Low-temperature carbonization furnace tow heating process three-dimensional simulation method based on OVERSET model
Technical Field
The invention relates to the technical field of design analysis methods of low-temperature carbonization furnaces used in the production process of carbon fibers.
Background
In the production process of carbon fiber production, a low-temperature carbonization furnace working in an environment of 300-1000 ℃ for a long time is one of key equipment, and mainly comprises a frame body (furnace shell), a heat insulation material, a stainless steel muffle, a muffle counterweight device, a heating element, a sensing element, an inlet nitrogen seal, an outlet cooling water tank, an outlet nitrogen seal, a muffle internal gas detection device, a high-purity nitrogen pipeline system, an electric appliance temperature control system and the like. Through development and development in the last forty years, although the carbon fibers in China have prepared products with the level similar to that of foreign T300-grade carbon fibers, the annual yield and the product performance of the carbon fibers still can not meet the requirements of domestic markets for the carbon fibers. Compared with the international advanced carbon fiber product technical level, the main problems of the domestic carbon fiber are obviously reflected in the poor uniformity and stability of the carbon fiber, and the main reasons are that the carbon fiber process is limited abroad, and the other important influencing factor is that the main production equipment in the carbon fiber production process lags behind abroad. If the current passive situation needs to be changed, the industrial safety threat is broken, the autonomous development of the carbon fiber production line equipment for realizing the localization and industrialization needs to be solved urgently, and professional researchers related to carbon fibers are also needed to continuously improve and research.
The temperature uniformity in the muffle cavity influences the production quality of carbon fibers, the quality of finished carbon fibers is generally detected, factors in the production process are difficult to control, the process cannot be continuously tracked through test equipment, and the quality of the carbon fibers cannot be guaranteed. Therefore, a reasonable design method needs to be selected, the furnace wall can reach the surface temperature meeting the specification, and the unit energy consumption is reduced. The aim of the research is to simulate the heating performance of the tows in the furnace chamber in the design process so as to judge whether the temperature of the surfaces of the tows meets the requirements of the production process, thereby optimally designing the structure of the furnace body and reducing the manufacturing cost of the low-temperature carbonization furnace on the premise of not reducing the existing heating effect.
Disclosure of Invention
In conclusion, the invention aims to reduce the experimental cost of furnace body structure design, provide theoretical support for reducing the energy consumption of carbon fiber production, and provide a basis for related numerical simulation research.
The technical scheme adopted for realizing the purpose of the invention is as follows:
a three-dimensional simulation method for a low-temperature carbonization furnace tow heating process based on an OVERSET model is characterized by comprising the following steps:
(1) constructing a three-dimensional mathematical model of the total flow field of the low-temperature carbonization furnace;
the three-dimensional continuity equation, the momentum equation and the energy conservation equation contained in the three-dimensional mathematical model for calculating the total flow field of the low-temperature carbonization furnace are respectively shown in formulas (1), (2) and (3):
three-dimensional continuity equation:
where ρ -fluid density; t-time; v-velocity vector, where u, V, w are the components of V in the three x, y and z directions;
the momentum equation:
wherein μ is dynamic viscosity, F b Is the volume force on the infinitesimal;
energy conservation equation:
wherein, C p Specific heat capacity, T-temperature, k-coefficient of heat transfer of the fluid, S T -a viscous dissipation term;
(2) according to the geometric parameters of the low-temperature carbonization furnace in the actual engineering, establishing a three-dimensional simulation model of a fluid calculation domain and a heated filament bundle in a muffle cavity of the low-temperature carbonization furnace by using SOLIDWORKS software, and setting related geometric parameters;
(3) respectively transmitting the fluid calculation domain established in the last step and the three-dimensional simulation model of the heated filament bundle to a Blocking module of ICEM software, and performing grid division on the fluid calculation domain and the three-dimensional simulation model of the heated filament bundle in the Blocking module in an O-Block mode; carrying out grid encryption on the position close to the surface wall surface of the filament bundle, ensuring that the number of grid layers is not less than five according to the requirement of a standard wall surface function, adopting a BiGeometric mode for a grid division strategy, setting a control ratio factor to be a default value of 1.2, ensuring that the grid quality of the whole structure is more than 0.85 according to the standard of the grid quality in ICEM software, and simultaneously defining the names of an inlet, an outlet and a wall surface boundary of a fluid calculation domain and a three-dimensional simulation model of the heated filament bundle;
(4) transmitting the fluid calculation domain divided with the grid and the three-dimensional simulation model of the heated filament bundle to a FLUENT calculation module in ANSYS software, and setting boundary conditions; the procedure for setting the FLUENT module in ANSYS software is as follows:
(4.1) introducing custom tow motion parameters compiled according to process parameters into a User Defined option, and controlling the motion state of the heated tows through UDF to realize the motion process of the tows in a low-temperature carbonization furnace;
(4.2) importing a background grid and a foreground grid which are required by calculation and are divided by ICEM software in the File option;
(4.3) in the General option, setting the y-direction probabilistic accumulation option as a preset value according to the actual situation, and setting the time option as Transient heat transfer;
(4.4) selecting an Energy Equation from the Models options, selecting a laminar model from the Viscous Models options, and introducing a Reynolds number for judging the motion state of the airflow in the furnace cavity for description, wherein the Reynolds number has a calculation formula as follows:
wherein v, rho and mu are respectively the flow velocity, density and viscosity coefficient of the fluid, and d is the characteristic length; selecting a turbulence model as a laminar model through the calculation of Reynolds number;
(4.5) selecting air and nitrogen in Materials Fluid option section; establishing physical parameters of the tows in a Materials Solid option, wherein the physical parameters comprise density, specific heat capacity and heat conductivity physical parameters;
(4.6) in the Cell Zone Conditions option, part of Fluid1 is set to nitrogen and part of Fluid2 is set to oxygen; setting Solid1 part as a tow;
(4.7) setting an inlet Boundary condition as Pressure-unlet in the Boundary Conditions option, setting the Velocity magnet as a preset value according to actual requirements, setting the Thermal option as UDF tm-unlet, setting an outlet Boundary condition as Pressure-outlet, setting one side wall surface as a convection heat exchange surface, defining a comprehensive temperature value of furnace wall air in each hour by UDF, setting a convection heat exchange coefficient as a preset value according to actual requirements, setting other wall surfaces as heat insulation wall surfaces, and setting a contact surface between the filament bundle and gas as Coupled;
(4.8) creating an interaction Interface in an Overset Interface option, selecting a Background grid in Background Zones option, selecting a foreground grid in Component Zones, and preprocessing an Overset model in calculation, wherein the preprocessing comprises point searching, hole digging and interpolation relation establishment;
(4.9) after selecting the Check Case, calculating based on the three-dimensional mathematical model of the low-temperature carbonization furnace full flow field in the step (1), and setting the calculation time according to parameters in actual engineering;
(5) transmitting the result obtained by the simulation operation to POST-processing software CFD-POST to realize the visualization of physical parameters in the heating process of the tows in the carbonization furnace;
(6) and under the same setting condition, setting different working temperatures and different tow movement speeds and repeating the steps (2) to (5) to perform multiple times of simulation calculation, judging the distribution state of the surface temperature of the tows at different furnace chamber temperatures and tow movement speeds, and predicting the heating performance of the furnace chamber on the tows, so that the distribution state is used as a basis for designing the muffle cavity structure and the operation process parameters of the low-temperature carbonization furnace.
The related parameters set according to the low-temperature carbonization furnace in the actual engineering in the step (2) comprise: the geometrical shape and the geometrical size of the muffle cavity, the geometrical shape and the geometrical size of the inlet and outlet seal, the inlet size of the inlet and outlet seal nitrogen gas pipe, the size of the outlet of the nitrogen gas pipe, and the geometrical shape and the geometrical size of the tows.
And (3) defining the boundary names of the inlet, the outlet and the wall surfaces of the three-dimensional simulation model in the step (3) to comprise the boundary names of the tow wall surface, the inlet and the outlet of the furnace chamber and the wall surface of the furnace chamber.
In the step (4), the central point of the three-dimensional simulation model of the fluid calculation domain is selected as a detection surface, the detection surface is an X-direction plane passing through the central point, the tow surface is selected as a detection surface, and the detection surface is an X-direction plane passing through the central point.
The simulation result in the step (5) comprises: and (3) detecting a temperature change cloud picture of the surface, and realizing visualization of a temperature field in a furnace cavity and a temperature field on the surface of the tows in the heating process of the tows by using POST-processing software CFD-POST.
The invention has the beneficial effects that: the invention is based on the flow field numerical calculation method, the heating capacity research is carried out on the surface temperature field characteristics of the filament bundle in the hearth under different production process conditions, the defects of the prior art at the design stage of the low-temperature carbonization furnace are overcome, and compared with the prior art, the invention has the following advantages:
(1) the calculation result is close to the actual result by introducing the moving state of the tows in the low-temperature carbonization furnace in CFD calculation software.
(2) Regarding the problem of heating performance of the tow in the low-temperature carbonization furnace, the conventional method is to measure the performance of the heated tow. The invention creatively utilizes the OVERSET model to simulate the movement state of the tows, and judges the heating capacity of the hearth through the cloud chart of the surface temperature change of the tows, thereby being capable of better measuring the structural design.
(3) The temperature distribution characteristics of the surface of the filament bundle at any moment in the process of moving in the low-temperature carbonization furnace can be intuitively and dynamically calculated.
(4) The method can be further used for researching the heating performance of the low-temperature carbonization furnace on the tows, thereby providing a reference for the design of the low-temperature carbonization furnace.
Drawings
FIG. 1 is a schematic diagram of a three-dimensional simulation model established in the simulation method of the present invention.
Fig. 2 is a flow chart of the implementation of the OVERSET model in numerical calculations.
FIG. 3 is a schematic representation of the temperature profile of the tow during heating in the furnace chamber at any point in the present invention.
FIG. 4 is a schematic representation of the temperature profile of the surface of the tow of the present invention.
Fig. 5 is a schematic view showing the temperature distribution in the cavity of the furnace according to the present invention.
Detailed Description
The structure of the present invention will be further described with reference to the accompanying drawings and preferred embodiments of the present invention.
The invention discloses a three-dimensional simulation method for a low-temperature carbonization furnace filament bundle heating process based on an OVERSET model, which comprises the following steps:
(1) constructing a three-dimensional mathematical model of the total flow field of the low-temperature carbonization furnace, and providing a theoretical basis for subsequent simulation calculation;
the three-dimensional continuity equation, the momentum equation and the energy conservation equation contained in the three-dimensional mathematical model for calculating the total flow field of the low-temperature carbonization furnace are respectively shown in formulas (1), (2) and (3):
three-dimensional continuity equation:
where ρ -fluid density; t-time; v-velocity vector, where u, V, w are the components of V in the three x, y and z directions;
the momentum equation:
wherein μ is dynamic viscosity, F b Is the volume force on the infinitesimal;
energy conservation equation:
wherein, C p Specific heat capacity, T-temperature, k-coefficient of heat transfer of the fluid, S T -a viscous dissipation term.
(2) According to the geometric parameters of the low-temperature carbonization furnace in the actual engineering, a three-dimensional simulation model of a fluid calculation domain and a heated filament bundle in a muffle cavity of the low-temperature carbonization furnace is established by adopting three-dimensional aided design software SOLIDWORKS (solid-state optical simulation system), as shown in figure 1, and relevant geometric parameters are set; at least comprises the following steps: the geometrical shape and the geometrical size of the muffle cavity, the geometrical shape and the geometrical size of the inlet and outlet seal, the inlet size of the inlet and outlet seal nitrogen gas pipe, the size of the outlet of the nitrogen gas pipe, and the geometrical shape and the geometrical size of the tows.
(3) Respectively transmitting the fluid calculation domain established in the last step and the three-dimensional simulation model of the heated filament bundle to a Blocking module of ICEM software, and performing grid division on the three-dimensional simulation model in the Blocking module in an O-Block mode; carrying out grid encryption on the position close to the surface wall surface of the filament bundle, ensuring that the number of grid layers is not less than five according to the requirement of a standard wall surface function, adopting a BiGeometric mode for a grid division strategy, setting a control ratio factor to be a default value of 1.2, ensuring that the grid quality of the integral structure is more than 0.85 according to the standard of the grid quality in ICEM software, and simultaneously defining the names of a fluid calculation domain and the inlet and outlet and wall surface boundary of a heated filament bundle three-dimensional simulation model in order to facilitate the later-stage setting of calculation conditions; the method mainly comprises the names of the tow wall surface, the inlet and the outlet of the furnace chamber and the boundary of the furnace chamber wall surface.
(4) Respectively transmitting the fluid calculation domain with the divided grids and the three-dimensional simulation model of the heated filament bundle to an ANSYS FLUENT calculation module and setting boundary conditions as shown in FIG. 1; the method comprises the steps of selecting a central point of a three-dimensional simulation model of a fluid calculation domain as a detection surface, wherein the detection surface is an X-direction plane passing through the central point, selecting a tow surface as the detection surface, and the detection surface is the X-direction plane passing through the central point.
The process of setting the ANSYS FLUENT module is as follows:
(4.1) introducing custom tow motion parameters compiled according to process parameters into a User Defined option, and controlling the motion state of the heated tows through UDF to realize the motion process of the tows in a low-temperature carbonization furnace;
(4.2) importing a background grid and a foreground grid which are required by calculation and are divided by ICEM software in the File option;
(4.3) in the General option, setting the y-direction visual access option as a preset value according to the actual condition, and setting the time option as Transient heat transfer;
(4.4) selecting an Energy Equation from the Models options, selecting a laminar model from the Viscous Models options, and introducing a Reynolds number for judging the motion state of the airflow in the furnace cavity for description, wherein the Reynolds number has a calculation formula as follows:
wherein v, rho and mu are respectively the flow velocity, density and viscosity coefficient of the fluid, and d is the characteristic length; selecting a turbulence model as a laminar model through the calculation of Reynolds number;
(4.5) selecting air and nitrogen in Materials Fluid option section; establishing physical parameters of the tows in a Materials Solid option, wherein the physical parameters comprise density, specific heat capacity and thermal conductivity physical parameters;
(4.6) in the Cell Zone Conditions option, part of Fluid1 is set to nitrogen and part of Fluid2 is set to oxygen; setting Solid1 part as a tow;
(4.7) setting an inlet Boundary condition as Pressure-inlet in a Boundary Conditions option, setting a Velocity map as a preset value according to an actual requirement, setting a Thermal option as UDF tm-inlet, setting an outlet Boundary condition as Pressure-outlet, setting a side wall surface as a convection heat exchange surface, defining a comprehensive temperature value of furnace wall air in each hour by UDF, setting a convection heat exchange coefficient as a preset value according to an actual requirement, setting other wall surfaces as heat insulation wall surfaces, and setting a contact surface of a filament bundle and gas as Coupled;
(4.8) creating an interaction Interface in an Overset Interface option, selecting a Background grid in Background Zones option, selecting a foreground grid in Component Zones, and preprocessing an Overset model in calculation, wherein the preprocessing comprises point searching, hole digging and interpolation relationship establishment, and is shown in FIG. 2;
and (4.9) after selecting the Check Case, calculating based on the three-dimensional mathematical model in the step (1), and setting the calculation time according to parameters in actual engineering.
(5) Transmitting the result obtained by the simulation operation to POST-processing software CFD-POST to realize the visualization of physical parameters in the heating process of the tows in the carbonization furnace; the simulation result comprises: and (3) detecting a temperature change cloud chart of the surface, and realizing visualization of a temperature field in a furnace cavity and a temperature field on the surface of the tows in the heating process of the tows by using POST-processing software CFD-POST (computational fluid dynamics-POST) as shown in figures 4 and 5. The three-dimensional calculation result can completely meet the requirement on precision, the types of output data are various, and the output result is more visual.
(6) Under the same setting condition, different working temperatures and different tow movement speeds are set, and the steps (2) to (5) are repeated to carry out simulation calculation for multiple times, the distribution state of the surface temperature of the tows is judged when the temperatures of the furnace chambers and the tow movement speeds are different, the heating performance of the furnace chambers to the tows can be well predicted, and the distribution state is used as a basis for designing the muffle cavity structure and the operation process parameters of the low-temperature carbonization furnace.
According to the invention, the tow motion rule is defined by udf, and the change rule of tow surface temperature distribution and the heat storage capacity in the muffle furnace in different tow motion states can be obtained by modifying the air flow speed in the inlet boundary velocity-inlet. And (3) analyzing the distribution of the surface temperature of the tows, wherein the temperature of the tows gradually increases along with the length of the tows entering the furnace chamber, and the temperature of the furnace chamber is kept constant all the time.
In conclusion, the surface temperature of the tows gradually rises in the process of entering the furnace chamber, the tows are heated, the wall surface of the furnace chamber has a good heating effect, and the heat storage performance is excellent; the schematic diagram of the temperature distribution of the filament bundle in the heating process in the furnace chamber at any moment is shown in fig. 3, and the schematic diagram of the temperature distribution of the surface of the filament bundle is shown in fig. 4, which shows that the temperature of the heating process of the surface of the filament bundle is increased in a gradient manner, and the temperature distribution of the surface of the filament bundle is uniform; the schematic diagram of the temperature distribution in the furnace chamber is shown in fig. 5, which shows that the temperature distribution in the muffle chamber is uniform, and the reasonable distribution of the airflow organization in the furnace chamber is illustrated. In order to verify the simulation result, simulation is carried out for multiple times, and the experimental result is compared and analyzed to obtain the optimal scheme of the movement speed of the tows and the heat storage performance of the muffle furnace chamber.
The embodiments of the present invention are described only for the preferred embodiments of the present invention, and not for the limitation of the concept and scope of the present invention, and various modifications and improvements made to the technical solution of the present invention by those skilled in the art without departing from the design concept of the present invention shall fall into the protection scope of the present invention, and the technical content of the present invention which is claimed is fully set forth in the claims.