A three-dimensional passive micro-mixer and its manufacturing and design method

Abstract

The present application provides a kind of three-dimensional passive micro-mixer and its manufacturing and design method.The three-dimensional passive micro-mixer includes main flow channel, the main flow channel has fluid inlet, fluid outlet and flow channel body, the flow channel body is connected between the fluid inlet and the fluid outlet;The depth of the flow channel body is nonlinear along the fluid flow direction, forms along the depth gradient;The flow channel body includes at least one curved section, the cross section of the curved section is configured as the shape of asymmetric about its bending plane, forms asymmetric cross section area;Wherein, the change position of the along the depth gradient is coupled with the spatial position of the asymmetric cross section area, so that the fluid flowing is synergized, generates and strengthens secondary vortex to promote fluid mixing.The present application can realize the efficient, fast mixing of fluid, and ensure that it has good and stable mixing performance in wide Reynolds number range.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of microfluidic technology, in particular to a three-dimensional passive micro-mixer for efficient mixing of fluids in a microfluidic chip and a manufacturing method and design method thereof. BACKGROUND

[0002] Microfluidic technology integrates the basic operation units such as sample preparation, reaction, separation and detection in the fields of biology, chemistry and medicine onto a chip with a micron scale, which has the advantages of less reagent consumption, fast analysis speed, high throughput, easy integration and automation, etc. Among numerous microfluidic operations, the rapid and uniform mixing of fluids is a crucial step, which directly affects the efficiency of subsequent reactions and the accuracy of detection.

[0003] Due to the flow under the scale of microfluidic channel is usually laminar flow (low Reynolds number Re), the mixing between fluids mainly relies on molecular diffusion, and the mixing efficiency is extremely low. In order to strengthen the mixing, passive micro-mixers disturb the flow field by designing special flow channel geometry to increase the fluid contact area, thereby promoting the mixing without external energy input. In the prior art, a large number of studies have introduced curved flow channels, obstacles, grooves and other structures to generate secondary flow (such as Dean vortex) to enhance mixing.

[0004] However, the existing passive micro-mixer research still has the following problems: first, the influence mechanism of geometric parameters on mixing performance is scattered, and there is a lack of systematic theoretical framework. The design process still largely depends on experience and numerical trial calculation, and there is a lack of theoretical tools for reverse derivation of optimal geometric parameters from the expected fluid dynamics target (such as a specific secondary flow intensity, flow line stretch rate), which restricts the scientificity, predictability and optimization efficiency of the design. Second, the research is mostly focused on static and isolated performance evaluation, and the dynamic research on the evolution and regulation mechanism of the internal flow field of the mixer under wide Reynolds number conditions is insufficient, which leads to the fact that the designed mixer often performs well only in a narrow flow rate range, and the environmental robustness is not strong and it is difficult to adapt to the wide Reynolds number fluctuation conditions naturally existing in river and estuary areas. Finally, the innovation source of the design paradigm is relatively fixed, mostly derived from the engineering application or local improvement of classical fluid mechanics principles, and there is a lack of systematic work on mechanical principle reconstruction and bionic migration from efficient mass transfer systems in nature (such as river bends and blood vessels).

[0005] Therefore, there is an urgent need for a new micro-mixer design that can achieve efficient and stable mixing in a wide Reynolds number range while maintaining low flow resistance and being easy to manufacture.

[0006] It should be noted that the information disclosed in the above background section is only for understanding the background of the present application, and therefore can include information that does not constitute prior art known to those of ordinary skill in the art. SUMMARY

[0007] This invention aims to address the aforementioned problems in the prior art by providing a three-dimensional passive micromixer. The technical problem it addresses is how to achieve efficient, rapid, and low-resistance mixing of fluids under laminar flow conditions with a wide Reynolds number range (e.g., Re=1-20), while ensuring good and stable mixing performance (i.e., high robustness) across this wide Reynolds number range. Furthermore, this invention also addresses how its manufacturing method can achieve high-precision, low-cost processing of complex three-dimensional structures, and how its design method can transition from empirical trial and error to directional design based on physical mechanisms.

[0008] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0009] In a first aspect, a three-dimensional passive micro-mixer is provided, comprising a main channel having a fluid inlet, a fluid outlet, and a channel body connected between the fluid inlet and the fluid outlet; the depth of the channel body varies non-linearly along the fluid flow direction, forming a depth gradient along the flow path; the channel body includes at least one curved section, the cross-section of which is configured to be asymmetrical about its curvature plane, forming an asymmetrical cross-sectional region; wherein the position of the variation of the depth gradient along the flow path is coupled to the spatial position of the asymmetrical cross-sectional region, so that the flowing fluid is synergistically acted to generate and enhance secondary vortices to promote fluid mixing.

[0010] Furthermore, the asymmetric cross-sectional area of ​​the curved section is configured such that the flow channel depth on the outer side of the curve is greater than the flow channel depth on the inner side of the curve.

[0011] Furthermore, the variation of the depth gradient along the path is a periodic fluctuation.

[0012] Furthermore, the three-dimensional passive micromixer has multiple sets of "at least two curved sections with the same fluid direction". In each set of "at least two curved sections with the same fluid direction", a local disturbance zone is provided between the two curved sections. The local disturbance zone is a second curved section, and the cross-section of the second curved section is also constructed to be asymmetrical about its curvature plane, forming an asymmetrical cross-section region. The asymmetrical cross-section region of the second curved section is constructed such that the flow channel depth on the outer side of the curve is less than the flow channel depth on the inner side of the curve. Alternatively, the flow channel depth of the local disturbance zone satisfies the following condition: when the fluid flows sequentially through the curved section before the local disturbance zone and the local disturbance zone, the depth on the outer side of the flow channel becomes shallower, and the depth on the inner side of the flow channel becomes deeper.

[0013] Furthermore, the ratio of the flow channel depth on the outer side of the bend to the flow channel depth on the inner side of the bend in the curved section is between 1.2 and 4.0; in at least two curved sections with the same fluid direction, the ratio of the flow channel depth on the outer side of the bend to the flow channel depth on the inner side of the bend in the preceding curved section is less than the ratio of the flow channel depth on the outer side of the bend to the flow channel depth on the inner side of the bend in the following curved section.

[0014] Secondly, a method for manufacturing a three-dimensional passive micromixer is provided. This method employs grayscale lithography, precision micromilling, or high-precision 3D printing to fabricate a main channel on a substrate. The main channel has a fluid inlet, a fluid outlet, and a channel body, with the channel body connecting the fluid inlet and the fluid outlet. The depth of the channel body varies non-linearly along the fluid flow direction, forming a depth gradient along the flow path. The channel body includes at least one curved section, the cross-section of which is constructed to be asymmetrical about its curvature plane, forming an asymmetrical cross-sectional region.

[0015] Thirdly, a microfluidic chip is provided, comprising a three-dimensional passive micromixer as described in any of the above.

[0016] Fourthly, a detection device is provided, comprising a three-dimensional passive micromixer as described in any of the preceding claims.

[0017] Fifthly, a computer implementation method for designing and optimizing the three-dimensional passive micromixer is provided. The method is implemented by a processor executing a computer program stored in a memory, and includes the following steps: a parameter input step: receiving target mixing condition parameters, including a target Reynolds number range; a first design step: determining the variation form of the friction depth gradient along the flow channel body based on the target Reynolds number range; a second design step: determining the shape parameters of the asymmetric cross-sectional region of the at least one curved section based on the target Reynolds number range; a coupling optimization step: optimizing the correlation configuration between the variation form and the shape parameters of the friction depth gradient and the spatial position of the asymmetric cross-sectional region, so that the mixing index and flow pressure drop obtained from the simulation meet preset requirements; and a result output step: outputting the optimized geometric model data of the three-dimensional passive micromixer.

[0018] Furthermore, the variation is a periodic fluctuation; the shape parameter includes the ratio of the flow channel depth on the outer side of the bend to the inner side of the bend in the curved section.

[0019] The present invention has the following beneficial effects:

[0020] This invention achieves efficient, low-resistance passive mixing over a wide Reynolds number range by spatially coordinating the overall depth gradient variation along the flow channel of a three-dimensional passive micromixer with the asymmetric cross-section design of the curved section. This dynamic programming of the generation, development, and intensification of secondary vortices in laminar fluid enables efficient control. Specifically, the depth gradient along the flow channel provides a pre-modulated velocity and pressure distribution background for the fluid flowing through the asymmetric cross-section, while the asymmetric cross-section applies directional secondary flow excitation to this pre-modulated fluid. The coupling effect of these two factors jointly programs the three-dimensional evolution path of the fluid from inlet to outlet. This synergistic mechanism is not a simple superposition of two effects, but rather achieves precise and efficient control of microscale laminar flow through dynamic programming of the entire secondary flow "generation-development-intensification" process. As a result, compared with the traditional structure, the present invention can maintain a high-intensity and structurally stable secondary vortex over a wider Reynolds number range (especially at low Re numbers), thereby significantly improving mixing efficiency. At the same time, since the flow is guided mainly by the smooth change of the main channel profile rather than by dense disturbance structures, the flow resistance can be better balanced while improving mixing efficiency, avoiding a significant increase in pressure drop compared to the same period last year.

[0021] Furthermore, the core feature of this invention is essentially the morphological change of the main contour of the flow channel, which can be directly formed through standardized micro-machining processes (such as grayscale lithography, precision micro-milling, and high-precision 3D printing) in one or a few steps, avoiding complex three-dimensional structures, making it highly feasible to process and conducive to industrialization.

[0022] Furthermore, the computer implementation method described above enables the reverse derivation of optimized geometric parameters based on target operating condition parameters, shifting the design process from trial and error based on experience to rational design based on physical mechanisms, thereby improving the scientific nature and efficiency of the design. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the three-dimensional passive micromixer in Embodiment 1 of the present invention.

[0024] Figure 2 This is a schematic diagram showing the experimental and simulation results of the three-dimensional passive micromixer in Embodiment 1 of the present invention.

[0025] Figure 3 This is a schematic diagram of the pressure drop at the fluid inlet and outlet of the three-dimensional passive micromixer in Embodiment 1 of the present invention.

[0026] Figure 4 This is a schematic diagram of the pressure drop at the fluid inlet and outlet of the three-dimensional passive micromixer in Embodiment 2 of the present invention. Detailed Implementation

[0027] The embodiments of the present invention will be described in detail below. It should be emphasized that the following description is merely exemplary and not intended to limit the scope and application of the present invention. Unless otherwise specified, the embodiments and features in the embodiments of this application can be combined with each other.

[0028] The core of this invention lies in the spatiotemporal coupling design of the depth gradient variation along the main flow channel and the asymmetric cross-section region of the curved section, thereby enabling precise programming of the generation, development, and intensification processes of secondary vortices in microscale laminar flow. This allows for efficient, low-resistance passive mixing over a wide Reynolds number range while ensuring the structure is easy to manufacture. The following embodiments will specifically demonstrate how this concept is implemented.

[0029] This invention provides a three-dimensional passive micromixer, including a main channel having a fluid inlet, a fluid outlet, and a channel body connected between the fluid inlet and the fluid outlet. The depth of the channel body varies non-linearly along the fluid flow direction (i.e., axial direction), forming a depth gradient along the flow path. The channel body includes at least one curved section, the cross-section of which is constructed to be asymmetrical about its curvature plane, forming an asymmetrical cross-sectional region. The location of the depth gradient variation is coupled to the spatial location of the asymmetrical cross-sectional region to synergistically generate and enhance secondary vortices to promote fluid mixing.

[0030] The coupling refers to the following: the friction depth gradient provides a dynamically changing flow background for the curved section, while the asymmetric cross-section of the curved section shapes and strengthens the secondary flow. The coupling of these two factors jointly programs the complex three-dimensional evolution path of the fluid from the inlet to the outlet. The working process of this three-dimensional passive micro-mixer is as follows: when two or more fluids flow into the main channel, the velocity profile and pressure distribution continuously change as they flow through the region with the friction depth gradient (wherein the entire main channel (whether straight or curved) has a friction depth gradient), pre-modulating the energy conditions for the generation of the secondary flow. When the fluid enters the curved section with an asymmetric cross-section (which also has a depth gradient in the cross-sectional direction), the asymmetric cross-section can change the vortex core distribution of the secondary vortex (Dean vortex), expanding its influence range to the entire cross-section, thus achieving efficient mixing. Specifically, under the combined action of the centrifugal force of the curved section and the asymmetric lateral pressure gradient, a secondary vortex with optimized strength and structure is generated. This vortex can efficiently stretch, fold, and laterally transport different fluid layers, ultimately achieving full mixing at the outlet.

[0031] In some embodiments, the asymmetric cross-sectional area of ​​the curved section is configured such that the flow channel depth on the outer side of the curve is greater than the flow channel depth on the inner side of the curve.

[0032] When the fluid enters the curved section, the high-speed fluid in the deep groove on the outside of the curve is thrown towards the inside of the curve by centrifugal force, but at the same time it is constrained by the shallow groove structure on the inside of the curve, which greatly enhances the lateral shear and streamline bending, and synergistically generates a stronger and more stable Dean vortex pair than a single asymmetric curve or a single depth gradient channel.

[0033] In some implementations, the variation of the friction depth gradient is a periodic fluctuation. By setting the variation of the friction depth gradient to a periodic fluctuation, the flow field can be customized for different flow conditions, enhancing the mixer's adaptability and robustness to wide Reynolds number conditions.

[0034] Preferably, the depth of the main flow channel can vary between 50 μm and 500 μm.

[0035] In some embodiments, the three-dimensional passive micromixer has multiple sets of "at least two curved sections with the same fluid direction." Within each set of "at least two curved sections with the same fluid direction," a local disturbance zone is provided between the two curved sections. The local disturbance zone is a second curved section, the cross-section of which is also constructed to be asymmetrical about its curvature plane, forming an asymmetrical cross-sectional area. Furthermore, the asymmetrical cross-sectional area of ​​this second curved section is constructed such that the channel depth on the outer side of the curve is less than the channel depth on the inner side of the curve (i.e., the second curved section has a shallow outer and deep inner structure, while the curved section has a deep outer and shallow inner structure). Alternatively, the channel depth of the local disturbance zone satisfies the following condition: as the fluid flows sequentially through the curved section preceding the local disturbance zone and through the local disturbance zone, the depth on the outer side of the channel becomes shallower, and the depth on the inner side of the channel becomes deeper (in this case, the channel of the local disturbance zone can be curved, straight, or of other shapes). By providing the local disturbance zone, the fluid flows sequentially through the preceding curved section, the local disturbance zone, and the subsequent curved section, further enhancing mixing.

[0036] In some implementations, the three-dimensional passive micromixer has multiple sets of three consecutive curved sections with fluids flowing in the same direction (e.g., all fluids flowing clockwise or all fluids flowing counterclockwise). Among these three consecutive curved sections, the middle curved section is the second curved section, serving as a local disturbance zone. The channel depth of this local disturbance zone satisfies the following condition: as the fluid flows sequentially through the curved section preceding the local disturbance zone and through the local disturbance zone, the depth on the outer side of the channel becomes shallower, and the depth on the inner side of the channel becomes deeper (more preferably, the outer side of the second curved section has both channel depths). The inner side of the bend has two flow channel depths, with the deeper flow channel on the inner side being greater than the deeper flow channel on the outer side. This can enhance the mixing between fluids. At the same time, the asymmetric cross-sectional area of ​​the two bends adjacent to the middle bend is a "deep outside, shallow inside" structure, where the flow channel depth on the outer side of the bend is greater than the flow channel depth on the inner side. By allowing the fluid to flow alternately through different bends, the centrifugal effect and asymmetric pressure gradient of the bends can be utilized more effectively to directionally stimulate and enhance secondary vortices (such as Dean vortices) of specific structures.

[0037] In some embodiments, the ratio of the flow channel depth on the outer side of the bend to the flow channel depth on the inner side of the bend is between 1.2 and 4.0; in at least two bends with the same fluid direction, the ratio of the flow channel depth on the outer side of the bend to the flow channel depth on the inner side of the bend in the preceding bend is less than the ratio of the flow channel depth on the outer side of the bend to the flow channel depth on the inner side of the bend in the following bend.

[0038] By controlling the channel depth ratio between the outer and inner sides of the bend in both bend sections to be between 1.2 and 4.0, it is possible to ensure effective secondary flow generation while avoiding excessive flow separation or a surge in pressure drop due to excessive depth difference, thus achieving a good balance between mixing efficiency and flow resistance. Specifically, when the channel depth ratio between the outer and inner sides of the bend is less than 1.2, the resulting lateral pressure gradient is insufficient to effectively generate a secondary vortex of considerable intensity; while when the depth ratio is greater than 4.0, flow separation or vortex breakup is easily triggered in the shallow region inside the bend, leading to a significant increase in pressure drop while the improvement in mixing efficiency is limited. This range was determined based on parametric CFD simulation results of the Dean number (De) and lateral flow intensity at different depth ratios. The depth ratio of the preceding bend is smaller than that of the following bend. This incremental design aims to achieve graded control of the "preheating" and "enhancing" of the secondary flow. First, the flow passes through a relatively mild asymmetric section to initially modulate the flow field and accumulate energy. Then, it passes through a local disturbance in the middle section and then through a stronger asymmetric section to fully excite the pre-modulated flow field, thereby generating a powerful secondary vortex more efficiently.

[0039] This invention also provides a method for manufacturing a three-dimensional passive micromixer, which uses grayscale photolithography, precision micromilling, or high-precision 3D printing to fabricate a main channel on a substrate; wherein the main channel has a fluid inlet, a fluid outlet, and a channel body, the channel body being connected between the fluid inlet and the fluid outlet; the depth of the channel body varies non-linearly along the fluid flow direction, forming a depth gradient along the flow path; the channel body includes at least one curved section, the cross-section of which is constructed to be asymmetrical about its curved plane, forming an asymmetrical cross-sectional region.

[0040] This invention also provides a microfluidic chip that includes the aforementioned three-dimensional passive micromixer.

[0041] The present invention also provides a detection device comprising the aforementioned three-dimensional passive micromixer.

[0042] This invention also provides a computer implementation method for designing and optimizing the three-dimensional passive micromixer. The method is implemented by a processor executing a computer program stored in a memory, and includes the following steps: a parameter input step: receiving target mixing condition parameters, including a target Reynolds number range; a first design step: determining the variation form of the friction depth gradient along the flow channel body based on the target Reynolds number range; a second design step: determining the shape parameters of the asymmetric cross-section region of the at least one curved section based on the target Reynolds number range; a coupling optimization step: optimizing the correlation configuration between the variation form and the shape parameters of the friction depth gradient and the spatial position of the asymmetric cross-section region, so that the mixing index and flow pressure drop obtained from simulation meet preset requirements; and a result output step: outputting the optimized geometric model data of the three-dimensional passive micromixer.

[0043] The mixer design method provided by this invention shifts the design process from trial and error based on experience to channel structure design based on physical mechanisms, ultimately achieving the comprehensive goal of maintaining excellent mixing performance (mixing index > 90%) over a wide Reynolds number range (Re = 1-20), maintaining a relatively low flow pressure drop, and being reliably manufactured through simple, standardized microfabrication processes in one or multiple steps.

[0044] In some implementations, the variation is a periodic fluctuation.

[0045] In some embodiments, the shape parameter includes the ratio of the flow channel depth on the outer side of the bend to the inner side of the bend in the curved section.

[0046] The present invention will be further described below through more specific embodiments.

[0047] Example 1

[0048] like Figure 1 As shown, the three-dimensional passive micromixer includes a main channel (i.e., the channel through which the fluid flows), which has a fluid inlet 1, a fluid outlet 2, and a channel body 3. The channel body 3 is connected between the fluid inlet 1 and the fluid outlet 2. The depth of the channel body 3 (the vertical height of the channel) varies non-linearly with periodic fluctuations along the fluid flow direction, forming a depth gradient along the flow path. The channel body 3 is arranged in a serpentine pattern, containing 25 consecutive curved segments. The cross-section of each curved segment is asymmetrical. Among them, in three consecutive curved segments with the same fluid direction (in this embodiment, except for one curved segment at the inlet and three curved segments at the outlet, the remaining 21 curved segments constitute 7 groups of "fluid in the same direction") In the three consecutive curved sections, the second curved section 32 in the middle is designated as a local disturbance region. Its asymmetric cross-section is constructed as follows: the outer side of the curve (outer side of the curved section) has two flow channel depths, 300 μm and 100 μm; the inner side of the curve (inner side of the curved section) has two flow channel depths, 400 μm and 100 μm. The asymmetric cross-sections of the other two curved sections before and after the second curved section 32 (namely, the first curved section 31, which the fluid flows through first, located in front of the second curved section 32, and the third curved section 33, which the fluid flows through later, located behind the second curved section 32) are constructed with a "deep outside, shallow inside" structure, where the flow channel depth on the outer side of the curve is greater than the flow channel depth on the inner side. Figure 1 As shown, in this embodiment, the depth of the fluid inlet and the fluid outlet is 200 μm, the flow channel depth on the outer side of the bend of the first bend section 31 is 300 μm, the flow channel depth on the inner side of the bend is 100 μm, the flow channel depth on the outer side of the bend of the third bend section 33 is 400 μm, and the flow channel depth on the inner side of the bend is 100 μm.

[0049] The working principle of this embodiment is as follows: Two fluids to be mixed flow into the fluid inlet 1, and the velocity profile and pressure distribution of the fluids are modulated by the depth gradient along the flow path, accumulating energy for the generation of secondary flows in the bend. When the fluids enter the bend with an asymmetric cross-section, under the synergistic effect of centrifugal force and the asymmetric lateral pressure gradient, high-intensity and structurally stable secondary flows such as Dean vortices are directionally generated. These secondary vortices efficiently stretch, fold, and laterally transport fluids from different flow layers, greatly promoting mixing. The spatial correlation between the depth gradient and the asymmetric cross-section ensures optimal timing matching of energy modulation and release.

[0050] To verify the performance of the mixer in this embodiment, a polydimethylsiloxane (PDMS) microfluidic chip with the aforementioned main channel was fabricated using high-precision photopolymerization 3D molding technology. Mixing was observed using fluorescence microscopy. The microfluidic experiments were conducted at Reynolds numbers Re=1, 5, 10, 15, and 20, with each model repeated three times. Specifically, deionized water and 1M rhodamine aqueous solution were injected at different flow rates (corresponding to Re=1, 5, 10, 15, and 20), and the mixing was observed using a fluorescence microscope. The mixing index (MI) was calculated through image processing.

[0051] like Figure 2 The figure shows the simulation and experimental results of the mixer in this embodiment. It can be seen that the measured mixing index (MI) changes with the Reynolds number (diffusion-dominant high → mixing trough → secondary flow-dominant rebound) highly matches the numerical simulation prediction, confirming the reliability of the simulation model and demonstrating its advantage of efficient mixing. Figure 2 In the experimental results, the experimental values ​​were generally slightly lower than the simulated values ​​by about 3%-5%, which is within a reasonable range. This deviation mainly stems from unavoidable systematic differences such as micro-dimensional deviations in processing, wall roughness, and fluctuations in flow rate and temperature of the experimental system. The error bars indicate good experimental repeatability.

[0052] like Figure 3 As shown, a pressure sensor was used to measure the pressure difference between the fluid inlet and outlet of the mixer in this embodiment. This pressure drop data confirmed the "low resistance" characteristic of the mixer and provided empirical evidence for the selection of mixers in different application scenarios.

[0053] Example 2

[0054] The difference from Example 1 lies in the structure of the local disturbance region, such as... Figure 4 As shown, in this embodiment, the second curved section 32a located in the middle is used as a local disturbance region. Its asymmetric cross-section region is constructed as a "shallow outside and deep inside" structure, where the flow channel depth on the outside of the curve is less than the flow channel depth on the inside of the curve: the flow channel depth on the outside of the curve (the outside of the curved section) is 100 μm, and the flow channel depth on the inside of the curve (the inside of the curved section) is 400 μm.

[0055] The embodiments of the present invention aim to solve the following core contradictions in existing passive micromixer technology: 1) Efficiency, flow resistance and operating condition adaptability are difficult to coordinate: Traditional designs cannot maintain high mixing efficiency and low flow resistance simultaneously in a wide Reynolds number range (especially in the low Re region); 2) Performance and manufacturability are seriously disconnected: Three-dimensional structures that can achieve extreme mixing performance are usually complex to process, costly and have low yield, while two-dimensional structures that are easy to process have limited performance.

[0056] The three-dimensional passive micromixer provided by this invention achieves precise and efficient control of microscale laminar flow through an innovative and easily implemented geometric coupling principle. It maintains excellent mixing performance (mixing index > 90%) over a wide Reynolds number range (Re = 1-20), maintains relatively low flow pressure drop, and can be reliably manufactured through simple, standardized microfabrication processes in one or multiple steps. Specifically, it has the following advantages:

[0057] Significantly improved mixing performance and enhanced robustness: By coupling depth gradients with curved asymmetric cross-sections, the flow field is not simply disturbed, but the entire process of secondary flow generation, development, and intensification is programmed. Compared to traditional two-dimensional curved or fixed-section three-dimensional structures, it can maintain high-intensity and structurally stable secondary flows over a wider Reynolds number range (especially at low Reynolds numbers), thus achieving higher and more robust mixing efficiency. Experiments show that the optimized model achieves mixing efficiency exceeding 90% within the Re=1-20 range.

[0058] A better balance between efficiency and flow resistance is achieved: This invention does not rely on dense micropillars or abrupt contraction and expansion to generate disturbances, but mainly relies on the smooth changes in the main contour of the flow channel to guide the flow. This design generates a strong secondary flow while maintaining a relatively smooth main flow path, thus significantly improving mixing efficiency without proportionally increasing the flow pressure drop, resolving the contradiction between efficiency and flow resistance in traditional designs.

[0059] Simplified structure, high processing feasibility, and reduced cost: The core features of this invention (depth gradient along the flow path and asymmetric cross-section of curved sections) are essentially morphological changes in the main contour of the flow channel, which can be directly formed through single-step or few-step processes such as single-color photolithography, precision micro-milling, or high-precision 3D printing. This avoids complex three-dimensional flow channel intersections, suspended structures, or multi-layer precision alignment, greatly reducing processing difficulty, improving yield, and reducing manufacturing costs, making it more suitable for industrial production and single-use.

[0060] The design principles are universal and highly scalable: This invention provides a clear design language corresponding to "structural features - flow field function". Although the mixer in the above embodiment has multiple curved sections, the cross-section of each curved section is constructed with an asymmetric shape about the curved plane and has a depth gradient along the flow path. In other embodiments, depending on user requirements (such as the pressure drop that the actual material or sealing scheme can withstand, flow rate threshold, etc.), only one or more curved sections can be constructed with an asymmetric shape about the curved plane. Therefore, by adjusting the location of the depth gradient change, the direction of the abrupt change in cross-section, the degree of cross-sectional asymmetry, and their combinations, micro-mixers suitable for different fluid properties, different target mixing rates, and pressure drop requirements can be customized, just like adjusting parameters, exhibiting high design flexibility and scalability.

[0061] Although this embodiment uses water as the medium, the fluid dynamics principles upon which this invention is based are also applicable to other Newtonian fluids. For non-Newtonian fluids, the mixing effect may vary depending on the rheological properties, requiring targeted optimization of the structural parameters based on the constitutive equations of the specific fluid.

[0062] The above description provides a further detailed explanation of the present invention in conjunction with specific / preferred embodiments, and it should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various substitutions or modifications can be made to these described embodiments without departing from the concept of the present invention, and all such substitutions or modifications should be considered within the scope of protection of the present invention. In the description of this specification, the reference to terms such as "an embodiment," "some embodiments," "preferred embodiment," "example," "specific example," or "some examples," etc., indicates that the specific features, structures, materials, or characteristics described in connection with that embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in any suitable manner in one or more embodiments or examples. Without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification and the features of different embodiments or examples. Although the embodiments of the present invention and their advantages have been described in detail, it should be understood that various changes, substitutions, and modifications can be made herein without departing from the scope of protection of the patent application.

Claims

1. A three-dimensional passive micromixer, characterized in that, The system includes a main channel with a fluid inlet, a fluid outlet, and a channel body connecting the fluid inlet and the fluid outlet. The depth of the channel body varies non-linearly along the fluid flow direction, forming a depth gradient. The channel body includes at least one curved section, the cross-section of which is constructed with an asymmetric shape about its curvature plane, forming an asymmetric cross-section region. The location of the variation of the depth gradient along the flow path is coupled with the spatial location of the asymmetric cross-section region to allow the flowing fluid to work synergistically, generating and enhancing secondary vortices to promote fluid mixing. This coupling means that the depth gradient along the flow path provides a dynamically changing flow background for the curved section, while the asymmetric cross-section region of the curved section shapes and enhances the secondary flow. The coupling of these two elements together programs the complex three-dimensional evolution path of the fluid from the inlet to the outlet.

2. The three-dimensional passive micromixer as described in claim 1, characterized in that, The asymmetric section of the curved segment is configured such that the flow channel depth on the outer side of the curve is greater than the flow channel depth on the inner side of the curve.

3. The three-dimensional passive micromixer as described in claim 1, characterized in that, The variation of the depth gradient along the path is a periodic fluctuation.

4. The three-dimensional passive micromixer as described in claim 2, characterized in that, The three-dimensional passive micromixer has multiple sets of "at least two of the curved sections with the same fluid direction". In each set of "at least two of the curved sections with the same fluid direction", a local disturbance zone is provided between the two curved sections. The local disturbance zone is a second curved section, and the cross-section of the second curved section is also constructed to be asymmetrical about its curvature plane, forming an asymmetrical cross-section region. The asymmetrical cross-section region of the second curved section is constructed such that the flow channel depth on the outer side of the curve is less than the flow channel depth on the inner side of the curve. Alternatively, the flow channel depth of the local disturbance zone satisfies the following condition: as the fluid flows sequentially through the curved section before the local disturbance zone and the local disturbance zone, the depth on the outer side of the flow channel becomes shallower, and the depth on the inner side of the flow channel becomes deeper.

5. The three-dimensional passive micromixer as described in claim 2 or 4, characterized in that, The ratio of the flow channel depth on the outer side of the bend to the flow channel depth on the inner side of the bend in the bend is between 1.2 and 4.0; in at least two bends in the same direction of fluid flow, the ratio of the flow channel depth on the outer side of the bend to the flow channel depth on the inner side of the bend in the preceding bend is less than the ratio of the flow channel depth on the outer side of the bend to the flow channel depth on the inner side of the bend in the following bend.

6. A method for manufacturing the three-dimensional passive micromixer according to claim 1, characterized in that, A main channel is fabricated on a substrate using grayscale photolithography, precision micro-milling, or high-precision 3D printing. The main channel has a fluid inlet, a fluid outlet, and a channel body, with the channel body connecting the fluid inlet and the fluid outlet. The depth of the channel body varies non-linearly along the fluid flow direction, forming a depth gradient along the flow path. The channel body includes at least one curved segment, the cross-section of which is constructed to be asymmetrical about its curvature plane, forming an asymmetrical cross-sectional region.

7. A microfluidic chip, characterized in that: It includes a three-dimensional passive micromixer as described in any one of claims 1-5.

8. A detection device, characterized in that, It includes a three-dimensional passive micromixer as described in any one of claims 1-5.

9. A computer implementation method for designing and optimizing the three-dimensional passive micromixer of claim 1, characterized in that, The method is implemented by a processor executing a computer program stored in memory, and includes the following steps: Parameter input steps: Receive target mixed operating condition parameters, including the target Reynolds number range; First design step: Based on the target Reynolds number range, determine the variation form of the depth gradient along the flow channel body; Second design step: Based on the target Reynolds number range, determine the shape parameters of the asymmetric section region of the at least one bending segment; Coupling optimization step: Based on the change form and the shape parameters, optimize the correlation configuration between the change position of the depth gradient along the flow path and the spatial position of the asymmetric cross-section region so that the mixing index and flow pressure drop obtained from the simulation meet the preset requirements; Output steps: Output the optimized geometric model data of the 3D passive micromixer.

10. The computer implementation method according to claim 9, characterized in that, The change pattern is a periodic fluctuation; the shape parameters include the ratio of the flow channel depth on the outer side of the bend to the inner side of the bend in the curved section.

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