A Design Method of Cigarette Filter Rod with High Cooling Efficiency

Abstract

A design method for cigarette filter rods with high cooling efficiency, which relates to the design of cigarette filter rods. The relationships between the temperature, pressure and filter rod length of filter rods with different shapes are obtained through numerical simulation; based on the interpolation method, the slope of the curve of flue gas temperature changing with filter rod length is calculated to obtain the length of the high-efficiency cooling section of filter rods with different shapes, which is used as the upstream part of the multi-component filter rod; based on the upstream flue gas temperature and the target outlet temperature, the shape and length of the downstream filter rod are obtained, and the upstream and downstream are spliced to obtain a filter rod with high cooling efficiency. The CFD model of the cigarette suction process is combined with the porous medium theory and the heat transfer model between gas and solid phases, and the relationships between the pressure drop, temperature drop and filter rod length during the suction process of filter rods with different shapes are obtained through simulation calculation. Based on this relationship, filter rods with different shapes are spliced to obtain a combined filter rod with high cooling efficiency. Considering the flow and heat transfer characteristics of the upstream and downstream during the cigarette suction process, filter rods with different shapes are spliced and designed to obtain filter rods with higher cooling efficiency.

Description

Technical Field

[0001] The present invention belongs to the field of cigarette filter rod design, and particularly relates to a design method of a cigarette filter rod with high cooling efficiency. Background Art

[0002] A heat-not-burn cigarette is a new type of cigarette that heats tobacco substances through a special heating element to atomize and release the atomization medium and flavor substances in the tobacco. However, due to the limitations of the filter rod length and the ability of the phase change cooling material, the temperature of the high-temperature atomized flue gas when it enters the mouth through the filter rod is higher than the temperature of the flue gas at the outlet of a conventional combustible cigarette, resulting in a slightly burning feeling in the consumer's mouth during smoking. Therefore, it is necessary to find ways to improve the cooling efficiency of the filter rod.

[0003] Currently, there are mainly two ways to cool the flue gas: one is to develop highly efficient cooling materials; the other is to design highly efficient cooling structures. However, the toxicological analysis of these cooling materials is not yet complete, and it is impossible to determine whether they are harmful to the human body. The cooling structure uses a physical cooling method, which is a relatively safer cooling method.

[0004] To comprehensively evaluate the cooling and pressure drop of the filter rod, the definition of cooling efficiency is introduced For most cooling structures, the increase in cooling capacity will inevitably lead to an increase in suction resistance, and there is a trend that the comprehensive cooling efficiency decreases as the cooling capacity increases. That is to say, when the shape of the filter rod changes, the change range of the pressure drop is much larger than the change in temperature drop. Summary of the Invention

[0005] The purpose of the present invention is to provide a design method of a cigarette filter rod with high cooling efficiency that can reduce the pressure drop while maintaining or even reducing the temperature of the flue gas at the outlet of the filter rod by analyzing the different flow and heat transfer characteristics of the flue gas when passing through the upstream and downstream of the filter rod. This method obtains the relationship between the temperature, pressure and filter rod length of different-shaped filter rods through numerical simulation. Then, based on the interpolation method, the slope of the curve of the flue gas temperature changing with the filter rod length is calculated to obtain the length of the highly efficient cooling section of different-shaped filter rods, which is used as the upstream part of the multi-component filter rod. Finally, based on the upstream flue gas temperature and the target outlet temperature, the shape and length of the downstream filter rod are obtained, and the upstream and downstream are spliced to obtain a filter rod with high cooling efficiency.

[0006] A design method of a filter rod with high cooling efficiency includes the following steps:

[0007] 1) Establish a CFD model for cigarette smoking: Establish a cigarette geometric model with different filter rod shapes according to the actual size of the cigarette, generate a three-dimensional computational domain grid, and determine the boundary conditions during the smoking process according to the ISO smoking standard;

[0008] 2) Determine the gas flow model and gas-solid heat transfer model in the porous medium: Determine the flow and heat transfer forms of the flue gas inside the porous medium according to the flow and heat transfer characteristics of the flue gas flowing through the porous medium region during the suction process;

[0009] 3) Based on the models established in step 2), use UDF to build FLUENT and dynamically connect it to the Fluent solver to implement the special physical models and boundary conditions during the cigarette suction process, and combine them with the CFD model in step 1);

[0010] 4) According to the numerical model established in step 3), simulate and analyze the cigarette suction process, and simulate and obtain the pressure and temperature distributions during the suction process of filter rods with different shapes;

[0011] 5) Based on the temperature distribution obtained in step 4), use the interpolation method to obtain the slope of the curve of the flue gas temperature changing with the filter rod length, set the target temperature of the outlet flue gas as T, and the critical slope as k 1 , select the filter rod shape a with strong cooling ability and the filter rod shape b with low suction resistance, and use the interpolation method to obtain the high-efficiency cooling section length L of the filter rod of shape a 1 and the corresponding flue gas temperature t 1 ;

[0012] 6) Based on the temperature distribution obtained in step 4), calculate the length L required for the filter rod of shape b to reduce the flue gas temperature from t 1 to T 2 ;

[0013] 7) Splice the filter rod of shape a obtained in step 5) and the filter rod of shape b obtained in step 6), connect them with a cavity in the middle, and obtain a cigarette filter rod with high cooling efficiency.

[0014] In step 1), according to a certain actual heated cigarette product, its diameter is 7.2 mm, the total length is 46 mm, of which the tobacco leaf section is 13 mm long and the filter rod section is 33 mm long; determine the available shapes of the filter rod according to the design requirements.

[0015] In step 1), the boundary conditions during the suction process are determined according to the ISO suction standard. During the suction process, 35 mL of flue gas is inhaled in a bell-shaped curve within 2 s, and the flue gas inlet velocity v = 0.7419sin(1.5708t), and the velocity unit is m / s; the inlet flue gas temperature is 22 °C, the cigarette paper wall surface is a natural convection heat transfer wall surface, the air incoming flow temperature is 22 °C, and the convective heat transfer coefficient is 10 W / (m 2 °C).

[0016] In step 2), the flow and heat transfer forms of the flue gas inside the porous medium are determined according to the flow and heat transfer characteristics of the flue gas flowing through the porous medium region during the suction process. The flow form inside the porous medium is divided into Darcy flow and non-Darcy flow based on the magnitude of the Reynolds number. The calculation formula for the pressure drop caused by the resistance loss of the fluid flowing through the porous medium during Darcy flow is as follows:

[0017]

[0018] In the formula, represents the Darcy velocity of the flue gas, K represents the permeability of the porous medium, μ represents the viscosity of the flue gas, represents the pressure drop;

[0019] The calculation formula for the pressure drop caused by the resistance loss of the fluid flowing through the porous medium during non-Darcy flow is as follows:

[0020]

[0021] In the formula, C 1 and C 2 represent the first and second Forchheimer coefficients respectively, and ρ represents the density of the flue gas. Based on the filling rate of the filter rod acetate tow and combined with the actual flow velocity inside the porous medium at a specific moment during the suction process, the Reynolds number of the flue gas flow is calculated, and then the flue gas flow form is determined and the corresponding pressure drop is calculated

[0022] The calculation formula for the Reynolds number when the flue gas flows through the porous medium region is as follows:

[0023]

[0024] In the formula, D is the equivalent size of the filler in the porous medium region of the filter rod, v is the Darcy velocity of the flue gas, and ε is the porosity of the porous medium. When the Reynolds number Re < 5, it is Darcy flow, and when the Reynolds number Re > 5, it is non-Darcy flow. According to the ISO suction standard, the flue gas flow velocity will change with time during the suction process. Therefore, it is necessary to calculate the corresponding Reynolds number based on the flow velocity at a specific moment and judge the flow form, and then select the corresponding pressure drop calculation method;

[0025] When the high-temperature flue gas flows through the porous medium region, the heat transfer between the gas and the solid follows the local non-thermal equilibrium model. The calculation method for the heat transfer amount between the gas and the solid is as follows:

[0026] Q = hA(T f - T s )

[0027] In the formula, Q represents the heat transfer rate between the gas and the solid, h represents the convective heat transfer coefficient between the gas and the solid, T represents the temperature, and the subscripts f and s represent the gas and the solid respectively.

[0028] In step 3), the gas flow model and gas-solid heat transfer model described in step 2) cannot be implemented on the FLUENT standard interface, and are built using UDF and dynamically connected to the Fluent solver to implement the special physical models and boundary conditions during cigarette puffing.

[0029] In step 4), for the simulation of the cigarette puffing process, based on the model established in step 3), according to the velocity field, temperature field, and pressure field obtained in the FLUENT simulation, calculate the curves of the static pressure and temperature of the flue gas changing with the length of the filter rod during the cigarette puffing process with filter rods of different shapes.

[0030] In step 5), the temperature distribution includes the temperature distributions of different filter rod shapes. Use the interpolation method to obtain the slope k of the curve of the flue gas temperature changing with the length of the filter rod, and set the critical slope to k 1 , and it is considered that for a filter rod of a certain specific shape, k > k 1 The region is the high-efficiency cooling section of the filter rod of this shape, and k < k 1 The region is the low-efficiency cooling section of the filter rod of this shape; set the target temperature of the outlet flue gas to T according to the flue gas cooling requirement during the cigarette puffing process; use the interpolation method to calculate the slope k for the slope curve 1 The corresponding length L of each shape of filter rod and the flue gas temperature t when the slope is k are selected, and the filter rod shape corresponding to the temperature t within the range [T, T + Δt] is selected as shape a; use the interpolation method to calculate the filter rod length L corresponding to the temperature t for the flue gas temperature distribution curve of the shape a filter rod 1 , and the flue gas temperature at this length is t 1 ; among the remaining filter rod shapes, select the filter rod shape b with a draw resistance less than that of the shape a filter rod and an outlet flue gas temperature lower than or close to T.

[0031] In step 6), calculate the length L 1 required for the shape b filter rod to reduce the flue gas temperature from t 2 to T using the interpolation method.

[0032] In step 7), the cigarette filter rod with high cooling efficiency is made by splicing three different-shaped unit filter rods. The first section uses shape a with a length of L 1 , the second section uses a cavity filter rod with a length L 3 = 33 - L 1 - L 2 , in mm, and the third section uses shape b with a length of L 2 ; the shape a filter rod is placed upstream, the shape b filter rod is placed downstream, and they are connected by a cavity in the middle.

[0033] The present invention has the following advantages:

[0034] 1. Establish a gas flow model and a gas-solid heat transfer model for the flue gas flowing through the porous medium during the cigarette puffing process;

[0035] 2. Based on the existing filter rod shape, through simple calculations and splicing, the present invention obtains a filter rod with higher cooling capacity and lower draw resistance, which is beneficial to the independent design and development of the heating cigarette filter rod. Brief Description of the Drawings

[0036] Figure 1 is the basic shape of the filter rod.

[0037] Figure 2 is the change of the flue gas temperature with the length during the suction process of filter rods with different shapes.

[0038] Figure 3 is the change of the static pressure of the flue gas with the length during the suction process of filter rods with different shapes.

[0039] Figure 4 is the shape of the spliced filter rod. Detailed Embodiment

[0040] In order to make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the following embodiments will further illustrate the present invention in conjunction with the drawings. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. On the contrary, the present invention covers any alternatives, modifications, equivalent methods and solutions made within the spirit and scope of the present invention defined by the claims.

[0041] The embodiments of the present invention include the following steps:

[0042] Step 1: According to the geometric parameters of the actual cigarette, establish a cigarette geometric model with filter rods of different shapes, and generate a three-dimensional computational domain grid. Determine the boundary conditions during the suction process according to the ISO suction standard.

[0043] Step 2: Determine the flow and heat transfer forms of the flue gas according to the flow characteristics of the flue gas flowing through the porous medium region during the suction process. The flow form in the porous medium is divided into Darcy flow and non-Darcy flow based on the magnitude of the Reynolds number. The calculation formula for the pressure drop caused by the resistance loss of the fluid flowing through the porous medium during Darcy flow is as follows:

[0044]

[0045] In the formula, represents the Darcy velocity of the flue gas, K represents the permeability of the porous medium, μ represents the viscosity of the flue gas, represents the pressure drop.

[0046] The calculation formula for the pressure drop caused by the resistance loss of the fluid flowing through the porous medium during non-Darcy flow is as follows:

[0047]

[0048] In the formula, C 1 , C 2 represent the first and second Forchheimer coefficients respectively, and ρ represents the flue gas density.

[0049] The calculation formula for the Reynolds number when the flue gas flows through the porous medium region is as follows:

[0050]

[0051] In the formula, D is the equivalent size of the filler in the porous medium region of the filter rod, v is the Darcy velocity of the flue gas, and ε is the porosity of the porous medium. When Re < 5, it is Darcy flow, and when Re > 5, it is non-Darcy flow. According to the ISO suction standard, the flue gas flow velocity changes with time during the suction process. Therefore, it is necessary to calculate the corresponding Reynolds number based on the flow velocity at a specific moment and judge the flow pattern, and then select the corresponding pressure drop calculation method.

[0052] When the high-temperature flue gas flows through the porous medium region, the heat transfer between the gas and the solid follows the local non-thermal equilibrium model, and the calculation method for the heat transfer amount between the gas and the solid is as follows:

[0053] Q = hA(T f - T s )

[0054] In the formula, Q represents the heat transfer rate between the gas and the solid, h represents the convective heat transfer coefficient between the gas and the solid, T represents the temperature, and the subscripts f and s represent the fluid and the solid respectively.

[0055] Step 3: The gas flow model and gas-solid heat transfer model described in Step 2 cannot be implemented in the FLUENT standard interface. Use UDF to build and dynamically connect to the Fluent solver to implement the special physical models and boundary conditions during the cigarette suction process.

[0056] Step 4: Simulate and simulate the cigarette suction process to obtain the changes in the flue gas temperature and static pressure with the filter rod length.

[0057] Step 5: For the temperature distribution of different filter rod shapes, use the interpolation method to obtain the slope k of the curve of the flue gas temperature changing with the filter rod length, and set the critical slope as k 1 , and it is considered that for a specific filter rod shape, the region where k > k 1 is the high-efficiency cooling section of the filter rod of this shape, and the region where k < k 1 is the low-efficiency cooling section of the filter rod of this shape.

[0058] Set the target temperature of the outlet flue gas as T according to the flue gas cooling requirement during the cigarette suction process. Use the interpolation method to calculate the slope as k 1For each shaped filter rod, the corresponding length L and flue gas temperature t are selected. The filter rod shape corresponding to the temperature t within the range [T, T+Δt] is selected as shape a. The interpolation method is used for the flue gas temperature distribution curve of the filter rod of shape a to calculate the filter rod length L corresponding to the temperature t 1 , and the flue gas temperature at this length is t 1 . Among the remaining filter rod shapes, a filter rod shape b with a draw resistance less than that of the filter rod of shape a and an outlet flue gas temperature lower than or close to T is selected.

[0059] Step 6: Use the interpolation method for the flue gas temperature distribution of the selected filter rod of shape b to calculate the length L required for the flue gas temperature of this shape to drop from t 1 to T 2 .

[0060] Step 7: Splice different shaped filter rods. The spliced multi-element filter rod is made by splicing three different shaped filter rods. The first section uses shape a with a length of L 1 , the second section uses a cavity filter rod with a length L 3 =33-L 1 -L 2 , with the unit of mm, and the third section uses shape b with a length of L 2 .

[0061] In this embodiment, according to a certain actual heated cigarette product, its diameter is 7.2 mm and the total length is 46 mm, including a tobacco leaf section of 13 mm and a filter rod section of 33 mm. The basic shape of the filter rod is as Figure 1 shown, and a certain number and size of grooves are opened at the outer periphery of the filter rod. The specific number and size of the grooves opened on the outer periphery of different shaped filter rods are shown in Table 1. Mesh generation is performed on the cigarette geometric model with different shaped filter rods.

[0062] Table 1 Number and size of outer peripheral grooves of different filter rod shapes

[0063]

[0064] During the suction process, according to the ISO suction standard, the single puff volume is 35 mL, the puff duration is 2 s, the puff frequency is 30 s, and the puff flow rate is distributed in a bell-shaped curve. Therefore, the flue gas inlet flow velocity v = 0.7419sin(1.5708t), where t is the puff time with the unit of s and the inlet flow velocity unit is m / s.

[0065] According to the flow characteristics during the suction process, when the flue gas flows through the porous medium region, the flow is divided into Darcy flow and non-Darcy flow based on the magnitude of the Reynolds number. The calculation formula for the pressure drop of the fluid flowing through the porous medium during Darcy flow is as follows:

[0066]

[0067] Wherein:

[0068]

[0069] In the formula, represents the Darcy velocity of the flue gas, K represents the permeability of the porous medium, μ represents the viscosity of the flue gas, represents the pressure drop, D represents the characteristic size of the porous medium, ε represents the porosity of the porous medium, C represents the Kozeny-Carman constant, which is usually taken as 5. In this embodiment, the filter rod filler is made of acetate tow of 8.0 / Y28000. At this time, D = 3.41×10 -5 m, ε = 0.916

[0070] The calculation formula for the pressure drop of the fluid flowing through the porous medium in non-Darcy flow is as follows:

[0071]

[0072] In the formula, C 1 and C 2 respectively represent the first and second Forchheimer coefficients, and ρ represents the density of the flue gas.

[0073] The calculation formula for the Reynolds number when the flue gas flows through the porous medium region is as follows:

[0074]

[0075] In the formula, D is the equivalent size of the porous medium region of the filter rod, v is the Darcy velocity of the flue gas, and ε is the porosity of the porous medium. When Re < 5, it is Darcy flow, and when Re < 5, it is non-Darcy flow. According to the ISO suction standard, the flow rate will change with time during the suction process. When writing the UDF, calculate the Reynolds number according to the real-time flow rate inside the cigarette, determine whether the fluid flow in the porous medium is Darcy flow or non-Darcy flow at that moment, and then select the corresponding pressure drop calculation method to calculate the pressure drop caused by the resistance loss.

[0076] When the high-temperature flue gas flows through the porous medium region, the heat transfer between the gas and the solid follows the local non-thermal equilibrium model. The calculation method for the heat transfer amount between the gas and the solid is as follows:

[0077] Q = hA(T f - T s )

[0078] In the formula, Q represents the heat transfer rate between the gas and the solid, h represents the convective heat transfer coefficient between the gas and the solid, T represents the temperature, and the subscripts f and s represent the gas and the solid respectively. In this embodiment,

[0079] User-Defined Function (UDF) is a C program written by users, which establishes a dynamic link with Fluent to meet special simulation requirements such as physical models, boundary conditions, source terms, reaction rates, and material properties that cannot be satisfied by the Fluent standard setting panel. Based on the above models and related parameters, the corresponding UDF is written to implement the cigarette suction process and simulate the flow and heat transfer of the smoke during the suction process.

[0080] The simulation calculations obtained the variations of the temperature and pressure of the smoke in different-shaped filter rods with the length of the filter rod, as shown in Figure 2 and 3 respectively.

[0081] Calculate Figure 2 the slope of the temperature distribution curve in 1 , set the critical slope k

[0082] Table 2 The lengths and smoke temperatures corresponding to each shaped filter rod when the critical slope is -1.0

[0083]

[0084] According to the smoke cooling requirement, in this embodiment, the target temperature of the outlet smoke is set to 50 °C. It can be seen from Table 2 that the smoke temperatures of Shape 1 and Shape 8 are in the range of [50, 60]. Select Shape 1 as the upstream filter rod, and the corresponding length of the high-efficiency cooling section is 14.35 mm, and the smoke temperature is 57.80 °C. Among the other shapes, the filter rod shapes with a draw resistance less than that of Shape 1 and an outlet smoke temperature lower than 50 °C or close to 50 °C are Shape 5, Shape 8, and Shape 9. In this embodiment, Shape 8 is selected as the downstream filter rod shape.

[0085] Interpolate the temperature distribution curve corresponding to Shape 8 in Figure 2 to obtain the length of the filter rod required for this shape to reduce the smoke temperature from 57.8 °C to 50 °C, which is 7.39 mm. The variation of the static pressure of the smoke with the length during the suction process of different-shaped filter rods is shown in Figure 3 .

[0086] Join Shape 1 and Shape 8 together. The spliced multi-element filter rod consists of three section unit filter rods. The first section uses Shape 1 with a length of 14.35 mm, and the third section uses Shape 8 with a length of 7.39 mm. To make the total length of the filter rod 33 mm, the second section uses a cavity filter rod with a length of 11.26 mm. The spliced filter rod is shown in Figure 4 as follows.

[0087] The present invention combines the CFD model of the cigarette smoking process with the porous media theory and the gas-solid two-phase heat transfer model, and simulates and calculates the relationship between the pressure drop, temperature drop and filter rod length during the smoking process of filter rods of different shapes. Based on this relationship, filter rods of different shapes are spliced ​​to obtain a combined filter rod with high cooling efficiency. The cooling efficiency refers to the ratio between the temperature drop of the smoke flow filter rod and the product of the pressure difference and the filter rod length. The present invention can comprehensively consider the flow heat transfer characteristics of the upstream and downstream during the cigarette smoking process, and splice filter rods of different shapes to obtain filter rods with higher cooling efficiency.

Claims

1. A design method for cigarette filter rods with high cooling efficiency, characterized in that it includes the following steps: 1) Establish a CFD model for cigarette puffing: According to the dimensions of actual cigarettes, establish a cigarette geometric model with different filter rod shapes, generate a three-dimensional computational domain grid, and determine the boundary conditions during the puffing process according to the ISO puffing standard; 2) Determine the gas flow model and gas-solid heat transfer model in the porous medium: Determine the flow and heat transfer forms of the flue gas inside the porous medium according to the flow and heat transfer characteristics of the flue gas flowing through the porous medium region during the puffing process; The flow and heat transfer forms of the flue gas inside the porous medium are determined according to the flow and heat transfer characteristics of the flue gas flowing through the porous medium region during the puffing process. The flow form inside the porous medium is divided into Darcy flow and non-Darcy flow based on the magnitude of the Reynolds number; The calculation formula for the pressure drop caused by the resistance loss of the fluid flowing through the porous medium during Darcy flow is as follows: In the formula, represents the Darcy velocity of the flue gas, K represents the permeability of the porous medium, and μ represents the viscosity of the flue gas, represents the pressure drop; The calculation formula for the pressure drop caused by the resistance loss of the fluid flowing through the porous medium during non-Darcy flow is as follows: where C 1 and C 2 represent the first and second Forchheimer coefficients respectively, and ρ represents the flue gas density; Based on the filling rate of the filter rod acetate tow, combine with the actual flow velocity inside the porous medium at a specific moment during the puffing process to calculate the Reynolds number of the flue gas flow, and then determine the flue gas flow form and calculate the corresponding pressure drop; The calculation formula for the Reynolds number when the flue gas flows through the porous medium region is as follows: In the formula, D is the equivalent size of the filler in the porous medium region of the filter rod, v is the Darcy velocity of the flue gas, ε is the porosity of the porous medium; When the Reynolds number Re < 5, it is Darcy flow, and when the Reynolds number Re > 5, it is non-Darcy flow; According to the ISO puffing standard, the flow velocity of the flue gas during the puffing process will change with time. Calculate the corresponding Reynolds number based on the flow velocity at a specific moment and judge the flow form, and then select the corresponding pressure drop calculation method; When the high-temperature flue gas flows through the porous medium region, the heat transfer between the gas and the solid follows the local non-thermal equilibrium model, and the calculation method for the heat transfer amount between the gas and the solid is as follows: Q = hA(T f - T s ) In the formula, Q represents the heat transfer rate between the gas and the solid, h represents the convective heat transfer coefficient between the gas and the solid, T represents the temperature, and the subscripts f and s represent the gas and the solid respectively; 3) According to the model established in step 2), use UDF to build FLUENT and dynamically connect it to the Fluent solver to implement the special physical model and boundary conditions during the cigarette puffing process, and combine it with the CFD model in step 1); 4) According to the numerical model established in step 3), simulate and simulate the cigarette puffing process to obtain the pressure and temperature distributions during the puffing process of filter rods with different shapes; 5) Obtain the slope of the curve of flue gas temperature varying with the filter rod length using interpolation based on the temperature distribution obtained in step 4). Set the target temperature of the outlet flue gas as T and the critical slope as k 1 , select the filter rod shape a with strong cooling ability and the filter rod shape b with low draw resistance, and obtain the length L of the high-efficiency cooling section of the filter rod of shape a using interpolation 1 and the corresponding flue gas temperature t 1 ; The temperature distribution includes temperature distributions of different filter rod shapes. The slope k of the curve of the flue gas temperature varying with the filter rod length is obtained by interpolation, and a critical slope is set as k 1 , and it is considered that for a filter rod of a specific shape, k > k 1 The region is the high-efficiency cooling section of the filter rod of this shape, and k < k 1 The region is the low-efficiency cooling section of the filter rod of this shape; the target temperature of the outlet flue gas is set as T according to the flue gas cooling requirement during cigarette smoking; interpolation is used for the slope curve to calculate the length L and the flue gas temperature t corresponding to each filter rod shape when the slope is k 1 , and the filter rod shape corresponding to the temperature t within the range [T, T + Δt] is selected as shape a; interpolation is used for the flue gas temperature distribution curve of the filter rod of shape a to calculate the filter rod length L corresponding to the temperature t 1 , and the flue gas temperature at this length is t 1 ; among the remaining filter rod shapes, a filter rod shape b with a draw resistance less than that of the filter rod of shape a and an outlet flue gas temperature lower than or close to T is selected; 6) Based on the temperature distribution obtained in step 4), calculate the length L required for the shaped filter rod b to reduce the flue gas temperature from t 1 to T 2 ; 7) Splice the filter rod of shape a obtained in step 5) and the filter rod of shape b obtained in step 6), connect them with a cavity in the middle, and obtain a cigarette filter rod with high cooling efficiency.

2. The design method for a cigarette filter rod with high cooling efficiency as described in claim 1, characterized in that in step 1), when establishing the cigarette geometric model with different filter rod shapes according to the dimensions of the actual cigarette, the diameter of a certain actual cigarette product is 7.2 mm, the total length is 46 mm, of which the tobacco leaf section is 13 mm long and the filter rod section is 33 mm long; Determine the available shapes of the filter rod according to the design requirements.

3. The design method for a cigarette filter rod with high cooling efficiency as described in claim 1, characterized in that In step 1), the boundary conditions during the suction process are determined according to the ISO suction standard. During the suction process, 35 mL of smoke is inhaled in a bell-shaped curve within 2 s, and the smoke inlet velocity v = 0.7419sin(1.5708t), where the velocity unit is m / s; the inlet smoke temperature is 22 °C, the cigarette paper wall surface is a natural convection heat transfer wall surface, the air incoming flow temperature is 22 °C, and the convective heat transfer coefficient is 10 W / (m 2 ℃).

4. A design method for a cigarette filter rod with high cooling efficiency as described in claim 1, characterized in that in step 3), the gas flow model and gas-solid heat transfer model described in step 2) cannot be implemented on the FLUENT standard interface, and are built using UDF and dynamically connected to the Fluent solver to implement the special physical models and boundary conditions during the cigarette suction process.

5. A design method for a cigarette filter rod with high cooling efficiency as described in claim 1, characterized in that in step 4), for the simulation of the cigarette suction process, based on the model established in step 3), according to the velocity field, temperature field, and pressure field obtained from the FLUENT simulation, calculate the curves of the static pressure and temperature of the smoke changing with the filter rod length during the cigarette suction process with filter rods of different shapes.

6. A design method for a cigarette filter rod with high cooling efficiency as described in claim 1, characterized in that In step 6), the length L required for the calculated shaped b filter rod to reduce the flue gas temperature from t 1 to T 2 is calculated using the interpolation method.

7. A design method for a cigarette filter rod with high cooling efficiency as described in claim 1, characterized in that In step 7), the cigarette filter rod with high cooling efficiency is made by splicing three different-shaped unit filter rods. The first section uses shape a with a length of L 1 , the second section uses a cavity filter rod with a length L 3 = 33 - L 1 - L 2 , with the unit of mm. The third section uses shape b with a length of L 2 ; The filter rod of shape a is placed upstream, the filter rod of shape b is placed downstream, and they are connected by a cavity in the middle.

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