A simulation method for drying granular materials in a drum dryer

Abstract

The present invention discloses a simulation method for drying particulate materials in a drum dryer. In the present invention, the particle shape, rolling friction, inter-particle force and evaporation model are comprehensively considered to model the drying process of particulate materials in the drum dryer, so that the model is closer to the actual process and the versatility of the model is enhanced. The model disclosed in the present invention can observe the moisture content and internal flow field of the material at any time and any position during the drying process, and can predict the distribution of particles and analyze the drying effect. In addition, by changing the drum shape, operating parameters, dry material shape, moisture content and other parameters, the material drying effect during the drying process can be comprehensively evaluated, providing a theoretical basis for process optimization.

Description

Technical Field

[0001] The invention belongs to the technical field of material drying, and in particular relates to a simulation method for drying granular materials in a drum dryer. Background Art

[0002] Drum dryer is a common drying equipment. It has the advantages of simple structure, large processing capacity and easy maintenance. It has been widely used in drying various materials. During the drying process, factors such as the shape of the material particles, the rotation mode of the drum, the interaction force between particles and the rolling friction will have a significant impact on the movement of the material, thereby affecting the efficiency and effect of the drying process. However, in actual experimental research, it is quite challenging to fully examine these influencing factors.

[0003] Computational simulation methods can be used to comprehensively study the drying process of materials in drum dryers, which can provide a deep understanding of the drying process, optimize equipment design, and improve energy efficiency. Through simulation, researchers can predict and analyze the drying process without actually building and testing physical equipment.

[0004] Some studies have simulated the drying of materials in drum dryers.

[0005] The Chinese patent "Numerical method for predicting heat and mass transfer law of tobacco in a drum dryer" with publication number CN109259291B can quickly obtain the heat and mass exchange law of tobacco in the drying process of the drum dryer under multi-variable conditions. However, this patent can only be used in a stable state and does not consider the shape of tobacco and the interaction between tobacco and the drum wall.

[0006] The journal article "Characteristics Simulation and Structural Optimization of Drum Sludge Dryer" uses CFD-DEM method to study the influence of drum structure on the movement path of materials and their drying effect when considering the collision between particles and the traction of hot air flow on materials. However, the shape of sludge particles, rolling resistance and water evaporation are not considered.

[0007] In summary, current simulation studies on material drying in drum dryers often ignore some important influencing factors in the drum drying process, such as material shape, water evaporation, and rolling resistance. A comprehensive general model that fully considers these factors has not yet been established, and it is impossible to study the moisture content of the material and the gas flow field at any time and position in the drum in the simulation. Summary of the invention

[0008] The object of the present invention is to provide a method for simulating the drying of granular materials in a drum dryer in order to solve the above-mentioned problems.

[0009] The technical solution adopted by the present invention is as follows: a method for simulating the drying of granular materials in a drum dryer, characterized in that the method comprises the following steps:

[0010] S1. Establish the geometric model of the drum dryer and perform mesh division;

[0011] S2, establishing a group of fluid phase control equations in the drum dryer;

[0012] The established fluid phase control equations are as follows:

[0013] The continuity equation for the fluid phase is:

[0014] ;

[0015] In the formula, is the particle porosity; is the fluid phase density; is the fluid phase velocity; is the mass source term, ,in is the particle mass, is the moisture content of the particles on a dry basis;

[0016] The momentum equation for the fluid phase is:

[0017] ;

[0018] In the formula, For pressure; is the fluid response force tensor, ,in, is the dynamic viscosity of the fluid phase, is the turbulent viscosity; is the acceleration due to gravity; is the momentum source term, which is calculated by the following formula: ,in, is the force exerted by the fluid on the particles, To calculate the mesh volume, To calculate the number of particles in the grid;

[0019] The energy equation for the fluid phase is:

[0020] ;

[0021] In the formula, is the specific enthalpy of the fluid phase; is the heat flux; is the energy source term, ,in, is the heat exchange rate between fluid and particles;

[0022] The turbulence equation for the fluid phase is:

[0023] ;

[0024] ;

[0025] in is the turbulent kinetic energy; is the turbulent kinetic energy dissipation rate; represents the turbulent kinetic energy due to the mean velocity gradient; ,in is the modulus of the strain tensor; =1.9; =1.0; =1.2;

[0026] The component transport equation of the fluid phase is:

[0027] ;

[0028] In the formula, is the mass fraction of the i-th component; is the source term of the i-th component; represents the diffusion flux, ,in, is the turbulent Schmidt number, which takes a value of 0.7. is the thermal diffusion coefficient of component i, is the mass diffusion coefficient of component i;

[0029] S3, simulate the rotation of the drum and set the drum operating conditions;

[0030] S4, establishing a particle model of the material;

[0031] S5, establishing a set of control equations for the particles;

[0032] The control equations of the established particles are as follows:

[0033] The equation of motion is:

[0034] ;

[0035] ;

[0036] ;

[0037] In the formula, is the particle velocity; is the force between particles and between particles and the wall; is the force exerted by the fluid on the particles, where only the drag force and pressure gradient force are considered; is the moment of inertia of the particle; is the angular velocity vector of the particle; is the moment generated by the tangential force; is the torque due to the velocity gradient of the fluid phase; is the drag coefficient; is the projection of the cross-sectional area of ​​the particle in the fluid; is the particle volume;

[0038] The energy equation is:

[0039] ;

[0040] ;

[0041] ;

[0042] In the formula, is the particle specific heat; is the particle temperature; is the heat conduction between particles and between particles and the wall; It is the convective heat transfer between particles and fluid; Provides heat for evaporation of moisture in particles; is the thermal conductivity coefficient; and are the temperature of the calculated particle and the temperature of the contacted particle or the contacted wall, respectively; is the average convective heat transfer coefficient of particles; is the specific surface area of ​​the particles; is the fluid phase temperature;

[0043] The evaporation model is:

[0044] ;

[0045] ;

[0046] ;

[0047] In the formula, is the latent heat of evaporation of water; is the evaporation rate; is the average evaporation rate of the particle surface; and are the water vapor densities at the particle surface and in the free stream, respectively; is the damping function, which is used to adjust the evaporation rate of particle water; ; , B is the adjustment factor; ; ; , They are the current moisture content, critical moisture content, and equilibrium moisture content of the particles respectively;

[0048] The contact force model includes normal contact force model and tangential contact force model;

[0049] The normal contact force model is:

[0050] ;

[0051] ;

[0052] ;

[0053] In the formula, and They are Moment and The normal contact force at the moment is is the time step; and are loading and unloading stiffness, respectively; yes The normal overlap changes at time, , and They are Moment and The normal overlap at the moment; λ is a dimensionless constant with a value of 0.001; and Used to identify the loading stiffness of different particles; and are the loading stiffness of the particle and the wall, , ,in, and are the Young’s moduli of the particle material and the wall material, respectively, and L is the particle size;

[0054] The tangential contact force model is:

[0055] ;

[0056] ;

[0057] ;

[0058] In the formula, and They are Moment and The magnitude of the tangential contact force at the moment; is the magnitude of the elastic tangential contact force at time t; is the coefficient of friction; is the tangential stiffness, ,in is the tangential stiffness ratio of the two surfaces when in contact; The particles are Tangential relative displacement within; and are the static friction coefficient and the dynamic friction coefficient respectively;

[0059] The rolling resistance model is:

[0060] ;

[0061] ;

[0062] ;

[0063] ;

[0064] In the formula, , They are Moment and The rolling resistance moment at the moment; for The elastic rolling resistance moment at the moment; is the rolling resistance moment limit; is the rolling stiffness, ; is the relative angular velocity vector, which is the difference between the angular velocity of the two contacting particles and the angular velocity of the particles on the wall; is the rolling resistance coefficient; is the rolling radius; is the normal contact force; and is the rolling radius of the contacting particles; is the rolling radius of the particle in contact with the wall;

[0065] S6. Setting model, particle and wall parameters and interactions;

[0066] S7, coupled solution calculation;

[0067] S8. Post-processing.

[0068] In a preferred embodiment, in step S1, the geometric model of the drum dryer is established using SolidWorks, and geometric processing is performed in SpaceClaim, and then imported into Fluent Meshing for meshing.

[0069] In a preferred embodiment, in step S1, the geometric model of the drum includes a drum front cover, a drum, and a drum rear cover. The drum front cover has an air inlet and a feed inlet, the air inlet is used to obtain heat energy, and the feed inlet is used to input materials. The middle of the drum rotates to speed up drying. The drum rear cover has an air outlet and a discharge port; the connections of the various parts of the established geometric model are not subjected to shared topology processing. Afterwards, the three parts of the drum geometric model are meshed separately, and the meshes of the three parts are connected using Interface.

[0070] In a preferred embodiment, in step S2, the fluid phase control equations in the drum dryer include a continuity equation, a momentum equation, an energy equation, a component transport equation and a turbulence equation.

[0071] In a preferred embodiment, in step S3, the rotation of the drum is realized by using a sliding grid method. The middle grid of the drum is set as a grid motion area, and rigid motion occurs to simulate the rotation of the drum. The front and rear grids of the drum are set as static areas. The data of the connection between the front and rear grids of the drum and the middle grid of the drum is transmitted through an interface, and the origin of the drum rotation axis, the rotation direction vector and the rotation speed are set at the same time.

[0072] In a preferred embodiment, in step S4, the particle model of the material is described using a polyhedron method, defining the basic shape, particle size, vertical aspect ratio, horizontal aspect ratio, angle, complexity, rolling resistance coefficient, rotation vector and rotation angle of the particles;

[0073] In a preferred embodiment, in step S5, the control equation group of the particle phase includes a motion equation, an energy equation, a water evaporation model, a contact force model, and a rolling resistance model.

[0074] In a preferred embodiment, in step S7, the control equations of the fluid and the control equations of the particles are solved separately and then coupled; the fluid field is initialized first, including the temperature, pressure, velocity, and humidity fields; the initialized fluid field is transmitted to the control equations of the particles to calculate the particle phase volume fraction and interaction terms (particle-fluid interaction force, heat flux, and evaporation rate). The results of the particle phase calculation are transmitted to the fluid phase for calculation, and the temperature, pressure, velocity, and humidity fields calculated by the fluid phase are then transmitted to the particle phase, and this process is repeated until the simulation ends.

[0075] In a preferred embodiment, the step S8 specifically includes: processing the calculation results according to the research requirements, visualizing or making chart analysis, and proposing optimization suggestions.

[0076] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0077] 1. In the present invention, the particle shape, rolling friction, inter-particle force and evaporation model are comprehensively considered to build a model, the moisture content and internal flow field of the material at any time and any position during the drying process are observed and analyzed, and the drying effect of different parameters on the material during the drying process is comprehensively analyzed.

[0078] 2. In the present invention, a drum drying model is established which comprehensively considers the shape of the material, water evaporation and rolling resistance, so that the model established by the present invention is more in line with the actual situation and has stronger versatility. At the same time, by changing the drum shape, operating parameters, shape of the dried material, moisture content and other parameters, the material drying effect in the drying process can be comprehensively analyzed, which can provide a theoretical basis for process optimization. BRIEF DESCRIPTION OF THE DRAWINGS

[0079] Figure 1 It is a schematic diagram of the method flow of the present invention;

[0080] Figure 2 It is a geometric model diagram of the drum dryer in the present invention;

[0081] Figure 3 This is a schematic diagram of the sludge particle model in the present invention;

[0082] Figure 4 This is a schematic diagram of the moisture distribution of sludge particles in the x-axis direction at the 60th second of the simulation in the present invention;

[0083] Figure 5 This is a schematic diagram of the change of the average evaporation rate of water in sludge particles over time in the present invention;

[0084] Figure 6 It is a schematic diagram of the cross-sectional humidity field of the drum dryer simulated at 60 seconds in the present invention, wherein (-) indicates no unit;

[0085] Figure 7 This is a schematic diagram of the moisture content distribution of materials in the drum dryer simulating the 60th second in the present invention.

[0086] Markings in the figure: 1- drum front cover, 2- drum middle, 3- drum rear cover, 4- drum upper air inlet, 5- mud inlet, 6- drum lower air inlet, 7- lifting plate, 8- air outlet, 9- material outlet. DETAILED DESCRIPTION

[0087] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0088] Example:

[0089] Reference Figure 1-7A method for simulating the drying of granular material in a drum dryer is used to simulate the drying of sludge in a drum dryer, comprising the following steps:

[0090] S1. Establish the geometric model of the drum dryer and perform mesh division.

[0091] like Figure 2 As shown: The geometric model of the drum dryer was established using SolidWorks, and the geometry was processed in SpaceClaim, and then imported into Fluent Meshing for meshing.

[0092] Specifically, the geometric model of the drum includes the drum front cover, the drum, and the drum rear cover. There are two air inlets and one mud inlet on the drum front cover. The upper air inlet is used for hot air recycling from other equipment, the lower air inlet directly obtains heat energy from the combustion equipment, and the mud inlet is used for sludge input. The inner wall in the middle of the drum is equipped with a lifting plate, which is used to lift the sludge to improve the drying efficiency. There is an air outlet and a discharge port on the drum rear cover. The air outlet is located at the upper part of the rear cover, and the discharge port is located at the lower part of the rear cover. The connections between the various parts of the established geometric model are not subjected to shared topology processing. After that, the three parts of the drum geometric model are meshed separately, and the meshes of the three parts are connected using Interface.

[0093] S2. Establish the fluid phase control equations in the drum dryer.

[0094] The fluid phase motion in the drum dryer complies with the conservation of mass, momentum and energy, and is also affected by turbulence, component transport and water evaporation. The fluid phase control equations established based on this are as follows:

[0095] The continuity equation for the fluid phase is:

[0096] ;

[0097] In the formula, is the porosity of the sludge; is the fluid phase density; is the fluid phase velocity; is the mass source term, ,in is the mass of sludge particles, is the moisture content of sludge particles on dry basis;

[0098] The momentum equation for the fluid phase is:

[0099] ;

[0100] In the formula, For pressure; is the fluid response force tensor, ,in, is the dynamic viscosity of the fluid phase, is the turbulent viscosity; is the acceleration due to gravity; is the momentum source term, which is calculated by the following formula: ,in, is the force exerted by the fluid on the sludge particles, To calculate the mesh volume, To calculate the number of sludge particles in the grid;

[0101] The energy equation for the fluid phase is:

[0102] ;

[0103] In the formula, is the relative enthalpy of the fluid; is the heat flux; is the energy source term, ,in, is the heat exchange rate between the fluid and the sludge particles;

[0104] The turbulence equation for the fluid phase is:

[0105] ;

[0106] ;

[0107] in is the turbulent kinetic energy; is the turbulent kinetic energy dissipation rate; represents the turbulent kinetic energy due to the mean velocity gradient; ,in is the modulus of the strain tensor; =1.9; =1.0; =1.2;

[0108] The component transport equation of the fluid phase is:

[0109] ;

[0110] In the formula, is the mass fraction of the i-th component; is the source term of the i-th component; represents the diffusion flux, ,in, is the turbulent Schmidt number, which takes a value of 0.7. is the thermal diffusion coefficient of component i, is the mass diffusion coefficient of component i;

[0111] S3, simulate the rotation of the drum and set the drum operating conditions;

[0112] The rotation of the drum is realized using the sliding mesh method. The mesh in the middle of the drum is set as the mesh motion area, and rigid motion occurs to simulate the rotation of the drum. The meshes of the front and rear covers of the drum are set as static areas. The data of the connection between the meshes of the front and rear covers of the drum and the meshes in the middle of the drum is transmitted through the interface. At the same time, the origin of the drum rotation axis (unit: mm) is set to (11500, 0, 0), the rotation direction vector is set to (1, 0, 0), and the rotation speed is set to 5 rpm.

[0113] Furthermore, the fluid phase parameters at the three inlets of the drum are set, see Table 1.

[0114] Table 1 Drum inlet fluid phase parameter settings

[0115] Combustion hot air inlet Recycled hot air inlet Sludge inlet Speed ​​(m / s) 15 7 0.01 Temperature (K) 650 550 300 Turbulence intensity (%) 3.49 3.81 8.74 Hydraulic diameter (mm) 188 200 185

[0116] S4. Establish a particle model of sludge;

[0117] like Figure 3 As shown: The particle model of sludge is described using the polyhedron method. The basic shape of the selected particle is a polyhedron, and the particle size is set to 10 mm, the vertical aspect ratio is 1.5, the horizontal aspect ratio is 0.75, the number of angles is 25, the complexity is 2.0, and the rolling resistance coefficient is 0.5.

[0118] The particle's rotation vector is set to (1,0,0) and the rotation angle is set to 0°. Figure 3 .

[0119] S5, establishing a set of governing equations for the particle phase;

[0120] The particle phase control equations include the motion equation, energy equation, evaporation model, contact force model, and rolling friction model.

[0121] The equation of motion is:

[0122] ;

[0123] ;

[0124] ;

[0125] In the formula, is the sludge particle velocity; It is the force between sludge particles and between sludge particles and drum wall; is the force of the fluid on the sludge particles, only the drag force and pressure gradient force are considered here; is the moment of inertia of the sludge particles; is the angular velocity vector of the sludge particle; is the moment generated by the tangential force; is the torque due to the velocity gradient of the fluid phase; is the drag coefficient, calculated by Huilin & Gidaspow drag model; is the projection of the cross-sectional area of ​​the sludge particles in the fluid; is the volume of sludge particles;

[0126] The energy equation is:

[0127] ;

[0128] ;

[0129] ;

[0130] In the formula, is the specific heat of sludge particles; is the sludge particle temperature; is the heat conduction between sludge particles and between sludge particles and the wall; It is the convection heat transfer between sludge particles and fluid phase; Provides heat for evaporation of water in sludge particles; is the thermal conductivity coefficient; and are the temperature of the calculated sludge particles and the temperature of the contacted sludge particles or the contacted wall surface respectively; is the average convective heat transfer coefficient of sludge particles; is the specific surface area of ​​sludge particles; is the fluid phase temperature;

[0131] The evaporation model is:

[0132] ;

[0133] ;

[0134] ;

[0135] In the formula, is the latent heat of evaporation of water; is the evaporation rate; is the average evaporation rate on the surface of sludge particles; and are the density of water vapor at the surface of sludge particles and in the free stream, respectively; is a damping function, which is used to adjust the evaporation rate of water in sludge particles; ; , where B is the regulating factor; ; ; , They are the current moisture content, critical moisture content, and equilibrium moisture content of sludge particles respectively;

[0136] The contact force model includes normal contact force model and tangential contact force model;

[0137] The normal contact force model is:

[0138] ;

[0139] ;

[0140] ;

[0141] In the formula, and They are Moment and The normal contact force at the moment is is the time step; and are loading and unloading stiffness, respectively; yes The normal overlap changes at time, , and They are Moment and The normal overlap at the moment; λ is a dimensionless constant with a value of 0.001; and Used to identify the loading stiffness of different sludge particles; and are the loading stiffness of sludge particles and drum wall, , ,in, and are the Young’s modulus of the particle material and the wall material, respectively, and L is the sludge particle size;

[0142] The tangential contact force model is:

[0143] ;

[0144] ;

[0145] ;

[0146] In the formula, and They are Moment and The magnitude of the tangential contact force at the moment; is the coefficient of friction; for The magnitude of the elastic tangential contact force at the moment; is the tangential stiffness, ,in is the tangential stiffness ratio of the two surfaces when in contact; The sludge particles are Tangential relative displacement within; and are the static friction coefficient and the dynamic friction coefficient respectively;

[0147] The rolling resistance model is:

[0148] ;

[0149] ;

[0150] ;

[0151] ;

[0152] In the formula, , They are Moment and Rolling resistance moment at time; for The elastic rolling resistance moment at the moment; is the rolling resistance moment limit; is the rolling stiffness, ; is the relative angular velocity vector, which is the difference between the angular velocity of the two contacting sludge particles and the angular velocity of the particles on the wall; is the rolling resistance coefficient; is the rolling radius; is the normal contact force; and is the rolling radius of the contacting sludge particles; is the rolling radius of the sludge particles in contact with the wall;

[0153] S6. Setting the model, sludge particles and wall parameters and interactions;

[0154] The drag model uses the Huilin & Gidaspow model, and the heat conduction model is selected as the Gunn model.

[0155] The sludge inlet rate of the drum dryer is 1 t / h, and the sludge inlet temperature is set to 300 K. The initial moisture content of the sludge particles is set to 0.6, the critical moisture content is set to 0.1, the equilibrium moisture content is set to 0.05, and the adjustment factor B is set to 1.2. The other parameters of the sludge particles and the drum wall are shown in Table 2, and the interaction is shown in Table 3.

[0156] Table 2 Parameters of sludge particles and drum wall

[0157] unit Sludge particles Drum wall Poisson's ratio - 0.4 0.3 Young's modulus Pa <![CDATA[1.1×10 7 ]]> <![CDATA[7×10 10 ]]> density <![CDATA[Kg / m 3 ]]> 1250 7800 Thermal conductivity W / (m K) 0.3 0.1 Specific Heat J / (kg K) 2000 1000 diameter mm 10 - Rolling resistance coefficient - 0.5 -

[0158] Table 3 Interactions between particles and between particles and walls

[0159] Particle-Particle Particle-wall Coefficient of restitution 0.4 0.4 Static friction coefficient 0.3 0.2 Dynamic friction coefficient 0.01 0.01 Tangential stiffness ratio 1 1

[0160] S7, coupled solution calculation;

[0161] In this embodiment, the fluid control equation is solved using Fluent, and the particle phase control equation is solved using Rocky. Specifically, the flow field is first initialized in Fluent, including temperature, pressure, velocity, and humidity fields. The initialized flow field is transmitted to Rocky, which is used to calculate the particle phase volume fraction and interaction terms (particle-fluid interaction force, heat flux, and evaporation rate) of the particles. The calculated results are passed to Fluent through UDF and calculated. The temperature, pressure, velocity, and humidity fields calculated by Fluent are then passed to Rocky, and this process is repeated until the simulation ends.

[0162] S8, post-processing;

[0163] Process the calculation results according to the research needs, visualize or make charts for analysis, and put forward optimization suggestions.

[0164] like Figure 4 As shown in the figure, the moisture distribution of sludge particles in the x-axis direction at the 60th second of the simulation is given. As can be seen from the figure, there is a large difference in the distribution of sludge moisture content at the front end of the drum. It can be inferred that part of the sludge is accumulated at the front end of the drum dryer and cannot move to the rear end of the drum. The feed structure and air intake structure at the front end of the drum can be optimized to reduce the accumulation of sludge at the front of the drum.

[0165] like Figure 5 As shown in the figure, the average evaporation rate of sludge particles in the drum dryer changes with time. From the trend of the curve, it can be seen that the evaporation rate of sludge particles is generally rising slowly within the 60 seconds of observation, which shows that the drying stability stage has not been reached yet. The simulation can be continued, and data analysis can be performed after the system is stable to improve the continuity of the system process.

[0166] like Figure 6As shown in the figure, the humidity field of the drum dryer section at the 60th second of the simulation is visualized. It can be seen from the figure that the humidity distribution inside the drum is uneven and the humidity is generally low. Therefore, the current sludge drying capacity has not reached the maximum processing capacity of the dryer. The sludge processing capacity can be increased or the hot air supply can be reduced to increase the system energy efficiency. It can be seen that the present invention can observe the flow field of the gas phase in the drum dryer at different times, and improve the system energy efficiency through analysis.

[0167] like Figure 7 As shown in the figure, the moisture content distribution of the material in the drum dryer at the 60th second of the simulation is visualized, and the movement and drying process of the sludge under the action of the lifting plate and hot air in the drum can be observed. It can be seen that the present invention can observe the drying conditions of the granular material in the drum dryer under different structures at different times.

[0168] From the above, it can be seen that in the present invention, the particle shape, rolling friction, inter-particle force and evaporation model are comprehensively considered to build a model, the moisture content and internal flow field of the material at any time and any position during the drying process are observed and analyzed, and the drying effect of different parameters on the material during the drying process is comprehensively analyzed.

[0169] In the present invention, a drum drying model is established which comprehensively considers the shape of the material, water evaporation and rolling resistance, so that the model established by the present invention is more in line with the actual situation and has stronger versatility. At the same time, by changing the drum shape, operating parameters, shape of the dried material, moisture content and other parameters, the material drying effect in the drying process can be comprehensively analyzed, which can provide a theoretical basis for process optimization.

[0170] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the term "comprise" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprise a ..." do not exclude the existence of other identical elements in the process, method, article or device including the elements.

[0171] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for simulating the drying of granular materials in a drum dryer, characterized in that: The method comprises the following steps: S1. Establish the geometric model of the drum dryer and perform mesh division; S2. Establishing a fluid phase control equation group in the drum dryer, the fluid phase control equation group includes a continuity equation, a momentum equation, an energy equation, a component transport equation and a turbulence equation; S3, simulate the rotation of the drum and set the drum operating conditions; S4, establishing a particle model of the material; S5. Establish a control equation group of particles, including motion equation, energy equation, water evaporation model, contact force model, and rolling resistance model; S6. Setting model, particle and wall parameters and interactions; S7, coupled solution calculation; S8, post-processing; In step S5, the contact force model includes a normal contact force model and a tangential contact force model; The normal contact force model is: In the formula, and are the normal contact force at time t and time t-Δt, respectively, where Δt is the time step; K nl and K nu are loading and unloading stiffness respectively; Δs n is the change in normal overlap at time t, s n and are the normal overlap at time t and time t-Δt respectively; λ is a dimensionless constant with a value of 0.001; and Used to identify the loading stiffness of different particles; K nl,p and K nl,b are the loading stiffness of the particle and wall materials, K nl,p =E p L.K nl,b =E b L, where E p and E b are the Young’s moduli of the particle material and the wall material, respectively, and L is the particle size; The tangential contact force model is: In the formula, and are the magnitudes of the tangential contact force at time t and time t-Δt respectively; is the magnitude of the elastic tangential contact force at time t; μ is the friction coefficient K τ is the tangential stiffness, K τ =r K K nl , where r K is the tangential stiffness ratio of the two surfaces when they are in contact, Δs τ is the tangential relative displacement of the particle within Δt; μ s and μ d are the static friction coefficient and the dynamic friction coefficient respectively; The rolling resistance model is: M r,lim =μ r R r F n ; In the formula, are the rolling resistance moments at time t and time t-Δt respectively; is the elastic rolling resistance moment at time t; M r,lim is the rolling resistance torque limit; K r is the rolling stiffness, ω rel is the relative angular velocity vector, which is the difference between the angular velocity of the two contacting particles and the angular velocity of the particles on the wall; μ r is the rolling resistance coefficient; R r is the rolling radius; F n is the normal contact force; r1 and r2 are the rolling radius of the contacting particles; r is the rolling radius of the particle in contact with the wall.

2. A method for simulating drying of granular materials in a drum dryer according to claim 1, characterized in that: In the step S1, the geometric model of the drum dryer is established using SolidWorks, and geometric processing is performed in SpaceClaim, and then imported into Fluent Meshing for meshing.

3. The method for simulating drying of granular materials in a drum dryer according to claim 1, characterized in that: In the step S1, the established geometric model of the drum includes a drum front cover, a drum, and a drum rear cover. The drum front cover has an air inlet and a feed port, the middle of the drum rotates, and the drum rear cover has an air outlet and a feed port. The connections between the various parts of the established geometric model are not subjected to shared topology processing. Thereafter, the three parts of the drum geometric model are meshed separately, and the meshes of the three parts are connected using an interface.

4. A method for simulating drying of granular materials in a drum dryer according to claim 1, characterized in that: In step S2, the fluid phase control equations established are as follows: The continuity equation for the fluid phase is: Where γ is the particle porosity; ρ f is the fluid phase density; u is the fluid phase velocity; S m is the mass source term, Where m p is the particle mass, Y is the particle dry basis moisture content; The momentum equation for the fluid phase is: Where p is pressure; T f is the fluid response force tensor, Among them, μ f is the dynamic viscosity of the fluid phase, μ t is the turbulent viscosity; g is the gravitational acceleration; F p→f is the momentum source term, Among them, F f→p is the force exerted by the fluid on the particles, V c is the volume of the calculated grid, N is the number of particles in the calculated grid; The energy equation for the fluid phase is: In the formula, h f is the relative enthalpy of the fluid; q f is the heat flux; Q p→f is the energy source term, calculated by the following formula: in, is the heat exchange rate between fluid and particles; The turbulence equation for the fluid phase is: Where k is the turbulent kinetic energy; ε is the turbulent kinetic energy dissipation rate; G k represents the turbulent kinetic energy due to the mean velocity gradient; Where S is the modulus of the strain tensor; C2 = 1.9; σ k =1.0;σ ε =1.2; The component transport equation of the fluid phase is: Where Y i is the mass fraction of the i-th component; S i is the source term of the i-th component; J represents the diffusion flux, Among them, Sc t is the turbulent Schmidt number, which takes a value of 0.7, D T,i is the thermal diffusion coefficient of component i, D i,m is the mass diffusion coefficient of component i.

5. The method for simulating drying of granular materials in a drum dryer according to claim 1, characterized in that: In step S3, the rotation of the drum is realized by using a sliding grid method; wherein the grid in the middle of the drum is set as a grid motion area, and rigid motion occurs to simulate the rotation of the drum; and the grids of the front and rear covers of the drum are set as static areas; and the data of the connection between the grids of the front and rear covers of the drum and the grid in the middle of the drum is transmitted through an interface.

6. A method for simulating drying of granular materials in a drum dryer according to claim 1, characterized in that: In step S4, the particle model of the material is described using the polyhedron method; the basic shape, particle size, vertical aspect ratio, horizontal aspect ratio, angle number, complexity, rolling resistance coefficient, rotation vector and rotation angle of the particles are defined.

7. A method for simulating drying of granular materials in a drum dryer according to claim 1, characterized in that: In step S5, the control equations of the particles are established as follows: The equation of motion is: In the formula, v p is the particle velocity; F c is the force between particles and between particles and the wall; F f→p is the force exerted by the fluid on the particle, only the drag force and pressure gradient force are considered here; I p is the moment of inertia of the particle; ω p is the angular velocity vector of the particle; M c is the moment generated by the tangential force; M f→p is the torque generated by the velocity gradient of the fluid phase; C D is the drag coefficient; A′ is the projection of the particle’s cross-sectional area in the fluid; V p is the particle volume; The energy equation is: In the formula, c p is the particle specific heat; T p is the particle temperature; is the heat conduction between particles and between particles and the wall; It is the convective heat transfer between particles and fluid; H is the heat of evaporation of water in particles; c is the thermal conductivity; T e and T η are the temperature of the calculated particle and the temperature of the contacted particle or the contacted wall, respectively; h is the average convective heat transfer coefficient of the particle; A p is the specific surface area of ​​the particles; T f is the fluid phase temperature; The evaporation model is: In the formula, h fg is the latent heat of evaporation of water; is the evaporation rate; h evp is the average evaporation rate of the particle surface; ρ v,s and ρ v,∞ are the water vapor densities at the particle surface and in the free stream, respectively; f(Y) is the damping function, which is used to adjust the evaporation rate of the particle water; a = 0.5; Where B is the regulating factor; Y cr , Y eq They are the critical moisture content and equilibrium moisture content of particles respectively.

8. A method for simulating drying of granular materials in a drum dryer according to claim 1, characterized in that: In step S7, the control equations of the fluid and the control equations of the particles are solved separately and then coupled; the fluid field is initialized first, including the temperature, pressure, velocity, and humidity fields; the initialized fluid field is transmitted to the control equations of the particles to calculate the particle phase volume fraction and the interaction terms; the results of the particle phase calculation are transmitted to the fluid phase for calculation, and the temperature, pressure, velocity and humidity fields calculated in the fluid phase are then transmitted to the particle phase, and this process is repeated until the simulation ends.

9. A method for simulating drying of granular materials in a drum dryer according to claim 1, characterized in that: The step S8 specifically includes: processing the calculation results according to the research requirements, visualizing or making chart analysis, and proposing optimization suggestions.

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