A numerical simulation method and device for the external flow field of a serrated spiral finned tube

Abstract

The present invention provides a numerical simulation method, device, equipment and storage medium for the external flow field of a serrated spiral finned tube. The method includes: establishing a physical model of the spiral finned tube, calculating the distribution of the external flow field, and recording the corresponding relationship between the pressure drop and the velocity; obtaining the wind tunnel test data of the numerical simulation of the flow field; calculating the pressure drop of the fluid along the annular fins at different directions and different inlet velocities; establishing a pressure drop prediction correlation formula according to the calculated pressure drop results; substituting the parameters of the spiral finned tube to obtain the corresponding pressure drop data, and using the corresponding relationship between the pressure drop and the velocity to obtain the resistance coefficient of the corresponding porous medium model; using an annular porous medium model to replace it for numerical simulation calculation, calculating the porosity and the effective thermal conductivity, substituting the obtained coefficients into the numerical simulation process, and calculating the external flow field data of the serrated spiral finned tube. Through the present invention, the problems of difficult modeling and excessive calculation amount in the numerical simulation calculation of the flue gas flow field of the heat exchanger can be solved.

Description

Technical Field

[0001] The present invention relates to the technical field of numerical simulation, and particularly relates to a method, device, equipment and storage medium for numerically simulating the external flow field of a serrated spiral finned tube. Background Art

[0002] In today's world, the issues of energy conservation and environmental protection are becoming increasingly urgent. Gas-steam combined cycle power generation belongs to a new type of energy-saving energy production method. Affected by power grid peak shaving operation and frequent rapid start-stop, cracks and other defects that were not considered in the initial design may occur in local areas of the boiler heating surface, resulting in an increase in maintenance costs. At present, the research on the failure of the heat exchange system mostly focuses on metal materials and welding quality, and there is little research on the influence of the overall boiler flow field and transient flow field on the heat exchange surface. Studying the internal flow field of the boiler and exploring the principle of defect generation through numerical simulation methods is relatively economical and efficient.

[0003] To make the combined cycle waste heat boiler structure compact, reduce the steel consumption, and lower the back pressure of the gas turbine, serrated spiral finned tubes with an extended heat transfer area are usually used to enhance the convective heat transfer on the flue gas side of the boiler. This type of heat exchange tube has the characteristics of a large heat transfer area, a high heat transfer coefficient, and less wear on the heating surface, so it has been widely used in the field of waste heat recovery and utilization. In a certain large waste heat boiler, there are more than thirty thousand twenty-meter-long serrated spiral finned tubes in the entire heat exchange system, and each serrated spiral finned tube has about one hundred and fifty thousand fins. It is precisely due to this characteristic that the modeling and mesh generation of serrated spiral finned tubes are very difficult in the process of numerical calculation, and the calculation process is difficult to carry out. Therefore, it is necessary to explore a numerical simulation scheme to calculate the external flow field of serrated spiral finned tubes. Summary of the Invention

[0004] The present invention aims to provide a method, device, equipment and storage medium for numerically simulating the external flow field of a serrated spiral finned tube to solve the problems of difficult modeling and excessive calculation amount in the numerical simulation calculation of the flue gas flow field of the heat exchanger.

[0005] To solve the above technical problems, the present invention provides a method for numerically simulating the external flow field of a serrated spiral finned tube, including:

[0006] Establish a physical model of a single serrated spiral finned tube with different specifications, calculate the external flow field distribution of a single serrated spiral finned tube at different inlet velocities, and monitor the corresponding relationship between the pressure drop and velocity of the fluid sweeping over the serrated spiral finned tube and the temperature difference between the inlet and outlet of the external flow field;

[0007] Conduct a wind tunnel test on the serrated spiral finned tube to experimentally verify the corresponding relationship between the pressure drop and velocity of the external flow field fluid sweeping over the serrated spiral finned tube, and obtain the wind tunnel test data of the numerical simulation of the flow field of a single serrated spiral finned tube;

[0008] An orthogonal experimental group was established based on the key dimensional parameters of the serrated spiral finned tube, and the fin parts of different serrated spiral finned tubes were unfolded. The pressure drops of the fluid along the axial, radial, and circumferential directions of the annular fin were calculated at different inlet velocities.

[0009] Based on the key dimensional parameters of the serrated spiral finned tube and the calculated pressure drop results, prediction correlation equations for the pressure drops of the annular fin in the axial, radial, and circumferential directions were fitted and established.

[0010] By substituting the parameters of the serrated spiral finned tube to be simplified into the obtained prediction correlation equations for the pressure drops, the pressure drops of the corresponding annular fin of the serrated spiral finned tube in the axial, circumferential, and radial directions at different inlet velocities were obtained. The inertial resistance coefficient and viscous resistance coefficient of the corresponding porous medium model were obtained by using the corresponding relationships between the pressure drops in the three directions and the velocity.

[0011] Based on the computational fluid dynamics software, the annular fin part of the actual serrated spiral finned tube was replaced with an annular porous medium model for numerical simulation calculation. The porosity and effective thermal conductivity of the porous medium model were calculated. The inertial resistance coefficient, viscous resistance coefficient, and effective thermal conductivity in the three directions obtained were substituted into the numerical simulation process of a single serrated spiral finned tube, and the external flow field data of the serrated spiral finned tube based on the porous medium model were calculated.

[0012] Furthermore, the establishment method of the prediction correlation equations for the pressure drops includes:

[0013] Based on the factors affecting the fin-side resistance characteristics, the pressure drop expression for the gas flowing across the fins of the finned tube was determined as:

[0014] Δp = F(U, ρ, μ, D0, H0, s, δ, H w , H a )

[0015] where U is the velocity of the gas flowing through the fins, ρ is the gas density, μ is the gas dynamic viscosity, D0 is the outer diameter of the finned tube base tube, H0 is the fin height, s is the fin thickness, δ is the fin pitch, H w is the fin width, and H a is the fin base height;

[0016] After obtaining the corresponding relationships between multiple groups of pressure drop data and the parameters of the above pressure drop expression, a prediction correlation equation for the pressure drop was established by fitting using a multivariate function fitting relationship:

[0017]

[0018] where A, B, C, D, E, F, G, and H are coefficients to be fitted.

[0019] Furthermore, obtaining the inertial resistance coefficient and viscous resistance coefficient of the corresponding porous medium model by using the corresponding relationships between pressure drops in three directions and velocity includes:

[0020] Obtaining a set of data of pressure drop varying with velocity;

[0021] Obtaining fitting coefficients a and b according to the fitting formula of the corresponding relationship between pressure drop and velocity; wherein, the fitting formula of the corresponding relationship between pressure drop and velocity is Δp = av 2 + bv, where Δp is the pressure drop across the studied area, and v is the velocity across the studied area;

[0022] In the momentum source term of the porous medium model in the fluid mechanics software, the pressure drop is expressed as: Δp = -S i Δn, where S i is the source term added to the fluid momentum equation, and Δn is the thickness of the porous medium;

[0023] The porous medium model in the fluid mechanics software is modeled by adding the momentum source term to the standard flow equation, and the source term equation is:

[0024]

[0025] where the right side of the source term equation consists of two parts: the viscous loss term and the inertial loss term, S i is the source term in the i direction, i is the x, y or z direction, |v| is the magnitude of the velocity, D and C are specified matrices; μ is the dynamic viscosity of the fluid, and ρ is the density of the fluid;

[0026] For the case of a simple homogeneous porous medium, the matrices D and C are reduced to diagonal matrices, and the diagonal elements are 1 / α and C2 respectively, and the remaining elements are zero, then the source term can be expressed as:

[0027]

[0028] where α is the permeability and C2 is the inertial resistance coefficient; here, two expressions for the source term are obtained, and 1 / α and C2 are obtained corresponding to the coefficients of the linear term and the quadratic term.

[0029] Furthermore, the calculation method of the porosity includes:

[0030] Calculating by using the ratio of the gas volume to the fin volume in the outer annular region of the base tube of the actual serrated spiral finned tube with a length of 100 mm; wherein, the porosity is the proportion of the fluid volume in the total volume in the annular porous region.

[0031] Furthermore, the calculation method of the effective thermal conductivity includes:

[0032] The heat transfer equation in the fluid mechanics software adopts the balanced heat transfer equation:

[0033]

[0034] Among them, E f is the total energy of the fluid, and E s is the total energy of the solid, ρ f is the density of the fluid, and ρ s is the density of the solid, γ is the porosity of the porous medium, and k eff is the effective thermal conductivity, is the enthalpy source term of the fluid;

[0035] k eff is the effective thermal conductivity, and its calculation formula is:

[0036] k eff =γk f +(1 - γ)k s

[0037] Among them, k f is the thermal conductivity of the fluid term, and k s is the thermal conductivity of the solid term.

[0038] Furthermore, the key dimensional parameters include the base tube diameter, fin height, fin width, and sawtooth height.

[0039] Furthermore, the numerical simulation method for the external flow field of the serrated helical finned tube further includes:

[0040] Comparing the calculated external flow field data of the serrated helical finned tube based on the porous medium model with the wind tunnel test data of the numerical simulation of the flow field of a single serrated helical finned tube, and correcting the fitted pressure drop prediction correlation according to the comparison result.

[0041] The present invention also provides a numerical simulation device for the external flow field of a serrated helical finned tube, including:

[0042] A pressure drop monitoring module, which is used to establish physical models of single serrated helical finned tubes of different specifications, calculate the external flow field distribution of a single serrated helical finned tube at different inlet velocities, and monitor the corresponding relationship between the pressure drop and velocity of the fluid sweeping over the serrated helical finned tube and the temperature difference between the inlet and outlet of the external flow field;

[0043] A wind tunnel test module, which is used to conduct wind tunnel tests on the serrated helical finned tube to experimentally verify the corresponding relationship between the pressure drop and velocity of the external flow field fluid sweeping over the serrated helical finned tube, and obtain the wind tunnel test data of the numerical simulation of the flow field of a single serrated helical finned tube;

[0044] The pressure drop calculation module is used to establish an orthogonal experimental group based on the key dimensional parameters of the serrated spiral finned tube, unfold the fin part of different serrated spiral finned tubes, and calculate the pressure drop of the fluid along the axial, radial, and circumferential directions of the annular fin at different inlet velocities;

[0045] The correlation establishment module is used to fit and establish the pressure drop prediction correlation formula of the annular fin in the axial, radial, and circumferential directions according to the key dimensional parameters of the serrated spiral finned tube and the calculated pressure drop results;

[0046] The coefficient calculation module is used to substitute the parameters of the serrated spiral finned tube to be simplified into the obtained pressure drop prediction correlation formula to obtain the pressure drop of the corresponding annular fin of the serrated spiral finned tube in the axial, circumferential, and radial directions at different inlet velocities, and use the corresponding relationship between the pressure drops in the three directions and the velocity to obtain the inertial resistance coefficient and viscous resistance coefficient of the corresponding porous medium model;

[0047] The flow field data calculation module is used to numerically simulate based on the computational fluid dynamics software, replace the annular fin part of the real serrated spiral finned tube with an annular porous medium model, calculate the porosity and effective thermal conductivity of the porous medium model, and substitute the inertial resistance coefficient, viscous resistance coefficient, and effective thermal conductivity in the three obtained directions into the numerical simulation process of a single serrated spiral finned tube to calculate the external flow field data of the serrated spiral finned tube based on the porous medium model.

[0048] The present invention also provides a terminal device, including a processor and a memory storing a computer program, and when the processor executes the computer program, the external flow field numerical simulation method of any one of the serrated spiral finned tubes is implemented.

[0049] The present invention also provides a non-transitory computer-readable storage medium, on which a computer program is stored, and when the computer program is executed by a processor, the external flow field numerical simulation method of any one of the serrated spiral finned tubes is implemented.

[0050] Compared with the prior art, the present invention has the following beneficial effects:

[0051] The present invention provides a method, device, equipment and storage medium for numerical simulation of the external flow field of a serrated spiral finned tube. The method includes: establishing a physical model of the spiral finned tube, calculating the distribution of the external flow field, and recording the corresponding relationship between the pressure drop and the velocity; conducting a wind tunnel test on the serrated spiral finned tube to obtain the wind tunnel test data for numerical simulation of the flow field; establishing an orthogonal experimental group according to the key dimensional parameters, and calculating the pressure drop of the fluid along the annular fins at different inlet velocities in different directions; establishing a pressure drop prediction correlation formula according to the calculated pressure drop results; substituting the parameters of the spiral finned tube to obtain the corresponding pressure drop data, and using the corresponding relationship between the pressure drop and the velocity to obtain the resistance coefficient of the corresponding porous medium model; replacing with an annular porous medium model for numerical simulation calculation, calculating the porosity and the effective thermal conductivity, substituting the obtained coefficients into the numerical simulation process, and calculating the external flow field data of the serrated spiral finned tube. Through the present invention, the problems of difficult modeling and excessive calculation amount in the numerical simulation calculation of the flue gas flow field of the heat exchanger can be solved. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1 FIG. is a schematic flow chart of the method for numerical simulation of the external flow field of the serrated spiral finned tube provided by the present invention;

[0053] Figure 2 FIG. is a simplified schematic diagram of a single tube based on a porous medium model provided by the present invention;

[0054] Figure 3 FIG. is a schematic diagram of the calculation model and boundary conditions of the internal and external flow fields of a single serrated spiral finned tube provided by the present invention;

[0055] Figure 4 FIG. is a schematic diagram of the dimensions of the serrated spiral finned tube provided by the present invention;

[0056] Figure 5 FIG. is a schematic diagram of the unfolded annular fins in one period and the calculation models of the flow fields along the axial, radial and circumferential directions provided by the present invention;

[0057] Figure 6 FIG. is a schematic diagram of the composition of the orthogonal test groups of the dimensions of the serrated spiral finned tube provided by the present invention;

[0058] Figure 7 FIG. is a schematic diagram of the corresponding relationship between the pressure drop and the velocity of the orthogonal test groups in each direction provided by the present invention;

[0059] Figure 8 FIG. is a schematic diagram of the fitting situation and deviation of the correlation in each direction provided by the present invention;

[0060] Figure 9 FIG. is a schematic diagram of the calculation domain for calculating the flow field of a single heat exchange tube using a porous medium model provided by the present invention;

[0061] Figure 10It is a schematic diagram for comparing the pressure drops of the external flow fields obtained from the sawtooth spiral finned tube, plain tube, and simplified porous medium model provided by the present invention;

[0062] Figure 11 It is a schematic diagram for comparing the temperature differences between the inlet and outlet of the external flow fields obtained from the sawtooth spiral finned tube and the porous medium model provided by the present invention;

[0063] Figure 12 It is a schematic diagram for comparing the flow fields of the sawtooth spiral finned tube bundle and the simplified porous medium model flow field provided by the present invention;

[0064] Figure 13 It is a schematic structural diagram of the numerical simulation device for the external flow field of the sawtooth spiral finned tube provided by the present invention. Specific Embodiments

[0065] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0066] Please refer to Figure 1 , the embodiments of the present invention provide a numerical simulation method for the external flow field of a sawtooth spiral finned tube, which may include the steps:

[0067] S1. Establish physical models of single sawtooth spiral finned tubes with different specifications, calculate the external flow field distributions of the single sawtooth spiral finned tubes at different inlet velocities, and monitor the corresponding relationship between the pressure drop and velocity of the fluid sweeping over the sawtooth spiral finned tube and the temperature difference between the inlet and outlet of the external flow field;

[0068] S2. Conduct a wind tunnel test on the sawtooth spiral finned tube to experimentally verify the corresponding relationship between the pressure drop and velocity of the fluid sweeping over the sawtooth spiral finned tube in the external flow field, and obtain the wind tunnel test data for the numerical simulation of the flow field of a single sawtooth spiral finned tube;

[0069] S3. Establish an orthogonal experimental group according to the key dimensional parameters of the sawtooth spiral finned tube, and expand the fin parts of different sawtooth spiral finned tubes, and calculate the pressure drops of the fluid along the axial, radial, and circumferential directions of the annular fins at different inlet velocities;

[0070] S4. Fit and establish prediction correlation formulas for the pressure drops of the annular fins in the axial, radial, and circumferential directions according to the key dimensional parameters of the sawtooth spiral finned tube and the calculated pressure drop results;

[0071] S5. Substitute the parameters of the serrated spiral finned tube to be simplified into the obtained pressure drop prediction correlation formula to obtain the pressure drops of the corresponding annular fins of the serrated spiral finned tube in the axial, circumferential, and radial directions at different inlet velocities. Then, use the corresponding relationships between the pressure drops in the three directions and the velocity to obtain the inertial resistance coefficient and viscous resistance coefficient of the corresponding porous medium model.

[0072] S6. Based on the computational fluid dynamics software, replace the annular fin part of the real serrated spiral finned tube with an annular porous medium model for numerical simulation. Calculate the porosity and effective thermal conductivity of the porous medium model. Substitute the inertial resistance coefficient, viscous resistance coefficient, and effective thermal conductivity in the three obtained directions into the numerical simulation process of a single serrated spiral finned tube to calculate the external flow field data of the serrated spiral finned tube based on the porous medium model.

[0073] In the embodiment of the present invention, further, the method for establishing the pressure drop prediction correlation formula includes:

[0074] Based on the factors affecting the fin-side resistance characteristics, determine the pressure drop expression for the gas flowing across the fins of the finned tube as:

[0075] Δp = F(U, ρ, μ, D0, H0, s, δ, H w , H a )

[0076] where U is the velocity of the gas flowing through the fins, ρ is the gas density, μ is the gas dynamic viscosity, D0 is the outer diameter of the finned tube base tube, H0 is the fin height, s is the fin thickness, δ is the fin distance, H w is the fin width, and H a is the fin base height;

[0077] After obtaining the corresponding relationships between multiple groups of pressure drop data and the parameters of the above pressure drop expression, use the multivariate function fitting relationship for fitting to establish the pressure drop prediction correlation formula:

[0078]

[0079] where A, B, C, D, E, F, G, and H are the coefficients to be fitted.

[0080] In the embodiment of the present invention, further, the method for obtaining the inertial resistance coefficient and viscous resistance coefficient of the corresponding porous medium model by using the corresponding relationships between the pressure drops in the three directions and the velocity includes:

[0081] Obtain a set of data on the variation of pressure drop with velocity;

[0082] According to the fitting formula of the corresponding relationship between the pressure drop and the velocity, obtain the fitting coefficients a and b; where the fitting formula of the corresponding relationship between the pressure drop and the velocity is Δp = av2 +bv, where Δp is the pressure drop across the region under study, and v is the velocity across the region under study;

[0083] In the momentum source term of the porous media model in the fluid dynamics software, the pressure drop is expressed as: Δp = -S i Δn, where S i is the source term added to the fluid momentum equation, and Δn is the thickness of the porous media;

[0084] The porous media model of the fluid dynamics software is modeled by adding the momentum source term to the standard flow equation. The source term equation is:

[0085]

[0086] where the right side of the source term equation consists of two parts: the viscous loss term and the inertial loss term. S i is the source term in the i direction, where i is the x, y, or z direction, |v| is the magnitude of the velocity, D and C are specified matrices; μ is the dynamic viscosity of the fluid, and ρ is the density of the fluid;

[0087] For the case of a simple homogeneous porous media, the matrices D and C are reduced to diagonal matrices, and the diagonal elements are 1 / α and C2 respectively, and the remaining elements are zero. Then the source term can be expressed as:

[0088]

[0089] where α is the permeability and C2 is the inertial resistance coefficient; two expressions for the source term are obtained here, and the coefficients corresponding to the linear term and the quadratic term are found to be 1 / α and C2.

[0090] In the embodiments of the present invention, further, the calculation method of the porosity includes:

[0091] Calculated using the ratio of the gas volume to the fin volume in the outer annular region of the actual serrated spiral finned tube base tube with a length of 100 mm; where the porosity is the proportion of the fluid volume in the total volume in the annular porous region.

[0092] In the embodiments of the present invention, further, the calculation method of the effective thermal conductivity includes:

[0093] The heat transfer equation in the fluid dynamics software uses the balance heat transfer equation:

[0094]

[0095] where E f is the total energy of the fluid, E s is the total energy of the solid, ρ f is the density of the fluid, ρ sis the density of the solid, γ is the porosity of the porous medium, and k eff is the effective thermal conductivity, is the enthalpy source term of the fluid;

[0096] k eff is the effective thermal conductivity, and its calculation formula is:

[0097] k eff = γk f +(1 - γ)k s

[0098] where k f is the thermal conductivity of the fluid term, and k s is the thermal conductivity of the solid term.

[0099] In the embodiments of the present invention, further, the key dimensional parameters include the base tube diameter, fin height, fin width, and sawtooth height.

[0100] In the embodiments of the present invention, further, the numerical simulation method for the external flow field of the serrated spiral finned tube further includes:

[0101] Comparing the calculated external flow field data of the serrated spiral finned tube based on the porous medium model with the wind tunnel test data of the numerical simulation of the flow field of a single serrated spiral finned tube, and correcting the fitted pressure drop prediction correlation according to the comparison result.

[0102] Compared with the prior art, the embodiments of the present invention have the following beneficial effects: The present invention provides a numerical simulation method for the external flow field of a serrated spiral finned tube based on the porous medium model, which considers the pressure drop when the air flow sweeps through from the axial, radial, and circumferential directions of the annular fin, summarizes the prediction correlations of the pressure drop in each direction with the parameters of the finned tube, and can quickly determine the inertial resistance coefficient and viscous resistance coefficient of the porous medium model of different specifications of spiral finned tubes with the help of the correlation. Combining with the balanced heat transfer equation for calculation can more accurately reflect the resistance and heat transfer effect of the actual spiral finned tube. Especially in the overall flow field simulation analysis of the heat exchanger, using this method will bring great convenience to the modeling and calculation, and the calculation amount is greatly reduced compared with the original model. It is worth mentioning that this method based on the porous medium model retains the main body of the heat exchange pipe, which is convenient for the fluid-solid coupling dynamics analysis of the heat receiving surface pipe, and provides convenience for further analyzing the generation mechanism of defects on the heat receiving surface of the heat exchanger.

[0103] The following will describe the embodiments of the present invention in detail with reference to the accompanying drawings, but the present invention can be implemented in many different ways defined and covered by the following:

[0104] Figure 1It is a flow chart of the method for establishing a porous medium model of a serrated spiral finned tube, mainly including establishing a physical model of a single serrated spiral finned tube with different specifications, and using computational fluid dynamics software to calculate the external flow field distribution of a single serrated spiral finned tube at different inlet velocities; conducting a wind tunnel test on the serrated spiral finned tube to obtain the corresponding relationship between the pressure drop and velocity of the external flow field fluid sweeping over the serrated spiral finned tube, and verifying the accuracy of the numerical simulation method for the flow field of a single serrated spiral finned tube; establishing an orthogonal experimental group according to the key dimensions such as the base tube diameter, fin height, fin width, and serration height of the serrated spiral finned tube, unfolding the fin parts of different serrated spiral finned tubes, and using computational fluid dynamics software to calculate the pressure drop of the fluid along the axial, radial, and circumferential directions of the annular fin at different inlet velocities; establishing a prediction correlation formula for the pressure drop of the annular fin in the axial, radial, and circumferential directions according to the key dimensions of the serrated spiral finned tube; substituting the parameters of the serrated spiral finned tube to be simplified into the obtained pressure drop prediction correlation formula to obtain the pressure drop of the corresponding annular fin of the serrated spiral finned tube in the axial, circumferential, and radial directions at different inlet velocities, and obtaining the inertial resistance coefficient and viscous resistance coefficient of the corresponding porous medium model by using the corresponding relationship between the pressure drop in the three directions and the velocity; based on computational fluid dynamics software, replacing the annular fin part of the actual serrated spiral finned tube with an annular porous medium for numerical simulation calculation. Calculate the porosity, effective thermal conductivity, etc. of the porous medium, substitute the inertial resistance coefficient and viscous resistance coefficient in the three directions obtained in step five into the numerical simulation process of a single serrated spiral finned tube, calculate the flow field of the serrated spiral finned tube based on the porous medium model, and compare it with the actual flow field of the serrated spiral finned tube.

[0105] Figure 2 It is a simplified schematic diagram of a single tube based on a porous medium model. In the embodiment of the present invention, an annular porous medium model is introduced to replace the external fins of the finned tube. In the numerical calculation of the flue gas flow field of the heat exchanger, different from the traditional method of simplifying the entire heating surface into a porous medium, this method only replaces the external fin area of the spiral finned tube with an annular porous medium area, simplifies the calculation amount of the numerical calculation, and at the same time can obtain richer flow field flow characteristics, and at the same time provides convenience for the fluid-structure coupling dynamics analysis of the heating surface.

[0106] Figure 3It is a schematic diagram of the calculation model and boundary conditions for the internal and external flow fields of a single serrated helical finned tube. To ensure that the fluid fully develops and evenly sweeps across the finned tube, and at the same time, due to the disturbance of the fluid on the fins, it is easy to form backflows and vortices, resulting in unstable air at the outlet section. Therefore, the geometric model for calculating the flow field of a single finned tube is provided with an inlet section and an outlet section, which are three times and nine times the outer diameter of the tube respectively. In addition, the actual heat transfer section of the finned tube is twice the outer diameter of the tube. At the inlet of the computational domain, the velocity inlet boundary condition is adopted, and the outlet is set as the pressure outlet condition. The upper and lower surfaces are periodic boundary conditions, and the left and right are symmetric boundary conditions. For the internal flow, the velocity inlet boundary condition is adopted. Different velocity boundaries are taken for the inlet of the external flow field for calculation, and the pressure difference of the airflow sweeping across the finned tube and the temperature difference between the inlet and outlet of the internal flow field can be obtained. In the wind tunnel test of a single helical finned tube, the incoming flow velocity corresponds to the inlet velocity in the numerical calculation, and the pressure drop data of the fluid sweeping across the finned tube at different inlet velocities are recorded to verify the accuracy of the numerical calculation.

[0107] Figure 4 It is a schematic diagram of the dimensions of the serrated helical finned tube. The key dimensions of the helical finned tube are listed in the figure, where D0 is the outer diameter of the base tube of the finned tube, H0 is the fin height, s is the fin thickness, δ is the fin pitch, H w is the fin width, and H a is the base height of the fin. When the airflow sweeps across the fins of the finned tube, the factors affecting the side resistance characteristics of the fins are: gas flow velocity, working fluid properties, fin structure, etc. Considering the above factors comprehensively, the resistance Δp of the airflow sweeping across the fins of the finned tube can be qualitatively expressed as:

[0108] Δp = F(U, ρ, μ, D0, H0, s, δ, H w , H a )

[0109] Therefore, the corresponding relationship formula between the pressure drop and the above parameters is specified as:

[0110]

[0111] To accurately describe the resistance characteristics of the fins of the helical finned tube, a cylindrical coordinate system is adopted to define the porous medium region. The three directions are the axial direction, the radial direction, and the circumferential direction respectively. By expanding the helical finned tube, the relationship between multiple groups of pressure drops and velocities is calculated from the three directions to obtain the resistance coefficients in each direction. Figure 5 It is the unfolded calculation model of the fin along the axial, radial, and circumferential directions. Similarly, an inlet section and an outlet section are added to the calculation model of the unfolded fin to calculate the pressure drop of the gas sweeping across the fin under different conditions.

[0112] Regarding the pressure drop relationship formula, it is proposed to set Figure 6Multiple groups of calculations are carried out for the orthogonal test groups shown. The orthogonal test groups cover common specifications of spiral finned tubes. The pressure drop data of the developed model of spiral finned tubes under multiple groups of different parameters are calculated. Figure 7 Figure 3-17 is the corresponding diagram of the pressure drop and velocity of the developed model test group in the axial, circumferential, and radial directions. Through the method of multi-variable function curve fitting, the relationship between the pressure drop Δp and each parameter of the fins of the spiral finned tube in this direction can be obtained as follows:

[0113]

[0114]

[0115] Figure 8 Figure 3-18 shows the numerical fitting error situation in the multi-variable function fitting process. The error in each direction is less than 10%. This relationship can be used as a general resistance model of the porous medium of spiral finned tubes. In subsequent calculations or other fields, the corresponding parameters can be directly substituted to obtain the pressure drop of the airflow sweeping the fins of the serrated spiral finned tube.

[0116] After obtaining the fitting relationship between the pressure drop and each parameter of the spiral finned tube, next, solve the viscous resistance coefficient and inertial resistance coefficient of the corresponding porous medium of the specific spiral finned tube. First, substitute the parameters of the tube to be solved to obtain a set of data of the pressure drop varying with the velocity.

[0117] Through the pressure drop and velocity fitting formula: Δp = av 2 + bv, where Δp is the pressure drop through the research area, and v is the velocity through the research area, to obtain the coefficients a and b.

[0118] In the momentum source term of the Fluent porous medium, the pressure drop can be expressed as: Δp = -S i Δn, where S i is the source term added to the fluid momentum equation, and Δn is the thickness of the porous medium, which represents the thickness of the fluid swept by the developed model of the spiral finned tube here;

[0119] The porous medium model is modeled by adding the momentum source term to the standard flow equation. The source term equation is:

[0120]

[0121] It consists of two parts: the viscous loss term (the first term on the right side) and the inertial loss term (the second term on the right side), where S i is the source term in the i (x, y or z) direction, |v is the magnitude of the velocity, and D and C are the specified matrices. This momentum sink helps the pressure gradient in the porous unit to generate a pressure drop proportional to the fluid velocity (or the square of the velocity) in the unit. μ is the dynamic viscosity of the fluid, and ρ is the fluid density.

[0122] For the case of a simple homogeneous porous medium, the source term can be expressed as:

[0123]

[0124] Where α is the permeability and C2 is the inertial resistance factor, which is equivalent to diagonalizing matrices D and C. The diagonal elements are 1 / α and C2 respectively, and the remaining elements are zero. Two expressions for the source term can be obtained, and the coefficients corresponding to the linear term and the quadratic term can be found to be 1 / α = b and C2 = a. 1 / α and C2 are the viscous resistance coefficient and the inertial resistance coefficient sought.

[0125] It should be noted that for the convenience of describing the resistance characteristics of the porous medium of the spiral finned tube, the cylindrical coordinate system is used here for description, namely the axial direction, the circumferential direction and the radial direction, which means that the corresponding relationship between the pressure drop and the velocity is required in all three directions, and then the viscous resistance coefficient and the inertial resistance coefficient in the three directions are obtained.

[0126] Figure 9 It is a schematic diagram of the computational domain for calculating the flow field of a single heat exchange tube using the porous medium model. Among them, an annular layer outside the tube is defined as the porous medium region in the calculation process to replace the role of the fins. The boundary conditions adopted are the same as those for the original finned tube flow field calculation. Calculation of the porosity in the Fluent porous medium model: the proportion of the fluid volume in the total volume in the porous region, which can be obtained by calculating the volume of the porous medium outside the spiral finned tube and the volume of the fins.

[0127] Related settings of the Fluent porous medium heat transfer equation:

[0128] Solve the Fluent porous medium balanced heat transfer equation:

[0129]

[0130] Where: E f is the total energy of the fluid, E s is the total energy of the solid, ρ f is the density of the fluid, ρ s is the density of the solid, γ is the porosity of the porous medium, k eff is the effective thermal conductivity, is the enthalpy source term of the fluid.

[0131] k eff is the volume average of the solid and the fluid, and its calculation formula is:

[0132] k eff = γk f +(1 - γ)k s

[0133] Where k fis the thermal conductivity of the fluid term, k s is the thermal conductivity of the solid term.

[0134] After the settings of each item of the porous medium are completed and the porous medium model is adopted for calculation, the flow field of the spiral finned tube is recorded. The pressure drop data of the fluid sweeping over the finned tube under different inlet conditions and the temperature difference between the inlet and outlet of the fluid in the tube are also recorded, and compared with the flow field data and experimental data of the original spiral finned tube. Figure 10 is the comparison of the pressure drop of the fluid sweeping model outside the flow field of the spiral finned tube, smooth tube, and simplified porous medium model Figure 11 is the comparison of the temperature difference between the inlet and outlet of the flow field outside the spiral finned tube and the porous medium model Figure 12 is the comparison of the flow field of the serrated spiral finned tube bundle and the flow field of the simplified porous medium model. It can be seen that the velocity field of the spiral finned tube based on the simplified Fluent porous medium method is approximately the same as that of the original spiral finned tube, and this method is considered reliable in engineering.

[0135] It should be noted that for the above method or process embodiments, for the sake of simple description, they are all expressed as a series of action combinations. However, those skilled in the art should know that the embodiments of the present invention are not limited by the described action sequence, because according to the embodiments of the present invention, certain steps can be performed in other sequences or simultaneously. Secondly, those skilled in the art should also know that the embodiments described in the specification are all optional embodiments, and the actions involved are not necessarily essential for the embodiments of the present invention.

[0136] Please refer to Figure 13 , the embodiments of the present invention also provide a numerical simulation device for the external flow field of a serrated spiral finned tube, including:

[0137] The pressure drop monitoring module 1 is used to establish a physical model of a single serrated spiral finned tube with different specifications, calculate the external flow field distribution of the single serrated spiral finned tube at different inlet velocities, and monitor the corresponding relationship between the pressure drop of the fluid sweeping over the serrated spiral finned tube and the velocity, as well as the temperature difference between the inlet and outlet of the external flow field.

[0138] The wind tunnel test module 2 is used to conduct a wind tunnel test on the serrated spiral finned tube to experimentally verify the corresponding relationship between the pressure drop of the fluid sweeping over the serrated spiral finned tube and the velocity, and obtain the wind tunnel test data of the numerical simulation of the flow field of a single serrated spiral finned tube.

[0139] The pressure drop calculation module 3 is used to establish an orthogonal experimental group according to the key dimensional parameters of the serrated spiral finned tube, expand the fin parts of different serrated spiral finned tubes, and calculate the pressure drop of the fluid along the axial, radial, and circumferential directions of the annular fins at different inlet velocities.

[0140] The correlation establishment module 4 is used to fit and establish the pressure drop prediction correlation of the annular fins in the axial, radial, and circumferential directions according to the key dimensional parameters of the serrated spiral finned tube and the calculated pressure drop results;

[0141] The coefficient calculation module 5 is used to substitute the parameters of the serrated spiral finned tube to be simplified into the obtained pressure drop prediction correlation formula, obtain the pressure drops of the corresponding annular fins of the serrated spiral finned tube in the axial, circumferential, and radial directions at different inlet velocities, and use the corresponding relationship between the pressure drops in the three directions and the velocity to obtain the inertial resistance coefficient and viscous resistance coefficient of the corresponding porous medium model;

[0142] The flow field data calculation module 6 is used to numerically simulate and calculate based on computational fluid dynamics software, replacing the annular fin part of the real serrated spiral finned tube with an annular porous medium model, calculating the porosity and effective thermal conductivity of the porous medium model, and substituting the obtained inertial resistance coefficient, viscous resistance coefficient, and effective thermal conductivity in the three directions into the numerical simulation process of a single serrated spiral finned tube to calculate the external flow field data of the serrated spiral finned tube based on the porous medium model.

[0143] It can be understood that the above device item embodiments correspond to the method item embodiments of the present invention. A device for numerically simulating the external flow field of a serrated spiral finned tube provided by the embodiments of the present invention can implement the method for numerically simulating the external flow field of a serrated spiral finned tube provided by any one of the method item embodiments of the present invention.

[0144] The present invention also provides a non-transitory computer-readable storage medium, on which a computer program is stored. When the computer program is executed by a processor, it implements the method for numerically simulating the external flow field of a serrated spiral finned tube described in any one of the above.

[0145] It should be noted that the device embodiments described above are merely illustrative. The units described as separate components may or may not be physically separated, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed to multiple network units. Some or all of the modules can be selected according to actual needs to achieve the purpose of the solution of this embodiment. In addition, in the attached drawings of the device embodiments provided by the present invention, the connection relationship between the modules indicates that they have a communication connection, which can be specifically implemented as one or more communication buses or signal lines. Those of ordinary skill in the art can understand and implement without creative efforts.

[0146] Those skilled in the art can clearly understand that for the convenience and simplicity, the specific working process of the device described above can refer to the corresponding process in the foregoing method embodiments, and will not be described in detail here.

[0147] The terminal device can be a computing device such as a desktop computer, notebook, handheld computer, and cloud server. The terminal device may include, but is not limited to, a processor and a memory.

[0148] The so-called processor can be a Central Processing Unit (CPU), or can also be other general-purpose processors, Digital Signal Processors (DSPs), Application Specific Integrated Circuits (ASICs), Field-Programmable Gate Arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. The general-purpose processor can be a microprocessor or the processor can also be any conventional processor, etc. The processor is the control center of the terminal device, connecting various parts of the entire terminal device using various interfaces and circuits.

[0149] The memory can be used to store the computer program. The processor realizes various functions of the terminal device by running or executing the computer program stored in the memory and calling the data stored in the memory. The memory may mainly include a program storage area and a data storage area. Among them, the program storage area can store an operating system, application programs required for at least one function, etc.; the data storage area can store data created according to the use of the mobile phone, etc. In addition, the memory can include high-speed random access memory, and can also include non-volatile memory, such as a hard disk, memory, plug-in hard disk, Smart Media Card (SMC), Secure Digital (SD) card, Flash Card, at least one magnetic disk storage device, flash device, or other volatile solid-state storage devices.

[0150] The storage medium is a computer-readable storage medium, and the computer program is stored in the computer-readable storage medium. When the computer program is executed by a processor, the steps of the above-described various method embodiments can be implemented. Among them, the computer program includes computer program code, and the computer program code can be in the form of source code, object code, executable file, or some intermediate form, etc. The computer-readable medium may include: any entity or device capable of carrying the computer program code, recording medium, USB flash drive, mobile hard disk, magnetic disk, optical disk, computer memory, read-only memory (ROM, Read-Only Memory), random access memory (RAM, Random Access Memory), electrical carrier signal, telecommunication signal, and software distribution medium, etc. It should be noted that the content included in the computer-readable medium can be appropriately increased or decreased according to the requirements of legislation and patent practice within the jurisdiction. For example, in some jurisdictions, according to legislation and patent practice, the computer-readable medium does not include electrical carrier signals and telecommunication signals.

[0151] The above is the preferred embodiment of the present invention. It should be pointed out that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements are also regarded as the protection scope of the present invention.

Claims

1. A numerical simulation method for the external flow field of a serrated spiral finned tube, characterized in that, including: Establish a physical model of a single serrated spiral finned tube with different specifications, calculate the external flow field distribution of the single serrated spiral finned tube at different inlet velocities, and monitor the corresponding relationship between the pressure drop and velocity of the fluid sweeping over the serrated spiral finned tube and the temperature difference at the inlet and outlet of the external flow field; Conduct a wind tunnel test on the serrated spiral finned tube to experimentally verify the corresponding relationship between the pressure drop and velocity of the fluid sweeping over the serrated spiral finned tube in the external flow field, and obtain the wind tunnel test data for the numerical simulation of the flow field of a single serrated spiral finned tube; Establish an orthogonal experimental group based on the key dimensional parameters of the serrated spiral finned tube, and unfold the fin parts of different serrated spiral finned tubes, and calculate the pressure drop of the fluid along the axial, radial, and circumferential directions of the annular fin at different inlet velocities; Based on the key dimensional parameters of the serrated spiral finned tube and the calculated pressure drop results, fit and establish a pressure drop prediction correlation formula for the annular fin in the axial, radial, and circumferential directions; Through the obtained pressure drop prediction correlation formula, substitute the parameters of the serrated spiral finned tube that need to be simplified, obtain the pressure drops of the corresponding annular fin of the serrated spiral finned tube along the axial, circumferential, and radial directions at different inlet velocities, and use the corresponding relationship between the pressure drops in the three directions and the velocity to obtain the inertial resistance coefficient and viscous resistance coefficient of the corresponding porous medium model; Based on computational fluid dynamics software, replace the annular fin part of the real serrated spiral finned tube with an annular porous medium model for numerical simulation calculation, calculate the porosity and effective thermal conductivity of the porous medium model, and substitute the inertial resistance coefficient, viscous resistance coefficient, and effective thermal conductivity obtained in the three directions into the numerical simulation process of a single serrated spiral finned tube to calculate the external flow field data of the serrated spiral finned tube based on the porous medium model; The establishment method of the pressure drop prediction correlation formula includes: Based on the factors affecting the fin side resistance characteristics, the pressure drop expression of the gas flowing across the fins of the finned tube is determined as: Among them, U is the velocity of the air flow passing through the fins, p is the gas density, is the gas dynamic viscosity, is the outer diameter of the finned tube base tube, is the fin height, s is the fin thickness, is the distance between the fins, is the fin width, is the base height of the fin; After obtaining the corresponding relationship between multiple groups of pressure drop data and the parameters of the above pressure drop expression, use the multivariate function fitting relationship for fitting to establish the pressure drop prediction correlation formula: where A, B, C, D, E, F, G, H are coefficients to be fitted.

2. The numerical simulation method for the external flow field of the serrated spiral finned tube according to claim 1, characterized in that, The method of obtaining the inertial resistance coefficient and viscous resistance coefficient of the corresponding porous medium model by using the corresponding relationship between the pressure drops in the three directions and the velocity includes: Obtain a set of data of the pressure drop varying with the velocity; The fitting coefficients a and b are obtained according to the fitting formula of the corresponding relationship between pressure drop and velocity; among them, the fitting formula of the corresponding relationship between pressure drop and velocity is , Δp is the pressure drop through the studied area, and v is the velocity through the studied area; In the momentum source term of the porous medium model of the fluid dynamics software, the pressure drop is expressed as: , where is the source term added to the fluid momentum equation, is the thickness of the porous medium; The porous medium model of the fluid mechanics software is modeled by adding a momentum source term to the standard flow equation, and the source term equation is: Among them, the right side of the source term equation consists of two parts: the viscous loss term and the inertial loss term. is the source term in the i direction, where i is the x, y, or z direction. is the magnitude of the velocity, and D and C are prescribed matrices. is the dynamic viscosity of the fluid. is the fluid density. For the case of a simple homogeneous porous medium, the matrices D and C are reduced to diagonal matrices, with the diagonal elements being 1 / and , respectively, and the remaining elements being zero. Then the source term can be expressed as: wherein is the permeability, is the inertial resistance coefficient; two expressions for the source term are obtained here, and the coefficients corresponding to the linear term and the quadratic term are found to be 1 / and .

3. The numerical simulation method for the external flow field of the serrated spiral finned tube according to claim 1, characterized in that, The calculation method of the porosity includes: Calculate using the ratio of the gas volume to the fin volume in the outer annular region of the base tube of the actual serrated spiral finned tube with a length of 100 mm; where the porosity is the proportion of the fluid volume in the total volume in the annular porous region.

4. The numerical simulation method for the external flow field of the serrated spiral finned tube according to claim 1, characterized in that, The calculation method of the effective thermal conductivity includes: The heat transfer equation in the fluid mechanics software adopts a balanced heat transfer equation: Among them, is the total energy of the fluid, is the total energy of the solid, is the density of the fluid, is the density of the solid, is the porosity of the porous medium, is the effective thermal conductivity, is the enthalpy source term of the fluid; is the effective thermal conductivity, and its calculation formula is as follows: wherein is the thermal conductivity of the fluid term, is the thermal conductivity of the solid term.

5. The numerical simulation method for the external flow field of the serrated spiral finned tube according to claim 1, wherein The key dimensional parameters include the base tube diameter, fin height, fin width, and serration height.

6. The numerical simulation method for the external flow field of the serrated spiral finned tube according to claim 1, characterized in that, Also included: Compare the calculated external flow field data of the serrated helical finned tube based on the porous medium model with the wind tunnel test data of the flow field numerical simulation of a single serrated helical finned tube, and correct the fitted pressure drop prediction correlation formula according to the comparison results.

7. A numerical simulation device for the external flow field of a serrated spiral finned tube, characterized in that, Including: A pressure drop monitoring module, which is used to establish a physical model of a single serrated helical finned tube with different specifications, calculate the external flow field distribution of a single serrated helical finned tube at different inlet velocities, and monitor the corresponding relationship between the pressure drop and velocity of the fluid sweeping over the serrated helical finned tube and the temperature difference between the inlet and outlet of the external flow field. A wind tunnel test module, which is used to conduct a wind tunnel test on the serrated helical finned tube to experimentally verify the corresponding relationship between the pressure drop and velocity of the external flow field fluid sweeping over the serrated helical finned tube, and obtain the wind tunnel test data of the flow field numerical simulation of a single serrated helical finned tube. A pressure drop calculation module, which is used to establish an orthogonal experimental group according to the key dimensional parameters of the serrated helical finned tube, unfold the fin part of different serrated helical finned tubes, and calculate the pressure drop of the fluid along the axial, radial, and circumferential directions of the annular fin at different inlet velocities. A correlation establishment module, which is used to fit and establish a pressure drop prediction correlation formula for the annular fin in the axial, radial, and circumferential directions according to the key dimensional parameters of the serrated helical finned tube and the calculated pressure drop results. A coefficient calculation module, which is used to substitute the parameters of the serrated helical finned tube that need to be simplified into the obtained pressure drop prediction correlation formula to obtain the pressure drop of the corresponding annular fin of the serrated helical finned tube in the axial, circumferential, and radial directions at different inlet velocities, and use the corresponding relationship between the pressure drop and velocity in the three directions to obtain the inertial resistance coefficient and viscous resistance coefficient of the corresponding porous medium model. A flow field data calculation module, which is used to numerically simulate and calculate based on computational fluid dynamics software, replace the annular fin part of the real serrated helical finned tube with an annular porous medium model, calculate the porosity and effective thermal conductivity of the porous medium model, and substitute the obtained inertial resistance coefficient, viscous resistance coefficient, and effective thermal conductivity in the three directions into the numerical simulation process of a single serrated helical finned tube to calculate the external flow field data of the serrated helical finned tube based on the porous medium model. The establishment method of the pressure drop prediction correlation formula includes: Based on the factors affecting the fin side resistance characteristics, the pressure drop expression of the air flowing across the fins of the finned tube is determined as: where U is the velocity of the gas flow through the fins, p is the gas density, is the gas dynamic viscosity, is the outer diameter of the base tube of the finned tube, is the fin height, s is the fin thickness, is the fin pitch, is the fin width, is the base height of the fin; After obtaining the corresponding relationship between multiple groups of pressure drop data and the parameters of the above pressure drop expression, use the multivariate function fitting relationship to fit and establish the pressure drop prediction correlation formula: Among them, A, B, C, D, E, F, G, and H are coefficients to be fitted.

8. A terminal device, comprising a processor and a memory storing a computer program, characterized in that, When the processor executes the computer program, it implements the numerical simulation method for the external flow field of the serrated helical finned tube according to any one of claims 1 to 6.

9. A non-transitory computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by the processor, it implements the numerical simulation method for the external flow field of the serrated helical finned tube according to any one of claims 1 to 6.

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