Mechanical Engineering / Makina Mühendisliği

Permanent URI for this collectionhttps://hdl.handle.net/11147/4129

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Access Right: Open AccessAuthor: search.filters.author.Uçar, Eren

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  • Article
    Citation - WoS: 2
    Citation - Scopus: 3
    Effect of Voxel Size in Flow Direction on Permeability and Forchheimer Coefficients Determined by Using Micro-Tomography Images of a Porous Medium
    (Inderscience Enterprises Ltd., 2015) Uçar, Eren; Mobedi, Moghtada; Altıntaş, Gökhan; Glatt, Erik
    The permeability and Forchheimer coefficients of a porous medium, volcanic rock, are determined using micro-tomography images. A cubic volume in the middle of the images is extracted as REV (representative volume). The voids in the REV are discretised into anisotropic voxels using the commercial program of GeoDict. Seven computational domains with different voxel size in flow direction are generated. The velocity and pressure fields in the voids are obtained for Reynolds numbers ranging from 0.01 to 10. The obtained fields are used to determine the permeability and the Forchheimer coefficients. The performed calculations show that the nominal pore size changes with the voxel size in flow direction, however permeability and the Forchheimer coefficient approaches to the constant values.
  • Letter
    Citation - WoS: 2
    Citation - Scopus: 3
    A Comment on Change of Nusselt Number Sign in a Channel Flow Filled by a Fluid-Saturated Porous Medium With Constant Heat Flux Boundary Conditions
    (Springer Verlag, 2013) Uçar, Eren; Mobedi, Moghtada; Özerdem, Barış; Pop, Ioan
    The aim of this Letter is to show that, the Nusselt number sign might be changed without changing of heat transfer direction at the wall of channels, even for flows without viscous dissipation. The sign of the Nusselt number is important for deciding on heat transfer direction at a solid wall. The change of the Nusselt number signmay be interpreted as the change of the direction of the heat transfer at a wall. There are studies, such as internal heat and fluid flow in a channel with viscous dissipation (Hung and Tso 2008, 2009; Mitrovic and Maletic 2007; Mobedi et al. 2010) or with an asymmetric heat flux boundary conditions (Cekmer et al. 2011) in which the sign of the wall Nusselt number changes. Nield and Kuznetsov (2008) studied in a very interesting paper the counter flow in a channel whose boundaries are asymmetrically heated and is consisted of two porous layers with different permeability values. These authors showed that even the sign of an overall Nusselt number defined based on the average wall temperatures and heat fluxes, and the mean permeability values of the two porous layers can also be changed and it can take negative values when a strong asymmetry heat flux is imposed to the boundaries. The change of Nusselt number sign at the walls are also observed in other studies of Kuznetsov (Kuznetsov and Nield 2010; Xiong and Kuznetsov 2000).
  • Article
    Citation - WoS: 29
    Citation - Scopus: 34
    Effect of an Inserted Porous Layer Located at a Wall of a Parallel Plate Channel on Forced Convection Heat Transfer
    (Springer Verlag, 2013) Uçar, Eren; Mobedi, Moghtada; Pop, Ioan
    A theoretical study is performed on heat and fluid flow in partially porous medium filled parallel plate channel. A uniform symmetrical heat flux is imposed onto the boundaries of the channel partially filled with porous medium. The dimensional forms of the governing equations are solved numerically for different permeability and effective thermal conductivity ratios. Then, the governing equations are made dimensionless and solved analytically. The results of two approaches are compared and an excellent agreement is observed, indicating correctness of the both solutions. An overall Nusselt number is defined based on overall thermal conductivity and difference between the average temperature of walls and mean temperature to compare heat transfer in different channels with different porous layer thickness, Darcy number, and thermal conductivity ratio. Moreover, individual Nusselt numbers for upper and lower walls are also defined and obtained. The obtained results show that the maximum overall Nusselt number is achieved for thermal conductivity ratio of 1. At specific values of Darcy number and thermal conductivity ratio, individual Nusselt numbers approach to infinity since the value of wall temperatures approaches to mean temperature.