CN115496013A - Method for Predicting the Fluid Flow Parameters of Water Copper Nanoparticles and the Movement State of Nanoparticles - Google Patents

Abstract

The invention relates to a method for predicting a flow parameter of a water-copper nanoparticle fluid and a motion state of nanoparticles, belonging to the technical field of molecular simulation. The method comprises the steps of establishing a model, defining atoms, balancing a force field, minimizing energy, relaxing temperature, achieving thermodynamic equilibrium, simulating and post-processing data. The invention provides a nano fluid simulation process, a flow channel model and nano particle establishment, which are mainly used for researching a micro fluid different from macroscopic motion, analyzing the speed, the temperature and the distribution of density in a channel, and analyzing the slippage and the aggregation time of nano particles in motion states of the nano particles at different times, thereby providing reference for experiments.

Description

Method for Predicting Fluid Flow Parameters of Water Copper Nanoparticles and the Movement State of Nanoparticles

technical field

The invention relates to a method for predicting fluid flow parameters of water copper nanoparticles and the movement state of nanoparticles, and belongs to the technical field of molecular simulation.

Background technique

Nanofluid is prepared by mixing base fluid and nanoparticles. As an emerging nanomaterial, its excellent heat transfer and transport capabilities must be studied in depth. Traditional macroscopic motion models have been unable to accurately predict microscopic fluid motion models. In the preparation of nanofluids, reagents are often added to prevent the agglomeration of nanoparticles. However, it is difficult to predict the expected effect from the preparation to the realization of the use before the preparation and application, as well as the various external complex conditions of the nanofluids after they are put into use. influences.

Contents of the invention

The purpose of the present invention is to provide a method for predicting the fluid flow parameters of water copper nanoparticles and the state of movement of nanoparticles, using non-equilibrium molecular dynamics to simulate nanofluid flow to achieve stable test speed, density, temperature, slip length, and nanoparticle The motion state at different times and the time of particle aggregation are used to study the motion law of water and copper nanoparticles in the copper wall flow channel, and provide motion reference for environments that cannot be realized by macroscopic experiments.

The technical scheme adopted in the present invention is: a method for predicting the fluid flow parameters of water copper nanoparticles and the state of movement of nanoparticles, comprising the following steps:

1) Model building: set the parameters required for model building in the molecular dynamics software lammps:

Establish the wall surface of the upper and lower flow channels of the model;

Divide the runner area;

Set the position of copper nanoparticles;

2) Define atoms, that is, fill the number of atoms corresponding to the flow channel area in step 1):

Fill the atoms and set the corresponding molar mass;

3) Force field balance, simulating the real force in reality:

Set different force field parameters to realize hydrophilic and hydrophobic walls;

4) Perform energy minimization:

Achieving system balance and preparing for simulation;

5) Perform temperature relaxation to reach thermodynamic equilibrium:

Set the temperature to 300K to reach room temperature;

6) Perform simulation:

Set the size of the force to make the fluid flow to a stable flow rate;

set the time step;

Layer the model, collect data and output data, the collected data includes temperature, velocity, density and movement parameters of nanoparticles;

7) Data post-processing:

For the data output in step 6), use the origin software to describe the velocity, density, temperature, and slip length data graphs of the fluid that has reached a stable flow rate, and use the ovito software to perform molecular visualization motion processing, including the movement of nanoparticles in nanofluids and final assembly time.

Specifically, in the step 1), the upper and lower walls restricting fluid flow are realized as circular, square, and triangular models to achieve rough walls of different shapes, and the block command is used to divide the required flow channel area. Copper nanoparticles Determine its position according to its center and radius.

Specifically, in the step 3), by changing the potential function, the influence of different hydrophilic (showing attraction to water molecules) and hydrophobic (not attractive to water molecules) wall surfaces on the fluid is simulated.

Specifically, in step 6), the magnitude of the applied force is changed according to the size of the model.

The beneficial effect of the invention is that it can accurately study the curve trend of the temperature velocity density slip length of the nanoparticle fluid under the microscopic Poiseuille flow, as well as the movement state and aggregation time of the nanoparticle.

Description of drawings

Fig. 1 is the simulation flow chart of this experiment;

Figure 2 is the suggested code diagram of the basic model;

Fig. 3 is a model diagram;

Figure 4 is a diagram of different roughness;

Figure 5 is a speed diagram;

Figure 6 is a density map;

Figure 7 is a temperature map;

Figure 8 is a speed slip diagram;

Figure 9 is a graph of nanoparticle movement and nanoparticle aggregation at different times.

detailed description

In order to better illustrate the technical solution of the present invention, the drawings and specific embodiments of the present invention will be described in detail below in conjunction with the accompanying drawings.

Embodiment 1: a kind of method of predicting water copper nanoparticle fluid flow parameter and nanoparticle motion state, it is characterized in that: comprise the following steps:

1) Model building: set the parameters required for model building in the lammps (molecular dynamics software) software:

Establish the wall surface of the upper and lower flow channels of the model;

Divide the runner area;

Set the position of copper nanoparticles;

2) Define atoms, that is, fill the number of atoms corresponding to the channel area in step 1):

Fill the atoms and set the corresponding molar mass;

3) Force field balance, simulating the real force in reality:

Set different force field parameters to achieve hydrophilic (attractive to water molecules) and hydrophobic (unattractive to water molecules) walls;

4) Perform energy minimization:

Achieving system balance and preparing for simulation;

5) Perform temperature relaxation to reach thermodynamic equilibrium:

Set the temperature to 300K to reach room temperature;

6) Perform simulation:

Set the force level; make the fluid flow to a steady flow rate

set the time step;

Layer the model, collect data and output data, the collected data includes temperature, velocity, density and movement parameters of nanoparticles;

7) For the data output in step 6), use the origin software to describe the velocity, density, temperature, and slip length data graph of the fluid that has reached a stable flow rate, and use the ovito software to perform molecular visualization motion processing, including the nanoparticle in the nanofluid Movement regularity and final assembly time.

Further, in the step 1), the upper and lower walls restricting fluid flow are realized as circular, square, and triangular modeling to realize rough wall surfaces of different shapes, and the required flow channel area is divided by using the block command, and the copper nanoparticles Determine its position according to its center and radius.

Further, in the step 3), by changing the potential function, the influence of different hydrophilic (showing attraction to water molecules) and hydrophobic (not attractive to water molecules) wall surfaces on the fluid is simulated.

Further, in step 6), the magnitude of the applied force is changed according to the size of the model.

The present invention will be described in detail below in conjunction with specific data.

Using lammps to model, first establish a model box to determine the size of the model, the model uses periodic conditions for infinite flow in x and y, and uses fixed boundary conditions to fix the boundary in the z direction, which corresponds to ppf in the instruction. Partitioning is carried out to build the copper atom wall, and the atoms are filled to achieve the establishment of the wall. The two walls are filled with water molecules to realize fluid conditions. And add the same nanoparticles in the fluid. Create the models needed for calculations. The code of the model is shown in Figure 2.

Change the shape of the runner to achieve different roughness. The roughness model and conventional fluid model are shown in Fig. 3 and Fig. 4.

Set the velocity+nvt initial temperature of the model and run it to reach a normal temperature of 300K to achieve equilibrium. The specific implementation code is as follows: velocity create 300.0 4922029rot yes distgaussian+fix all nve, velocity represents the initial temperature creation command, create represents the creation temperature, 300k represents temperature, 4922029 represents random numbers, and rotyesdistgaussian represents obeying the Gaussian distribution. fix represents an ensemble command, all represents the model invented in this paper and nve represents an ensemble command.

A force in the direction of the channel is applied to the water molecules in the flow channel to make the fluid reach a stable flow rate. The specific implementation code is as follows, fix addforce 0.0006 0.0 0.0, fix represents the force command, addforce represents the magnitude of the force command, 0.006 represents the force in the x direction, and two 0.0 represent the force in the y and z directions is 0.

Stratify the fluid that reaches a stable flow rate, and count the velocity, density, and temperature distribution. Visualize the nanoparticle fluid and collect the movement state data of nanoparticles at different times.

Use the graphing software origin to analyze the data of velocity, density, temperature distribution and velocity slip to start drawing graphs and analyze them. Get velocity, density, temperature velocity slip distribution diagram. As shown in Figure 5, Figure 6, Figure 7, and Figure 8.

The molecular visualization software ovito was used to analyze the movement rules of nanoparticles at different times and the movement diagram of the final nanoparticle agglomeration is shown in Figure 9.

The specific embodiments of the present invention have been described in detail above in conjunction with the accompanying drawings, but the present invention is not limited to the above embodiments. Variations.

Claims (4)

1. A method for predicting the fluid flow parameters and the motion state of water-copper nanoparticles is characterized in that: the method comprises the following steps:

1) Establishing a model: parameters required for model establishment are set in the molecular dynamics software lammps:

establishing walls of an upper flow passage and a lower flow passage of a model;

dividing a runner area;

positioning copper nanoparticles;

2) Defining atoms, namely the number of atoms corresponding to the flow channel region in the filling step 1):

filling atoms, and setting corresponding molar mass;

3) Balancing a force field, and simulating real force in reality:

setting different force field parameters to realize hydrophilic and hydrophobic wall surfaces;

4) Performing energy minimization:

system balance is achieved, and simulation preparation is carried out;

5) Temperature relaxation is carried out to reach thermodynamic equilibrium:

setting the temperature to 300k to reach normal temperature;

6) Carrying out simulation:

setting the force to make the fluid flow to a stable flow rate;

setting a time step length;

layering the model, collecting data and outputting the data, wherein the collected data comprises temperature, speed, density and motion parameters of the nano particles;

7) And (3) data post-processing:

and (3) describing a data graph of speed, density, temperature and slip length of the fluid reaching the stable flow rate through origin software for the data output in the step 6), and performing molecular visualization motion processing including different time motion states and agglomeration time of the nanoparticles in the nano fluid through ovito software.

2. The method for predicting the fluid flow parameters and nanoparticle motion states of the water copper nanoparticles as claimed in claim 1, wherein: in the step 1), the wall surface for limiting the fluid flow up and down is modeled to be round, square and triangular to realize rough wall surfaces with different shapes, a required flow channel area is divided by adopting a blocking command, and the position of the copper nano-particle is determined according to the circle center and the radius.

3. The method of predicting the fluid flow parameters and nanoparticle motion states of copper nanoparticles as claimed in claim 1, wherein: in the step 3), the influence of different hydrophilic and hydrophobic wall surfaces on the fluid is simulated by changing the potential function.

4. The method of predicting the fluid flow parameters and nanoparticle motion states of copper nanoparticles as claimed in claim 1, wherein: in the step 6), the magnitude of the applied force is changed according to the magnitude of the model.

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