Numerical simulation and characterization method of thermal processing characteristics of tobacco strips during rehumidification under complex working conditions

Abstract

This invention discloses a method for numerically simulating and characterizing the thermal processing characteristics of tobacco strips during the conditioning process under complex operating conditions. This method aims to address the difficulty in accurately characterizing changes in tobacco strip temperature and moisture content during conditioning. The method first uses three-dimensional spatial perception technology to acquire a three-dimensional model of the drum conditioning machine and its associated dimensional parameters. This modeling is then performed using geometric modeling data derived from field measurements. Subsequently, a multi-field coupled numerical model of the flexible tobacco strip particles and the flow field within the drum is constructed based on CFD (computational fluid dynamics) and DEM (discrete element method) theory to simulate the movement, temperature, and moisture content changes of the tobacco strips during conditioning. By extracting sensitive process parameters and equipment operating parameters, the method conducts multi-condition numerical simulation analysis to verify the accuracy of the numerical model, ultimately achieving visualization and digital characterization of the thermal processing characteristics of the tobacco strips. Experimental results demonstrate that this method accurately simulates the temperature distribution and moisture content changes of the tobacco strips during conditioning, providing theoretical support for optimizing conditioning process parameters and ensuring the inherent quality stability of the tobacco strip conditioning process.

Description

Technical Field

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

[0002] Loosening and tempering is a key step in the thermal processing of tobacco strips. This process significantly impacts the tobacco strip's processing resistance, removal of impurities, and improved taste. The quality of the tempering process directly determines the inherent quality of the cigarette. Currently, research on loosening and tempering focuses on the correlation between tempering process parameters and the outlet moisture content and temperature of tobacco strips, as well as on controlling the stability of the outlet moisture content of the tempered 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; some 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 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; some studies have designed a loose rehumidification machine water addition system, changing "front water addition" to "front water addition as the main method and back 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 has become an important technical tool for parameter design and process analysis related to agricultural and industrial production. However, its application in cigarette production is relatively limited. CFD has been used to analyze the temperature and humidity fields inside tobacco ovens, while Fluent has simulated water addition and tobacco movement in rehumidification cylinders and optimized nozzle layouts. DEM simulates the tensile behavior of tobacco leaves and outputs their tensile strength and Young's modulus. These studies typically apply CFD or DEM in isolation to cigarette production, without considering the interaction between multiphase flow and tobacco leaves.

[0004] During the loosening and rehumidification process of tobacco strips, complex interphase flows occur between the three phases (gas, liquid, and solid): hot air, mixed water, and tobacco strip particles. Because the rehumidification process involves heating and humidifying the tobacco strips, physical processes such as heat conduction and moisture transfer between the three phases are crucial. Computational fluid dynamics (CFD) and discrete element methods (DEM) are widely used in the study of multiphase flow and particulate matter, but they have not been fully integrated into the simulation analysis of the loosening and rehumidification process of tobacco strips. Because the rehumidification machine is a closed space, the changes in moisture content and temperature of the tobacco strips within the cylinder under the influence of hot air and mixed water are difficult to characterize, making it difficult to truly ensure the stability of the tobacco strips' inherent processing quality. Summary of the Invention

[0005] To address the shortcomings of the existing technology, the present invention provides a method for numerically simulating and characterizing the thermal processing characteristics of tobacco strips during the rehumidification process under complex working conditions. This method utilizes the Euler multiphase flow model in computational fluid dynamics to construct a CFD-DEM coupling framework. This framework enables simulation and analysis of the temperature field within the rehumidification drum during the loosening and rehumidification of tobacco strips, as well as the moisture content and temperature of the strips.

[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:

[0007] Step (1) according to the production equipment of the drum-type blade rehumidification machine, the original three-dimensional model and related size parameters of the rehumidification drum are obtained by three-dimensional space perception technology;

[0008] 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;

[0009] Step (3) measuring the size parameters and position parameters of the rake nails and the copying plate in the cylinder on site, performing geometric modeling, and assembling them with the three-dimensional model of the moisture-recovery cylinder to form a complete three-dimensional model of the moisture-recovery cylinder;

[0010] Step (4) Use SpaceCliam to pre-process the three-dimensional model of the resurgence 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;

[0011] Step (5) mesh the fluid domain in Ansys-meshing and name the hot air inlet, mixed water inlet, smoke inlet, exhaust air outlet, and smoke outlet;

[0012] Step (6) collecting the production process data of the rehumidifier, extracting sensitive process parameters and equipment operating parameters, and preprocessing the collected data to extract four groups of typical operating parameters;

[0013] Step (7) simplifies the inlet data, and simplifies the steam and industrial water that are not directly involved in the work and the direct injection steam into one inlet, unified as the mixed water inlet;

[0014] Step (8) In Ansys-Fluent, set the multiphase flow model to the Euler model, where the multiphase flow includes hot air and mixed water, and set the relevant parameters;

[0015] 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;

[0016] Step (10) Based on 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;

[0017] Step (11) using DEM-Rocky to conduct a simulation experiment on the angle of repose of a cigarette sheet, and compare and verify it with the actual experiment;

[0018] Step (12) constructing a CFD-DEM coupled simulation model, performing full-process simulation of the flow field-discrete element method for the rehumidification process of tobacco sheets, and analyzing the temperature change of the flow field, the temperature of tobacco sheet particles, and the change of moisture content with position;

[0019] Step (13) draws a temperature-position curve based on the changes in the temperature and moisture content of the tobacco particles at different positions to characterize the processing intensity of the loosening and rehydration process.

[0020] The aforementioned SpaceCliam pre-processing of the three-dimensional model of the resurgence cylinder refers to: first, using SpaceClaim to finely process the curved surface of the resurgence cylinder and merge the various separated surfaces to form a continuous, complete three-dimensional geometric model. This step is an important basis for ensuring that the physical properties of the model are accurately reflected in subsequent simulations. Next, the boundaries and lines of each surface are checked to ensure that there are no defects or discontinuities; the deflection angle is set 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 motion and interaction. After this processing, the geometry of the resurgence cylinder will be more suitable for subsequent discrete element method (DEM) simulations and can better simulate the behavior in actual operations. In addition, the fluid domain needs to be extracted. This step is to construct the CFD-Fluent simulation model. By correctly identifying and defining the fluid domain, the characteristics of the fluid flow, including velocity, pressure, and temperature distribution, can be effectively analyzed.

[0021] The multiphase flow model is set as the Euler model in Ansys-Fluent, specifically establishing the corresponding volume fraction equation, mass conservation equation, momentum conservation equation, and energy conservation equation for each phase;

[0022] Volume fraction equation: There are hot air and mixed water in the loose tempering 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 over the domain, and the sum of the volume fractions of the two phases is 1.

[0023] use Indicates hot air or mixed water (gas or liquid phase), then The volume of a phase can be expressed as:

[0024]

[0025]

[0026] In the formula for Phase volume; for Phase volume fraction; is the volume of the fluid domain in the loose rehumidification cylinder.

[0027] Mass conservation equation: When the tobacco flakes are loosened and moistened, hot air and mixed water exist in the continuous phase. The mass conservation equation of the hot air and mixed water needs to be solved. The entire set of model equations is solved for each grid in the CFD grid. However, physically, the phase only exists where the volume fraction is greater than 0. Therefore, the volume fractions of the hot air and mixed water need to be considered. There is mass transfer between the hot air and mixed water, and there is sedimentation.

[0028]

[0029] 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.

[0030] Momentum conservation equation: When tobacco flakes loosen and regain moisture, two momentum equations are required 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 between all phases, and the pressure field is used to combine the hot air and the mixed water. 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.

[0031]

[0032] In the formula for 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.

[0033] 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. During 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.

[0034]

[0035] In the formula For Bihan; is the heat flux density; is the interphase heat transfer intensity; Energy transfer for component diffusion.

[0036] 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, enhances the physical representation of turbulence, especially in high curvature and rotating flow fields, and can better predict flow separation and vortex characteristics. Its turbulent kinetic energy and turbulent dissipation rate They are defined as:

[0037]

[0038] In the formula is the density of the mixture; for speed; is the molecular viscosity; is the flow time; is the turbulent Planck number; is the turbulent kinetic energy generated by the mean velocity gradient; 、 is other energy source terms; 、 is the model constant.

[0039] The DEM-Rocky simulation experiment for the angle of repose of tobacco sheets first requires constructing a three-dimensional model of tobacco sheet particles and setting the corresponding physical parameters, including particle density, Poisson's ratio, elastic modulus, friction coefficient, and adhesion. In DEM simulations, particle interactions are described using collision and contact models, and the settings of these parameters directly affect the simulation results of the angle of repose. Next, the discrete element method (DEM) in Rocky software is used to simulate the tobacco sheet accumulation process. Typically, tobacco sheet particles fall freely from above under specified initial conditions and naturally accumulate to form a conical pile. By observing the stable shape of the accumulated particles, the resulting angle of repose (the maximum stable angle of the particle pile) is calculated. This angle of repose is an important indicator of particle flowability and stacking stability. After the simulation, the numerical results of the angle of repose are compared with actual experimental data to verify the accuracy of the DEM model. If there are significant discrepancies, the particle physical parameters or contact model need to be adjusted, and the simulation should be repeated until the results are consistent.

[0040] The CFD-DEM coupled simulation model described above simulates the entire flow field and discrete element model during the rehumidification process of tobacco leaves. Specifically, the numerical simulation utilizes Fluent CFD-Rocky DEM bidirectional coupling, simulating the motion of particles in the fluid while also accounting for the impact of particles on fluid flow. The coupled calculation principle is as follows: Fluent performs flow field calculations for one time step, inputs the calculated data into Rocky to calculate interphase forces, uses these interphase forces to introduce particle motion equations, and calculates particle position. The calculated volume fraction, along with the interphase forces, is then transmitted back to Fluent for the next time step. This process repeats until the calculation is complete.

[0041] Compared with the existing technology, the above technical solution has the following beneficial effects:

[0042] (1) Multi-field coupling analysis: This invention is based on the CFD-DEM coupling framework and combines computational fluid dynamics and discrete element method. It can simulate the interaction between cigarette particles and fluid simultaneously, solving the deficiency of the existing technology that only simulates the flow field or discrete particles separately, and realizes a more accurate simulation of the complex flow process between the three phases of gas, liquid and solid (hot air-mixed water-cigarette particles).

[0043] (2) Visualization of the tempering process: By simulating and analyzing the temperature field and moisture content of tobacco strips during the tempering process, the present invention realizes the visualization and digital representation of the tempering process of tobacco strips, overcoming the technical bottleneck of the traditional tempering process in which it is difficult to accurately represent the temperature and moisture content of tobacco strips in the barrel, and providing a reliable digital tool for optimizing the tempering process.

[0044] (3) Improving process optimization accuracy: By extracting sensitive process parameters and equipment operating parameters and combining multiple groups of typical working conditions, the present invention can effectively predict the changes in tobacco strip temperature and moisture content with position, thereby guiding the optimization of the rehumidification machine equipment and process, and ensuring the stability of the processing quality of tobacco strips during the rehumidification process. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 is a flow chart of the present invention;

[0046] Figure 2 Schematic diagram of flow field grid division of the drum-type blade rehumidifier of the present invention;

[0047] Figure 3 This is a diagram showing the grid independence verification results of the present invention;

[0048] Figure 4 Schematic diagram of the grid division of tobacco strips and artificial tobacco leaves of the present invention;

[0049] Figure 5 This 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;

[0050] Figure 6 This is a diagram of the CFD-DEM coupling calculation process of the present invention;

[0051] Figure 7 This is the flow field axial temperature cloud diagram of the present invention;

[0052] Figure 8 is the flow field average temperature diagram of the present invention;

[0053] Figure 9 The moisture content-temperature curve of the tobacco slices of the present invention is

[0054] Figure 10 This is a comparison chart of the flow field temperature between the simulation and actual production of the present invention. DETAILED DESCRIPTION

[0055] The following is a clear and complete description of the technical solutions in the embodiments of the present invention, in conjunction with the accompanying drawings. The examples provided are only some of the embodiments of the present invention, not all of them. All other embodiments derived by persons of ordinary skill in the art based on the embodiments without creative effort are within the scope of protection of the present invention.

[0056] See also Figure 1 , which is a numerical simulation and characterization method for the thermal processing characteristics of tobacco sheets during the rehumidification process under complex working conditions provided in an embodiment of the present invention, comprising the following steps:

[0057] Step (1) according to the production equipment of the drum-type blade rehumidification machine, the original three-dimensional model and related size parameters of the rehumidification drum are obtained by three-dimensional space perception technology;

[0058] 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;

[0059] Step (3) measuring the size parameters and position parameters of the rake nails and the copying plate in the cylinder on site, performing geometric modeling, and assembling them with the three-dimensional model of the moisture-recovery cylinder to form a complete three-dimensional model of the moisture-recovery cylinder;

[0060] Step (4) Use SpaceCliam to pre-process the three-dimensional model of the resurgence 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;

[0061] Step (5) mesh the fluid domain in Ansys-meshing and name the hot air inlet, mixed water inlet, smoke inlet, exhaust air outlet, and smoke outlet;

[0062] Step (6) collecting the production process data of the rehumidifier, extracting sensitive process parameters and equipment operating parameters, and preprocessing the collected data to extract four groups of typical operating parameters;

[0063] Step (7) simplifies the inlet data, and simplifies the steam and industrial water that are not directly involved in the work and the direct injection steam into one inlet, unified as the mixed water inlet;

[0064] Step (8) In Ansys-Fluent, set the multiphase flow model to the Euler model, where the multiphase flow includes hot air and mixed water, and set the relevant parameters;

[0065] 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;

[0066] Step (10) Based on 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;

[0067] Step (11) using DEM-Rocky to conduct a simulation experiment on the angle of repose of a cigarette sheet, and compare and verify it with the actual experiment;

[0068] Step (12) constructing a CFD-DEM coupled simulation model, performing full-process simulation of the flow field-discrete element method for the rehumidification process of tobacco sheets, and analyzing the temperature change of the flow field, the temperature of tobacco sheet particles, and the change of moisture content with position;

[0069] Step (13) draws a temperature-position curve based on the changes in the temperature and moisture content of the tobacco particles at different positions to characterize the processing intensity of the loosening and rehydration process.

[0070] The aforementioned SpaceCliam pre-processing of the three-dimensional model of the resurgence cylinder refers to: first, using SpaceClaim to finely process the curved surface of the resurgence cylinder and merge the various separated surfaces to form a continuous, complete three-dimensional geometric model. This step is an important basis for ensuring that the physical properties of the model are accurately reflected in subsequent simulations. Next, the boundaries and lines of each surface are checked to ensure that there are no defects or discontinuities; the deflection angle is set 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 motion and interaction. After this processing, the geometry of the resurgence cylinder will be more suitable for subsequent discrete element method (DEM) simulations and can better simulate the behavior in actual operations. In addition, the fluid domain needs to be extracted. This step is to construct the CFD-Fluent simulation model. By correctly identifying and defining the fluid domain, the characteristics of the fluid flow, including velocity, pressure, and temperature distribution, can be effectively analyzed.

[0071] The multiphase flow model is set as the Euler model in Ansys-Fluent, specifically establishing the corresponding volume fraction equation, mass conservation equation, momentum conservation equation, and energy conservation equation for each phase;

[0072] Volume fraction equation: There are hot air and mixed water in the loose tempering 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 over the domain, and the sum of the volume fractions of the two phases is 1.

[0073] use Indicates hot air or mixed water (gas or liquid phase), then The volume of a phase can be expressed as:

[0074]

[0075]

[0076] In the formula for Phase volume; for Phase volume fraction; is the volume of the fluid domain in the loose rehumidification cylinder.

[0077] Mass conservation equation: When the tobacco flakes are loosened and moistened, hot air and mixed water exist in the continuous phase. The mass conservation equation of the hot air and mixed water needs to be solved. The entire set of model equations is solved for each grid in the CFD grid. However, physically, the phase only exists where the volume fraction is greater than 0. Therefore, the volume fractions of the hot air and mixed water need to be considered. There is mass transfer between the hot air and mixed water, and there is sedimentation.

[0078]

[0079] In the formula for Phase physical density; for Phase velocity; For to The mass transfer of the phase is the same, and vice versa.

[0080] Momentum conservation equation: When tobacco flakes loosen and regain moisture, two momentum equations are required 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 between all phases, and the pressure field is used to combine the hot air and the mixed water. 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.

[0081]

[0082] In the formula for 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.

[0083] 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. During 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.

[0084]

[0085] In the formula For Bihan; is the heat flux density; is the interphase heat transfer intensity; Energy transfer for component diffusion.

[0086] 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, enhances the physical representation of turbulence, especially in high curvature and rotating flow fields, and can better predict flow separation and vortex characteristics. Its turbulent kinetic energy and turbulent dissipation rate They are defined as:

[0087]

[0088] In the formula is the density of the mixture; for speed; is the molecular viscosity; is the flow time; is the turbulent Planck number; is the turbulent kinetic energy generated by the mean velocity gradient; 、 is other energy source terms; 、 is the model constant.

[0089] The DEM-Rocky simulation experiment for the angle of repose of tobacco sheets first requires constructing a three-dimensional model of tobacco sheet particles and setting the corresponding physical parameters, including particle density, Poisson's ratio, elastic modulus, friction coefficient, and adhesion. In DEM simulations, particle interactions are described using collision and contact models, and the settings of these parameters directly affect the simulation results of the angle of repose. Next, the discrete element method (DEM) in Rocky software is used to simulate the tobacco sheet accumulation process. Typically, tobacco sheet particles fall freely from above under specified initial conditions and naturally accumulate to form a conical pile. By observing the stable shape of the accumulated particles, the resulting angle of repose (the maximum stable angle of the particle pile) is calculated. This angle of repose is an important indicator of particle flowability and stacking stability. After the simulation, the numerical results of the angle of repose are compared with actual experimental data to verify the accuracy of the DEM model. If there are significant discrepancies, the particle physical parameters or contact model need to be adjusted, and the simulation should be repeated until the results are consistent.

[0090] The CFD-DEM coupled simulation model described above simulates the entire flow field and discrete element model during the rehumidification process of tobacco leaves. Specifically, the numerical simulation utilizes Fluent CFD-Rocky DEM bidirectional coupling, simulating the motion of particles in the fluid while also accounting for the impact of particles on fluid flow. The coupled calculation principle is as follows: Fluent performs flow field calculations for one time step, inputs the calculated data into Rocky to calculate interphase forces, uses these interphase forces to introduce particle motion equations, and calculates particle position. The calculated volume fraction, along with the interphase forces, is then transmitted back to Fluent for the next time step. This process repeats until the calculation is complete.

[0091] Reference Figure 2 This is a numerical simulation and characterization method for the thermal processing characteristics of tobacco leaf rehumidification under complex working conditions, provided in an embodiment of the present invention. A schematic diagram of the flow field meshing for a drum-type blade rehumidifier is provided. The mesh is a key component of the finite element model and the basis for finite element calculations. Meshing discretizes the actual model into a finite number of elements, which are connected by nodes for numerical analysis. Meshing directly affects the accuracy of the calculation results. The rehumidifier model is complex, and the flow field within the drum is irregular. Direct meshing results in a large number of meshes and poor quality. Based on overlapping mesh technology, the entire computational domain is partitioned, allowing mesh overlap between subdomains without requiring shared boundaries between subdomains. This facilitates information transfer and reduces the difficulty of mesh generation within each subdomain. Structured meshing is used throughout the drum-type blade rehumidifier, reducing the number of meshes while increasing their quality, effectively improving computational efficiency and accuracy. The number of structured meshes is 615,998, with a minimum element quality of 0.32159 and a minimum orthogonal quality of 0.39881.

[0092] Reference Figure 3, which is a numerical simulation and characterization method for the thermal processing characteristics of tobacco leaf rehumidification under complex working conditions provided in an embodiment of the present invention, and a grid independence verification result diagram; further, to ensure 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. In this experiment, the CFD-DEM coupling is weakly coupled, so the grid independence verification is only performed in CFD. The grid numbers 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 the gas and liquid phases at 100 sampling points on the central axis of the drum with different grid numbers was obtained. The results show that when the grid number is less than 615998, the gas and liquid phase temperatures vary greatly. When the grid number is 615998, the temperature distribution tends to be stable. The influence of the grid number on temperature change is small, with a variation of about 1%. The flow field simulation tends to be stable, so the grid number of 615998 with a smaller number of grids is selected to solve the subsequent simulation.

[0093] Reference Figure 4 , which is a numerical simulation and characterization method for the thermal processing characteristics of tobacco strip rehumidification process under complex working conditions provided in an embodiment of the present invention, and a schematic diagram of the grid division of tobacco strips 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 strips. In this experiment, tobacco strips and reconstituted tobacco leaves at the feed inlet of the loose rehumidification stage of a tobacco factory were randomly selected, and then 500 pieces were randomly selected from them. The size screening was carried out based on the longest side, the middle width of the tobacco strips was measured, and the average value of the longest side and the average value of the middle width of each group were calculated. Due to the folding phenomenon of tobacco strips and the similar thickness of reconstituted tobacco leaves and tobacco strips, the average thickness was taken as 0.8mm. Combined with the shapes of tobacco strips and reconstituted tobacco leaves, the tobacco strips were based on the average length dimension of the longest side and the average width dimension of the middle. The shape was set to be approximately long, and the shape of reconstituted tobacco leaves was defined as a rectangle. The model was 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.

[0094] Reference Figure 5, 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 fixed funnel method is used to simulate the repose angle of the tobacco sheet and the result diagram; further, the fixed funnel method is used to measure the repose angle of the tobacco sheet, and the funnel is fixed 200mm above the coordinate paper, so that the tobacco sheet slowly falls along the wall of the funnel, forming a pile on the coordinate paper. When the pile has no obvious sliding, the tobacco sheet is stopped from being added, 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 sheet, and then the repose angle of the tobacco sheet is measured, and the weight of the tobacco sheet 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. This was verified in Rocky 2022 R1.2, and an experimental model was established. "Constant Adhesive Force" was selected as the adhesion force model, which simulates adherent particle behavior that does not exhibit 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. Simulations were performed with a flow rate of 260.28 g. After the simulation, the angle of repose of the mixed sheet was measured using contour fitting. The results showed that the simulated angle of repose of the mixed sheet was 34.88°, while the actual angle of repose was 35.56°, with a relative error of 1.91%.

[0095] Reference Figure 6 This is a numerical simulation and characterization method for the thermal processing characteristics of tobacco strip rehumidification under complex working conditions, as provided in an embodiment of the present invention. A diagram of the CFD-DEM coupled calculation process is also provided. Furthermore, the loose rehumidification thermal processing process primarily relies on controlling the moisture content and temperature of tobacco strips. In actual production, many factors influence this, such as ambient temperature and humidity, industrial water flow, steam flow, hot air velocity, hot air temperature, and drum speed. In a certain factory, to ensure production efficiency and coordination and synchronization between various processes, the default hot air velocity, temperature, and drum speed were 3.95 m / s, 110°C, and 11 rpm. The parameters of the mixed water formed by the mixture of steam and atomized water are shown in (Table 1). Four operating conditions were set in Fluent, with a time step of 4200, a time step size of 0.05, and a total time of 210 seconds. Standard initialization was performed, the drum temperature was set to 63°C, and a .cas file was saved. Discrete element settings were performed in Rocky 2022 R1.2, including the CFD-coupled drying model and the CFD-coupled particle statistical model. 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 the model was coupled with Fluent. Fluent used CPU calculations, while Rocky used GPU calculations.

[0096] Table 1 Typical working parameters of loose regain

[0097] 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

[0098] Table 2 Smoke data of each working condition

[0099] 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

[0100] Reference Figure 7 , which is a numerical simulation and characterization method for the thermal processing characteristics of tobacco leaf rehumidification 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 contains hot air and mixed water, which is a two-phase flow, gas phase and liquid phase respectively. The initial flow field temperature is 63° after the preheating is completed. Figure 7 This is a temperature profile of the axial flow field during the production phase of Condition 1. At the front end of the drum, hot air and mixed water enter from above, gradually increasing the temperature inside the drum. As the drum rotates, heat is transferred to the rear end, increasing the temperature. The discharge chamber, driven by the dehumidification fan, maintains a relatively low temperature. Tobacco flakes enter the drum from below, absorbing heat, resulting in a relatively low temperature at the flake entrance and a large temperature difference between the upper and lower parts. After 40 seconds of flow field simulation, the average flow field temperature remains essentially unchanged, and the flow field within the drum approaches a constant state. The average temperature of 100 points along the central axis of the flow field is plotted as a function of time for four conditions. The average flow field temperature rises rapidly during the first 40 seconds, then gradually slows as the flakes enter the drum. After 40 seconds, the flow field temperature approaches a constant state, with fluctuations of no more than 2°C. The average flow field temperatures for the four conditions after 40 seconds are 99.07°C, 99.31°C, 99.24°C, and 98.02°C, respectively. The temperature differences are minimal, ensuring a stable flake processing environment.

[0101] Reference Figure 8 This is a numerical simulation and characterization method for the thermal processing characteristics of tobacco strips during the rehumidification process under complex working conditions, provided in an embodiment of the present invention. The flow field average temperature diagram shows that the hot air inlet temperature is 110°C, and the temperature at the top of the drum approaches 110°C due to the hot air. The mixed water inlet temperature is 77.88°C, and the temperature rises slightly under the action of the hot air. The tobacco strips inlet temperature is 30.68°C, and upon entering the drum, it absorbs heat, resulting in a lower temperature at the bottom of the drum. Due to the interaction between the hot air, mixed water, and tobacco strips at the front end of the drum, the temperature fluctuates significantly. As the drum rotates, it drives the tobacco strips toward the outlet, and the interaction strength among the three decreases, causing the flow field temperature to gradually approach a constant value. At 5.555m on the X-axis, i.e., within the discharge chamber, the dehumidification fan lowers the temperature at the bottom of the discharge chamber, approaching room temperature. The dehumidification air outlet temperature at the top is greater than 63°C.

[0102] Reference Figure 9, which is a numerical simulation and characterization method for the thermal processing characteristics of the tobacco strip rehumidification process under complex working conditions provided in an embodiment of the present invention, and a tobacco strip moisture content-temperature curve diagram; further, during the tobacco strip loosening and rehumidification process, the tobacco strip moisture content and temperature change with time and with the change of position in the drum. The thermal state of the tobacco strip itself can be used to characterize the processing intensity of the loosening and rehumidification process, that is, the rate of change of temperature per unit distance corresponds to the rate of change of moisture content per unit distance. The moisture content-temperature curve is shown as follows: Figure 9 As shown, before the moisture content of the tobacco strips reaches its maximum, the moisture content is positively correlated with temperature. After reaching its maximum, the strips begin to dehydrate, and the moisture content gradually decreases. The temperature continues to increase despite the high temperature inside the barrel. At the outlet, due to the lower temperature in the discharge chamber, the moisture content of the tobacco strips decreases slightly. Throughout the thermal processing process, temperature and moisture content vary closely, with Condition 4 achieving the highest processing intensity and Condition 1 achieving the lowest.

[0103] Reference Figure 10, which shows the numerical simulation and characterization method for the thermal processing characteristics of tobacco strip rehumidification under complex working conditions provided in an embodiment of the present invention, and a temperature comparison chart between the simulation and the actual production flow field; furthermore, 9 temperature detection points are set in the flow field, from the inlet to the outlet, with coordinates of 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), and 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 is completed, the average flow field temperature of the detection point is taken and compared with the 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 measured value are used as the vertical coordinate to draw four groups of working condition comparison charts. For all four operating conditions, the measured values ​​were lower than the simulated values. This is because, in actual production, the movement of tobacco leaves within the cylinder affects the sensor's measurement accuracy. For the four operating conditions, the temperature at detection points A through H gradually increases, while that at points H through I decreases. Condition 1D has the smallest relative error, at 1.02%, while point A has the largest relative error, at 1.84%, with an average relative error of 1.33%. Condition 2H has the smallest relative error, at 1.02%, while point A has the largest relative error, at 1.70%, with an average relative error of 1.36%. Condition 3C has the smallest relative error, at 0.22%, while point G has the largest relative error, at 1.55%, with an average relative error of 1.19%. Condition 4D has the smallest relative error, at 0.74%, while point A has the largest relative error, at 2.09%, with an average relative error of 1.20%. The average relative error for each condition is less than 2%. Therefore, the CFD-DEM simulation of the tobacco loosening and rehydration process has a certain degree of reliability, and the experimental results have certain reference value.

[0104] The specific implementation methods described above further illustrate the objectives, technical solutions, and beneficial effects of the present invention. It should be understood that the above description is merely 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 shall be included in the scope of protection of the present invention.

Claims

1. Numerical simulation and characterization method of thermal processing characteristics of tobacco sheets during rehumidification under complex working conditions, characterized by: The specific steps include: Step (1) according to the production equipment of the drum-type blade rehumidification machine, the original three-dimensional model and related size parameters of the rehumidification drum 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 copying plate in the cylinder on site, performing geometric modeling, and assembling them with the three-dimensional model of the moisture-recovery cylinder to form a complete three-dimensional model of the moisture-recovery cylinder; Step (4) Use SpaceCliam to pre-process the three-dimensional model of the resurgence 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) mesh the fluid domain in Ansys-meshing and name the hot air inlet, mixed water inlet, smoke inlet, exhaust air outlet, and smoke outlet; Step (6) collecting the production process data of the rehumidifier, extracting sensitive process parameters and equipment operating parameters, and preprocessing the collected data to extract four groups of typical operating parameters; Step (7) simplifies the inlet data, and simplifies the steam and industrial water that are not directly involved in the work and the direct injection steam into one inlet, unified as the mixed water inlet; Step (8) In Ansys-Fluent, set the multiphase flow model to the Euler model, where the multiphase flow includes hot air and mixed water, and set the relevant parameters; 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) Based on 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 cigarette sheet, and compare and verify it with the actual experiment; Step (12) constructing a CFD-DEM coupled simulation model, performing full-process simulation of the flow field-discrete element method for the rehumidification process of tobacco sheets, and analyzing the temperature change of the flow field, the temperature of tobacco sheet particles, and the change of moisture content with position; Step (13) draws a temperature-position curve based on the changes in the temperature and moisture content of the tobacco particles at different positions to characterize the processing intensity of the loosening and rehydration process.

2. The method for numerical simulation and characterization of thermal processing characteristics of tobacco sheets during rehumidification 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 motion trajectory and stress state of the tobacco strip particles.

3. The method for numerical simulation and characterization of thermal processing characteristics of tobacco sheets during rehumidification 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 of the rehumidifier, humidity, hot air flow rate, inlet and outlet moisture content of the tobacco leaves, tobacco leaf 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 sheets during rehumidification 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 sheets during rehumidification 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 particles and fluid, including flow field temperature, humidity, particle temperature and motion characteristics of tobacco particles, so as to optimize the process parameters and equipment structure of the tobacco rehumidification process.

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