by normal impingement of air or liquid jets are an order of magnitude higher than other conventional methods. They produce very high convective heat transfer rates with minimal expenditures of coolant. In the impingement cooling systems high intensity transfer of large surface areas can be accomplished by an array of closely spaced jets impinging normal to the surface from a perforated plate placed close to the surface. XIHowever an enormous variety of specific geometries are encountered in the cooling of electronic equipment which make it different from the industrial applications. In spite of having flat surface like turbine blade, in electronic cooling the flow passages are frequently of irregular shape. In a typical electronic package, the surface geometry is characterised by block like elements attached to an otherwise flat surface The work reported here is focused on mainly two different jet cooling systems: a) Average surface heat transfer coefficients under a perforated plate of multiple, square array, round impinging air jets. b) Local heat transfer coefficients by normally impinging axisymetric, submerged and confined liquid jet of FC-77 (perfluorinated di electric liquid ) The purpose of this investigation was to solve the problem numerically by using mathematical statistical regression method. Correlation is made in terms of perforated plate geometries, fluid properties and system pressure drops. The mathematical modelling of the problem is very important to get successful results from regression method. Actually the purpose of regression is to predict Y values from X values. But in this work regression was used to estimate the equation ( ie. relationship) from determined X and Y values. Relevant independent numbers namely, Nusselt number, Reynolds number, Re =“°K'% (2) Prandtl number c. u / Pr= '% (3) distance between impingement plate and target surface Zn /d, jet to jet spacing X”/d, nozzle length 1 /d, have been used for to obtain general dimensionless equation : Nu^=C^dm'Yf-{ZnldfiXnldf^ldJ'{rldf (4) Although previous works in the literature, has been explained the problem in graphical form, in this investigation was founded the solution written as equation form by handling the same data, for the purpose of being able to compare the results. For the multiple, square array, round impinging air jets was investigated in such as limited ranges are below: XllZ“ /d of 1.0 to 14 X”/d of 1.0 to 25 Re of 1000 to 40.200 ( ie. Ve < 130 m/s; Mach < 1.08 ) T +T Air properties at film temperature Tf = s ° ( 5 ) and table ( 3.2 ) was used. Prandtl number : 0,71, n = 1/3 was chosen Since 1 /d < 1.0 for air jet impingement it has been assumed that there is no effects of 1 /d on heat transfer coefficients. For the average heat transfer: equation h = - jf hds ( 6 ) was used s As a result equation: Nu= 0J422Re0'83.Pr0'33.(2«/^)0'153.(^2/^)-1-52 ( 7 ) was obtained for air jet impingement. The heat transfer data obtained from ( 7 ) should provide sufficient information to design air jet impingement cooling configurations consisting of turbulent jets. And data obtained from equation ( 7 ) matches with previous experimental studies. ( figure 1 ) 4000 6000 8000 10000 Re - * - Zn/d=3_ I - ?- Zn/d=10_ll - A - Zn/d=3,regression - ® - Zn/d=1 0.regression 20000 30000 Fig. 1 Average heat transfer coefficients for X“/d=10, d= 2.5 mm Some significant conclusions resulted from this empirical ( 7 ) equation are below: i. The heat transfer coefficients decrease with increasing jet to jet spacing, X”Xlllii. Increasing of perforated plate to target surface distance Zn, increases heat transfer coefficients without cross flow condition. But in a cross flow condition this situation becomes reverse ie. the heat transfer coefficients decrease with increasing Z“ iii. Heat transfer coefficients increase with increasing open area Af iv. Decreasing hole diameter with increasing number of holes, everything else being equal, improves heat transfer performance v. For large X”/d > 25 average heat transfer coefficients are nearly independent of Zn For the submerged and unconfined, axisymetric impingement single liquid jet of FC- 77: The parameters ( Reynolds number, nozzle to target surface spacing and nozzle geometry ) were investigated in such as limited ranges are below: Z“/dofl.0tol4 l/dof0.25tol2 Re of 4000 to 23.000 FC-77 properties at film temperature ( 5 ) and table ( 3.3 ) was used. Pr= 25,3 at T0= 20 °C and n = 0.4 was chosen ( Garimella and Boris, pp.2921, 1996 ) Separate correlation's were found for the stagnation Nusselt number in the ranges Zn /d of 1.0 to 5, equation: m=Q,5VJte0>Tft°'\(2h/4°'m(l/4^ (8) and Z”/d of 6 to 14, equation: Nu = 0,543Re°-7155.PrM(2>2 / d)^9“ {l I d)^039 ( 9 ) was found. Although equation ( 4.36) and ( 4.37 ) were considered at stagnation point, equation : iV«=0J()4Rea542PrM(^/^-0-099(//^^102(r/^^202 ( 10) was shown the effects of r /d on the local heat transfer coefficients. The heat transfer coefficient decreases as radial distance from the stagnation point increases. The heat transfer has a bell shaped distribution with a peak at stagnation point. In equation ( 10 ) this trend was also obtained for the r /d of 1.0 to 7.0 (figure 2) However for the r /d of 0 to 1.0, results aren't logical Experimentally studies was shown that at very small nozzle aspect ratios ( 1 /d < 1), the heat transfer coefficients are the highest. XIVRe1=8500 Tahminh Re2=13000 Tahmini2 ooooooooo omomomoioo CsT t-”t-“ o”O“ O”r-“ t-”CM“ ' ' ' ' r/d Fig.2 Distribution of local heat transfer coefficients at Re=8500, Zn/d=3 and Re=13000, Z”/d=4 As the aspect ratio is increased to values of 1 to 4 the heat transfer coefficients drop sharply, but further increases, the heat transfer coefficients increases gradually. Also same trend has been evaluated from the correlation 'r' of the 1 /d in equation (10). However, further increasing of the aspect ratios still have positive effects on heat transfer coefficients. In FC-77 liquid jet impinging, the other correlation parameter of equation ( 7 ), Z* /d is nozzle to target surface distance has less pronounced effects on heat transfer coefficients than air impinging systems. However heat transfer coefficients decreases with increasing of Z" As a conclusion, in aforementioned conditions, four new equations was found in this study that have a good fit with the previous studies XV
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