Master Degree / Yüksek Lisans Tezleri

Permanent URI for this collectionhttps://hdl.handle.net/11147/3008

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Subject: search.filters.subject.Heat--Transmission

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Now showing 1 - 5 of 5
  • Master Thesis
    Numerical Determination of Permeability and Interfacial Convective Heat Transfer Coefficient for Non-Isotropic and Periodic Dual Scale Porous Medium
    (Izmir Institute of Technology, 2015) Sabet, Safa; Barışık, Murat; Mobedi, Moghtada
    In this study, the fluid flow and heat transfer in a periodic, non-isotropic dual scale porous media consisting of permeable square rods in inline arrangement is analyzed to determine permeability and interfacial convective heat transfer coefficient, numerically. A periodical representative elementary volume (REV) with the dimensions of H×H is chosen as the computational domain. The flow in the REV is assumed fully developed and periodical. The permeable square particles are placed with in-line arrangement. There are two symmetrical intraparticle pores considered here which are in longitudinal flow direction. The continuity, Navier-Stokes and energy equations are solved to obtain the velocity, pressure and temperature distributions in the unit structures of the dual scale porous media. The obtained fields are upscaled by using volume average method to obtain the intrinsic inter and intraparticle permeabilities, bulk permeability tensor, interfacial convective heat transfer coefficients and the corresponding Nusselt numbers of the dual scale porous media for different values of inter and intraparticle porosities. The study is performed for interparticle porosities between 0.4 and 0.75 and for intraparticle porosities range of 0.2 to 0.8. A correlation based on Kozeny-Carman theory in terms of interparticle and intraparticle porosities and permeabilities is proposed to determine the bulk permeability tensor of the dual scale porous media. The intraparticle porosity value increase the flow rate passes through the porous media and the particle becomes more permeable. However; for high interparticle porosity values, the intraparticle porosity does not have importance effect on bulk permeability. Additionally, the results predicts that the interfacial convective heat transfer coefficient increases with increase of Reynolds number and the ratio of intra to interparticle porosity, while the increase rate shows variation with the porosity ratio and Reynolds number values.
  • Master Thesis
    Experimental and Numerical Analysis of Heat Transfer Performance of Off-Set Strip Fins
    (Izmir Institute of Technology, 2009) Durmaz, Gürcan; Özkol, Ünver; Özkol, Ünver
    The aim of this study is to computationally and experimentally investigate the heat transfer and pressure drop characteristics of an offset-strip fin. In the present study, experiments are conducted at the range of Reynolds number from 150 to 3500 and a 3-D numerical domain, which is investigated as a conjugate problem, is created for finite volume computations. The computations are conducted by assuming that the flow in the offset-strip fin channels is steady and laminar at the range of Reynolds numbers from 200 to 5000. In this thesis, the effects of the flow behaviors in the offset strip fin channels on Colbourn j factor, which is the non-dimensional form of heat transfer coefficient, and fanning friction f factor, which is the non-dimensional form of pressure drop, are investigated. Also, the heat transfer boundary conditions and the Prandtl numbers of the fluids are kept different for these fins in order to see the effect of those.The effect of Prandtl number is investigated by using air, 0.707 < Pr < 0.71 and water, 2 < Pr < 4.35 and ethylene glycol, 94 < Pr < 138. The effect of the thermal boundary conditions is investigated by using constant heat flux and uniform temperature. Moreover, all results are compared with Kays and London.s experiments (1964) and also the results of Manglik and Bergles.s correlations (1995). The results show a very good agreement between the results of Kays and London (1964) and of Manglik and Bergles.s correlations (1995). It is also observed that results obtained from the two alternatives for the thermal boundary condition are very close to each other. According to obtained results, it is concluded that our computational results from laminar flow assumption and experiments are reliable at almost all the range of Reynolds numbers studied.
  • Master Thesis
    Conjugate Natural Convection Heat Transfer in a Cavity With Finite Wall Thickness
    (Izmir Institute of Technology, 2009) Hakyemez, Erinç; Mobedi, Moghtada
    The effects of a heat barrier, located in the thick ceiling wall of a square enclosure, on conjugate conduction and natural convection heat transfer are investigated numerically. The analysis is performed by numerical solution of the continuity, unsteady momentum conservation and energy equations with finite difference solution method based on the streamfunction-vorticity formulation. The vertical walls of the enclosure are differentially heated and horizontal walls are adiabatic. A thin heat barrier, having infinite thermal resistance, is located in the ceiling wall at different locations. The calculations are made for different Rayleigh numbers (103 Ra 106), thermal conductivity ratios (1 K 100), dimensionless locations of heat barrier (0<Xh<1) and two dimensionless ceiling wall thicknesses (D . 0.05 and D . 0.20). By using the results of the computer program, streamlines and isotherms are plotted. Heatline visualization technique is used to simulate heat transport and the effect of heat barrier is presented by comparing and plotting heatlines for the cavity and for the solid region with and without heat barrier. The study is performed for air with Prandtl number 0.71. It is found that the effect of heat barrier is more significant in the cavity with high thermal conductivity ratio but low Rayleigh number. There are certain reductions in the average Nusselt number at the vertical walls of the cavity and dimensionless heat transfer rate of the solid region walls for high conductivity ratios, but the reduction in dimensionless heat transfer rate is greater.
  • Master Thesis
    A Study on Mixed Convection Heat Transfer Through a Channel Partially Filled With Porous Medium
    (Izmir Institute of Technology, 2012) Çelik, Hasan; Mobedi, Moghtada
    A study on mixed convection heat transfer in a laminar, fully developed, vertical channel is performed for three different cases: i) clear fluid channel ii) saturated porous medium filled channel iii) partially porous medium filled channel. For the all analyzed cases, motion and heat transfer equations are solved both analytically and numerically. The governing equations are presented both in dimensional and dimensionless forms. The dimensional forms of the governing equations are solved by numerical method while dimensionless equations are solved analytically. The dimensional results, obtained by numerical method, are converted into dimensionless values and compared with dimensionless results of analytical solutions. Good agreement between analytical and numerical results is observed. Based on the obtained results, velocity and temperature profiles are plotted for different values of Gr/Re, Da and porous layer thickness. A detailed discussion is performed on the obtained results. Moreover, heatline functions are obtained and plotted for different values of Gr/Re, Da and Peclet number. It is found that flow reversals in the channel highly depends on Gr/Re value and flow reversals occurs in the channel if Gr/Re exceeds threshold value. It is also found that for low Peclet numbers (i.e., Pe = 0.01), the path of heat flow is independent of Gr/Re and Darcy number. However, for high Peclet numbers (i.e., Pe = 5), the ratio of Gr/Re, Darcy number and thermal conductivity ratio influence heatline patterns, considerably.
  • Master Thesis
    A Mathematical Model of the Human Thermal System
    (Izmir Institute of Technology, 2005) Yıldırım, Eda Didem; Özerdem, Mehmet Barış
    Mathematical model of the human thermal system, which has been greatly developed in recent years, has applications in many areas. It is used to evaluate the environmental conditions in buildings, in car industry, in textile industries, in the aerospace industry, in meteorology, in medicine, and in military applications. In these disciplines, the model can serve for research into human performance, thermal acceptability and temperature sensation, safety limits. Present study investigates the mathematical modeling of the passive part of the human thermal system. The Bio-Heat Equation is derived in order to solve the heat transfer phenomena in the tissue and with environment. It is assumed that the body is exposed to combination of the convection, evaporation and radiation which are taken into account as boundary conditions when solving the Bio-Heat Equation. Finite difference technique is used in order to find out the temperature distribution of human body. The derived equation by numerical method is solved by written software called Bio-Thermal. Bio-Thermal, is used to determine temperature distribution at succeeding time step of the viscera, lung, brain all tissue type of the torso, neck, head, leg, foot, arm, hand, and mean temperature of torso, neck, head, leg, foot, arm, hand. Additionally, for overall body, mean temperature of the bone tissue, muscle tissue, fat tissue, and skin tissue and mean temperature of the total body can be obtained by Bio-Thermal Software. Also, the software is to be capable of demonstrating the sectional view of the various body limbs and full human body. In order to verify the present study, predictions of the present system model are compared with the available experimental data and analytical solution and show good agreement is achieved.