A method for repairing ancient books by spraying based on fluid shear thinning characteristics

Abstract

This invention discloses a method for spraying and restoring ancient books based on the shear-thinning properties of fluids, belonging to the field of cultural relic protection and restoration technology. The restoration method provided by this invention includes the following steps: preparing a 1% (wheat starch) solution as the restoration liquid; pumping the restoration liquid into a nozzle and accelerating it at the nozzle outlet to form a jet; causing the jet to impact the surface of the ancient book paper moving at a constant speed, forming a wet film, which is then dried to form a dry film reinforcement layer. This invention, through the coordination of process steps such as the concentration and flow rate of the restoration liquid, the nozzle structure, and the speed of the ancient book's movement, enables the restoration liquid to penetrate the ancient book paper without damage under low pressure. Utilizing its shear-thinning properties, the viscosity decreases upon impact to facilitate penetration, and then recovers to a high viscosity under the influence of the ancient book paper to stabilize the film layer, achieving uniform, precise, and damage-free coating of the restoration liquid onto the surface of the ancient book paper.

Description

Technical Field

[0001] This invention belongs to the field of cultural relic protection and restoration technology, specifically relating to a method for spraying and restoring ancient books based on the shear-thinning properties of fluids. Background Technology

[0002] As an ancient country with a long history, my country possesses a vast collection of ancient books since the invention of papermaking, representing a vital part of the country's historical heritage. However, due to the limitations of ancient preservation conditions, most ancient books have suffered varying degrees of damage. Insect infestation, acidification, corrosion, water stains, and fire are common causes of damage, making ancient book restoration a crucial aspect of the cultural relics industry. Traditional ancient book restoration methods, such as manually applying paste, suffer from uneven coating thickness and are prone to tearing fragile paper, resulting in irreversible physical and mechanical damage. Current mechanized spraying methods largely employ conventional Newtonian fluid theory, which struggles to resolve the contradiction between high-viscosity restoration solutions that cannot penetrate the paper's micropores and low-viscosity solutions that tend to spread and wrinkle on the paper surface. Summary of the Invention

[0003] To address the technical problems in the background art, this invention provides a method for spraying and restoring ancient books based on the shear-thinning properties of fluids, achieving uniform, precise, and non-destructive application of the restoration liquid to the surface of ancient book paper.

[0004] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0005] A method for spraying and restoring ancient books based on the shear-thinning properties of fluids includes the following steps:

[0006] Prepare a 1% (w / w) wheat starch solution as the repair solution;

[0007] A nozzle is provided, the nozzle having an inlet straight pipe section, a reduced diameter section and an outlet straight pipe section connected in sequence; the repair fluid is pumped into the nozzle at a set mass flow rate, so that the repair fluid is accelerated at the nozzle outlet to form a jet;

[0008] The ancient book to be restored is moved at a constant speed below the nozzle outlet;

[0009] The jet of repair fluid impacts the surface of the ancient book paper, which is moving at a constant speed, forming a wet film. When the repair fluid impacts the surface of the ancient book paper, a high shear rate is generated in the impact area at the moment of impact, which instantly reduces its viscosity to penetrate the micropores of the ancient book paper. Subsequently, due to the movement of the ancient book paper, the shear rate inside the wet film disappears, and the viscosity of the repair fluid returns to a high viscosity state, thereby inhibiting the spread of the wet film and stabilizing its formation.

[0010] The wet film is dried to form a dry film reinforcement layer.

[0011] The principle behind this invention's use of a 1% (w / w) wheat starch solution as the repair solution is as follows:

[0012] (1) Experiments show that a 1% starch solution exhibits ideal rheological parameters. At this concentration, the fluid can maintain a stable laminar flow state when passing through millimeter-sized micro-pores. This avoids nozzle clogging caused by high-concentration fluids and atomization and sputtering caused by low-concentration fluids. This stable flow state ensures that the repair agent can be uniformly and gently deposited on the fragile surface of ancient books, achieving non-destructive reinforcement. When the wheat starch concentration is below 1%, the cross-linking network formed by starch molecules between the aging fibers of the paper is not dense enough to provide effective tensile strength; while when the concentration exceeds 1%, the repair solution will form an excessively thick film on the fragile paper surface, causing irreversible shrinkage stress after the paper dries, resulting in hardening, brittleness and edge warping. By selecting a 1% wheat starch solution as the repair solution, the safety of cultural relics, the effectiveness of repair, and the stability of the fluid process can be taken into account.

[0013] (2) Wheat starch possesses unique physicochemical properties and molecular structure in the restoration of paper artifacts, characterized by the following three core aspects. First, unlike other starches, wheat starch naturally exhibits a bimodal distribution of large particles (approximately 15-35 micrometers in diameter) and small particles (approximately 2-10 micrometers in diameter). During the restoration process, the small particles can deeply penetrate into the tiny fiber gaps of ancient paper, anchoring and cross-linking internally; while the large particles remain on the surface of the paper, forming a uniform, breathable protective film. Second, in the continuous spraying process, the fluid generates extremely high shear rates at the wall surface. When subjected to such high shear forces, the molecular chains of wheat starch exhibit excellent mechanical stability, making it difficult for molecular chains to break or for viscosity to decrease irreversibly. Third, after wheat starch gelatinizes into a film, its aging rate is slow, and even decades after drying and curing, it can still be gently washed away by moderate warm water wetting, ensuring the safety of artifacts during future secondary restorations.

[0014] As a preferred technical solution, the diameter of the nozzle's inlet straight pipe section is larger than the diameter of the outlet straight pipe section; the narrowing section is funnel-shaped, with a 60° angle between the sidewall of the narrowing section and its central axis, forming a 60° contraction angle. The large orifice of the inlet straight pipe section transitions to the small orifice of the outlet straight pipe section through the narrowing section. More preferably, the total length of the nozzle is 15mm, the radius of the inlet straight pipe section is 4mm, transitioning to an outlet radius of 1mm after the narrowing section; the length of the outlet straight pipe section is 4-6mm, preferably 5mm; and the ratio of the length to the diameter of the outlet straight pipe section is (2-10):1. In industrial spraying, nozzle design typically pursues a shorter nozzle structure and higher pressure differential to achieve atomization. This design can generate finer spray particles at higher flow rates, facilitating uniform coating coverage. However, this design may also introduce droplet instability and aerodynamic instability during spraying, leading to uneven spraying and affecting coating quality. This invention improves upon the traditional nozzle structure by introducing a high aspect ratio outlet straight pipe section and a contraction angle design, enabling stable spraying of the repair fluid under low pressure. This ensures the repair effect while avoiding damage to the original structure of the artifact being repaired.

[0015] As a preferred technical solution, the mass flow rate of the repair solution entering the nozzle is 1-4 g / s; more preferably 2 g / s. The fluid is accelerated by the aforementioned nozzle structure, ensuring that when the fluid is ejected and impacts the paper surface, a stable maximum stagnation pressure of approximately 70-80 Pa is formed, accompanied by an extremely high local shear strain rate. At this point, the viscosity of the starch solution undergoes a physical abrupt change, dropping sharply to approximately 0.24 Pa·s, promoting the penetration of the repair solution into the micropores of the fragile paper surface of the ancient book, achieving initial anchoring.

[0016] The setting of the mass flow rate of the repair fluid in this invention needs to consider the following physical and technological factors. First, the flow rate directly determines the flow velocity, which in turn affects the Reynolds number. In this invention, it is necessary to ensure that the fluid is in a robust laminar flow region to avoid turbulent impact damage to fragile paper. Second, the flow rate determines the shear rate of the nozzle wall, which must be sufficient to activate the shear-thinning properties of wheat starch to reduce pumping resistance, while avoiding excessive shear leading to mechanical degradation of starch macromolecular chains. Third, the flow rate affects the impact momentum through the flow velocity. For brittle ancient books, the flow rate needs to be controlled within a range that does not produce mechanical penetration or fiber displacement, ensuring that the repair fluid is gently deposited on the surface of the ancient book pages. Finally, the flow rate needs to ensure that the jet prevents droplet formation at low flow rates or splashing at high flow rates after leaving the nozzle. Based on the above factors, the mass flow rate is set to 1-4 g / s to maintain laminar spraying. Optimally, a mass flow rate of 2 g / s achieves the best deposition effect.

[0017] As a preferred technical solution, the translation speed of the ancient book is 0.02 m / s. The velocity is 0.5 m / s, more preferably 0.1 m / s. When the repair liquid is sprayed from the nozzle onto the surface of the ancient book paper, it moves with the book. During this movement, the relative velocity difference causes the shear rate to decrease rapidly, and the viscosity of the repair liquid rises back to a high-viscosity state. This locks in the geometry of the wet film, inhibiting further diffusion and wrinkling. In this invention, the paper's moving speed and the repair liquid spraying flow rate form a dynamic balance, achieving uniform filling of micropores without damaging the fiber structure. Experiments have shown that at 0.02... Within a speed range of 0.5 m / s, adjusting the moving speed allows for flexible adaptation to paper artifacts of varying thicknesses and deterioration levels, ensuring optimal restoration results. When the speed is below 0.02 m / s, excessive movement leads to excessive accumulation of starch solution in certain areas, causing over-saturation of the paper. When the speed is above 0.5 m / s, excessive movement results in insufficient deposition of the restoration solution, failing to form an effective cross-linked network structure between the fibers, leading to poor reinforcement.

[0018] As a preferred technical solution, the thickness of the dry film reinforcing layer is 10–80 μm. 10 μm is the minimum value, achieving structural reinforcement. 80 μm is the maximum, ensuring that the shrinkage stress generated by the repair solution is lower than the yield strength of the paper, avoiding paper embrittlement and deformation. This range achieves the effect of improving the physical strength of the paper while maintaining its supple feel.

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

[0020] The ancient book spraying restoration method provided by this invention involves the following coordination relationships among various process steps, such as the concentration of the restoration solution, the flow rate of the restoration solution, the nozzle structure, and the translation speed of the ancient book:

[0021] (1) Matching the concentration and flow rate of the repair solution: The 1% concentration of the repair solution determines the consistency coefficient of the fluid. If the concentration increases, the pumping pressure must be increased to maintain the target flow rate, but this will cause a surge in shear rate, which may damage the branched structure of wheat starch. By matching the 1% concentration with a specific flow rate, the shear rate in the nozzle falls exactly in the linear shear thinning zone of the starch solution, which ensures both fluidity and binding activity.

[0022] (2) The matching of nozzle structure and repair fluid jet pattern: The nozzle structure and repair fluid flow rate together determine the Reynolds number. The matching of nozzle structure and repair fluid concentration ensures that the fluid is in a laminar flow state at the moment of exiting the nozzle. This avoids the problem of inaccurate positioning due to jet atomization.

[0023] (3) The flow rate of the restoration solution is matched with the speed of the ancient book translation to ensure that the thickness of the liquid film formed by the restoration solution on the paper surface of the ancient book is sufficient to penetrate the fiber, and its water content is not too high to avoid deformation after drying.

[0024] This invention, through the coordinated processes of each step, enables the repair solution to penetrate the ancient book paper without damage under extremely low stagnation pressure. Utilizing its transient shear-thinning properties, it achieves effective wetting under low pressure, rather than the traditional high mechanical pressure, thus protecting the extremely fragile ancient book paper. Furthermore, the thickness of the dry film reinforcement layer formed on the paper surface is precisely controllable. By eliminating the speed difference, an extremely stable thickness layer is formed, achieving automation and standardization of the coating process. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the nozzle structure;

[0026] Figure 2 This is a schematic diagram of the velocity vector distribution of the repair fluid in the nozzle.

[0027] Figure 3 Velocity contour plots of the repair fluid in the nozzle and in the air;

[0028] Figure 4 Three-phase volume fraction morphology diagram of ancient book paper in contact with the spraying of restoration liquid (t=1s).

[0029] Figure 5 This is a graph showing the distribution of impact pressure at the stagnation point on the paper.

[0030] Figure 6 The local shear rate curve is shown from the moment of impact of the repair fluid to the stable state of film formation.

[0031] Figure 7 The dynamic viscosity change curve of the repair fluid from the moment of impact to the stable film formation state;

[0032] Figure 8 A curve showing the change in the gas-liquid interface position for stabilizing the thickness of the starch coating.

[0033] Attached label: 1-Inlet straight pipe section, 2-Reduced diameter section, 3-Outlet straight pipe section. Detailed Implementation

[0034] The present invention will be further described below with reference to embodiments, so that those skilled in the art can better understand and implement the present invention, but the embodiments are not intended to limit the present invention. Furthermore, unless otherwise specified, the preparation processes in the following embodiments are conventional methods in the prior art, and therefore will not be described in detail. All raw materials used in the present invention are commercially available products.

[0035] This invention provides an automated spray-coating repair method for fragile ancient book paper. In traditional processes, if the concentration of the repair solution is too high, it is difficult to penetrate the paper fibers; if the concentration is too low, it easily spreads on the paper surface, causing wrinkling and deformation. This invention utilizes the shear-thinning rheological properties of a 1% wheat starch solution and perfectly solves this problem by strictly controlling the spraying process parameters. The method includes the following steps:

[0036] Preparation of the repair solution and establishment of rheological parameters: First, a 1% (w / v) wheat starch solution was prepared as the repair solution. Rheometer testing and Ansys CFX numerical simulation verified that the solution exhibited significant non-Newtonian power-law fluid characteristics. Its core rheological parameters were calibrated as follows: consistency coefficient K = 2 Pa·s, power-law exponent n = 0.6. This fluid possesses extremely high viscosity under static or low-shear conditions, while its viscosity decreases sharply under high-shear conditions.

[0037] Spraying system structure and boundary condition constraints: The above-mentioned repair fluid is pumped into a nozzle with a specific structure. A schematic diagram of the nozzle structure is provided below. Figure 1 It has an inlet straight pipe section 1, a reduced diameter section 2, and an outlet straight pipe section 3 connected in sequence. The specific geometric dimensions of the nozzle used in the following embodiments are optimized as follows: the radius of the inlet straight pipe section 1 is 4 mm, and after passing through the reduced diameter section 2 with a 60° contraction angle, it smoothly transitions to the outlet straight pipe section 3 with a radius of 1 mm and a length of 5 mm.

[0038] Fluid dynamics settings: The inlet mass flow rate of the repair fluid is precisely controlled at 2 g / s by the supply pump.

[0039] Base motion settings: The conveyor belt carrying the ancient book paper to be restored moves along a single Y-axis at a constant speed of 0.1m / s; the distance between the nozzle outlet and the ancient book paper is 20mm.

[0040] Multiphase flow model application: The VOF (Volume of Fluid) method was used to accurately track the free interface between a 2mm starch liquid column and air. The simulation incorporated a real starch liquid density of 1050 kg / m³. 3 And the surface tension coefficient is 0.07 N / m.

[0041] Computational stability and accuracy assurance: During the simulation, the Max Courant Number is monitored and maintained between 1.0 and 2.0, with a time step of 10. -6 s can accurately capture the necking phenomenon during the liquid column's descent and the spreading behavior at the moment of contact with the paper.

[0042] Example

[0043] High-precision transient numerical simulation of multiphase flow was performed using Ansys CFX. The specific physical process and parameter demonstration of this embodiment are as follows:

[0044] A method for spraying and restoring ancient books based on the shear-thinning properties of fluids includes the following steps:

[0045] (1) Prepare a wheat starch solution with a mass concentration of 1% as a repair solution;

[0046] (2) Pump the repair fluid into the nozzle at a mass flow rate of 2 g / s, so that the repair fluid is accelerated at the nozzle outlet to form a jet; Figure 2 This is a schematic diagram of the velocity vector distribution of the repair fluid in the nozzle. This velocity vector diagram shows the three-dimensional spatial trajectory of the starch solution throughout the nozzle and the external flow field. The red marker in the diagram indicates a maximum velocity of 1.132 m / s. This is highly consistent with the 1.033 m / s obtained from the two-dimensional cross-sectional diagram and the manually calculated average velocity of 1.078 m / s for a 1.5 mm diameter. The diagram shows acceleration within the tube; in the thinnest cylinder in the middle, the vector appears bright cyan / green, with a velocity of approximately 0.4-0.6 m / s. The core velocity is highest along the center line, decreasing towards the tube wall. Observing the inside of the nozzle and the core area immediately after spraying, almost all arrows point directly forward, i.e., in the positive Z-axis direction. There is no obvious fluid rotation or lateral scattering, indicating good jet focusing, which is beneficial for precise spraying.

[0047] Figure 3 The velocity contour plots of the restoration fluid in the nozzle and in the air show that the maximum velocity in the core area of ​​the nozzle reaches approximately 1.033 m / s, then passes through the air and finally reaches the interface of the ancient book paper at the bottom. It can be seen that after the restoration fluid jet impacts the bottom surface, its velocity rapidly decreases and shifts to the surrounding areas.

[0048] (3) Make the ancient book to be repaired move at a constant speed of 0.1 m / s below the nozzle outlet;

[0049] (4) The jet of restoration fluid impacts the surface of the ancient book paper, which is moving at a constant speed. At the moment of impact, kinetic energy is converted into pressure energy. Simulation results show that the maximum static pressure at the impact center is only about 77 Pa. This extremely low impact pressure avoids mechanical and physical damage to the fragile ancient book fibers. More importantly, the fluid undergoes a 90-degree reversal at the moment of impact, generating a local shear strain rate in the impact area, with a peak value of 190 s⁻¹. -1Under this shearing action, the starch solution undergoes instantaneous shear thinning, with its local dynamic viscosity dropping sharply from tens of Pascals per second at rest to approximately 0.24 Pa·s. This allows the repair fluid to be squeezed into the microfiber pores on the paper surface under a micro-pressure of 77 Pa, forming a strong initial anchor and a liquid film. As the paper continues to translate at a speed of 0.1 m / s, the repair fluid adhering to the paper surface is carried into the downstream region of the nozzle. In the downstream region, the repair fluid and paper move synchronously, and the relative velocity difference between the layers within the liquid film approaches zero, causing the shear strain rate in this region to drop to near 0 s². -1 After the loss of shear force, the non-Newtonian properties of the starch solution cause it to quickly return to its intrinsic high viscosity state. This high viscosity state adheres the repair solution to the paper surface, effectively preventing secondary diffusion of the fluid. Ultimately, an extremely uniform wet film with a stable thickness of 2.3 mm is formed on the paper surface. After natural drying, the wet film forms a dry film reinforcement layer with a thickness of approximately 15.3 μm.

[0050] The relevant process and results are analyzed as follows:

[0051] Figure 4 The three-phase volume fraction profile of the ancient book paper in contact with the sprayed restoration fluid (t=1s) shows that the fluid at the 1s mark is very continuous and dense at the constriction section and nozzle exit. This proves that at low Reynolds numbers, the laminar flow model captures the behavior of viscous fluids more accurately than the turbulent flow model. The phase interface at the red and blue boundary is very sharp, with no obvious numerical diffusion. This indicates that the current mesh is well-matched with the laminar flow setting. The bottom contour plot shows that the starch volume fraction in the core region has reached 96.69%. This indicates that the deposition layer is thick enough to represent the actual sprayed coating. This not only reflects the fluid flow at the bottom but also indirectly confirms that the moving boundary conditions are in effect.

[0052] Figure 5 For the paper-based stagnation point impact pressure distribution curve, from Figure 5 As can be seen, the curve reaches its highest point near 0 on the Y-axis, with a vertical reading of approximately 77 Pa. This is the center point of the jet core impacting the paper, the stagnation point where the fluid's kinetic energy is most concentrated in pressure energy. In a normal static jet impact, the pressure curve should be bilaterally symmetrical. Figure 4The curve shows a very pronounced rightward skew. Looking to the left from Y=0, with the negative Y-axis pointing against the direction of motion, a significant drop in pressure is observed. At Y = -0.003 m, or 3 mm off-center, the pressure has already dropped to 0 Pa. This indicates that when the fluid attempts to spread against the direction of paper movement, it encounters frictional resistance from the paper, resulting in a short flow. Looking to the right from Y=0, with the positive Y-axis pointing in the direction of motion, the pressure decrease is relatively gradual, even forming a small plateau of approximately 15-20 Pa near Y = 0.005 m. This is the starch coating being dragged forward by the moving paper. From... Figure 4 It can also be seen that the area where the starch solution is forced into the pores of the paper by the mechanical pressure of the jet is concentrated in a narrow range of 2-3 mm before and after the impact point. In the downstream region where Y>0.005m, the pressure of the starch coating on the paper surface has dropped to tens of Pascals or even lower. This means that most of the starch solution coated on the surface of the ancient book slowly seeps into the interior of the paper.

[0053] Figure 6 This is a local shear rate curve from the moment of impact to the stable film formation state of the repair fluid. The graph is mainly divided into three regions: the impact center (Y≈0), the downstream region (Y>0.005), and the upstream region (Y<0). The following phenomena are observed in each region:

[0054] At the impact center where Y≈0, there is a shear extremum and instantaneous thinning. In the central region where the jet impacts the paper, i.e., Y is between -0.002 and 0.002 m, the shear rate increases sharply, reaching a peak of approximately 190 s. -1 This is because the fluid is forced to make a sharp 90-degree turn at this point. Wheat starch solution is a typical shear-thinning fluid. Based on the set consistency coefficient K=2 and power-law exponent n=0.6, its local viscosity drops significantly under high shear rates, with the extremely low viscosity y at the impact point being approximately 0.24 Pa·s. This indicates that the originally viscous starch solution becomes very thin upon contact with the paper. This instantaneous low viscosity facilitates the solution's entry into the micropores of the paper surface upon impact, forming initial anchorage.

[0055] In the downstream region where Y > 0.005, zero shear and viscosity recovery phenomena exist. Along the direction of paper movement, i.e., the positive Y-axis, the shear rate drops significantly after Y = 0.002m, and decreases to near 0s in the region where Y > 0.005m. -1 When the liquid film is carried away by the paper, the relative velocity difference between the layers within the liquid and between the liquid and the paper surface disappears. With zero relative velocity, the shear rate tends to zero. Due to the reversibility of shear thinning, the viscosity of this starch coating quickly returns to its extremely high initial state, allowing the coating to adhere firmly to the paper surface.

[0056] In the upstream region where Y<0, i.e., against the direction of paper movement, the shear rate, although not as high as at the center point, is maintained for 30–50 seconds over a considerable distance. -1 The shear rate is moderately high. Here, the fluid attempts to spread to the left, but the paper drags it to the right. The fluid encounters a velocity conflict with the wall, increasing friction and thus maintaining a high shear rate.

[0057] Figure 7 This is a dynamic viscosity change curve of the repair fluid from the moment of impact to the stable film formation state. The graph is divided into three regions: the impact center (Y≈0), the downstream region (Y>0.005), and the upstream region (Y<0). Among them:

[0058] The impact center is located in the central region where the jet impacts the paper surface, and the viscosity curve shows a trough, reaching a minimum of approximately 0.24 Pa·s. This indicates that the originally extremely viscous starch solution experiences a significant decrease in viscosity at the moment of impact with the paper surface.

[0059] A stable coating forms in the downstream region. Looking along the direction of paper movement, the viscosity begins to increase after crossing Y=0.002, reaching a peak of 1.6 Pa·s between Y=0.005 and 0.006. This corresponds to... Figure 6 This phenomenon indicates that the shear rate in this region approaches zero. Because the fluid has been carried away by the paper, internal frictional shearing no longer occurs, and the fluid reverts to its high viscosity.

[0060] On the left side, opposite to the direction of paper movement, i.e., in the upstream countercurrent region, the viscosity remains at a moderately low level of 0.4 to 0.5 Pa·s. The interaction between fluid diffusion and paper movement keeps this region consistently characterized by high shear friction, thus placing the starch solution in a semi-thin state.

[0061] Figure 8 The curve showing the change in the gas-liquid interface position during the stable formation of the starch coating thickness reveals the following information:

[0062] X = 0.035 m represents the paper surface, and the velocity in the Y direction of the curve falls precisely at 0.1 m / s. The first layer of starch molecules adhering to the paper surface moves at the same speed as the paper, without relative slippage.

[0063] X = 0.035m to 0.0327m represents the interior of the starch coating. Viewed from the paper to the left, within this small distance representing the thickness of the starch coating (approximately 2.3 mm), the fluid velocity fluctuates slightly between 0.1 m / s and 0.105 m / s, remaining at a relatively high level. This indicates that once the starch solution spreads on the paper surface, due to its internal viscosity, this 2.3 mm thick liquid film is carried forward by the underlying paper. This demonstrates the absence of drastic velocity stratification within the coating. This implies that the coating is stable and will not experience surface cracking, wrinkling, or uneven thickness during paper movement.

[0064] X = 0.0327m represents the gas-liquid interface. Between approximately 0.0327m and 0.027m, the velocity drops sharply from 0.1m / s to below 0m / s. This is the boundary between air and the starch solution. The high-viscosity, high-speed liquid film here rubs against the surrounding stationary air, propelling a thin layer of air close to the liquid surface forward.

[0065] X < 0.025 m represents the external air region. In the pure air region far from the liquid film, the velocity becomes a negative value between approximately -0.01 m / s and -0.02 m / s. This is caused by jet entrainment, where the high-speed jet of liquid and the forward-moving paper draw away some air within the enclosed air region, causing the surrounding air to flow back in the opposite direction to fill the gap, thus forming a weak air vortex.

[0066] Summary of implementation results:

[0067] This invention utilizes fluid dynamics parameters such as concentration and flow rate of the repair solution to precisely control the physical phase of the repair solution, which not only enables continuous automated production of uniform coatings but also maximizes the protection of the ancient books and cultural relics themselves, thus possessing extremely high engineering application value.

[0068] It should be noted that, in other embodiments, the optimal mass flow rate of 2 g / s in the above embodiments achieves the best results for the restoration fluid. While mass flow rates of 1 g / s and 4 g / s can also achieve some restoration effects on ancient books, they are not as effective as 2 g / s. Table 1 below lists the relevant parameters during the restoration process for mass flow rates of 1 g / s, 2 g / s, and 4 g / s:

[0069] Table 1. Relevant parameters of the repair process under different mass flow rates.

[0070]

[0071] It can be seen that when the mass flow rate is 1 g / s, the low velocity results in insufficient outlet kinetic energy, and the fluid is prone to stagnation at the nozzle edge, making it impossible to guarantee the accuracy of local restoration of ancient books. When the mass flow rate is 4 g / s, although it is still in the laminar flow region, its peak velocity reaches 2.15 m / s. For the brittle fibers commonly found in ancient books, excessive impact kinetic energy can cause physical indentations or tears on the paper surface. Therefore, a mass flow rate of 2 g / s is chosen to ensure the stability of the jet while avoiding damage to the ancient books due to excessive impact intensity.

[0072] Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

Claims

1. A method for spraying and restoring ancient books based on the shear-thinning properties of fluids, characterized in that, Includes the following steps: Prepare a 1% (w / w) wheat starch solution as the repair solution; A nozzle is provided, the nozzle having an inlet straight pipe section, a reduced diameter section and an outlet straight pipe section connected in sequence; the repair fluid is pumped into the nozzle at a set mass flow rate, so that the repair fluid is accelerated at the nozzle outlet to form a jet; The ancient book to be restored is moved at a constant speed below the nozzle outlet; The jet of repair fluid impacts the surface of the ancient book paper, which is moving at a constant speed, forming a wet film; wherein: when the repair fluid impacts the surface of the ancient book paper, a high shear rate is generated in the impact area at the moment of impact, which causes its viscosity to decrease instantaneously so as to penetrate the micropores of the ancient book paper. Subsequently, the translation of the ancient book paper causes the restoration fluid to move, which causes the shear rate inside the wet film to disappear and the viscosity of the restoration fluid to return to a high viscosity state, thereby inhibiting the spread of the wet film and stabilizing its formation. The wet film is dried to form a dry film reinforcement layer; The mass flow rate of the repair fluid entering the nozzle is 1-4 g / s; The speed of the translation of the ancient book is 0.

02. 0.5 m / s.

2. The method for spraying and restoring ancient books according to claim 1, characterized in that, The diameter of the inlet straight pipe section is larger than the diameter of the outlet straight pipe section; the reduced diameter section is funnel-shaped, and the angle between the side wall of the reduced diameter section and its central axis is 60°.

3. The method for spraying and restoring ancient books according to claim 1, characterized in that, The nozzle outlet straight pipe section is cylindrical, and the length of the outlet straight pipe section is 4-6mm; the ratio of the length to the diameter of the outlet straight pipe section is (2-10):

1.

4. The method for spraying and restoring ancient books according to claim 3, characterized in that, The length of the outlet straight pipe section is 5mm, and the outlet radius of the nozzle is 1mm.

5. The method for spraying and restoring ancient books according to claim 1, characterized in that, The mass flow rate of the repair fluid entering the nozzle is 2 g / s.

6. The method for spraying and restoring ancient books according to claim 1, characterized in that, The repair fluid creates a stagnation pressure of 70-80 Pa upon impact with the paper surface, accompanied by a local shear strain rate ≥190 s⁻¹. -1 .

7. The method for spraying and restoring ancient books according to claim 1, characterized in that, The speed at which the ancient book was translated was 0.1 m / s.

8. The method for spraying and restoring ancient books according to claim 1, characterized in that, The thickness of the dry film reinforcement layer is 10–80 μm.

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