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17 pages, 5267 KiB

Open AccessArticle

Mixing Performance of a Passive Micromixer Based on Split-to-Circulate (STC) Flow Characteristics

by Makhsuda Juraeva and Dong-Jin Kang

Micromachines 2024, 15(6), 773; https://doi.org/10.3390/mi15060773 - 10 Jun 2024

Viewed by 526

Abstract

We propose a novel passive micromixer leveraging STC (split-to-circulate) flow characteristics and analyze its mixing performance comprehensively. Three distinct designs incorporating submerged circular walls were explored to achieve STC flow characteristics, facilitating flow along a convex surface and flow impingement on a concave [...] Read more.

We propose a novel passive micromixer leveraging STC (split-to-circulate) flow characteristics and analyze its mixing performance comprehensively. Three distinct designs incorporating submerged circular walls were explored to achieve STC flow characteristics, facilitating flow along a convex surface and flow impingement on a concave surface. Across a broad Reynolds number range (0.1 to 80), the present micromixer substantially enhances mixing, with a degree of mixing (DOM) consistently exceeding 0.84. Particularly, the mixing enhancement is prominent within the low and intermediate range of Reynolds numbers (

0.1 < R e < 20)

. This enhancement stems from key flow characteristics of STC: the formation of saddle points around convex walls and flow impingement on concave walls. Compared to other passive micromixers, the DOM of the present micromixer stands out as notably high over a broad range of Reynolds numbers (

0.1 \leq R e \leq 80

). Full article

(This article belongs to the Special Issue Microreactors and Their Applications)

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14 pages, 6071 KiB

Open AccessArticle

Degradation of Stains from Metal Surfaces Using a DBD Plasma Microreactor

by Fajun Wang, Zhikun Miao, Chengdong Li and Liangliang Lin

Micromachines 2024, 15(3), 297; https://doi.org/10.3390/mi15030297 - 21 Feb 2024

Viewed by 876

Abstract

The surface cleaning of metals plays a pivotal role in ensuring their overall performance and functionality. Dielectric barrier discharge (DBD) plasma, due to its unique properties, has been considered to be a good alternative to traditional cleaning methods. The confinement of DBD plasma [...] Read more.

The surface cleaning of metals plays a pivotal role in ensuring their overall performance and functionality. Dielectric barrier discharge (DBD) plasma, due to its unique properties, has been considered to be a good alternative to traditional cleaning methods. The confinement of DBD plasma in microreactors brings additional benefits, including excellent stability at high pressures, enhanced density of reactive species, reduced safety risks, and less gas and energy consumption. In the present work, we demonstrated a DBD plasma-based method for the degradation of stains from metal surfaces in a microreactor. Aluminum plates with capsanthin stains were used to investigate the influence of operational parameters on the decolorization efficiency, including plasma discharge power, plasma processing time, and O₂ content in the atmosphere. The results revealed that an increase in plasma discharge power and plasma processing time together with an appropriate amount of O₂ in the atmosphere promote the degradation of capsanthin stains. The optimum processing condition was determined to be the following: plasma power of 11.3 W, processing time of 3 min, and Ar/O₂ flow rate of 48/2 sccm. The evolution of composition, morphology, bonding configuration, and wettability of aluminum plates with capsanthin and lycopene stains before and after plasma treatment were systematically investigated, indicating DBD plasma can efficiently degrade stains from the surface of metals without damage. On this basis, the DBD plasma cleaning approach was extended to degrade rhodamine B and malachite green stains from different metals, suggesting it has good versatility. Our work provides a simple, efficient, and solvent-free approach for the surface cleaning of metals. Full article

(This article belongs to the Special Issue Microreactors and Their Applications)

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15 pages, 2958 KiB

Open AccessArticle

Biocatalytic Performance of β-Glucosidase Immobilized on 3D-Printed Single- and Multi-Channel Polylactic Acid Microreactors

by Andreas-Georgios Vasios, Anastasia Skonta, Michaela Patila and Haralambos Stamatis

Micromachines 2024, 15(2), 288; https://doi.org/10.3390/mi15020288 - 18 Feb 2024

Viewed by 1125

Abstract

Microfluidic devices have attracted much attention in the current day owing to the unique advantages they provide. However, their application for industrial use is limited due to manufacturing limitations and high cost. Moreover, the scaling-up process of the microreactor has proven to be [...] Read more.

Microfluidic devices have attracted much attention in the current day owing to the unique advantages they provide. However, their application for industrial use is limited due to manufacturing limitations and high cost. Moreover, the scaling-up process of the microreactor has proven to be difficult. Three-dimensional (3D) printing technology is a promising solution for the above obstacles due to its ability to fabricate complex structures quickly and at a relatively low cost. Hence, combining the advantages of the microscale with 3D printing technology could enhance the applicability of microfluidic devices in the industrial sector. In the present work, a 3D-printed single-channel immobilized enzyme microreactor with a volume capacity of 30 μL was designed and created in one step via the fused deposition modeling (FDM) printing technique, using polylactic acid (PLA) as the printing material. The microreactor underwent surface modification with chitosan, and β-glucosidase from Thermotoga maritima was covalently immobilized. The immobilized biocatalyst retained almost 100% of its initial activity after incubation at different temperatures, while it could be effectively reused for up to 10 successful reaction cycles. Moreover, a multi-channel parallel microreactor incorporating 36 channels was developed, resulting in a significant increase in enzymatic productivity. Full article

(This article belongs to the Special Issue Microreactors and Their Applications)

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13 pages, 2333 KiB

Open AccessArticle

The Effect of Random Roughness on the Electromagnetic Flow in a Micropipe

by Zhili Wang, Yanjun Sun and Yongjun Jian

Micromachines 2023, 14(11), 2054; https://doi.org/10.3390/mi14112054 - 2 Nov 2023

Cited by 3 | Viewed by 903

Abstract

The features of stationary random processes and the small parameter expansion approach are used in this work to examine the impact of random roughness on the electromagnetic flow in cylindrical micropipes. Utilizing the perturbation method, the analytical solution until second order velocity is [...] Read more.

The features of stationary random processes and the small parameter expansion approach are used in this work to examine the impact of random roughness on the electromagnetic flow in cylindrical micropipes. Utilizing the perturbation method, the analytical solution until second order velocity is achieved. The analytical expression of the roughness function ζ, which is defined as the deviation of the flow rate ratio with roughness to the case having no roughness in a smooth micropipe, is obtained by integrating the spectral density. The roughness function can be taken as the functions of the Hartmann number Ha and the dimensionless wave number λ. Two special corrugated walls of micropipes, i.e., sinusoidal and triangular corrugations, are analyzed in this work. The results reveal that the magnitude of the roughness function rises as the wave number increases for the same Ha. The magnitude of the roughness function decreases as the Ha increases for a prescribed wave number. In the case of sinusoidal corrugation, as the wave number λ increases, the Hartmann number Ha decreases, and the value of ζ increases. We consider the λ ranging from 0 to 15 and the Ha ranging from 0 to 5, with ζ ranging from −2.5 to 27.5. When the λ reaches 15, and the Ha is 0, ζ reaches the maximum value of 27.5. At this point, the impact of the roughness on the flow rate reaches its maximum. Similarly, in the case of triangular corrugation, when the λ reaches 15 and the Ha is 0, ζ reaches the maximum value of 18.7. In addition, the sinusoidal corrugation has a stronger influence on the flow rate under the same values of Ha and λ compared with triangular corrugation. Full article

(This article belongs to the Special Issue Microreactors and Their Applications)

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11 pages, 4196 KiB

Open AccessArticle

A Low-Cost Microfluidic and Optically Transparent Water Antenna with Frequency-Tuning Characteristics

by Abdullah Abdullah, Syed Imran Hussain Shah, Sakobyly Kiv, Jinwoo Ho and Sungjoon Lim

Micromachines 2023, 14(11), 2052; https://doi.org/10.3390/mi14112052 - 1 Nov 2023

Viewed by 1304

Abstract

In this study, a novel microfluidic frequency reconfigurable and optically transparent water antenna is designed using three-dimensional (3D) printing technology. The proposed antenna consists of three distinct parts, including a circularly shaped distilled water ground, a sea water-based circular segmented radiator, and a [...] Read more.

In this study, a novel microfluidic frequency reconfigurable and optically transparent water antenna is designed using three-dimensional (3D) printing technology. The proposed antenna consists of three distinct parts, including a circularly shaped distilled water ground, a sea water-based circular segmented radiator, and a circularly shaped distilled water-based load, all ingeniously constructed from transparent resin material. The presented antenna is excited by a disk-loaded probe. The frequency of the antenna can be easily tuned by filling and emptying/evacuating sea water from the multisegmented radiator. The radiator consists of three segments with different radii, and each segment has a different resonant frequency. When the radiator is filled, the antenna resonates at the frequency of the segment that is filled. When all the radiator segments are filled, the antenna operates at the resonant frequency of 2.4 GHz and possesses an impedance bandwidth of 1.05 GHz (40%) in the range of 2.10–3.15 GHz. By filling different radiator segments, the frequency could be tuned from 2.4 to 2.6 GHz. In addition to the frequency-switching characteristics, the proposed antenna exhibits high simulated radiation efficiency (with a peak performance reaching 95%) and attains a maximum realized gain of 3.8 dBi at 2.9 GHz. The proposed antenna integrates water as its predominant constituent, which is easily available, thereby achieving cost-effectiveness, compactness, and transparency characteristics; it also has the potential to be utilized in future applications, involving transparent and flexible electronics. Full article

(This article belongs to the Special Issue Microreactors and Their Applications)

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Review

Jump to: Research

29 pages, 4670 KiB

Open AccessReview

Review on Microreactors for Photo-Electrocatalysis Artificial Photosynthesis Regeneration of Coenzymes

by Haixia Liu, Rui Sun, Yujing Yang, Chuanhao Zhang, Gaozhen Zhao, Kaihuan Zhang, Lijuan Liang and Xiaowen Huang

Micromachines 2024, 15(6), 789; https://doi.org/10.3390/mi15060789 - 15 Jun 2024

Viewed by 432

Abstract

In recent years, with the outbreak of the global energy crisis, renewable solar energy has become a focal point of research. However, the utilization efficiency of natural photosynthesis (NPS) is only about 1%. Inspired by NPS, artificial photosynthesis (APS) was developed and utilized [...] Read more.

In recent years, with the outbreak of the global energy crisis, renewable solar energy has become a focal point of research. However, the utilization efficiency of natural photosynthesis (NPS) is only about 1%. Inspired by NPS, artificial photosynthesis (APS) was developed and utilized in applications such as the regeneration of coenzymes. APS for coenzyme regeneration can overcome the problem of high energy consumption in comparison to electrocatalytic methods. Microreactors represent a promising technology. Compared with the conventional system, it has the advantages of a large specific surface area, the fast diffusion of small molecules, and high efficiency. Introducing microreactors can lead to more efficient, economical, and environmentally friendly coenzyme regeneration in artificial photosynthesis. This review begins with a brief introduction of APS and microreactors, and then summarizes research on traditional electrocatalytic coenzyme regeneration, as well as photocatalytic and photo-electrocatalysis coenzyme regeneration by APS, all based on microreactors, and compares them with the corresponding conventional system. Finally, it looks forward to the promising prospects of this technology. Full article

(This article belongs to the Special Issue Microreactors and Their Applications)

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34 pages, 13785 KiB

Open AccessReview

A Review of Pressure Drop and Mixing Characteristics in Passive Mixers Involving Miscible Liquids

by Arijit Ganguli, Viraj Bhatt, Anna Yagodnitsyna, Dipak Pinjari and Aniruddha Pandit

Micromachines 2024, 15(6), 691; https://doi.org/10.3390/mi15060691 - 24 May 2024

Viewed by 492

Abstract

The present review focuses on the recent studies carried out in passive micromixers for understanding the hydrodynamics and transport phenomena of miscible liquid–liquid (LL) systems in terms of pressure drop and mixing indices. First, the passive micromixers have been categorized based on the [...] Read more.

The present review focuses on the recent studies carried out in passive micromixers for understanding the hydrodynamics and transport phenomena of miscible liquid–liquid (LL) systems in terms of pressure drop and mixing indices. First, the passive micromixers have been categorized based on the type of complexity in shape, size, and configuration. It is observed that the use of different aspect ratios of the microchannel width, presence of obstructions, flow and operating conditions, and fluid properties majorly affect the mixing characteristics and pressure drop in passive micromixers. A regime map for the micromixer selection based on optimization of mixing index (MI) and pressure drop has been identified based on the literature data for the Reynolds number (Re) range (1 ≤ Re ≤ 100). The map comprehensively summarizes the favorable, moderately favorable, or non-operable regimes of a micromixer. Further, regions for special applications of complex micromixer shapes and micromixers operating at low Re have been identified. Similarly, the operable limits for a micromixer based on pressure drop for Re range 0.1 < Re < 100,000 have been identified. A comparison of measured pressure drop with fundamentally derived analytical expressions show that Category 3 and 4 micromixers mostly have higher pressure drops, except for a few efficient ones. An MI regime map comprising diffusion, chaotic advection, and mixed advection-dominated zones has also been devised. An empirical correlation for pressure drop as a function of Reynolds number has been developed and a corresponding friction factor has been obtained. Predictions on heat and mass transfer based on analogies in micromixers have also been proposed. Full article

(This article belongs to the Special Issue Microreactors and Their Applications)

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24 pages, 6483 KiB

Open AccessReview

Biomedical Applications of Deformable Hydrogel Microrobots

by Qinghua Cao, Wenjun Chen, Ying Zhong, Xing Ma and Bo Wang

Micromachines 2023, 14(10), 1824; https://doi.org/10.3390/mi14101824 - 24 Sep 2023

Viewed by 1742

Abstract

Hydrogel, a material with outstanding biocompatibility and shape deformation ability, has recently become a hot topic for researchers studying innovative functional materials due to the growth of new biomedicine. Due to their stimulus responsiveness to external environments, hydrogels have progressively evolved into “smart” [...] Read more.

Hydrogel, a material with outstanding biocompatibility and shape deformation ability, has recently become a hot topic for researchers studying innovative functional materials due to the growth of new biomedicine. Due to their stimulus responsiveness to external environments, hydrogels have progressively evolved into “smart” responsive (such as to pH, light, electricity, magnetism, temperature, and humidity) materials in recent years. The physical and chemical properties of hydrogels have been used to construct hydrogel micro-nano robots which have demonstrated significant promise for biomedical applications. The different responsive deformation mechanisms in hydrogels are initially discussed in this study; after which, a number of preparation techniques and a variety of structural designs are introduced. This study also highlights the most recent developments in hydrogel micro-nano robots’ biological applications, such as drug delivery, stem cell treatment, and cargo manipulation. On the basis of the hydrogel micro-nano robots’ current state of development, current difficulties and potential future growth paths are identified. Full article

(This article belongs to the Special Issue Microreactors and Their Applications)

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