A Design Method for the Scraping Blade of a Wiped Film Evaporator

Abstract

The present invention belongs to the technical field of evaporation equipment and relates to a design method for the scraper of a wiped film evaporator, including the steps of: (1) determining the application scenario, obtaining the total length of a single-row scraper in the wiped film section, the number of sections n and the installation interval between sections, as well as η at the upper inlet and η at the lower outlet according to actual production experience 01 , η 0n ; (2) obtaining the corresponding η of the i-th section 0i and the grooving ratio of m i ; (3) establishing a model of one wiped film section; (4) verifying after performing n times of flow field and evaporation simulations on this model; (5) for the i-th section, establishing m i models of wiped film sections, the grooving ratio of whose scrapers corresponds to that of the i-th section; (6) performing one flow field and evaporation simulation on each of these m i models of wiped film sections (the zero shear viscosity of the material is the same as the corresponding η of the i-th section 0i ), obtaining m i mass transfer fluxes of the mass transfer film, and taking the model of the wiped film section with the largest mass transfer flux of the mass transfer film as the best model of the wiped film section of the i-th section, and setting the parameters of the i-th section the same as those of the best model of the wiped film section of the i-th section.

Description

Technical Field

[0001] The present invention belongs to the technical field of evaporation equipment and relates to a design method for a scraper 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 wiper, and the liquid is heated and evaporated on the wall surface. At the same time, the wiper drives the liquid to flow forcibly, significantly improving the convective heat transfer and evaporation efficiency. In a large-capacity wiped film evaporator, several rows of scrapers are usually installed on the rotating shaft at equal circumferential intervals, and each row of scrapers is composed of multiple axially installed scrapers spliced together. During operation, the rotating shaft drives the scrapers to rotate, and the tips of the scrapers maintain a clearance fit with the inner wall of the evaporator. Through mechanical scraping, 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 scraper 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 scraper movement direction and the lower liquid film will form a high-intensity radial convection on the low-fluidity liquid film, optimizing the heat transfer effect. As Figure 1 shown, the scraper usually includes a base body 1, a protrusion 2, and a slot 3; the slot 3 is located on the long side of the scraper close to the wall surface and is periodically distributed at equal intervals and with equal widths. A single slot 3 is in the shape of a straight slot with an arc bottom; the slot 3 can strengthen the shear thinning effect of pseudoplastic fluids, promote the radial mass exchange between the near-wall liquid film and the far-wall liquid mass, improve the evaporation efficiency, and at the same time disperse the liquid mass accumulated in front of the scraper, 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 scraper edge (as Figure 1 shown, a single slot 3 is in the shape of a straight slot with an arc bottom, 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 scraper slotting ratios need to be matched in different axial regions: in the high-viscosity region, if the scraper slotting is too small, it will cause liquid mass accumulation; while in the low-viscosity region, if the scraper slotting is too large, it will break the surface tension balance and cause the film-forming property of the material to decline.

[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 inability 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, number of segments n, and installation interval between segments of a single row of scraping plates in the scraping section, 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) Establish a scraping section model using SolidWorks;

[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 1 scraping section model in step (3), after performing n times of flow field and evaporation simulations, perform 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, establish m i scraping section models using SolidWorks. The scraping plate grooving ratios of the m i scraping section models 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 along the advancing direction of all scrapers on this circumferential surface, and the film mass transfer flux can be obtained.

[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 of the material corresponding to the first section, take η 0n as the zero shear viscosity of the material corresponding to the n-th section, perform exponential interpolation between η 01 and η 0n , insert a total of n - 2 gradually increasing values, and respectively correspond them as the zero shear viscosities of the materials 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 gradually increasing values, and record them as r2~r n-1 in sequence. Select m n adjacent ones in sequence and including r i from r1~ri The m corresponding to the i-th segment is taken as one 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 process, first, SpaceClaim is used to extract the fluid domain of the wiped film section model, and then Fluent is used to perform unstructured grid division on the fluid domain. The complex areas are locally refined and the grid quality is controlled (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, 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 the steady-state solution is calculated.

[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 simulation evaporation rates are obtained, and the sum of the n simulation 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 simulation 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 simulation 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 axial direction 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 axial direction.

[0031] 2. The scraping blade design method of the wiped film evaporator of the present invention is adapted to 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 slotting 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 working 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 from the 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 a 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 sections (6 sections), and installation interval between sections (10 mm) of the single-row scraper 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 that conforms to the Carreau model;

[0042] (2) Obtain the zero-shear viscosity η corresponding to the i-th section 0i and the m i grooving 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 section 0i is as follows: Take η 01 as the zero-shear viscosity corresponding to the first section, and take η 06 as the zero-shear viscosity corresponding to the sixth section. Perform exponential interpolation between η 01 and η 06 , and insert 4 sequentially increasing values, which are respectively corresponding to the zero-shear viscosities of the 2nd to 5th sections (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 grooving ratios corresponding to the i-th section is as follows: According to actual production experience, obtain the grooving ratio r1 (5%, as shown in 01 a in Figure 2 ) corresponding to η 06 and the grooving ratio r6 (33.33%, as shown in Figure 2 f in Figure 2 ). Perform linear interpolation between r1 and r6, and insert 4 sequentially increasing values, which are correspondingly denoted as r2 to r5 (10.67% (as shown in Figure 2 b in 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, and then Fluent is used to perform unstructured grid division on the fluid domain. The complex areas are locally refined and the grid quality is controlled (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 the steady-state solution is calculated;

[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 as shown in 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 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 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 the 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 scraped film section models. The scraping plate slotting ratio of the m i scraped 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 scraped film section models are the same as those of the scraped film section model in step (3);

[0060] (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;

[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 scraped film section model corresponding to the maximum cluster film exchange flux as the best scraped film section model of the i-th section, and set the parameters of the i-th section the same as those of the best scraped 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 its rotational operation (referred to as the scraping plate tip swept circumferential surface) as the analysis object. This circumferential surface takes the evaporator rotating shaft as the axis and passes through the cluster film exchange region, which is the position where the material exchange between the liquid cluster and the liquid film is the most intense. The liquid phase radial velocity with the vector direction perpendicular to this circumferential surface represents the exchange behavior between the liquid cluster and the liquid film. Obtain the liquid phase radial velocity contour map of this circumferential surface in 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 region within 0° - 4° of the circumference in the leading edge direction of the scraping plate movement on each column of this circumferential surface is the region where the cluster film exchange occurs. Integrate the liquid phase radial velocity within this angular range over the area of the circumferential surface to obtain the cluster film exchange flux. The cluster film exchange flux is a physical quantity that measures the intensity of the cluster film exchange;

[0063] Such as Figure 5As shown in the figure, the four film exchange 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%), and 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 film exchange 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%), and 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 film exchange 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%), and 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 film exchange 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%), and 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 film exchange 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%), and 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 film exchange 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%), and 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 design method for the scraping blade of 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 (n > 1), and the installation interval between sections. 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 falling-film evaporation section model; The height of the falling-film evaporation section model is 1000 mm, and other parameters are the same as those of the prototype; (4) For the one falling-film evaporation 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 scraping film section models. The scraping plate slotting ratios of the m i scraping film section models are the same as the m i slotting ratios corresponding to 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). (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 the flow field and evaporation simulation process, and 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 taken 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 for 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 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 along the forward direction of all scrapers on this circumferential surface to obtain the mass transfer flux of the agglomerated film.

2. The scraping blade 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: Take η 01 as the zero shear viscosity of the material corresponding to the first segment, and take 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 correspond 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 from r1~r i as the m i grooving ratios corresponding to the i-th segment.

3. A scraping blade design method for 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 falling-film evaporation section model, then use Fluent to perform unstructured grid division on the fluid domain, locally refine the complex areas and control the grid quality. Finally, import the grid in 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 design method of the scraper 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 grid 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: Add a gas-phase flow flux monitoring point at the steam outlet during the simulation solution process. 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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