PİMLİ ÜÇ BOYUTLU DİKDÖRTGEN KUTULARDA ISI TRANSFERİ

Öz

Üç boyutlu gri yüzeyli dikdörtgen geometrili kutularda termal radyasyon ile doğal taşınımın etkileşimi sayısal olarak incelenmiştir. Dikdörtgen kutuda dikey karşıt izotermal duvarlar ısıtılıp soğutulurken, diğer tüm duvarlar yalıtılmıştır. Pimler sıcak duvara eklenmiştir. Katılımcı olmayan ortamda akışkanın hava (Pr=0.71) ve akışın laminer olduğu kabul edilmiştir. Boussinesq yaklaşımının kullanıldığı yoğunluk dışındaki tüm termofiziksel özelliklerinin sabit olduğu varsayılmıştır. Momentum, enerji denklemleri ve radyasyon transferi ticari CFD kodu ANSYS ile çözülmüştür. Taşınım terimlerinin ayrıklaştırılmasında ikinci dereceden ayrıklaştırma şeması, çözüm yöntemi olarak da SIMPLE algoritması ve yüzey ışınım hesabında S2S (Surface to Surface) ışınım modeli kullanılmıştır. Rayleigh sayısı (Ra), yüzey emissivitesi (ε), pim sayısı, boyutsuz pim çapları (D=d/H) ve uzunlukları (B=b/H), dikdörtgen kutunun genişlik yükseklik oranı (W/H) parametrik olarak değiştirilmiştir. Üç boyutlu kutunun, incelik oranı, W/H=0.5, 1.0 ve 2.0 olarak ele alınmıştır. Kutudaki pimlerin sayısı ise 9, 13, 17, 21 ve 25 olarak değiştirilmiştir. Rayleigh sayısı, yüzey emissivitesi, boyutsuz pim uzunlukları ve çapları, sırasıyla 103≤Ra≤106, 0.0≤ε≤1.0, 0.05≤B≤0.6, 0.025≤D≤0.1, değer aralıklarında değiştirilmiştir. Ortalama taşınım, radyasyon ve toplam Nusselt sayıları, her durum için Rayleigh sayısının bir fonksiyonu olarak hesaplanmıştır. Ayrıca ele alınan tüm durumlar için akış ve sıcaklık dağılımları verilmiş ve tartışılmıştır.

Anahtar Kelimeler

• Üç boyutlu
• Doğal taşınım
• S2S Işınım
• Dikdörtgen kutular

HEAT TRANSFER IN THREE-DIMENSIONAL RECTANGULAR CAVITIES WITH PINS

Öz

The interaction of natural convection with thermal radiation in three dimensional rectangular cavities with gray surfaces is studied numerically. The cavity is heated and cooled from the vertical opposing isothermal walls while all other side walls are adiabatic. The pins are placed to the active wall. The fluid is nonparticipating air (Pr=0.71), and the flow of air is assumed to be laminar. The fluid properties are taken to be constant at mean values, except for the density for which the Boussinesq approximation is employed. The governing flow, energy and the radiative transfer equations are solved by a commercial CFD code-ANSYS. The convection terms are discretized using a second order upwind scheme, and SIMPLE algorithm is adapted as the solution algorithm. The surface to surface (S2S) model is used for radiative heat transfer simulations. The Rayleigh number (Ra), the surface emissivity (ε), the number of pins, the dimensionless pin length and diameter (B=b/H and D=d/H), the slenderness of the cavity (W/H) are variable parameters of this study. The slenderness ration of W/H=0.5, 1.0 and 2.0 are considered. Enclosure with pin arrangements of 9, 13, 17, 21 and 25 are considered. The Rayleigh number, the surface emissivity, the dimensionless pin lengths and diameters are varied in the following intervals 103≤Ra≤106, 0.0≤ε≤1.0, 0.05≤B≤0.6, 0.025≤D≤0.1, respectively. The mean Nusselt numbers for convection and radiation, as well as total, were computed as a function of the Rayleigh number for each case. Also the flow and temperature distribution for some cases have been presented and discussed.

Anahtar Kelimeler

• Three-dimensional
• Natural convection
• S2S Radiation
• Rectangular cavities

Kaynakça

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