جستجوی مقالات مرتبط با کلیدواژه « Mixing index » در نشریات گروه « مکانیک »

The enhanced specific strength of SiC Particulate Metal Matrix Composites (PMMC) has been the major contributing factor which helps to find applications in the aerospace and automotive industries. Uniform distribution of the particulates in PMMC controls the attainment of better mechanical properties. The most accepted method for producing such a composite is stir casting in which the homogeneity of particulate reinforcement is a significant challenge. This research work proposes a new method for mixing the particulate reinforcement with the liquid and semi-solid aluminium matrix to ensure a uniform mix of the particulates using a gyro shaker. Gyro shaker is a dual rotation mixer commonly used for mixing high viscous fluids. It rotates about two mutually perpendicular axes which help in thoroughly mixing of the ingredients. Developed Computational Fluid Dynamics (CFD) simulation model of the mixing device in finding the mixing performance while mixing SiC particulates with glycerol. The results of the simulation were also validated by experimentation. Analogue fluid simulation of gyro casting was carried out using water and glycerol/water mixture which are having a closer value of viscosity as that of liquid aluminium and semi-solid aluminium. The mixing time obtained in the water system at gyration speeds of 29.63 rpm, 58.18 rpm, 72.73 rpm and 87.27 rpm was 61.84 sec, 43.44 sec, 26.85 sec and 27.24 sec respectively. The mixing time obtained in glycerol/water system at gyration speeds of 58.18 rpm, 87.27 rpm, 116.36 rpm and 145.45 rpm was 26.34 sec, 15.97 sec, 9.8 sec and 6.26 sec respectively. The distribution of the SiC particulates obtained from simulation was compared with stir casting simulations. The homogeneous distribution of particulates was observed in the gyro casting simulation.

Laminar mixing of glycerin in a chaotic mixer is carried by means of the blob deformation method. The mixer was a cylindrical vessel with two rotational blades which move along two different circular paths with a stepwise motion protocol. The flow visualization was performed by marking of the free surface of the flow with a tracer. The effects of controlling parameters such as rotational speed of blades, blades length, and rotational speed amplitude on mixing efficiency and time were analyzed by measuring of the area covered by the tracer. The results revealed that increasing rotational speed intensifies stretching and folding phenomenon, and consequently better mixing can be obtained. Also, the better condition in flow kinematic was provided to blend as stepwise motion protocol with wider amplitude adopted. A reduction in mixing time could be observed as the blades with longer length were used. In addition, it was also found that the promotion of mixing by rotational speed is more effective than that of two other parameters. The quantitative data and qualitative observations proved the potential of proposed chaotic mixer in wide range of industrial processes including chemical reaction and food processing in which laminar mixing is required.

In this study, a numerical investigation was performed on the mixing of non-Newtonian power-law fluids in curved micromixers with power-law indices between 0.49 and 1 and Reynolds numbers between 0.1-300. The properties of water and CMC solution were used for simulation of Newtonian and non-Newtonian fluid flows, respectively. The effects of grooves embedded on the bottom wall of micromixers and geometrical parameters such as depth and angle of grooves on mixing performance were examined. The mixing of nonNewtonian fluids using this kind of micromixers has not been studied before. Eventually, using of inclined grooves with 30° inclination angle was studied. Open source CFD code of OpenFOAM was utilized to simulate the mixing process. The results showed that the grooves caused chaotic advection and improved the mixing performance but had no significant effect on dimensionless pressure drop. Also, the grooves with 30◦ angle showed better mixing index for all values of power-law indices.

Micro and nano-fluidic mixing nowadays is a very important area in research due to its crucial role in new technologies and applications such as biomedical and biochemical synthesis. Due to the low velocities associated with microscale flow, it is often very difficult to mix fluids in a rapid and homogeneous manner. One of the methods of enhancing fluid mixing is to obstruct the fluid flow using vanes or panels known as baffles. In this paper, a Computational Fluid Dynamics (CFD) approach is used to study the effect of baffles on the mixing performance in a passive micromixer. The numerical method is verified by comparing its obtained results with experiments and numerical results published earlier. Rectangular, semi-circular and triangular baffles have been considered for investigating the effects of baffle geometry on mixing performance. Furthermore, the effects of channel inlet angle and baffles offset in mixing performance are studied. As the results show, there is a two-fold increase in mixing performance in the baffled cases as opposed to the simple case.

In recent years, impinging streams have received increasing interest for their high efficiency in heat and mass transfer. This numerical study was conducted to investigate flow and heat transfer characteristics of one-way opposing jets of non-Newtonian fluids. Effects of Reynolds number impinging angle, momentum ratio and flow behavior index on mixing index were evaluated. The results showed improvement of thermal mixing due to an increase in Reynolds number, flow behavior index and momentum ratio in impinging zone. This study also demonstrated that thermal mixing along the channel increased as the Reynolds number and momentum ratio decreased. Nevertheless, augmentation of the flow behavior index resulted in higher thermal mixing along the channel. The impinging angle had no significant effect on thermal mixing along the channel; but, with increasing impinging angle, thermal mixing improved in the impinging zone.