Design method of special-shaped cavity filter stick in heat-not-burn cigarette based on CFD (computational fluid dynamics) calculation

Abstract

The invention discloses a CFD calculation-based design method for a special-shaped cavity filter stick in a heat-not-burn cigarette, and belongs to the technical field of novel tobaccos. The filter stick is formed by compositing a supporting section, a cooling section and a filtering section. The cooling section of the filter stick is designed to be a non-traditional circular special-shaped cavity flow channel, the sectional area of the special-shaped cavity is scaled according to the length-width equal ratio, the filter stick with different opening sectional areas can be designed, and in addition, the special-shaped cavity can also present diversified torsion angles along the axis of the cigarette. According to the design method of the special-shaped cavity filter stick in the heating non-combustion cigarette, the temperature of smoke in the filter stick and the temperature of smoke at an outlet of the filter stick are obtained through CFD pretreatment, boundary condition defining, external flow field calculation domain designing and component transportation and discrete phase model building. The defects that a traditional filter stick is long in design time and high in cost are overcome, meanwhile, the cooling performance of a single filter stick of an existing heating non-combustion cigarette and the cooling performance of a proposed special-shaped cavity filter stick can be visually and quantitatively compared, and a faster and more economical method is provided for design of a novel filter stick.

Description

Technical Field

[0001] The present invention belongs to the technical field of novel tobacco, and in particular relates to a design method for a special-shaped cavity filter rod in a heat-not-burn cigarette based on CFD calculation. Background Art

[0002] Heat-not-burn (HBN) cigarettes, as a new tobacco product, use an electric heater to heat tobacco materials sufficiently to release key components without burning the tobacco. This results in significant advantages such as low temperature, excellent taste, and reduced release of harmful substances. This concept has driven the global tobacco industry to invest in research and development, striving to produce higher-quality cigarette products. Despite their impressive performance in harm reduction, HBN cigarettes still face numerous challenges, such as balancing smoke temperature reduction performance and key component retention within the filter rod. As a core component of HBN cigarettes, the structural design of the filter rod is directly related to the effectiveness of smoke temperature regulation. Traditional filter rod designs often struggle to effectively control smoke temperature at the filter rod outlet within a limited length. Furthermore, traditional temperature measurement experimental methods, which rely on trial and error and require long development cycles, lack the ability to visually reveal the temperature distribution within the filter rod, limiting our understanding of heat transfer mechanisms. Therefore, research on the design and optimization of HBN cigarette filter rods, as well as the exploration of more efficient control and temperature measurement methods, is urgently needed.

[0003] In order to optimize the filter rod structure design and reduce the smoke temperature at the outlet of the filter rod of the heat-not-burn cigarette, the researchers prepared filter rods with different structures through experimental means and conducted temperature measurement experiments on them. Chinese patent CN208211457U discloses a heat-not-burn cigarette with a filtering structure, which aims to improve the smoke temperature control and smoking taste by introducing a flow limiting plate and a spiral smoke flow channel. However, the design adopts a two-stage structure and lacks the ability to fine-tune the regulation of different temperature zones. In addition, the design of the multi-layer spiral channel increases the production cost and manufacturing difficulty, and leads to an increase in the suction resistance, affecting the user's smoking experience. Chinese patent CN109645552A discloses a heat-not-burn cigarette with a hollow and groove structure, which includes a flavor-producing section, a hollow cooling section, and a filter section. In order to effectively reduce the smoke temperature, the invention has a special-shaped structure in the center of the hollow cooling section and grooves around it. However, the large number of openings increases the difficulty of manufacturing, and the grooves around them are prone to collapse under high temperatures. At the same time, it may cause uneven airflow distribution, causing local temperatures to be too high or too low, thus affecting the taste of the smoke.

[0004] In addition to experimentally investigating the temperature of heat-not-burn cigarettes, many researchers have used simulation techniques to investigate the heat transfer process within heat-not-burn cigarettes. Chinese patent CN107677761A proposes a computational fluid dynamics model for simulating cigarette combustion, which accurately simulates the temperature field and / or substance concentration field during cigarette combustion. However, this method uses a two-dimensional geometric model and has limitations when dealing with more complex three-dimensional geometric structures. Chinese patent CN117910371A discloses a simulation method for the heat and mass transfer process of smoke released from circumferentially electrically heated cigarettes. This method addresses the unclear heat and mass transfer patterns of smoke released from heated cigarettes and provides information on the internal temperature, flow field, and smoke composition distribution during the smoke release process of circumferentially electrically heated cigarettes. However, this method primarily focuses on the temperature inside the cigarette and fails to capture critical data: smoke temperature at the filter outlet. During actual smoking, smoke temperature at the filter outlet is an important indicator for evaluating cigarette performance and directly affects the user's smoking experience and taste. Summary of the Invention

[0005] The purpose of this invention is to provide a design method for irregular-shaped cavity filter rods in heat-not-burn cigarettes based on CFD calculations. This method enables systematic and stable monitoring and analysis of the temperature distribution within the filter rod and the smoke temperature at the filter rod outlet, assessing the cooling performance of irregular-shaped cavity filter rods. This overcomes the time-consuming and costly shortcomings of traditional filter rod design, provides a reliable basis for novel filter rod design, and promotes technological innovation and development in heat-not-burn cigarettes.

[0006] The method of the present invention is implemented in a special-shaped cavity filter rod in a heat-not-burn cigarette. The special-shaped cavity filter rod is composed of a supporting section, a cooling section, and a filtering section which are coaxially abutted in sequence and wrapped by cigarette paper.

[0007] The support section is a small inner diameter cylindrical hollow channel with a specific size range, with a length controlled at 6 to 14 mm, preferably 6 mm; its inner diameter range is 4.2 to 6.2 mm, with a preferred inner diameter of 4.2 mm, so that the support section has a smaller inner diameter (i.e., the acetate fiber bundle filling volume is larger), thereby preventing a large amount of overheated smoke from flowing through the support section and causing the cigarette to deform or collapse, improving the mechanical strength of the cigarette and helping to evenly distribute the heat conducted from the heating element; the space between the hollow channel and the cigarette paper is filled with acetate fiber bundles.

[0008] The cooling section design adopts non-traditional, geometrically optimized special-shaped cavity flow channels, and the special-shaped cavity structure is designed into various shapes such as straight line, cross, and five-star. The cross-sectional area of ​​the special-shaped cavity can be designed according to the principle of proportional scaling of length and width to design filter rods with different opening cross-sectional areas. The opening cross-sectional area of ​​the special-shaped cavity can be controlled in the range of 2 to 12 mm. 2 , preferably the opening cross-sectional area is 4 to 10 mm 2By controlling the cross-sectional area of ​​the opening of the special-shaped cavity, the flow rate of the smoke in the filter rod segment can be effectively adjusted, and then the airflow resistance can be regulated to achieve the control of the smoke temperature at the filter rod outlet; in addition, the length of the special-shaped cavity ranges from 11 to 19 mm, with a preferred length of 19 mm, and the cavity is twisted along the axis of the cigarette stick at a twisting rate of 0 to 1, with a preferred twisting rate of 0 to 0.8. The twisted channel can extend the smoke flow channel without increasing the overall length of the filter rod, while increasing the contact area between the smoke and the filter rod material, enhancing heat exchange and maintaining a low suction resistance, and the twisted special-shaped cavity channel is simple to manufacture and requires less consumables.

[0009] The length of the filter section is set to 6 to 10 mm, preferably 8 mm, and the inner diameter is uniformly 7.2 mm. The interior of the filter section is filled with acetate fiber bundles with a porosity of 0.6936. The filter section is intended to intercept and reduce harmful substances from entering the respiratory system of the smoker.

[0010] To obtain the temperature distribution inside the special-shaped cavity filter rod in heat-not-burn cigarettes and the smoke temperature at the filter rod outlet, the present invention mainly relies on CFD modeling and calculation methods.

[0011] 1) Computational Domain Modeling and Meshing: The model's computational domain was refined based on actual conditions. The three-dimensional computational domain modeling included the filter rod region and the external flow field region. This region, a 2 mm cylindrical extension domain, was added to the rear end of the filter section during simulation. This region facilitated accurate measurement of the flue gas temperature 1 mm from the center of the filter rod outlet while effectively preventing flue gas backflow and ensuring the authenticity of the simulation results. Design Modeler was used to perform 3D geometric modeling of the computational domain, and Poly-Hexcore hybrid mesh generation technology was employed in FluentMeshing to achieve 3D model meshing.

[0012] In step 1), the three-dimensional model is meshed, and local size control, geometric structure description, and boundary layer thickening processing are performed on the computational domain to ensure that the filter rod mesh quality meets the Fluent solution requirements, such as the maximum inclination of the surface mesh does not exceed 0.5, the minimum orthogonal quality of the volume mesh is not less than 0.15, and the maximum aspect ratio is not higher than 30.

[0013] 2) Boundary condition setting: Connect the divided grid to the fluid mechanics simulation solver Ansys Fluent software, set the boundary conditions according to the actual situation, and dynamically set the inlet velocity to , unit is m / s; outlet pressure is set to 0 Pa; the internal surface thermal state of the cigarette is set to a constant heat flux density, and the cigarette paper wall adopts a convection heat transfer model to simulate the heat transfer process between the incoming flow and the cigarette paper under room temperature conditions, with a heat transfer coefficient of 10 W / (m 2 ·K), the thickness of cigarette paper is 0.075 mm.

[0014] 3) Model building: A component transport model and a discrete phase model are built in Ansys Fluent to describe smoke flow and the heat transfer process between the four key smoke components: glycerol, nicotine, propylene glycol, and water. The component transport model considers the effect of component enthalpy on material diffusion and activates the Diffusion energy source term so that the energy equation in the Ansys Fluent solver includes the component transport term. The discrete phase model focuses on the movement of particulate matter and the heat and mass transfer process. During the inhalation process, the smoke flows toward the filter section and condenses, and part of the smoke changes from gas to aerosol droplets. The smoke is regarded as a continuous phase and the aerosol droplets as a discrete phase. The heat and mass transfer between the continuous term and the discrete phase are considered to improve the accuracy of the simulation results.

[0015] 4) Temperature measurement and verification: The flue gas temperature measurement point at the filter rod outlet is the flue gas temperature data 1 mm from the center outlet of the filter rod. This simulation data is compared with the actual temperature measurement experiment to ensure that the simulation results truly reflect the actual puffing conditions.

[0016] Compared with the prior art, the technical effects and outstanding advantages of the present invention are:

[0017] 1. The special-shaped cavity filter rod of the present invention features a unique design of support, cooling, and filtration sections, each with distinct functions. The small inner diameter of the support section enhances the mechanical strength of the cigarette and prevents deformation caused by overheated smoke. The cooling section utilizes a geometrically optimized special-shaped cavity flow channel. By adjusting the opening cross-sectional area and twist rate, the smoke flow rate and airflow resistance within the filter rod section can be precisely adjusted, effectively controlling the smoke temperature at the filter rod outlet. The twisted channel is simple to manufacture and requires minimal consumables, enhancing heat exchange while maintaining low draw resistance. The filtration section effectively intercepts harmful substances, and the overall structural design is more scientific and reasonable, balancing smoke temperature cooling performance with the interception performance of key components.

[0018] 2. The present invention uses advanced CFD technology to improve the computational domain modeling, increase the external flow field area and the cylindrical extension domain of a specific length, and can accurately obtain the flue gas temperature 1mm at the center outlet of the filter rod and avoid flue gas blockage and backflow. Professional modeling and meshing tools are used to ensure that the mesh quality meets the solution requirements and accurately simulate the internal structure of the filter rod. By reasonably setting the boundary conditions, dynamically setting the inlet velocity according to the Canadian deep inhalation standard, and setting other parameters in combination with the actual situation, the simulation is more in line with the real situation. The constructed component transport model and discrete phase model comprehensively consider the heat and mass transfer processes of each component in the flue gas, significantly improving the accuracy of the simulation results and providing reliable data support for filter rod design.

[0019] 3. Through actual application cases, the present invention can accurately simulate the temperature distribution inside the filter rod, and the simulation results are highly consistent with the smoke temperature at the filter rod outlet measured in actual experiments, effectively verifying the accuracy of the model. By simulating special-shaped cavity filter rods with different structural parameters, the influence of the opening cross-sectional area and the twist rate on the smoke temperature is summarized. According to the specific application scenario, the manufacturing cost of the cigarette and the difficulty of the process, the appropriate configuration, opening cross-sectional area and the twist rate of the special-shaped channel can be selected for the cooling section to achieve precise control of the smoke temperature, overcome the defects of the traditional filter rod design that is time-consuming and costly, and effectively promote the innovative development of heat-not-burn cigarette technology, improving product performance and user smoking experience. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 Schematic diagram of the I-shaped cavity filter rod structure (opening cross-sectional area 4 mm 2 , distortion rate 0).

[0021] Figure 2 This is a schematic diagram of the external flow field simulation design and temperature measurement points.

[0022] Figure 3 Schematic diagram of Fluent Meshing grid division of the I-shaped cavity filter rod structure (opening cross-sectional area 4 mm 2 , distortion rate 0).

[0023] Figure 4 Temperature distribution cloud diagram inside the I-shaped cavity filter rod (opening cross-sectional area 4 mm 2 , distortion rate 0).

[0024] Figure 5 Schematic diagram of the I-shaped cavity filter rod structure (opening cross-sectional area 4 mm 2 , distortion rate 0.4).

[0025] Figure 6 Schematic diagram of the I-shaped cavity filter rod structure (opening cross-sectional area 4 mm 2 , distortion rate 0.8).

[0026] Figure 7 Schematic diagram of the cross-shaped cavity filter rod structure (opening cross-sectional area 4 mm 2 , distortion rate 0).

[0027] Figure 8 Schematic diagram of the five-star cavity filter rod structure (opening cross-sectional area 4 mm 2 , distortion rate 0).

[0028] Among them, 1-support section, 2-cooling section, 3-special-shaped cavity, 4-filtration section, 5-cigarette paper, 6-external flow field, 7-smoke temperature measurement point 1 mm from the filter rod outlet. DETAILED DESCRIPTION

[0029] In order to further understand the present invention, the following embodiments will describe the present invention in conjunction with the accompanying drawings and embodiments.

[0030] An embodiment of a method for designing a special-shaped cavity filter rod in a heat-not-burn cigarette based on CFD calculations includes the following steps:

[0031] 1) Design of a Special-Shaped Cavity Filter Rod Structure: A special-shaped cavity filter rod specifically for heat-not-burn cigarettes was designed. The rod consists of a support section, a cooling section, and a filter section, all coaxially connected and wrapped in cigarette paper. The support section consists of a cylindrical hollow channel with a small inner diameter within a specific size range to ensure structural stability. The cooling section utilizes a non-traditional, geometrically optimized, special-shaped cavity flow channel to enhance cooling. The filter section is filled with acetate tow for efficient filtration. The support section is a cylindrical hollow channel with a length ranging from 6 to 14 mm, preferably 6 mm, and an inner diameter ranging from 4.2 to 6.2 mm, preferably 4.2 mm. The space between the hollow channel and the cigarette paper is filled with acetate tow. The filter section has a length ranging from 6 to 10 mm, preferably 8 mm, and a uniform inner diameter of 7.2 mm. The filter section is filled with acetate tow with a porosity of 0.6936, as measured by CT scanning.

[0032] 2) Multi-parameter collaborative optimization of the special-shaped cavity structure: The special-shaped cavity described in step 1) is designed into different shapes, and the cavity opening is scaled proportionally according to the length and width of the cross section to produce filter rods with different opening areas. In addition, these special-shaped cavities also present different torsion angles along the axis of the cigarette; the special-shaped cavity structure is designed into various shapes such as straight line, cross, and five-star; the cross-sectional area of ​​the special-shaped channel opening ranges from 2 to 12 mm 2 , preferably the opening cross-sectional area is 4 to 10 mm 2 The irregular cavity is twisted along the central axis at a twist rate of 0 to 1, preferably 0 to 0.8; the cavity length ranges from 11 to 19 mm, preferably 19 mm; the cavity channel and the cigarette paper are filled with acetate fiber bundles.

[0033] 3) 3D Computational Domain Modeling and Meshing: Based on the actual smoking conditions and complex smoke flow characteristics of cigarettes, an external flow field was designed at the filter outlet described in step 1) to improve the CFD computational domain. 3D geometric modeling was performed using Design Modeler, and the Poly-Hexcore hybrid mesh generation technology was used in Fluent Meshing to achieve 3D model meshing. The external flow field was a 2 mm cylindrical extension domain added to the rear end of the filter during the simulation. Simulation results from this region facilitated accurate determination of smoke outlet temperature while effectively preventing smoke backflow and ensuring the reliability of the simulation results.

[0034] 4) Simulation model construction and solution: Connect the grid divided in step 3) to the fluid mechanics simulation solver Ansys Fluent software, and set precise boundary conditions, including inlet velocity, outlet pressure, wall thermal state, etc. that are dynamically adjusted according to the HCI (HCI, Health Canada intensive) smoking standard. Build a complex simulation system including component transport model and discrete phase model, and describe the smoke flow and heat transfer between the four key components of smoke, glycerin, nicotine, propylene glycol, and water in the smoke through transient simulation calculations. In the Ansys Fluent, boundary conditions are set according to actual conditions, and the inlet velocity is dynamically set to 0.0 ... , unit is m / s; outlet pressure is set to 0 Pa; the thermal state of the internal surface of the cigarette is set to a constant heat flux density; the convection heat transfer model is used on the cigarette paper wall to simulate the heat transfer process between the incoming flow and the cigarette paper at room temperature, and the heat transfer coefficient is 10 W / (m 2 K), and the cigarette paper thickness is 0.075 mm. The component transport model considers the effect of component enthalpy on material diffusion, allowing the energy equation in the Ansys Fluent solver to include component transport terms. The discrete phase model focuses on particle movement and heat and mass transfer. During the puff process, smoke flows toward the filter section and condenses, with some smoke transforming from gas into aerosol droplets. In this process, the smoke is considered the continuous phase and the aerosol droplets the discrete phase. Heat and mass transfer between the continuous and discrete phases are considered to improve the accuracy of the simulation results.

[0035] 5) Data Acquisition and Cooling Performance Evaluation: CFD calculations were performed using the numerical model established in step 4). Efficient data post-processing was performed using CFD-Post. Temperature distribution contours within various cavity filter rods at different puff times were obtained, along with flue gas temperature data at the outlet. This systematic evaluation of the filter rod's cooling performance provided a reliable basis for new filter rod design. The flue gas temperature at the filter rod outlet was measured 1 mm from the center of the filter rod outlet. This data was compared with actual temperature measurement experiments to ensure that the simulation results accurately reflected actual puffing conditions.

[0036] The following examples take a special-shaped cavity filter rod in a heat-not-burn cigarette as an example. Figure 1 As shown. The special-shaped cavity filter rod is a composite structure, with the support section, cooling section, and filtration section coaxially connected in sequence and wrapped by cigarette paper. The design parameters and functions of each section of the filter rod are as follows: the support section is a cylindrical hollow channel with a length of 6 mm and an inner diameter of 4.2 mm. The space between the hollow channel and the cigarette paper is filled with acetate fiber bundles to ensure structural stability and smooth airflow. The interior of the cooling section is designed as a straight-line special-shaped cavity with a length of 19 mm and a straight-line opening cross-sectional area of ​​4 mm.2 The cavity twist rate is 0 (i.e., no twist). The space between the hollow channel and the cigarette paper is filled with acetate tow. This design maximizes the contact area between smoke and air and optimizes the airflow path. The filter section is 8 mm long and 7.2 mm in inner diameter. The interior of the filter section is filled with acetate tow with a porosity of 0.6936, which exhibits excellent filtration performance and effectively intercepts aerosol particles in the smoke. Cigarette paper, 0.075 mm thick and 33 mm long, wraps the entire outer surface of the filter rod, securing the components and ensuring the integrity and aesthetics of the cigarette during use.

[0037] The model calculation domain is improved according to the actual situation. The three-dimensional calculation domain modeling includes the filter rod area and the external flow field area, such as Figure 2 The area shown by number 7 in the figure is a cylindrical extension domain with a length of 2 mm added at the rear end of the filter section during simulation. This area helps to accurately obtain the flue gas temperature 1 mm from the center outlet of the filter rod, while effectively avoiding flue gas blockage and backflow, ensuring the reliability of the simulation results. Design Modeler is used to perform three-dimensional geometric modeling on the complete calculation domain, and Poly-Hexcore hybrid mesh generation technology is used in Fluent Meshing. At the same time, local size control, geometric structure description and boundary layer thickening processing are performed on the calculation domain, so that the mesh quality of the filter rod meets the standard and is suitable for Fluent solution. The mesh quality indicators are as follows: the maximum skewness of the surface mesh is 0.4379, the minimum orthogonal quality of the volume mesh is 0.1977, and the maximum aspect ratio is 29.79. These indicators all meet the requirements of Fluent solution, indicating that the mesh division quality of the filter rod is good, which can ensure the accuracy and stability of the numerical simulation and realize the mesh division of the three-dimensional model, as shown in the figure. Figure 3 shown.

[0038] The divided grid is connected to the fluid dynamics simulation solver Ansys Fluent software, and the boundary conditions are set according to the actual situation. The inlet velocity is dynamically set to , unit is m / s; outlet pressure is set to 0 Pa; the internal surface thermal state of the cigarette is set to a constant heat flux density, and the cigarette paper wall adopts a convection heat transfer model to simulate the heat transfer process between the incoming flow and the cigarette paper under room temperature conditions, with a heat transfer coefficient of 10 W / (m 2 ·K), the thickness of cigarette paper is 0.075 mm.

[0039] Based on the heat transfer characteristics of smoke inside the filter rod, a component transport model and a discrete phase model were constructed in Ansys Fluent to describe smoke flow and the heat transfer between the four key smoke components: glycerol, nicotine, propylene glycol, and water. The component transport model considers the effect of component enthalpy on material diffusion and activates the Diffusion energy source term, so that the energy equation in the Ansys Fluent solver includes the component transport term. The discrete phase model focuses on the movement of particulate matter and the heat and mass transfer process. During the inhalation process, the smoke flows toward the filter section and condenses, and part of the smoke changes from gas to aerosol droplets. The smoke is regarded as the continuous phase and the aerosol droplets as the discrete phase. The heat and mass transfer between the continuous term and the discrete phase are considered to improve the accuracy of the simulation results.

[0040] According to the established numerical model, through simulation calculation, it can be obtained from Figure 4 The internal temperature distribution of the filter rod was observed. Flue gas flows along the z-axis toward the suction end, exchanging heat with the inner wall of the hollow flow channel in the cooling section and the acetate fiber bundle in the filtration section, effectively reducing the flue gas temperature at the filter rod outlet. Specifically, flue gas, with a temperature of 410.00°C, first flows through the support section, then flows into the hollow flow channel of the straight-lined cooling section, where it rapidly cools to 139.88°C. Finally, it passes through the filtration section, and its temperature further drops to 64.36°C by the time it reaches the filter rod outlet.

[0041] In addition, through post-processing, we can obtain the highest flue gas temperature (first puff) of 64.36°C at 1 mm from the center outlet of the special-shaped cavity filter rod, which is consistent with the temperature measured in the actual experiment. Therefore, the model can accurately predict the heat transfer process of flue gas in the special-shaped cavity filter rod. Through simulation, the highest flue gas temperature (first puff) at the outlet of the straight-shaped cavity filter rod is obtained, as shown in Table 1. The structure of the rest of the special-shaped cavity filter rod is as follows Figures 5 to 8 shown.

[0042] Table 1 Maximum flue gas temperature at the outlet of the straight-shaped cavity filter rod

[0043]

[0044] Simulation results reveal significant differences in the maximum flue gas temperature at the outlet of filter plugs with different straight-shaped cavities. When the torsion ratio of the hollow channel of a shaped filter plug remains constant, the larger the cross-sectional area of ​​the opening in the shaped structure, the higher the flue gas temperature at the outlet. This is because the airflow encounters less resistance when passing through a filter plug with a larger opening cross-sectional area, reducing friction between the flue gas and the inner wall of the hollow channel, thereby reducing heat loss. This weakens the cooling effect of the flue gas as it passes through the filter plug, resulting in a relatively higher flue gas temperature at the outlet. Furthermore, a larger opening area increases the total flue gas flow through the cooling section, shortening the heat exchange time between the flue gas and the filter plug's cooling material, leading to higher flue gas temperature at the outlet. When the cross-sectional area of ​​the opening in a shaped filter plug remains constant, the torsion ratio of the hollow channel in the shaped structure is positively correlated with the flue gas outlet temperature. This is because the twisted channel lengthens the flue gas flow path, allowing the flue gas to dissipate heat more efficiently within the filter plug section, thereby reducing the flue gas temperature at the outlet.

[0045] In summary, the design can be optimized according to the specific application scenario, and the manufacturing cost and process difficulty of the cigarette can be taken into consideration to select the appropriate configuration, opening cross-sectional area, and special-shaped channel torsional ratio for the cooling section, thereby achieving controllable flue gas temperature.

[0046] The present invention designs the cooling section of the filter rod as a non-traditional circular, irregularly shaped cavity flow channel. The irregularly shaped cavity cross-sectional area is scaled proportionally by length and width, allowing for the design of filter rods with varying opening cross-sectional areas. Furthermore, the irregularly shaped cavity can exhibit a variety of twist angles along the cigarette axis. By designing the structure of the irregularly shaped cavity filter rod and performing multi-parameter collaborative optimization, the present invention primarily relies on CFD modeling and calculations. Through CFD pre-processing, boundary condition definition, external flow field calculation domain design, and model establishment, the smoke temperature inside the filter rod and at its outlet is determined. Utilizing advanced CFD simulation technology, the simulation allows for systematic, stable, and real-time monitoring and analysis of the temperature distribution inside the filter rod and the smoke temperature at the filter rod outlet, as well as evaluation of the cooling performance of various irregularly shaped cavity filter rods. This method not only overcomes the time-consuming and costly drawbacks of traditional filter rod design but also provides a visual and quantitative comparison of the cooling performance of existing single filter rods for heat-not-burn cigarettes with the proposed irregularly shaped cavity filter rod. This method provides a faster, more economical method and more reliable results for the design of new filter rods, contributing to the continued innovation and development of heat-not-burn cigarette technology.

[0047] The above embodiments are only preferred embodiments of the present invention and should not be considered to limit the scope of the present invention. All equivalent changes and improvements made within the scope of the present invention should still fall within the scope of the patent of the present invention.

Claims

1. A design method for a special-shaped cavity filter rod in a heat-not-burn cigarette based on CFD calculation, characterized in that The following steps are involved: 1) Design of special-shaped cavity filter rod structure: Design a special-shaped cavity filter rod specially used for heat-not-burn cigarettes. The filter rod consists of a support section, a cooling section, and a filtering section which are coaxially connected in sequence and wrapped by cigarette paper. The support section is a small inner diameter cylindrical hollow channel with a specific size range, which is used to maintain the stability of the filter rod structure. The cooling section adopts a non-traditional, geometrically optimized special-shaped cavity flow channel to enhance the cooling effect. The interior of the filtering section is filled with acetate fiber bundles to achieve efficient filtration of smoke. 2) Multi-parameter collaborative optimization of the special-shaped cavity structure: the special-shaped cavity described in step 1) is designed into different shapes, and the cavity opening is scaled in proportion to the length and width of the cross section to manufacture filter rods with different opening areas; at the same time, the special-shaped cavity is made to present different torsion angles along the axis of the cigarette stick; 3) Three-dimensional computational domain modeling and meshing: According to the actual working conditions of cigarette smoking and the complex smoke flow characteristics, the external flow field is designed at the outlet of the filter section in step 1) to improve the CFD computational domain; the Design Modeler software is used for three-dimensional geometric modeling, and the Poly-Hexcore hybrid mesh generation technology is used in Fluent Meshing to realize the meshing of the three-dimensional model; 4) Simulation model construction and solution: Connect the grid divided in step 3) to the fluid dynamics simulation solver AnsysFluent software, set precise boundary conditions, including the inlet velocity, outlet pressure, and wall thermal state dynamically adjusted according to the HCI suction standard; build a complex simulation system including component transport model and discrete phase model, and describe the smoke flow and heat transfer between the four key components of smoke, glycerin, nicotine, propylene glycol, and water, through transient simulation calculation; 5) Data acquisition and cooling performance evaluation: CFD calculations are performed using the numerical model established in step 4), and CFD-Post is used for data post-processing to obtain temperature distribution cloud maps inside various special-shaped cavity filter rods at different suction times and smoke temperature data at the outlet, thereby systematically evaluating the cooling performance of the filter rods and providing a reliable basis for the design of new filter rods.

2. A method for designing a special-shaped cavity filter rod in a heat-not-burn cigarette based on CFD calculation as claimed in claim 1, characterized in that In step 1), the support section is a cylindrical hollow channel with a length ranging from 6 to 14 mm, preferably 6 mm; an inner diameter ranging from 4.2 to 6.2 mm, preferably 4.2 mm; and the space between the hollow channel and the cigarette paper is filled with acetate fiber bundles.

3. A method for designing a special-shaped cavity filter rod in a heat-not-burn cigarette based on CFD calculation as claimed in claim 1, characterized in that In step 1), the length of the filter section ranges from 6 to 10 mm, preferably 8 mm; the inner diameter is uniformly 7.2 mm, and the porosity of the filter section is filled The porosity of acetate tow is 0.6936, which is measured based on CT scanning.

4. A method for designing a special-shaped cavity filter rod in a heat-not-burn cigarette based on CFD calculation as claimed in claim 1, characterized in that In step 2), the special-shaped cavity structure is designed into a straight line, a cross, or a five-star shape; the cross-sectional area of ​​the special-shaped channel opening ranges from 2 to 12 mm 2 The special-shaped cavity is twisted along the central axis at a twisting rate of 0 to 1, and the cavity length ranges from 11 to 19 mm; the cavity channel and the cigarette paper are filled with acetate fiber bundles.

5. A method for designing a special-shaped cavity filter rod in a heat-not-burn cigarette based on CFD calculation as claimed in claim 4, characterized in that In step 2), the cross-sectional area of ​​the opening of the special-shaped channel is preferably 4 to 10 mm 2 ; The special-shaped cavity is twisted along the central axis at a twisting rate of 0 to 0.8; the cavity length is 19 mm.

6. A method for designing a special-shaped cavity filter rod in a heat-not-burn cigarette based on CFD calculation as claimed in claim 1, characterized in that In step 3), the external flow field is a cylindrical extension domain with a length of 2 mm added at the rear end of the filtration section during the simulation process. The simulation results of this area help to accurately obtain the flue gas temperature at the outlet, while effectively avoiding flue gas blockage and backflow, ensuring the reliability of the simulation results.

7. A method for designing a special-shaped cavity filter rod in a heat-not-burn cigarette based on CFD calculation as claimed in claim 1, characterized in that In step 4), the boundary conditions are set in the Ansys Fluent according to the actual situation, and the inlet velocity is dynamically set to , in m / s; the outlet pressure is set to 0 Pa; the thermal state of the internal surface of the cigarette is set to a constant heat flux density; the convection heat transfer model is used on the cigarette paper wall to simulate the heat transfer process between the incoming flow and the cigarette paper under room temperature conditions, and the heat transfer coefficient is 10 W / (m 2 ·K) The thickness of cigarette paper is 0.075 mm.

8. A method for designing a special-shaped cavity filter rod in a heat-not-burn cigarette based on CFD calculation as claimed in claim 1, characterized in that The component transport model described in step 4) considers the effect of component enthalpy on material diffusion, so that the energy equation in the Ansys Fluent solver includes component transport terms; the discrete phase model focuses on the movement of particles and the heat and mass transfer process. During the inhalation process, the smoke flows to the filter section and is accompanied by condensation. Part of the smoke changes from gas to aerosol droplets. In this process, the smoke is regarded as a continuous phase and the aerosol droplets are regarded as a discrete phase. The heat and mass transfer between the continuous term and the discrete phase are considered to improve the accuracy of the simulation results.

9. A method for designing a special-shaped cavity filter rod in a heat-not-burn cigarette based on CFD calculation as claimed in claim 1, characterized in that In step 5), the flue gas temperature at the filter rod outlet is the flue gas temperature data at 1 mm from the center outlet of the filter rod. This data is compared with the actual temperature measurement experiment to ensure that the simulation results truly reflect the actual suction conditions.

10. A special-shaped cavity filter rod designed according to the method for designing a special-shaped cavity filter rod in a heat-not-burn cigarette based on CFD calculation as claimed in any one of claims 1 to 9.

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