A method for bubble coalescence and detachment on porous surfaces based on tree-shaped superaerophilic orbitals

Abstract

The application relates to a method for bubble coalescence and separation on a porous surface based on a tree-shaped super-philic gas track, and relates to the technical field of multiphase flow. The application aims to solve the problem that carbon dioxide bubbles on the porous surface of a methanol fuel cell anode gas diffusion layer are difficult to discharge. The application utilizes the gas-philic property of the super-philic gas track and the diffusion property of the multi-stage bifurcated structure to make the micro-bubbles on the porous surface coalesce and grow rapidly to the extent of easily separating from the porous surface, the tree-shaped multi-stage bifurcated structure super-philic gas track strengthens the coalescence behavior of the micro-bubbles, improves the separation possibility of the large bubbles, the tree-shaped multi-stage bifurcated structure has a high space utilization rate in a planar arrangement form, the multi-stage bifurcated arc-shaped track conforms to the drag reduction dynamics behavior, and has the purpose of rapidly coalescing the carbon dioxide bubbles and separating the carbon dioxide bubbles from the porous surface, so that the performance of the methanol fuel cell is improved. The application can obtain a method for bubble coalescence and separation on a porous surface based on a tree-shaped super-philic gas track.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of multiphase flow, in particular to a method for bubble coalescence and detachment on porous surface based on dendritic superhydrophilic tracks. BACKGROUND

[0002] Methanol fuel cell technology has the advantages of high energy density, fast start, low operating temperature, zero emission and fuel fast charging, and becomes one of the application options for today and next generation portable electronic devices. However, the growth and coalescence of CO2 bubbles on the porous surface of the anode gas diffusion layer of the methanol fuel cell will cause the gas coverage on the porous electrode surface of the flow channel, which hinders the fuel transport in the flow channel and the diffusion layer, and greatly restricts the performance of the methanol fuel cell.

[0003] In order to promote the discharge of CO2 bubbles on the porous surface of the anode gas diffusion layer of the methanol fuel cell, it is necessary to design a method for rapid bubble removal on the porous surface, which is used to guide the migration and coalescence of CO2 gas on the anode surface of the methanol fuel cell, so as to achieve the purpose of rapid bubble detachment from the porous medium surface. SUMMARY

[0004] The purpose of the present application is to solve the problem of difficult discharge of CO2 bubbles on the porous surface of the anode gas diffusion layer of the methanol fuel cell, and to provide a method for bubble coalescence and detachment on porous surface based on dendritic superhydrophilic tracks.

[0005] A dendritic superhydrophilic track is arranged on the surface of the anode gas diffusion layer substrate of the methanol fuel cell, and the dendritic superhydrophilic track is composed of a plurality of dendritic multi-stage bifurcation structure superhydrophilic tracks, wherein the dendritic multi-stage bifurcation structure superhydrophilic track is an open patterned track.

[0006] The dendritic multi-stage bifurcation structure superhydrophilic track is composed of a K-stage bifurcation structure and two K+1-stage bifurcation structures, the K-stage bifurcation structure is composed of a K-stage coalescence segment and a K-stage flow guide segment, the front end opening of the K-stage bifurcation structure serves as the outlet of the K-stage coalescence segment, and the end opening of the K-stage bifurcation structure serves as the inlet of the K-stage coalescence segment; the K+1-stage bifurcation structure opening is composed of a K+1-stage coalescence segment and two K+1-stage flow guide segments, the front end of the K+1-stage bifurcation structure serves as the outlet of the K+1-stage coalescence segment, and the end opening of the K+1-stage bifurcation structure serves as the inlet of the K+1-stage flow guide segment; the front end of the K+1-stage bifurcation structure is in communication with the end of the K-stage bifurcation structure, the K-stage coalescence segment and the K+1-stage coalescence segment are straight segments, the K-stage flow guide segment and the K+1-stage flow guide segment are curved segments, and K=1.

[0007] A preparation method of a dendritic superhydrophilic track is carried out in the following steps:

[0008] Step one, the surface of the methanol fuel cell anode gas diffusion layer substrate is cleaned and wiped, and then the surface of the methanol fuel cell anode gas diffusion layer substrate is uniformly sprayed with a super gas-wetting material with a thickness of 50-100 μm, and then dried at a temperature of 140-180 ℃ for 15-25 min to obtain a dried super gas-wetting coating.

[0009] Step two, the dried super gas-wetting coating is engraved by using a CNC engraving machine to drive a spring needle tip to scratch the super gas-wetting coating, to obtain a tree-shaped super gas-wetting track.

[0010] A method for making a tree-shaped super gas-wetting track by the above method makes the methanol fuel cell anode gas diffusion layer substrate porous surface bubble coalescence and detachment method, which is carried out according to the following steps:

[0011] The carbon dioxide bubbles enter from the end of the K+1 level bifurcated structure under the action of the flowing methanol solution, the carbon dioxide bubbles in the two ends of the K+1 level bifurcated structure are guided by the K+1 level guiding section, and then converge and merge into one carbon dioxide bubble in the K+1 level coalescence section, and the carbon dioxide bubbles meeting the detachment condition are detached in the K+1 level coalescence section or the K level guiding section; the carbon dioxide bubbles not detached are further guided by the K level guiding section, and then converge and merge into one carbon dioxide bubble with another carbon dioxide bubble entering the K level coalescence section through the K level guiding section, and the carbon dioxide bubbles meeting the detachment condition are detached in the K level coalescence section; the carbon dioxide bubbles not detached stay at the front end of the K level bifurcated structure, and then merge into one carbon dioxide bubble with the next carbon dioxide bubble flowing into the K level coalescence section, and finally the carbon dioxide bubble is detached from the tree-shaped multi-level bifurcated structure super gas-wetting track; the direction from the end of the K+1 level bifurcated structure to the front end of the K level bifurcated structure on the tree-shaped multi-level bifurcated structure super gas-wetting track is the flowing direction of the methanol solution;

[0012] Let the minimum volume equivalent diameter of the carbon dioxide bubble detached from the surface of the methanol fuel cell anode gas diffusion layer substrate be D0, the width W k i of the K level coalescence section is D, and D≤D0, K represents the level number, K=1;

[0013] 1) the width W k j of the K level guiding section is the width W k i of the K level coalescence section, the width W k j of the K level guiding section is equal to the width W k+1 i of the K+1 level coalescence section, namely:

[0014] W k j= W k i / 2=W k+1 i =2 K-1 W k (1)

[0015] 2) The curvature length S of the K-level guide section k for:

[0016] S k =πR k θ / 90=β k-1 πR k θ / 90 (2)

[0017] In the formula, π is the mathematical constant pi, θ is the central angle, β is the radius reduction coefficient of the K-level guide section curve, and R k The radius of curvature of the K-level guide section.

[0018] This invention uses a super-aerophilic coating material combined with surface printing technology to form multiple fractal tree-like super-aerophilic orbitals on the surface of a porous media substrate. The fractal tree-like structure is a tree-like fractal aggregate network structure, and the original wettability of the base material is maintained in other areas of the substrate.

[0019] As small bubbles gradually permeate the porous medium surface, they gradually slide horizontally along with the flow of fluid on the porous surface inside the flow channel. At this time, the size of the small bubbles is too small, and under the influence of the porous wall, the flow velocity of the flow field where the bubbles are located is relatively small, making it difficult for the bubbles to detach from the porous surface.

[0020] After touching the end of the superaerobic orbit of the bifurcation tree structure, the horizontally sliding small bubbles slide along the superaerobic orbit. Guided by the superaerobic orbit, the small bubbles gradually merge into larger bubbles in the orbit merging section. After multiple merging in the multi-level tree structure superaerobic orbit merging section, the bubbles gradually increase in size.

[0021] As the bubble size increases, the flow field around the bubble gradually moves away from the porous wall. When the bubble size increases to a certain extent, under the action of a large flow field velocity away from the porous wall, the shear force of the flow field exceeds the adhesion force of the substrate surface to the bubble, and the bubble begins to detach from the porous surface, thus achieving the purpose of the bubble quickly detaching from the surface of the porous medium.

[0022] The multi-level tree-shaped superaerophilic orbital material uses a superaerophilic coating material combined with surface printing technology to print on the surface of a porous material, forming an orbital coating with a thickness on the micrometer level.

[0023] The multi-level tree-shaped superaerophilic orbital adopts a multi-level tree structure, such as... Figure 1 As shown, they are arranged in a reasonable manner with specific intervals and staggered patterns. The multi-level tree structure is composed of multi-level binary branching structures.

[0024] The bifurcated structure, as shown in Figure 2 The bifurcated structure, as shown in

[0025] The beneficial effects of the present application are as follows:

[0026] The present application is aimed at the problem that CO2 bubbles are difficult to discharge from the porous surface of the anode gas diffusion layer of a methanol fuel cell, and proposes a method for bubble coalescence and detachment from the porous surface based on a dendritic supergasphil track, which uses the gasphilicity of the supergasphil track and the diffusion of the multi-stage bifurcated structure to make the microbubbles on the porous surface coalesce and grow rapidly to the extent that they can easily detach from the porous surface. The dendritic multi-stage bifurcated structure supergasphil track strengthens the coalescence behavior of the microbubbles and improves the detachment possibility of the large bubbles. The planar arrangement of the dendritic multi-stage bifurcated structure has a high space utilization rate, and the multi-stage bifurcated arc-shaped track conforms to the drag reduction dynamics behavior, thus achieving the purpose of rapidly coalescing and detaching CO2 microbubbles from the porous surface, thereby greatly improving the performance of the methanol fuel cell. In addition, the supergasphil track is simple to prepare and has a low manufacturing cost, and the effective time of the supergasphil track is long, so it can be repeatedly used to achieve the purpose of reasonable resource conservation.

[0027] The present application can obtain a method for bubble coalescence and detachment from the porous surface based on a dendritic supergasphil track. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 The present application is aimed at the problem that CO2 bubbles are difficult to discharge from the porous surface of the anode gas diffusion layer of a methanol fuel cell, and proposes a method for bubble coalescence and detachment from the porous surface based on a dendritic supergasphil track, which uses the gasphilicity of the supergasphil track and the diffusion of the multi-stage bifurcated structure to make the microbubbles on the porous surface coalesce and grow rapidly to the extent that they can easily detach from the porous surface. The dendritic multi-stage bifurcated structure supergasphil track strengthens the coalescence behavior of the microbubbles and improves the detachment possibility of the large bubbles. The planar arrangement of the dendritic multi-stage bifurcated structure has a high space utilization rate, and the multi-stage bifurcated arc-shaped track conforms to the drag reduction dynamics behavior, thus achieving the purpose of rapidly coalescing and detaching CO2 microbubbles from the porous surface, thereby greatly improving the performance of the methanol fuel cell. In addition, the supergasphil track is simple to prepare and has a low manufacturing cost, and the effective time of the supergasphil track is long, so it can be repeatedly used to achieve the purpose of reasonable resource conservation.

[0029] Figure 2 The present application is aimed at the problem that CO2 bubbles are difficult to discharge from the porous surface of the anode gas diffusion layer of a methanol fuel cell, and proposes a method for bubble coalescence and detachment from the porous surface based on a dendritic supergasphil track, which uses the gasphilicity of the supergasphil track and the diffusion of the multi-stage bifurcated structure to make the microbubbles on the porous surface coalesce and grow rapidly to the extent that they can easily detach from the porous surface. The dendritic multi-stage bifurcated structure supergasphil track strengthens the coalescence behavior of the microbubbles and improves the detachment possibility of the large bubbles. The planar arrangement of the dendritic multi-stage bifurcated structure has a high space utilization rate, and the multi-stage bifurcated arc-shaped track conforms to the drag reduction dynamics behavior, thus achieving the purpose of rapidly coalescing and detaching CO2 microbubbles from the porous surface, thereby greatly improving the performance of the methanol fuel cell. In addition, the supergasphil track is simple to prepare and has a low manufacturing cost, and the effective time of the supergasphil track is long, so it can be repeatedly used to achieve the purpose of reasonable resource conservation.

[0030] Figure 3 The present application is aimed at the problem that CO2 bubbles are difficult to discharge from the porous surface of the anode gas diffusion layer of a methanol fuel cell, and proposes a method for bubble coalescence and detachment from the porous surface based on a dendritic supergasphil track, which uses the gasphilicity of the supergasphil track and the diffusion of the multi-stage bifurcated structure to make the microbubbles on the porous surface coalesce and grow rapidly to the extent that they can easily detach from the porous surface. The dendritic multi-stage bifurcated structure supergasphil track strengthens the coalescence behavior of the microbubbles and improves the detachment possibility of the large bubbles. The planar arrangement of the dendritic multi-stage bifurcated structure has a high space utilization rate, and the multi-stage bifurcated arc-shaped track conforms to the drag reduction dynamics behavior, thus achieving the purpose of rapidly coalescing and detaching CO2 microbubbles from the porous surface, thereby greatly improving the performance of the methanol fuel cell. In addition, the supergasphil track is simple to prepare and has a low manufacturing cost, and the effective time of the supergasphil track is long, so it can be repeatedly used to achieve the purpose of reasonable resource conservation.

[0031] Figure 4 Figure 1 is a schematic diagram of K+1 level bifurcated structure super gas affinity track bubble coalescence of the present application, 1 is the anode gas diffusion layer substrate of methanol fuel cell, 10 is the bubble. DETAILED DESCRIPTION

[0032] Embodiment one: the tree-shaped super gas affinity track of the present embodiment is arranged on the surface of the anode gas diffusion layer substrate 1 of methanol fuel cell, and the tree-shaped super gas affinity track is composed of several tree-shaped multi-level bifurcated structure super gas affinity tracks 3, wherein the tree-shaped multi-level bifurcated structure super gas affinity track 3 is a high-precision open pattern track.

[0033] The tree-shaped multi-level bifurcated structure super gas affinity track 3 is composed of one K level bifurcated structure 12 and two K+1 level bifurcated structures 13, the K level bifurcated structure 12 is composed of a K level coalescence section 14 and a K level flow guide section 15, the front end 4 of the K level bifurcated structure is open as the outlet of the K level coalescence section 14, and the tail end 9 of the K level bifurcated structure is open as the inlet of the K level coalescence section 14; the K+1 level bifurcated structure 13 is composed of one K+1 level coalescence section 16 and two K+1 level flow guide sections 17, the front end 11 of the K+1 level bifurcated structure is open as the outlet of the K+1 level coalescence section 16, and the tail end 5 of the K+1 level bifurcated structure is open as the inlet of the K+1 level flow guide section 17; the front end 11 of the K+1 level bifurcated structure is communicated with the tail end 9 of the K level bifurcated structure, the K level coalescence section 14 and the K+1 level coalescence section 16 are straight sections, the K level flow guide section 15 and the K+1 level flow guide section 17 are curved sections, and K=1.

[0034] Embodiment two: the difference between the present embodiment and embodiment one is that the curved section of the K level flow guide section 15 is composed of two arc sections with the same central angle θ and radius R K and opposite directions, the curved section of the K+1 level flow guide section 17 is composed of two arc sections with the same central angle θ and radius R K+1 and opposite directions; the surface of the anode gas diffusion layer substrate 1 of methanol fuel cell is provided with pores 2, and the pore diameter of the pores 2 is less than 100 μm.

[0035] The other steps are the same as those in embodiment one.

[0036] Embodiment three: the preparation method of the tree-shaped super gas affinity track of the present embodiment is carried out according to the following steps:

[0037] Step one, the surface of the methanol fuel cell anode gas diffusion layer substrate 1 is cleaned, wiped, and then the surface of the methanol fuel cell anode gas diffusion layer substrate 1 is uniformly sprayed with a super gas material with a thickness of 50-100 μm, and then dried at a temperature of 140-180 ℃ for 15-25 min to obtain a dried super gas coating;

[0038] Step two, the dried super gas coating is engraved by using a CNC engraving machine to drive a spring needle tip to scratch the super gas coating, to obtain a tree-shaped super gas track.

[0039] Specific embodiment four: the difference between this embodiment and specific embodiment three is that the methanol fuel cell anode gas diffusion layer substrate 1 is a carbon black-polytetrafluoroethylene composite material or a mesh metal nickel.

[0040] The other steps are the same as specific embodiment three.

[0041] Specific embodiment five: the difference between this embodiment and specific embodiment three or four is that in step one, the surface of the methanol fuel cell anode gas diffusion layer substrate 1 is first ultrasonically cleaned for 10-20 min, and then wiped with ethanol for 3-5 times.

[0042] The other steps are the same as specific embodiment three or four.

[0043] Specific embodiment six: the difference between this embodiment and one of specific embodiments three to five is that in step one, the super gas material is Glaco solution, which is composed of 15% isopropyl alcohol, 14% liquefied petroleum gas, and 1% nanosilica.

[0044] The other steps are the same as specific embodiments three to five.

[0045] Specific embodiment seven: the difference between this embodiment and one of specific embodiments three to six is that in step two, the positioning accuracy of the CNC engraving machine is 25-35 μm, and the scratch width of the spring needle tip is 40-50 μm.

[0046] The other steps are the same as specific embodiments three to six.

[0047] Specific embodiment eight: a method for making the methanol fuel cell anode gas diffusion layer substrate porous surface bubble coalescence and detachment by using the tree-shaped super gas track prepared by the above method, according to the following steps:

[0048] Carbon dioxide bubbles enter from the end 5 of the K+1 stage bifurcated structure under the action of the flowing methanol solution. The carbon dioxide bubbles in the two ends 5 of the K+1 stage bifurcated structure are guided by the K+1 stage guiding section 17 and merge into a single carbon dioxide bubble in the K+1 stage coalescing section 16. Carbon dioxide bubbles that meet the detachment conditions detach in the K+1 stage coalescing section 16 or the K-stage guiding section 15. The carbon dioxide bubbles that do not detach are further guided by the K-stage guiding section 15 and merge with another carbon dioxide gas that has entered the K-stage coalescing section 14 through the K-stage guiding section 15. Bubbles merge into a single carbon dioxide bubble. Carbon dioxide bubbles that meet the detachment conditions detach in the K-stage coalescence section 14. Carbon dioxide bubbles that do not detach remain at the front end 4 of the K-stage bifurcation structure and merge with the next carbon dioxide bubble flowing to the K-stage coalescence section 14 to form a single carbon dioxide bubble. Finally, the carbon dioxide bubble detaches from the super-aerobic orbit 3 of the tree-shaped multi-stage bifurcation structure. The direction from the end 5 of the K+1 stage bifurcation structure to the front end 4 of the K-stage bifurcation structure on the super-aerobic orbit 3 of the tree-shaped multi-stage bifurcation structure is the flow direction of the methanol solution.

[0049] Let D0 be the minimum volumetric equivalent diameter of carbon dioxide bubbles detaching from the substrate surface of the anode gas diffusion layer in a methanol fuel cell, and W be the width of the K-level coalescing segment 14. k i Let D be a series, and D≤D0, and K represent a series, K=1;

[0050] 1) Width W of K-level guide section 15 k j The width W of the K-level aggregation segment 14 k i 1 / 2, the width W of the K-level guide section 15 k j Width W of the K+1 level cluster segment 16 k+1 i Equal, that is:

[0051] W k j = W k i / 2=W k+1 i =2 K-1 W k (1)

[0052] 2) The curvature length S of the K-level guide section 15 k for:

[0053] S k =πR k θ / 90=β k-1 πR k θ / 90 (2)

[0054] wherein π is a constant of the circle, θ is a central angle, β is a radius reduction coefficient of the curved section of the Kth guide section 15, and R k is the radius of the curved section of the Kth guide section 15.

[0055] Specific Embodiment Nine: The difference between this embodiment and the eighth embodiment is that: 1) the length ratio α of the K+1th merging section 16 to the Kth merging section 14 is:

[0056] α = L k+1 i / L k = N -1 / η (3)

[0057] wherein N is the number of branches, N = 2; η is a length dimension, which is a real number between 1 and 2; the length L of the Kth merging section 14 can be obtained from equation 3) as follows: k i

[0058] L k i = L k i γ k-1 = L k i N -k+1 / η (4)

[0059] 2) the length of the straight section of the Kth guide section 15 is 1 / 2 times the length of the Kth merging section 14, i.e.:

[0060] L k j = L k i / 2 = 1 / 2 * L k i N -k+1 / η (5).

[0061] The other steps are the same as those in the eighth embodiment.

[0062] Specific Embodiment Ten: The difference between this embodiment and the eighth or ninth embodiment is that: the length L of the Kth merging section 14 is 1D-5D; the length L of the Kth guide section 15 is 1D-2.5D, the radius R of the curved section of the Kth guide section 15 is 1D-5D; and the central angle θ of the curved section of the Kth guide section 15 and the curved section of the K+1th guide section 17 is 30-60°. K i K j K

[0063] The other steps are the same as those in the eighth or ninth embodiment.

[0064] ​​​​The beneficial effects of the present application are verified by the following examples:

[0065] Example 1: A preparation method of a dendritic super-philic gas track, which is carried out according to the following steps:

[0066] Step one, the surface of the methanol fuel cell anode gas diffusion layer substrate 1 is ultrasonically cleaned for 10 minutes, then wiped with ethanol for 3 times, then the super-philic gas material with a thickness of 50-100 μm is uniformly sprayed on the surface of the methanol fuel cell anode gas diffusion layer substrate 1 (repeat 2-3 times to ensure complete coverage and uniformity of the super-philic gas material), then dried at a temperature of 160℃ for 20 minutes to obtain a dried super-philic gas coating;

[0067] The methanol fuel cell anode gas diffusion layer substrate 1 is a carbon black-polytetrafluoroethylene composite material or a mesh metal nickel; the super-philic gas material is Glaco solution, which is purchased from SOFT99 Corporation, model SF04172; the Glaco solution is composed of 15% isopropyl alcohol, 14% liquefied petroleum gas and 1% nano silicon dioxide.

[0068] Step two, the dried super-philic gas coating is engraved by a CNC engraving machine driven spring stylus scraping method to obtain a dendritic super-philic gas track.

[0069] In order to make the super-philic gas track exhibit excellent bubble manipulation ability, it is necessary to ensure the roughness of the edge of the super-philic gas track, and the ordinary preparation method of the super-philic gas track (laser ablation method, solution immersion method, electrochemical method, etc.) has the disadvantages of high cost, complex steps and low precision, etc. In this embodiment, a spring stylus scraping method driven by a CNC engraving machine (positioning accuracy of 25-35 μm) is used to scrape the non-track part, and the remaining part is the super-philic gas track. A relatively sharp stylus is selected to make the stylus scratch width of 40-50 μm, and a spring is installed between the stylus and the bottom of the shell to keep the pressure of the stylus acting on the super-philic surface large and constant, which can effectively control the roughness of the edge of the track and protect the bottom of the substrate from damage. This method makes the preparation of the super-philic gas track avoid the coffee ring effect at low cost and can be compiled.

[0070] The fractal dendritic structure super-philic gas track adopts a multi-stage dendritic structure, as shown in Figure 2 The structure is composed of a multi-stage bifurcation structure. The bifurcation structure is composed of a converging segment and a flow guiding segment, wherein the flow guiding segment includes a curved segment and a straight segment. The length of the converging segment of the k-stage bifurcation structure is L k i , the width is W k , the length of the straight segment of the flow guiding segment is L k j , and the width of the flow guiding segment is W k+1The curved section of the flow guiding section is composed of two arc segments with opposite directions and with a central angle of θ and a radius of R k Here, the first level bifurcated structure front end 4 and the last level bifurcated structure end 5 of the multi-level bifurcated structure are designed as rectangles, which can also be sectors or other irregular shapes to better capture nearby micro-bubbles.

[0071] Example 2: A method for bubble coalescence and detachment on the porous surface of the anode gas diffusion layer substrate of a methanol fuel cell using a dendritic supergasphil track prepared in Example 1, which is performed according to the following steps:

[0072] The carbon dioxide bubbles enter from the K+1 level bifurcated structure end 5 under the action of the flowing methanol solution, the two carbon dioxide bubbles in the K+1 level bifurcated structure end 5 are guided by the K+1 level flow guiding section 17, merge and combine into one carbon dioxide bubble in the K+1 level coalescence section 16, and the carbon dioxide bubbles that meet the detachment conditions detach in the K+1 level coalescence section 16 or the K level flow guiding section 15; the carbon dioxide bubbles that do not detach are further guided by the K level flow guiding section 15, merge and combine with another carbon dioxide bubble that enters the K level coalescence section 14 through the K level flow guiding section 15 into one carbon dioxide bubble, and the carbon dioxide bubbles that meet the detachment conditions detach in the K level coalescence section 14; the carbon dioxide bubbles that do not detach stay at the K level bifurcated structure front end 4 and combine with the next carbon dioxide bubble flowing into the K level coalescence section 14 into one carbon dioxide bubble, and the final carbon dioxide bubble detaches from the dendritic multi-level bifurcated structure supergasphil track 3; the direction from the K+1 level bifurcated structure end 5 to the K level bifurcated structure front end 4 of the dendritic multi-level bifurcated structure supergasphil track 3 is the flow direction of the methanol solution;

[0073] Let the minimum volume equivalent diameter of the carbon dioxide bubbles detaching from the surface of the anode gas diffusion layer substrate of the methanol fuel cell be D0, the width W k i of the K level coalescence section 14 is D, and D≤D0, K represents the level number, K=1;

[0074] The fractal dendritic supergasphil track is generated according to the design requirements of ideal capture capacity, bubble slip velocity, and stability:

[0075] 1) The width W k j of the K level flow guiding section 15 is 1 / 2 of the width W k i of the K level coalescence section 14, and the width W k j of the K level flow guiding section 15 is equal to the width W k+1 i of the K+1 level coalescence section 16, that is:

[0076] Wk j = W k i / 2 = W k+1 i = 2 K-1 W k (1)

[0077] 2) Length S of curved section of K-stage flow guiding section 15 k is:

[0078] S k = πR k θ / 90 = β k-1 πR k θ / 90 (2)

[0079] where π is a circular constant, θ is a central angle, β is a radius reduction coefficient of curved section of K-stage flow guiding section 15, R k is a radius of curved section of K-stage flow guiding section 15;

[0080] 3) Length ratio α of K+1-stage converging section 16 and K-stage converging section 14 is:

[0081] α = L k+1 i / L k = N -1 / η (3)

[0082] where N is a branch number, N = 2; η is a length dimension, which is a real number of 1-2; length L k i of K-stage converging section 14 is:

[0083] L k i = L k i γ k-1 = L k i N -k+1 / η (4)

[0084] 4) Length of straight section of K-stage flow guiding section 15 is 1 / 2 times of K-stage converging section 14, that is:

[0085] L k j = L k i / 2 = 1 / 2 * L k i N -k+1 / η (5).

[0086] Length L K i1D~5D; the length L of the K-stage flow guide section 15 K j 1D~2.5D, the radius R of the curved section of the K-stage flow guide section 15 K 1D~5D; the central angle θ of the curved section of the K-stage flow guide section 15 and the curved section of the K+1-stage flow guide section 17 is 30~60°.

[0087] The tree-shaped super-philic gas track is designed to maximize the space utilization of the track position layout, as shown in Figure 3 The first bifurcated structure front end a 6, the first bifurcated structure front end b 7 and the first bifurcated structure front end c 8 are arranged in the x and y directions as positioning reference, specifically: the first bifurcated structure front end a 6 and the first bifurcated structure front end b 7 are spaced 6.5D along the x-axis direction, and 12.5D along the y-axis direction; the first bifurcated structure front end b 7 and the first bifurcated structure front end c 8 are spaced 13.5D along the x-axis direction. In this embodiment, the bifurcated tree structure is designed to take η as 2, and appropriate R1(3~5D) and L k i (4~7D), so that the track overlap phenomenon does not occur.

[0088] As shown in Figure 4 , it is a bubble coalescence process of bifurcated structure. With the gradual penetration of the surface of the methanol fuel cell anode gas diffusion layer substrate 1 to form bubbles 10, small bubbles gradually slide horizontally with the flow of the fluid in the flow channel. At this time, the size of the small bubbles is too small, and under the influence of the porous wall, the flow rate of the flow field where the bubbles are located is small, and the bubbles are not easy to separate from the porous surface.

[0089] The small bubbles that slide horizontally touch the end of the bifurcated tree-shaped super-philic gas track and slide along the super-philic gas track. Under the guidance of the super-philic gas track, the small bubbles gradually coalesce to form larger bubbles in the coalescence section of the super-philic gas track. The bubbles gradually increase in size after multiple coalescence in the coalescence section of the multi-stage bifurcated tree-shaped super-philic gas track.

[0090] With the increase of the size of the bubbles, the flow field where the bubbles are located gradually moves away from the porous wall. When the size of the bubbles increases to a certain extent, under the action of the large flow field flow rate far away from the porous wall, the shear force of the flow field exceeds the adhesion of the bubble to the surface of the substrate, and the bubble begins to separate from the porous surface and is quickly discharged.

[0091] In summary, the method of this embodiment based on the bifurcated tree-shaped super-philic gas track can effectively achieve the purpose of coalescence of the bubbles on the porous surface along the track and then separation from the surface and rapid discharge, and the preparation method of this embodiment is simple and low in cost, so it has great value in improving the working performance of the methanol fuel cell.

Claims

1. A method for bubble coalescence and detachment from the porous surface of a methanol fuel cell anode gas diffusion layer substrate using a dendritic hyperphobic track, characterized in that This method is performed in the following steps: Carbon dioxide bubbles enter from the end (5) of the K+1 stage bifurcation structure under the action of the flowing methanol solution. The carbon dioxide bubbles in the two ends (5) of the K+1 stage bifurcation structure are guided by the K+1 stage guiding section (17) and merge into a single carbon dioxide bubble in the K+1 stage coalescence section (16). Carbon dioxide bubbles that meet the detachment conditions detach in the K+1 stage coalescence section (16) or the K-stage guiding section (15). The carbon dioxide bubbles that do not detach are further guided by the K-stage guiding section (15) and merge with another carbon dioxide bubble that enters the K-stage coalescence section (14) through the K-stage guiding section (15). Carbon bubbles merge into a single carbon dioxide bubble. Carbon dioxide bubbles that meet the detachment conditions detach in the K-level coalescence section (14). Carbon dioxide bubbles that do not detach remain at the front end (4) of the K-level bifurcation structure and merge with the next carbon dioxide bubble flowing to the K-level coalescence section (14) to form a single carbon dioxide bubble. Finally, the carbon dioxide bubble detaches from the super-aerobic orbit (3) of the tree-shaped multi-level bifurcation structure. The direction from the end (5) of the K+1 level bifurcation structure to the front end (4) of the K-level bifurcation structure on the super-aerobic orbit (3) of the tree-shaped multi-level bifurcation structure is the flow direction of the methanol solution. Let the minimum volume-equivalent diameter of the carbon dioxide bubbles that detach from the surface of the anode gas diffusion layer substrate of the methanol fuel cell be D0, and the width of the K-stage coalescence section (14) be W k i D, and D≤D0, and K represents the stage number, K=1. 1) the width W of the Kth draft section (15) k j the width W of the Kth merging section (14) k i the width W of the Kth draft section (15) k j the width W of the K+1th merging section (16) k+1 i i.e.: W k j = W k i / 2 = W k+1 i = 2 K-1 W k (1) 2) Length S of curved section of K-class flow guiding section (15) k is: S k = πR k θ / 90 = β k-1 πR k θ / 90 (2) In the formula, π is the ratio of a circle, θ is the central angle, β is the radius reduction coefficient of the curved section of the K-stage guide section (15), R k is the radius of the curved section of the K-stage guide section (15). The tree-shaped super-acidic track is set on the surface of the anode gas diffusion layer substrate (1) of the methanol fuel cell. The tree-shaped super-acidic track is composed of several tree-shaped multi-level bifurcation super-acidic tracks (3). The tree-shaped multi-level bifurcation super-acidic track (3) is an open-type patterned track. The tree-like multi-stage bifurcation superhydrophilic orbit (3) consists of a K-stage bifurcation structure (12) and two K+1-stage bifurcation structures (13). The K-stage bifurcation structure (12) consists of a K-stage coalescing section (14) and a K-stage guiding section (15). The opening at the front end (4) of the K-stage bifurcation structure serves as the outlet of the K-stage coalescing section (14), and the opening at the end (9) of the K-stage bifurcation structure serves as the inlet of the K-stage coalescing section (14). The opening of the K+1-stage bifurcation structure (13) is formed by a K+1-stage coalescing section. The structure consists of a segment (16) and two K+1 level guide segments (17). The front end (11) of the K+1 level bifurcation structure serves as the outlet of the K+1 level merging segment (16), and the opening at the end (5) of the K+1 level bifurcation structure serves as the inlet of the K+1 level guide segment (17). The front end (11) of the K+1 level bifurcation structure is connected to the end (9) of the K-level bifurcation structure. Both the K-level merging segment (14) and the K+1 level merging segment (16) are straight segments, while both the K-level guide segment (15) and the K+1 level guide segment (17) are curved segments. K = 1. The method for preparing the aforementioned tree-shaped superhydrophilic orbitals is carried out according to the following steps: Step one, the surface of the methanol fuel cell anode gas diffusion layer substrate (1) is cleaned, wiped, and then the super gas-wetting material with a thickness of 50-100 μm is uniformly sprayed on the surface of the methanol fuel cell anode gas diffusion layer substrate (1), and then dried at a temperature of 140-180 ℃ for 15-25 min to obtain a dried super gas-wetting coating; Step two, the dried super gas-wetting coating is engraved by using a CNC engraving machine to drive a spring needle tip to scratch the super gas-wetting coating, thereby obtaining a tree-shaped super gas-wetting track.

2. The method for bubble coalescence and detachment of the porous surface of the methanol fuel cell anode gas diffusion layer substrate by using a tree-shaped super gas-wetting track according to claim 1, characterized in that: 1) the length ratio α of the K+1 order coalescence section (16) to the K order coalescence section (14) is: a = L k+1 i / L k = N -1 / η (3) wherein N is the number of branches, N=2; η is the length dimension, a real number between 1 and 2; the length L of the Kth stage of combining section (14) is obtained from equation 3) k i is: L k i = L k i γ k-1 = L k i N -k+1 / η (4) 2) the straight section length of the K order flow guide section (15) is 1 / 2 of the length of the K order coalescence section (14), i.e.: L k j = L k i = 1 / 2 * L k i N -k+1 / η (5).

3. The method for bubble coalescence and detachment from the porous surface of the anode gas diffusion layer substrate of a methanol fuel cell using a dendritic hyperphobic track according to claim 1, wherein Length L of K-stage merging section (14) K i Length L of K-stage guide section (15) K j Radius R of curved section of K-stage guide section (15) K Central angle θ of curved section of K-stage guide section (15) and curved section of K+1-stage guide section (17) is 30-60°.

4. The method for bubble coalescence and detachment from the porous surface of the anode gas diffusion layer substrate of a methanol fuel cell using a dendritic superhydrophilic track according to claim 1, wherein: The curved section of the K-stage flow guide section (15) is composed of two arc sections with a same central angle θ and a same radius R K and opposite directions, and the curved section of the K+1-stage flow guide section (17) is composed of two arc sections with a same central angle θ and a same radius R K+1 and opposite directions. The surface of the methanol fuel cell anode gas diffusion layer substrate (1) is provided with pores (2) with a pore size less than 100 μm.

5. The method for agglomerating and detaching bubbles on the porous surface of the anode gas diffusion layer substrate of a methanol fuel cell using a tree-shaped superaerophilic orbital according to claim 1, characterized in that: The methanol fuel cell anode gas diffusion layer substrate (1) is a carbon black-polytetrafluoroethylene composite material or a mesh-shaped metal nickel.

6. The method for agglomerating and detaching bubbles on the porous surface of the anode gas diffusion layer substrate of a methanol fuel cell using a tree-shaped superaerophilic orbital according to claim 1, characterized in that: In step one, the surface of the methanol fuel cell anode gas diffusion layer substrate (1) is first ultrasonically cleaned for 10-20 min, and then wiped with ethanol for 3-5 times.

7. The method for facilitating the coalescence and detachment of bubbles on the porous surface of the anode gas diffusion layer substrate of a methanol fuel cell using a tree-shaped superaerophilic orbital according to claim 1, characterized in that: The super gas-wetting material in step one is Glaco solution, which is composed of 15% isopropyl alcohol, 14% liquefied petroleum gas, and 1% nano silicon dioxide.

8. The method for bubble coalescence and detachment from the porous surface of the anode gas diffusion layer substrate of a methanol fuel cell using a dendritic superhydrophilic track of claim 1, wherein: In step two, the positioning accuracy of the CNC engraving machine is 25-35 μm, and the scratch width of the spring needle tip is 40-50 μm. ​

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