Scopus İndeksli Yayınlar Koleksiyonu / Scopus Indexed Publications Collection
Permanent URI for this collectionhttps://hdl.handle.net/11147/7148
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Article Citation - WoS: 12Citation - Scopus: 13A General Expression for the Stagnant Thermal Conductivity of Stochastic and Periodic Structures(The American Society of Mechanical Engineers(ASME), 2018) Bai, X.; Çelik, Hasan; Mobedi, Moghtada; Nakayama, AkiraA general expression has been obtained to estimate thermal conductivities of both stochastic and periodic structures with high-solid thermal conductivity. An air layer partially occupied by slanted circular rods of high-thermal conductivity was considered to derive the general expression. The thermal conductivity based on this general expression was compared against that obtained from detailed three-dimensional numerical calculations. A good agreement between two sets of results substantiates the validity of the general expression for evaluating the stagnant thermal conductivity of the periodic structures. Subsequently, this expression was averaged over a hemispherical solid angle to estimate the stagnant thermal conductivity for stochastic structures such as a metal foam. The resulting expression was found identical to the one obtained by Hsu et al., Krishnan et al., and Yang and Nakayama. Thus, the general expression can be used for both stochastic and periodic structures.Article Citation - WoS: 33Citation - Scopus: 35Thermal Dispersion in Porous Media - a Review on the Experimental Studies for Packed Beds(American Society of Mechanical Engineers, 2013) Özgümüş, Türküler; Mobedi, Moghtada; Özkol, Ünver; Nakayama, AkiraThermal dispersion is an important topic in the convective heat transfer in porous media. In order to determine the heat transfer in a packed bed, the effective thermal conductivity including both stagnant and dispersion thermal conductivities should be known. Several theoretical and experimental studies have been performed on the determination of the effective thermal conductivity. The aim of this study is to review the experimental studies done on the determination of the effective thermal conductivity of the packed beds. In this study, firstly brief information on the definition of the thermal dispersion is presented and then the reported experimental studies on the determination of the effective thermal conductivity are summarized and compared. The reported experimental methods are classified into three groups: (1) heat addition/removal at the lateral boundaries, (2) heat addition at the inlet/ outlet boundary, (3) heat addition inside the bed. For each performed study, the experimental details, methods, obtained results, and suggested correlations for the determination of the effective thermal conductivity are presented. The similarities and differences between experimental methods and reported studies are shown by tables. Comparison of the correlations for the effective thermal conductivity is made by using figures and the results of the studies are discussed. Copyright © 2013 by ASME.Article Citation - WoS: 32Citation - Scopus: 38Fully Developed Forced Convection in a Parallel Plate Channel With a Centered Porous Layer(Springer Verlag, 2012) Çekmer, Özgür; Mobedi, Moghtada; Özerdem, Barış; Pop, IoanIn this study, fully developed heat and fluid flow in a parallel plate channel partially filled with porous layer is analyzed both analytically and numerically. The porous layer is located at the center of the channel and uniform heat flux is applied at the walls. The heat and fluid flow equations for clear fluid and porous regions are separately solved. Continues shear stress and heat flux conditions at the interface are used to determine the interface velocity and temperature. The velocity and temperature profiles in the channel for different values of Darcy number, thermal conductivity ratio, and porous layer thickness are plotted and discussed. The values of Nusselt number and friction factor of a fully clear fluid channel (Nu cl = 4. 12 and fRe cl = 24) are used to define heat transfer increment ratio (ε th = Nu p/Nu cl)and pressure drop increment ratio (ε p = f Re p/f Re cl) and observe the effects of an inserted porous layer on the increase of heat transfer and pressure drop. The heat transfer and pressure drop increment ratios are used to define an overall performance (ε = ε th/ε p) to evaluate overall benefits of an inserted porous layer in a parallel plate channel. The obtained results showed that for a partially porous filled channel, the value of ε is highly influenced from Darcy number, but it is not affected from thermal conductivity ratio (k r) when k r > 2. For a fully porous material filled channel, the value of ε is considerably affected from thermal conductivity ratio as the porous medium is in contact with the channel walls.Article Citation - WoS: 61Citation - Scopus: 66The Use of Metal Piece Additives To Enhance Heat Transfer Rate Through an Unconsolidated Adsorbent Bed(Elsevier Ltd., 2010) Demir, Hasan; Mobedi, Moghtada; Ülkü, SemraThe effects of metal piece additives on effective thermal conductivity and diffusivity of an unconsolidated adsorbent bed in which adsorbent is silica gel were investigated. The metal piece additives were copper, brass, aluminum and stainless steel with two different sizes as 1.0-2.8 mm and 2.8-4.75 mm. The effective thermal conductivity and diffusivity of the mixed bed were predicted by comparison of the experimental results with the solution of dimensionless heat conduction equation for the bed. The performed experiments showed that the addition 15wt% of aluminum pieces with sizes between 1.0 and 2.8 mm enhances the effective thermal diffusivity and conductivity of a pure silica gel bed by 157% and 242%, respectively. © 2010 Elsevier Ltd and IIR.