Method for judging film scraping period of scraper in evaporation process of high-viscosity material

Abstract

The invention belongs to the field of liquid film evaporation heat transfer, and particularly relates to a method for judging the film scraping period of a scraper in the evaporation process of a high-viscosity material. Comprising the following steps: (1) establishing a calculation fluid domain geometric model, and setting parameters of the calculation fluid domain geometric model; the calculation fluid domain geometric model is of a cubic structure, the bottom surface is a heating wall surface, and the part above the bottom surface is a liquid film and gas area; (2) performing grid division on the geometric model of the computational fluid domain, and performing local grid encryption on a heating wall surface; (3) performing transient evaporation calculation on the geometric model of the computational fluid domain to obtain a change curve of the evaporation rate of the bottom of the liquid film along with time; and (4) analyzing the change curve of the evaporation rate of the bottom of the liquid film along with time, wherein the difference value between the moment tb corresponding to the highest point and the moment ta corresponding to the starting point is the film scraping period of the scraper. According to the method, the optimal scraping time of the high-viscosity material can be judged, the gas film is effectively damaged, the heat transfer coefficient is increased, the evaporation rate is increased, and the evaporation efficiency is optimized.

Description

Technical Field

[0001] The invention belongs to the field of liquid film evaporation heat transfer, and in particular relates to a method for determining a scraper film scraping cycle in the evaporation process of a high-viscosity material. Background Art

[0002] As a highly efficient evaporation equipment, the scraped film evaporator is widely used in many industries such as chemical, pharmaceutical, food, textile, etc., mainly for concentrating raw material solutions. Its structure is mainly composed of three parts, which are the material distribution area, scraped film area and extrusion area in the height direction. Among them, the scraped film area undertakes the most critical evaporation and concentration tasks. After the material enters the scraped film area, it is evenly distributed on the heated wall surface through the forced scraping of the scraper. Figure 1 As shown in the figure, the flow field in the scraped film evaporator can be mainly divided into two areas: a circular wave is formed at the front edge of the scraper, and this part of the fluid flows downward in a spiral shape; between the trailing edge of the scraper and the next circular wave, the effect of the scraper disappears and becomes a laminar liquid film. In this process, the volatile components in the material continue to absorb heat and undergo phase change to gas, thereby achieving the purpose of concentrating the raw material solution.

[0003] When dealing with high-viscosity materials, their inherent poor fluidity and high resistance to heat and mass transfer bring many challenges to the evaporation process. In the scraped film evaporator, the high-viscosity material is scraped by the scraper to form a liquid film, and a large number of bubbles will be generated. Due to the extremely high viscosity of the material, the liquid film formed is relatively thick, and the bubbles generated at the bottom of the liquid film are difficult to escape. They gradually gather at the bottom of the liquid film and then form an air film. The appearance of this air film has an extremely adverse effect on the evaporation efficiency. From the perspective of heat transfer, the air film is like an insulating layer, which seriously hinders the transfer of heat from the heated wall to the inside of the material. Heat needs to pass through the air film with difficulty to reach the material, and the thermal resistance of the air film is much higher than that of the material itself, which directly leads to a sharp increase in the heat transfer temperature difference and a significant increase in energy consumption. From the perspective of mass transfer, the existence of the air film hinders the escape of moisture in the material. The literature (A Brief Discussion on the Structural Design of Scraper Plates in Scraper-type Thin Film Evaporators (Part 1) [J]. Pharmaceutical Engineering Design, 2000, (04): 145-146.) mentioned that in order to allow moisture to escape smoothly from the inside of the material, the air film needs to be broken as quickly as possible to refresh the heat transfer surface. The author used a scraper with a corrugated end face to achieve the above purpose. However, the author did not study the timing of breaking the air film; in addition, the author also mentioned that the specific scraper structure will be different depending on the material and the feeding state, but no further discussion was made.

[0004] In industrial production practice, the common means of dealing with the gas film problem faced when evaporating high-viscosity materials is to increase the number of scraper columns or speed up the scraper speed. However, simply increasing the number of scraper columns will not only significantly increase the cost of the equipment, but also due to the lack of targeted adaptation design for specific materials, it is difficult to accurately determine the most suitable number of scraper columns, resulting in the evaporation capacity of the equipment cannot be fully utilized. In fact, the core purpose of increasing the number of scraper columns is to increase the frequency of the liquid film being scraped, but this frequency is not only determined by the number of scraper columns, but the scraper speed also plays a key role. The existing technology has deeply explored the influence of scraper speed on evaporator performance through experiments. The results show that with the increase of scraper speed, the total heat transfer coefficient and evaporation intensity will show a trend of first increasing and then decreasing. Moreover, in actual operation, it often takes a long time of trial and error and fine adjustment to adjust the scraper speed in order to barely achieve a relatively good evaporation efficiency.

[0005] It is worth noting that for highly viscous materials, if the scraper scrapes too frequently, that is, too many scraper rows or too fast scraper speed, in addition to causing problems such as increased costs and energy consumption, it is also easy to cause the scraper to scrape the liquid film too early, resulting in insufficient evaporation of the liquid film, which ultimately affects the concentration effect. On the contrary, if the scraper scrapes too late, the thermal resistance effect of the gas film will be aggravated, seriously affecting the heat transfer effect.

[0006] In summary, in order to effectively avoid the above series of problems, it is particularly important to accurately determine the best scraping time during the evaporation of high-viscosity materials in the scraped film evaporator. Only by finding this best time can we ensure the evaporation efficiency and concentration effect while taking into account the equipment cost and energy consumption control, and give full play to the performance advantages of the scraped film evaporator in processing high-viscosity materials. Summary of the invention

[0007] The purpose of the present invention is to solve the problems existing in the prior art and provide a method for determining the scraping cycle of a scraper during the evaporation process of a high-viscosity material.

[0008] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0009] A method for determining a scraper film scraping cycle during the evaporation process of a high-viscosity material comprises the following steps:

[0010] (1) Establish a computational fluid domain geometry model and set the parameters of the computational fluid domain geometry model;

[0011] The geometric model of the computational fluid domain is a cubic structure, with the bottom surface being the heating wall, and the part above the bottom surface being the liquid film and the gas region, with the gas region being located above the liquid film;

[0012] The parameters of the computational fluid domain geometric model include the thickness of the liquid film, the thickness of the gas region and the size of the bottom surface of the computational fluid domain geometric model;

[0013] The thickness of the liquid film is obtained by collecting the thickness of the liquid film formed by the high-viscosity material in the scraped film evaporator during the historical production process and taking the average value;

[0014] The thickness of the gas area is obtained by collecting the thickness of the gas area formed by high-viscosity materials in the scraped film evaporator during the historical production process and taking the average value;

[0015] High-viscosity materials are materials whose evaporable components are transformed into gas during evaporation and cannot escape from the bottom of the liquid film;

[0016] (2) Meshing the geometric model of the computational fluid domain and locally encrypting the mesh of the heated wall;

[0017] (3) Setting the boundary condition parameters of the computational fluid domain, performing transient evaporation calculation on the computational fluid domain geometric model, and obtaining the time-varying curve of the evaporation rate at the bottom of the liquid film to simulate the heating process of the liquid film before being scraped;

[0018] (4) Analyze the curve of the evaporation rate at the bottom of the liquid film changing with time. The time corresponding to the starting point is recorded as ta, and the time corresponding to the highest point is recorded as tb. The difference between tb and ta is the scraping cycle of the scraper. The scraping cycle of the scraper is the time it takes for adjacent scrapers in the scraped film evaporator to scrape the same liquid film.

[0019] As the preferred technical solution:

[0020] In the method for determining the scraping cycle of a scraper during the evaporation of a high-viscosity material as described above, in step (1), the bottom surface of the geometric model of the computational fluid domain is a rectangle with a length of 20-60 mm and a width of 20-60 mm. Since it is a simplified microelement evaporation, the length and width are set based on the following considerations: first, the size cannot be too small to fully develop the flow and heat transfer; second, the size cannot be too large to consider the computational resources and computational accuracy. The length and width are finally set to balance the two.

[0021] In the above-mentioned method for determining the scraping cycle of a scraper during the evaporation of a high-viscosity material, in step (2), the mesh is divided using a polyhedron-hexahedron hybrid mesh (Poly-Hexcore), such as Figure 2 As shown in (c).

[0022] In the above-mentioned method for determining the scraping cycle of a scraper during the evaporation process of a high-viscosity material, in step (2), meshing the computational fluid domain geometric model refers to meshing the computational fluid domain geometric model using ANSYS Fluent Meshing software.

[0023] In the method for determining the scraping cycle of a scraper during the evaporation process of a high-viscosity material as described above, in step (3), the boundary condition parameters of the calculated fluid domain include the temperature of the heated wall (determined according to the process in the industrial production process), the viscosity of the liquid film, and the initial temperature of the liquid film. The initial temperature of the liquid film is the same as the saturation temperature of the high-viscosity material (i.e., the heat absorption temperature of the high-viscosity material rises to reach the critical temperature for evaporation).

[0024] In the method for determining the scraping cycle of a scraper during the evaporation process of a high-viscosity material as described above, in step (3), when calculating transient evaporation, the proportion of the evaporable components of the liquid film is first set through the Species Transport model, and then the gas-liquid interface is tracked based on the VOF model, wherein the liquid phase is the high-viscosity material and the gas phase is steam, and finally the phase change conversion between the liquid-gas phases of the evaporable components in the high-viscosity material is realized based on the Lee model.

[0025] In the method for determining the scraping cycle of a scraper during the evaporation process of a high-viscosity material as described above, in step (3), when calculating transient evaporation, the time step is 0.001 s, the number of time steps is 1000 steps, and the total calculation time is 1 s.

[0026] In the above-mentioned method for determining the scraping cycle of a scraper during the evaporation of a high-viscosity material, in step (3), the process of obtaining the curve of the evaporation rate of the bottom of the liquid film over time is as follows: with a time interval of 0.1 s, the evaporation rate of the bottom of the liquid film at each time is calculated, and after obtaining discrete data points, fitting is performed to obtain the curve of the evaporation rate of the bottom of the liquid film over time.

[0027] In the above-mentioned method for determining the scraping cycle of the scraper during the evaporation of a high-viscosity material, the steps for obtaining the evaporation rate at the bottom of the liquid film at each moment are as follows:

[0028] (a) Obtain the liquid phase volume fraction of the discrete layered cross section of the computational fluid domain geometric model along the height direction at each time, and perform fitting after obtaining the discrete data points to obtain the variation curve of the liquid phase volume fraction with the height of the computational fluid domain geometric model at each time;

[0029] (b) Analyze the variation curve of the liquid phase volume fraction with the height of the computational fluid domain geometric model at each time, and find the minimum value ha of the computational fluid domain geometric model height when the liquid phase volume fraction is 0.5 at each time;

[0030] (c) The volume of the area with a height less than ha in the computational fluid domain geometric model at each time and the phase change mass transfer rate are calculated, and the evaporation rate at the bottom of the liquid film at each time is calculated by the following formula;

[0031] ;

[0032] In the formula, Represents the evaporation rate at the bottom of the liquid film at each time, in kg / s; Represents the phase change mass transfer rate of the area with a height less than ha in the computational fluid domain geometric model at each time, in kg / m 3 ·s; Represents the volume of the area whose height is less than ha in the computational fluid domain geometric model at each time, in m 3 .

[0033] Beneficial effects:

[0034] (1) The present invention aims to solve the problem of using scraped film evaporators to process high-viscosity materials and constructs an innovative evaporation calculation model for high-viscosity materials. This model simplifies the complex and large three-dimensional model of the scraped film area into a tiny liquid film model, which fully reflects the influence of components on evaporation and greatly shortens the calculation time and saves computing resources. At the same time, the model associates the evolution of the gas film with the quantification of transient heat transfer. By integrating multi-parameter data such as gas film thickness, wall heat flux density, and evaporation rate, the scraping frequency is accurately determined and the optimal scraping time is determined. This innovative measure not only avoids the problem of insufficient evaporation of the liquid film caused by premature scraping, but also effectively suppresses the thermal resistance effect of the gas film, thereby achieving optimal control of heat transfer enhancement.

[0035] (2) Thanks to the above model and method, the present invention can effectively destroy the gas film, improve the heat transfer coefficient, and accelerate the evaporation rate. At the same time, by accurately controlling the optimal scraping time, the evaporation efficiency is closer to the optimal value, which significantly improves the performance of the scraped film evaporator in processing high-viscosity materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 Schematic diagram of the flow field distribution inside the wiped film evaporator; (a) is a three-dimensional diagram, and (b) is a top view;

[0037] Figure 2 (a) is the geometric model of the computational fluid domain, (b) is the schematic diagram of liquid film evaporation, (c) is the grid division diagram, and (d) is the local grid encryption diagram;

[0038] Figure 3 This is the cloud diagram of gas-liquid distribution of liquid film under different proportions of evaporable components;

[0039] Figure 4 The curves of the liquid phase volume fraction of liquid films with different evaporable component ratios at different times as the height of the geometric model of the computational fluid domain;

[0040] Figure 5 The curve of the evaporation rate at the bottom of the liquid film changing with time under different proportions of evaporable components;

[0041] Figure 6 This is the curve of heat flux density changing with time under different proportions of evaporable components. DETAILED DESCRIPTION

[0042] 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 are not intended 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 fall within the scope limited by the appended claims of the application equally.

[0043] A method for determining the scraping film scraping cycle during the evaporation process of high-viscosity materials, the specific steps are as follows:

[0044] (1) Establish a computational fluid domain geometry model and set the parameters of the computational fluid domain geometry model;

[0045] like Figure 2 As shown in (a), the geometric model of the computational fluid domain is a rectangular parallelepiped structure with a bottom length of 20 mm, a bottom width of 20 mm, a height of 6 mm, and a bottom heating wall; Figure 2 As shown in (b), the part above the bottom surface is the liquid film (3 mm thick) and the gas area. The gas area is located above the liquid film, and the top surface is the steam outlet.

[0046] (2) The computational fluid domain is meshed using ANSYS Fluent Meshing software, using a polyhedron-hexahedron hybrid mesh (e.g. Figure 2 (c)), and the local mesh of the heated wall is refined (as shown in Figure 2 (d));

[0047] (3) Set the boundary condition parameters of the computational fluid domain, perform transient evaporation calculation on the computational fluid domain geometric model (time step is 0.001 s, time step number is 1000 steps, total calculation time is 1 s), and obtain the evaporation rate curve of the bottom of the liquid film over time;

[0048] The boundary condition parameters of the computational fluid domain include the temperature of the heated wall (104°C), the viscosity of the liquid film (200 Pa·s), and the initial temperature of the liquid film (100°C). The initial temperature of the liquid film is the same as the saturation temperature of the high-viscosity material (cellulose pulp, the raw material for producing lyocell fiber).

[0049] When calculating transient evaporation, the Species Transport model is used to set the proportion of the evaporable component of the liquid film (the evaporable component is water, and the proportion of the evaporable component is 10wt%, 20wt%, 30wt%, and 40wt%). Then, the VOF model is used to track the gas-liquid interface, in which the liquid phase is a high-viscosity material and the gas phase is steam. Finally, the Lee model is used to realize the phase change between the liquid and gas phases of the evaporable component in the high-viscosity material.

[0050] The process of obtaining the curve of the evaporation rate at the bottom of the liquid film changing with time is as follows: with a time interval of 0.1s, the evaporation rate at the bottom of the liquid film at each time is calculated, and after obtaining discrete data points, fitting is performed to obtain the curve of the evaporation rate at the bottom of the liquid film changing with time;

[0051] like Figure 5 As shown in the figure, the evaporation rate of the bottom of the liquid film with different evaporable component ratios has the same trend with time, which increases rapidly at the beginning of heating, then increases slowly, and finally stabilizes; the liquid film with an evaporable component ratio of 40wt% slightly decreases after 0.5s and then stabilizes at around 0.4mg / s, and the liquid film with an evaporable component ratio of 30wt% slightly decreases after 0.7s and then stabilizes at around 0.3mg / s; the liquid film with an evaporable component ratio of 20wt% and the liquid film with an evaporable component ratio of 10wt% continue to rise slightly after the slow rising stage, reaching the boundary values ​​of 0.24mg / s and 0.13mg / s respectively after 0.9s; here we focus on the solid-liquid interface with a relatively large evaporation rate, and ignore the gas-liquid interface with a relatively small evaporation rate; therefore, Figure 5 The statistical law of the evaporation rate at the bottom of the liquid film changing with time largely characterizes the overall situation of the liquid film evaporation;

[0052] The steps for obtaining the evaporation rate at the bottom of the liquid film at each time are as follows:

[0053] (a) Obtain the liquid phase volume fraction of the discrete layered section of the computational fluid domain geometric model along the height direction at each time, and perform fitting after obtaining the discrete data points to obtain the variation curve of the liquid phase volume fraction with the height of the computational fluid domain geometric model at each time, as shown in Figure 4 As shown;

[0054] (b) Analyze the variation curve of the liquid phase volume fraction with the height of the computational fluid domain geometric model at each time, and find the minimum value ha of the computational fluid domain geometric model height when the liquid phase volume fraction is 0.5 at each time;

[0055] When the liquid phase volume fraction is 0.5, the minimum value ha of the height of the fluid domain geometric model is calculated, that is, the thickness of the gas phase film at the bottom of the liquid film. Figure 4 It can be seen that the higher the proportion of evaporable components, the greater the thickness of the gas phase film at the bottom of the liquid film at the same time. Figure 3The liquid film gas-liquid distribution cloud diagram shown also confirms this view. In the liquid film gas-liquid distribution cloud diagram, the blue area is the area where the liquid volume fraction in the liquid film is greater than 0.5, representing the liquid film, and the light blue area is the area where the liquid volume fraction in the liquid film is less than or equal to 0.5, representing the gas film. When the proportion of the evaporable component is 20wt%, 30wt%, and 40wt%, there are two light blue areas, among which the light blue area at the bottom represents the gas film at the bottom of the liquid film.

[0056] (c) The volume of the area with a height less than ha in the computational fluid domain geometric model at each time and the phase change mass transfer rate are calculated, and the evaporation rate at the bottom of the liquid film at each time is calculated by the following formula;

[0057] ;

[0058] In the formula, Represents the evaporation rate at the bottom of the liquid film at each time, in kg / s; Represents the phase change mass transfer rate of the area with a height less than ha in the computational fluid domain geometric model at each time, in kg / m 3 ·s; Represents the volume of the area whose height is less than ha in the computational fluid domain geometric model at each time, in m 3 ;

[0059] (4) Analyze the curve of the evaporation rate at the bottom of the liquid film changing with time. The time corresponding to the starting point is recorded as ta, and the time corresponding to the highest point is recorded as tb. The difference between tb and ta is the scraping cycle of the scraper. The scraping cycle of the scraper is the time it takes for adjacent scrapers in the scraped film evaporator to scrape the same liquid film.

[0060] Next, by determining the rate at which the heated wall transfers heat to the liquid film, we can derive the time-varying pattern of the wall heat flux density. Specifically, we count the wall heat flux density at each grid node at the bottom of the liquid film, and then calculate its average value, which is used as the average heat flux density between the heated wall and the liquid film. Next, we calculate the average wall heat flux density at each time interval of 0.1s. In the case of different proportions of evaporable components, we also calculate according to the above method, and finally get the following: Figure 6 The change pattern shown. Figure 6It can be seen that the wall heat flux density first decreases rapidly as the heating process progresses, then decreases slowly and gradually stabilizes. Under the same heating conditions, the liquid film with a high evaporable component ratio has a higher wall heat flux density. For example, the initial heat flux density of the liquid film with an evaporable component ratio of 40wt% is 4175W / m², the initial heat flux density of the liquid film with an evaporable component ratio of 30wt% is 3640W / m², the initial heat flux density of the liquid film with an evaporable component ratio of 20wt% is 2994W / m², and the initial heat flux density of the liquid film with an evaporable component ratio of 10wt% is 2196W / m². In the actual application scenario of thin liquid film heat transfer, we expect that on the one hand, the liquid film can quickly exchange heat with the heated wall, and on the other hand, the liquid film can evaporate quickly to take away heat. Because the evaporation rate of the high-viscosity material liquid film is the largest during the evaporation process, and an air film will be generated at the bottom, and the wall heat flux density will continue to decrease with time. Therefore, in order to obtain better heat transfer effect and increase the evaporation rate of the liquid film, it is necessary to break the air film during the heating process to enhance heat transfer. When the evaporation rate at the bottom of the liquid film reaches the maximum, it is the most appropriate time to break the air film. Figure 5 The law of the change of the evaporation rate of the liquid film with time under the conditions of different evaporable component ratios can be determined: when the evaporable component ratio is 40wt%, the best time to break the gas film is 0.5s; when the evaporable component ratio is 30wt%, the best time to break the gas film is 0.7s; when the evaporable component ratio is 20wt% and the evaporable component ratio is 10wt%, the best time to break the gas film is 0.9s. When we determine the best time to break the gas film, we can reversely design the number of scraper columns and the speed of the scraper based on this. It should be clear that the time to break the gas film is the time it takes for adjacent scrapers in the scraped film evaporator to scrape the same liquid film. If a shorter scraping time is required, and the scraper speed is not limited by energy consumption and structural strength, then the scraper speed can be precisely controlled to achieve the best scraping time for the liquid film, thereby significantly improving the evaporation efficiency. If a shorter scraping time is required, but the scraper speed cannot be further increased due to energy consumption and structural strength limitations, the number of scraper rows can be precisely increased and a completely new structure can be designed, which can also greatly improve the efficiency of the scraped film evaporator.

Claims

1. A method for determining the scraping cycle of a scraper during the evaporation of a high-viscosity material, characterized in that: The following steps are involved: (1) Establish a computational fluid domain geometry model and set the parameters of the computational fluid domain geometry model; The geometric model of the computational fluid domain is a cubic structure, with the bottom surface being the heating wall, and the part above the bottom surface being the liquid film and the gas region, with the gas region being located above the liquid film; The parameters of the computational fluid domain geometric model include the thickness of the liquid film, the thickness of the gas region and the size of the bottom surface of the computational fluid domain geometric model; The thickness of the liquid film is obtained by collecting the thickness of the liquid film formed by the high-viscosity material in the scraped film evaporator during the historical production process and taking the average value; The thickness of the gas area is obtained by collecting the thickness of the gas area formed by high-viscosity materials in the scraped film evaporator during the historical production process and taking the average value; High-viscosity materials are materials whose evaporable components are transformed into gas during evaporation and cannot escape from the bottom of the liquid film; (2) Meshing the geometric model of the computational fluid domain and locally encrypting the mesh of the heated wall; (3) Set the boundary condition parameters of the computational fluid domain, perform transient evaporation calculation on the geometric model of the computational fluid domain, and obtain the curve of the evaporation rate at the bottom of the liquid film changing with time; (4) Analyze the curve of the evaporation rate at the bottom of the liquid film changing with time. The time corresponding to the starting point is recorded as ta, and the time corresponding to the highest point is recorded as tb. The difference between tb and ta is the scraping cycle of the scraper. The scraping cycle of the scraper is the time it takes for adjacent scrapers in the scraped film evaporator to scrape the same liquid film.

2. The method for determining the scraping film scraping cycle during the evaporation of a high-viscosity material according to claim 1, characterized in that: In step (1), the bottom surface of the computational fluid domain geometric model is a rectangle with a length of 20-60 mm and a width of 20-60 mm.

3. The method for determining the scraping cycle of a scraper during the evaporation of a high-viscosity material according to claim 1, characterized in that: In step (2), the mesh is divided into polyhedron-hexahedron hybrid mesh.

4. The method for determining the scraping cycle of a scraper in the evaporation process of a high-viscosity material according to claim 3, characterized in that: In step (2), meshing the computational fluid domain geometric model refers to meshing the computational fluid domain geometric model using ANSYS Fluent Meshing software.

5. The method for determining the scraping cycle of a scraper in the evaporation process of a high-viscosity material according to claim 1, characterized in that: In step (3), the boundary condition parameters of the calculated fluid domain include the temperature of the heated wall, the viscosity of the liquid film, and the initial temperature of the liquid film. The initial temperature of the liquid film is the same as the saturation temperature of the high-viscosity material.

6. The method for determining the scraping cycle of a scraper in the evaporation process of a high-viscosity material according to claim 5, characterized in that: In step (3), when calculating transient evaporation, the proportion of the evaporable components of the liquid film is first set through the Species Transport model, and then the gas-liquid interface is tracked based on the VOF model, where the liquid phase is a high-viscosity material and the gas phase is steam. Finally, the phase change between the liquid and gas phases of the evaporable components in the high-viscosity material is realized based on the Lee model.

7. The method for determining the scraping cycle of a scraper during the evaporation of a high-viscosity material according to claim 1, characterized in that: In step (3), when calculating transient evaporation, the time step is 0.001s, the number of time steps is 1000, and the total calculation time is 1s.

8. The method for determining the scraping cycle of a scraper in the evaporation process of a high-viscosity material according to claim 7, characterized in that: In step (3), the process of obtaining the curve of the evaporation rate of the bottom of the liquid film changing with time is as follows: with a time interval of 0.1 s, the evaporation rate of the bottom of the liquid film at each time is calculated, and after obtaining discrete data points, fitting is performed to obtain the curve of the evaporation rate of the bottom of the liquid film changing with time.

9. The method for determining the scraping cycle of a scraper in the evaporation process of a high-viscosity material according to claim 8, characterized in that: The steps for obtaining the evaporation rate at the bottom of the liquid film at each time are as follows: (a) Obtain the liquid phase volume fraction of the discrete layered cross section of the computational fluid domain geometric model along the height direction at each time, and perform fitting after obtaining the discrete data points to obtain the variation curve of the liquid phase volume fraction with the height of the computational fluid domain geometric model at each time; (b) Analyze the variation curve of the liquid phase volume fraction with the height of the computational fluid domain geometric model at each time, and find the minimum value ha of the computational fluid domain geometric model height when the liquid phase volume fraction is 0.5 at each time; (c) The volume of the area with a height less than ha in the computational fluid domain geometric model at each time and the phase change mass transfer rate are calculated, and the evaporation rate at the bottom of the liquid film at each time is calculated by the following formula; ； In the formula, Represents the evaporation rate at the bottom of the liquid film at each time, in kg / s; Represents the phase change mass transfer rate of the area with a height less than ha in the computational fluid domain geometric model at each time, in kg / m 3 ·s; Represents the volume of the area whose height is less than ha in the computational fluid domain geometric model at each time, in m 3 .

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