İZOTROPİK SAÇILMA ORTAMLI KARE GEOMETRİ İÇİNDE TÜRBÜLANSLI DOĞAL TAŞINIM VE IŞINIM ISI TRANSFERİ

Farklı ısıtılmış kapalı kare bir geometri içindeki türbülanslı doğal taşınım ve ısıl ışınımın etkisi sayısal olarak incelenmiştir. Kapalı kutu sağ duvardan ısıtılır ve sol duvardan soğutulur. Diğer duvarların adyabatik olduğu varsayılmaktadır. Reynolds Averaged Navier Stokes (RANS) formülasyonu, Realizable k–modeli ile birlikte türbülanslı akışları analiz etmek için kullanılmıştır. Ayrıca, ışınım transfer denklemini (RTE) çözmek için kesikli ordinatlar metodu (DOM) kullanılmıştır. Rayleigh sayısı (Ra), optik kalınlık (), Planck sayısı (Pl), saçılma albedosu () ve duvar yayma oranı ( ) parametrelerinin etkisi, akış ve sıcaklık dağılımı kapalı kare geometri içinde sayısal olarak çalışılmıştır. Türbülanslı doğal taşınım ve ışınımda parametrelerin karakterize edilmesine odaklanan detaylı bir parametrik çalışmanın nadiren ayrıntılı olarak ele alındığını belirtmek ilginçtir. Çözümler 109 ila 1012 arasında değişen Rayleigh sayısı için elde edilmiştir. Işınım ısı transferinin geometri içinde akış alanlarının özelliklerini değiştirdiği bulunmuştur. Optik kalınlığın arttırılması, sabit bir Rayleigh sayısı için birleşik ısı transferinde bir azalmaya neden olurken ve ışınımla birlikte düşük optik kalınlıkta maksimum ısı transferi elde edilmiştir. =0.2 ve 5 için sırasıyla =87.796 ve 82.351 elde edilmiştir (Ra=1010, Pl=0.02 ve =0). Isı transferi azalan Planck sayısı ile artar ve artan saçılma albedo ile azalır. Pl=0.001 ve 10 için sırasıyla =445.837 ve 68.100 bulunmuştur (Ra=1010, =1 ve =0). Aktif duvarlar siyah, yalıtılmış duvarlar yansıtıcı olduğunda, Ra=1010, Pl=0.02, =1 ve =0 için =85.507 elde edilmiştir.

Anahtar Kelimeler:

Türbülanslı doğal taşınım, RANS, Isıl ışınım, İzotropik saçılmalı ortam, Kare geometri

TURBULENT NATURAL CONVECTION AND RADIATION HEAT TRANSFER IN SQUARE ISOTROPIC SCATTERING MEDIUM

The influence of turbulent natural convection and thermal radiation in a differentially heated square enclosure is numerically investigated. The enclosure is heated from the right wall and cooled from the left wall. The other walls are assumed to be adiabatic. The Reynolds Averaged Navier Stokes (RANS) formulation was employed for analyzing turbulent flows together with a Realizable k– model. In addition, the discrete ordinates method (DOM) was used to solve the radiative transfer equation (RTE). Influence of Rayleigh number (Ra), optical thickness (), Planck number (Pl), scattering albedo () and wall emissivity ( ) parameters were studied numerically on square enclosure for the flow and temperature distribution. It is interesting to note that a detailed parametric study focusing on characterizing parameters in turbulent natural convection and radiation was rarely dealt with in details. Solutions were obtained for a range of Rayleigh numbers varying from 109 to 1012. It was found that the radiation heat transfer alters the characteristics of flow fields in the enclosure. Increasing the optical thickness results in a decrease in combined heat transfer for a fixed Rayleigh number and the maximum of heat transfer occurred for low optical thickness with radiation presence. =87.796 and 82.351 is obtained for =0.2 and 5, respectively (Ra=1010, Pl=0.02 and =0). The heat transfer increases with decreasing Planck number, and decreases with the increasing scattering albedo. =445.837 and 68.100 is obtained for Pl=0.001 and 10, respectively (Ra=1010, =1 and =0). When the active walls are black and the insulated walls are reflected, =85.507 is obtained for Ra=1010, Pl=0.02, =1 and =0.

Keywords:

Turbulent natural convection, RANS, thermal radiation, isotropic scattering medium, square enclosure,

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