جستجوی مقالات مرتبط با کلیدواژه "non-newtonian" در نشریات گروه "مکانیک"

In the current investigation, the combined influence of altering the angle of stent branches and the enclosed area within each stent cell on the intravascular flow has been systematically examined using numerical simulations. The finite volume method is adopted to solve the governing flow equations. A uniform flow condition is assumed within the vessel, and the mesh structure utilized employs unstructured tetrahedral elements without a boundary layer, for all stent configurations. The blood is treated as flowing at a consistent velocity, with a developed flow pattern, and the stent is modeled as rigid. A total of 22 stent configurations have been scrutinized. The outcomes indicate that an augmented stent cell area corresponds to elevated shear stress along the vessel wall. Moreover, when the angle of stent branches aligns parallel or perpendicular to the flow direction, there is a decrease in wall shear stress.

In this study, the natural convection in a square cavity filled by two immiscible Newtonian and non-Newtonian liquids heated partially from bottom wall was numerically investigated. The heat source placed on the bottom of a cavity produces a uniform heat flux of q˳". The remaining parts of the bottom wall of the cavity are insulated and the vertical and top walls are kept at cold temperature of TC. The study investigates the effects of relevant parameters such as the Non-Newtonian to Newtonian volume ratio (0≤H≤0.7), the power-law index (n=0.6 and 1.4), Rayleigh number (103 ≤Ra≤106 ) and the Non-Newtonian Prandtl (Pr2=100 and 1000) on flow and temperature fields and the rate of heat transfer. The governing dimensionless equations for the power-law and Newtonian fluids flow, based on properties of Newtonian fluid with Pr1=100, are solved with the numerical finite difference method based on the control volume formulation and SIMPLE algorithm. In order to evaluate the code, its results were compared to another paper in the field of non-Newtonian fluids. Increasing the average Nusselt number for heat source means that the source temperature difference with the cold walls decreases. The results show that increasing the non-Newtonian fluid Prandtl number due to decreasing the thermal conductivity of the non-Newtonian fluid increases the heat source temperature and decreases the average Nusselt number. Also with stronger natural convection in the square enclosure, the average Nusselt number for non-Newtonian fluid increase with decreased power law index.

The common carotid artery is a large vessel which supplies oxygenated blood to the large front of the brain. The artery geometry is extracted from computed tomography angiography images of a healthy 20-year-old volunteer. ANSYS-Fluent commercial software is utilized to simulate the blood transient laminar flow in common, external and internal carotid arteries. In addition to the Newtonian viscosity model, two non-newtonian generalized power law and the modified Casson models have been selected for comparison. The quantitative and qualitative results include the distribution of the low density lipoprotein concentration, the wall shear stress and its fluctuations, and the volume and shape of the recirculation zone. Computations show that the low density lipoprotein Concentration estimated by non-Newtonian models is higher than by the Newtonian model. On the other hand, the carotid bulb and the beginning part of the external carotid artery, contain a large volume of the recirculation flow. Also, the low density lipoprotein particles concentration Comparison between the two modified Casson and Newtonian models in the common carotid artery zone shows the difference of about 12.5 percent. The results of this study show that the vortex region volume and shape are changed during the cardiac period cycle. The findings also reveal that Newtonian and non-Newtonian models present different results in predicting the flow parameters and secondary flow estimation.

One of the most common cardiovascular deseases is stenotic arteries. In this study, blood flow with different models of viscosity in a stenotic artery with the assumption of a wall has been investigated. Stenosis geometry is modeled by cosine relation. for The problem equations including continuity, momentum, energy, Hooke's law for linear elastic material, and the method (ALE) for fluid-solid interaction are defined and solved as finite element code. The results showed that the vessel wall had the most displacement near the stenosis region. Assuming the fluid-solid interaction reduces the wall shear stres. For example, the maximum wall shear stress in the stenotic region decreases from 2.32 to 2.23 with Carreau viscosity and from 2.1 to 2 with Newtonian viscosity. It was also observed that applying heat flux on the outer surface of the vessel wall causes a significant increase in blood flow and the wall temperature in the stenotic region.

The main purpose of this study is to investigate the effect of using an elliptical absorber system with helical ribbed tube on the energy efficiency of linear parabolic collectors. For this purpose, energy efficiency has been measured and presented for different modes, and finally different optimal models are introduced in terms of having the highest energy efficiency, and finally the best model is determined. Based on the obtained results, the highest energy efficiency in different Reynolds is related to the new collector and single-phase model. According to the results of this dissertation, the use of grooved pipe has an effect on increasing the efficiency of the collector. As the number of grooves increases from 1 to 3, the collector efficiency increases. It was also found that the collector efficiency increases with increasing step and slope amplitude. by increasing the groove angle from 10 ° to 50 °, the collector efficiency increases and the maximum value of η is obtained at ° ξ = 60. However, by increasing the groove angle from 50 ° to 60 °, the collector efficiency decreases.

The stresses induced in the rubber by pressure loss and unbalanced velocities at exit is the main factor that affect the swelling of rubber cross-section after exiting the die. In this research, the effect of velocity distribution at the die exit on the rubber dimensions is experimentally and numerically studied with the aid of finite volume method. Three-dimensional simulation of non-Newtonian high-viscosity flow was performed to predict the distribution of velocity and pressure in the die channels. This can eliminates the experimental trial and error procedure for modifying the shape of channels to achieve a uniform velocity distribution and reduction of pressure loss. According to the importance of recognition of the soft and hard materials boundaries in multi-material cross-sections, the two-phase VOF method is employed. A comparison between primary and modified dies shows more precise dimensions of the modified die. The results show that in the narrow portions of the profile in the vicinity of wide regions, because of the impossibility of achieving a uniform velocity distribution, the produced cross-section is smaller than the design value. By the employed numerical method reduces the pressure loss in the modified die by 40% in comparison with that of the primary designed die.

simulation of blood flow in bypass grafts can help medical evaluation. Numerical simulation of blood flow in Configurations recommended by the surgeon Such as the configurations of Y is the aim of this study in order to predict hemodynamic parameters of this configuration in a patient with double stenosis 65 and 50 percent is examined at rest and during exercise. The computational domain was created from CT images from the human cardiac. In this study, blood is assumed homogeneous, non-Newtonian and pulsatile. For real modeling of flow and blood pressure, lumped model is used in outlet at rest and exercise states.The results indicate using this configuration is compensated the pressure drop and flow and time average wall shear stress has reduced in stenosis region and oscillatory shear index and relative residence time range has reduced in area pre and post-stenosis.Y bypass grafting investigation indicates time average wall shear is low at the bifurcation graft and There is possibility of creating restenosis in these areas, but These parameters are in the ideal range at the exercise state.

Numerical simulation of blood flow in Configurations is the aim of this study. In order to predict the best configuration in a patient with double stenosis 65 and 50 percent is examined at rest. The computational domain was created from CT. In this study, blood is assumed homogeneous, non- Newtonian and pulsatile. To consider non-Newtonian effects the Carreau model is used and, a Seven– element lumped model is used in outlet coronary artery and a Three-element Windkessel model is used in outlet aorta. Results of the Comparison between configurations indicate that is TAWSS minimum is less than the critical value 0.4 in the junction in parallel with the host vessel, In bed and the surrounding junction, furthermore OSI maximum is more than critical value 0.1, Because of sharp curvature of graft branch on the vascular graft. The parallel sequential is more prone than cross with respect to fat accumulation and diseases such as intima hyperplasia. The results of this study indicate by doing bypass surgery, sequential parallel and cross can be improve critical values of shear stress in the area of stenosis and it reduced the risk of rupture of plaque fat and moves the heap toward downstream vessels.

Passive micro-mixers have simpler manufacturing in comparison with active micro-mixers and only require energy for flow pumping. In the present study, non-Newtonian fluids and non-Newtonian power-law fluid’s mixing behavior in passive micro-mixers have been studied. Simulation has been performed, using computational fluid dynamics commecrical code of Ansys fluent and two different approaches of two-component mixing have investigated. The first approach studies fluid’s mixing behavior by changing flow behavior index and flow consistency index in 5 different 3D geometries as multiple T-micromixer with aligned and non-aligned inputs in one and two plane, respectively, multiple T-micromixer, double T-micromixer, and T-micromixer, while the second approach studies mixing behavior by changing flow behavior index while flow consistency index is constant in two multiple 3D geometries with non-aligned inputs. In all studies, water was used as Newtonian fluid and carboxymethyl cellulose solution was used as non-Newtonian fluid. The studied range of Reynolds number was 1 to 100. In both approaches, the results for mixing index and pressure drop for power-law index according to criterion are reverse of each other; it means that in the first approach, with increasing power-law index, the mixing index increased and the pressure drop decreased and in second approach, this procedure is reversed. But, procedure of non-dimensional fully developed velocities in two approaches investigated is similar in comparison to geometries with non-aligned inputs.

The purpose of this study is to numerically investigate the heat and mass transfer of magnetic nanoparticles inside a 3D capillary with non-Newtonian blood flow, Under the influence of external non-uniform magnetic field. For this purpose, the governing equations including continuity, momentum, energy, Maxwell, and concentration were coupled and solved by COMSOL, a finite element based software. Blood is assumed as non-Newtonian fluid with Carreau viscosity model and the vessel wall is assumed to be rigid. the results indicate that the concentration of magnetic nanoparticles in the upper wall of the vessel at long times reaches a constant value. This accumulation affects the blood flow temperature. Magnetic field strength, magnetic susceptibility, and concentration of nanoparticles are directly related to the temperature of the bloodstream at the location of particles accumulation. By increasing the size of nanoparticles and inlet velocity, the blood flow temperature decreases so that in sizes above 70 nm, the thermal effect of particles becomes very low. Also, the non-Newtonian blood assumption has significant effect on the results.

Underbalanced drilling and managed pressure drilling with foam have been gained attention of the world oil companies due to its many benefits. The advantages of this method include oil and gas production during drilling, high-speed drilling, drill bit life increase, better cutting transfer and reduced formation damage. In this paper cutting handling by foam was investigated in which foam was assumed to be a homogeneous, single-phase, compressible and non-Newtonian fluid whose rheological properties can be well described by power law model. The assumptions and governing equations of transient two-fluid model were expressed in Euler-Euler coordinate for fluid-particle (foam-cuttings). The upstream method is used to discretizing the equations and the results of the numerical solution are reported in the form of pressure, speed, cutting concentration, quality and density of the foam logs along the well. The impact of back-pressure, ROP, injection rate of gas and liquid, shape and size of cuttings, water influx and oil production on cutting concentration and bottom-hole pressure have been investigated. With increasing parameters such as back-pressure, liquid and gas flow rate, size of the cuttings and ROP, bottom hole pressure and cutting concentration increases. Cutting concentration decreases with increasing liquid and gas flow rate and increases by increasing back-pressure, cutting size and ROP. For validating, the results of the numerical solution are compared with field data obtained from well FR-1 located in the Santa Catarina state of Brazil which show about 16.5 percent errors.