Design method for directionally transporting micro-groove texture through magnetic field driven nano-magnetofluid and micro-groove texture

Abstract

The invention discloses a design method of a magnetic field driven nano-magnetofluid directional transportation micro-groove texture and the micro-groove texture, and directional transportation is realized by designing a conical micro-groove texture and matching with an external magnetic field driven nano-magnetofluid. And recording the contact point of the nanofluid and the micro-groove texture and the time from the middle end point of the nanofluid to the small end of the channel, designing a calculation method for measuring the overall speed of the liquid drop, optimizing the micro-texture taper angle by taking the fastest overall speed of the liquid drop as a target, and calculating the non-dimensional energy of the liquid drop to obtain the micro-groove texture. The microtexture small end diameter is optimized with the maximum dimensionless energy difference as the target; and calculating the magnetic field force borne by the liquid drop, and optimizing the magnetic flux density by taking the maximum magnetic field force as a target. According to the design method, the optimal micro-texture structure can be optimized, and the fastest rate transportation of liquid is realized.

Description

Technical Field

[0001] The present invention relates to the field of microfluidics, and specifically relates to a design method for a microgroove texture for the directional transport of magnetic nanoparticles by magnetic fields and the microgroove texture. Background Art

[0002] Traditional microfluidic systems usually rely on external pumps or electric fields to drive fluids, while the method of directional transport of magnetic nanoparticles by magnetic fields provides a contactless and highly controllable alternative. By designing specific microgroove textures, fluid manipulation can be achieved without introducing complex external equipment. In drug delivery systems, by using magnetic fields to drive magnetic nanoparticles, the directional delivery of drugs in the body can be realized, ensuring that the drugs accurately reach the target site and reducing side effects. In the development of micro-biosensors, by using the directional transport of magnetic nanoparticles in microgrooves, heat can be efficiently conducted from electronic components to the heat dissipation area, improving the heat dissipation efficiency and extending the device life. In fields such as ships and pipelines, dirt and biological attachment on the surface will reduce the device performance and increase the maintenance cost. By designing a surface with a specific microgroove texture and using the directional transport of magnetic nanoparticles by magnetic fields, the active removal of dirt can be realized, keeping the surface clean and reducing the maintenance requirements.

[0003] However, most of the current fluid directional transport design technologies mostly adopt bionic structures or rely on fixed magnetic fields for driving. Although unidirectional fluid transport is achieved to a certain extent, the driving method is single, the design structure is relatively complex, and there is no method for optimizing microgroove parameters by magnetic field driving. The following deficiencies generally exist: lack of a systematic design and optimization mechanism, making it difficult to quantitatively evaluate the transport efficiency; single driving mechanism, unable to achieve the collaborative optimization of the structure and the external field, restricting the actual application effect in complex environments. Summary of the Invention

[0004] Object of the Invention: The present invention provides a design method for a microgroove texture for the directional transport of magnetic nanofluids by magnetic fields, and realizes an efficient and controllable fluid directional transport process through the collaborative optimization of multi-dimensional parameters.

[0005] Technical Solution: A design method for a microgroove texture for the directional transport of magnetic nanoparticles by magnetic fields proposed by the present invention includes the following steps:

[0006] Step 1: Establish a conical microgroove model for the directional transport of magnetic nanoparticles by magnetic fields based on simulation software, including a conical microgroove texture and magnetic nanoparticles. The magnetic nanoparticles are water-based magnetic nanodroplets. Set the cone angle and the small-end diameter of the conical microgroove texture. The two ends of the conical microgroove texture are set to atmospheric pressure, and a uniformly varying magnetic field is set using the magnetic field module of the simulation software.

[0007] Step 2: Establish conical micro-groove textures with multiple different cone angles, simulate the nano-magnetic fluid under other same conditions, drive the nano-magnetic fluid to move in the conical micro-groove texture, optimize the cone angle of the micro-groove by calculating the overall velocity of the nano-magnetic fluid, and obtain the optimal cone angle θ when the overall velocity v of the nano-magnetic fluid is the fastest;

[0008] Step 3: Establish conical micro-groove textures with multiple different small-end diameters, simulate the nano-magnetic fluid under other same conditions, calculate the dimensionless energy of the nano-magnetic fluid using the dimensionless energy equation, and the dimensionless energy difference of the nano-magnetic fluid is the dimensionless energy of the nano-magnetic fluid at the initial position, is the dimensionless energy of the nano-magnetic fluid flowing to the small end of the micro-groove; optimize the small-end diameter d: obtain the optimal small-end diameter d when the dimensionless energy difference ΔU of the nano-magnetic fluid is the largest;

[0009] Step 4: Establish conical micro-groove textures with multiple different magnetic flux densities, simulate the nano-magnetic fluid under other same conditions, calculate the magnetic force received by the nano-magnetic fluid using the magnetic force calculation equation, and optimize the magnetic flux density B: obtain the optimal magnetic flux density B when the magnetic force F received by the nano-magnetic fluid is the largest.

[0010] Preferably, in Step 1, the nano-magnetic fluid is a water-based magnetic nano-droplet with a volume fraction of Fe3O4 of 0.5%, the diameter of the Fe3O4 particles is 30 nm, the initial position of the droplet is 0.5 mm away from the large end of the micro-groove, and the initial shape of the droplet is spherical.

[0011] Preferably, in Step 1, the magnetic field is a variable magnetic field that uniformly increases along the direction of the small end of the conical micro-groove texture, the magnetic flux density at the large end of the conical micro-groove texture is 0 mT, and the magnetic flux density at the small end of the conical micro-groove texture is B, where B is 20 mT - 80 mT.

[0012] Preferably, in Step 1, the cone angle of the conical micro-groove texture is 3 - 35°, and the small-end diameter is 0.04 - 0.18 mm.

[0013] Preferably, Step 2 specifically includes drawing the displacement-time images of the contact point between the droplet and the micro-groove texture and the midpoint of the droplet during the movement of the droplet, recording the times t1 and t2 when the two points reach the small end of the channel, and respectively calculating the movement velocities of the droplet X1 and X2 are the displacements of the contact point and the midpoint respectively, and the calculation formula for the overall velocity of the droplet is:

[0014] v = k1v1 + k2v2 (1)

[0015] Among them, k1 = 0.3 - 0.5, k2 = 0.5 - 0.7, k1 + k2 = 1, k1 is the velocity weight of the contact point, and k2 is the velocity weight of the mid-end point.

[0016] Preferably, the dimensionless energy equation of the droplet in step three is:

[0017]

[0018] In the formula, is the dimensionless energy of the droplet in the conical micro-groove; θ Y is the solid-liquid contact angle between the droplet and the micro-groove, in degrees; U is the energy of the droplet in the conical micro-groove, in J; S1 is the liquid-gas interface surface area of the droplet near the small end of the conical micro-groove, in mm 2 ; S2 is the liquid-gas interface surface area of the droplet near the large end of the conical micro-groove, in mm 2 ; S3 is the solid-liquid interface surface area of the droplet in the conical micro-groove, in mm 2 ; κ is the capillary length, in 1 / mm 2 .

[0019] Preferably, the calculation equation of the capillary length is γ is the surface tension of the liquid-gas interface, ρ is the density of the nanofluid, and g is the acceleration due to gravity.

[0020] Preferably, the calculation equation of the magnetic force in step four is

[0021]

[0022] In the formula, F(x) is the magnetic force at different positions x, in N; H(x) and H(y) are the magnetic field intensities at different positions x and y, in A / m; B(x) and B(z) are the magnetic flux densities at different positions x and z, in T; V f is the volume fraction of the nanofluid;

[0023] If the magnetic field application range is large enough, then:

[0024]

[0025] The magnetic force received by the nanofluid is:

[0026]

[0027] S yz (x) is the area of the nanofluid on the yz cross-section at different positions x, in m 2 .

[0028] Beneficial effects: The present invention utilizes the dual driving forces of conical microgrooves and magnetic fields to enhance the fluid transport speed; a new method for optimizing the overall speed of nanofluids is proposed, which can optimize the best channel structure parameters and magnetic field strength to achieve the maximum rate of liquid self-transport efficacy; the conical channels designed by this method can be applied to multiple fields such as microfluidic devices, micro-drug transportation without external force, and heat dissipation of electronic devices. Description of the Drawings

[0029] Figure 1 It is a schematic diagram of a conical microgroove model for magnetic field-driven nanofluids;

[0030] Figure 2 It is a schematic diagram of different methods for measuring the speed of nanofluids;

[0031] In the figure, 1 is the small-end diameter, 2 is the cone angle, 3 is the nanofluid, 4 is the magnetic field, 5 is the conical microgroove texture, 6 is the displacement of the contact point between the nanofluid and the microgroove texture, and 7 is the displacement of the midpoint of the nanofluid. Detailed Embodiments

[0032] As Figure 1 and Figure 2 shown, the present invention will be further described in detail below:

[0033] A design method for a microgroove texture for magnetic field-driven nanofluid directional transport includes the following steps:

[0034] Step 1: Establish a conical microgroove model for magnetic field-driven nanofluids based on the COMSOL simulation software, including the conical microgroove texture 5 and the nanofluid 3. The nanofluid 3 is a water-based magnetic nanodroplet. Set the cone angle 2 and the small-end diameter 1 of the conical microgroove texture 5. The two ends of the conical microgroove texture 5 are set to atmospheric pressure, and a uniformly varying magnetic field 4 is set using the magnetic field module of the simulation software;

[0035] The nanofluid 3 is a water-based magnetic nanodroplet with a Fe3O4 volume fraction of 0.5%. The diameter of the Fe3O4 particles is 30 nm. The initial position of the droplet is 0.5 mm away from the large end of the microgroove, and the initial shape of the droplet is spherical. The magnetic field 4 is a variable magnetic field that uniformly increases along the small-end direction of the conical microgroove texture 5. The magnetic flux density at the large end of the conical microgroove texture 5 is 0 mT, and the magnetic flux density at the small end of the conical microgroove texture 5 is B, where B is 20 mT - 80 mT. The cone angle 2 of the conical microgroove texture 5 is 3 - 35°, and the small-end diameter 1 is 0.04 - 0.18 mm.

[0036] Step 2: Establish multiple conical micro-groove textures 5 with different cone angles 2, simulate the nano-magnetic fluid 3 under other same conditions, drive the nano-magnetic fluid 3 to move in the conical micro-groove texture 5, draw the displacement-time images of the contact points between the nano-magnetic fluid during the movement process and the micro-groove texture and the end points in the nano-magnetic fluid, record the times t1 and t2 when the two points reach the small end of the channel, and calculate the movement speeds of the nano-magnetic fluid respectively X1 and X2 are the displacements of the contact point and the mid-end point respectively. The calculation formula for the overall speed of the nano-magnetic fluid is:

[0037] v = k1v1 + k2v2 (1)

[0038] where v is the overall speed of the nano-magnetic fluid, k1 = 0.3 - 0.5, k2 = 0.5 - 0.7, k1 + k2 = 1, k1 is the speed weight of the contact point, and k2 is the speed weight of the mid-end point. Optimize the cone angle 2 of the micro-groove by calculating the overall speed of the nano-magnetic fluid 3. When optimizing the cone angle θ, take the overall speed v of the nano-magnetic fluid as the objective function, draw the curve of the speed v changing with the cone angle θ, and select the corresponding θ with the maximum v value as the optimal cone angle. This optimization process is based on: the cone angle θ directly determines the opening degree of the conical micro-groove, affecting the driving force and fluid viscous resistance received by the nano-magnetic fluid 3. When the cone angle is small, the conical micro-groove texture 5 approaches a straight channel and the driving force is small; while when the cone angle is too large, the resistance of the nano-magnetic fluid 3 increases sharply during the transportation process. Therefore, there is an optimal cone angle θ that can achieve a balance between the increase in driving force and the increase in resistance, so that the speed of the nano-magnetic fluid 3 is the maximum. The optimal cone angle θ is obtained when the overall speed v of the nano-magnetic fluid 3 is the fastest;

[0039] Step 3: Establish multiple conical micro-groove textures 5 with different small-end diameters 1, simulate the nano-magnetic fluid 3 under other same conditions, and calculate the dimensionless energy of the nano-magnetic fluid using the dimensionless energy equation. The dimensionless energy equation is:

[0040]

[0041] In the formula, is the dimensionless energy of the nano-magnetic fluid in the conical micro-groove; θ Y is the solid-liquid contact angle between the nano-magnetic fluid and the micro-groove, in degrees; U is the energy of the nano-magnetic fluid in the conical micro-groove, in J; S1 is the liquid-gas interface surface area of the nano-magnetic fluid near the small end of the conical micro-groove, in mm 2 ; S2 is the liquid-gas interface surface area of the nano-magnetic fluid near the large end of the conical micro-groove, in mm 2 ; S3 is the solid-liquid interface surface area of the nano-magnetic fluid in the conical micro-groove, in mm 2 ; κ is the capillary length, γ is the surface tension of the liquid-gas interface, ρ is the density of the nanofluid, and g is the acceleration due to gravity, with the unit 1 / mm 2 The dimensionless energy difference of the nanofluid is the dimensionless energy of the nanofluid at the initial position, is the dimensionless energy of the nanofluid (3) when it flows to the small end of the microgroove; plot the variation of ΔU with the small end diameter d, and take the d corresponding to the maximum ΔU as the optimal small end diameter. This optimization principle is based on the fact that the nanofluid slides from a high energy state to a low energy state, and the change in the small end diameter of the microgroove causes a change in the energy difference between the two ends. The greater the energy difference, the greater the energy release of the nanofluid from the high energy state to the low energy state, thereby generating a greater spontaneous transport force and better directional movement performance of the nanofluid. The optimal small end diameter d is obtained when the dimensionless energy difference ΔU of the nanofluid is the largest;

[0042] Step 4: Establish conical microgroove textures (5) with different magnetic flux densities, simulate the nanofluid (3) under other same conditions, and calculate the magnetic force on the nanofluid (3) using the magnetic force calculation equation. The magnetic force calculation equation is

[0043]

[0044] where F(x) is the magnetic force at different positions x, with the unit N; H(x) and H(y) are the magnetic field intensities at different positions x and y, with the unit A / m; B(x) and B(z) are the magnetic flux densities at different positions x and z, with the unit T; V f is the volume fraction of the nanofluid;

[0045] If the magnetic field application range is large enough, then:

[0046]

[0047] The magnetic force on the nanofluid is:

[0048]

[0049] S yz (x) is the area of the nanofluid on the yz cross-section at different positions x, with the unit m 2 . Plot the curve of the magnetic force F varying with the magnetic flux density B. Select the magnetic flux density B corresponding to the maximum F as the optimal value. This optimization process is based on the combined action of the magnetic flux density gradient and the volume of the magnetic nanofluid to generate the magnetic force. When the geometric shape of the microgroove is the same, the greater the magnetic force, the higher the acceleration of the nanofluid, which is beneficial for rapid directional transport. The optimal magnetic flux density B is obtained when the magnetic force F on the nanofluid 3 is the largest.

[0050] Example 1

[0051] A design method for a micro-groove texture of magnetic field-driven nano-magnetic fluid directional transport proposed by the present invention includes the following steps:

[0052] Step 1: Establish a conical micro-groove model of magnetic field-driven nano-magnetic fluid based on the COMSOL simulation software. The nano-magnetic fluid 3 is a water-based magnetic nano-droplet. Set the micro-groove cone angle 2 and the small-end diameter 1, and set both ends of the channel to atmospheric pressure. Use the COMSOL magnetic field module to set a uniformly varying magnetic field 4.

[0053] Step 2: Drive the droplet to move in the conical micro-groove model 5, draw the displacement-time images of the contact point between the droplet and the micro-groove texture and the midpoint of the droplet during the movement of the droplet, record the times t1 and t2 when the two points reach the small end of the channel, and calculate the movement speeds of the nano-magnetic fluid respectively X1 and X2 are the displacements of the contact point and the midpoint respectively.

[0054] Calculation method for measuring the overall speed of the nano-magnetic fluid:

[0055] v = k1v1 + k2v2 (1)

[0056] k1 = 0.3, k2 = 0.7. k1 is the speed weight of the contact point, and k2 is the speed weight of the midpoint. Taking the fastest overall speed v of the nano-magnetic fluid as the measurement index, the optimal cone angle θ is optimized to be 3°;

[0057] Step 3: Calculate the dimensionless energy of the nano-magnetic fluid using the dimensionless energy equation of the nano-magnetic fluid:

[0058]

[0059] In the formula, is the dimensionless energy of the nano-magnetic fluid in the conical micro-groove; U is the energy of the nano-magnetic fluid in the conical micro-groove, with the unit J; θ Y is the solid-liquid contact angle between the nano-magnetic fluid and the micro-groove, with the unit °; S1 is the liquid-gas interface surface area of the nano-magnetic fluid near the small end of the conical micro-groove, with the unit mm 2 ; S2 is the liquid-gas interface surface area of the nano-magnetic fluid near the large end of the conical micro-groove, with the unit mm 2 ; S3 is the solid-liquid interface surface area of the nano-magnetic fluid in the conical micro-groove, with the unit mm 2 ; κ is the capillary length, with the unit 1 / mm 2 , γ is the surface tension of the liquid-gas interface, ρ is the density of the nano-magnetic fluid, and g is the acceleration due to gravity.

[0060] Dimensionless energy difference of the nano-magnetic fluid: is the dimensionless energy of the nano-magnetic fluid at the initial position, It is the dimensionless energy when the nanofluid flows to the small end of the microgroove. With the maximum dimensionless energy difference ΔU of the nanofluid as the measurement index, the optimized small end diameter d is 0.18 mm.

[0061] Step 4: Use the magnetic force calculation equation:

[0062]

[0063] In the formula, F(x) is the magnetic force at different positions x, with the unit of N; H(x) and H(y) are the magnetic field intensities at different positions x and y, with the unit of A / m; B(x) and B(z) are the magnetic flux densities at different positions x and z, with the unit of T; V f is the volume fraction of the nanofluid. If the magnetic field application range is large enough, then:

[0064]

[0065] The magnetic force received by the nanofluid is:

[0066]

[0067] S yz (x) is the area of the nanofluid on the yz cross-section at different positions x, with the unit of m 2 .

[0068] With the maximum magnetic force F received by the nanofluid as the measurement index, the optimized magnetic flux density B is 80 mT.

[0069] In this embodiment, the nanofluid is a water-based magnetic nanodroplet with a volume fraction of 0.5% of Fe3O4, the diameter of the Fe3O4 particles is 30 nm, the initial position of the droplet is 0.5 mm away from the large end of the microgroove, and the initial shape of the droplet is spherical. The external magnetic field is a variable magnetic field that uniformly increases along the negative x-axis direction, the magnetic flux density at the large end of the microgroove is 0 mT, and the magnetic flux density at the small end of the microgroove is B, where B is 80 mT. The cone angle θ of the conical microgroove texture is 3°, and the small end diameter d is 0.18 mm.

[0070] Example 2

[0071] A design method for a microgroove texture for magnetic field-driven nanofluid directional transport, including the following steps:

[0072] Step 1: Based on the COMSOL simulation software, establish a conical microgroove model for magnetic field-driven nanofluid. Set the microgroove cone angle 2 and the small end diameter 1 for the water-based magnetic nanodroplet of the nanofluid 3, and set the two ends of the channel to atmospheric pressure. Use the COMSOL magnetic field module to set a uniformly varying magnetic field 4.

[0073] Step 2: Drive the nanofluid to move in the conical micro-groove model 5, draw the displacement-time images of the contact points between the nanofluid and the micro-groove texture and the mid-end points in the nanofluid during the movement of the nanofluid, record the times t1 and t2 when the two points reach the small end of the channel, and calculate the movement speeds of the nanofluid respectively X1 and X2 are the displacements of the contact point and the mid-end point respectively

[0074] A calculation method for measuring the overall speed of the nanofluid:

[0075] v = k1v1 + k2v2 (1)

[0076] k1 = 0.4, k2 = 0.6. k1 is the speed weight of the contact point, and k2 is the speed weight of the mid-end point. Taking the fastest overall speed v of the nanofluid as the measurement index, the optimal cone angle θ is optimized to be 15°

[0077] Step 3: Calculate the dimensionless energy of the nanofluid by using the dimensionless energy equation of the nanofluid

[0078]

[0079] In the formula is the dimensionless energy of the nanofluid in the conical micro-groove; U is the energy of the nanofluid in the conical micro-groove, with the unit J; S1 is the liquid-gas interface surface area of the nanofluid near the small end of the conical micro-groove, with the unit mm 2 ; S2 is the liquid-gas interface surface area of the nanofluid near the large end of the conical micro-groove, with the unit mm 2 ; S3 is the solid-liquid interface surface area of the nanofluid in the conical micro-groove, with the unit mm 2 ; κ is the capillary length, with the unit 1 / mm 2 , γ is the surface tension of the liquid-gas interface, ρ is the density of the nanofluid, and g is the acceleration due to gravity. The dimensionless energy difference is the dimensionless energy of the nanofluid at the initial position, is the dimensionless energy of the nanofluid when it flows to the small end of the micro-groove. Taking the maximum dimensionless energy difference ΔU of the nanofluid as the measurement index, the small end diameter d is optimized to be 0.10 mm

[0080] Step 4: Use the magnetic force calculation equation

[0081]

[0082] Where F(x) is the magnetic force at different positions x, with the unit of N; H(x) and H(y) are the magnetic field intensities at different positions x and y, with the unit of A / m; B(x) and B(z) are the magnetic flux densities at different positions x and z, with the unit of T; V f is the volume fraction of the nanofluid. If the applied magnetic field range is large enough, then:

[0083]

[0084] The magnetic force on the nanofluid is:

[0085]

[0086] S yz (x) is the area of the nanofluid on the yz cross-section at different positions x, with the unit of m 2 .

[0087] Taking the maximum magnetic force F on the nanofluid as the measurement index, the optimized magnetic flux density B is 20 mT.

[0088] In this embodiment, the nanofluid is a water-based magnetic nanodroplet with a volume fraction of 0.5% of Fe3O4, the diameter of the Fe3O4 particles is 30 nm, the initial position of the droplet is 0.5 mm away from the large end of the microgroove, and the initial shape of the droplet is spherical. The applied magnetic field is a variable magnetic field that uniformly increases along the negative x-axis direction, the magnetic flux density at the large end of the microgroove is 0 mT, and the magnetic flux density at the small end of the microgroove is B, where B is 20 mT. The cone angle θ of the tapered microgroove texture is 15°, and the small end diameter d is 0.10 mm.

[0089] Example 3: A design method for a microgroove texture for magnetic field-driven nanofluid directional transport, including the following steps:

[0090] Step 1: Based on the COMSOL simulation software, establish a conical microgroove model for magnetic field-driven nanofluid. The nanofluid 3 is a water-based magnetic nanodroplet. Set the microgroove cone angle 2 and the small end diameter 1, and set the two ends of the channel to atmospheric pressure. Use the COMSOL magnetic field module to set a uniformly varying magnetic field 4.

[0091] Step 2: Drive the nanofluid to move in the conical microgroove model 5, draw the displacement-time images of the contact point between the nanofluid and the microgroove texture and the midpoint of the nanofluid during the movement process, record the times t1 and t2 when the two points reach the small end of the channel, and calculate the nanofluid movement speeds X1 and X2 are the displacements of the contact point and the midpoint, respectively.

[0092] A calculation method for measuring the overall speed of the nanofluid:

[0093] v = k1v1 + k2v2 (1),

[0094] k1 = 0.5, k2 = 0.5. Here, k1 is the velocity weight at the contact point and k2 is the velocity weight at the midpoint. Taking the fastest overall velocity v of the nanofluid as the measurement index, the optimal cone angle θ is optimized to be 35°;

[0095] Step 3: Calculate the dimensionless energy of the nanofluid using the dimensionless energy equation of the nanofluid:

[0096]

[0097] In the formula, is the dimensionless energy of the nanofluid in the conical microgroove; U is the energy of the nanofluid in the conical microgroove, with the unit J; θ Y is the solid-liquid contact angle between the nanofluid and the microgroove, with the unit °; S1 is the liquid-gas interface surface area of the nanofluid near the small end of the conical microgroove, with the unit mm 2 ; S2 is the liquid-gas interface surface area of the nanofluid near the large end of the conical microgroove, with the unit mm 2 ; S3 is the solid-liquid interface surface area of the nanofluid in the conical microgroove, with the unit mm 2 ; κ is the capillary length, with the unit 1 / mm 2 , γ is the surface tension of the liquid-gas interface, ρ is the density of the nanofluid, and g is the acceleration due to gravity. The dimensionless energy difference is the dimensionless energy of the nanofluid at the initial position, is the dimensionless energy of the nanofluid when it flows to the small end of the microgroove. Taking the maximum dimensionless energy difference ΔU of the nanofluid as the measurement index, the optimized small end diameter d is 0.04 mm.

[0098] Step 4: Use the magnetic force calculation equation:

[0099]

[0100] In the formula, F(x) is the magnetic force at different positions x, with the unit N; H(x) and H(y) are the magnetic field intensities at different positions x and y, with the unit A / m; B(x) and B(z) are the magnetic flux densities at different positions x and z, with the unit T; V f is the volume fraction of the nanofluid. If the magnetic field application range is large enough, then:

[0101]

[0102] The magnetic force received by the nanofluid is:

[0103]

[0104] S yz (x) is the area of the nanofluid on the yz cross-section at different positions x, with the unit of m 2 。

[0105] With the maximum magnetic force F on the nanofluid as the measurement index, the magnetic flux density B is optimized to be 50 mT.

[0106] In this embodiment, the nanofluid is a water-based magnetic nanodroplet with a volume fraction of Fe3O4 of 0.5%, the diameter of the Fe3O4 particles is 30 nm, the initial position of the droplet is 0.5 mm away from the large end of the microgroove, and the initial shape of the droplet is spherical. The applied magnetic field is a variable magnetic field that increases uniformly along the negative x-axis direction. The magnetic flux density at the large end of the microgroove is 0 mT, and the magnetic flux density at the small end of the microgroove is B, where B is 50 mT. The cone angle θ of the tapered microgroove texture is 35°, and the diameter d of the small end is 0.04 mm.

Claims

1. A design method for a micro-groove texture with magnetic field-driven nano-magnetic fluid directional transport, characterized in that, It includes the following steps: Step 1: Establish a magnetic field-driven nano-magnetic fluid conical micro-groove model based on simulation software, including a conical micro-groove texture (5) and nano-magnetic fluid (3). The nano-magnetic fluid (3) is a water-based magnetic nano-droplet. Set the cone angle (2) and the small-end diameter (1) of the conical micro-groove texture (5). The two ends of the conical micro-groove texture (5) are set to atmospheric pressure, and use the magnetic field module of the simulation software to set a uniformly varying magnetic field (4); Step 2: Establish conical micro-groove textures (5) with multiple different cone angles (2), simulate the nano-magnetic fluid (3) under other same conditions, drive the nano-magnetic fluid (3) to move in the conical micro-groove texture (5), and optimize the micro-groove cone angle (2) by calculating the overall velocity of the nano-magnetic fluid (3). When the overall velocity v of the nano-magnetic fluid (3) is the fastest, the optimal cone angle θ is obtained; Step 3: Establish conical micro-groove textures (5) with multiple different small-end diameters (1), simulate the nanofluid (3) under other same conditions, calculate the dimensionless energy of the nanofluid (3) using the dimensionless energy equation, and the dimensionless energy difference of the nanofluid (3). is the dimensionless energy of the nanofluid (3) at the initial position. is the dimensionless energy of the nanofluid (3) flowing to the small end of the micro-groove; optimize the small-end diameter d: obtain the optimal small-end diameter d when the dimensionless energy difference ΔU of the nanofluid (3) is the largest. Step 4: Establish conical micro-groove textures (5) with multiple different magnetic flux densities, simulate the nano-magnetic fluid (3) under other same conditions, calculate the magnetic force received by the nano-magnetic fluid (3) using the magnetic force calculation equation, and optimize the magnetic flux density B: When the magnetic force F received by the nano-magnetic fluid (3) is the largest, the optimal magnetic flux density B is obtained.

2. The design method of the micro-groove texture for magnetic-field-driven nano-magnetic fluid directional transport according to claim 1, characterized in that In the step 1, the nano-magnetic fluid (3) is a water-based magnetic nano-droplet with a volume fraction of Fe3O4 of 0.5%. The diameter of the Fe3O4 particles is 30 nm. The initial position of the droplet is 0.5 mm away from the large end of the micro-groove, and the initial shape of the droplet is spherical.

3. The design method of the microgroove texture for magnetic field-driven nano-magnetic fluid directional transport according to claim 1, characterized in that In the step 1, the magnetic field (4) is a variable magnetic field that uniformly increases along the small-end direction of the conical micro-groove texture (5). The magnetic flux density at the large end of the conical micro-groove texture (5) is 0 mT, and the magnetic flux density at the small end of the conical micro-groove texture (5) is B, where B is 20 mT - 80 mT.

4. The design method of the microgroove texture for magnetic field-driven nano-magnetic fluid directional transport according to claim 1, characterized in that In step 1, the cone angle (2) of the conical micro-groove texture is 3 - 35°, and the small-end diameter (1) is 0.04 - 0.18 mm.

5. The design method of the microgroove texture for magnetic field-driven nano-magnetic fluid directional transport according to claim 1, wherein Step 2 specifically includes drawing a displacement-time image of the contact point between the droplet and the micro-groove texture and the midpoint of the droplet during the movement of the droplet, recording the times t1 and t2 when the two points reach the small end of the channel, and respectively calculating the movement speed of the droplet X1 and X2 are the displacements of the contact point and the midpoint respectively, and the calculation formula for the overall speed of the droplet is: v = k1v1 + k2v2 (1) Among them, k1 = 0.3 - 0.5, k2 = 0.5 - 0.7, k1 + k2 = 1. k1 is the velocity weight of the contact point, and k2 is the velocity weight of the midpoint.

6. The design method of the micro-groove texture for magnetic field-driven nano-magnetic fluid directional transport according to claim 1, characterized in that The dimensionless energy equation of the droplet in the step 3 is: In the formula, is the dimensionless energy of the droplet in the conical micro-groove; θ Y is the solid-liquid contact angle between the droplet and the micro-groove, in degrees; U is the energy of the droplet in the conical micro-groove, in joules; S1 is the liquid-gas interface surface area of the droplet near the small end of the conical micro-groove, in square millimeters 2 ; $S_2$ is the liquid-gas interface surface area where the droplet approaches the large end of the conical microgroove, with the unit of $mm$. 2 ; $S_3$ is the solid-liquid interface surface area of the droplet in the conical microgroove, with the unit of $mm$ 2 ; $\kappa$ is the capillary length, with the unit of $1 / mm$ 2 .

7. The design method of the microgroove texture for magnetic field-driven nano-magnetic fluid directional transport according to claim 6, characterized in that The capillary length calculation equation is γ is the surface tension of the liquid-gas interface, ρ is the density of the nanofluid, and g is the acceleration due to gravity.

8. The design method of the micro-groove texture for magnetic field-driven nano-magnetic fluid directional transport according to claim 1, characterized in that The magnetic force calculation equation in the step 4 is where F(x) is the magnetic force at different positions x, with the unit of N; H(x) and H(y) are the magnetic field intensities at different positions x and y, with the unit of A / m; B(x) and B(z) are the magnetic flux densities at different positions x and z, with the unit of T; V f is the volume fraction of the nanofluid; If the magnetic field application range is large enough, then: The magnetic force received by the nano-magnetic fluid is: S yz (x) is the area of the nanofluid on the yz cross-section at different positions x, with the unit of m 2 .

9. The micro-groove texture designed by the design method of the magnetic field-driven nano-magnetic fluid directional transport micro-groove texture according to any one of claims 1 - 8.

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