Yazar "Bilir, Sefik" seçeneğine göre listele

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    Comparison of turbulence models and CFD solution options for a plain pipe
    (E D P SCIENCES, 2018) Canli, Eyub; Ates, Ali; Bilir, Sefik
    Present paper is partly a declaration of state of a currently ongoing PhD work about turbulent flow in a thick walled pipe in order to analyze conjugate heat transfer. An ongoing effort on CFD investigation of this problem using cylindrical coordinates and dimensionless governing equations is identified alongside a literature review. The mentioned PhD work will be conducted using an in-house developed code. However it needs preliminary evaluation by means of commercial codes available in the field. Accordingly ANSYS CFD was utilized in order to evaluate mesh structure needs and asses the turbulence models and solution options in terms of computational power versus difference signification. Present work contains a literature survey, an arrangement of governing equations of the PhD work, CFD essentials of the preliminary analysis and findings about the mesh structure and solution options. Mesh element number was changed between 5,000 and 320,000. k-epsilon, k-omega, Spalart-Allmaras and Viscous-Laminar models were compared. Reynolds number was changed between 1,000 and 50,000. As it may be expected due to the literature, k-epsilon yields more favorable results near the pipe axis and k-. yields more convenient results near the wall. However k-epsilon is found sufficient to give turbulent structures for a conjugate heat transfer problem in a thick walled plain pipe.
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    Conjugate heat transfer for turbulent flow in a thick walled plain pipe
    (E D P SCIENCES, 2018) Canli, Eyub; Ates, Ali; Bilir, Sefik
    Laminar and turbulent flow have their own characteristics in respect of heat transfer in pipes. While conjugate heat transfer is a major concern for a thick walled pipe with laminar flow inside it, there are limited studies about a turbulent flow in a thick walled plain pipe considering the conjugate heat transfer. In order to conduct such a work by means of in-house developed code, it was desired to make a preliminary investigation with commercially available CFD codes. ANSYS CFD was selected as the tool since it has a positive reputation in the literature for reliability. Defined heat transfer problem was solved with SIMPLE and Coupled Schemes for pressure velocity coupling and results are presented accordingly.
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    EFFECTS OF WALL CONJUGATION AND FLUID AXIAL CONDUCTION IN CIRCUMFERENTIALLY PARTLY HEATED PIPES AND MINIPIPES
    (BEGELL HOUSE INC, 2017) Atmaca, Ulas; Bilir, Sefik; Ates, Ali
    Transient conjugated heat transfer in circumferentially partly heated thick-walled pipes and minipipes with thermally developing laminar flows is investigated, involving three-dimensional wall conduction and fluid axial conduction. The problem is handled for an initially isothermal, two-regional infinite pipe, for which the upstream region is completely insulated and the downstream region is circumferentially partly insulated by considering an instant increase in the outer wall temperature of the other circumferential part in the downstream region. Solution is made numerically by a finite-difference method, and a parametric study is conducted to analyze the effects of four defining parameters, namely, the Peclet number, wall-to-fluid thermal conductivity ratio, wall-to-fluid thermal diffusivity ratio, and wall thickness ratio, on heat transfer characteristics. The results show that in both the wall and the fluid sides, besides backward heat transfer due to axial conduction, a large amount of heat is transferred because of angular conduction from the circumferentially heated to the unheated part of the pipe. Wall conjugation highly compensates the effects of partial heating and an important percentage of heat transfer to fluid is realized from the unheated circumferential part of the pipe. The results are also seen to be much affected by the parameter values.
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    Experimental investigation of the effects of orientation angle on heat transfer performance of pin-finned surfaces in natural convection
    (PERGAMON-ELSEVIER SCIENCE LTD, 2011) Sertkaya, Ahmet Ali; Bilir, Sefik; Kargici, Suna
    Natural convection heat transfer in air from a pin-finned surface is investigated experimentally by considering the effect of radiation heat transfer. The plate was oriented as the pin arrays facing either downwards or upwards from vertical axis with different angles and the experiments were performed for different values of heater power input. From the results of the experiments it is observed that the pin fins increase the heat transfer considerably when compared to the unpinned surface. The upfacing pins are more enhancing heat transfer than the downfacing pins and the enhancement is decreasing with increasing orientation angle from the vertical axis. (C) 2011 Elsevier Ltd. All rights reserved.
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    Transient conjugated heat transfer for simultaneously developing laminar flow in thick walled pipes and minipipes
    (PERGAMON-ELSEVIER SCIENCE LTD, 2015) Darici, Selcuk; Bilir, Sefik; Ates, Ali
    Transient conjugated heat transfer in simultaneously developing laminar pipe flow is analyzed involving two-dimensional wall and fluid axial conduction. The problem is solved numerically by a finite difference method in a thick walled semi-infinite pipe which is initially isothermal, with hydrodynamically and thermally developing flow and with a sudden change in the ambient temperature. A parametric study is done to analyze the effects of six parameters, namely, wall thickness ratio, wall-to-fluid thermal conductivity ratio, wall-to-fluid thermal diffusivity ratio, the Peclet number, the Biot number and the Prandtl number. Heat transfer characteristics are seen to be highly affected by the parameter values. (C) 2014 Elsevier Ltd. All rights reserved.
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    Unsteady conjugated heat transfer in thick walled pipes involving two-dimensional wall and axial fluid conduction with uniform heat flux boundary condition
    (PERGAMON-ELSEVIER SCIENCE LTD, 2010) Ates, Ali; Darici, Selcuk; Bilir, Sefik
    Transient conjugated heat transfer in thick walled pipes for thermally developing laminar flow is investigated involving two-dimensional wall and axial fluid conduction. The problem is solved numerically by a finite-difference method for hydrodynamically developed flow in a two-regional pipe, initially isothermal in which the upstream region is insulated and the downstream region is subjected to a suddenly applied uniform heat flux. A parametric study is done to analyze the effects of four defining parameters namely, wall thickness ratio, wall-to-fluid thermal conductivity ratio, wall-to-fluid thermal diffusivity ratio and the Peclet number. The results are given by non-dimensional interfacial heat flux values, and it is observed that, heat transfer characteristics are strongly dependent on the parameter values. (C) 2010 Elsevier Ltd. All rights reserved.