Phd Degree / Doktora
Permanent URI for this collectionhttps://hdl.handle.net/11147/2869
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Doctoral Thesis An Experimental and Numerical Study on Interfacial Convective Heat Transfer Coefficient and Thermal Dispersion Conductivity of a Periodic Porous Medium Under Mixed Convection Heat Transfer(Izmir Institute of Technology, 2017) Çelik, Hasan; Özkol, Ünver; Mobedi, MoghtadaThe need on effective heat transfer enhancement has been increasing day by day. Because of that, researchers/engineers who work on heat transfer are required to obtain new techniques to address raising accumulation of heat transfer. Heat transfer can be enhanced by active and passive methods and passive methods are mostly chosen, as no external power input is required. Porous media is one of the most popular passive heat transfer techniques. Porous media can be divided into periodic and stochastic structures. In this thesis, the analysis of heat and fluid flow in 2D periodic structure and 3D aluminum and ceramic foam structures under mixed and forced convection heat transfer are studied. The governing equations are solved at pore scale and volume-averaged transport parameters as permeability, inertia coefficient, interfacial heat transfer coefficient and thermal dispersion are obtained by using volume averaging of the obtained pore scale velocity, pressure and temperature. For the change of periodic structure, the interfacial heat transfer coefficient and thermal dispersion with respect to Reynolds, Richardson and porosity under mixed convection are studied probably for the first time in literature. For foam structure, the changes of permeability, inertia coefficient, interfacial heat transfer coefficient and thermal dispersion with respect to Re are discussed. The determination of thermal dispersion by using tomography method is probably reported for the first time. For 2D periodic structures, the interfacial convective heat transfer coefficient successfully found while for the thermal dispersion conductivity the Volume Averaging Technique fails for high Richardson numbers under mixed convection. Based on good agreement between the computational values of this study and reported correlation in literature, it is observed that the use of micro-tomography technique for determination of volume-averaged transport parameters yield satisfactory results if properly used. The comprehensive methods for inspection, verification and validation of the obtained computational results for 3D digitally generated foam are suggested.Doctoral Thesis An Experimental and Numerical Study on Effects of Pore To Throat Size Ratio on Macroscopic Transport Parameters in Porous Media(Izmir Institute of Technology, 2015) Özgümüş, Türküler; Mobedi, Moghtada; Özkol, ÜnverHeat and fluid flow in porous media are frequently encountered in natural and industrial applications, such as oil recovery, water supply management in hydrogeology, ground heat storage, nuclear waste disposals, and ground water flow modeling. Fluid flow and heat transfer analyses in porous media have gained recent attention. The theoretical analysis of heat and fluid flow in porous media is troublesome. That’s why some methods were developed to overcome the difficulties. One of these methods is the macroscopic method in which the solid and fluid phases are combined and the porous media is represented as an imaginary continuum domain. For the application of the macroscopic method onto a porous medium, the macroscopic transport properties such as permeability and thermal dispersion of the corresponding medium should be known. Many parameters such as pore to throat size ratio, porosity, Reynolds number, solid-to-fluid thermal conductivity ratio influence the macroscopic transport parameters. In this study, the fluid flow and heat transfer in porous media are examined numerically to determine the effects of pore to throat size ratio on permeability, interfacial convective heat transfer and thermal dispersion coefficients. The heat and fluid flow in periodic porous media consisting of rectangular rods are investigated. A representative elementary volume is considered and the continuity, Navier-Stokes and energy equations are solved to determine the velocity, pressure and temperature fields in the voids between the rods. It is shown that the pore to throat size ratio is a significant parameter which should be taken into account to suggest a wide applicable correlation. Based on obtained computational results, correlations for determination of Kozeny constant and interfacial heat transfer coefficient in terms of pore to throat size ratio and other related parameters are proposed. An experimental study was conducted to validate the numerical results of the present study. In the experimental part, a porous channel of square rods is used and the permeability and thermal dispersion coefficient are validated with the aid of experimental measurements. A good agreement between the experimental and numerical results is observed.Doctoral Thesis An Experimental and Numerical Study on Heat and Mass Transfer in Adsorbent Bed of an Adsorption Heat Pump(Izmir Institute of Technology, 2012) Gediz İliş, Gamze; Mobedi, MoghtadaBecause of the limited conventional energy sources, the improvement of thermal heat pumps has gained attentions of researchers in recent years. Adsorption heat pump, which is a kind of thermal heat pump, can be directly operated with the low temperature heat sources such as waste heat, geothermal and solar energy. Although, adsorption heat pump has many advantages compared to the conventional heat pump, there are still many difficulties for its practical application. Adsorbent bed is one the most important component of adsorption heat pump. Heat and mass transfer in the adsorbent bed should be accelerated in order to attain a small sized, high powered adsorption heat pump. In this thesis, a theoretical and experimental study is performed on heat and mass transfer in an adsorbent bed. A detailed literature survey on the design of adsorbent bed is done. The designed adsorbent beds are classified, and their advantages and disadvantages are discussed. In order to analyze heat and mass transfer in an adsorbent bed, transport of adsorptive in an adsorbent particle should be well known. A theoretical study on heat and mass transfer in a single adsorbent particle located in an infinite adsorptive medium is performed to understand the effects of internal and external heat and mass transfer resistances. Heat and mass transfer equations for an annular adsorbent bed are derived for uniform and non-uniform pressure approaches and numerically solved to determine temperature and concentration profiles in the bed. These equations are also non-dimensionalized to reduce number of governing parameters. The non-dimensionalization of the equations yields important dimensionless parameters that can be used not only to describe heat and mass transfer in an adsorbent bed but also employ them during design of the bed. Furthermore, an experimental setup was designed and constructed to validate the obtained numerical results. The experimental results were compared with the solution of the numerical results and a good agreement was obtained between them.