Scopus İndeksli Yayınlar Koleksiyonu / Scopus Indexed Publications Collection
Permanent URI for this collectionhttps://hdl.handle.net/11147/7148
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Article Interfacial Convective Heat Transfer for Randomly Generated Porous Media(Begell House, 2018) Uçar, Eren; Mobedi, Moghtada; Ahmadi, AzitaHeat and fluid flow in 20 random porous media is investigated by using the Monte Carlo (MC) procedure. Each porous medium consists of long square rods distributed randomly in flow direction. The continuity, momentum, and energy equations are solved for a row of porous media representing the entire domain of a random porous medium. The microstructure properties of each random porous medium which are the mean and standard deviations of the Voronoi areas, the nearest neighbor distance and orientation are obtained. The rods in the domain are classified into three groups as blocker, active, and passive rods according to their effects on the penetration of heat in porous media. 'The interfacial convective heat transfer coefficients for each rod and entire porous medium are calculated and plotted for different Reynolds numbers. A characteristic length based on the microstructure properties of the generated porous media is defined, and three correlations relating to the upper limit, lower limit, and mean of the overall interfacial convective heat transfer coefficient are proposed.Article Citation - WoS: 13Citation - Scopus: 19Effect of Pore To Throat Size Ratio on Interfacial Heat Transfer Coefficient of Porous Media(The American Society of Mechanical Engineers(ASME), 2015) Özgümüş, Türküler; Mobedi, MoghtadaIn this study, the effects of pore to throat size ratio on the interfacial heat transfer coefficient for a periodic porous media containing inline array of rectangular rods are investigated, numerically. The continuity, Navier-Stokes, and energy equations are solved for the representative elementary volume (REV) of the porous media to obtain the microscopic velocity and temperature distributions in the voids between the rods. Based on the obtained microscopic temperature distributions, the interfacial convective heat transfer coefficients and the corresponding Nusselt numbers are computed. The study is performed for pore to throat size ratios between 1.63 and 7.46, porosities from 0.7 to 0.9, and Reynolds numbers between 1 and 100. It is found that in addition to porosity and Reynolds number, the parameter of pore to throat size ratio plays an important role on the heat transfer in porous media. For the low values of pore to throat size ratios (i.e., β = 1.63), Nusselt number increases with porosity while for the high values of pore to throat size ratios (i.e., β = 7.46), the opposite behavior is observed. Based on the obtained numerical results, a correlation for the determination of Nusselt number in terms of porosity, pore to throat size ratio, Reynolds and Prandtl numbers is proposed.Article Citation - WoS: 11Citation - Scopus: 11Comparison of Uniform and Non-Uniform Pressure Approaches Used To Analyze an Adsorption Process in a Closed Type Adsorbent Bed(Springer Verlag, 2013) Gediz İliş, Gamze; Mobedi, Moghtada; Ülkü, SemraHeat and mass transfer in an annular adsorbent bed filled with silica gel particles is numerically analyzed by uniform and non-uniform pressure approaches. The study is performed for silica gel-water pair, particle radius from 0.025 to 1 mm and two bed radii of 10 and 40 mm. For uniform pressure approach, the energy equation for the bed and the mass transfer equation for the particle are solved. For non-uniform pressure approach, the continuity and Darcy equations due to the motion of water vapor in the bed are added, and four coupled partial differential equations are solved. The changes of the adsorbate concentration, pressure, and temperature in the bed throughout the adsorption process for both approaches are obtained and compared. The obtained results showed that the particle size plays an important role on the validity of uniform pressure approach. Due to the interparticle mass transfer resistance, there is a considerable difference between the results of the uniform pressure and non-uniform pressure approaches for the beds with small size of particles such as 0.025 mm.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: 91Citation - Scopus: 108A Heatline Analysis of Natural Convection in a Square Inclined Enclosure Filled With a Cuo Nanofluid Under Non-Uniform Wall Heating Condition(Elsevier Ltd., 2012) Öztop, Hakan Fehmi; Mobedi, Moghtada; Abu-Nada, Eiyad; Pop, IoanHeatline visualization technique is used to understand heat transport path in an inclined non-uniformly heated enclosure filled with water based CuO nanofluid. The cavity has square cross-section and it is non-uniformly heated from a wall and cooled from opposite wall while other walls are adiabatic. The governing equations which are continuity, momentum and energy equations are solved using finite volume method. The dimensionless heatfunction for nanofluid heat flow is defined and solved to determine heatline patterns. Calculations were performed for Rayleigh numbers of 10 3, 10 4 and 10 5, inclination angle of 0°, 30°, 60°and 90°, and nanoparticle fraction of 0, 0.02, 0.04, 0.06, 0.08 and 0.1. It is observed that heat transfer in the cavity increases by adding nanoparticles. The rate of increase is greater for the enclosures with low Rayleigh number. Visualization of heatline is successfully applied to nanoparticle convective flows. Based on the heatline patterns, three heat transfer regions are observed and discussed in details. © 2012 Elsevier Ltd. All rights reserved.Article Citation - WoS: 23Citation - Scopus: 25A Dimensionless Analysis of Heat and Mass Transport in an Adsorber With Thin Fins; Uniform Pressure Approach(Elsevier Ltd., 2011) Gediz İliş, Gamze; Mobedi, Moghtada; Ülkü, SemraA numerical study on heat and mass transfer in an annular adsorbent bed assisted with radial fins for an isobaric adsorption process is performed. A uniform pressure approach is employed to determine the changes of temperature and adsorbate concentration profiles in the adsorbent bed. The governing equations which are heat transfer equation for the adsorbent bed, mass balance equation for the adsorbent particle, and conduction heat transfer equation for the thin fin are non-dimensionalized in order to reduce number of governing parameters. The number of governing parameters is reduced to four as Kutateladze number, thermal diffusivity ratio, dimensionless fin coefficient and dimensionless parameter of Γ which compares mass diffusion in the adsorbent particle to heat transfer through the adsorbent bed. Temperature and adsorbate concentration contours are plotted for different values of defined dimensionless parameters to discuss heat and mass transfer rate in the bed. The average dimensionless temperature and average adsorbate concentration throughout the adsorption process are also presented to compare heat and mass transfer rate of different cases. The values of dimensionless fin coefficient, Γ number and thermal diffusivity ratio are changed from 0.01 to 100, 1 to 10 -5 and 0.01 to 100, respectively; while the values of Kutateladze number are 1 and 100. The obtained results revealed that heat transfer rate in an adsorbent bed can be enhanced by the fin when the values of thermal diffusivity ratio and fin coefficient are low (i.e., α -=0.01, δ=0.01). Furthermore, the use of fin in an adsorbent bed with low values of γ number (i.e. γ=10 -5) does not increase heat transfer rate, significantly.Article Citation - WoS: 12Citation - Scopus: 11A Parametric Study on Isobaric Adsorption Process in a Closed Adsorbent Bed(Elsevier Ltd., 2010) Gediz İliş, Gamze; Mobedi, Moghtada; Ülkü, SemraA numerical study on heat and mass transfer in an annular adsorbent bed filled with adsorbent granules for an isobaric adsorption process is performed. In order to reduce the number of independent parameters that influences heat and mass transfer in the bed, the governing equations and related initial and boundary conditions for the problem are non-dimensionalized and this yields two dimensionless parameters as G and Γ. The G dimensionless parameter is the ratio of heat of adsorption to sensible heat stored by adsorbent particle and Γ parameter compares mass diffusion within the adsorbent particle and heat diffusion in the radial direction of the adsorbent bed. The obtained results show that the total dimensionless time for an adsorption process can be reduced by increasing of Γ value. The total dimensionless time is independent from G for low values of Γ (i.e. Γ=105). The results also show that the instantaneous equilibrium model can provide accurate results only for an adsorbent bed with a low value of Γ (i.e. Γ=105). The present study is performed for Γ values from 105 to 1 and G value from 1 to 100. © 2010 Elsevier Ltd.Article Citation - WoS: 19Citation - Scopus: 18Heat Transfer Reduction Due To a Ceiling-Mounted Barrier in an Enclosure With Natural Convection(Taylor and Francis Ltd., 2011) Gediz İliş, Gamze; Mobedi, Moghtada; Öztop, Hakan FehmiEffects of a ceiling-mounted barrier on natural convection heat transfer in a square cavity with differentially heated wall are numerically investigated. A limit case, in which the partition has small thickness and low thermal conductivity, is studied. The study is performed for nine different locations of barrier on the ceiling, two different lengths of barrier as 15 and 50% of the side wall, and Rayleigh numbers from 103 to 106. The vorticity and streamfunction approach is used to obtain velocity distribution, and the energy equation is solved to determine temperature field in the cavity. The variations of the local Nusselt number on the hot and cold walls and the change of mean Nusselt number with the location of barrier in the cavities with different Rayleigh numbers are presented. The obtained results show that a wall-mounted barrier can be used to reduce heat transfer rate through the cavity; however, its effectiveness depends on length and location of barrier and Rayleigh number.Article Citation - WoS: 357Citation - Scopus: 385Effect of Aspect Ratio on Entropy Generation in a Rectangular Cavity With Differentially Heated Vertical Walls(Elsevier Ltd., 2008) Gediz İliş, Gamze; Mobedi, Moghtada; Sunden, BengtIn the present study, entropy generation in rectangular cavities with the same area but different aspect ratios is numerically investigated. The vertical walls of the cavities are at different constant temperatures while the horizontal walls are adiabatic. Heat transfer between vertical walls occurs by laminar natural convection. Based on the obtained dimensionless velocity and temperature values, the distributions of local entropy generation due to heat transfer and fluid friction, the local Bejan number and local entropy generation number are determined and related maps are plotted. The variation of the total entropy generation and average Bejan number for the whole cavity volume at different aspect ratios for different values of the Rayleigh number and irreversibility distribution ratio are also evaluated. It is found that for a cavity with high value of Rayleigh number (i.e., Ra = 105), the total entropy generation due to fluid friction and total entropy generation number increase with increasing aspect ratio, attain a maximum and then decrease. The present results are compared with reported solutions and excellent agreement is observed. The study is performed for 102 < Ra < 105, 10- 4 < φ{symbol} < 10- 2, and Pr = 0.7.