Design method for scraping plate of wiped-film evaporator

Abstract

The invention belongs to the technical field of evaporation equipment, and relates to a scraping plate design method of a wiped-film evaporator, which comprises the following steps: (1) determining an application scene, and acquiring the total length of a single-row scraping plate of a wiped-film section, the section number n, the inter-section mounting interval, and eta 01 and eta 0n at an upper end inlet and a lower end outlet according to actual production experience; (2) acquiring eta0i and mi slotting proportions corresponding to the ith section; (3) establishing a wiped film section model; (4) verifying the model after n times of flow field and evaporation simulation; (5) aiming at the ith section, establishing mi film scraping section models, and enabling the slotting proportion of a scraping plate to correspond to that of the ith section; and (6) performing flow field and evaporation simulation once on the mi wiped membrane section models (the zero shear viscosity of the material is equal to the eta0i corresponding to the ith section) to obtain mi cluster membrane exchange fluxes, taking the wiped membrane section model with the maximum cluster membrane exchange flux as the optimal wiped membrane section model of the ith section, and setting the parameters of the ith section to be the same as the optimal wiped membrane section model of the ith section.

Description

Technical Field

[0001] The present invention belongs to the technical field of evaporation equipment and relates to a design method for the scraping blade of a wiped film evaporator. Background Art

[0002] As a new type of high-efficiency evaporator, a wiped film evaporator forces a liquid to form a film through a rotating wiping blade, and the liquid is heated and evaporated on the wall surface. At the same time, the scraping blade drives the liquid to flow forcibly, significantly improving the convective heat transfer and evaporation efficiency. In a large-capacity wiped film evaporator, several columns of scraping blades are usually installed equidistantly along the circumference on the rotating shaft, and each column of scraping blades is composed of multiple scraping blades installed axially. During operation, the rotating shaft drives the scraping blades to rotate, and the tip of the scraping blade maintains a clearance fit with the inner wall of the evaporator. Through the mechanical scraping action, the material continuously forms a film on the inner wall of the evaporator and then is heated and evaporated.

[0003] When processing high-viscosity materials with pseudoplastic characteristics, the high shear rate between the rotating scraping blade and the wall surface can dilute the materials, facilitating film formation. Moreover, the forced velocity gradient formed between the liquid mass accumulated at the front of the scraping blade movement direction and the liquid film below will form a high-intensity radial convection on the low-fluidity liquid film, optimizing the heat transfer effect. As Figure 1 shown, the scraping blade usually includes a base body 1, a protrusion 2, and a slot 3; the slot 3 is located on the long side of the scraping blade close to the wall surface, and is periodically distributed at equal intervals and with equal widths. A single slot 3 has a straight groove with an arc bottom shape; the slot 3 can strengthen the shear thinning effect of pseudoplastic fluids, promote the radial mass exchange between the liquid film near the wall surface and the liquid mass far from the wall surface, improve the evaporation efficiency, and at the same time disperse the liquid mass accumulated in front of the scraping blade, enhancing the axial transport efficiency of high-viscosity materials to be applicable to the evaporation treatment of high-viscosity materials.

[0004] The slotting ratio of the scraping blade edge (as Figure 1 shown, a single slot 3 has a straight groove with an arc bottom shape, the slotting period is L, the slotting length is l, the length of a single protrusion 2 is (L - l), and the slotting depth is H; l / L is defined as the slotting ratio, which is used to represent the proportion of the slotting length in the total period length within one period) is a key factor affecting the material exchange intensity and needs to be designed differently according to the zero-shear viscosity characteristics of the material. During the axial evaporation process of the wiped film evaporator, the zero-shear viscosity of the material shows a significant gradient change. Therefore, corresponding scraping blade slotting ratios need to be matched in different axial regions: in the high-viscosity region, if the slotting of the scraping blade is too small, it will cause liquid mass accumulation; while in the low-viscosity region, if the slotting of the scraping blade is too large, it will break the surface tension balance, resulting in a decline in the film-forming property of the material.

[0005] However, currently, the scraping film evaporator generally adopts a scraping plate grooving design with equal spacing and equal width. This design lacks flexibility and cannot be adaptively adjusted according to the change of the zero shear viscosity of the material at different positions, resulting in difficulty in achieving the best film-forming effect of the material at different positions in the evaporator and also unable to achieve efficient mass and energy exchange. Therefore, the existing scraping plate grooving design urgently needs to be improved. Summary of the Invention

[0006] The object of the present invention is to solve the problems existing in the prior art and provide a scraping plate design method for a scraping film evaporator.

[0007] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0008] A scraping plate design method for a scraping film evaporator includes the following steps:

[0009] (1) Determine the application scenario of the scraping film evaporator. According to actual production experience, obtain the total length of a single row of scraping plates in the scraping section, the number of segments n, and the installation interval between segments, where n > 1. At the same time, obtain the zero shear viscosity η of the material at the upper inlet of the scraping section 01 and the zero shear viscosity η of the material at the lower outlet 0n ;

[0010] (2) Obtain the zero shear viscosity η of the material corresponding to the i-th segment 0i and m i grooving ratios, where i = 1, 2,..., n and m i > 1;

[0011] (3) Use SolidWorks to establish a model of one scraping section;

[0012] The height of the scraping section model is 1000 mm, and other parameters are the same as those of the prototype machine. Specifically, in the present invention, the inner wall (i.e., the inner surface of the housing) diameter is set to 1690 mm, the distance between the outer edge of the scraping plate and the inner wall is 4.5 mm, the number of scraping plate rows is 40, the scraping plate grooving period is 150 mm, the scraping plate grooving ratio is 33.33%, and the scraping plate grooving depth is 26 mm;

[0013] (4) For the model of one scraping section in step (3), after performing n times of flow field and evaporation simulations, conduct simulation verification;

[0014] In the process of n times of flow field and evaporation simulations, only the zero shear viscosity of the material is different. The zero shear viscosity of the material in the i-th flow field and evaporation simulation is the same as the zero shear viscosity η of the material corresponding to the i-th segment 0i ;

[0015] (5) For the i-th segment, use SolidWorks to establish m i models of the scraping section. The scraping plate grooving ratios of the m i models of the scraping section are the same as the m corresponding to the i-th segmenti Slotting ratio, m i Other parameters of the film scraping section model are the same as those of the film scraping section model in step (3);

[0016] (6) For the m i film scraping section models corresponding to the i-th section in step (5), perform 1 flow field and evaporation simulation for each;

[0017] The flow field and evaporation simulation process is only different in the zero shear viscosity of the material from the flow field and evaporation simulation process in step (4), and the zero shear viscosity of the material is the same as the zero shear viscosity η 0i ;

[0018] After the flow field and evaporation simulation, m i film mass transfer fluxes are obtained. The film scraping section model corresponding to the maximum value of the film mass transfer flux is used as the optimal film scraping section model for the i-th section, and the parameters of the i-th section are set the same as those of the optimal film scraping section model for the i-th section;

[0019] The process of obtaining the film mass transfer flux is as follows: Take the circumferential surface swept by the tip of the scraper during its rotational operation as the analysis object, obtain the liquid-phase radial velocity contour map of this circumferential surface, and extract the radial velocity on this circumferential surface. Integrate the liquid-phase radial velocity perpendicular to the circumferential surface and outward within the 0°-4° circumferential range of all scrapers along the forward direction on this circumferential surface to obtain the film mass transfer flux.

[0020] As a preferred technical solution:

[0021] In the method for designing the scraper of a film scraping evaporator as described above, in step (2), the process of obtaining the zero shear viscosity η 0i corresponding to the i-th section is as follows: Take η 01 as the zero shear viscosity corresponding to the first section, take η 0n as the zero shear viscosity corresponding to the n-th section, perform exponential interpolation between η 01 and η 0n , insert a total of n - 2 sequentially increasing values, and respectively correspond them as the zero shear viscosities corresponding to the 2nd to n - 1st sections;

[0022] The process of obtaining the m i slotting ratios corresponding to the i-th section is as follows: According to actual production experience, obtain the slotting ratio r1 corresponding to η 01 and the slotting ratio r 0n corresponding to η n , perform linear interpolation between r1 and r n , insert a total of n - 2 sequentially increasing values, denoted as r2~r n-1 in sequence, and select m n adjacent ones in sequence and including r i from r1~ri The m corresponding to the i-th segment is a data i slotting ratio.

[0023] For the scraper design method of a wiped film evaporator as described above, in step (4), during the flow field and evaporation simulation, first, the fluid domain of the wiped film section model is extracted using SpaceClaim, then the fluid domain is meshed with unstructured grids using Fluent, local refinement is performed on complex regions and the grid quality is controlled (skewness < 0.95). Finally, the grid is imported into Fluent, the energy equation is enabled, the turbulence model and mass transfer model are set, the material properties (zero shear viscosity, density, specific heat, etc. of the material) and boundary conditions (mass flow rate inlet, pressure outlet, etc.) and process parameters (including feed rate, rotation speed) are defined, and steady-state solution calculations are performed.

[0024] For the scraper design method of a wiped film evaporator as described above, in step (4), the RNG k-ε model is selected as the turbulence model.

[0025] For the scraper design method of a wiped film evaporator as described above, in step (4), the LEE model is selected as the mass transfer model.

[0026] For the scraper design method of a wiped film evaporator as described above, in step (4), after n times of flow field and evaporation simulation, n simulated evaporation rates are obtained, and the sum of the n simulated evaporation rates is denoted as v ts ;

[0027] During simulation verification, the actual evaporation rate at the production site is collected. The machine used at the production site is the same as the prototype machine in step (3), and the material properties and process parameters processed at the production site are the same as those in the simulation process of step (4). The actual evaporation rate at the production site is divided by w to obtain v tr , where w is the ratio of the height of the prototype machine in step (3) to the height of the wiped film section model, and it is judged whether the relative error of v ts and v tr (= |v ts - v tr | / v tr × 100%) exceeds 20%. If so, check whether the physical modeling, boundary conditions, and material property settings are accurate, and adjust the grid quality and mass transfer model parameters. Otherwise, no adjustment is made.

[0028] For the scraper design method of a wiped film evaporator as described above, in step (4), the process of obtaining the simulated evaporation rate is as follows: During the simulation solution process, a flow flux monitoring point for the gas phase is added at the steam outlet. When the simulation converges, the average value of the flow values measured at this monitoring point for the last 1000 steps is taken as the simulated evaporation rate.

[0029] Beneficial effects:

[0030] 1. The scraping blade design method of the wiped film evaporator of the present invention determines the distribution of the zero shear viscosity of the material in each section along the axis of the evaporator, establishes the mapping relationship between the optimal slotting ratio and the zero shear viscosity of the material, thereby obtaining the distribution of the optimal slotting ratio at different axial heights, and then adopts a segmented slotting scheme to design a scraping blade with a slotting ratio that varies along the axis.

[0031] 2. The scraping blade design method of the wiped film evaporator of the present invention is suitable for different material viscosities: in the low viscosity region, smaller slots are used to ensure the integrity of the liquid film; in the high viscosity region, the slot size is increased to promote the smooth exchange between the liquid mass and the liquid film and the axial transport along the liquid strand.

[0032] 3. The scraping blade design method of the wiped film evaporator of the present invention enables the material with the current properties to achieve the best exchange effect at different axial heights in the evaporator, improves the exchange intensity of the material in the evaporator, strengthens the mass and energy exchange between the liquid film and the liquid mass, greatly improves the heat transfer effect and evaporation rate, and significantly increases the evaporation capacity.

[0033] 4. The scraping blade design method of the wiped film evaporator of the present invention takes into account both energy efficiency and environmental protection performance, provides a comprehensive optimization solution for equipment with similar structures and operating conditions, helps industrial production move towards a sustainable and environmentally friendly development path, is expected to be widely applied in the industry, and promotes the industrial development towards the direction of green and high efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a schematic diagram of the scraping blade structure (only one section of the scraping blade is shown) and the slotting ratio; wherein, 1 - substrate, 2 - protrusion, 3 - slot.

[0035] Figure 2 It is a schematic diagram of different slotting ratios;

[0036] Figure 3 It is a schematic diagram of the flow field pattern obtained by single - pass flow field and evaporation simulation; wherein, A is the liquid film, B is the liquid mass, and C is the liquid strand.

[0037] Figure 4 It is a contour map of the radial velocity distribution of the circumferential surface swept by the tip of the scraping blade;

[0038] Figure 5 It is the four mass - film exchange fluxes obtained from the four wiped film section models corresponding to the first section. DETAILED DESCRIPTION OF THE INVENTION

[0039] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims of this application.

[0040] A method for designing the scraper of a wiped film evaporator, the specific steps are as follows:

[0041] (1) Determine the application scenario of the wiped film evaporator (taking the production of lyocell stock solution as an example). According to actual production experience, obtain the total length (8750 mm), number of segments (6 segments), and installation interval between segments (10 mm) of a single row of scrapers in the wiping section. At the same time, obtain the zero-shear viscosity η of the material at the upper inlet of the wiping section 01 (0.05 Pa·s) and the zero-shear viscosity η of the material at the lower outlet 06 (12000 Pa·s). The material is a pseudoplastic fluid conforming to the Carreau model;

[0042] (2) Obtain the zero-shear viscosity η corresponding to the i-th segment 0i and m i slotting ratios, where i = 1, 2,..., 6 and m i = 4;

[0043] The process of obtaining the zero-shear viscosity η corresponding to the i-th segment 0i is as follows: Take η 01 as the zero-shear viscosity corresponding to the first segment, and take η 06 as the zero-shear viscosity corresponding to the sixth segment. Perform exponential interpolation between η 01 and η 06 , inserting a total of 4 sequentially increasing values, and respectively corresponding them as the zero-shear viscosities corresponding to the 2nd to 5th segments (0.60 Pa·s, 7.10 Pa·s, 84.55 Pa·s, 1000 Pa·s in sequence);

[0044] The process of obtaining the m i slotting ratios corresponding to the i-th segment is as follows: According to actual production experience, obtain the slotting ratio r1 (5%, as shown in a of 01 ) corresponding to η Figure 2 and the slotting ratio r6 (33.33%, as shown in f of 06 ) corresponding to η Figure 2 . Perform linear interpolation between r1 and r6, inserting a total of 4 sequentially increasing values, and correspondingly denoted as r2 to r5 (10.67% (as shown in b of Figure 2 ), 16.33% (as shown in c of Figure 2 ), 22% (as shown in d of Figure 2as shown in d), 27.67% (as shown in Figure 2 e)), select m consecutive and adjacent data from r1 to r6 that include r i as the m i slotting ratios corresponding to the i-th segment; i The 4 slotting ratios corresponding to the first segment are: 0%, 5%, 10.67%, 16.33%;

[0045] The 4 slotting ratios corresponding to the second segment are: 5%, 10.67%, 16.33%, 22%;

[0046] The 4 slotting ratios corresponding to the third segment are: 10.67%, 16.33%, 22%, 27.67%;

[0047] The 4 slotting ratios corresponding to the fourth segment are: 16.33%, 22%, 27.67%, 33.33%;

[0048] The 4 slotting ratios corresponding to the fifth segment are: 16.33%, 22%, 27.67%, 33.33%;

[0049] The 4 slotting ratios corresponding to the sixth segment are: 16.33%, 22%, 27.67%, 33.33%;

[0050] The 4 slotting ratios corresponding to the sixth segment are: 16.33%, 22%, 27.67%, 33.33%;

[0051] (3) Establish 1 film scraping section model using SolidWorks;

[0052] The height of the film scraping section model is 1000 mm, and other parameters are the same as those of the prototype machine; specifically, the inner wall (i.e., the inner surface of the housing) diameter is set to 1690 mm, the distance between the outer edge of the scraper and the inner wall is 4.5 mm, the number of scraper rows is 40, the scraper slotting period is 150 mm, the scraper slotting ratio is 33.33%, and the scraper slotting depth is 26 mm;

[0053] (4) For the 1 film scraping section model in step (3), after performing 6 times of flow field and evaporation simulations, conduct simulation verification;

[0054] During the flow field and evaporation simulation process, first, SpaceClaim is used to extract the fluid domain of the wiped film section model. Then, Fluent is used to perform unstructured grid division on the fluid domain, locally refine complex regions, and control the grid quality (skewness < 0.95). Finally, the grid is imported into Fluent, the energy equation is turned on, the turbulence model and mass transfer model are set (RNG k-ε model is selected for the turbulence model, and LEE model is selected for the mass transfer model), the material properties (zero shear viscosity, density, specific heat, etc. of the material) and boundary conditions (mass flow rate inlet, pressure outlet, etc.) and process parameters (including feed rate, rotation speed, the feed rate is 7.78 kg / s, and the rotation speed is 100 rpm) are defined, and steady-state solution calculation is carried out;

[0055] During the 6 times of flow field and evaporation simulation processes, only the zero shear viscosity of the material is different. The zero shear viscosity of the material in the i-th flow field and evaporation simulation is the same as the zero shear viscosity η of the material corresponding to the i-th section 0i ;

[0056] After a single flow field and evaporation simulation, the flow field pattern shown as Figure 3 is obtained. After 6 times of flow field and evaporation simulation, 6 simulation evaporation rates corresponding to the 1st to 6th sections are obtained. The obtaining process is as follows: During the simulation solution process, a flow flux monitoring point of the gas phase is added at the steam outlet. When the simulation converges, the average value of the flow values measured at this monitoring point in the last 1000 steps is taken as the simulation evaporation rate; The sum of the 6 simulation evaporation rates is denoted as v ts ;

[0057] During simulation verification, the actual evaporation rate at the production site is collected. The machine used at the production site is the same as the prototype machine in step (3). The material properties and process parameters processed at the production site are the same as those in the simulation process of step (4). The actual evaporation rate at the production site is divided by w to obtain v tr , where w is the ratio of the height of the prototype machine in step (3) to the height of the wiped film section model (the height of the prototype machine is 1450 mm, that is, w = 1.45). Judge whether the relative error of v ts and v tr (= |v ts - v tr | / v tr ×100%) exceeds 20%. If so, check whether the physical modeling, boundary conditions, and material property settings are accurate, and adjust the grid quality and mass transfer model parameters. Otherwise, no adjustment is made;

[0058] The 6 simulation evaporation rates corresponding to the 1st to 6th sections are 94.28 g / s, 66.21 g / s, 58.21 g / s, 51.87 g / s, 52.92 g / s, and 61.36 g / s respectively. Then v ts = 384.85 g / s; The actual evaporation rate at the production site is 611 g / s. Then v tr= 421.38 g / s, it can be known that v ts and v tr has a relative error of 8.67%;

[0059] (5)For the i-th section, use SolidWorks to establish m i scraping film section models. The scraping plate slotting ratio of the m i scraping film section models is the same as the corresponding m i slotting ratio of the i-th section. The other parameters of the m i scraping film section models are the same as those of the scraping film section model in step (3);

[0060] (6)For the m i scraping film section models corresponding to the i-th section in step (5), perform 1 flow field and evaporation simulation for each;

[0061] The flow field and evaporation simulation process is only different in the zero shear viscosity of the material from that in step (4). The zero shear viscosity of the material is the same as the zero shear viscosity η 0i of the material corresponding to the i-th section;

[0062] After the flow field and evaporation simulation, obtain m i cluster film exchange fluxes. Take the scraping film section model corresponding to the maximum value of the cluster film exchange flux as the optimal scraping film section model of the i-th section, and set the parameters of the i-th section the same as those of the optimal scraping film section model of the i-th section. The process of obtaining the cluster film exchange flux is as follows: Take the circumferential surface swept by the tip of the scraping plate during rotation (referred to as the scraping plate tip swept circumferential surface) as the analysis object. This circumferential surface takes the evaporator rotation axis as the center and passes through the cluster film exchange area, which is the position where the liquid cluster and liquid film mass exchange is the most intense. The liquid phase velocity vector perpendicular to this circumferential surface is the liquid phase radial velocity. This velocity vector can characterize the exchange behavior of the liquid cluster and liquid film. Obtain the liquid phase radial velocity contour map of this circumferential surface from the simulation results (in the first section, the liquid phase radial velocity contour map corresponding to a slotting ratio of 5% is as shown in Figure 4 a, the liquid phase radial velocity contour map corresponding to a slotting ratio of 10.67% is as shown in Figure 4 b, and the liquid phase radial velocity contour map corresponding to a slotting ratio of 16.33% is as shown in Figure 4 c), and extract the liquid phase radial velocity data. The area within 0° - 4° of the circumference in the leading edge direction of each column of the scraping plate movement on this circumferential surface is the area where the cluster film exchange occurs. Integrate the liquid phase radial velocity within this angular range over the circumferential surface to obtain the cluster film exchange flux. The cluster film exchange flux is the physical quantity that measures the intensity of the cluster film exchange;

[0063] As shown in Figure 5As shown, the four mass transfer fluxes obtained from the four wiped film section models corresponding to the first section are: 0.51 L / s (corresponding to a slotting ratio of 0%), 0.76 L / s (corresponding to a slotting ratio of 5%), 0.79 L / s (corresponding to a slotting ratio of 10.67%), 0.69 L / s (corresponding to a slotting ratio of 16.33%). Therefore, the wiped film section model with a slotting ratio of 10.67% is the best wiped film section model for the first section;

[0064] The four mass transfer fluxes obtained from the four wiped film section models corresponding to the second section are: 0.67 L / s (corresponding to a slotting ratio of 5%), 0.70 L / s (corresponding to a slotting ratio of 10.67%), 0.64 L / s (corresponding to a slotting ratio of 16.33%), 0.67 L / s (corresponding to a slotting ratio of 22%). Therefore, the wiped film section model with a slotting ratio of 10.67% is the best wiped film section model for the second section;

[0065] The four mass transfer fluxes obtained from the four wiped film section models corresponding to the third section are: 0.61 L / s (corresponding to a slotting ratio of 10.67%), 0.63 L / s (corresponding to a slotting ratio of 16.33%), 0.62 L / s (corresponding to a slotting ratio of 22%), 0.59 L / s (corresponding to a slotting ratio of 27.67%). Therefore, the wiped film section model with a slotting ratio of 16.33% is the best wiped film section model for the third section;

[0066] The four mass transfer fluxes obtained from the four wiped film section models corresponding to the fourth section are: 0.48 L / s (corresponding to a slotting ratio of 16.33%), 0.50 L / s (corresponding to a slotting ratio of 22%), 0.55 L / s (corresponding to a slotting ratio of 27.67%), 0.54 L / s (corresponding to a slotting ratio of 33.33%). Therefore, the wiped film section model with a slotting ratio of 27.67% is the best wiped film section model for the fourth section;

[0067] The four mass transfer fluxes obtained from the four wiped film section models corresponding to the fifth section are: 0.35 L / s (corresponding to a slotting ratio of 16.33%), 0.37 L / s (corresponding to a slotting ratio of 22%), 0.40 L / s (corresponding to a slotting ratio of 27.67%), 0.38 L / s (corresponding to a slotting ratio of 33.33%). Therefore, the wiped film section model with a slotting ratio of 27.67% is the best wiped film section model for the fifth section;

[0068] The four mass transfer fluxes obtained from the four wiped film section models corresponding to the sixth section are: 0.09 L / s (corresponding to a slotting ratio of 16.33%), 0.10 L / s (corresponding to a slotting ratio of 22%), 0.12 L / s (corresponding to a slotting ratio of 27.67%), 0.15 L / s (corresponding to a slotting ratio of 33.33%). Therefore, the wiped film section model with a slotting ratio of 33.33% is the best wiped film section model for the sixth section.

[0069] After adjusting the prototype machine in step (3) according to the grooving ratio corresponding to the optimal film scraping section model in paragraphs 1 to 6, it is used for the actual production of lyocell stock solution. The material properties and process parameters processed at the production site are the same as those in the simulation process of step (4). Finally, the actual evaporation rate at the production site is 614.27 g / s, which is 10.08% higher than that of the prototype machine in step (3) before adjustment under the same other conditions.

Claims

1. A scraping blade design method for a wiped film evaporator, characterized in that, It includes the following steps: (1) Determine the application scenario of the wiped film evaporator. According to actual production experience, obtain the total length of a single scraper in a single row of the wiping section, the number of sections n, and the installation interval between sections, where n > 1. At the same time, obtain the zero-shear viscosity η of the material at the upper inlet of the wiping section 01 and the zero-shear viscosity η of the material at the lower outlet 0n ; (2)Obtain the zero shear viscosity η of the material corresponding to the i-th segment 0i and m i slotting ratios, where i = 1, 2…, n, and m i > 1; (3) Establish one wiped film section model; The height of the wiped film section model is 1000 mm, and other parameters are the same as those of the prototype; (4) For the one wiped film section model in step (3), after performing n times of flow field and evaporation simulations, conduct simulation verification; The nth flow field and evaporation simulation processes only differ in the zero shear viscosity of the material. The zero shear viscosity of the material in the ith flow field and evaporation simulation is the same as the zero shear viscosity η of the material corresponding to the ith section. 0i ; (5) For the i-th section, establish m i film scraping section models. The scraping blade slotting ratios of the m i film scraping section models are the same as the m i slotting ratios corresponding to the i-th section. The other parameters of the m i film scraping section models are the same as those of the film scraping section model in step (3); (6) For the m i scraped film section models corresponding to the i-th section in step (5), perform 1 flow field and evaporation simulation for each; The flow field and evaporation simulation process in step (4) is only different in the zero shear viscosity of the material from that in the flow field and evaporation simulation process. The zero shear viscosity of the material is the same as the zero shear viscosity η of the material corresponding to the i-th section 0i ; After the flow field and evaporation simulations, m i membrane exchange fluxes of clusters are obtained. The wiped film section model corresponding to the maximum value of the membrane exchange flux of clusters is used as the optimal wiped film section model for the i-th section, and the parameters of the i-th section are set the same as those of the optimal wiped film section model of the i-th section; The process of obtaining the mass transfer flux of the agglomerated film is as follows: Take the circumferential surface swept by the tip of the wiper blade during its rotational operation as the analysis object, obtain the liquid-phase radial velocity contour map of this circumferential surface, extract the radial velocity on this circumferential surface, and perform area integration on the liquid-phase radial velocity perpendicular to the circumferential surface and outward within the 0°-4° circumferential range along the forward direction of all wiper blades on this circumferential surface, and then the mass transfer flux of the agglomerated film can be obtained.

2. The scraping plate design method of a wiped film evaporator according to claim 1, characterized in that In step (2), the zero-shear viscosity η of the material corresponding to the i-th segment 0i is obtained as follows: Taking η 01 as the zero-shear viscosity of the material corresponding to the first segment, and taking η 0n as the zero-shear viscosity of the material corresponding to the n-th segment, perform exponential interpolation between η 01 and η 0n to insert a total of n - 2 sequentially increasing values, and respectively corresponding them as the zero-shear viscosities of the materials corresponding to the 2nd to (n - 1)-th segments; The m corresponding to the i-th segment i The process of obtaining the grooving ratio is as follows: According to actual production experience, obtain η 01 The corresponding grooving ratio r1 and η 0n The corresponding grooving ratio r n , perform linear interpolation between r1 and r n , insert a total of n - 2 sequentially increasing values, denoted as r2~r n-1 , select m n successively adjacent data including r i as the m i grooving ratios corresponding to the i-th segment i .

3. The scraping plate design method of a wiped film evaporator according to claim 1, characterized in that, In step (4), during the flow field and evaporation simulation process, first use SpaceClaim to extract the fluid domain of the wiped film section model, then use Fluent to perform unstructured grid division on the fluid domain, locally refine the complex areas and control the grid quality, and finally import the grid into Fluent, turn on the energy equation, set the turbulence model and mass transfer model, define the material properties, boundary conditions and process parameters, and perform steady-state solution calculations.

4. A scraping blade design method for a wiped film evaporator according to claim 3, characterized in that In step (4), the RNG k-ε model is selected as the turbulence model.

5. A scraping blade design method for a wiped film evaporator according to claim 3, characterized in that In step (4), the LEE model is selected as the mass transfer model.

6. The scraping plate design method of a wiped film evaporator according to claim 3, characterized in that, In step (4), after n times of flow field and evaporation simulations, n simulated evaporation rates are obtained, and the sum of the n simulated evaporation rates is denoted as v ts ; During simulation verification, collect the actual evaporation rate at the production site. The machine used at the production site is the same as the prototype machine in step (3), and the material properties and process parameters processed at the production site are the same as those in the simulation process of step (4). Divide the actual evaporation rate at the production site by w to obtain v tr , where w is the ratio of the height of the prototype machine in step (3) to the height of the wiped film section model, and judge v ts and v tr Whether the relative error exceeds 20%. If so, check whether the physical modeling, boundary conditions, and material property settings are accurate, and adjust the mesh quality and mass transfer model parameters. Otherwise, no adjustment is required.

7. A scraping blade design method for a wiped film evaporator according to claim 6, characterized in that, In step (4), the process of obtaining the simulated evaporation rate is as follows: During the simulation solution process, add a gas-phase flow flux monitoring point at the steam outlet. After the simulation converges, take the average value of the flow values measured at this monitoring point for the last 1000 steps as the simulated evaporation rate.

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