Hydrogen-sensitive colorimetric detection gel porosity calculation method and preparation method of detection gel

Abstract

This invention belongs to the field of polymer technology, specifically relating to a method, system, and device for calculating the porosity of a hydrogen-sensitive colorimetric detection gel. It aims to solve the problems of existing tape detection methods, such as limited detection range, reliability limited by tape thickness and adhesion, and susceptibility to missed detections; and the complex preparation and poor final product quality of hydrogels, where porosity cannot be accurately calculated. This invention includes: a set of heat and mass transfer equations characterizing hydrogen molecule diffusion in a hydrogel, expressed in dimensionless form; obtaining equations for hydrogen flow and diffusion migration in the hydrogel by combining boundary motion constraints; solving for the physical properties of the material and calculating the hydrogel porosity; and preparing the hydrogen-sensitive colorimetric detection gel based on the hydrogel porosity. This invention calculates the porosity of the hydrogel and controls porosity during preparation, achieving precise location detection of hydrogen leaks, reducing the likelihood of missed detections. The preparation process is simple, the gel is recyclable, and the cost is low and safety is high.

Description

Technical Field

[0001] This invention belongs to the field of polymer technology, and specifically relates to a method, system and equipment for calculating the porosity of hydrogen-sensitive colorimetric detection gel. Background Technology

[0002] With the national long-term strategic planning and the proposal of carbon neutrality and carbon peaking goals, the development and utilization of new energy sources has become an important direction for future development. As a renewable energy source, hydrogen energy has attracted increasing research. In the process of extensive scientific research and practice, the preparation, storage and transportation of hydrogen energy have received widespread attention. However, due to the high energy flux density and high explosion limit (4%-75%) of hydrogen, which leads to its high risk characteristics, hydrogen energy has not been widely promoted and applied for a long time.

[0003] To efficiently promote the large-scale application of hydrogen energy, it is crucial to address the safety hazards it presents. Particularly during hydrogen storage and transportation, because hydrogen atoms are extremely small, they can easily permeate through iron atoms in steel containers and react with carbon elements inside the material, leading to container failure. Similarly, flanges and pipe welds at stations and between pipeline sections are also prone to micro-leakage, leakage, and even pipeline rupture. Therefore, early prediction and detection of micro-leakage / leakage sources are key to improving the safety of hydrogen energy utilization.

[0004] Existing research mainly focuses on the use of hydrogen-sensitive color-changing active materials, including tape detection devices that achieve color change upon contact with hydrogen gas or liquid hydrogen by using rare metals (Pt platinum, Pd palladium, Rh rhodium, La lanthanum) as active materials and color-developing oxidants (WO3, SiO2, TiO2, SnO2, etc.) as compositions.

[0005] However, tape detection still faces two significant challenges: First, the detection range is limited by the tape's width. For large tanks, tape detection severely impacts operation, and the contact characteristics between the tape's adhesive layer and the tank wall surface also affect detection effectiveness. Furthermore, even with insulation measures, condensation on the outer wall of cryogenic liquid hydrogen tanks is common, raising concerns about the impact of water on the adhesive layer and hydrogen-sensitive material. Second, the reliability of tape detection depends on the tape's thickness. The leakage aperture determines the hydrogen penetration depth, and the effective detection components in the hydrogen-sensitive tape are reflected in the tape's thickness, which also depends on the adhesive properties of the layer. If a micro-leak occurs, hydrogen is likely to escape through the adhesive gaps, leading to missed detections. Summary of the Invention

[0006] To address the aforementioned problems in existing technologies—namely, the limited detection range and reliability of current tape detection methods, which are constrained by tape thickness and adhesion, leading to frequent missed detections—and the lack of methods for controlling and calculating porosity in the synthesis of hydrogel materials with specific functions, resulting in uncontrolled gel synthesis and poor synthesis effects without a technical description of preparing hydrogels within a specific porosity range, this invention provides a hydrogen-sensitive colorimetric detection method for calculating gel porosity. This method includes:

[0007] Step S10: Based on the gas transport law in porous media, the heat and mass transfer equations for hydrogen molecule diffusion in hydrogel are characterized by the Darcy-Brinkman model.

[0008] Step S20: Based on the balance between convection and diffusion terms in the hydrogel, the heat and mass transfer equations are expressed in dimensionless form.

[0009] Step S30: Combining the motion constraints of the hydrogel solid material at the boundary, obtain the equations for hydrogen flow and diffusion migration in the hydrogel.

[0010] Step S40: Based on the hydrogen flow and diffusion migration equation, obtain the Knudsen number, which characterizes the relationship between pore size and hydrogen free path, and obtain the physical properties satisfied by the hydrogel preparation material.

[0011] Step S50: Obtain the permeability equation for hydrogen diffusion in the hydrogel crosslinker; combine the permeability equation, the Knudsen number, and the physical properties satisfied by the hydrogel preparation material to obtain the hydrogel porosity.

[0012] Furthermore, the heat and mass transfer equations for the diffusion of hydrogen molecules in the hydrogel are expressed as follows:

[0013]

[0014]

[0015]

[0016]

[0017]

[0018] Where U represents the dimensionless velocity in the x-direction, V represents the dimensionless velocity in the y-direction, X represents the x-coordinate, Y represents the y-coordinate, P represents the dimensionless pressure, T represents the dimensionless temperature of the gas, S represents the mass concentration of the diffusing fluid, τ represents the dimensionless time, and R... e =u ref Hφ -1 D represents the dimensionless control parameter Reynolds number.a =k / H 2 Representing Darcy numbers, Representing the Grashof number, P r =vφ / α represents the Prandtl number, S c =vφ / D represents the Schmidt number, H, u ref Δ t Δs represents the length scale, the actual flow velocity at the top as a velocity scale, the temperature scale, and the concentration scale, respectively; v = μ / ρ represents the kinematic viscosity of the fluid; α represents the thermal diffusivity; D represents the mass diffusivity; g represents the gravitational acceleration; k represents the permeability of the porous medium; φ represents the porosity of the hydrogel; β t ρ represents the volume expansion coefficient, μ represents the kinematic viscosity, and ρ represents the fluid density at temperature t0.

[0019] Furthermore, in step S20, the heat and mass transfer equations are expressed in dimensionless form, as follows:

[0020] (X, Y) = (x, y) / H

[0021] (U, V) = (u, v) / u ref

[0022] τ=τ * / (H / u ref )

[0023]

[0024] T=(t-t0) / Δt

[0025] S=(s-s0) / Δs

[0026] Δt=(t1-t0)

[0027] Δs=(s1-s0)

[0028] Where (x, y) represents the actual coordinates of the fluid motion, (u, v) represents the fluid velocity, and τ * The flow time is represented by ρ and ρ0, respectively, which represent the fluid density at temperature t0 and the fluid density at heat source temperature t0. g represents acceleration per kilometer. t, t0, and t1 represent the fluid temperature parameters, initial temperature, and final temperature, respectively. s, s0, and s1 represent the concentration parameters, initial concentration, and final concentration, respectively. H / u ref Represents a time scale.

[0029] Furthermore, the motion constraint conditions of the hydrogel solid material at the boundary are as follows:

[0030] At the opening boundary: U0 = 1, V = 0, T = 0.

[0031] Bottom wall: U=0, V=0

[0032] Sidewall surface: U = 0, V = 0

[0033] Intermediate solid block: λ solid =λ fluid ,ρD solid =0;

[0034] Where U0 represents the dimensionless initial velocity, λ solid and λ fluid D represents the thermal conductivity of solids and the thermal conductivity of fluids. solid This represents the diffusion coefficient of the solid mass.

[0035] Furthermore, the equations for hydrogen flow and diffusion migration in the hydrogel are expressed as follows:

[0036] f = R e ·D a

[0037] Among them, R e =u ref Hφ -1 D represents the dimensionless control parameter Reynolds number. a =k / H 2 Represents Darcy number, u ref The top actual flow velocity is represented as a velocity scale, H represents the length scale, k represents the permeability of the porous medium, and φ represents the porosity of the porous medium.

[0038] Furthermore, the Knudsen number, which characterizes the relationship between pore size and hydrogen free path, is expressed as:

[0039]

[0040] Where Kn is the Knuthian number, k B Here, σ is Boltzmann's constant, T represents the dimensionless temperature of the gas, p is the pressure, and σ is the diameter of a hydrogen molecule. This represents the characteristic size of the hydrogel pores.

[0041] Furthermore, the permeability equation for the diffusion of hydrogen gas in the hydrogel crosslinker is as follows:

[0042]

[0043] Where κ represents the permeability of hydrogen diffusion in the hydrogel crosslinker, α represents the thermal diffusivity, A represents the average diameter of the hydrogel crosslinker, and λ represents the average diameter of the hydrogel crosslinker. max D represents the diameter of the maximum aperture. fThese are parameters that characterize the fractal coefficients and dimension.

[0044] Furthermore, the porosity of the hydrogel is:

[0045]

[0046] Where φ represents the porosity of the hydrogel, and D a =k / H 2 Here, β represents the Darcy number, k represents the permeability of the porous medium, H represents the length scale, and β = R / l represents the ratio of chain length to pore diameter, where R represents chain length and l represents pore diameter.

[0047] In another aspect, the present invention provides a method for preparing a detection gel, based on the above-described method for calculating the porosity of a hydrogen-sensitive colorimetric detection gel, the preparation method comprising:

[0048] In step A10, using 2M acrylamide as a monomer, 0.001MN, N'-dimethylbisacrylamide as a crosslinking agent, 0.002M 2-hydroxy-4′-(2-hydroxyethoxy)-2-methylphenylacetone as a UV initiator, and Tween20 at a concentration of 0.05 g / cm3 as a surfactant, oleyl alcohol is dispersed in the aqueous phase as small droplets.

[0049] Step A20: After stirring the solution thoroughly, pour it into a mold. Under the protection of 99.99% pure nitrogen gas, at a power density of 4 mW / cm³... 2 PAAm hydrogel was obtained by irradiating with ultraviolet light at a wavelength of 365nm for 8 hours.

[0050] Step A30: The PAAm hydrogel is repeatedly swollen in deionized water three times and then dried in an oven at 70°C for different times to obtain hydrogel materials with different water contents and set porosities; the porosity of the hydrogel material is adjusted by adjusting the content of the surfactant.

[0051] Step A40: Tungsten trioxide micro powder and soluble lanthanum are mixed in a set ratio and then refined and activated by high-energy ball milling to obtain a hydrogen-sensitive color-changing material suspension.

[0052] Step A50: Immerse hydrogel materials with different water contents and set porosities in the suspension of the hydrogen-sensitive color-changing material, and make the hydrogel materials fully swell by mechanical vibration;

[0053] Step A60: Vacuum dry the fully swollen hydrogel material to obtain a hydrogen-sensitive colorimetric detection hydrogel.

[0054] In some preferred embodiments, step A40 includes:

[0055] Step A41: Obtain tungsten trioxide micro powder and soluble lanthanum according to the set ratio, and dissolve the tungsten trioxide micro powder in sodium hydroxide at the set temperature and concentration;

[0056] Step A42: Add the set weight of anhydrous ethanol to the solution containing dissolved tungsten trioxide powder and stir until homogeneous;

[0057] Step A43: Add concentrated hydrochloric acid to the well-stirred solution until yellow tungstic acid is formed, stir again and heat the solution to obtain condensed tungstic acid.

[0058] Step A44: Add soluble lanthanum to the condensed tungstic acid to obtain a lanthanum-doped tungsten trioxide suspension as a hydrogen-sensitive color-changing material suspension.

[0059] The beneficial effects of this invention are:

[0060] (1) The method for calculating the porosity of hydrogen-sensitive colorimetric detection gel in this invention, based on the analysis of the permeation and diffusion law of hydrogen in hydrogel and the dispersion characteristics of cross-linked network and hydrogen-sensitive material dispersed phase, determines the dispersed particle size of Pt (platinum) powder and WO3 (tungsten trioxide) in hydrogel, as well as the type and composition ratio of cross-linked materials. Finally, the detection hydrogel has high sensitivity to hydrogen, and the detection results are accurate and precise, and it is not easy to miss the detection.

[0061] (2) The method for calculating the porosity of the hydrogen-sensitive colorimetric detection gel of the present invention is as follows: when the air humidity near the test surface is high or the wall surface is condensed, the detection hydrogel of the present invention absorbs water and quickly adsorbs it onto the test surface. When the air humidity near the test surface is low, the water contained in the hydrogel can wet the wall surface, effectively improving the adhesion between the hydrogel and the test surface and achieving accurate positioning detection.

[0062] (3) The method for calculating the porosity of hydrogen-sensitive colorimetric detection gel of the present invention allows the gel to detach on its own after the water in the gel is evaporated, and it can be recycled and reused, effectively reducing costs and resource consumption.

[0063] (4) The method for calculating the porosity of hydrogen-sensitive colorimetric detection gel of the present invention can directly scrape off the gel during the maintenance and inspection process without causing wall adhesion damage or paint peeling, which further improves the safety of hydrogen storage and transportation. Attached Figure Description

[0064] Other features, objects, and advantages of this application will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings:

[0065] Figure 1 This is a schematic flowchart of the method for calculating the porosity of a hydrogen-sensitive colorimetric detection gel according to the present invention.

[0066] Figure 2This is a schematic diagram of the cross-linking structure change of hydrogel after being subjected to force in one embodiment of the hydrogen-sensitive colorimetric detection gel porosity calculation method of the present invention.

[0067] Figure 3 This is a simplified analysis module and boundary condition diagram of an embodiment of the hydrogen-sensitive colorimetric detection gel porosity calculation method of the present invention;

[0068] Figure 4 This is a schematic diagram illustrating the effect of permeability on flow in one embodiment of the hydrogen-sensitive colorimetric detection gel porosity calculation method of the present invention;

[0069] Figure 5 This is a graph showing the horizontal flow velocity curves along the vertical centerline at different Darcy numbers in one embodiment of the hydrogen-sensitive colorimetric detection gel porosity calculation method of the present invention.

[0070] Figure 6 This is a schematic diagram illustrating the influence of dimensionless parameters on near-vertical velocity distribution in one embodiment of the hydrogen-sensitive colorimetric detection gel porosity calculation method of the present invention. Detailed Implementation

[0071] The present application will now be described in further detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the invention. Furthermore, it should be noted that, for ease of description, only the parts relevant to the invention are shown in the accompanying drawings.

[0072] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. This application will now be described in detail with reference to the accompanying drawings and embodiments.

[0073] Currently, the simplest and quickest method for leak detection during manual pipeline inspections is to use soapy water or foaming water for initial leak location inspection. This is mainly because the visual appearance of bubbles in soapy water gives the approximate location of the leak; or leak detection tape is used to wrap around the leak and observe a color change in a certain area as a leak indicator. However, these two methods cannot provide the morphology and location of micro-leaks, and cannot provide more information for subsequent maintenance and protection. This may lead to missed detections or failed risk assessments, resulting in subsequent pipeline ruptures or production accidents.

[0074] This invention provides a method for calculating the porosity of a hydrogen-sensitive colorimetric detection gel. This method considers that the prepared detection material needs to be directly coated onto the pipe wall or the outside of the tank, and also needs to possess good water environment characteristics and surface adhesion characteristics. The detection material is prepared as a hydrogel. When the air humidity is high or condensation forms on the wall surface, the gel absorbs water and quickly adsorbs onto the surface to be detected, adhering firmly. When the air humidity is low, the water contained in the gel can wet the wall surface, achieving precise positioning detection. After the water in the gel evaporates, the gel can detach on its own and can be recycled and reused. During maintenance and inspection, the gel can be directly scraped off without causing wall adhesion damage or paint peeling. To prepare a hydrogen-sensitive colorimetric detection hydrogel that achieves the above properties, this method calculates the preparation parameters of the detection gel from three aspects: (1) analyzing the permeation and diffusion law of hydrogen in the hydrogel; (2) analyzing the dispersion characteristics of the cross-linked network and the dispersed phase of the hydrogen-sensitive material; (3) based on (1) and (2), determining the dispersed particle size of Pt (platinum) powder and WO3 (tungsten trioxide) in the hydrogel, as well as the type and composition ratio of the cross-linking material.

[0075] The present invention provides a method for calculating the porosity of a hydrogen-sensitive colorimetric detection gel, the method comprising:

[0076] Step S10: Based on the gas transport law in porous media, the heat and mass transfer equations for hydrogen molecule diffusion in hydrogel are characterized by the Darcy-Brinkman model.

[0077] Step S20: Based on the balance between convection and diffusion terms in the hydrogel, the heat and mass transfer equations are expressed in dimensionless form.

[0078] Step S30: Combining the motion constraints of the hydrogel solid material at the boundary, obtain the equations for hydrogen flow and diffusion migration in the hydrogel.

[0079] Step S40: Based on the hydrogen flow and diffusion migration equation, obtain the Knudsen number, which characterizes the relationship between pore size and hydrogen free path, and obtain the physical properties satisfied by the hydrogel preparation material.

[0080] Step S50: Obtain the permeability equation for hydrogen diffusion in the hydrogel crosslinker; combine the permeability equation, the Knudsen number, and the physical properties satisfied by the hydrogel preparation material to obtain the hydrogel porosity.

[0081] To more clearly explain the method for calculating the porosity of the hydrogen-sensitive colorimetric detection gel of the present invention, the following is in conjunction with... Figure 1 The steps in the embodiments of the present invention will be described in detail below.

[0082] The method for calculating the porosity of a hydrogen-sensitive colorimetric detection gel according to the first embodiment of the present invention includes steps S10-S50, each of which is described in detail below:

[0083] For hydrogels, compared to the chemical structures of polyacrylamide (PAAm) and ammonium alginate (AIg), the hydrogen atom has a radius of only 0.79 angstroms, making it the smallest atom in nature, and its diffusion rate is 3.8 times that of natural gas. When it diffuses within the cross-linking groups of macromolecules, the diffusion and transport of hydrogen are hindered, resulting in continuous collisions within the macromolecules. At this point, under the influence of Pt powder dispersed in the colloid, hydrogen reacts with hydrogen-sensitive colorimetric materials such as WO3 to produce a colorimetric reaction. After the reaction, this colorimetric material continues to diffuse towards the direction of hydrogen leakage under the influence of the concentration gradient, further reacting and thus allowing the detection of hydrogen leakage points.

[0084] like Figure 2 The diagram shown illustrates the change in the cross-linking structure of a hydrogel under stress, according to an embodiment of the hydrogen-sensitive colorimetric detection gel porosity calculation method of the present invention. Figure 2 (a) in the text indicates the synthesis of flexible macromolecular chains using PAAm materials. Figure 2 (b) in the diagram represents the semi-rigid chain molecular structure of sodium alginate. The two are prepared by mixing them in a specific ratio to form... Figure 2 The leftmost hydrogel body in (c) is shown. When it absorbs water, due to its special molecular structure, the two cross-linked bodies inside the hydrogel will rearrange themselves when stretched and twisted to resist deformation; when it re-swells, the internal structure of the hydrogel will rearrange itself under the action of water, so that the gel's properties remain excellent.

[0085] Because hydrogen atoms have extremely small particle sizes, they diffuse and migrate in hydrogels under pressure difference and concentration. Considering that hydrogels are composed of macromolecular organic matter, nanoscale metals or oxide powders, the heat and mass transfer process of hydrogen molecule diffusion in hydrogels can be characterized by the gas transfer law in porous media.

[0086] Step S10: Based on the gas transport law in porous media, the heat and mass transfer equations for hydrogen molecule diffusion in hydrogel are characterized by the Darcy-Brinkman model.

[0087] like Figure 3 As shown, this is a simplified analysis module and boundary condition diagram of an embodiment of the hydrogen-sensitive colorimetric detection gel porosity calculation method of the present invention. The xoy axis represents the coordinate system of the simplified dimensionless model, where H and W represent the dimensionless length and width, respectively. The shaded part in the figure is the porous medium region. The two boxes represent the solid blocks in the calculation region (introduced only to more accurately describe the physical process). g represents the gravitational acceleration, U0 represents the initial velocity of the outer surface of the external dimensionless region. The upper boundary in the model is the opening boundary, the left and right sides are the thermal insulation thermal boundary and the wall surface no-slip velocity boundary, and the bottom contains the source term. The specific constraints are: (1) At the opening boundary: U0=1, V=0, T=0, (2) Bottom wall: U = 0, V = 0, (3) Sidewall surface: U = 0, V = 0, (4) Intermediate solid block: λ solid =λ fluid ,ρD solid =0.

[0088] Assuming the porous medium space is homogeneous, has constant physical properties, and is isotropic, and is in local thermal equilibrium (i.e., the heat transfer between the solid and pores within a certain computational grid is in equilibrium), the flow process within the space is considered laminar and incompressible, and the thermal buoyancy force due to temperature difference must be considered, while viscous dissipation and inertial resistance within the porous medium are ignored. When the saturated fluid is hydrogen, the effect of thermal buoyancy force caused by fluid density change is characterized by Boussinesq, as shown in Equation (1):

[0089] ρ=ρ0[1-β t (t-t0)] (1)

[0090] Where ρ0 represents the density of the fluid (hydrogen) at the heat source temperature t0, β t It is the coefficient of thermal expansion of the fluid (hydrogen).

[0091] Based on the above description, the heat and mass transfer equations for the diffusion of hydrogen molecules in hydrogels are shown in equations (2) to (6):

[0092]

[0093]

[0094]

[0095]

[0096]

[0097] Where U represents the dimensionless velocity in the x-direction, V represents the dimensionless velocity in the y-direction, X represents the x-coordinate, Y represents the y-coordinate, P represents the dimensionless pressure, T represents the dimensionless temperature of the gas, S represents the mass concentration of the diffusing fluid, τ represents the dimensionless time, and R... e =u ref Hφ -1 D represents the dimensionless control parameter Reynolds number. a =k / H 2 Representing Darcy numbers, Representing the Grashof number, P r =vφ / α represents the Prandtl number, S c =vφ / D represents the Schmidt number, H, u refΔt and Δs represent the length scale, the actual flow velocity at the top as a velocity scale, the temperature scale, and the concentration scale, respectively; v = μ / ρ represents the kinematic viscosity of the fluid; α represents the thermal diffusivity; D represents the mass diffusivity; g represents the gravitational acceleration; k represents the porous medium permeability; φ represents the hydrogel porosity; β t ρ represents the volume expansion coefficient, μ represents the kinematic viscosity, and ρ represents the fluid density at temperature t0.

[0098] When calculating the solid block inside the computational space, the surface velocity of its region is 0. Therefore, the convection terms in equations (5) and (6) are 0. The convection terms are the terms obtained by taking the partial derivative of the left side of the above expressions. in To solve for the physical quantity, u i x i All are tensors.

[0099] Step S20: Based on the balance between convection and diffusion terms in the hydrogel, the heat and mass transfer equations are expressed in dimensionless form.

[0100] Considering that convection and diffusion must be kept in balance, and taking into account the range of control parameters, the corresponding variables of the above equations are subjected to dimensionless quantization, as shown in equations (7)-(14):

[0101] (X, Y) = (x, y) / H (7)

[0102] (U, V) = (u, v) / u ref (8)

[0103] τ=τ* / (H / u ref (9)

[0104]

[0105] T=(t-t0) / Δt (11)

[0106] S=(s-s0) / Δs (12)

[0107] Δt=(t1-t0) (13)

[0108] Δs=(s1-s0) (14)

[0109] Where (x, y) represents the actual coordinates of the fluid motion, (u, v) represents the fluid velocity, and τ *The flow time is represented by ρ and ρ0, respectively, which represent the fluid density at temperature t0 and the fluid density at heat source temperature t0. g represents acceleration per kilometer. t, t0, and t1 represent the fluid temperature parameters, initial temperature, and final temperature, respectively. s, s0, and s1 represent the concentration parameters, initial concentration, and final concentration, respectively. H / u ref Represents a time scale.

[0110] Step S30: Combining the motion constraints of the hydrogel solid material at the boundary, the equations for hydrogen flow and diffusion migration in the hydrogel are obtained.

[0111] The boundary motion constraint conditions for hydrogel solid materials are:

[0112] At the opening boundary: U0 = 1, V = 0, T = 0.

[0113] Bottom wall: U=0, V=0

[0114] Sidewall surface: U = 0, V = 0

[0115] Intermediate solid block: λ solid =λ fluid ,ρD solid =0;

[0116] Where U0 represents the dimensionless initial velocity, λ solid and λ fluid D represents the thermal conductivity of solids and the thermal conductivity of fluids. solid This represents the diffusion coefficient of the solid mass.

[0117] The equations are solved through the above process to obtain the streamline diagram inside the cavity, as shown below. Figure 4 The diagram shown illustrates the effect of permeability on flow in one embodiment of the hydrogen-sensitive colorimetric detection gel porosity calculation method of the present invention. Figure 4 (a) Darcy number D a =0.01, Figure 4 (b) Darcy number D a =0.005, Figure 4 (c) Darcy number D a =0.001, and its corresponding dimensionless control parameter Reynolds number R e Both are 2000.

[0118] like Figure 5 The figure shows the horizontal flow velocity curves along the vertical centerline at different Darcy numbers in one embodiment of the hydrogen-sensitive colorimetric detection gel porosity calculation method of the present invention. The three curves correspond to Darcy numbers D. a =0.01, D a =0.001 and Da When the value is 0.005, the horizontal axis represents the dimensionless coordinate position in the X direction, and the vertical axis represents the dimensionless horizontal velocity on the vertical center line.

[0119] Step S40: Based on the hydrogen flow and diffusion migration equations, obtain the Knudsen number, which characterizes the relationship between pore size and hydrogen free path, and obtain the physical properties satisfied by the hydrogel preparation material.

[0120] The equations for hydrogen flow and diffusion migration in hydrogels can be derived from the above formulas, as shown in equation (15):

[0121] F = R e ·D a (15)

[0122] Among them, R e =u ref Hφ -1 D represents the dimensionless control parameter Reynolds number. a =k / H 2 Represents Darcy number, u ref The top actual flow velocity is represented as a velocity scale, H represents the length scale, k represents the permeability of the porous medium, and φ represents the porosity of the porous medium.

[0123] Equation (15) indicates that fluid diffusion in porous media is influenced by three factors: inertial force, viscous force, and pore resistance. These three factors encompass many practical factors such as fluid viscosity, inlet velocity, porous media permeability, permeability, and geometry. For a given fluid, the dimensionless control parameter Reynolds number R... e The higher the Darcy number D a The higher the value, the greater the inlet velocity and the stronger the permeability of the porous medium.

[0124] Depend on Figure 4 It can be seen that Darcy number D a This reflects the permeability of the fluid during the diffusion process, when the Darcy number D... a The larger the porous medium, the more intense the heat and mass transfer processes become, resulting in a main vortex in the center of the solid block and smaller vortices near the sides. Due to the high intensity of mass transfer diffusion, the temperature distribution is relatively uniform during gas release. Figure 5 It can be seen that during gas diffusion, the velocity distribution along the vertical centerline is mainly influenced by the Darcy number D. a Impact, Darcy number D a The larger the value, the more uniform the velocity distribution.

[0125] In one embodiment of the present invention, the dimensionless control parameter Reynolds number R is fixed. e Adjust Darcy number D a To obtain different Darcy numbers D aThe impact on the flow structure. For example... Figure 6 The diagram illustrates the influence of dimensionless parameters on near-vertical velocity distribution in one embodiment of the hydrogen-sensitive colorimetric detection gel porosity calculation method of the present invention, where f = R. e ·D a =2×10 n Observe the flow structure diagrams for n = -2, -1, 0, and 1 under different dimensionless control parameters (Reynolds number). Figure 6 The dimensionless control parameter Reynolds number R in (a) e =200, Figure 6 The dimensionless control parameter Reynolds number R in (b) e =2000, Figure 6 The dimensionless control parameter Reynolds number R in (c) e =10000. It can be seen that the critical condition for the flow structure transition is R. e ·D a =0.1, meaning that vortices begin to appear at this point. When R e ·D a When R = 10, the flow structure changes from a single-vortex structure to a multi-vortex structure, as R... e ·D a As the number of eddies continues to increase, the eddies begin to significantly affect gas permeability, and the flow is entirely concentrated in the top layer. From this, the dimensionless control parameter Reynolds number R can be derived. e ≤2400, therefore, Darcy number D a ∈[8.333×10 -5 , 4.1667×10 -3 ].

[0126] Step S50: Obtain the permeability equation for hydrogen diffusion in the hydrogel crosslinker; combine the permeability equation, the Knudsen number, and the physical properties satisfied by the hydrogel preparation material to obtain the hydrogel porosity.

[0127] The Knudsen number, which characterizes the relationship between pore size and hydrogen free path, is shown in equation (16):

[0128]

[0129] Where Kn is the Knuthian number, k B Here, σ is Boltzmann's constant, T represents the dimensionless temperature of the gas, p is the pressure, and σ is the diameter of a hydrogen molecule. This represents the characteristic size of the hydrogel pores.

[0130] The diffusion process of hydrogen in hydrogel crosslinks can be analogous to that of shaped fabric fiber assemblies. Let the similarity between the two be α. The permeability equation for the diffusion of hydrogen in hydrogel crosslinks is shown in equation (17):

[0131]

[0132] Where κ represents the permeability of hydrogen diffusion in the hydrogel crosslinker, α represents the thermal diffusivity, A represents the average diameter of the hydrogel crosslinker, and λ represents the average diameter of the hydrogel crosslinker. max D represents the diameter of the maximum aperture. f Parameters characterizing the fractal coefficients and dimension. D f It can be found in a general fractal parameter table, or obtained through simple calculations by material analogy.

[0133] The ultimate goal of this invention is to obtain the porosity φ. The unit structure area A can be characterized by the average diameter of the cross-linked body, and the maximum pore diameter λ. max D is related to the size of the network formed by the crosslinking. f Set to 2.

[0134] Finally, the porosity of the hydrogel is shown in equation (18):

[0135]

[0136] Where φ represents the porosity of the hydrogel, and D a =k / H 2 Here, β represents the Darcy number, k represents the permeability of the porous medium, H represents the length scale, and β = R / l represents the ratio of chain length to pore diameter, where R represents chain length and l represents pore diameter.

[0137] If the single chain can be wound into a ring, then β has a maximum value. Combining Darcy's number range D a ∈[8.333×10 -5 , 4.1667×10 -3 The porosity can be calculated to be in the range of φ∈[0.02, 0.05].

[0138] A second embodiment of the present invention provides a method for preparing a detection gel, based on the above-described method for calculating the porosity of a hydrogen-sensitive colorimetric detection gel. This preparation method mainly consists of three stages:

[0139] The first stage is the preparation of hydrogel materials, the second stage is the preparation of hydrogen-sensitive color-changing water material suspensions, and the third stage is the preparation of hydrogen-sensitive color-changing hydrogel materials.

[0140] For the preparation of hydrogel materials in the first stage, the hydrogel involved in this invention takes polyacrylamide (PAAm) material as an example, but the application is not limited to PAAm hydrogel material. Other materials can be selected according to the application scenario. These will not be described in detail here.

[0141] In step A10, using 2M acrylamide as a monomer, 0.001MN,N'-dimethylbisacrylamide as a crosslinking agent, 0.002M 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylphenylacetone as a UV initiator, and Tween20 at a concentration of 0.05 g / cm3 as a surfactant, oleyl alcohol is dispersed in the aqueous phase as small droplets.

[0142] Step A20: After stirring the solution thoroughly, pour it into a mold. Under the protection of 99.99% pure nitrogen gas, at a power density of 4 mW / cm³... 2 PAAm hydrogel was obtained by irradiating with ultraviolet light at a wavelength of 365nm for 8 hours.

[0143] Step A30: The PAAm hydrogel is repeatedly swollen in deionized water three times and then dried in an oven at 70°C for different times to obtain hydrogel materials with different water contents and set porosities; the porosity of the hydrogel material is adjusted by adjusting the content of the surfactant.

[0144] The porosity and pore size distribution of the hydrogel material itself (in its dehydrated state) can be controlled to ensure the filling and dispersion effect of subsequent hydrogen-sensitive metal particles in the pore structure. The hydrogel is synthesized using an emulsion template method to control pore characteristics. Templates include, but are not limited to, emulsions formed with Tween 20, Tween 80, and oleyl alcohol, as well as polydimethylsiloxane (PDMS). Changing the amount of Tween 20 can adjust the pore size of the hydrogel. For example, under an O / W volume ratio of 6 / 6, when the Tween 20 content is [not specified], the resulting hydrogel has a pore size distribution in the range of 1–10 μm and a porosity of approximately 40%.

[0145] The material prepared by this invention has a gelation rate of over 99.9%; it has strong water absorption capacity, is transparent in color, is manufactured in one go, and its thickness, shape, and size are all controllable, allowing for large-scale production; it has good mechanical properties and can be stretched more than twice its own size; it has good environmental stability, and its weight retention rate is over 90% after 4 hours at 65% RH.

[0146] For the preparation of the hydrogen-sensitive color-changing water material suspension in the second stage, this invention takes lanthanum tungsten trioxide (WO3 / La) as an example, but its application is not limited to lanthanum tungsten trioxide (WO3 / La). Other materials can be selected according to the application scenario, which will not be described in detail here.

[0147] Step A40: Tungsten trioxide micro powder and soluble lanthanum are mixed in a set ratio and then refined and activated by high-energy ball milling to obtain a hydrogen-sensitive color-changing material suspension.

[0148] Step A41: Obtain tungsten trioxide micropowder and soluble lanthanum (which can be lanthanum nitrate, lanthanum chloride, lanthanum sulfate, etc.) according to a set ratio. Dissolve the tungsten trioxide micropowder in sodium hydroxide at a set temperature and concentration; the molar ratio of lanthanum to tungsten is 1:50-1:20 (in the experiment, this includes 1:50, 1:40, 1:30, and 1:20). To ensure that the WO3 hydrogen-sensitive material particles can smoothly enter the pores of the hydrogel material, they can be refined and activated by high-energy ball milling.

[0149] Step A42: Add the set weight of anhydrous ethanol to the solution containing dissolved tungsten trioxide powder and stir until homogeneous;

[0150] Step A43: Add concentrated hydrochloric acid to the well-stirred solution until yellow tungstic acid is formed, stir again and heat the solution to obtain condensed tungstic acid.

[0151] Step A44: Add soluble lanthanum to the condensed tungstic acid to obtain a lanthanum-doped tungsten trioxide suspension as a hydrogen-sensitive color-changing material suspension.

[0152] The third stage of preparation of the hydrogen-sensitive color-changing hydrogel material includes:

[0153] Step A50: Immerse hydrogel materials with different water contents and set porosities in the suspension of the hydrogen-sensitive color-changing material, and make the hydrogel materials fully swell by mechanical vibration;

[0154] Step A60: Vacuum dry the fully swollen hydrogel material to obtain a hydrogen-sensitive colorimetric detection hydrogel.

[0155] The amount of hydrogen-sensitive color-changing material filled is controlled by adjusting the water content of the unsaturated PAAm hydrogel material. By weight percentage, after the hydrogen-sensitive color-changing hydrogel material is saturated with water, the hydrogen-sensitive material accounts for 5-10%, and the hydrogel accounts for 90-95%. After vacuum drying, the hydrogen-sensitive color-changing hydrogel is rehydrated and swells. After the color-developing gel absorbs water, the hydrogen-sensitive material either adheres to the pore walls or is suspended in a confined water area, allowing for long-term storage in a humid environment at room temperature.

[0156] SEM observation revealed that the prepared hydrogel material has a porous and interconnected structure with tortuous pore paths, which provides a longer diffusion path for hydrogen to complete the colorimetric reaction.

[0157] The PAAm hydrogel prepared by this invention is transparent in color. The process can be adjusted by dehydration / swelling and mechanical vibration. For example, the material thickness can be appropriately increased according to the application scenario to prevent missed detection. When applied to valve ports, pipe and tank connections, the thickness of the hydrogel can be increased by 2-10 mm.

[0158] The hydrogen-sensitive color-changing hydrogel of this invention is in a water-unsaturated state before use. Based on the diffusion law of gas in porous media, the water content is controlled to adjust the porosity φ∈[0.02, 0.05]. The porosity φ can be determined by the Archimedes water displacement method, as shown in equation (19):

[0159]

[0160] Where m1 is the mass of the hydrogen-sensitive color-changing hydrogel material in its unsaturated state (unit: g), m2 is the suspended mass of the hydrogen-sensitive color-changing hydrogel material in its water-saturated state in water (unit: g), and m3 is the mass of the hydrogen-sensitive color-changing hydrogel material in its water-saturated state in air (unit: g).

[0161] Through testing, it was found that the water absorption of the hydrogen-sensitive color-changing hydrogel prepared by this invention can be controlled to be 90%-95% of the saturated water absorption capacity during use.

[0162] When using this product, the wall of the tube or tank to be tested must first be cleaned and moistened. This way, even on a concave surface, the hydrogen-sensitive color-changing hydrogel of this invention can achieve a dense fit after absorbing moisture from the surface and the air, preventing hydrogen leakage and enabling accurate detection.

[0163] Although the steps in the above embodiments are described in the above order, those skilled in the art will understand that in order to achieve the effect of this embodiment, different steps do not need to be executed in such an order. They can be executed simultaneously (in parallel) or in a reverse order. These simple variations are all within the protection scope of this invention.

[0164] The terms “first”, “second”, etc., are used to distinguish similar objects, not to describe or indicate a specific order or sequence.

[0165] The term "comprising" or any other similar term is intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus / device that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent in such process, method, article, or apparatus / device.

[0166] The technical solution of the present invention has been described above with reference to the preferred embodiments shown in the accompanying drawings. However, it will be readily understood by those skilled in the art that the scope of protection of the present invention is obviously not limited to these specific embodiments. Without departing from the principles of the present invention, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after these changes or substitutions will all fall within the scope of protection of the present invention.

Claims

1. A method for calculating the porosity of a hydrogen-sensitive colorimetric detection gel, characterized in that, The method for calculating gel porosity includes: Step S10: Based on the gas transport law in porous media, the heat and mass transfer equations for hydrogen molecule diffusion in hydrogel are characterized by the Darcy-Brinkman model. Step S20: Based on the balance between convection and diffusion terms in the hydrogel, the heat and mass transfer equations are expressed in dimensionless form. Step S30: Combining the boundary motion constraints of the hydrogel solid material, the equations for hydrogen flow and diffusion migration in the hydrogel are obtained. It is represented as: ； in, Represents the dimensionless control parameter Reynolds number. Representing Darcy numbers, Represents the actual flow velocity at the top as a velocity scale. Represents a length scale. Represents the permeability of porous media; Step S40: Based on the hydrogen flow and diffusion migration equation, obtain the physical properties that the hydrogel preparation satisfies, wherein the range of Reynolds number and Darcy number is obtained as the physical properties according to the critical conditions of flow structure transformation and eddy structure change characteristics. Step S50: Obtain the permeability equation for hydrogen diffusion in the hydrogel crosslinker; combine the permeability equation, the Knudsen number, and the physical properties satisfied by the hydrogel preparation material to obtain the hydrogel porosity; and combine the range of Darcy number values ​​to obtain the range of porosity values. Among them, the Knudsen number is represented as: ； in, For Knudsen numbers, Boltzmann's constant, Represents the dimensionless temperature of the gas. For pressure, The diameter of a hydrogen molecule, The characteristic size of the hydrogel pores; The permeability equation is expressed as follows: ； in, The permeability representing the diffusion of hydrogen gas in the hydrogel crosslinker. Represents the thermal diffusivity. Represents the average diameter of the hydrogel crosslinks. The diameter representing the maximum aperture. These are parameters characterizing the fractal coefficients and dimension; The porosity of the hydrogel is expressed as: ； in, Represents the porosity of the hydrogel. This represents the ratio of chain length to void diameter. Represents chain length, Represents the diameter of the void.

2. The method for calculating the porosity of a hydrogen-sensitive colorimetric detection gel according to claim 1, characterized in that, The heat and mass transfer equations for the diffusion of hydrogen molecules in the hydrogel are expressed as follows: ； ； ； ； ； in, Represents dimensionless Directional velocity, Represents dimensionless Directional velocity, represent coordinate, represent coordinate, Represents dimensionless pressure. Represents the dimensionless temperature of the gas. Represents the mass concentration of the diffusing fluid. Represents dimensionless time. Represents the dimensionless control parameter Reynolds number. Representing the Grashof number, Representing Prandtl numbers, Represents the Schmitt number, , , , These represent the length scale, the actual top flow velocity as a velocity scale, the temperature scale, and the concentration scale, respectively. Represents the kinematic viscosity of the fluid. Represents the thermal diffusivity. Represents the mass diffusion coefficient. Represents gravitational acceleration. Represents the permeability of porous media. Represents the porosity of the hydrogel. Represents the coefficient of volume expansion. Represents kinematic viscosity. The fluid temperature is represented by t Fluid density at 0.

3. The method for calculating the porosity of a hydrogen-sensitive colorimetric detection gel according to claim 2, characterized in that, In step S20, the heat and mass transfer equations are expressed in dimensionless form, and the method is as follows: ； ； ； ； ； ； ； ； in, The true coordinates representing fluid motion Represents the fluid flow velocity. Represents the flow of time. and These represent the fluid temperatures as follows: t The fluid density and heat source temperature at 0 are: t Fluid density at 0 Represents acceleration per kilometer. , , Represents fluid temperature parameters, initial temperature, and final temperature. , , Represents concentration parameters, initial concentration, and final concentration. Represents a time scale.

4. The method for calculating the porosity of a hydrogen-sensitive colorimetric detection gel according to claim 3, characterized in that, The boundary constraint conditions for the motion of the hydrogel solid material are as follows: At the opening boundary: , , , ; Bottom wall: , , , ; Side wall surface: , , , ; Intermediate solid block: , ; in, Represents a dimensionless initial velocity. and Represents the thermal conductivity of solids and the thermal conductivity of fluids. This represents the diffusion coefficient of the solid mass.

5. A method for preparing a detection gel, characterized in that, Based on the method for calculating the porosity of hydrogen-sensitive colorimetric detection gel according to any one of claims 1-4, the preparation method includes: Step A10: Using 2M acrylamide as the monomer, 0.001MN,N'-dimethylbisacrylamide as the crosslinking agent, and 0.002M 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylphenylacetone as the UV initiator, with a content of 0.05 g / cm³... 3 Tween20 is a surfactant that disperses oleyl alcohol in the aqueous phase into small droplets; Step A20: After stirring the solution thoroughly, pour it into a mold. Under the protection of 99.99% pure nitrogen gas, at a power density of 4 mW / cm³... 2 PAAm hydrogel was obtained by irradiating with ultraviolet light at a wavelength of 365nm for 8 hours. Step A30: The PAAm hydrogel is repeatedly swollen in deionized water three times and then dried in an oven at 70°C for different times to obtain hydrogel materials with different water contents and set porosities; the porosity of the hydrogel material is adjusted by adjusting the content of the surfactant. Step A40: Tungsten trioxide micro powder and soluble lanthanum are mixed in a set ratio and then refined and activated by high-energy ball milling to obtain a hydrogen-sensitive color-changing material suspension. Step A50: Immerse hydrogel materials with different water contents and set porosities in the hydrogen-sensitive color-changing material suspension, and make the hydrogel materials fully swell by mechanical vibration; Step A60: Vacuum dry the fully swollen hydrogel material to obtain a hydrogen-sensitive colorimetric detection hydrogel.

6. The method for preparing the detection gel according to claim 5, characterized in that, Step A40 includes: Step A41: Obtain tungsten trioxide micro powder and soluble lanthanum according to the set ratio, and dissolve the tungsten trioxide micro powder in sodium hydroxide at the set temperature and concentration; Step A42: Add the set weight of anhydrous ethanol to the solution containing dissolved tungsten trioxide powder and stir until homogeneous; Step A43: Add concentrated hydrochloric acid to the well-stirred solution until yellow tungstic acid is formed, stir again and heat the solution to obtain condensed tungstic acid. Step A44: Add soluble lanthanum to the condensed tungstic acid to obtain a lanthanum-doped tungsten trioxide suspension as a hydrogen-sensitive color-changing material suspension.

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