Numerical simulation and characterization method for hot working characteristics of tobacco strip moisture regaining process under complex working conditions

Abstract

The invention discloses a numerical simulation and characterization method for thermal processing characteristics of a tobacco strip moisture regaining process under a complex working condition, and aims to solve the problem that changes of temperature and moisture content of tobacco strips in the moisture regaining process are difficult to accurately characterize. The method comprises the following steps: firstly, acquiring a three-dimensional model and related size parameters of drum-type damping machine equipment through a three-dimensional space sensing technology, carrying out geometric modeling in combination with field measurement data, then, constructing a multi-field coupling numerical model of flexible particles of the tobacco lamina and a flow field in a drum based on CFD (computational fluid dynamics) and DEM (discrete element method) theories, and finally, constructing a multi-field coupling numerical model of the flexible particles of the tobacco lamina and the flow field in the drum. Movement, temperature change and moisture content change rules of the tobacco lamina in the moisture regaining process are simulated. According to the method, through extraction of sensitive process parameters and equipment operation parameters, multi-working-condition numerical simulation analysis is carried out, the accuracy of a numerical model is verified, and finally visual and digital representation of the flue-cured tobacco strip hot processing characteristics is achieved. Experimental results show that the method can accurately simulate the temperature distribution and moisture content change of the tobacco lamina in the moisture regaining process, theoretical support is provided for moisture regaining process parameter optimization, and the inherent quality stability of the tobacco lamina in the moisture regaining process is ensured.

Description

Technical Field

[0001] The invention relates to the technical field of tobacco strip processing, and in particular to a numerical simulation and characterization method for thermal processing characteristics of tobacco strips during rehumidification under complex working conditions. Background Art

[0002] Loosening and rehydration is one of the key links in the hot processing of tobacco strips. The loosening and rehydration process has a significant impact on the processing resistance of tobacco strips, the removal of impurities, and the improvement of taste characteristics. The quality of the rehydration process directly determines the quality of the internal quality of cigarettes. At present, the research on the loosening and rehydration process mainly focuses on the correlation and influence between the rehydration process parameters and the moisture content and outlet temperature of tobacco strips, as well as the stability control of the moisture content of rehydration outlet tobacco strips. Some studies have established a loose rehumidification network model through the Bayesian network analysis method, and studied the influence weights of various process parameters on the outlet moisture content and outlet temperature during the production process, but have not clarified the process influence of process parameters on the outlet moisture content and outlet temperature; other studies have used artificial neural networks and multivariate regression modeling methods to analyze the influence of different methods on the prediction accuracy of outlet moisture content, but these predictions are only based on adding water to the tobacco leaves and humidifying them, and do not consider the influence of hot air in the barrel; in addition, some studies have proposed an outlet moisture content prediction model based on neural networks and principal component regression methods, but have not provided specific control measures; other studies have designed a loose rehumidification machine water adding system, changing "front water addition" to "front water addition as the main method, and rear water addition for adjustment", which solves the problem of large fluctuations in the outlet moisture content of loose rehumidification, but this method does not consider the influence of tobacco leaf temperature on moisture content.

[0003] With the development of computational fluid dynamics (CFD) and discrete element method (DEM), CFD-DEM coupling method has become an important technical means for parameter design and process analysis related to agricultural and industrial production. However, its application in cigarette production is relatively rare. CFD has been used to analyze the temperature and humidity fields inside the tobacco oven, Fluent simulates the water addition and tobacco movement in the rehumidification cylinder and optimizes the nozzle layout, while DEM simulates the tension behavior of tobacco leaves and outputs the tensile strength and Young's modulus of tobacco leaves. These studies are usually separate applications of CFD or DEM in cigarette production, without considering the interaction between multiphase flow and tobacco leaves.

[0004] During the loosening and rehumidification process of tobacco sheets, there is a complex interphase flow between the three phases of gas, liquid and solid (hot air-mixed water-tobacco sheet particles). Since the rehumidification process involves heating and humidifying the tobacco sheets, physical processes such as heat conduction and moisture transfer between the three phases are very important. In the existing technology, computational fluid dynamics (CFD) and discrete element method (DEM) are widely used in the study of multiphase flow and particulate matter, but have not been fully combined for simulation analysis of the loosening and rehumidification process of tobacco sheets. Since the rehumidification machine is a closed space, under the influence of hot air and mixed water, the change law of the moisture content and temperature of the tobacco sheets in the cylinder is difficult to characterize, and it is difficult to truly guarantee the stability of the internal processing quality of the tobacco sheets. Summary of the invention

[0005] In order to solve the deficiencies in the prior art, the present invention provides a numerical simulation and characterization method for the thermal processing characteristics of tobacco strips during the rehumidification process under complex working conditions. The method uses the Euler multiphase flow model in computational fluid dynamics to construct a CFD-DEM coupling framework. Through this framework, the temperature field in the rehumidification cylinder during the loose rehumidification of tobacco strips and the moisture content and temperature of the tobacco strips can be simulated and analyzed.

[0006] The present invention provides a method for numerically simulating and characterizing the thermal processing characteristics of tobacco sheets during the rehumidification process under complex working conditions, comprising the following steps: Step (1) according to the production equipment of the drum-type blade rehumidifier, the original three-dimensional model and relevant size parameters of the rehumidifier are obtained by three-dimensional space perception technology; Step (2) using SolidWorks to construct a three-dimensional model of the moisture-recovery cylinder based on the original three-dimensional model of the moisture-recovery cylinder and the size parameters of the moisture-recovery cylinder; Step (3) measuring the size parameters and position parameters of the rake nails and the lifting plate in the cylinder on site, performing geometric modeling, and assembling them with the three-dimensional model of the moisture-replenishing cylinder to form a complete three-dimensional model of the moisture-replenishing cylinder; Step (4) Use SpaceCliam to pre-process the three-dimensional model of the moisture return cylinder, simplify the three-dimensional model, set the deflection angle to 1.5°, and use it as a DEM-Rocky simulation model; and extract the fluid domain as a CFD-Fluent simulation model; Step (5) meshing the fluid domain in Ansys-meshing, and naming the hot air inlet, mixed water inlet, smoke inlet, dehumidification air outlet, and smoke outlet; Step (6) collecting the production process data of the rehumidifier, extracting sensitive process parameters and equipment operation parameters, and preprocessing the collected data to extract four groups of typical operating parameters; Step (7) simplifying the inlet data, simplifying the steam and industrial water that are not directly involved in the work and the direct injection steam into one inlet, unified as a mixed water inlet; Step (8) In Ansys-Fluent, the multiphase flow model is set to the Euler model, the multiphase flow includes hot air and mixed water, and the relevant parameters are set; Step (9) Use the processed working condition parameters as CFD simulation boundary conditions, simulate the flow field separately in Fluent, and perform grid independence verification to ensure the accuracy of the simulation results; Step (10) According to the actual shape of the tobacco flakes, two-dimensional modeling of the loose rehumidified tobacco flakes is performed in SpaceCliam, and the model is imported into Rocky in the form of a custom shell to construct flexible tobacco flake particles; Step (11) using DEM-Rocky to conduct a simulation experiment on the angle of repose of a piece of cigarette, and compare and verify it with the actual experiment; Step (12) constructing a CFD-DEM coupling simulation model, performing full-process simulation of the flow field-discrete element method for the rehumidification process of the tobacco sheet, and analyzing the flow field temperature change, tobacco sheet particle temperature, and moisture content change process with position; Step (13) draws a temperature-position curve according to the changes in the temperature and moisture content of the tobacco particles at different positions to characterize the processing intensity of the loosening and rehumidification process.

[0007] The SpaceCliam pre-processing of the three-dimensional model of the re-humidification cylinder refers to: first, the curved surface of the re-humidification cylinder is finely processed by SpaceClaim, and each separated surface is merged to form a continuous and complete three-dimensional geometric model. This step is an important basis for ensuring that the physical characteristics of the model are accurately reflected in the subsequent simulation. Next, check the boundaries and lines of each surface to ensure that there are no defects or discontinuities; set the deflection angle to 1.5°. This parameter is crucial for the creation of the DEM-Rocky simulation model because it directly affects the calculation accuracy of particle movement and interaction. After this processing, the geometry of the re-humidification cylinder will be more suitable for subsequent discrete element method (DEM) simulation and can better simulate the behavior in actual operation. In addition, the fluid domain needs to be extracted. This step is to build a CFD-Fluent simulation model. By correctly identifying and defining the fluid domain, the characteristics of fluid flow, including velocity, pressure and temperature distribution, can be effectively analyzed.

[0008] The multiphase flow model is set as the Euler model in Ansys-Fluent, specifically, the corresponding volume fraction equation, mass conservation equation, momentum conservation equation, and energy conservation equation are established for each phase; Volume fraction equation: There are hot air and mixed water in the loose conditioning cylinder, which are gas phase and liquid phase respectively. The volumes of hot air and mixed water are calculated by integrating their respective volume fractions on the domain, and the sum of the volume fractions of the two phases is 1.

[0009] use Indicates hot air or mixed water (gas or liquid phase), then The volume of a phase can be expressed as:

[0010]

[0011] In the formula for Phase volume; for Phase volume fraction; is the volume of the fluid domain in the loose rehumidification cylinder.

[0012] Mass conservation equation: When the tobacco flakes are loosened and moistened, hot air and mixed water exist in the continuous phase, and the mass conservation equation of hot air and mixed water needs to be solved. The whole set of model equations is solved for each grid in the CFD grid, but physically, the phase only exists where the volume fraction is greater than 0, so the volume fractions of hot air and mixed water need to be considered. There is mass transfer between hot air and mixed water, and there is sedimentation.

[0013]

[0014] In the formula is the phase physical density; for Phase velocity; For to The mass transfer of the phase is the same, and vice versa.

[0015] Momentum conservation equation: The smoke flakes loosen and regain moisture, and two momentum equations are needed to solve the continuous phase, namely the momentum equation for the hot air velocity and the momentum equation for the mixed water velocity. The pressure field is shared among all phases, and the hot air and mixed water are combined using the pressure field. The source term is used to represent the momentum transfer between phases. When mass transfer occurs between the two phases at a velocity v, energy transfer is obtained through mass transfer. In addition, additional forces must be considered to obtain additional momentum transfer between phases.

[0016]

[0017] In the formula for The compressive stress tensor of the phase; is the interphase force; is the interphase slip velocity; is the external body force; for lift; is the wall slip force; is the virtual mass force; is the turbulent diffusion force.

[0018] Energy conservation equation: Hot air and atomized water are continuous media, and their respective energy conservation equations need to be solved to better capture the temperature distribution and heat exchange of the continuous phase. In the loose rehumidification process, energy is transferred between the hot air and the mixed water over time and the movement of the drum, so convection, conduction and source terms between energy must be considered.

[0019]

[0020] In the formula For Bihan; is the heat flux density; is the interphase heat transfer intensity; Energy transfer for component diffusion.

[0021] The multiphase flow includes hot air and mixed water, and the relevant parameters are set. Specifically, this study involves the mixed flow of hot air and mixed water. The fluid flow Reynolds number is large, and there is sliding, rotation, and mixing in adjacent flow layers. The simulated geometric structure is relatively complex, so the Realizable k-epsilon model is selected as the turbulence model. This model introduces improved turbulent kinetic energy and dissipation rate equations, and enhances the physical representation of turbulence, especially in high curvature and rotating flow fields, which can better predict flow separation and vortex characteristics. Its turbulent kinetic energy and turbulent dissipation rate They are defined as:

[0022]

[0023] In the formula is the density of the mixture; for speed; is the molecular viscosity; is the flow time; is the turbulent Planc number; is the turbulent kinetic energy generated by the mean velocity gradient; , is other energy source term; , is the model constant.

[0024] The use of DEM-Rocky to perform a simulation experiment on the repose angle of a sheet cigarette, the use of DEM-Rocky to perform a simulation experiment on the repose angle of a sheet cigarette, first of all, needs to construct a three-dimensional model of the sheet cigarette particles, and set the corresponding physical parameters, including the density, Poisson's ratio, elastic modulus, friction coefficient and adhesion of the particles. In the DEM simulation, the interaction of the particles is described by the collision and contact models, and the setting of these parameters directly affects the simulation results of the repose angle. Next, the discrete element method (DEM) in the Rocky software is used to simulate the stacking process of the sheet cigarette. Usually, the sheet cigarette particles fall freely from above and naturally accumulate under the specified initial conditions to form a conical pile. By observing the stable morphology of the particles after accumulation, the repose angle (the maximum stable angle of the particle pile) formed is calculated. This repose angle is an important indicator for measuring the fluidity and stacking stability of the particles. After the simulation, the numerical results of the repose angle are compared with the actual experimental data to verify the accuracy of the DEM model. If the difference is large, it is necessary to adjust the physical parameters or contact model of the particles, and repeat the simulation until the results match.

[0025] The CFD-DEM coupling simulation model is constructed to simulate the flow field-discrete element of the rehumidification process of the tobacco slices. Specifically, Fluent CFD-Rocky DEM bidirectional coupling is used for numerical simulation, which can simulate the movement behavior of particles in the fluid while also considering the influence of the existence of particles on the fluid flow. The coupling calculation principle is: Fluent performs a flow field calculation for one time step, and the calculation data is input into Rocky to calculate the interphase force. The interphase force is introduced into the particle motion equation to calculate the particle position, and the calculated volume fraction is transmitted back to Fluent together with the interphase force to perform the next time step calculation. The calculation is repeated through this process until the calculation is completed.

[0026] Compared with the prior art, the above technical solution has the following beneficial effects: (1) Multi-field coupling analysis: The present invention is based on the CFD-DEM coupling framework, combining computational fluid dynamics and discrete element method, and can simultaneously simulate the interaction between cigarette particles and fluid, solving the deficiency of the prior art of only performing separate simulation analysis on flow field or discrete particles, and achieving a more accurate simulation of the complex flow process between the three phases of gas, liquid and solid (hot air-mixed water-cigarette particles).

[0027] (2) Visualization of the rehumidification process: By simulating and analyzing the temperature field and moisture content of the tobacco strips during the rehumidification process, the present invention realizes the visualization and digital representation of the tobacco strips rehumidification process, overcoming the technical bottleneck of the traditional rehumidification process in which it is difficult to accurately represent the temperature and moisture content of the tobacco strips in the barrel, and providing a reliable digital tool for optimizing the rehumidification process.

[0028] (3) Improving process optimization accuracy: The present invention extracts sensitive process parameters and equipment operating parameters and combines them with multiple groups of typical working conditions to effectively predict the changes in tobacco sheet temperature and moisture content with location, thereby guiding the optimization of the conditioning machine equipment and process and ensuring the stability of the processing quality of tobacco sheets during the conditioning process. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 is a flow chart of the present invention; Figure 2 It is a schematic diagram of the flow field grid division of the drum-type blade rehumidifier of the present invention; Figure 3 This is a graph showing the grid independence verification result of the present invention; Figure 4 It is a schematic diagram of the grid division of tobacco strips and artificial tobacco leaves of the present invention; Figure 5 It is a diagram showing the process and results of simulating the repose angle of a sheet of tobacco using the fixed funnel method of the present invention; Figure 6 It is a CFD-DEM coupling calculation process diagram of the present invention; Figure 7 It is the flow field axial temperature cloud diagram of the present invention; Figure 8 is the average temperature diagram of the flow field of the present invention; Fig. 9 The moisture content-temperature curve of the tobacco slices of the present invention is Fig.10 This is a comparison chart of the flow field temperature between the simulation and the actual production of the present invention. DETAILED DESCRIPTION

[0030] The following is a clear and complete description of the technical solutions in the embodiments of the present invention in conjunction with the drawings in the embodiments of the present invention, wherein the implementation examples are only part of the embodiments of the present invention, not all. Based on the embodiments in the embodiments, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0031] See also Figure 1 , which is a numerical simulation and characterization method for the thermal processing characteristics of tobacco sheet moisture recovery process under complex working conditions provided in an embodiment of the present invention, comprising the following steps: Step (1) according to the production equipment of the drum-type blade rehumidifier, the original three-dimensional model and relevant size parameters of the rehumidifier are obtained by three-dimensional space perception technology; Step (2) using SolidWorks to construct a three-dimensional model of the moisture-recovery cylinder based on the original three-dimensional model of the moisture-recovery cylinder and the size parameters of the moisture-recovery cylinder; Step (3) measuring the size parameters and position parameters of the rake nails and the lifting plate in the cylinder on site, performing geometric modeling, and assembling them with the three-dimensional model of the moisture-replenishing cylinder to form a complete three-dimensional model of the moisture-replenishing cylinder; Step (4) Use SpaceCliam to pre-process the three-dimensional model of the moisture return cylinder, simplify the three-dimensional model, set the deflection angle to 1.5°, and use it as a DEM-Rocky simulation model; and extract the fluid domain as a CFD-Fluent simulation model; Step (5) meshing the fluid domain in Ansys-meshing, and naming the hot air inlet, mixed water inlet, smoke inlet, dehumidification air outlet, and smoke outlet; Step (6) collecting the production process data of the rehumidifier, extracting sensitive process parameters and equipment operation parameters, and preprocessing the collected data to extract four groups of typical operating parameters; Step (7) simplifying the inlet data, simplifying the steam and industrial water that are not directly involved in the work and the direct injection steam into one inlet, unified as a mixed water inlet; Step (8) In Ansys-Fluent, the multiphase flow model is set to the Euler model, the multiphase flow includes hot air and mixed water, and the relevant parameters are set; Step (9) Use the processed working condition parameters as CFD simulation boundary conditions, simulate the flow field separately in Fluent, and perform grid independence verification to ensure the accuracy of the simulation results; Step (10) According to the actual shape of the tobacco flakes, two-dimensional modeling of the loose rehumidified tobacco flakes is performed in SpaceCliam, and the model is imported into Rocky in the form of a custom shell to construct flexible tobacco flake particles; Step (11) using DEM-Rocky to conduct a simulation experiment on the angle of repose of a piece of cigarette, and compare and verify it with the actual experiment; Step (12) constructing a CFD-DEM coupling simulation model, performing full-process simulation of the flow field-discrete element method for the rehumidification process of the tobacco sheet, and analyzing the flow field temperature change, tobacco sheet particle temperature, and moisture content change process with position; Step (13) draws a temperature-position curve according to the changes in the temperature and moisture content of the tobacco particles at different positions to characterize the processing intensity of the loosening and rehumidification process.

[0032] The SpaceCliam pre-processing of the three-dimensional model of the re-humidification cylinder refers to: first, the curved surface of the re-humidification cylinder is finely processed by SpaceClaim, and each separated surface is merged to form a continuous and complete three-dimensional geometric model. This step is an important basis for ensuring that the physical characteristics of the model are accurately reflected in the subsequent simulation. Next, check the boundaries and lines of each surface to ensure that there are no defects or discontinuities; set the deflection angle to 1.5°. This parameter is crucial for the creation of the DEM-Rocky simulation model because it directly affects the calculation accuracy of particle movement and interaction. After this processing, the geometry of the re-humidification cylinder will be more suitable for subsequent discrete element method (DEM) simulation and can better simulate the behavior in actual operation. In addition, the fluid domain needs to be extracted. This step is to build a CFD-Fluent simulation model. By correctly identifying and defining the fluid domain, the characteristics of fluid flow, including velocity, pressure and temperature distribution, can be effectively analyzed.

[0033] The multiphase flow model is set as the Euler model in Ansys-Fluent, specifically, the corresponding volume fraction equation, mass conservation equation, momentum conservation equation, and energy conservation equation are established for each phase; Volume fraction equation: There are hot air and mixed water in the loose conditioning cylinder, which are gas phase and liquid phase respectively. The volumes of hot air and mixed water are calculated by integrating their respective volume fractions on the domain, and the sum of the volume fractions of the two phases is 1.

[0034] use Indicates hot air or mixed water (gas or liquid phase), then The volume of a phase can be expressed as:

[0035]

[0036] In the formula for Phase volume; for Phase volume fraction; is the volume of the fluid domain in the loose rehumidification cylinder.

[0037] Mass conservation equation: When the tobacco flakes are loosened and moistened, hot air and mixed water exist in the continuous phase, and the mass conservation equation of hot air and mixed water needs to be solved. The whole set of model equations is solved for each grid in the CFD grid, but physically, the phase only exists where the volume fraction is greater than 0, so the volume fractions of hot air and mixed water need to be considered. There is mass transfer between hot air and mixed water, and there is sedimentation.

[0038]

[0039] In the formula for Phase physical density; for Phase velocity; For to The mass transfer of the phase is the same, and vice versa.

[0040] Momentum conservation equation: The smoke flakes loosen and regain moisture, and two momentum equations are needed to solve the continuous phase, namely the momentum equation for the hot air velocity and the momentum equation for the mixed water velocity. The pressure field is shared among all phases, and the hot air and mixed water are combined using the pressure field. The source term is used to represent the momentum transfer between phases. When mass transfer occurs between the two phases at a velocity v, energy transfer is obtained through mass transfer. In addition, additional forces must be considered to obtain additional momentum transfer between phases.

[0041]

[0042] In the formula for The compressive stress tensor of the phase; is the interphase force; is the interphase slip velocity; is the external body force; for lift; is the wall slip force; is the virtual mass force; is the turbulent diffusion force.

[0043] Energy conservation equation: Hot air and atomized water are continuous media, and their respective energy conservation equations need to be solved to better capture the temperature distribution and heat exchange of the continuous phase. In the loose rehumidification process, energy is transferred between the hot air and the mixed water over time and the movement of the drum, so convection, conduction and source terms between energy must be considered.

[0044]

[0045] In the formula For Bihan; is the heat flux density; is the interphase heat transfer intensity; Energy transfer for component diffusion.

[0046] The multiphase flow includes hot air and mixed water, and the relevant parameters are set. Specifically, this study involves the mixed flow of hot air and mixed water. The fluid flow Reynolds number is large, and there is sliding, rotation, and mixing in adjacent flow layers. The simulated geometric structure is relatively complex, so the Realizable k-epsilon model is selected as the turbulence model. This model introduces improved turbulent kinetic energy and dissipation rate equations, and enhances the physical representation of turbulence, especially in high curvature and rotating flow fields, which can better predict flow separation and vortex characteristics. Its turbulent kinetic energy and turbulent dissipation rate They are defined as:

[0047]

[0048] In the formula is the density of the mixture; for speed; is the molecular viscosity; is the flow time; is the turbulent Planc number; is the turbulent kinetic energy generated by the mean velocity gradient; , is other energy source term; , is the model constant.

[0049] The use of DEM-Rocky to perform a simulation experiment on the repose angle of a sheet cigarette, the use of DEM-Rocky to perform a simulation experiment on the repose angle of a sheet cigarette, first of all, needs to construct a three-dimensional model of the sheet cigarette particles, and set the corresponding physical parameters, including the density, Poisson's ratio, elastic modulus, friction coefficient and adhesion of the particles. In the DEM simulation, the interaction of the particles is described by the collision and contact models, and the setting of these parameters directly affects the simulation results of the repose angle. Next, the discrete element method (DEM) in the Rocky software is used to simulate the stacking process of the sheet cigarette. Usually, the sheet cigarette particles fall freely from above and naturally accumulate under the specified initial conditions to form a conical pile. By observing the stable morphology of the particles after accumulation, the repose angle (the maximum stable angle of the particle pile) formed is calculated. This repose angle is an important indicator for measuring the fluidity and stacking stability of the particles. After the simulation, the numerical results of the repose angle are compared with the actual experimental data to verify the accuracy of the DEM model. If the difference is large, it is necessary to adjust the physical parameters or contact model of the particles, and repeat the simulation until the results match.

[0050] The CFD-DEM coupling simulation model is constructed to simulate the flow field-discrete element of the rehumidification process of the tobacco slices. Specifically, Fluent CFD-Rocky DEM bidirectional coupling is used for numerical simulation, which can simulate the movement behavior of particles in the fluid while also considering the influence of the existence of particles on the fluid flow. The coupling calculation principle is: Fluent performs a flow field calculation for one time step, and the calculation data is input into Rocky to calculate the interphase force. The interphase force is introduced into the particle motion equation to calculate the particle position, and the calculated volume fraction is transmitted back to Fluent together with the interphase force to perform the next time step calculation. The calculation is repeated through this process until the calculation is completed.

[0051] Reference Figure 2 , a numerical simulation and characterization method for the hot processing characteristics of the tobacco rehumidification process under complex working conditions provided in an embodiment of the present invention, and a schematic diagram of the mesh division of the flow field of the drum blade rehumidifier; the mesh is an important component of the finite element model and the basis of the finite element calculation. The mesh division discretizes the actual model into a finite number of units, and the units are connected by nodes for numerical calculation and analysis. Meshing directly affects the accuracy of the calculation results. The rehumidifier model is complex and the flow field in the cylinder is irregular. If the mesh division is performed directly, the number of meshes is large and the quality is poor. Based on the overlapping grid technology, the entire calculation domain is partitioned, the grid overlap between subdomains is allowed, and the subdomains are not required to share boundaries, so as to realize information transmission and reduce the difficulty of grid generation in each subdomain. Structured grids are used for the drum blade rehumidifier, which reduces the number of grids while increasing the quality of the grids, effectively increasing the calculation efficiency and improving the calculation accuracy. The number of structured grids is 615998, the minimum unit quality is 0.32159, and the minimum orthogonal quality is 0.39881.

[0052] Reference Figure 3, which is a numerical simulation and characterization method for the hot processing characteristics of the tobacco rehumidification process under complex working conditions provided in an embodiment of the present invention, and a grid independence verification result diagram; further, in order to determine that the number of grids in the grid division method is small and the simulation results are more accurate, the same problem is repeatedly solved using different numbers of grids in the model to determine the appropriate number of grids. The CFD-DEM coupling in this experiment is weakly coupled, so the grid independence verification is only performed in CFD. The numbers of grids selected are: 255751, 315379, 398357, 452182, 615998, 1170324, 1467662, and 2445844 for grid independence verification, and working condition No. 1 is selected for solution. Fluid simulation involves two phases: gas (hot air) and liquid (mixed water). The average temperature distribution of gas and liquid phases at 100 collection points on the central axis of the drum with different numbers of grids was made. The results showed that when the number of grids was less than 615998, the temperature of the gas and liquid phases changed greatly. When the number of grids was 615998, the temperature distribution tended to be stable. The influence of the number of grids on temperature change was small, with a variation of about 1%. The flow field simulation tended to be stable, so the grid number of 615998 with a smaller number of grids was selected to solve the subsequent simulation.

[0053] Reference Figure 4 , which is a numerical simulation and characterization method for the thermal processing characteristics of the tobacco sheet rehumidification process under complex working conditions provided in an embodiment of the present invention, and a schematic diagram of the grid division of tobacco sheets and artificial tobacco leaves; further, in the actual production process of loose rehumidification, in order to improve the quality of cigarettes and reduce the tar content of cigarettes, reconstituted tobacco leaves are usually added to the tobacco sheets. In this experiment, tobacco sheets and reconstituted tobacco leaves at the feed inlet of a tobacco factory in the loose rehumidification stage are randomly selected, and then 500 pieces are randomly selected from them. The size screening is carried out based on the longest side as the standard, the middle width of the tobacco sheets is measured, and the average value of the longest side and the average value of the middle width of each group are calculated. Due to the folding phenomenon of tobacco sheets and the similar thickness of reconstituted tobacco leaves and tobacco sheets, the average thickness is taken as 0.8mm. Combined with the shapes of tobacco sheets and reconstituted tobacco leaves, the tobacco sheets are based on the average value of the longest side as the basic length dimension and the average value of the middle as the basic width dimension. The shape is set to be approximately long, and the shape of reconstituted tobacco leaves is defined as a rectangle. The model is created in SpaceClaim and Rocky 2022 It is imported into R1.2 in the form of a custom shell and meshed. Due to the difficulty of calculation, the number of meshes is simplified to 16, so that the model consists of triangular meshes with uniform thickness, thereby realizing the simulation calculation of flexible particles.

[0054] Reference Figure 5, which is a numerical simulation and characterization method for the thermal processing characteristics of the rehumidification process of tobacco sheets under complex working conditions provided in an embodiment of the present invention, and a fixed funnel method is used to simulate the repose angle of tobacco sheets and the result diagram; further, the fixed funnel method is used to measure the repose angle of tobacco sheets, and the funnel is fixed 200mm above the coordinate paper, so that the tobacco sheets slowly fall along the wall of the funnel and form an accumulation on the coordinate paper. When the accumulation does not slide obviously, the tobacco sheets are stopped from being put in, and the background is deleted and the image is binarized to obtain the binarization of the edge contour of the repose angle of the tobacco sheets, and then the repose angle of the tobacco sheets is measured, and the weight of the tobacco sheets is weighed. The experiment is repeated 10 times, and the average repose angle is measured to be 35.56° and the average mass is 260.28g. It was verified in Rocky 2022 R1.2, and an experimental model was established. "Constant Adhesive Force" was selected as the adhesion force model, which is used to simulate the behavior of adhesion particles that do not show stress consolidation effects, such as liquid bridge force. "Hysteretic Linear spring" was set as the normal force model, "Linear Spring Coulomb Limit" as the tangential force model, and Linear Spring Rolling Limit as the rolling resistance model. The sheet flow rate was set to 260.28g for simulation calculation. After the simulation, the repose angle of the mixed sheet was measured by contour fitting. The results showed that the repose angle of the mixed sheet measured by simulation was 34.88°, the actual repose angle was 35.56°, and the relative error was 1.91%.

[0055] Reference Figure 6 , which is a numerical simulation and characterization method for the thermal processing characteristics of the rehumidification process of tobacco sheets under complex working conditions provided in the embodiment of the present invention, and a CFD-DEM coupling calculation process diagram; further, the loose rehumidification thermal processing process mainly focuses on the control of the moisture content and temperature of tobacco sheets. In actual production, there are many influencing factors, such as ambient temperature, ambient humidity, industrial water flow, steam flow, hot air speed, hot air temperature, drum speed, etc. In the production process of a certain factory, in order to ensure production efficiency and coordination and synchronization between various processes, the default hot air speed is 3.95m / s, the temperature is 110℃, the drum speed is 11r / min, and the parameters of the mixed water formed by the mixture of steam and atomized water are shown in (Table 1) Four working conditions are set in Fluent, the time step number is 4200, the time step length is 0.05, the total time is 210s, and the standard initialization is performed. The temperature in the drum is 63℃ and the .cas file is saved. Discrete element settings were performed in Rocky 2022 R1.2, and the CFD-coupled drying model and CFD-coupled particle statistical model were set. The initial moisture content and initial temperature of the tobacco flakes were set (Table 2). The tobacco flake flow rate was 1000 kg / h, the simulation time was set to 210 s, and it was coupled with Fluent. Fluent used CPU calculations, and Rocky used GPU calculations.

[0056] Table 1 Typical working parameters of loose regain Working conditions Atomized water flow rate (kg / h) Direct injection steam flow rate (kg / h) Steam temperature (℃) 1 22.71 52.25 123.85 2 25.82 54.02 129.14 3 27.57 54.00 128.39 4 35.56 54.17 122.36 Table 2 Smoke data of each working condition Working conditions Import moisture content Inlet temperature Export moisture content Outlet temperature 1 13.37 30.68 15.30 54.34 2 13.92 34.12 16.10 56.86 3 13.87 33.14 16.35 56.85 4 13.14 29.63 16.79 54.58 Reference Figure 7 , which is a numerical simulation and characterization method for the thermal processing characteristics of the tobacco rehumidification process under complex working conditions provided in an embodiment of the present invention, and a flow field axial temperature cloud diagram; further, in this experiment, the flow field includes hot air and mixed water, which is a two-phase flow, namely, gas phase and liquid phase, and the initial temperature of the flow field is 63° after the preheating is completed, Figure 7 The axial temperature cloud diagram of the flow field in the production stage of working condition 1 shows the change of the temperature cloud diagram. At the front end of the drum, hot air and mixed water enter from the top, and the temperature in the drum gradually increases. The drum rotates, and the heat is transferred to the rear end of the drum, and the temperature rises. Under the action of the dehumidification fan, the temperature of the discharge chamber is relatively low; the tobacco leaves enter the drum from the bottom and absorb heat, resulting in a relatively low temperature at the entrance of the tobacco leaves, and a large temperature difference between the upper and lower parts. After the flow field simulation reaches 40s, the average temperature of the flow field remains basically unchanged, and the flow field in the drum tends to be constant. The average temperature of 100 points at the center axis of the flow field is taken to make the average temperature change curve of the flow field with time for four groups of working conditions. In the first 40s, the average temperature of the flow field rises rapidly, and as the tobacco leaves enter the drum, the increase gradually slows down. After 40s, the flow field temperature tends to be constant, and the fluctuation amplitude is no more than 2℃. The average temperature of the flow field of the four groups of working conditions after 40s is taken, which is 99.07℃, 99.31℃, 99.24℃, and 98.02℃, respectively. The temperature difference is very small, which ensures the stability of the tobacco leaves processing environment.

[0057] Reference Figure 8 , which is a numerical simulation and characterization method for the thermal processing characteristics of the rehumidification process of tobacco sheets under complex working conditions provided in an embodiment of the present invention, and a flow field average temperature diagram; further, the hot air inlet temperature is 110°C, and the temperature of the upper part of the drum tends to 110°C due to the action of the hot air; the mixed water inlet temperature is 77.88°C, and the temperature rises to a certain extent under the action of the hot air; the tobacco sheet inlet temperature is 30.68°C, and it absorbs heat after entering the drum, resulting in a lower temperature at the bottom of the drum. Due to the interaction between the hot air, mixed water, and tobacco sheets at the front end of the drum, the temperature changes greatly. As the drum rotates, it drives the tobacco sheets to move toward the outlet end, and the interaction intensity among the three decreases, and the flow field temperature gradually tends to be constant. When the X-axis is 5.555m, that is, when it is located in the discharge chamber, under the action of the dehumidification fan, the temperature at the lower end of the discharge chamber decreases and tends to normal temperature, and the outlet temperature of the dehumidification air at the upper end is greater than 63°C.

[0058] Reference Fig. 9, is a numerical simulation and characterization method for the thermal processing characteristics of the tobacco sheet rehumidification process under complex working conditions provided in an embodiment of the present invention, and a moisture content-temperature curve of the tobacco sheet; further, in the process of loosening and rehumidifying the tobacco sheet, the moisture content and temperature of the tobacco sheet change with time and with the change of the position in the drum. The thermal state of the tobacco sheet itself can be used to characterize the processing intensity of the loosening and rehumidification process, that is, the rate of change of temperature within a unit distance corresponds to the rate of change of moisture content within a unit distance. The moisture content changes with temperature curve is as follows Fig. 9 As shown in the figure, before the moisture content of the tobacco flakes reaches the maximum value, the moisture content is positively correlated with the temperature. After the moisture content reaches the maximum value, the tobacco flakes begin to dehydrate, and the moisture content gradually decreases. The temperature is still increasing under the high temperature environment in the barrel. At the outlet, due to the low temperature of the discharge chamber, the tobacco flakes decrease in a small range. During the entire hot processing process, the temperature and moisture content are closely related, and the processing intensity of working condition 4 is the highest, and the processing intensity of working condition 1 is the lowest.

[0059] Reference Fig.10, which is a numerical simulation and characterization method for the thermal processing characteristics of the tobacco rehumidification process under complex working conditions provided in an embodiment of the present invention, and a temperature comparison diagram of the simulation and actual production flow field; further, 9 temperature detection points are set in the flow field, from the inlet to the outlet, and the coordinates are A (0.6061, -0.0159, 0), B (1.2121, -0.0317, 0), C (1.8181, -0.0476, 0), D (2.4242, -0.0635, 0), E (3.0303, -0.0793, 0), F (3.6363, -0.0952, 0) , G (4.2424, -0.1111, 0), H (4.8484, -0.1269, 0), I (5.3939, -0.1412, 0), in actual production, industrial sensors are installed at the same position, and the temperature sensor is Raytek RAYGPRSF infrared thermometer (temperature measurement range is -18℃~538℃, measurement accuracy is ±1℃). 210s after the calculation ends, the average flow field temperature of the detection point is taken and compared with the actual measured values ​​of each detection point in the cylinder at this time. The x-coordinate of each detection point is used as the horizontal coordinate, and the temperature simulation value and the actual measured value are used as the vertical coordinate to draw four groups of working condition comparison charts. The measured values ​​of the four working conditions are all smaller than the simulated values. This is because in actual production, the movement of tobacco leaves in the cylinder will affect the measurement accuracy of the sensor. In the four working conditions, the temperature of detection points A~H gradually increases, and the temperature of H~I decreases. The relative error of detection point 1D in working condition is the smallest, which is 1.02%, and the relative error of point A is the largest, which is 1.84%, and the average relative error is 1.33%; the relative error of detection point 2H in working condition is the smallest, which is 1.02%, and the relative error of point A is the largest, which is 1.70%, and the average relative error is 1.36%; the relative error of detection point 3C in working condition is the smallest, which is 0.22%, and the relative error of point G is the largest, which is 1.55%, and the average relative error is 1.19%; the relative error of detection point 4D in working condition is the smallest, which is 0.74%, and the relative error of point A is the largest, which is 2.09%, and the average relative error is 1.20%. The average relative error of each working condition is less than 2%. Therefore, the simulation of the loosening and rehumidification process of tobacco leaves using CFD-DEM has certain reliability, and the experimental results have certain reference value.

[0060] The specific implementation methods described above further illustrate the purpose, technical solutions and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. Numerical simulation and characterization method of thermal processing characteristics of tobacco sheet rehumidification process under complex working conditions, characterized in that: The specific steps include: Step (1) according to the production equipment of the drum-type blade rehumidifier, the original three-dimensional model and relevant size parameters of the rehumidifier are obtained by three-dimensional space perception technology; Step (2) using SolidWorks to construct a three-dimensional model of the moisture-recovery cylinder based on the original three-dimensional model of the moisture-recovery cylinder and the size parameters of the moisture-recovery cylinder; Step (3) measuring the size parameters and position parameters of the rake nails and the lifting plate in the cylinder on site, performing geometric modeling, and assembling them with the three-dimensional model of the moisture-replenishing cylinder to form a complete three-dimensional model of the moisture-replenishing cylinder; Step (4) Use SpaceCliam to pre-process the three-dimensional model of the moisture return cylinder, simplify the three-dimensional model, set the deflection angle to 1.5°, and use it as a DEM-Rocky simulation model; and extract the fluid domain as a CFD-Fluent simulation model; Step (5) meshing the fluid domain in Ansys-meshing, and naming the hot air inlet, mixed water inlet, smoke inlet, dehumidification air outlet, and smoke outlet; Step (6) collecting the production process data of the rehumidifier, extracting sensitive process parameters and equipment operation parameters, and preprocessing the collected data to extract four groups of typical operating parameters; Step (7) simplifying the inlet data, simplifying the steam and industrial water that are not directly involved in the work and the direct injection steam into one inlet, unified as a mixed water inlet; Step (8) In Ansys-Fluent, the multiphase flow model is set to the Euler model, the multiphase flow includes hot air and mixed water, and the relevant parameters are set; Step (9) Use the processed working condition parameters as CFD simulation boundary conditions, simulate the flow field separately in Fluent, and perform grid independence verification to ensure the accuracy of the simulation results; Step (10) According to the actual shape of the tobacco flakes, two-dimensional modeling of the loose rehumidified tobacco flakes is performed in SpaceCliam, and the model is imported into Rocky in the form of a custom shell to construct flexible tobacco flake particles; Step (11) using DEM-Rocky to conduct a simulation experiment on the angle of repose of a piece of cigarette, and compare and verify it with the actual experiment; Step (12) constructing a CFD-DEM coupling simulation model, performing full-process simulation of the flow field-discrete element method for the rehumidification process of the tobacco sheet, and analyzing the flow field temperature change, tobacco sheet particle temperature, and moisture content change process with position; Step (13) draws a temperature-position curve according to the changes in the temperature and moisture content of the tobacco particles at different positions to characterize the processing intensity of the loosening and rehumidification process.

2. The method for numerical simulation and characterization of thermal processing characteristics of tobacco sheet moisture regeneration process under complex working conditions according to claim 1 is characterized in that: The deflection angle of 1.5° set in step (4) is used to improve the fluidity and simulation accuracy of the particles in the fluid domain during the rehumidification process of the tobacco strips, so as to more accurately characterize the movement trajectory and stress state of the tobacco strip particles.

3. The method for numerical simulation and characterization of thermal processing characteristics of tobacco sheet moisture regeneration process under complex working conditions according to claim 1 is characterized in that: The sensitive process parameters collected in step (6) include the inlet and outlet temperature, humidity, hot air flow rate of the rehumidifier, the inlet and outlet moisture content of the tobacco leaves, the tobacco leaves temperature, and the rotation speed of the rake nails and the lifting plate.

4. The method for numerical simulation and characterization of thermal processing characteristics of tobacco sheet moisture regeneration process under complex working conditions according to claim 1 is characterized in that: The tobacco particle model in step (10) adopts a flexible particle modeling method to accurately simulate the deformation of tobacco particles during the rehumidification process and their interaction with the fluid and other particles.

5. The method for numerical simulation and characterization of thermal processing characteristics of tobacco sheet moisture regeneration process under complex working conditions according to claim 1 is characterized in that: The CFD-DEM coupled simulation model constructed in step (12) is used to simultaneously simulate the interaction between tobacco sheet particles and fluid, including flow field temperature, humidity, particle temperature and movement characteristics of tobacco sheet particles, so as to optimize the process parameters and equipment structure of the tobacco sheet rehumidification process.

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