Nanofluids are engineered by suspending nanoparticles with average sizes below 100 nm. The ever increasing thermal loads in such applications require advanced operational fluid characteristics, for example, high thermal conductivity dielectric oils in transformers and car radiators. These fluids require high thermal conduction, as well as electrical insulation. In the present work the thermophysical and rheological properties of the nanofluids such as thermal conductivity, viscosity and density are obtained from molecular dynamics simulations. These results serve as initial data for Computational fluid dynamics simulations to calculate heat transfer coefficient. The results show that, adding titanium oxide nanosheet in the base fluid enhanced the thermal conductivity and increased the viscosity and density of the base fluid. The theoretical calculations confirmed the molecular dynamics simulation results and the simulation methods accuracy. The Computational fluid dynamics results show that increasing the amount of titanium oxide nanosheet in the base fluid increases the heat transfer coefficient and increasing ethylene glycol ratio in base fluid leads to lower heat transfer coefficient. Also, nonequilibirium molecular dynamics method can be used as an effective and accurate method for nanofluids investigation. The coding that is used to obtain the thermal conductivity of nanofluid is a novel and modified type of non-equlibiruim molecular dynamics method. By using this coding the error persentages of simulations is decreased. The other advantage of this code is reducing the simulation process, because the molecular dynamics simulations need a long time for processing.

In this paper, a multi-objective optimization method is implemented by using of genetic algorithm techniques in order to determine optimum configuration of solar chimney power plant. The objective function which is simultaneously considered in the analysis is output power of the plant. Output power of the system is maximized. Design parameters of the considered plant include collector radius (Rc), collector height (Hc), chimney height (Ht), chimney radius (Rt) and heat flux (q”). The multi-objective optimization results show that there are a strong positive correlation between the chimney height and the output power, as well as a negative correlation between the solar collector radius and the output power. Also, it was concluded that, output power of the plant could be considerably increased with increasing solar chimney height while increasing collector radius could slightly reduce output power This study may be useful for the preliminary estimation of power plant performance and the power-regulating strategy option for solar chimney turbines. q

The accuracy of experimental procedure used to calculate the drag coefficient of an Autonomous underwater vehicle (AUV) in a towing tank is investigated using Computational fluid dynamics. Effects of struts, used to connect the AUV model to towing carriage, on the hydrodynamics coefficient of the AUV at various relative submergence depths, at AUV speeds of 1. 5 and 2. 5 m/s are numerically simulated. Various numerical modeling are performed to investigate the effects of free surface with and without presence of struts on the drag coefficient of the AUV. Volume of fluid (VOF) model is used to solve the two phase flow RANS equations. The drag coefficients obtained from two phase flow simulations are compared with those obtained from single phase flow at corresponding velocities. The results obtained from experiments conducted in the towing tank of the Subsea Science and Technology centre, on a full-scale model of the AUV developed in this Centre, agreed well with those obtained by numerical simulations.

In this paper, a numerical modeling of heat transfer and turbulent flow in a solar heater with Delta-Winglet vortex generators is presented. Calculations by the finite volume are conducted using the SIMPLE algorithm.Air turbulent flow with various mass flow rates under the Reynolds number of 5000-22000 was investigated. The (CFD) predictions were compared with the experimental data and good agreement was observed. The results showed that Nusselt number and friction factor in a system fitted with combined rib and delta-winglet vortex generators are higher than those of traditional ribbed systems. In addition, a system fitted with combined ribbed top and bottom walls and vortex generators through the inlet was proposed, and increase in Nusselt number was shown in comparison with previous systems.

Heat treatment furnaces play an important role in refinery and petrochemical systems. The emission of a huge amount of environmental pollutants such as nitrogen oxides (NOx) and carbon dioxide (CO2)، along with the cost of repairs and periodic overhauls have given more attention to the optimization of the furnaces. Flameless combustion as a newly emerging process، with features such as reducing emissions of pollutant gases، uniform distribution of temperature profile along with reducing thermal stresses، and noise pollution in the torch، promising to change the conventional combustion systems and move them toward emission، operational، and maintenance costs reduction. In this study، the burner made by Sholeh-Sanat Company was investigated using the Computational fluid dynamics under pre-heating conditions and oxygen concentrations of 3 and 6%. The furnace performance was considered in steady flameless conditions with eddy-dissipation concept (EDC). Flameless combustion characteristics were obtained in the torch and compared to conventional combustion; moreover، the temperature peaks were eliminated، and the temperature profile became more uniform. Also، in the 6% state، the mass fraction of nitrogen oxides and carbon dioxide compounds were observed to be about 400 and 3000 times decreasing respectively. Working under 3% mode، more uniform temperature profile and less nitrogen oxides were observed.

In order to protect the bank and prevent their erosion spur dike is used. Importance of these structures in the bend is more, because of secondary flows and consequently bank erosion. In this paper the flow pattern around series of vertical spure dikes in the 90° bend is investigated by a 3D RANS solver. In order to simulate the complex behavior of free surface and turbulent flow the volume of fluid method and realizable k-ɛ closure have been used, respectively. Two lengths spure dike (equal to 15 and 25 percent of width), two spacing (3 and 5 three times the length) and two depths (3 and 5cm) in constant discharge 25 lit/s in the mild bend flume with width 0. 7m and depth 0. 12 m has been examined. Comparison among the results with experimental data shows good agreement among them. Also, the results illustrate spure dike deviations maximum velocity to the inner bank in entrance of bend and then deviations to the middle flume. Increasing the length of the spure dikes increases the velocity but it has no effect on the location of the maximum velocity as in all arrangement occurrence in 71 to 81 degree of bend. In the case of shear stress, the maximum value is in the range of 71 to 81˚ .

Introduction: Investigation of the blood flow in the cerebral arteries has important clinical applications. There is a dearth of research on fluid flow in the circle of Willis, analysis of shear stress on the arterial wall, and the effect of hyperelasticity of the arterial wall and fluidstructure interactions in different gravities. This study has practical implications in aerospace medicine. Materials & Methods: In this study, Computational fluid dynamics methods were used to study the blood flow in the cerebral arteries and the stresses on the arterial walls through alternations in gravity. The circle of Willis was introduced as a flexible tube with hyperelastic material properties. The solution of the flow was evaluated using the method of fluidstructure interactions in two gravitational accelerations of zero and 9. 8 m/s2. A total number of 248 computed tomography angiography images were used to design the geometry. The boundary conditions considering the multi-branching and autoregulation were assumed at the inlet and outlet of the arteries. Findings: Regarding the 9. 8 m/s2 gravity, the maximum stress was equal to 3. 9 Pascal. On the other hand, when gravity was neglected, the corresponding value was equal to 6. 5 Pascal. Considering the results of blood flow in 9. 8 m/s2 gravity, the blood pressure in the upper arteries and the circle of Willis was significantly reduced, compared to the blood pressure output from the heart. Discussion & Conclusions: The rate of production of biochemical materials due to a mechanical stimulation had a direct relationship with shear stress. Therefore, it is anticipated that those chemical reactions occurred more in the anterior and posterior communicating arteries. The results of this study can be used in physiological experiments on the astronauts, mechanobiological studies of the cerebral arteries in pathological conditions, and investigations of tissue growth and repair in regenerative medicine.

In this paper, the (CFD)-MBD numerical coupled model has been proposed for an accurate evaluation of the behavior of the partially filled railway tank wagon. The vibration response of the wagon has been obtained by the fourth-order Runge-Kutta method based on the threedimensional multibody dynamic (MBD) model with 19 degrees of freedom comprising car-body, two bogies, and four wheel-sets. The model of transient fluid sloshing inside the tank has been analyzed using the Computational fluid dynamics ((CFD)) method combined with the volume of fluid (VOF) technique for solving the Navier-Stokes equations and tracing the fluid free surface, respectively. Validation of the numerical results has been carried out using experimental data. Then, the simultaneous interaction of the transient fluid slosh and the wagon dynamics has been considered through the development of the numerical process of coupling (CFD) and MBD models. The dynamic characteristics of a partially filled tank wagon have been derived in braking conditions using parametric study on the filled-volume, tank cross-section shape, and fluid viscosity. The results indicate that the filled-volume increase decreases the amplitude of the fluid’ s center of gravity coordinate. The lowest fluid slosh in the different filled-volumes has been related to the modified-oval cross-section. The fluid viscosity has a slight effect on the longitudinal fluid slosh force and the stopping distance of the railway tank wagon.

The numerical study in this paper investigates the effect of inlet and outlet areas of micromixer channels on fluid flow behavior and mass transfer performance. The ratio of the outlet to the junction area is varied from 0. 6−, 2 while the ratio of the inlet to junction area is from 0. 6−, 1. 4. The flow patterns obtained for various mixers indicate that vortices or recirculation zones are created as the two fluids turn and enter the outlet channel. The formation of recirculation regions results in enhanced mixing rates. The micromixers are evaluated in terms of mixing quality, pressure drop, and mixing effectiveness parameters. The mixing quality increases up to 10 times when the outlet area ratio increases from 0. 6 to 2. The rise in pressure drop due to the increased outlet area is about 50%. The inlet area also influences the mixing rate and pressure drop. The mixing quality first increases and then decreases with an increase in area. The pressure drop, whereas, continuously decreases when the inlet area ratio increases from 0. 6 to 1. 4. Suitable dimensions of micromixers are suggested based on mixing effectiveness. A mixer device with an outlet/junction area ratio of 1. 2 and an inlet/junction area ratio 0. 8−, 1 is found to provide better performance.

Despite numerous studies of shell and helically coiled tube heat exchangers, a few investigations on the heat transfer and flow characteristic consider the geometrical effects like coil pitch. Moreover, this scarcity is highlighted for the shell side of this type of heat exchangers. This study reports experimental and Computational fluid dynamics ((CFD)) investigations on heat transfer and flow characteristics of a shell and helically coiled tube heat exchanger. The experiments were carried out using a helically coiled tube, which was placed in a cylindrical shell. Hot and cold water were used as the process fluids on the tube and shell side, respectively. The (CFD) modeling technique was employed to describe the experimental results, fluid flow pattern, and temperature profiles as well as dead zones in the heat exchanger. Quantitative predicted results of (CFD) modeling show a good agreement with the experimental data for temperature. The effect of the coil pitch on heat transfer rate was numerically studied and it was found that the heat transfer coefficient intensifies with an increase in coil pitch. The average turbulent kinetic energy (k) for the old coil tube and twice coil pitch heat exchanger was computed as 2.9×10-3 and 3.3×10-3 m2/s2, respectively. This indicates an increase of about 14% in flow turbulent kinetic energy. Nusselt numbers were compared with those estimated using published correlation and a mean relative error (MRE) of 14.5% was found between the experimental and predicted data. However, a good agreement was obtained in lower shell Reynolds numbers (lower than Re=200).