Enhancement of Mixing Performance of Non-Newtonian Fluids using Curving and Grooving of Microchannels

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 non-Newtonian 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

Analysis, Design and Fabrication of Micromixers

This book includes an editorial and 12 research papers on micromixers collected from the Special Issue published in Micromachines. The topics of the papers are focused on the design of micromixers, their fabrication, and their analysis. Some of them proposed novel micromixer designs. Most of them deal with passive micromixers, but two papers report studies on electrokinetic micromixers. Fully three-dimensional (3D) micromixers were investigated in some cases. One of the papers applied optimization techniques to the design of a 3D micromixer. A review paper is also included and reports a review of recently developed passive micromixers and a comparative analysis of 10 typical micromixers

DESIGN AND MIXING PERFORMANCE OF PASSIVE MICROMIXERS: A CRITICAL REVIEW

This study extracts and reports notable findings on passive micromixers by conducting an exhaustive review of designs, their features, and mixing performance. The study has covered the relevant articles on passive micromixers published from 2010 to 2020. The analysis of filtered and selected articles sums up passive micromixers into four categories: designed inlets, designed mixing-channel, lamination-based, and flow obstacles-based. The prominent mixing channel categories identified in the study are split-and-recombine (SAR), convergent-divergent (C-D), and mixed (SAR, C-D, and others). Moreover, differences in mixing channel designs, number of inlets, and evaluation methods have been used in comparing the mixing performance of passive micromixers. The SAR and the obstacles-based micromixers were found to outperform the others. The designs covered in the present review show significant improvements in the mixing index. However, these studies were conducted in an isolated environment, and most of the time, their fabrication and device integration issues were ignored. The assortment and critical analysis of micromixers based on their design features and flow parameters will be helpful to researchers interested in designing new passive micromixers for microfluidic applications

Modelling and experiments of microchannels incorporating microengineered structures

Microreaction technology was conceived, thanks to the advances on microfabrication by the semiconductor industry. The �first applications of microchannels used for performing reactions date back to the early nineties. Since then, many conferences dedicated to this topic are held worldwide such as the International Microreaction Technology Conference (IMRET) or the International Conference on Microchannels and Minichannels. The small dimensions of the microchannels lead to very high heat and mass transfer rates, reactions are therefore performed very efficiently on these devices. However, the small dimensions of the channels lead to high pressure drops. In addition, microchannels are very susceptible to clogging. This thesis studies the e�ffect of di�fferent microchannel configurations in terms of mixing, mass transfer, residence time distribution and reaction. The objective is to design microreactors which incorporate di�fferent structures which make them efficient in terms of heat/mass transfer, but do not have the issue of high pressure drop and channel blockage

Analysis, Design and Fabrication of Micromixers, Volume II

Micromixers are an important component in micrototal analysis systems and lab-on-a-chip platforms which are widely used for sample preparation and analysis, drug delivery, and biological and chemical synthesis. The Special Issue "Analysis, Design and Fabrication of Micromixers II" published in Micromachines covers new mechanisms, numerical and/or experimental mixing analysis, design, and fabrication of various micromixers. This reprint includes an editorial, two review papers, and eleven research papers reporting on five active and six passive micromixers. Three of the active micromixers have electrokinetic driving force, but the other two are activated by mechanical mechanism and acoustic streaming. Three studies employs non-Newtonian working fluids, one of which deals with nano-non-Newtonian fluids. Most of the cases investigated micromixer design

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

Passive Micromixers

Micro-total analysis systems and lab-on-a-chip platforms are widely used for sample preparation and analysis, drug delivery, and biological and chemical syntheses. A micromixer is an important component in these applications. Rapid and efficient mixing is a challenging task in the design and development of micromixers. The flow in micromixers is laminar, and, thus, the mixing is primarily dominated by diffusion. Recently, diverse techniques have been developed to promote mixing by enlarging the interfacial area between the fluids or by increasing the residential time of fluids in the micromixer. Based on their mixing mechanism, micromixers are classified into two types: active and passive. Passive micromixers are easy to fabricate and generally use geometry modification to cause chaotic advection or lamination to promote the mixing of the fluid samples, unlike active micromixers, which use moving parts or some external agitation/energy for the mixing. Many researchers have studied various geometries to design efficient passive micromixers. Recently, numerical optimization techniques based on computational fluid dynamic analysis have been proven to be efficient tools in the design of micromixers. The current Special Issue covers new mechanisms, design, numerical and/or experimental mixing analysis, and design optimization of various passive micromixers

Microreactor engineering studies for asymmetric chalcone epoxidation.

Advances in the field of microreaction technology offer the opportunity to combine the benefits of continuous processing with the flexibility and versatility desired in the pharmaceutical and fine chemicals industry. Microreactor devices, also offer their own unique advantages over traditional continuous processing, such as improved heat and mass transfer, safer handling of exothermic reactions and easy containment of explosive and toxic materials. A reaction system can be quickly scaled-up to production levels by increasing the number of units operating in parallel, allowing significant savings in time and R&D costs. Most studies of microreactor systems to date focus on the development and performance of individual microdevices. However, a top down approach is preferred, with the focus on the requirements of the process and a suitable device design derived to meet those requirements. This work aims to demonstrate the suitability of the poly-L-leucine catalysed asymmetric epoxidation of chalcone reaction for continuous processing as well as the process and choices of designing and scaling a microchemical system. A suitable continuous reaction protocol was established for this reaction system, achieving a conversion of 88.4 % and enantioselectivity of 88.8 %. Mixing was found to be critical due to the low diffusivity ( 10"u) of the polymeric catalyst. Design criteria were established and a microstructured reactor with a footprint of 110 mm x 85 mm and production rate of - 0.5 g/day was designed for the system. An external scale-out structure was selected. The staggered herringbone mixer was selected for enhancing the mixing in the microstructured reactor. A method for characterizing the mixing performance in the staggered herringbone mixer based on stretching computations using particle tracking methods was developed, which allowed the required mixer length to be derived directly. Mixer lengths of 40 mm were provided for both deprotonation and epoxidation mixers. The effects of varying operating temperature, residence time and reactant concentrations on reaction performance in the fabricated microstructured reactor were investigated. The base case condition (13.47 g/1 PLL, 0.132 mol/1 H202, 0.0802 mol/1 chalcone, 0.22 mol/1 DBU) was found to be optimal, achieving a conversion of 86.7 % and enantioselectivity of 87.6 %. Several unexpected phenomena such as bubble clogging and increased viscosity due to the polymeric catalyst were encountered. A scaled-out system was designed and experiments carried out. Flow maldistribution, attributed to fabrication errors and bubble clogging, resulted in poor reaction performance (conversion -31.4 % and enantioselectivity 82.7 %) due to unequal residence times and imperfect mixing ratios of reactants. The commercial potential of the research was evaluated. Micro and macro level analysis of the market and industry were favourable and a suitable commercialisation route was suggested

Fluid Mechanics in Innovative Food Processing Technology

Generally, food industries employ traditional technologies and bulk devices for mixing, aeration, oxidation, emulsification and encapsulation. These processes are characterized by high energy consumption and result in high cost product, with limited diversity and usually with non-competitive quality. Moreover, the byproduct is also high. In recent years immense efforts have been dedicated to overcome these issues and major advances in food engineering have come from transfer and adaptation of knowledge from related fields such as chemical and mechanical engineering. It is well known that the majority of elements contribute to transport properties, physical and rheological behavior, texture and sensorial traits of foods are in micro-level. In this context invention at microscopic level is of critical importance to improve the existing foods quality while targeting also the development of new products. Therefore, microfluidics has a significant role in future design, preparation and characterization of food micro-structure. The diminutive scale of the flow channels in microfluidic systems increases the surface to volume ratio and is therefore advantageous for many applications. Furthermore, high quality food products can be manufactured by means of innovative microfluidic technology characterized by less energy consumption and a continuous process in substitution to the problematic batch one. To meet these challenges, this work is focused on main two tasks: (i) efficient micromixing, and (ii) production of microbubbles and microdroplets. Firstly, two novel 3D split and recombine (SAR) micromixers are designed on an extensive collection of established knowledge. Mixing characteristics of two species were elucidated via experimental and numerical studies associated with microchannels at various inlet flow-rate ratios for a wide range of Reynolds numbers (1-100); at the same time, results are compared with two well-known micromixers. It was found that performances of the mixers are significantly affected by their design, inlet flow-rate ratios and Reynolds numbers. The proposed micromixers show better efficiency (more than 90%) in all examined range of Reynolds numbers than the well-known basic mixers at each desired region; the required pressure-drop is also significantly less than that of the previous mixers. Furthermore, numerical residence time distribution (RTD) was also explored, which successfully predicts the experimental results. In a word, the presented new micromixers have advantages of high efficiency, low pressure-drop, simple fabrication, easy integration and ease for mass production. Secondly, four micro-devices are designed for the mono-dispersed droplets and bubbles generation. Two different experimental setups were used to create water droplet in silicone oil (W/O) and air bubble in silicone oil (A/O) for continuous flow rate from 10 ml/h to 230 ml/h. The mean size of droplet and bubble as well as frequency of generation can be controlled by dispersed and continuous flow rate. Besides, squeezing and dripping flow regimes are observed inside the four devices over a broad range of Capillary numbers: 0.01~0.18. Among the examined four devices, T-1 and T-2 provide smaller droplet (100 µm) and higher production rate. Furthermore, negative pressure setup provides more robust bubble generation but positive pressure yields better production rate. In addition, droplet and bubble diameter is about four times less than the microchannel dimension, therefore small droplet and bubble can be generated spending less energy. In summary, the investigation in this dissertation reflects that both SAR micromixers and micro-devices are very efficient and can be applied to meet the growing demands of food industries. The first part of the thesis, chapters 1 to 5, addresses state of art, design, experimental technique and results of micromixers. The second part, chapters 6 to 9, presents background, construction of devices, tests and results related to the production of microdroplets and microbubbles. Finally, chapter 10 summaries the whole presented work