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Multiphysics Modeling of Surface Charge and Pressure-Driven Electrokinetic Flow in Micro/Nano Scale Porous Media
(Izmir Institute of Technology, 2021) Şen, Tümcan; Barışık, Murat
Accurate characterization of fluid transport in micro/nano confinements is essential for numerous applications from industrial, agricultural, and medical sciences. In these applications, electrokinetic interactions dominate the fluid behavior, which causes conventional fluid dynamics to become incomplete. Specifically, near-wall hydrodynamics and liquid/solid coupling at the interface varies by electrokinetic effects. Therefore, the current study focuses on characterization of the fluid transport at various porous systems and ionic conditions. The Poisson-Nernst-Planck (PNP) equations were numerically solved coupled with the Navier-Stokes (NS) equations. Charge regulation (CR) boundary condition is employed to calculate the charging behavior of the surfaces. First, the surface charging of nano-scale systems was analyzed by considering the electric double layer (EDL) overlap and inlet/outlet effects. While EDL overlap decreased the surface charge, inlet/outlet effects presented an opposite behavior. Then, transport is characterized by calculating the hydraulic conductivity from Darcy's law under electrokinetic and boundary slip effects. The results showed that electrokinetic effects decrease the hydraulic conductivity with increasing concentrations and decreasing confinement sizes. At slipping condition with a constant slip length applied, velocity slip developing on surface showed strong dependence on porosity and ionic conditions. For low porosities and high concentrations almost no-slip conditions were observed even at high slip lengths. Results showed that the transport in micro/nano-scale porous systems is dominated by electrokinetic interactions depending on porous system parameters and ionic conditions.
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, Moghtada
Because 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.

Phd Degree / Doktora

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