Method for calculating distribution of particles in reactor based on Fluent simulation under ultrasonic effect

Abstract

Based on Fluent simulation, distribution condition calculation of particles in a reactor under the action of ultrasonic waves is carried out, and the method comprises the following steps: designing and drawing a three-dimensional reactor geometric model; performing grid division on the geometric model in ICEM CFD, checking the grid quality, and importing the divided high-quality grid into Fluent; setting required materials and physical properties thereof; a Mixture model is set, and a two-phase flow is selected; in order to simulate the change of pressure waves caused by excitation end surface ultrasonic waves in the flow field, the bottom of the wall surface is set to be Moving wall, and a wall surface function and ultrasonic frequency and amplitude are set; setting unit areas and entrance and exit conditions; setting a solver and a solving method; initializing a flow field, and starting iterative calculation; and carrying out post-processing analysis on the calculation result. According to the method, the effectiveness and accuracy of simulation are proved through calculation of a plurality of examples and data analysis of test results, the experiment cost and time can be effectively reduced, and the working efficiency is improved.

Description

Technical Field

[0001] The present invention is based on the fields of CFD computational fluid dynamics and Fluent numerical simulation, is suitable for simulating the influence of ultrasound on particle phase distribution in a reactor, and specifically provides a method for simulating ultrasound in a multiphase flow field. Background Art

[0002] At present, the main methods used for wastewater treatment include adsorption and chemical precipitation. Among them, adsorption is the most common method, which has the advantages of effectively separating the target substance, simple operation, low cost, no secondary pollution, and environmental friendliness, but has the disadvantage of low adsorption efficiency. Ultrasonic waves will produce shear force, pressure and microflow effects in liquid media, and will produce cavitation effects when propagating in water. The cavitation bubbles will release huge energy instantly when they collapse. Based on this, a method is proposed to use the cavitation effect of ultrasonic waves to make the adsorbent more evenly dispersed in the flow field to improve the adsorption efficiency of the adsorbent.

[0003] Ultrasonic cavitation effect refers to a series of nonlinear processes in which the bubbles of vapor or gas in liquid form, expand, contract and eventually collapse at high speed under the action of ultrasonic vibration. Since the collapse process takes a very short time, only a few to hundreds of microseconds, the local area where the cavitation effect occurs will instantly generate extremely high pressure and flow rate and can change the movement trajectory of the particle phase in the area, making it evenly distributed in the fluid.

[0004] In practical applications, ultrasonic technology is widely used, including the treatment of diseases in the medical field, welding processing in the industrial field, sewage treatment in the environmental protection field, marine exploration, etc. And Fluent, as a widely used software in the field of computational fluid dynamics, has the advantages of covering physical models of various physical phenomena, including advanced numerical algorithms, powerful processors, supporting multi-physical field coupling, and allowing users to carry out customized development. After calculation, the calculation results can be exported through CFD-Post to obtain relevant pressure cloud maps, velocity cloud maps, motion trajectories and various data indicators. Therefore, using Fluent to simulate the role of ultrasound can contribute to multiple industries and provide them with fast and accurate simulation results.

[0005] In order to accurately simulate the distribution of the particle phase in the reactor, it is necessary to first create a three-dimensional geometric model of the reactor, divide the mesh through CFD, and obtain a mesh model with high mesh quality. Then import it into Fluent software for multi-physical field coupling, and use Moving Wall to simulate the vibration of ultrasound in the reactor. After calculation, the distribution of the particle phase in the reactor can be accurately simulated, which can save time and cost for related research. Summary of the invention

[0006] The purpose of the present invention is to propose a method for simulating ultrasound using Fluent, which can be used in many fields to simulate and analyze the distribution of particle phases in a reactor.

[0007] In order to achieve the above purpose, based on the Fluent numerical simulation method, the specific steps are as follows:

[0008] Step 1: Create a 3D model of the reactor in Creo and import the model into CFD;

[0009] Step 2: Mesh the model in CFD, check the mesh quality, and import the mesh into Fluent;

[0010] Step 3: Select the required material in Fluent and set its corresponding physical properties;

[0011] Step 4: Set the required multiphase flow model, and select the Mixture model;

[0012] Step 5: Set the unit area and entry and exit conditions;

[0013] Step 6: Set the wall in the boundary condition to Moving Wall and set the wall function to simulate ultrasonic waves;

[0014] Step 7: Set the required solution method and solver;

[0015] Step 8: Initialize the flow field and start iterative calculation;

[0016] Step 9: After the calculation is completed, import the results into CFD-Post for post-processing;

[0017] Step 10: Check whether the simulation results are consistent with the design. If they are, end the calculation. If they are not consistent with the actual situation, check the corresponding steps from step 1 until they are consistent with the actual situation.

[0018] The advantage of the present invention is that when performing grid division in step 2, a structured grid is selected, and the aspect ratio (Aspect Ratio) of the grid quality after division is close to 1, and the determinant (Determinant 2x2x2) is greater than 0.6. Finally, a grid independence verification is performed to fully prove the stability and reliability of the results, as well as the convergence of the numerical solution.

[0019] The advantage of the present invention is that the aqueous phase and particle properties of the material selected in step three are both from the Fluent material library.

[0020] The advantage of the present invention is that the multi-phase flow model in step 4 selects the Mixture model, which is set as a two-phase flow, with the main term being the water phase and the secondary phase being the granularity, and adopts the SST K-omega turbulence model.

[0021] The advantage of the present invention lies in selecting a suitable unit area in step five and setting a proper inlet velocity and particle phase volume fraction.

[0022] The advantage of the present invention is that in step six, the boundary condition of the wall is set to a moving wall, and the ultrasonic vibration law satisfies the sinusoidal motion, so the moving position of the wall can be expressed as:

[0023] z=A·sin(2·π·f·t) (1)

[0024] The moving speed is:

[0025]

[0026] In formulas (1) and (2), A represents the ultrasonic amplitude, f represents the ultrasonic frequency, and t represents the vibration time.

[0027] The advantage of the present invention is that in step 7, the solution method and solver are selected according to the specific flow characteristics and grid type. The present invention selects the Coupled algorithm to solve the model, uses PRESTO! for pressure solution, uses QUICK for volume fraction solution, and uses the second-order upwind format for turbulent kinetic energy solution.

[0028] The present invention can make full use of the advantages of Fluent and simulate the distribution of particle phase in the reactor under the action of ultrasound by moving the wall, which can greatly save time and cost. The simulation verification of multiple examples has proved its high efficiency and accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is the overall flow chart of the present invention;

[0030] Figure 2 A three-dimensional geometric model diagram of a reactor of the present invention;

[0031] Figure 3 A grid division diagram of a three-dimensional model of a reactor according to the present invention;

[0032] Figure 4 is a graph of the reactor grid quality aspect ratio of the present invention;

[0033] Figure 5 is the reactor grid quality determinant (Determinant 2x2x2) diagram of the present invention;

[0034] Figure 6 The volume fraction distribution cloud diagram of the particle phase on the bottom surface of the initial reactor of the present invention;

[0035] Figure 7The volume fraction distribution cloud diagram of the particle phase on the bottom surface of the reactor after running for 300 seconds and stabilizing without the action of ultrasound in the present invention;

[0036] Figure 8 The volume fraction distribution cloud diagram of the particle phase in different cross sections of the reactor after stabilization for 300 seconds under the action of 40kHz ultrasound in the present invention;

[0037] Fig. 9 The volume fraction distribution cloud diagram of the particle phase in different longitudinal sections of the reactor after stabilization for 300 seconds under the action of 40kHz ultrasound;

[0038] Fig.10 This is a distribution cloud diagram of the particle phase volume fraction on the bottom surface of the reactor after stabilization for 300 seconds under the action of 40kHz ultrasound;

[0039] Fig.11 The volume fraction distribution cloud diagram of the particle phase in different cross sections of the reactor after stabilization for 300 seconds under the action of 50kHz ultrasound in the present invention;

[0040] Fig.12 The volume fraction distribution cloud diagram of the particle phase in different longitudinal sections of the reactor after stabilization for 300 seconds under the action of 50kHz ultrasound;

[0041] Fig.13 This is a distribution cloud diagram of the particle phase volume fraction on the bottom surface of the reactor after stabilization for 300 seconds under the action of 50kHz ultrasound; DETAILED DESCRIPTION

[0042] In order to clearly and completely describe the objectives and technical solutions of the present invention, the present invention needs to be further described in detail in combination with the following specific implementation details and drawings.

[0043] The technical solutions in the embodiments of the present invention are described clearly and completely below. The examples described are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, except for the ultrasound-related parameters in step 6, which are set according to different working conditions, the parameters in the remaining steps are set to the parameters in the following embodiments.

[0044] Example 1

[0045] The present invention is based on Fluent simulation of the distribution of particles in the reactor under the action of ultrasound. Figure 1 The present invention is further described, comprising the following steps:

[0046] (1) The three-dimensional geometric model of the reactor was established in Creo drawing software. Figure 2The three-dimensional model of the reactor is shown in Figure 1. The length of the geometric model is 18 cm, the width is 2 cm, and the height is 2 cm. After the model is established, it is imported into CFD.

[0047] (2) Meshing the geometric model in CFD, such as Figure 3 As shown, the present invention adopts a structured grid with a grid number of 640,000 and performs grid independence verification.

[0048] (3) Figure 4 , Figure 5 This is a mesh quality inspection diagram. After the mesh quality inspection is passed, the mesh file is imported into Fluent.

[0049] (4) After opening the mesh in Fluent, perform a mesh quality check to ensure that there are no errors in the mesh during Fluent operation. Then set the gravity direction to the z direction and the size to -9.81ms. -2 .

[0050] (5) Select the required material in the Fluent material library and specify its physical properties, where the density of the water phase is set to 998.2 kg / m 3 , the viscosity was set to 0.001003 kg / (m·s); the density of the solid phase was set to 5180 kg / m 3 .

[0051] (6) Set the model to a multiphase flow model, select the Mixture model, and set it to a two-phase flow, where the main phase of the two-phase flow is the water phase and the secondary phase is the particle phase.

[0052] The equations to be solved in this example are the mass conservation equation (continuity equation) and the momentum conservation equation (NS equation), and their control equations are described in the following form.

[0053] Fluent obtains the calculation and analysis results of relevant variables by solving the mass conservation equation (continuity equation), momentum conservation equation (Navier-Stokes equation) and energy conservation equation. Since the present invention only involves fluid flow problems, only the continuity equation and NS equation need to be calculated. Its control equation is described in the following form. The mass conservation equation is:

[0054]

[0055] Where ρ is the density, and u, v, and w are the components of the velocity vector in the x, y, and z directions. The momentum equation is as follows:

[0056]

[0057] Where μ is the dynamic viscosity, S u ,Sv ,S w is the generalized source term of the momentum conservation equation.

[0058] (7) Set boundary conditions: the inlet is a velocity inlet, the velocities of the water phase and the particle phase are both 0.02 m / s, and the volume fraction of the particle phase is set to 0.005. The outlet is a pressure outlet, and the other walls are all walls, which are set to no-slip walls.

[0059] (8) Select the Coupled algorithm to solve the model, use PRESTO! to solve the pressure, use QUICK to solve the volume fraction, and use the second-order upwind scheme to solve the turbulent kinetic energy.

[0060] (9) Initialize the flow field from the inlet, and further patch it, setting the volume fraction of the initial particle phase to 0. The time step is 0.01 s, the number of iterations is 30,000, and the iterative solution begins.

[0061] (10) After the calculation is completed, check whether the residual curve converges. After the convergence result is obtained, the calculation result is imported into CFD-Post for post-processing to obtain the distribution cloud map of the particle phase in the reactor. Figure 6 This is a cloud diagram of the volume fraction distribution of the particle phase on the bottom surface of the reactor at the initial 0 second of the present invention; Figure 7 This is a cloud diagram of the volume fraction distribution of the particle phase on the bottom surface of the reactor after the reactor is stabilized for 300 seconds without the action of ultrasonic waves;

[0062] (11) Check whether the calculated results are consistent with the actual situation. If they are consistent, the simulation is completed; if the calculated results are inconsistent with the actual situation, check and modify each step from the first step until it is consistent with the actual situation. Complete the calculation method of particle distribution in the reactor without ultrasound based on Fluent simulation.

[0063] Example 2

[0064] The present invention is based on Fluent simulation of the distribution of particles in the reactor under the action of ultrasound. Figure 1 The present invention is further described, comprising the following steps:

[0065] (1) The three-dimensional geometric model of the reactor was established in Creo drawing software. Figure 2 The three-dimensional model of the reactor is shown in Figure 1. The length of the geometric model is 18 cm, the width is 2 cm, and the height is 2 cm. After the model is established, it is imported into CFD.

[0066] (2) Meshing the geometric model in CFD, such as Figure 3 As shown, the present invention adopts a structured grid with a grid number of 640,000 and performs grid independence verification.

[0067] (3) Figure 4 , Figure 5 This is a mesh quality inspection diagram. After the mesh quality inspection is passed, the mesh file is imported into Fluent.

[0068] (4) After opening the mesh in Fluent, perform a mesh quality check to ensure that there are no errors in the mesh during Fluent operation. Then set the gravity direction to the z direction and the magnitude to -9.81 m·s -2 .

[0069] (5) Select the required material in the Fluent material library and specify its physical properties, where the density of the water phase is set to 998.2 kg / m 3 , the viscosity was set to 0.001003 kg / (m·s); the density of the solid phase was set to 5180 kg / m 3 .

[0070] (6) Set the model to a multiphase flow model, select the Mixture model, and set it to a two-phase flow, where the main phase of the two-phase flow is the water phase and the secondary phase is the particle phase.

[0071] The equations to be solved in this example are the mass conservation equation (continuity equation) and the momentum conservation equation (NS equation), and their control equations are described in the following form.

[0072] Fluent obtains the calculation and analysis results of relevant variables by solving the mass conservation equation (continuity equation), momentum conservation equation (Navier-Stokes equation) and energy conservation equation. Since the present invention only involves fluid flow problems, only the continuity equation and NS equation need to be calculated. Its control equation is described in the following form. The mass conservation equation is:

[0073]

[0074] Where ρ is the density, and u, v, and w are the components of the velocity vector in the x, y, and z directions. The momentum equation is as follows:

[0075]

[0076] Where μ is the dynamic viscosity, S u ,S v ,S w is the generalized source term of the momentum conservation equation.

[0077] (7) Set boundary conditions, the inlet is a velocity inlet, the velocity of the water phase and the particle phase are both 0.02 m / s, and the volume fraction of the particle phase is set to 0.005. The outlet is a pressure outlet, and the other walls are set to Moving Wall. The ultrasonic vibration law satisfies the sinusoidal motion, so the moving position of the wall can be expressed as:

[0078] z=A·sin(2·π·f·t) (1)

[0079] The moving speed is:

[0080]

[0081] In formula (1) and (2), A represents the ultrasonic amplitude, f represents the ultrasonic frequency, and t represents the vibration time. In the present invention, A is set to 1 and f is 40000 Hz.

[0082] (8) Select the Coupled algorithm to solve the model, use PRESTO! to solve the pressure, use QUICK to solve the volume fraction, and use the second-order upwind scheme to solve the turbulent kinetic energy.

[0083] (9) Initialize the flow field from the inlet, perform patching, and set the volume fraction of the initial particle phase to 0. The time step is 0.01 s, the number of iterations is 30,000, and the iterative solution begins.

[0084] (10) After the calculation is completed, check whether the residual curve converges. After the convergence result is obtained, the calculation result is imported into CFD-Post for post-processing to obtain the distribution cloud map of the particle phase in the reactor. Figure 8 , Fig. 9 , Fig.10 This is a cloud diagram of the volume fraction distribution of the particle phase in different cross sections, different longitudinal sections and the bottom of the reactor after stabilization for 300 seconds under the action of 40kHz ultrasound:

[0085] (11) Check whether the calculated results are consistent with the actual situation. If they are consistent, the simulation is completed; if the calculated results are inconsistent with the actual situation, check and modify each step starting from the first step until it is consistent with the actual situation. Complete the calculation method of particle distribution in the reactor under the action of 40kHz ultrasound based on Fluent simulation.

[0086] Example 3

[0087] The present invention is based on Fluent simulation of the distribution of particles in the reactor under the action of ultrasound. Figure 1 The present invention is further described, comprising the following steps:

[0088] (1) The three-dimensional geometric model of the reactor was established in Creo drawing software. Figure 2The three-dimensional model of the reactor is shown in Figure 1. The length of the geometric model is 18 cm, the width is 2 cm, and the height is 2 cm. After the model is established, it is imported into CFD.

[0089] (2) Meshing the geometric model in CFD, such as Figure 3 As shown, the present invention adopts a structured grid with a grid number of 640,000 and performs grid independence verification.

[0090] (3) Figure 4 , Figure 5 This is a mesh quality inspection diagram. After the mesh quality inspection is passed, the mesh file is imported into Fluent.

[0091] (4) After opening the mesh in Fluent, perform a mesh quality check to ensure that there are no errors in the mesh during Fluent operation. Then set the gravity direction to the z direction and the magnitude to -9.81 m·s -2 .

[0092] (5) Select the required material in the Fluent material library and specify its physical properties, where the density of the water phase is set to 998.2 kg / m 3 , the viscosity was set to 0.001003 kg / (m·s); the density of the solid phase was set to 5180 kg / m 3 .

[0093] (6) Set the model to a multiphase flow model, select the Mixture model, and set it to a two-phase flow, where the main phase of the two-phase flow is the water phase and the secondary phase is the particle phase.

[0094] The equations to be solved in this example are the mass conservation equation (continuity equation) and the momentum conservation equation (NS equation), and their control equations are described in the following form.

[0095] Fluent obtains the calculation and analysis results of relevant variables by solving the mass conservation equation (continuity equation), momentum conservation equation (Navier-Stokes equation) and energy conservation equation. Since the present invention only involves fluid flow problems, only the continuity equation and NS equation need to be calculated. Its control equation is described in the following form. The mass conservation equation is:

[0096]

[0097] Where ρ is the density, and u, v, and w are the components of the velocity vector in the x, y, and z directions. The momentum equation is as follows:

[0098]

[0099] Where μ is the dynamic viscosity, S u ,Sv ,S w is the generalized source term of the momentum conservation equation.

[0100] (7) Set boundary conditions, the inlet is a velocity inlet, the velocity of the water phase and the particle phase are both 0.02 m / s, and the volume fraction of the particle phase is set to 0.005. The outlet is a pressure outlet, and the other walls are set to Moving Wall. The ultrasonic vibration law satisfies the sinusoidal motion, so the moving position of the wall can be expressed as:

[0101] z=A·sin(2·π·f·t) (1)

[0102] The moving speed is:

[0103]

[0104] In formula (1) and (2), A represents the ultrasonic amplitude, f represents the ultrasonic frequency, and t represents the vibration time. In the present invention, A is set to 1 and f is 50000 Hz.

[0105] (8) Select the Coupled algorithm to solve the model, use PRESTO! to solve the pressure, use QUICK to solve the volume fraction, and use the second-order upwind scheme to solve the turbulent kinetic energy.

[0106] (9) Initialize the flow field from the inlet, perform patching, and set the volume fraction of the initial particle phase to 0. The time step is 0.01 s, the number of iterations is 30,000, and the iterative solution begins.

[0107] (10) After the calculation is completed, check whether the residual curve converges. After the convergence result is obtained, the calculation result is imported into CFD-Post for post-processing to obtain the distribution cloud map of the particle phase in the reactor. Figure 8 , Fig. 9 , Fig.10 The volume fraction distribution cloud diagram of the particle phase in different cross sections, different longitudinal sections and the bottom of the reactor after stabilization for 300 seconds under the action of 50kHz ultrasound;

[0108] (11) Check whether the calculated results are consistent with the actual situation. If they are consistent, the simulation is completed; if the calculated results are inconsistent with the actual situation, check and modify each step starting from the first step until it is consistent with the actual situation. Complete the calculation method of particle distribution in the reactor under the action of 50kHz ultrasound based on Fluent simulation.

Claims

1. Based on Fluent simulation, the distribution of particles in the reactor under the influence of ultrasound is simulated as follows: Step 1: Create a 3D geometric model of the reactor in Creo and import the geometric model into CFD; Step 2: Perform meshing in CFD, check the mesh quality, and import the mesh into Fluent; Step 3: Select the required material in Fluent and set its corresponding physical properties; Step 4: Set the required multiphase flow model, select the Mixure model, and set it to two-phase flow; Step 5: Set the unit area and entry and exit conditions; Step 6: Set the wall in the boundary condition to Moving Wall and set the wall function to simulate ultrasonic waves; Step 7: Set the required solution method and solver; Step 8: Initialize the flow field and start iterative calculation; Step 9: After the calculation is completed, import the results into CFD-Post for post-processing; Step 10: Check whether the simulation results are consistent with the design. If they are, end the calculation. If they are not consistent with the actual situation, check the corresponding steps from step 1 until they are consistent with the actual situation.

2. According to the simulation of the distribution of the particle phase in the reactor under ultrasound as described in claim 1, the specific requirements are: when performing grid division in step 2, a structured grid is selected, and the aspect ratio (AspectRatio) of the grid quality after division is within 20, and the determinant (Determinant 2x2x2) is greater than 0.

6.

3. According to the simulation of the distribution of the particle phase in the reactor under ultrasound as described in claim 1, the specific requirement is: in step three, the required water phase and particle properties are selected in the Fluent material library.

4. According to the method of simulating the distribution of the particle phase in the reactor under ultrasound as described in claim 1, the specific requirement is: in the multi-phase flow model of step 4, the Mixture model is selected and set to two-phase flow, the main phase is water, and the secondary phase is particle nature.

5. According to claim 1, the method for simulating the distribution of the particle phase in the reactor under ultrasound has the following specific requirements: in step 6, the boundary condition of the wall is set to Moving Wall, and the ultrasonic vibration law satisfies the sinusoidal motion, so the moving position of the wall can be expressed as: z=A·sin(2·π·f·t) (1) The moving speed is: In formulas (1) and (2), A represents the ultrasonic amplitude, f represents the ultrasonic frequency, and t represents the vibration time.

6. According to claim 1, the method for simulating the distribution of the particle phase in the reactor under ultrasound has the following specific requirements: in step seven, the solution method and solver are determined according to the specific flow characteristics and grid type.

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