Vane induced two phase flow mixing

Micromixers are used for mixing of multiphase fluids in microchannels. Passive micromixers help in mixing of fluids by having a designed periphery in their structure. In the current study, a Y micro-channel section of 25 mm length with an inlet diameter of 2 mm is considered. Vane shaped micromixers are placed inside the channel to mix fluids of two different concentrations. The vanes are positioned at specific places inside the channel to enhance mixing in the stratified flow stream. The presence of vanes during the flow induces mixing of the stratified fluids without requiring additional components. The study is carried out using COMSOL Multiphysics. The mixing index increases with increase in the number of vanes and no considerable change in velocity is observed downstream of the last vane. Further, when the thickness of the vane is increased, it is found that the mixing index also increases.

Numerical analysis of non-aligned inputs M-type micromixers with different shaped obstacles for biomedical applications

Fluid mixing in lab-on-a-chip devices at laminar flow conditions result in a low mixing index. The reason is dominant diffusion over the convection process. The mixing index can be improved by certain changes in the micromixer structural design like introducing obstacles in the path of fluid flow. These obstacles will make dominant the advection process over the diffusion process. The main contribution of this work is based on proposing the novel hybrid type micromixer design for enhancing the mixing quality. Three non-aligned M-type and non-aligned M-type with obstacles passive type micromixers are analyzed by COMSOL5.5. These designs are hybrid types because different structural changes are combined in a single design for mixing improvement. First of all the straight non-aligned inlets, M-type passive micromixer (SMTM) is analyzed. It is observed that mixing performance is improved because of M-shaped mixing units and non-aligned inlets. This improvement is deemed to be not enough so different shaped obstacles are introduced in the micromixer design. These designs based on obstacles are named horizontal rectangular M-type micromixer, square M-type micromixer, and vertical rectangular M-type micromixer. The mixing index for SMTM, square M-type micromixer, horizontal rectangular M-type micromixer, and vertical rectangular M-type micromixer at Reynolds number Re = 60 is respectively given by 71.1%, 83.21%, 84.45%, and 89.99%. The mixing index of vertical rectangular M-type micromixer was 59.34% − 87.65% for Re = 0.5–100. Vertical rectangular M-type micromixer is concluded with the better-mixing capability design among the proposed ones. Based on these simulation results, the vertical rectangular M-type micromixer design can be utilized for mixing purposes in biomedical applications like nanoparticle synthesis and biomedical sample preparation for drug delivery.

Numerical study of mixing index in offset inlets 3-D T mixer with bend shape mixing channel

The objective of this paper is the computational analysis on the mixing index of simple T shape mixer, offset inlets T shape mixer, and offset inlets T mixer with bend shape mixing channel by CFD simulation. Computational fluid dynamics software package solves conservation of mass equation, conservation of momentum equation, and conservation of energy equation. In the case of offset inlets T shape mixer, as the aspect ratio (height to width ratio) of mixing channel increased so mixing quality also increased and offset inlets T mixer with bend shape is a combination of increased aspect ratio as well as chaotic advection mechanisms, so it provides advanced mixing index than offset inlets T shape mixer and simple T shape mixer. Pressure fall in offset inlets T shape mixer is excess than simple T shape mixer but narrowly degraded than offset inlets T mixer with bend shape. Chaotic advection rooted microchannel generates secondary flow because of which motives a high-pressure drop in the microchannel.

Optimization of slanted grooved micromixer with a serpentine channel at a lower Reynolds number

In Lab-On-Chip (LOC) applications, micromixing is the most important step to obtain fast analytical response in many biochemical and biological detections. Design and realization of smaller and shorter mixers with higher efficiency has become a necessity more than a recommendation. In this work, a numerical optimization of a passive mixer with a serpentine-shaped channel is proposed. By considering a laminar flow regime, the continuity and momentum equations, along with the advection-diffusion equation, are solved to evaluate the mixing performance. The optimization of the slanted grooves micromixer with a serpentine channel is achieved using computational fluid dynamics (CFD) and response surface methodology (RSM) based on Box-Behnken design. This method is used to find a second-order polynomial regression model and to obtain the optimal groove design. The considered objective function is the mixing index, while the four design variables are: the number of grooves per half cycle (N), the groove angle (θ), the groove depth to channel height ratio (d/h) and the ratio of groove width to channel width (Wd/W). The optimization results indicate that the highest values of each selected interval of the groove depth to channel height ratio (d/h) and the angle between the radius and the groove (θ), on the other hand, the ratio of groove width to channel width (Wd/W) of about 0.45 are desirable to promote faster mixing. The Flow behaviour in optimized “slanted grooves mixer (SGM) with serpentine channel was tested for low Reynolds number Re ranging between 0.3 and 5, and the results have shown that in the range of Re from 0.3 to 0.7 the mixing index is greater than 85%, for large range of Re from 1 to 4.5, the mixing index reaches the value of 93% in the first cycle of the channel and it approaches 100% for channel length of 1.25 mm from the inlet of the channel. Thus the most important result of this work shows that higher efficiency is obtained for short distance and the required pressure drops decreases. This micromixer can be selected as a good candidate in applications that require a high degree of mixing with relatively small length mixing as polymerase chain reaction (PCR) in the analysis and extraction of DNA.

Rapid Microfluidic Mixing Method Based on Droplet Rotation Due to PDMS Deformation

Droplet-based micromixers have shown great prospects in chemical synthesis, pharmacology, biologics, and diagnostics. When compared with the active method, passive micromixer is widely used because it relies on the droplet movement in the microchannel without extra energy, which is more concise and easier to operate. Here we present a droplet rotation-based microfluidic mixer that allows rapid mixing within individual droplets efficiently. PDMS deformation is used to construct subsidence on the roof of the microchannel, which can deviate the trajectory of droplets. Thus, the droplet shows a rotation behavior due to the non-uniform distribution of the flow field, which can introduce turbulence and induce cross-flow enhancing 3D mixing inside the droplet, achieving rapid and homogenous fluid mixing. In order to evaluate the performance of the droplet rotation-based microfluidic mixer, droplets with highly viscous fluid (60% w/w PEGDA solution) were generated, half of which was seeded with fluorescent dye for imaging. Mixing efficiency was quantified using the mixing index (MI), which shows as high as 92% mixing index was achieved within 12 mm traveling. Here in this work, it has been demonstrated that the microfluidic mixing method based on the droplet rotation has shown the advantages of low-cost, easy to operate, and high mixing efficiency. It is expected to find wide applications in the field of pharmaceutics, chemical synthesis, and biologics.

Analysis of the effect of stirrer and container rotation direction on mixing index (Ip)

The paper discusses the effect of the stirrer and container rotation direction on the mixing index (Ip). The chaos theory is the result of an in-depth study of various problems that cannot be answered by the two previous major theories, namely quantum mechanics and the theory of relativity. Effective mixing of the flow area does not depend on rapid stirring. This study uses a container with a double stirrer, camera, programmable logic controller, tachometer, 6 A adapter, and a computer. DC electric motor (25 V) for turning stirrers and housings. The diameter of the primary and secondary stirrers is Dp=38 mm and Ds=17 mm. The diameter of the container made of transparent plastic is Dw=160 mm and height is 170 mm. Primary stirrer rotation (np)=10 rpm, secondary stirrer rotation (ns)=22.3 rpm, and container rotation (nw)=13 rpm, the angular velocity of the container is Ww=360° while the angular speed of the primary stirrer is Wp=180°. The liquid consists of a mixture of water and paint (white). For dye, a mixture of water and paint (red) is used. For testing the Brookfield viscometer, the viscosity of the liquid and dye is used. The results showed that turning the stirrer in the opposite direction to the container, there will be stretching, bending, and folding around the stirrer, and the smallest mixing index was P2V-b (0.94). In addition, based on the mixing index value above, the highest mixing effectiveness level is obtained, namely: P2V-b, P2S-b, P2B-b, P2V-a, P2B-a, and finally P2S-a. The mixing index is inversely related to the effectiveness level. So the highest effectiveness level is given by the following treatment: 1. Variation rotation (between opposite rotating mixers), 2. Opposite rotation (stirrer rotation opposite direction to the container), 3. Unidirectional rotation (stirrer rotation in the direction of the container)

Effect of Thermal Energy and Ultrasonication on Mixing Efficiency in Passive Micromixers

Micromixing is a key process in microfluidics technology. However, rapid and efficient fluid mixing is difficult to achieve inside the microchannels due to unfavourable laminar flow. Active micromixers employing ultrasound and thermal energy are effective in enhancing the micromixing process; however, integration of these energy sources within the devices is a non-trivial task. In this study, ultrasound and thermal energy have been extraneously applied at the upstream of the micromixer to significantly reduce fabrication complexity. A novel Dean micromixer was laser-fabricated to passively increase mixing performance and compared with T- and Y-micromixers at Reynolds numbers between 5 to 100. The micromixers had a relatively higher mixing index at lower Reynolds number, attributed to higher residence time. Dean micromixer exhibits higher mixing performance (about 27% better) than T- and Y-micromixers for 40 ≤ Re ≤ 100. Influence of ultrasound and heat on mixing is more significant at 5 ≤ Re ≤ 20 due to the prolonged mechanical effects. It can be observed that mixing index increases by about 6% to 10% once the temperature of the sonicated fluids increases from 30 °C to 60 °C. The proposed method is potentially useful as direct contact of the inductive energy sources may cause unwanted substrate damage and structural deformation especially for applications in biological analysis and chemical synthesis.

Mixing of Particles in a Rotating Drum with Inclined Axis of Rotation

Various experimental and numerical studies have been carried out to study the mixing processes inside rotating drums with a horizontal axis of rotation in the past, but little effort has been made to investigate the rotating drums with an inclined axis of rotation, though such inclined drums exist in industrial waste management, food processing, power and pharmaceutical industries. To fill this gap, in this work, the discrete element method was used to study the mixing phenomena of a rotating drum for different angles of inclination from 0° to 15°. It was found that for inclined rotating drums, the whole bed Lacey mixing index is higher than that for the horizontal drum by 7.2% when the angle of inclination is 10°. The mixing index is related to the area ratio of the active region to the whole bed and volumetric fill. Increase in volumetric fill would lead to the decrease of the mixing index. The mixing index and area ratio exhibit similar patterns along the length of the drum for different angles of inclination.

On effects of shape, aspect ratio and position of obstacle on the mixing enhancement in micromixer with hexagonal-shaped chambers

The micromixer geometry presented consists of T-type micromixer with premixing chamber, hexagonal shaped chambers and obstacles. In order to observe influences of obstacle shape, aspect ratio and position, simulations are carried out for two types of obstacle shapes viz. rectangular and triangular for the Reynold number in the range from 0.1 to 75. Flow and mixing dynamics are studied to investigate the effect of geometric modifications for identifying the mixing mechanisms. The effect of obstacle shape, aspect ratio and position is investigated using the performance characteristics viz. mixing index and pressure drop quantitatively. Both the micromixers demonstrate different mixing mechanisms, including transverse flow, vortices and chaotic advection due to split and recombination action. The mixing performance is diffusion dominated below Re < 5 and it is advection dominated beyond Re > 5. At Re ≥ 20, the mixing index observed is 0.80 in all the micromixer design configurations.