Study and Development of New Passive Micromixers Based on Split and Recombination Principle

Micromixers have been a major topic of research in the past decade and progress on recent development of micromixers has been reviewed by many researchers. Developing devices for microfluidic technology has been a major concern for industry and microfluidic devices offer many advantages over conventional techniques. Compared to conventional macroscopic methods, microfluidic devices have the advantages of reduced solvent, reagent and cell consumption, shorter reaction times, portability, low cost and low power consumption. Also, micromixers are key elements in microfluidic technology and have been addressed by a large body of research. Interestingly, the historical development of microfluidics and its preoccupation with micromixing are the main fields of microtechnology. Micromixers have a wide variety of potential applications in industry. In modern technology, micromixers are applied in microtechnologies such as biological systems, as microreactors for chemical reactions, and as MEMS and lab-on-a-chip devices. This means that the community of engineers and scientist now engaged in microfluidic devices and also mixing process in micro scales. Indeed, they have entered the field from a variety of different backgrounds and they would have been confronted by the problems of mixing processing and mass transport at the micro scales. According to the survey carried out in my research, the main driving forces for this investigation are applications in incompressible mixing processing at low Reynolds number range, 0.08<Re<4.16. As far as we know, the technology and science of microfluidics cover a wide spectrum ranging from fundamental studies to real applications in laboratories and industries. This research focuses on an important subject of microfluidics, namely mixing processing at the microscale. The science of such mixing has carried out on newly fabricated micro scale devices on an extensive collection of established knowledge. Due to its applied nature, my research discuss practical outcome in the design and characterization of micromixers. In this thesis, first and foremost, I describe the method that I've used for analyzing the experimental data. The laminar flow regime (0.08<Re<4.16) was considered during tests and image-based techniques are used to evaluate mixing efficiency. This study propose a novel generation of 3D splitting and recombination passive micromixers. Mixing characteristics of two species are elucidated via experimental and numerical studies associated with microchannels with various inlet flow rates (velocities) and results compared with the previous well-known micromixers. It was found that mixing performance is significantly affected by the split and recombination (SAR) flows and depends on Reynolds number (inlet velocities). As well as the efficiencies of my proposed mixer are almost quite the same with the well-known basic mixers at each desired region, the required pressure drop is approximately two times less than previous mixers. This is a good particular result that with higher efficiency the required pressure drop decreases. Hence, this new geometries satisfies both of targets in micromixer design which are higher mixing efficiency and lower pressure drop in comparison with previous well-known mixers. These results open the new operating windows for rapid mixing in the microchannel to overcome the fluid mixing which strongly limited to laminar regime with lower required pressure dro

A novel generation of 3D SAR-based passive micromixer: efficient mixing and low pressure drop at low Reynolds number

Abstract This study introduces a novel generation of 3D splitting and recombination (SAR) passive micromixer with microstructures placed on the top and bottom floors of microchannels called a ‘chain mixer’. Both experimental verification and numerical analysis of the flow structure of this type of passive micromixer have been performed to evaluate the mixing performance and pressure drop of the microchannel, respectively. We propose here two types of chain mixer—chain 1 and chain 2—and compare their mixing performance and pressure drop with other micromixers, T-, O- and tear-drop micromixers. Experimental tests carried out in the laminar flow regime with a low Reynolds number range, 0.083 Re 4.166, and image-based techniques are used to evaluate the mixing efficiency. Also, the computational fluid dynamics code, ANSYS FLUENT-13.0 has been used to analyze the flow and pressure drop in the microchannel. Experimental results show that the chain and tear-drop mixer’s efficiency is very high because of the SAR process: specifically, an efficiency of up to 98% can be achieved at the tested Reynolds number. The results also show that chain mixers have a lower required pressure drop in comparison with a tear-drop micromixer

Numerical investigation on heat transfer enhancement inside a rectangular microchannel with vortex generator using TiO2, Cuo-water nanofluids

One of the innovative ways to improve heat transfer properties of heat exchangers, is using nanofluids instead of traditional fluids. Due to presence of metal and oxides of metal particles in nanofluids structure, they have better potential in different environments and conditions than conventional fluids and having higher thermal conductivity causes improvements in heat transfer properties. In this research flow of two different nanofluids through a rectangular microchannel consisting of different number of longitudinal vortex generators (lvgs), has been investigated. Simulations conducted under laminar flow boundary condition and for different Reynolds numbers from 100 to 250. Considered volumetric concentration in this paper is 1, 1/6 and 2/3 %. Results showed, nanofluids and the LVGs remarkably enhance the heat transfer rates inside the microchannel. havg improved with increasing the nanoparticles volume concentrations and Reynolds number, whereas the opposite trends observed for pressure drop. havg improved for 4 to 12 and 9 to 18% for TiO2 and CuO nanofluids, respectively for different volume concentrations in simple microchannel. For lvg-enhanced microchannel the amount of improvements is about 9-14 and 5-10% for CuO and TiO2, respectively. Also using vortex generators alone improved havg for 15-25% for different number of lvgs

experimental investigation of split and recombination micromixer in confront with basic t and o type micromixers

The paper presents an experimental comparison of three types of static micromixer. Efficiencies of a split and recombination micromixer (SAR) based on plate symmetrical modules (PSM) and basic T-type and O-type mixers are examined. Experimental tests were carried out in the laminar flow regime with a low Reynolds number range, 0.083 ≤ Re ≤ 4.166 and image-based techniques were used to evaluate mixing efficiency. Experimental results illustrate that the micromixers with splitting and recombination have outstanding mixing efficiency than those of without SAR process. Indeed split and recombine (SAR) structures of the flow channels result in the reduction of the diffusion distance of two fluids and optimize the diffusion process and after a short distance from inlet high mixing efficiency can be achieved. Also, experimental data show that the SAR PSM mixer is up to 99% efficient, and that efficiency reaches 90% in a short distance, demonstrating this type of mixer's high mixing performance and the effect of splitting and recombination on the degree of mixing and the efficiency of the micromixer.Both of the T- and O-type micromixers are designed and fabricated from plexiglas using a computer milling process

Investigation on the Effect of Length and Amplitude of Sinusoidal Wavy Vortex Generators on the Heat Transfer Rate, Pressure Drop, and London Factor in Compact Heat Exchangers: the effect of length and amplitude of sinusoidal wavy vortex generators in compact heat exchangers

Compact heat exchangers (CHE) improve the heat transfer rate with lighter weight and lower volume than other counterparts. An important point in CHEs is their higher pressure drop relative to conventional heat exchangers. This study aims to investigate the heat transfer rate and pressure drop in some proposed models of these heat exchangers with/without vortex generators (VGs) in different cases. A hot fluid of temperature 350°C flowing through tubes and a cold fluid of temperature 300°C circulating inside the shell are assumed. To this end, several VGs with sinusoidal wavy shapes are designed and examined with different amplitudes of the sine wave and different lengths to determine the effects of these parameters on the heat transfer rate of tubes and pressure drop along the heat exchanger length. In the 2D steady-state laminar fluid flow, governing equations are discretized using the finite element method and analyzed for Reynolds numbers 400 to 1000 in the ANSYS software. Finally, with a 5.06% increase in the Nusselt number, the sinusoidal VGs of amplitude 1 and length 6 mm quantitatively indicated the best performance in terms of the heat transfer rate and pressure drop (London factor) among the studied cases

Experimental comparative mixing performance of passive micromixers with H-shaped sub-channels

This paper presents a new type of passive microfluidicmixer called the ‘‘H-micromixer''.This type of passive micromixeris based on the splitting and recombination (SAR)process, meaning that the two fluids to be mixed are split and recombined to optimized the diffusion process.The paperalso describes an experimental investigation of the mixing process in three different geometries:T-micromixer,O-micromixer and H-micromixer. The laminar flowregime(0.08<Re<4.16)was considered during tests and image-based techniques were used to evaluate mixing efficiency.At all tested flowrates, experimental data show that the H-micromixer is more efficient than the other tested microdevices.The H-micromixer's efficiency is very high due to the SAR process: specifically,efficiency up to 98%can beachieved at Re=0.08

Nanofluid heat transfer between two pipes considering Brownian motion using AGM

Nanofluid flow between two circular cylinders is studied in existence of magnetic field. KKL model is applied for nanofluid. Thermal radiation effect has been considered in energy equation. AGM is selected for solving ODEs. Semi analytical procedures are examined for various active parameters namely; aspect ratio, Hartmann number, Eckert number and Reynolds number. Results indicate that temperature gradient enhances with rise of Ha, Ec and η but it reduces with augment of Re. Velocity reduces with rise of Lorentz forces but it augments with rise of Reynolds number