In this study, flow simulation has been carried out based on lattice Boltzmann method by using finite element to observe the influence of the Reynolds number and expansion ratio on the vortex characteristics that generated near bottom of the channel. For this purpose, the Numerical simulation of both developing and developed fluid flow through a channel with constant width, as well as the fluid flow in cavity and channel with backward facing step has been simulated by means of the finite element Lattice Boltzmann method. Macroscopic flow variables such as velocity fields, streamlines and the reattachment point In different Reynolds numbers and expansion ratios were calculated and compared with reported values by other researchers. The results of this study shows that finite element Lattice Boltzmann method is efficient in analyzing fluid flow with different geometries and is very well suited to the results of other numerical methods. As a general conclusion, it can be stated that with the increase of the Reynolds numbers, the reattachment point due to increased inertia effect of the fluid is transferred to the downstream of the stream, and by increasing the expansion coefficient the reattachment point is transferred to the downstream of the stream, also the method used in this study has a significant ability in simulating behavior of the flow in the backward facing step channel and is more optimal due to the simplicity and the need for coarser meshes compared to the current Lattice Boltzmann method.

 In this thesis, the laminar fluid flow of homogeneous water/Al2O3 in a horizontal tube is simulated by the axisymmetric Lattice Boltzmann method to study the flow and the forced convection heat transfer. The velocity and temperature at the inlet is uniform, the duct walls are on the constant heat flux condition and At the exit, fully developed condition for velocity and temperature has been used. By examining the results, it was found that the increase of the volume fraction of the nanofluid does not affect the hydrodynamic parameters of the flow, such as the velocity distribution and the surface friction coefficient. Nanofluid have beter heat transfer performance rather than base fluid and enhancement increases with increase of nanoparticle concentration .Comparison of performance of nanofluid through channel with two different inlet temperature shows that there is a higher increase in convection heat transfer coefficient and Nusselt number in lower inlet temperature for the same condition in laminar flows. Also, with increasing Reynolds number, the percentage of improvement of the forced convection heat transfer coefficient and Nusselt number has increased

Energy and exergy analyzing of a gasoline direct injection combustion engines (GDI) are investigated in this thesis. A two zone model has been applied to simulating engine combustion. Temperature, pressure and other relation parameters within the cylinder of engine have been computed by the first law of thermodynamics. For validation, the modeled data were compared to the availible experimental data of Design, Research and Production of automobile engines company (IPCO) and good agreement was achived. By development of second law, some of parameters like exergy of transferring work, heat transfer exergy, and efficiency of second law of thermodynamics were calculated. Results of this study showed that, less fuel consumption, less acceptable production NOx emissions were achived by a gasoline direct engine compare to port fuel injection gasoline engine. In addition, first and second law efficiency of the GDI engine are higher than the port fuel injection gasoline engine for the same engine. The Alfa Romeo 159 2.2 lit JTS 2005 GDI engine has been analysis for the modeling. High output torque, low fuel consumption and emissions of this engine, besides the ability to use different fuel are reasons of this selection

 In Venturi channel Flow (Nuzzle-Diffuser), sometimes there occurs Cavitation phenomenon. In addition to complicating the flow, Cavitation indicates that analysis of the flow requires the use of high accuracy numerical methods. For this purpose in present study, Lattice Boltzmann method with Large Eddy turbulence model (LES-LB) was used. Also to simulate the formation and movement of Cavitation bubbles in the flow (two-phase flow), Shan-Chen two-phase Method was used. In order to Validate the numerical code, Laplace, bubble relaxiation and phases separation tests were solved and the results were compared with values reported in the literature. Therefore the lattice Boltzmann Method was applied to solve the stable two-dimensional incompressible cavitation flow through a venturi and the obtained results of the simulation are compared with results of experiments and classical CFD methods. Finally, the results showed good accuracy of Lattice Boltzmann method in numerical simulation of cavitation in venturi. In addition, time-averaged velocity profile and void ratio of the fluid in the throat from this research have a good agreement with the experimental results in the literature.

<p style="text-align: left;">Free convection heat transfer of nanofluids in a two-dimensional square enclosure and right triangular enclosure is investigated by lattice boltzmann method numerically. In square enclosure, the horizontal walls are adiabatic and the vertical walls are at specified isothermal temperature and in triangular enclosure, the right wall and bottom wall are at isothermal temperature and incline wall is adiabatic. Nanofluid in the cavity is incompressible, boussinesq and has particles with same diameter and homogenous distribution with no chemical reaction between them. The fluid flow is assumed to be steady and two-dimensional. Isotherms, streamlines and average Nusselt numbers have been scrutinized for different values of Rayleigh numbers and volume fraction of nanoparticles. The results show that lattice boltzmann method is Efficient at Simulation natural convection heat transfer of nanofluids with using different geometries. Further, with using nanofluids in enclosures, higher natural heat transfer is formed.</p>

 Two-dimentional incompressible turbulent flow in a porous medium was simulated. The porous media is selected as a periodic array of square sylinders. Lattice Boltzman method with Multiple-Relaxation-Time was used to solve the flow-field. Large-Eddy-Simulation method with Smagorinsky subgrid model has been used to modeling turbulence. The Reynolds number varried from 1,000 to 100,000 and different values of porosities are considered in the calculations. In order to validate numerical code written, Laminar flow within a square cavity and the porous media were solved, and the results were compared with reported values in the literature. At the end, the results of simulations of turbulent flow were compared with those presented by other researchers and it was noted that these results are in good agreement with the results of other numerical methods. The macroscopic pressure gradients for all considered porosities are in good agreement with Ergun’s equation in the range of large Reynolds numbers and the maximum calculated relative error is less than 20 percent.

In recent decades, optimizing the performance of engine is subjected in many researchers in this field. Availability analysis is used as as an effective tool to identify inefficiencies in energy conversion systems and move towards optimizing performance. In present investigation, a computer program of the Single-zone combustion model was written in order to determine fuel heat release. After the validation results obtained, the governing equations of availability analysis are applied to the result program. Also, in this thesis the possible application of biodiesel obtained from sunflower oil in a diesel engine (MT4-244), Thermodynamically-mathematical simulation is investigated. The different parts of exergy were compared to pure diesel fuel and biodiesel according crank angle, individually, The effect of biodiesel on the Irreversibility and first and second laws of thermodynamics efficiency (energy and exergy) were investigated. The results showed that, Pure biodiesel combustion is done as improper, Consequently, the energy and exergy efficiencies, respectively 2.72 and 2.61 percent decrease. On the other, because of the clean-burningbiodiesel,CO is decreased. Then, Optimal equivalence ratio for Reducing of emissions, Improvement performance variables and Evaluation of various parts of the exergy, Was determined, The amount for diesel fuel is 0.75, and for biodiesel is 0.7. The results showed that, changing the equivalence ratio, engine efficiency were optimized with biodiesel and It reaches a value close to diesel efficiency.The optimal equivalence ratio, energy and exergy efficiency increases, exergy exhaust gases from the cylinder for diesel and biodiesel fuel becomes less and greater percentage of the fuel exergy is converted to useful work.

In this study, heat transfer in porous media is modeled. The solution of microscopic equations in porous media are very difficult. A periodic array of square or circular cylinders are used instead of complicated geometry following a systematic analysis of several porous media modeled by different unit-cell geometry. As such, just one unit-cell, together with periodic boundary conditions for mass, momentum and energy equations, was used to represent the medium. The numerical methodology herein employed is based on the control-volume.
In this study a periodic array of cylinders with every surface area that a macroscopic flow with macroscopic gradient temperature in the same direction of flow or transversal of it is assumed. After solution of velocity field and macroscopic temperature on unit cell, the passive terms such as thermal dispersion and tortuosity after volume-average on energy equation, that is found from direct solution.
So this results are compared with other person’s results and showed a good agreement. When the passive terms of macroscopic energy equation are found so this equation is solved on 10 continue cell and compared with microscopic results.