Simulation method for adsorption characteristics of vehicle air dryer

Abstract

The application discloses a kind of vehicle air dryer adsorption characteristic simulation method, comprising: obtaining the characteristic parameters of closed air supply system dryer: suppose that adsorbent has attractive field in a certain space away from adsorption surface, gas molecules around solid surface are immediately adsorbed once entering this attractive field, again suppose that the mass transfer between drying agent and compressed air in adsorption process is linear driving mass transfer, thereby establishing the adsorption mathematical model of drying agent material;In three-dimensional modeling software, establish the three-dimensional model of vehicle closed air supply system air dryer, divide air dryer modeling into drying agent area and non-drying agent area;The grid of air dryer three-dimensional model is divided using finite element pre-processing software;The grid model of air dryer is imported into CFD analysis software, simulation is carried out, and the simulation calculation result of air dryer adsorption characteristic is obtained.The application solves the problem that the influence of air dryer on water vapor adsorption is not considered.

Description

Technical Field

[0001] This invention belongs to the field of automotive air dryer optimization design, and specifically relates to a simulation method for the adsorption characteristics of automotive air dryers. Background Technology

[0002] Air suspension is widely used in the automotive industry due to its excellent performance. Currently, passenger cars at home and abroad generally use a closed air supply system to provide compressed air for the air suspension. If an air dryer is not installed, the dryness of the compressed air will not meet the requirements, which can easily lead to water accumulation in the pipelines and air tanks. This can cause the pipelines and air tanks to rust or freeze, and rust particles and impurities can adhere to the valves, causing air leaks. This affects the normal operation of the system pipeline valves and can also enter the air springs and air tanks with the compressed air. The humid air corrodes the internal components of the air springs, causing the product assembly to fail prematurely, which in turn affects the vibration damping performance of the air suspension and poses many safety hazards.

[0003] Currently, closed-loop air supply systems primarily use air dryers to dry compressed air. An air dryer generally consists of a dryer shell, a desiccant, and components for securing the desiccant. When the closed-loop air supply system detects that the pressure in the air tank is too low, it automatically activates the air tank filling mode. At this time, the outside air is compressed by the compressor to form high-pressure gas. The compressed air passes through the air dryer. The desiccant has pressure swing adsorption characteristics. The partial pressure of water vapor in the compressed air is greater than that in the desiccant. Therefore, the water vapor in the compressed air diffuses into the desiccant. Based on this characteristic, the desiccant in the air dryer physically dries the compressed air, thereby ensuring the cleanliness and dryness of the air in the air pipeline.

[0004] Currently, when designing air dryers, the distribution of streamlines, pressure, and velocity within the drying tank is often directly obtained by setting up a porous medium. The filtration performance of the drying tank is optimized by improving its structure, and the pressure drop of the gas passing through the tank is reduced. However, this modeling method cannot calculate the actual water vapor adsorption capacity of different air dryers, nor can it obtain the adsorption performance of different air dryers for water vapor.

[0005] The aforementioned method for testing the adsorption capacity of air dryers involves directly configuring the air dryer with a porous medium to optimize its structure. While this method is simple to operate, it fails to consider the influence of the air dryer on water vapor adsorption by directly prototyping the dryer for optimization. For practical engineering applications, this method leads to inaccurate results and hinders further structural optimization of the air dryer. Therefore, establishing a simulation model of the adsorption characteristics of automotive air dryers to calculate and analyze their adsorption performance is of great significance. Summary of the Invention

[0006] To address the problems existing in the prior art, this invention provides a simulation method for the adsorption characteristics of automotive air dryers. This method combines adsorption kinetics with the establishment of an adsorption mathematical model of the desiccant material. Then, a simulation model is established using the three-dimensional numerical model of the dryer and the adsorption mathematical model of the desiccant material. The drying performance of the automotive air dryer is analyzed through simulation.

[0007] To achieve the objective of this invention, a simulation method for the adsorption characteristics of an automotive air dryer is provided, which is implemented according to the following steps:

[0008] Obtain the characteristic parameters of the dryer in the closed air supply system:

[0009] Assuming that the adsorbent has an attractive field in a certain space away from the adsorption surface, gas molecules around the solid surface will be immediately adsorbed once they enter this attractive field. Furthermore, assuming that the mass transfer between the desiccant and compressed air during the adsorption process is linear driven mass transfer, a mathematical model of the adsorption of the desiccant material is established.

[0010] A 3D model of an air dryer for a closed-loop air supply system in a vehicle is created using 3D modeling software. In this system, air is compressed by a compressor and then enters the dryer through the air drying inlet. After being evenly distributed by an air orifice plate distributor, the compressed gas enters the porous desiccant region, which is filled with isotropic spherical molecular sieve desiccant. Therefore, the air dryer model is divided into a desiccant region and a non-desiccant region, and the 3D model is imported into finite element preprocessing software.

[0011] The 3D model of the air dryer was meshed using finite element preprocessing software.

[0012] The mesh model of the air dryer was imported into CFD analysis software for simulation, and the simulation calculation results of the adsorption characteristics of the air dryer were obtained.

[0013] Furthermore, the steps for obtaining the characteristic parameters include: conducting drying tests on the dryer under various operating conditions and storage tank filling modes using an air dryer test bench in a constant temperature and humidity environment, and recording the dryer inlet pressure P under different operating conditions. in Export pressure P out And the inlet flow rate v, and then the dryer inlet pressure P under different operating conditions obtained by bench testing. in Export pressure P out Based on the inlet velocity v, the viscous drag coefficient 1 / α and the inertial drag coefficient C2 of the compressed air passing through the desiccant region are obtained according to the momentum loss equation.

[0014] Furthermore, the momentum loss equation is as follows:

[0015]

[0016] In the formula: μ is the dynamic viscosity; 1 / α is the viscous resistance coefficient; C2 is the inertial resistance coefficient; Δn is the length of the desiccant region.

[0017] Furthermore, the steps for establishing the adsorption mathematical model of the desiccant material include:

[0018] Assuming the adsorbent possesses an attractive field in a certain space away from the adsorption surface, gas molecules surrounding the solid surface are immediately adsorbed once they enter this attractive field. The adsorption equilibrium model equation for the desiccant material is established as follows:

[0019]

[0020] In the formula, q m The equilibrium adsorption amount is M; the molar mass of water vapor is ρ. ad T is the density of water vapor; c p is the critical temperature of water vapor. c T is the critical pressure of water vapor; e The temperature at equilibrium; p i ρ is the partial pressure of water vapor; a, b, and c are the adsorption constants;

[0021] Assuming that the mass transfer between the desiccant and compressed air during adsorption is linearly driven, a mathematical model for the adsorption of the desiccant material is established:

[0022] q n =q n-1 +k(q m -q n-1 )(t n -t n-1 )

[0023] In the formula, q n q represents the actual adsorption amount. n-1 The actual adsorption amount in the previous step; k is the mass transfer coefficient; t n , t n-1 These represent the current time and the previous time, respectively.

[0024] Write a user-defined function program based on a mathematical model of desiccant adsorption using a general-purpose computer programming language.

[0025] Furthermore, to ensure computational accuracy and improve computational efficiency, hexahedral meshes were used to mesh the desiccant region, and tetrahedral meshes were used to mesh the non-desiccant region, with the mesh size controlled within 3 mm.

[0026] Furthermore, the mesh model of the air dryer is imported into CFD analysis software for simulation to obtain the simulation calculation results of the air dryer's adsorption characteristics, including the following steps:

[0027] Import the air dryer mesh model into the CFD analysis software. Use the user-defined function in the CFD software to load the user-defined function program compiled with a general-purpose computer programming language and set the user-defined scalar source terms. Select the pressure-based solver as the solution type and set the time to transient.

[0028] Set up the model module, enable the energy equation, select the feasible k-ε turbulence model for the turbulence model, and select the component transport model for the component model. When setting up the material, the material type is mixed fluid, the mixed fluid components are water vapor and air, the density type is ideal gas, and the specific heat type is the default mixing law.

[0029] The computational domain properties and boundary conditions modules are set up. The porous media model is selected for the computational domain properties of the desiccant region. The viscous drag coefficient 1 / α and inertial drag coefficient C2 of air passing through the desiccant region are set. The porosity ε of the desiccant region is set. The desiccant material properties are set. The particle density, specific heat and thermal conductivity of the adsorbent are set according to the adsorbent physical property parameters. According to the compilation of the user-defined function, the computational source terms of the desiccant region are matched one-to-one with the user-defined function macro. The boundary condition types are selected as flow inlet and pressure outlet. The inlet flow rate and outlet pressure are set according to the operating conditions of the closed air supply system to be simulated.

[0030] Set the simulation parameters, start the simulation, and obtain the simulation calculation results of the adsorption characteristics of the vehicle closed air supply system.

[0031] Furthermore, the simulation parameter settings include setting the simulation time, setting the simulation step size, and initialization assignment.

[0032] Compared with the prior art, the present invention has at least the following advantages:

[0033] (1) The simulation method of the present invention is based on the porous media model in CFD software. By solving the custom programming equation, a gas-solid two-phase adsorption model of the dryer of the vehicle closed air supply system is established, which solves the problem of not considering the influence of the air dryer on water vapor adsorption and can realize the visualization adjustment in the simulation process.

[0034] (2) The method of the present invention can be used to model different dryer inlet layout schemes, and simulation analysis of the model can guide the design of dryer inlet layout schemes.

[0035] (3) This invention improves the original modeling method by establishing a gas-solid two-phase adsorption model for the dryer and adding the adsorption relationship between water vapor and desiccant in the porous medium model. This allows for the calculation of the actual adsorption amount of water vapor by the air dryer, thereby obtaining the adsorption performance of the air dryer for water vapor. When simulating different air dryers, adjustments can be made to the gas-solid two-phase adsorption model to obtain the actual adsorption amount of water vapor by different air dryers, thus obtaining the adsorption performance of different air dryers for water vapor. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of a dryer for a closed-loop air supply system in a vehicle.

[0037] The markings on the map are: 1. Non-desiccant area, 2. Desiccant area, 3. Exit, 4. Inlet.

[0038] Figure 2 This is a schematic diagram of the piping of a test bench for a closed-loop air supply system dryer.

[0039] Figure 3 This is a grid model diagram of a dryer for a closed-loop air supply system in a vehicle.

[0040] Figure 4 This is a schematic diagram illustrating the simulation of the adsorption capacity of the dryer in a closed-loop air supply system for vehicles, provided in an embodiment of the present invention.

[0041] Figure 5 This is a simulation result diagram showing the change of adsorption capacity of the dryer in the vehicle closed air supply system over time in an embodiment of the present invention. Detailed Implementation

[0042] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0043] The present invention provides a simulation method for an automotive air dryer, comprising the following steps:

[0044] (1) Obtain the characteristic parameters of the dryer in the closed air supply system:

[0045] Under constant temperature and humidity conditions, the air dryer was tested using an air dryer test bench under various operating conditions and storage tank filling modes. The inlet pressure P of the dryer under different operating conditions was recorded. in Export pressure P out and inlet flow rate v;

[0046] The momentum loss equation for air passing through the dryer can be expressed as:

[0047]

[0048] In the formula: μ is the dynamic viscosity; 1 / α is the viscous resistance coefficient; C2 is the inertial resistance coefficient; Δn is the length of the desiccant region.

[0049] The inlet pressure P of the dryer under different operating conditions was obtained using bench tests. in Export pressure P out Given the inlet velocity v, the viscous drag coefficient 1 / α and inertial drag coefficient C2 of the compressed air passing through the desiccant region can be obtained according to the momentum loss equation.

[0050] (2) Establish an adsorption mathematical model for desiccant materials:

[0051] Assuming the adsorbent possesses an attractive field in a certain space far from the adsorption surface, gas molecules surrounding the solid surface are immediately adsorbed once they enter this attractive field. The work required to attract a unit mass of gas from an infinite boundary to a certain position around the adsorbent can be expressed by the following formula:

[0052]

[0053] Where: R is the universal gas constant; ε is the adsorption potential; P0 is the saturated vapor pressure of water vapor at temperature T; P i Let T be the equilibrium pressure at temperature T, and P be the water vapor pressure at temperature T.

[0054] The saturated vapor pressure P0 of water vapor can be expressed by the following formula:

[0055]

[0056] In the formula: T c p is the critical temperature of water vapor. c This is the critical pressure of water vapor.

[0057] Define the pores in which the gas is adsorbed in the adsorbent as the adsorption space ω:

[0058]

[0059] In the formula: q m The equilibrium adsorption amount is given; M is the molar mass of water vapor. This represents the density of water vapor.

[0060] There is a negative correlation between the adsorption potential ε and the adsorption space ω. The relationship between the adsorption potential ε and the adsorption space ω can be expressed by the following equation:

[0061] ε=a+bω c (5)

[0062] In the formula: a, b, and c are adsorption constants.

[0063] Therefore, combining equations (2) to (5), the adsorption equilibrium model equation for the desiccant material can be obtained as follows:

[0064]

[0065] In the formula: T e The temperature at equilibrium; p i This is the partial pressure of water vapor.

[0066] When air passes through an air dryer, assuming the mass transfer between the desiccant and compressed air during adsorption is linearly driven, the actual amount of water vapor adsorbed when air passes through the air dryer can be calculated using the following formula:

[0067] q n =q n-1 +k(q m -q n-1 )(t n -t n-1 (7)

[0068] In the formula: q n q represents the actual adsorption amount. n-1 The actual adsorption amount in the previous step; k is the mass transfer coefficient; t n , t n-1 These represent the current time and the previous time, respectively.

[0069] Write a user-defined function program based on a mathematical model of desiccant adsorption using a general-purpose computer programming language.

[0070] (3) A 3D model of the air dryer in a closed-loop air supply system for vehicles was created in 3D modeling software. In the closed-loop air supply system, air is compressed into compressed air by a compressor, and then the compressed gas enters the dryer through the air drying inlet. After being evenly distributed by the air orifice plate distributor, it enters the porous media area of ​​the desiccant relatively uniformly. This area is filled with isotropic spherical molecular sieve desiccant. Therefore, the air dryer model is divided into a desiccant area and a non-desiccant area, and the 3D model of the air dryer is imported into the finite element preprocessing software.

[0071] (4) Use finite element preprocessing software to mesh the three-dimensional model of the air dryer.

[0072] In some embodiments of the present invention, to ensure computational accuracy and improve computational efficiency, hexahedral meshes are used to mesh the desiccant region, and tetrahedral meshes are used to mesh the non-desiccant region. The mesh size is controlled within 3 mm. The mesh model of the dryer in a vehicle closed-loop air supply system is shown below. Figure 1 As shown.

[0073] (5) Import the air dryer mesh model into the CFD analysis software, perform simulation, and obtain the simulation calculation results of the air dryer adsorption characteristics.

[0074] Step 5.1: Load the user-defined function program compiled with a general-purpose computer programming language through the user-defined function in the CFD software, set the user-defined scalar source term, select the pressure-based solver as the solution type, and set the time to transient.

[0075] Step 5.2: Set up the model module, enable the energy equation, select the feasible k-ε turbulence model for the turbulence model, and select the component transport model for the component model. When setting the material, the material type is mixed fluid, and water vapor and air are selected in the mixed fluid components. The density type is selected as ideal gas, and the specific heat type is the default mixing law.

[0076] Step 5.3: Set the computational domain attributes and boundary conditions module. Select the porous media model for the computational domain attributes of the desiccant region. Set the viscous drag coefficient 1 / α and inertial drag coefficient C2 for air passing through the desiccant region. Set the porosity ε of the desiccant region. Set the desiccant material properties. Set the adsorbent particle density, specific heat and thermal conductivity according to the adsorbent physical property parameters. According to the compilation of the user-defined function, match the computational source terms of the desiccant region with the user-defined function macro one by one. Select the flow inlet and pressure outlet for the boundary conditions. Set the inlet flow rate and outlet pressure according to the operating conditions of the closed air supply system to be simulated.

[0077] Step 5.4: Set the simulation parameters and start the simulation to obtain the simulation calculation results of the adsorption characteristics of the vehicle closed air supply system.

[0078] In some embodiments of the present invention, the calculation method is set to SIMPLE, the time step is 0.001s, the time step is set according to the running time, the model is initialized, the water vapor mass fraction is assigned an initial value according to the air humidity, the calculation is submitted to start the simulation, and after the simulation is completed, the simulation calculation results of the air dryer adsorption characteristics are read in the post-processing software.

[0079] In some embodiments of the present invention, the simulation calculation results obtained are as follows: Figure 5 As shown, Figure 5The relationship between the adsorption capacity of the dryer and the adsorption time is shown, indicating that the established gas-solid two-phase adsorption model of the dryer can be used to estimate the actual adsorption capacity of water vapor by the air dryer.

[0080] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A simulation method for the adsorption characteristics of an automotive air dryer, characterized in that, Includes the following steps: Obtain the characteristic parameters of the dryer in the closed air supply system: Assuming that the adsorbent has an attractive field in a certain space away from the adsorption surface, gas molecules around the solid surface will be immediately adsorbed once they enter this attractive field. Furthermore, assuming that the mass transfer between the desiccant and compressed air during the adsorption process is linear driven mass transfer, a mathematical model of the adsorption of the desiccant material is established. A 3D model of the air dryer of the vehicle closed air supply system was created in 3D modeling software. The air dryer model was divided into a desiccant area and a non-desiccant area. The 3D model of the air dryer was then imported into the finite element preprocessing software. The 3D model of the air dryer was meshed using finite element preprocessing software. The mesh model of the air dryer was imported into CFD analysis software for simulation, and the simulation results of the adsorption characteristics of the air dryer were obtained. The steps for establishing the adsorption mathematical model of the desiccant material include: Assuming the adsorbent possesses an attractive field in a certain space far from the adsorption surface, the adsorption equilibrium model equation for the desiccant material is obtained. This adsorption equilibrium model equation is: In the formula, To balance the adsorption amount; The molar mass of water vapor; The density is the water vapor density. This is the critical temperature for water vapor; This is the critical pressure of water vapor; The temperature at equilibrium; It is the partial pressure of water vapor; The adsorption constant is denoted by . Assuming linear mass transfer, the adsorption mathematical model of the desiccant is obtained: In the formula, This represents the actual adsorption amount. This represents the actual adsorption amount in the previous step. The mass transfer coefficient; , These represent the current time and the previous time, respectively.

2. The simulation method for the adsorption characteristics of an automotive air dryer according to claim 1, characterized in that, The steps to obtain the characteristic parameters include: conducting drying tests on the dryer under various operating conditions and storage tank filling modes using an air dryer test bench in a constant temperature and humidity environment, and recording the inlet pressure of the dryer under different operating conditions. Export pressure and inlet flow rate And by combining the momentum loss equation, the viscous drag coefficient 1 / of compressed air passing through the desiccant region is obtained. and inertial drag coefficient .

3. The simulation method for the adsorption characteristics of an automotive air dryer according to claim 2, characterized in that, The momentum loss equation is as follows: In the formula: Dynamic viscosity; 1 / It is the viscous drag coefficient; This is the inertial drag coefficient; The length of the desiccant region; The real-time inlet pressure of the dryer was obtained through testing. Export pressure and inlet flow rate Based on the momentum loss equation, the viscous resistance coefficient 1 / inlet and outlet of the dryer is determined. and inertial drag coefficient .

4. The simulation method for the adsorption characteristics of an automotive air dryer according to claim 1, characterized in that, Write a user-defined function program based on a mathematical model of desiccant adsorption using a general-purpose computer programming language.

5. The simulation method for the adsorption characteristics of an automotive air dryer according to claim 1, characterized in that, When performing mesh generation, hexahedral meshes are used to mesh the desiccant region, and tetrahedral meshes are used to mesh the non-desiccant region.

6. A simulation method for the adsorption characteristics of an automotive air dryer according to any one of claims 1-5, characterized in that, The mesh model of the air dryer is imported into CFD analysis software for simulation to obtain simulation results of the air dryer's adsorption characteristics, including the following steps: Import the mesh model of the air dryer into the CFD analysis software and set the solution type and time. Configure the model module, enable the energy equation, and determine the turbulence model, composition model, material type, density type, and specific heat type; The module for setting computational domain attributes and boundary conditions; Set the simulation parameters, start the simulation, and obtain the simulation results of the adsorption characteristics of the vehicle closed air supply system.

7. The simulation method for the adsorption characteristics of an automotive air dryer according to claim 6, characterized in that, Turbulence Model Selection For the turbulence model, select the component transport model. When setting the material, select the mixed fluid type, water vapor and air as the mixed fluid components, select ideal gas as the density type, and use the default mixing law as the specific heat type.

8. The simulation method for the adsorption characteristics of an automotive air dryer according to claim 6, characterized in that, The computational domain property for the desiccant region is selected as a porous media model, and the viscous resistance coefficient of air passing through the desiccant region is set to 1 / and inertial drag coefficient Set the porosity of the desiccant region ε Set the desiccant material properties, and set the adsorbent particle density, specific heat and thermal conductivity according to the adsorbent physical property parameters. According to the compilation of the user-defined function, match the desiccant region calculation source terms with the macros of the user-defined function one by one. Select the flow inlet and pressure outlet as the boundary condition types, and set the inlet flow rate and outlet pressure according to the operating conditions of the closed air supply system to be simulated.

9. The simulation method for the adsorption characteristics of an automotive air dryer according to claim 6, characterized in that, Simulation parameter settings include setting the simulation time, setting the simulation step size, and initialization assignment.

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