A helical three-dimensional micro-mixer for liquid-liquid high-efficiency mixing

Abstract

The application discloses a spiral three-dimensional structure micro-mixer for liquid-liquid high-efficiency mixing, and relates to the field of chemical micro-fluid mixing. The micro-mixer is a three-dimensional structure, comprising two square inlet pipes in the same horizontal plane and parallel to each other, a circular outlet pipe perpendicular to the plane of the inlet pipe, and a main mixing area; the main mixing area is a cavity surrounded by an outer side, an inner side and a top surface; the two square inlet pipes are tangent to the main mixing area, and the square inlet pipes are in communication with the main mixing area. Fluids enter the main mixing area through the inlet pipes, spiral downward, collide and mix, and finally flow out from the outlet. The fluids in the mixer flow spirally, continuously change the flow direction and flow shape, and generate vortex flow to improve the mixing effect.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of chemical microfluidic mixing, and in particular to a spiral three-dimensional micro-mixer for liquid-liquid efficient mixing. BACKGROUND

[0002] Micro-mixers are used to achieve rapid and uniform mixing of samples in microfluidic systems. With the development of microfluidic and microfabrication technologies, micro-mixers are used in various fields such as medical detection, chemical reaction, drug synthesis, etc. Compared with macroscopic reaction systems, microfluidic systems have the advantages of high reaction efficiency, high sensitivity, high precision, and low reagent consumption, etc. Due to the sufficient mixing between reactants, the products are more stable and uniform. In some specific cases, the particle size distribution of the products can also be adjusted by controlling the mixing time. Due to its high sensitivity, high precision and micro-amount of reagents, micro-mixers have great potential in the detection field.

[0003] According to its mixing mechanism, micro-mixers can be divided into active and passive types. Active micro-mixers use external energy fields such as electric field, magnetic field, acoustic field, thermal field and pressure field to affect the fluid state. This method is very effective and flexible, so active micro-mixers have a wide prospect. However, active micro-mixers need to implant components to make the external field effective, and usually have a more complex structure, which is not easy to manufacture. Moreover, the external energy field will have adverse effects on the fluid state, such as heating. Passive mixers rely on their special geometric structure to affect the fluid state, such as vortex, stretching, folding fluid, etc. Passive micro-mixers have simple structure and small volume. However, the mixing conditions are relatively strict, and the degree of influence on the fluid state is usually not as good as that of active micro-mixers.

[0004] The Reynolds number in the micro-mixer is usually small, and the flow is in a laminar state. Without special design, mixing is usually dominated by diffusion, and the effect is not good. By designing the structure of the micro-mixer to increase the contact area between fluids, mixing can be effectively promoted. Common mixing forms of passive micro-mixers include: 1. increasing the cross-sectional area to shorten the diffusion distance; 2. dispersing and recombining to induce fluid collision to form Dean vortices; 3. setting baffles to change the flow direction and generate separation vortices; 4. forming expansion vortices based on contraction and expansion effects; 5. changing the flow direction and flow pattern to form vortex flow. Existing passive mixers are usually planar structures, and have problems such as long mixing time and poor mixing effect. SUMMARY

[0005] To solve the problems in the prior art, the present application provides a spiral three-dimensional micro-mixer for liquid-liquid efficient mixing.

[0006] The helical three-dimensional micro-mixer for liquid-liquid high-efficiency mixing is a three-dimensional structure, comprising two square inlet pipes in the same horizontal plane and parallel to each other, a circular outlet pipe perpendicular to the plane of the inlet pipe and a main mixing zone;

[0007] The main mixing zone is a cavity surrounded by an outer side, an inner side and a top surface, wherein the inner side is an inverted conical surface, the top surface is a circular ring surface, and the outer side comprises a cylindrical surface and a circular frustum surface connected to each other from top to bottom; the central axes of the conical surface, the circular ring surface, the cylindrical surface and the circular frustum surface are collinear, the circular ring surface is horizontally arranged, and the inner ring of the circular ring surface is connected to the bottom surface of the inverted conical surface; the cylindrical surface is connected to the outer ring of the circular ring surface; the circular frustum surface gradually shrinks in diameter from top to bottom, the taper angle of the circular frustum surface is the same as that of the conical surface, and both are alpha; the opening of the lower bottom surface of the circular frustum surface is connected to the circular outlet pipe.

[0008] The two square inlet pipes are installed on the cylindrical surface, the square inlet pipe is tangent to the cylindrical surface, the square inlet pipe is connected to the main mixing zone, and the height of the cylindrical surface is the same as that of the square inlet pipe.

[0009] As a preferred scheme of the present application, the inner ring diameter d3 of the circular ring surface is equal to the diameter of the bottom surface of the inverted conical surface, and the outer ring diameter d2 is equal to the diameter of the cylindrical surface.

[0010] As a preferred scheme of the present application, the taper angle alpha of the circular frustum surface and the conical surface ranges from 90° to 140°.

[0011] As a preferred scheme of the present application, the hydraulic diameter of the square inlet pipe is equal to that of the circular outlet pipe.

[0012] As a preferred scheme of the present application, the hydraulic diameter of the square inlet pipe and the circular outlet pipe is d1, and 0.5mm < d1 < 2mm.

[0013] As a preferred scheme of the present application, the outer ring diameter of the circular ring surface is d2, and the inner ring diameter is d3, and 10mm < d3 < d2 < 20mm.

[0014] As a preferred scheme of the present application, the length of the inlet pipe is L1, and L1 >= 5*d1, wherein d1 is the hydraulic diameter of the square inlet pipe.

[0015] As a preferred scheme of the present application, the length of the outlet pipe is L2 >= 0.5*(d2-d1)*cot(alpha / 2), wherein d1 is the hydraulic diameter of the circular outlet pipe, and d2 is the outer ring diameter of the circular ring surface.

[0016] The circular frustum side of the main mixing zone and the side of the conical body form a curved surface parallel relationship. The cross section of the micro-mixer is approximately Y-shaped.

[0017] The advantages of the present application are:

[0018] 1. The present application utilizes helical flow to change the flow direction and flow pattern of fluid, and increases the contact area of fluid flow through three-dimensional structure. The conical groove (formed by the inverted conical inner side) in the main mixing zone further guides the flow direction, while the change of flow direction and flow pattern forms vortex flow inside the main mixing zone, increases the contact between fluids, effectively promotes mixing, and improves the mixing effect.

[0019] 2. The present application has simple structure, only including inlet pipe, outlet pipe and main mixing zone, easy to manufacture; no dead zone, small pressure drop in mixing process, and less energy loss. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 It is the structural front view of the present application.

[0021] Figure 2 It is the cross-section view of the present application passing through the central axis.

[0022] Figure 3 It is the mixing index MI simulation diagram under different Reynolds numbers.

[0023] Figure 4 It is the velocity distribution and streamline simulation diagram of the cross-section of the present application, and the inlet Reynolds number is 15, wherein a is the cross-section view perpendicular to the inlet plane, and b is the cross-section view parallel to the inlet plane.

[0024] Figure 5 It is the velocity distribution and streamline simulation diagram of the cross-section of the present application, and the inlet Reynolds number is 150, wherein a is the cross-section view perpendicular to the inlet plane, and b is the cross-section view parallel to the inlet plane.

[0025] Figure 6 It is the velocity distribution and streamline simulation diagram of the cross-section of the present application, and the inlet Reynolds number is 600, wherein a is the cross-section view perpendicular to the inlet plane, and b is the cross-section view parallel to the inlet plane.

[0026] Figure 7 It is the outlet plane velocity distribution diagram of the present application. The inlet Reynolds numbers of a, b and c are 15, 150 and 600 respectively.

[0027] Figure 8 It is the physical map of the present application printed by using 3D printing technology.

[0028] Figure 9 It is the experimental result diagram of verifying the mixing effect by using potassium iodide-potassium iodate reaction system, which is X s With total flow variation diagram. DETAILED DESCRIPTION

[0029] The present application will be further described and explained with specific embodiments. The embodiments are only exemplary of the present disclosure and do not delimit the scope of the present disclosure. The technical features of various embodiments of the present application can be combined in a corresponding manner without conflict, provided that there is no conflict.

[0030] As shown in Figure 1 , Figure 2 The present application is a helical three-dimensional structure, comprising two mutually parallel square inlet pipes 1 and 2, a circular outlet pipe 3 perpendicular to the plane of the inlet pipe, and a main mixing zone 5. The two square inlet pipes 1 and 2 are parallel to each other and tangent to the main mixing zone 5. The main mixing zone is a cavity surrounded by an outer side, an inner side, and a top surface. The inner side is an inverted conical surface 4, the top surface is a circular ring surface 7, and the outer side includes a cylindrical surface 8 and a circular frustum surface 6 connected to each other from top to bottom. The central axes of the conical surface 4, the circular ring surface 7, the cylindrical surface 8, and the circular frustum surface 6 are collinear, and the circular ring surface 7 is horizontally arranged with its inner circle connected to the bottom surface of the inverted conical surface 4. The cylindrical surface 8 is connected to the outer circle of the circular ring surface 7. The circular frustum surface 6 tapers from top to bottom, and the taper angle of the circular frustum surface 6 is the same as that of the conical surface 4, both being α. The opening of the lower bottom surface of the circular frustum surface 6 is connected to the circular outlet pipe 3. The circular frustum surface 6 of the main mixing zone 5 forms a curved surface parallel relationship with the conical surface 4. The bottom surface of the smaller side of the main mixing zone 5 is connected to the outlet pipe 3. The cross section of the micro-mixer is approximately Y-shaped.

[0031] The hydraulic diameter of the inlet pipe and the outlet pipe of the present application is d1, and 0.5mm < d1 < 2mm. The diameter of the upper bottom surface of the circular frustum surface of the main mixing zone (i.e. the diameter of the cylindrical surface and the diameter of the outer circle of the circular ring surface) is d2, the diameter of the lower bottom surface of the circular frustum surface of the main mixing zone is equal to the diameter of the outlet pipe, which is d1, and the diameter of the bottom surface of the inverted conical surface (i.e. the diameter of the inner circle of the circular ring surface) is d3, 8mm < d3 < d2 < 20mm. The taper angle α of the circular frustum surface and the conical surface ranges from 90° to 140°. The length of the inlet pipe (measured from the outer plane tangent to the main mixing zone) is L1, and L1 ≥ 5*d1. The length of the outlet pipe is L2, and L2 ≥ 0.5*(d2-d1)*cot(α / 2).

[0032] The working principle of the present application is as follows: two streams of fluid to be mixed flow into the inlet pipes 1 and 2 at a certain flow rate ratio, the two streams of fluid meet and mix in the main mixing zone 5, and finally flow out of the outlet pipe 3.

[0033] The mixing effect of the present application is good in the selected range. The mixing effect of the present application is verified in combination with an example, in which d1 = 1.5 mm, d2 = 12.3 mm, d3 = 9.3 mm, L1 = 10 mm, L2 = 6.5 mm, and a = 120°. The mixer is printed using 3D printing technology. The mixing effect of the present application is verified by numerical simulation using the method of computational fluid dynamics. This simulation is performed using the commercial software ANSYS Fluent. The boundary conditions are set as follows: both square inlets 1 and 2 are velocity inlets, and outlet 3 is a pressure outlet. The model is selected as the Mixture model under Multiphase. The two fluids are set to have the same physical properties, a density of 1000 kg / m 3 , and a viscosity of 0.001 Pa·s, and the feed flow ratio is 1:1. The standard deviation value of the outlet plane is detected, and substituted into the MI calculation formula to solve.

[0034] The simulation results are shown in Figures 3 to 7 . As can be seen from Figure 3 , when the Reynolds number is low, the mixing effect of the mixer is poor; when the Reynolds number is greater than 470, the MI index is greater than 0.9, indicating that the mixing effect is good.

[0035] As can be seen from Figure 4 , 5, and 6, when the Reynolds number is low, no vortex flow is generated in the main mixing zone, and the mixing between the fluids mainly relies on diffusion, and the mixing effect is poor. With the increase of the Reynolds number, vortex flow is generated under the action of fluid collision and curvature effect, and the mixing effect between the fluids gradually becomes good. It can be seen that the increase of the Reynolds number increases the turbulence degree of the fluid, which is reflected in the size and strength of the vortex flow.

[0036] As can be seen from Figure 7 , at low Reynolds number, the effect of spiral flow is not obvious, and the velocity gradually decreases from the center to the outside. When the Reynolds number is increased to a certain degree, the velocity distribution changes obviously, as shown in Figure 7 c, the velocity first increases and then decreases from the center to the outside. This is because at high Reynolds number, the two fluids converge at a high flow rate, and the spiral flow shape flows out of the outlet plane, and the velocity is superimposed to finally form the velocity distribution diagram shown in Figure 7 . This flow shape effectively promotes mixing and enhances the mixing effect.

[0037] The mixing index MI is widely used to quantify the mixing effect, and its formula is:

[0038]

[0039]

[0040] where σ is the standard deviation of the concentration of the substance on the analyzed cross section, and N is the total number of units on the analyzed cross section. C i and are the concentration of the substance of the i-th unit and the concentration of the substance when completely mixed, respectively. σ max is the standard deviation of the concentration of the substance when completely unmixed. Therefore, according to the definition of the formula, MI changes between 0 and 1, the better the mixing effect, the closer MI is to 1; the worse the mixing effect, the closer MI is to 0.

[0041] In order to understand the mixing performance at the microscale in more detail and intuitively, the Villermaux-Dushman method is usually used, specifically the potassium iodide-iodate reaction system, which includes the following parallel competitive reactions:

[0042]

[0043]

[0044]

[0045] Reaction 1 is a quasi-instantaneous reaction, and the reaction rate is much greater than that of reaction 2. Reaction 2 generates I2, and I2 and I - are generated by reaction The absorbance is measured at a wavelength of 353 nm using a UV-visible spectrophotometer, and then converted according to the Lambert-Beer law to obtain the concentration of in the product.

[0046] Another microscale mixing index, segregation index X s , is used to quantify the mixing effect, and its expression is:

[0047]

[0048]

[0049]

[0050] where Y is the ratio of the amount of H + involved in reaction 2 to the amount of H + added, T ST is the value of T when the mixing process is infinitely slow. X s equals 0 indicates complete mixing, and X s equals 1 indicates complete segregation. Generally, the mixing state is between the two, i.e., X s is between 0 and 1.

[0051] This example uses the potassium iodide-potassium iodate system to verify the mixing effect of the present application, and uses 3D printing technology to print the micro-mixer of the present application, and the actual effect is as followsFigure 8 As shown in the figure. It is connected to the syringe pump via a thread for subsequent experiments. The concentrations of each component in this experiment are shown in Table 1.

[0052] Table 1 Concentration of each component

[0053]

[0054] In this experiment, two fluids, A and B, were used. Solution A contained KI, KIO3, H3BO3, and NaOH, while solution B contained H2SO4. The flow rate ratio of A to B was 7:1. The absorbance of the solutions after the reaction was measured and calculated using Beer-Lambert's law. The quantity, calculate the offset index X s .

[0055] The outset index X s As the total flow changes, Figure 9 As shown. By Figure 9 Analysis shows that as the total flow increases (i.e., the Reynolds number increases), X s The value gradually decreases, indicating that the mixing effect gradually increases.

[0056] Both computational fluid dynamics simulation results and experimental results show that the spiral three-dimensional micromixer of the present invention for efficient liquid-liquid mixing has a strong mixing effect.

[0057] The above-described embodiments are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. Those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention.

Claims

1. A helical three-dimensional micro-mixer for liquid-liquid high efficiency mixing, characterized in that, The micro-mixer is a three-dimensional structure, comprising two square inlet pipes in the same horizontal plane and parallel to each other, a circular outlet pipe perpendicular to the plane of the inlet pipes and a main mixing zone; The main mixing zone is a cavity surrounded by an outer side, an inner side and a top surface, wherein the inner side is an inverted conical surface, the top surface is a circular ring surface, and the outer side comprises a cylindrical surface and a circular frustum surface connected to each other from top to bottom; the central axes of the conical surface, the circular ring surface, the cylindrical surface and the circular frustum surface are collinear, the circular ring surface is horizontally arranged, and its inner circle is connected to the bottom surface of the inverted conical surface; the cylindrical surface is connected to the outer circle of the circular ring surface; the circular frustum surface gradually shrinks in diameter from top to bottom, the taper angle of the circular frustum surface is the same as that of the conical surface, and both are α; the lower bottom surface of the circular frustum surface is connected to the circular outlet pipe; The two square inlet pipes are installed on the cylindrical surface, the square inlet pipes are tangent to the cylindrical surface, the square inlet pipes are connected to the main mixing zone, and the height of the cylindrical surface is the same as that of the square inlet pipes.

2. The helical three-dimensional micro-mixer for liquid-liquid mixing according to claim 1, wherein The inner circle diameter d3 of the circular ring surface is equal to the diameter of the bottom surface of the inverted conical surface, and the outer circle diameter d2 is equal to the diameter of the cylindrical surface.

3. The helical three-dimensional micro-mixer for efficient mixing of liquid-liquid according to claim 1, wherein, The taper angle α of the circular frustum surface and the conical surface ranges from 90° to 140°.

4. The helical three-dimensional micro-mixer for efficient mixing of liquid-liquid according to claim 1, wherein, The hydraulic diameter of the square inlet pipe is equal to that of the circular outlet pipe.

5. The helical three-dimensional micro-mixer for liquid-liquid mixing according to claim 4, wherein The hydraulic diameter of the square inlet pipe and the circular outlet pipe is d1, and 0.5mm < d1 < 2mm.

6. The helical three-dimensional micro-mixer for liquid-liquid mixing according to claim 5, wherein The outer circle diameter of the circular ring surface is d2, and the inner circle diameter is d3, 10mm < d3 < d2 < 20mm.

7. The helical three-dimensional micro-mixer for efficient mixing of liquid-liquid according to claim 4, wherein, The length of the inlet pipe is the length of the outer plane tangent to the main mixing zone, and the length is L1, L1 ≥ 5*d1, and d1 is the hydraulic diameter of the square inlet pipe.

8. The helical three-dimensional micro-mixer for efficient mixing of liquid-liquid according to claim 4, wherein, The length of the outlet pipe L2 ≥ 0.5*(d2-d1)*cot(α / 2), d1 is the hydraulic diameter of the circular outlet pipe, and d2 is the outer circle diameter of the circular ring surface.

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