Traditionally Shell-and-tube heat exchangers are designed using correlation based approaches like Kern method and Bell-Delaware method. With the advances in Computational Fluid Dynamics (CFD) software, it is now possible to design small heat exchangers using CFD. In this thesis, shell-and-tube heat exchangers are modeled and numerically analyzed using a commercial finite volume package. The modeled heat exchangers are relatively small, have single shell and tube passes. The leakage effects are not taken into account in the design process. Therefore, there is no leakage from baffle orifices and no gap between baffles and the shell. This study is focused on shell side flow phenomena. First, only shell side is modeled and shell side heat transfer and flow characteristics are analyzed with a series of CFD simulations. Various turbulence models are tried for the first and second order discretization schemes using different mesh densities. CFD predictions of the shell side pressure drop and the heat transfer coefficient are obtained and compared with correlation based method results. After selecting the best modeling approach, the sensitivity of the results to the flow rate, the baffle spacing and baffle cut height are investigated. Then, a simple double pipe heat exchanger is modeled. For the double pipe heat exchanger, both the shell (annulus) side and the tube side are modeled. Last, analyses are performed for a full shell-and-tube heat exchanger model. For that last model, a small laminar educational heat exchanger setup is used. The results are compared with the available experimental results obtained from the setup. Overall, it is observed that the flow and temperature fields obtained from CFD simulations can provide valuable information about the parts of the heat exchanger design that need improvement. The correlation based approaches may indicate the existence of a weakness in design, but CFD simulations can also pin point the source and the location of the weakness.

ABSTRACT SIMULATION OF FLOW TRANSIENTS IN LIQUID PIPELINE SYSTEMS Ko&ccedil / , Gen&ccedil / er M.S., Department of Mechanical Engineering Supervisor: Prof. Dr. O. Cahit Eralp November 2007, 142 pages In liquid pipeline systems, transient flow is the major cause of pipeline damages. Transient flow is a situation where the pressure and flow rate in the pipeline rapidly changes with time. Flow transients are also known as surge and Waterhammer which originates from the hammering sound of the water in the taps or valves. In liquid pipelines, preliminary design parameters are chosen for steady state operations, but a transient check is always necessary. There are various types of transient flow situations such as valve closures, pump trips and flow oscillations. During a transient flow, pressure inside the pipe may increase or decrease in an unexpected way that cannot be foreseen by a steady state analysis. Flow transients should be considered by a complete procedure that simulates possible transient flow scenarios and by the obtained results, precautions should be taken. There are different computational methods that can be used to solve and simulate flow transients in computer environment. All computational methods utilize basic v flow equations which are continuity and momentum equations. These equations are nonlinear differential equations and some mathematical tools are necessary to make these equations linear. In this thesis a computer program is coded that utilizes &ldquo / Method of Characteristics&rdquo / which is a numerical method in solving partial differential equations. In pipeline hydraulics, two partial differential equations, continuity and momentum equations are solved together, in order to obtain the pressure and flow rate values in the pipeline, during transient flow. In this thesis, MATLAB 7.1 is used as the programming language and obtained code is converted to a C# language to be able to integrate the core of the program with a user friendly Graphical User Interface (GUI). The Computer program is verified for different scenarios with the available real pipeline data and results of various reputable agencies. The output of the computer program is the tabulated pressure and flow rate values according to time indexes and graphical representations of these values. There are also prompts for users warning about possible dangerous operation modes of the pipeline components.

In this study, the thermal management system of a notebook computer is investigated by using a commercial finite volume Computational Fluid Dynamics (CFD) software. After taking the computer apart, all dimensions are measured and all major components are modeled as accurately as possible. Heat dissipation values and necessary characteristics of the components are obtained from the manufacturer&#039 / s specifications. The different heat dissipation paths that are utilized in the design are investigated. Two active fans and aluminum heat dissipation plates as well as the heat pipe system are modeled according to their specifications. The first and second order discretization schemes as well as two different mesh densities are investigated as modeling choices. Under different operating powers, adequacy of the existing thermal management system is observed. Average and maximum temperatures of the internal components are reported in the form of tables. Thermal resistance networks for five different operating conditions are obtained from the analysis of the CFD simulation results. Temperature distributions on the top surface of the chassis where the keyboard and touchpad are located are investigated considering the user comfort.

Active flow control by a jet over a 12.5% thick elliptic profile is investigated numerically. Unsteady flowfields are calculated with a Navier Stokes solver. The numerical method is first validated without the jet and with the presence of steady-blowing and pulsating jets. Three jet types, namely steady, pulsating and synthetic jets, are next compared with each other and it is shown that the most drag reduction is achieved by a synthetic jet and the most lift enhancement is achieved by a steady jet. The influences of the jet location, the jet velocity, the jet frequency, the jet slot length and the jet angle on the flowfield is parametrically studied. It is shown that the jet location and the jet velocity are the most effective parameters. The jet parameters are optimized to minimize the drag coefficient while keeping the jet power constant. The drag is reduced by 32.5% for the angle of attack 0 and by 24% for the angle of attack 4.

Francis type turbines are commonly used in hydropower generation. Main components of the turbine are spiral case, stay vanes, guide vanes, turbine runner and the draft tube. The dimensions of these parts are dependent mainly on the design discharge, head and the speed of the rotor of the generators. In this study, a methodology is developed for parametric optimization by incorporating Matlab codes developed and commercial Computational Fluid Dynamics (CFD) codes into the design process. The design process starts with the selection of initial dimensions from experience curves, iterates to improve the overall hydraulic efficiency and obtain the detailed description of the final geometry for manufacturing with complete visualization of the computed flow field. A Francis turbine designed by the procedure developed has been manufactured and installed for energy production.

In this thesis, effects of sonic lateral jets on aerodynamics of missiles and missilelike geometries are investigated numerically by commercial Computational Fluid Dynamics (CFD) software FLUENT. The study consists of two parts. In the first part, two generic missile-like geometries with lateral jets, of which experimental data are available in literature, are analyzed by the software for validation studies. As the result of this study, experimental data and CFD results are in good agreement with each other in spite of some discrepancies. Also a turbulence model study is conducted by one of test models. It is also found out that k-&epsilon / turbulence model is the most suitable model for this kind of problems in terms of accuracy and ease of convergence. In the second part of the thesis, parametric studies are conducted on a generic supersonic missile, NASA TCM, to see the effect of jet parameters on missile and component force and moments in pitch plane. Variable parameters are jet location, jet mass flow rate and angle of attack. As a result, it was found out that downstream influence zone of jet exit is more than the upstream influence zone. Normal force occurring by the interaction of the free stream and jet plume are amplified whenever the jet exit is located between lifting surfaces. Greater pitching moments are obtained when the jet exit moment arm with respect to moment reference center or jet mass flow rate is increased.

In this thesis, a parametric methodology is investigated to design a Pump-Turbine system using Computational Fluid Dynamics ( CFD ). The parts of Pump-Turbine are created parametrically according to the experience curves and theoretical design methods. Then, these parts are modified to obtain 500 kW turbine working as a pump with 28.15 meters head. The final design of Pump-Turbine parts are obtained by adjusting parameters according to the results of the CFD simulations. The designed parts of the Pump-Turbine are spiral case, stay vanes, guide vanes, runner and draft tube. These parts are designed to obtain not only turbine mode properties but also pump mode properties.

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