Prediction method for thermal performance of NaCl-KCl-SiO2 composite molten salt
Through molecular dynamics simulation, a NaCl-KCl-SiO2 composite molten salt material model was established to predict the thermal performance parameters of chloride molten salt at high temperature, solving the problem that is difficult to test with existing technologies and achieving accurate prediction of thermal performance at high temperatures.
Patent Information
- Application Number
- CN202510840380.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-06-23
- Publication Date
- 2025-09-30
AI Technical Summary
It is difficult to test the thermal properties of chloride molten salts at high temperatures with existing technologies, especially the heat transfer coefficient, shear viscosity and specific heat capacity.
Molecular dynamics simulation method was used to establish a NaCl-KCl-SiO2 composite molten salt material model. The model was constructed using LAMMPS software. The Fumi-Tosi potential function and BKS potential function were combined to describe the interaction between ions and nanoparticles. The thermal performance parameters were predicted using the Muller-Plathe method.
The thermal performance parameters of chloride molten salt, especially the heat transfer coefficient, shear viscosity and specific heat capacity at high temperature, were effectively predicted. The results were in good agreement with the experimental values with an error within 10%.
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Figure CN120727140A_ABST
Abstract
Description
Technical Field
[0001] The invention relates to the field of molten salt thermal performance prediction, and particularly relates to a method for predicting the thermal performance of a NaCl-KCl-SiO2 composite molten salt. Background Art
[0002] Molten chloride salt mixtures offer advantages such as a wide operating temperature range, high thermal stability, and low vapor pressure. However, they also suffer from poor thermal conductivity, low specific heat capacity, and high viscosity. They are often used as energy storage materials in centralized photovoltaic power plants. However, conventional experiments have made it difficult to test the thermal properties of molten chloride salt mixtures at high temperatures (above 1000K). Summary of the Invention
[0003] In view of the technical problems existing in the background technology, the purpose of the present invention is to provide a method for predicting the thermal properties of NaCl-KCl-SiO2 composite molten salt.
[0004] In order to achieve the above object, the present invention adopts the following technical solutions:
[0005] A first aspect of the present invention provides a method for predicting the thermal properties of a NaCl-KCl-SiO2 composite molten salt, comprising the following steps:
[0006] S1. Establish SiO2 nanoparticle model;
[0007] S2. Establish a NaCl-KCl-SiO2 composite molten salt material model;
[0008] S3. Molecular dynamics simulation of NaCl-KCl-amorphous SiO2 composite molten salt material model;
[0009] S4. Prediction and calculation of thermal performance parameters, including heat transfer coefficient, shear viscosity, and specific heat capacity.
[0010] Preferably, in step S1, the establishment of the SiO2 nanoparticle model specifically includes the following steps: using Materials Studio software to construct a single crystalline SiO2 cluster consisting of 933 atoms, and then disrupting the arrangement of SiO2 by high temperature and high pressure to achieve amorphous modeling, and exporting the obtained single amorphous SiO2 model as a data file that can be recognized by LAMMPS, cutting out a particle with a radius of Amorphous SiO2 nanoparticle model.
[0011] Preferably, in step S2, the establishment of the NaCl-KCl-SiO2 composite molten salt material model specifically includes the following steps: first, using the read_data command of the LAMMPS software to convert a single The amorphous SiO2 model was added to the simulation box, and then the Na, K, and Cl molecular templates were used to generate 4222 Na ions, 4222 K ions, and 8444 Cl ions into the simulation box through the create_atoms command to create the NaCl-KCl-amorphous SiO2 composite molten salt material model.
[0012] Preferably, in step S3, the molecular dynamics simulation of the NaCl-KCl-amorphous SiO2 composite molten salt material model comprises:
[0013] The chloride molten salt ions are added to the simulation box by molecular templates of Na, K, and Cl. The interactions between the ions in the chloride molten salt are represented by the Fumi-Tosi potential function, which is specifically expressed as follows:
[0014]
[0015] in, is the electrostatic potential energy term, which represents the Coulomb electrostatic interaction between the two ions; q i q j represents the charge of the two ions; r ij represents the distance between two ions; is the exponential repulsion term, which is used to describe the short-range repulsion between ions. ij When the value is less than σij, the exponential function increases sharply, indicating a strong repulsive force, which usually corresponds to the contact or very close situation between ions. The parameter Aij is used to adjust the strength and range of the repulsion, and σij represents the sum of the radii of the two ions. is a polynomial attraction term used to describe the long-range attraction between ions, usually corresponding to van der Waals forces or dispersion forces, represents the dipole-dipole interaction, represents the dipole-quadrupole interaction;
[0016] Simulate the energy of amorphous SiO2 nanoparticle models, including bonding energy and non-bonding energy;
[0017] The non-bonded energy is calculated using the BKS potential function, which combines the Buckingham potential and the long-range Coulomb interaction. It is specifically expressed as follows:
[0018]
[0019] A ij , C ij Used to adjust the interaction strength and range between different atomic pairs; r ij represents the distance between atoms i and j, q i and q jrepresent the charges of atoms i and j respectively.
[0020] The bond energy is calculated by the following formula:
[0021] E bond =K b (R-R0) 2 +K θ (θ-θ0) 2
[0022] Among them, K b and K θ are the force constants for the bond length term and the bond angle term, respectively; R and θ are the bond length and bond angle constants, respectively.
[0023] Preferably, in step S3, the molecular dynamics simulation of the NaCl-KCl-amorphous SiO2 composite molten salt material model further includes:
[0024] The interaction between chloride salt and SiO2 is simulated using the Lennard-Jones (LJ) potential of the Coulomb term, which is expressed as follows:
[0025]
[0026] in, is the Coulomb term, which represents the Coulomb interaction between charged particles i and j, q i and q j denote the charges of charged particles i and j, r ij represents the distance between charged particles i and j;
[0027] is the Lennard-Jones term, which is used to describe the van der Waals interaction between charged particles i and j, where ε ij is the depth of potential energy, indicating the strength of interaction between particles; σ ij is the diameter of the particle, which represents the distance scale between charged particles i and j; The term represents the repulsive force between particles. When r is less than σ, the term increases rapidly, indicating a strong repulsive force; The term represents the attraction between particles. When r is greater than σ, the term gradually decreases, indicating a weak attraction.
[0028] Preferably, in step S4, the heat transfer coefficient is predicted using the Muller-Plathe (velocity exchange) method. The entire system is divided into 20 layers along the X direction. The temperature of the middle layer of the system is gradually increased, while the temperature at both ends is gradually decreased. After several steps, when the energy exchange rate and the conduction rate are equal, the temperature distribution of the entire system reaches equilibrium. The temperature gradient is calculated to obtain the heat transfer coefficient data.
[0029] Preferably, in step S4, the shear viscosity is predicted using the Muller-Plathe method. The entire system is divided into 20 regions in the z direction. The velocity gradient is constructed by exchanging the momentum components of the atoms in the x direction in regions 1 and 20 and region 11 to form a shear field. During the exchange, the physical momentum exchange amount in the z direction is statistically calculated to calculate the shear viscosity.
[0030] Preferably, in step S4, the specific heat capacity is predicted by heating the system from 1000K to 1800K, recording the temperature and total energy changes during the heating process, and performing a linear fit to obtain Then use the formula Get the specific heat capacity.
[0031] Beneficial effects
[0032] The present invention enhances the thermal properties of chloride molten salt by adding SiO2 nanoparticles to NaKCl2 molten salt, solving the technical problem that conventional experiments make it difficult to test thermal properties at high temperatures (above 1000K). Thermal performance parameters such as the material's heat transfer coefficient, viscosity, and specific heat capacity are characterized through simulation. BRIEF DESCRIPTION OF THE DRAWINGS
[0033] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.
[0034] Figure 1 Schematic diagram of a method for predicting the thermal properties of a NaCl-KCl-SiO2 composite molten salt;
[0035] Figure 2 Schematic diagram of the structure of a single SiO2 nanoparticle;
[0036] Figure 3 Schematic diagram of the structure of NaCl-KCl-SiO2 composite molten salt;
[0037] Figure 4 Schematic diagram of the principle of calculating heat transfer coefficient, i.e. thermal conductivity, using the MP method;
[0038] Figure 5 Schematic diagram of the MP method for calculating shear viscosity;
[0039] Figure 6 Calculate data graph for thermal conductivity;
[0040] Figure 7 Calculate data graph for viscosity;
[0041] Figure 8 :(a) is the temperature and total energy change diagram; Figure 8 (b) Comparison of specific heat capacity and absorbed energy. DETAILED DESCRIPTION
[0042] In the following description, specific details such as specific system structures and technologies are provided for the purpose of illustration rather than limitation to facilitate a thorough understanding of the embodiments of the present invention. However, it should be clear to those skilled in the art that the present invention may also be implemented in other embodiments without these specific details.
[0043] Example 1
[0044] NaKCl2 molten salt was prepared by adding different amounts of SiO2 nanoparticles to a 1:1 molar ratio of NaCl to KCl. The effects of SiO2 nanoparticles on the thermal properties of the molten salt at different temperatures were investigated. The entire system was simulated using LAMMPS software.
[0045] See Figure 1 A method for predicting the thermal properties of NaCl-KCl-SiO2 composite molten salt comprises the following steps:
[0046] S1. Establish SiO2 nanoparticle model;
[0047] Specifically, Materials Studio software was used to construct a single crystalline SiO2 cluster consisting of 933 atoms. The arrangement of SiO2 was then disrupted by high temperature and high pressure to achieve amorphous modeling. The resulting single amorphous SiO2 model was exported as a data file that can be recognized by LAMMPS. Amorphous SiO2 nanoparticle model;
[0048] Composed of homogeneous spherical nanoparticles, multiple nanoparticles are generated by replicating a single SiO2 nanoparticle model and placing it at different locations, see Figure 2-3 .
[0049] S2. Establish a NaCl-KCl-SiO2 composite molten salt material model;
[0050] Specifically, a single amorphous SiO2 model is first added to the simulation box through the read_data command of the LAMMPS software, and then 4222 Na ions, 4222 K ions, and 8444 Cl ions are generated in the simulation box using the create_atoms command using the Na, K, and Cl molecular templates to create a NaCl-KCl-amorphous SiO2 composite molten salt material model; here, 1, 3, 5, or 8 amorphous SiO2 nanoparticles can be added to the NaCl and KCl system, and different numbers of SiO2 nanoparticles can be added for comparison to explore changes in the thermal properties of the composite material.
[0051] S3. Molecular dynamics simulation of NaCl-KCl-amorphous SiO2 composite molten salt material model;
[0052] Molecular dynamics simulations were conducted through thermal performance prediction studies to investigate the heat transfer coefficient, shear viscosity, and specific heat capacity of a mixture of amorphous SiO2 nanoparticles and NaKCl2 molten salt. These factors are crucial for the efficient operation of energy storage devices in centralized photovoltaic power plants. Thermal performance predictions were performed to calculate the heat transfer coefficient (thermal conductivity), shear viscosity, and specific heat capacity of the NaCl-KCl-amorphous SiO2 composite molten salt.
[0053] The NaCl-KCl-amorphous SiO2 composite molten salt material model consists of molten chloride salt and amorphous SiO2 nanoparticles.
[0054] The chloride molten salt base ions are added to the simulation box by molecular templates of Na, K, and Cl. The interaction between the ions in the chloride molten salt is represented by the Fumi-Tosi potential function, which is specifically expressed as follows:
[0055]
[0056] in, is the electrostatic potential energy term, which represents the Coulomb electrostatic interaction between the two ions; q i q j represents the charge of the two ions; r ij represents the distance between two ions; is the exponential repulsion term, which is used to describe the short-range repulsion between ions. ij When the value is less than σij, the exponential function increases sharply, indicating a strong repulsive force, which usually corresponds to the contact or very close situation between ions. The parameter Aij is used to adjust the strength and range of the repulsion, and σij represents the sum of the radii of the two ions. is a polynomial attraction term used to describe the long-range attraction between ions, usually corresponding to van der Waals forces or dispersion forces, represents the dipole-dipole interaction, represents the dipole-quadrupole interaction. The parameters of the Fumi-Tosi potential function for the NaCl-KCl binary system are shown in Table 1.
[0057] Table 1
[0058]
[0059] The energy of the amorphous SiO2 nanoparticle model includes bonding energy and non-bonding energy;
[0060] The non-bonded energy is calculated using the BKS potential function, which combines the Buckingham potential and the long-range Coulomb interaction. It is specifically expressed as follows:
[0061]
[0062] A ij , C ij Used to adjust the interaction strength and range between different atomic pairs; r ij represents the distance between atoms i and j, q i and q j represent the charges of atoms i and j respectively.
[0063] The bond energy is calculated by the following formula:
[0064] E bond =K b (R-R0) 2 +K θ (θ-θ0) 2
[0065] Among them, K b and K θ are the force constants for the bond length and bond angle terms, respectively; R and θ represent the bond length and bond angle constants, respectively. The non-bonded and bonded parameters of SiO2 are shown in Table 2.
[0066] Table 2
[0067]
[0068] The interaction between chloride salt and SiO2 is simulated using the Lennard-Jones (LJ) potential of the Coulomb term, which is expressed as follows:
[0069]
[0070] in, is the Coulomb term, which represents the Coulomb interaction between charged particles i and j, q i and q j denote the charges of charged particles i and j, rij represents the distance between charged particles i and j.
[0071] is the Lennard-Jones term, which is used to describe the van der Waals interaction between charged particles i and j, where ε ij is the depth of potential energy, indicating the strength of interaction between particles; σ ij is the diameter of the particle, which represents the distance scale between charged particles i and j; The term represents the repulsive force between particles. When r is less than σ, the term increases rapidly, indicating a strong repulsive force; The term represents the attraction between particles. When r is greater than σ, the term decreases gradually, indicating a weak attraction. The LJ potential parameters of chloride molten salt and silica are shown in Table 3.
[0072] Table 3
[0073]
[0074] The periodic boundary condition (PBC) method is used to keep the number of particles constant and eliminate obvious boundary effects. The initial velocities of the particles are randomly distributed and obey the Gaussian distribution.
[0075] The velocity Verlet method is used to solve Newton's equations of motion to obtain the trajectories of the atoms. is cut off at , while the interaction between amorphous SiO2 and the interaction between chloride salts and SiO2 is The charge values of Na, K, Cl, Si, and O atoms are +1, +1, -1, +1.91, and -0.95, respectively.
[0076] Long-range interactions were treated using the Ewald method for long-range dispersion. The simulation time step was 0.002. To make the simulation system more realistic, the simulation began with an annealing operation on the NaCl-KCl molten salt mixture. All simulations were performed in an NPT system at a pressure of 0.1 MPa and a temperature ramp rate of 2 K / ps. At each desired temperature, the system was then run in the NPT ensemble at a pressure of 0.1 MPa for 1 ns to reach equilibrium.
[0077] S4. Prediction and calculation of thermal performance parameters, including heat transfer coefficient (thermal conductivity), shear viscosity, and specific heat capacity.
[0078] The Muller-Plathe (velocity exchange) method is used to predict the heat transfer coefficient. Figure 4The entire system is divided into 20 layers along the X-axis. The temperature of the middle layer is gradually increased, while the temperature at the ends is gradually decreased. After several steps, when the energy exchange rate and the conduction rate are equal, the temperature distribution of the entire system reaches equilibrium. The temperature gradient is calculated to obtain the heat transfer coefficient data. By calculating the thermal conductivity of different SiO2 nanoparticle quantities at different temperatures, the effect of the number of SiO2 nanoparticles on the thermal conductivity can be determined, as well as the change in thermal conductivity with increasing temperature.
[0079] The Muller-Plathe method is used to predict shear viscosity. Figure 5 The entire system is divided into 20 regions along the z-direction. By exchanging the x-direction momentum components of atoms in regions 1 and 20 with those in region 11, a velocity gradient is constructed, thereby forming a shear field. This momentum exchange process is non-physical and artificially constructed. Simultaneously, the physical z-direction momentum exchange is calculated for use in the calculations. The calculated results reveal how the viscosity of the system changes with temperature and the number of SiO2 nanoparticles.
[0080] The specific heat capacity was predicted by heating the system from 1200K to 1800K, recording the temperature and total energy changes during the heating process, and performing a linear fit to obtain Then use the formula The specific heat capacity is obtained, and then the change of specific heat capacity with temperature and the number of SiO2 nanoparticles is obtained.
[0081] Based on the obtained heat transfer coefficient, shear viscosity and specific heat capacity, the thermal properties of NaCl-KCl-amorphous SiO2 composite molten salt were effectively predicted. Figure 6-8 .
[0082] Depend on Figure 6 The results show that the simulated values of the thermal conductivity of molten salt are very consistent with the experimental values in the range of 1000K-1400K, with the maximum relative error of 9.66% occurring at 1200K. This shows that the simulation method and force field type selected in this invention can be used to study the problem of heat transfer coefficient.
[0083] Depend on Figure 7 The results show that the experimental value of the specific heat capacity of the mixed molten salt is 1.0716 J / (g·K), and the simulation calculation result is 1.1282 J / (g·K). The error between the specific heat capacity of the basic molten salt and the experimental result is 5.28%.
[0084] Depend on Figure 8 The results show that as the temperature gradually increases, the degree of agreement between the simulation data and the experimental data is significantly improved, especially under the condition of 1200K, the error between the two is only 7.6%, which proves that the RNEMD method is reliable in calculating the viscosity of chloride fluids.
[0085] The present invention is not limited to the above-mentioned specific implementation methods. Various changes made by ordinary technicians in this field based on the above-mentioned concept without creative work are all within the scope of protection of the present invention.
Claims
1. A method for predicting the thermal properties of NaCl-KCl-SiO2 composite molten salt, characterized in that: The following steps are involved: S1. Establish SiO2 nanoparticle model; S2. Establish a NaCl-KCl-SiO2 composite molten salt material model; S3. Molecular dynamics simulation of NaCl-KCl-amorphous SiO2 composite molten salt material model; S4. Prediction and calculation of thermal performance parameters, including heat transfer coefficient, shear viscosity, and specific heat capacity.
2. The method for predicting thermal properties of NaCl-KCl-SiO2 composite molten salt according to claim 1, characterized in that: In step S1, the establishment of the SiO2 nanoparticle model specifically includes the following steps: using Materials Studio software to construct a single crystalline SiO2 cluster consisting of 933 atoms, and then disrupting the arrangement of SiO2 by high temperature and high pressure to achieve amorphous modeling, and exporting the obtained single amorphous SiO2 model as a data file that can be recognized by LAMMPS, cutting out a particle with a radius of Amorphous SiO2 nanoparticle model.
3. The method for predicting thermal properties of NaCl-KCl-SiO2 composite molten salt according to claim 1, characterized in that: In step S2, the NaCl-KCl-SiO2 composite molten salt material model is established, which specifically includes the following steps: first, the single The amorphous SiO2 model was added to the simulation box, and then the Na, K, and Cl molecular templates were used to generate 4222 Na ions, 4222 K ions, and 8444 Cl ions into the simulation box through the create_atoms command to create the NaCl-KCl-amorphous SiO2 composite molten salt material model.
4. The method for predicting thermal properties of NaCl-KCl-SiO2 composite molten salt according to claim 1, characterized in that: In step S3, the molecular dynamics simulation of the NaCl-KCl-amorphous SiO2 composite molten salt material model includes: The chloride molten salt ions are added to the simulation box by molecular templates of Na, K, and Cl. The interactions between the ions in the chloride molten salt are represented by the Fumi-Tosi potential function, which is specifically expressed as follows: in, is the electrostatic potential energy term, which represents the Coulomb electrostatic interaction between the two ions; q i q j represents the charge of the two ions; r ij represents the distance between two ions; is the exponential repulsion term, which is used to describe the short-range repulsion between ions. ij When the value is less than σij, the exponential function increases sharply, indicating a strong repulsive force, which usually corresponds to the contact or very close situation between ions. The parameter Aij is used to adjust the strength and range of the repulsion, and σij represents the sum of the radii of the two ions. is a polynomial attraction term used to describe the long-range attraction between ions, usually corresponding to van der Waals forces or dispersion forces, represents the dipole-dipole interaction, represents the dipole-quadrupole interaction; Simulate the energy of amorphous SiO2 nanoparticle models, including bonding energy and non-bonding energy; The non-bonded energy is calculated using the BKS potential function, which combines the Buckingham potential and the long-range Coulomb interaction. It is specifically expressed as follows: A ij , C ij Used to adjust the interaction strength and range between different atomic pairs; r ij represents the distance between atoms i and j, q i and q j represent the charges of atoms i and j respectively. The bond energy is calculated by the following formula: E bond =K b (R-R0) 2 +K θ (θ-θ0) 2 Among them, K b and K θ are the force constants for the bond length term and the bond angle term, respectively; R and θ are the bond length and bond angle constants, respectively.
5. The method for predicting thermal properties of NaCl-KCl-SiO2 composite molten salt according to claim 4, characterized in that: In step S3, the molecular dynamics simulation of the NaCl-KCl-amorphous SiO2 composite molten salt material model further includes: The interaction between chloride salt and SiO2 is simulated using the Lennard-Jones potential of the Coulomb term, which is expressed as follows: in, is the Coulomb term, which represents the Coulomb interaction between charged particles i and j, q i and q j denote the charges of charged particles i and j, r ij represents the distance between charged particles i and j; is the Lennard-Jones term, which is used to describe the van der Waals interaction between charged particles i and j, where ε ij is the depth of potential energy, indicating the strength of interaction between particles; σ ij is the diameter of the particle, which represents the distance scale between charged particles i and j; The term represents the repulsive force between particles. When r is less than σ, the term increases rapidly, indicating a strong repulsive force; The term represents the attraction between particles. When r is greater than σ, the term gradually decreases, indicating a weak attraction.
6. The method for predicting thermal properties of NaCl-KCl-SiO2 composite molten salt according to claim 1, characterized in that: In step S4, the heat transfer coefficient is predicted using the Muller-Plathe method. The entire system is divided into 20 layers along the X-axis. The temperature of the middle layer of the system is gradually increased, while the temperature at the ends is gradually decreased. After several steps, when the energy exchange rate and the conduction rate are equal, the temperature distribution of the entire system reaches equilibrium. The temperature gradient is calculated to obtain the heat transfer coefficient data.
7. The method for predicting thermal properties of NaCl-KCl-SiO2 composite molten salt according to claim 1, characterized in that: In step S4, the shear viscosity is predicted using the Muller-Plathe method. The entire system is divided into 20 regions in the z direction. The velocity gradient is constructed by exchanging the momentum components of the atoms in the x direction in regions 1 and 20 with those in region 11 to form a shear field. During the exchange, the physical momentum exchange in the z direction is statistically analyzed to calculate the shear viscosity.
8. The method for predicting thermal properties of NaCl-KCl-SiO2 composite molten salt according to claim 1, characterized in that: In step S4, the specific heat capacity is predicted by heating the system from 1200K to 1800K, recording the temperature and total energy changes during the heating process, and performing a linear fit to obtain Then use the formula Get the specific heat capacity.