CN112560359A - Simulation method for heat transfer characteristics of shell-and-tube heat exchanger in scaling state - Google Patents
Simulation method for heat transfer characteristics of shell-and-tube heat exchanger in scaling state Download PDFInfo
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Abstract
The invention discloses a method for simulating heat transfer characteristics of a shell-and-tube heat exchanger in a scaling state, which comprises the following steps: s1, establishing a shell-and-tube heat exchanger solid calculation domain model; s2, reading the established three-dimensional model of the shell-and-tube heat exchanger, and filling to generate a tube-side and shell-side fluid calculation domain model; s3, reading a solid calculation domain model and a fluid calculation domain model of the shell-and-tube heat exchanger, and performing grid division on the whole calculation domain to generate a grid file; s4, establishing a calculation model capable of solving the equivalent thermal conductivity of the heat exchange tube and the baffle plate to obtain the equivalent thermal conductivity of the heat exchange tube and the baffle plate of the shell-and-tube heat exchanger in a scaling state; s5, reading the grid file, setting the material properties and boundary conditions of the solid and fluid calculation domains, and performing solution calculation until convergence; and S6, entering a post-processor to observe, analyze and calculate results to obtain the temperature distribution conditions of the tube side and the shell side of the shell-and-tube heat exchanger.
Description
Technical Field
The invention relates to the technical field of chemical equipment, in particular to a method for simulating heat transfer characteristics of a shell-and-tube heat exchanger in a scaling state.
Background
The heat exchanger can reasonably adjust the temperature of the working medium to meet the requirements of the process flow and recycle waste heat and waste heat, and is widely applied to the fields of chemical industry, petroleum, pharmacy and the like. The shell-and-tube heat exchanger has the characteristics of mature design and processing technology, simple structure, safety, reliability, strong adaptability and the like, and is most widely applied. Due to the long-term use of the heat exchanger, dirt or water scale with a certain thickness can be formed on the heat exchange wall surface, and the heat resistance generated by the dirt also seriously influences the heat exchange efficiency of the heat exchanger. Dirt not only blocks the heat exchanger, but also corrodes the wall of the heat exchange tube, thereby causing perforation of the wall surface, leakage of materials and even explosion. In order to eliminate potential safety hazards caused by scaling, equipment management departments perform cleaning and dredging operations on heat exchangers every year. At present, no effective means is available for rapidly evaluating the influence of the scaling of the heat exchanger on the heat exchange effect of the heat exchanger, so that each heat exchanger needs to be treated, and the management cost is increased.
In recent years, domestic and foreign scholars have successively conducted researches on the influence of dirt thermal resistance on the heat transfer performance of a heat exchanger. Ozden et al, in the literature, Computational analysis of fouling by low energy sources (Computational analysis of low energy surface fouling), performed numerical simulation of the fouling problem of dairy products in heat exchange tubes using Fluent software; owen et al, in the literature, "thermal analysis of the thermal resistance of non-uniform fouling on cross-flow heat exchanger tubes" (Theoretical analysis of the thermal resistance of non-uniform fouling in cross-flow heat exchanger tubes), programmed a finite difference program to predict the effect of non-uniform fouling on the surface of heat exchanger tubes on the heat transfer performance; liuyang proposes a calculation method of equivalent heat conductivity coefficient of dirt based on a porous medium model and a finite element method in the literature 'calculation of equivalent heat conductivity coefficient of dirt based on a finite element method'; wu Guaizhong establishes a three-dimensional simplified model of the shell-and-tube heat exchanger in the literature 'research on influence of scaling on flow heat exchange of the shell-and-tube heat exchanger' to carry out numerical simulation on a heat transfer process, and learns that the pressure drop of a scaling side inlet and outlet is increased and the heat exchange performance is reduced.
At present, although scholars at home and abroad make a great deal of research on the dirt of heat exchange equipment, most of the work mainly aims at the heat transfer problem of the dirt of a single-side pipe of a heat exchanger, the general regularity research on the dirt inside and outside the pipe is lacked, and meanwhile, the heat transfer calculation simulation analysis of the heat exchanger containing the dirt is difficult to be carried out by the existing computer hardware. Therefore, a common shell-and-tube heat exchanger is selected as a research object, a calculation model capable of solving the equivalent thermal conductivity of the heat exchange tube and the baffle plate is established, the equivalent thermal conductivity of the heat exchange tube and the baffle plate in a scaling state is obtained through calculation, and the equivalent thermal conductivity is set as the material attribute of simulation calculation; the method comprises the following steps of (1) carrying out flow heat transfer numerical simulation on a tube pass and a shell pass simultaneously under an operation condition, and researching the convection and heat transfer problems of dirt inside and outside the tube pass of a heat exchanger and on a baffle plate; and technical support is provided for the optimal design and application of the heat exchanger.
Disclosure of Invention
Aiming at the problems, the invention provides a method for simulating the heat transfer characteristic of a shell-and-tube heat exchanger in a scaling state. Adopting three-dimensional digital modeling software, fully considering various information characteristics of a research object, and establishing a three-dimensional geometric model which is more in line with the actual shell-and-tube heat exchanger; establishing a calculation model capable of solving the equivalent heat conductivity coefficients of the heat exchange tube and the baffle plate to obtain the equivalent heat conductivity coefficients of the heat exchange tube and the baffle plate in a scaling state, and setting the equivalent heat conductivity coefficients as the material attributes of simulation calculation; the numerical simulation analysis of flow heat transfer is carried out on the tube pass and the shell pass simultaneously by using Fluent software, so that the problems of convection and heat conduction of scaling inside and outside the tube pass of the heat exchanger and on the baffle plate are solved, the calculation efficiency is greatly improved, the research cost is saved, and the safety of the research process is improved; the system efficiently analyzes the temperature distribution conditions of the tube side and the shell side of the shell-and-tube heat exchanger in the scaling state, and provides technical support for the optimization design and equipment management of the heat exchanger.
The invention is realized by at least one of the following technical schemes.
A method for simulating heat transfer characteristics of a shell-and-tube heat exchanger in a fouling state comprises the following steps:
s1, establishing a solid domain three-dimensional model of the shell-and-tube heat exchanger by using three-dimensional digital modeling software;
s2, reading the well established solid domain three-dimensional model of the shell-and-tube heat exchanger by using the Ansys-Fluent, and performing filling (Fill) operation on the three-dimensional model in a geometric (Geometry) module of the Ansys-Fluent to generate a fluid calculation domain three-dimensional model;
s3, reading the generated fluid calculation domain three-dimensional model by using the Ansys-Fluent, selecting a Mesh division mode in a Mesh (Mesh) module of the Ansys-Fluent, setting the size of the Mesh division, and carrying out Mesh division on the whole calculation domain to generate a Mesh file;
s4, establishing a calculation model of equivalent heat conductivity coefficients of the heat exchange tubes and the baffle plates: calculating equivalent thermal conductivity coefficients of the heat exchange tube and the baffle plate in the scaling state, namely solving to obtain the equivalent thermal conductivity coefficients of the heat exchange tube and the baffle plate of the shell-and-tube heat exchanger in the scaling state according to the heat transfer capacity of the cylinder with unit length and the heat transfer capacity of the unit area of the multilayer flat wall, and taking the equivalent thermal conductivity coefficients as material attributes of simulation calculation;
s5, reading a computational domain grid model by using the Ansys-Fluent, selecting a standard k-epsilon turbulence model in an Ansys-Fluent setting (Setup) module, setting the material properties and boundary conditions of solid and fluid computational domains according to the actual operating conditions and the equivalent thermal conductivity calculated in the step S4, and performing solving calculation in an Ansys-Fluent solving (Solution) module until the calculation result is converged and a specific monitoring value is stable;
s6, after the solving calculation is completed in the step S5, the calculation result is observed and analyzed in an Ansys-Fluent result (Results) post-processing module, and the tube side and shell side temperature distribution conditions of the shell-and-tube heat exchanger are obtained.
Preferably, the three-dimensional digital modeling software of step S1 is Solidworks.
Preferably, the establishing of the three-dimensional solid domain model of the shell-and-tube heat exchanger comprises the steps of drawing a two-dimensional outline of the three-dimensional solid domain model of the shell-and-tube heat exchanger on a reference surface of a Solidworks drawing area by using a sketch tool, defining the size of a two-dimensional graph, realizing three-dimensional drawing of the two-dimensional outline and combined forming of components by using characteristic tools such as stretching, rotating, cutting, array and the like, and generating the three-dimensional solid domain model of the shell-and-tube heat exchanger.
Preferably, the calculation domain in step S2 is the region of the tube-side and shell-side internal flow velocity, temperature, pressure distribution of the shell-and-tube heat exchanger.
Preferably, the mesh division manner described in step S3 is an automatic mesh division manner, the Capture Curvature (Capture Curvature) and Capture Proximity (Capture Proximity) options are set to Yes, the Smoothing processing (Smoothing) is set to Medium, and both the set Curvature minimum Size (Curvature Min Size) Size and the set Proximity minimum Size (Proximity Min Size) are set to half the Size of the thinnest point of the heat exchanger.
Preferably, in step S4, the equivalent thermal conductivity λ of the heat exchange pipee1And equivalent thermal conductivity of the baffle plate lambdae2Solved by the following equation:
heat transfer amount per unit length of cylinder:
heat transfer per unit area by multilayer flat wall:
delta T is the temperature difference between two sides of the heat exchange tube and lambdaiCoefficient of thermal conductivity, delta, for fouling in heat exchange tubesiIs the thickness of dirt in the heat exchange tube diIs the inner diameter, lambda, of the heat exchange tubesIs the heat conductivity coefficient, d, of the heat exchange tubeoIs the outer diameter, lambda, of the heat exchange tubeoCoefficient of thermal conductivity, delta, for fouling outside heat exchange tubesoIs the thickness of dirt outside the heat exchange tube, delta is the thickness of the baffle plate, lambdae1Is equivalent heat conductivity coefficient, lambda of heat exchange tubee2Is the equivalent thermal conductivity of the baffle.
Preferably, the material properties include the thermal conductivity of heat exchange tubes and baffles of the heat exchanger, and the physical parameters of shell-side and tube-side fluids.
Preferably, the boundary conditions include the inlet temperature and the inlet flow rate of the tube side.
Preferably, the standard k-epsilon turbulence model of step S5 satisfies the following expression:
where ρ is the density of the fluid; t is time; k is the turbulence energy; ε is the diffusivity; μ is the dynamic viscosity of the fluid; u. ofiIs the component of the fluid velocity in a certain direction; x is the number ofi、xjAre different directional components; mu.sτIs a turbulent or vortex viscosity; gkIs the turbulent kinetic energy due to the average velocity gradient; gbIs turbulent kinetic energy generated by buoyancy; y isMContribution to overall diffusivity for pulsatile expansion in incompressible turbulent flow; sigmak、σεPrandtl numbers for k and epsilon; c1ε、C2ε、C3εIs a constant term; skAnd SεAnd customizing the source item for the user.
Preferably, the judgment criterion for convergence of the calculation result in step S5 is determined in two ways: mode 1, judging by the change of the residual value, namely, when the residual value is reduced to 10 lower than the standard value by default-3When yes, the convergence is considered; mode 2, monitoring and judgingThe performance parameters are considered to converge when the mass, kinetic energy, etc. of the entire system are conserved.
Compared with the prior art, the invention has the following advantages and beneficial effects:
the method adopts three-dimensional digital modeling software to establish a three-dimensional geometric model of the shell-and-tube heat exchanger which is more in line with the reality; establishing a calculation model capable of solving the equivalent heat conductivity coefficients of the heat exchange tube and the baffle plate to obtain the equivalent heat conductivity coefficients of the heat exchange tube and the baffle plate in a scaling state, and setting the equivalent heat conductivity coefficients as the material attributes of simulation calculation; the general Fluent software is used for carrying out flow heat transfer numerical simulation analysis on the tube side and the shell side simultaneously, so that the problems of convection and heat conduction of scaling inside and outside the tube side of the heat exchanger and on the baffle plate are solved, the calculation efficiency is greatly improved, and the research cost is saved; the system can effectively analyze the temperature distribution of the tube side and the shell side of the shell-and-tube heat exchanger in the scaling state.
Drawings
FIG. 1 is a flow chart of a simulation method of heat transfer characteristics of a shell-and-tube heat exchanger in a fouling state according to the present embodiment;
FIG. 2 is a Solidworks three-dimensional model diagram of the shell-and-tube heat exchanger of the present embodiment;
FIG. 3 is a three-dimensional model diagram of the computational domain of the shell-and-tube heat exchanger of the present embodiment;
FIG. 4 is a computational domain grid model diagram of the shell-and-tube heat exchanger of the present embodiment;
FIG. 5 is a cloud of temperature profiles of the shell-and-tube heat exchanger of this example under different fouling conditions;
FIG. 6 is the effect of scale thickness on the logarithmic mean temperature difference of the shell-and-tube heat exchanger in this example;
FIG. 7 is a structural view of the shell-and-tube heat exchanger of this embodiment.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, but the embodiments of the present invention are not limited thereto. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
As shown in FIG. 7, the heat exchanger of this example is a shell-and-tube heat exchanger model AEM159-2.5 manufactured by a company. The heat exchanger tube side and shell side media are respectively circulating water and reduced top gas; the length L of the heat exchanger is 1m, and the shell side inner diameter D is 159 mm; the number n of heat exchange tubes is 7, and the inner diameter d of the tubesi20mm, outside diameter doThe basic parameters of the heat exchanger and the qualitative temperature physical properties are shown in table 1. The heat conductivity coefficients of the heat exchange tubes and the baffle plates are obtained by solving the equivalent heat conductivity coefficient model and are shown in table 2.
TABLE 1AEM159-2.5 model Heat exchanger basic parameters
As shown in fig. 1, a method for simulating heat transfer characteristics of a shell-and-tube heat exchanger in a fouling state includes the following steps:
s1, establishing a three-dimensional model of a solid domain of the shell-and-tube heat exchanger according to the shell-and-tube heat exchanger described in the previous section by using three-dimensional digital modeling software Solidworks, as shown in FIG. 2;
s2, reading the well established three-dimensional model of the solid domain of the shell-and-tube heat exchanger by using Ansys-Fluent, and performing filling (Fill) operation on the three-dimensional model in a geometric (Geometry) module of the Ansys-Fluent to generate a three-dimensional model of a calculation domain, namely, a tube pass and shell pass internal flow velocity, temperature and pressure distribution region of the shell-and-tube heat exchanger, wherein the three-dimensional model is a three-dimensional model diagram of a tube pass and shell pass flow field region of the shell-and-tube heat exchanger shown in figure 3;
s3, using the Ansys-Fluent to read the generated three-dimensional model of the computational domain, selecting a Mesh partitioning manner from a Mesh (Mesh) module of the Ansys-Fluent as an automatic partitioning manner, setting a Capture Curvature (Capture Curvature) and a Capture Proximity (Capture Proximity) option as Yes, setting a Smoothing process (Smoothing) as Medium, setting a Curvature minimum Size (currmeasure Min Size) and a Proximity minimum Size (Proximity Min Size) as half of a thinnest Size of the heat exchanger, and performing Mesh partitioning on the entire computational domain to obtain tetrahedral meshes with uniform Size, moderate number and smooth transition, wherein the Mesh partitioning result is that the number of Mesh nodes is 1505249, the total number of Mesh units of the entire computational domain is 5915629, and a flow-fixed computational domain Mesh model is generated to achieve the effects of ensuring the accuracy of the computational result and not excessively consuming computer resources, as shown in fig. 4.
S4 basic parameters of AEM159-2.5 shell and tube heat exchanger according to table 1 and the following formula:
heat transfer per unit length of cylinder
Heat transfer per unit area of multi-layer flat wall
Delta T is the temperature difference between two sides of the heat exchange tube and lambdaiCoefficient of thermal conductivity, delta, for fouling in heat exchange tubesiIs the thickness of dirt in the heat exchange tube diIs the inner diameter, lambda, of the heat exchange tubesIs the heat conductivity coefficient, d, of the heat exchange tubeoIs the outer diameter, lambda, of the heat exchange tubeoCoefficient of thermal conductivity, delta, for fouling outside heat exchange tubesoIs the thickness of dirt outside the heat exchange tube, delta is the thickness of the baffle plate, lambdae1Is equivalent heat conductivity coefficient, lambda of heat exchange tubee2Is the equivalent thermal conductivity of the baffle.
Calculating equivalent thermal conductivity coefficients of the heat exchange tube and the baffle plate in the scaling state, solving to obtain the equivalent thermal conductivity coefficients of the heat exchange tube and the baffle plate of the shell-and-tube heat exchanger in the scaling state according to the heat transfer quantity of the cylinder in unit length and the heat transfer quantity of the unit area of the multiple layers of flat walls, and taking the obtained equivalent thermal conductivity coefficients of the heat exchange tube and the baffle plate of the shell-and-tube heat exchanger in the scaling state (shown in table 2) as material attributes of simulation calculation;
TABLE 2 calculation of equivalent thermal conductivity
S5, reading the computational domain grid model by using the Ansys-Fluent, opening an energy equation in a setting (Setup) module of the Ansys-Fluent, selecting a Standard k-epsilon turbulence model, and selecting a Standard Wall function (Standard Wall Functions). The heat transfer coefficients of the heat exchange tubes and the baffle plates of the heat exchanger and the physical parameters of shell-side and tube-side fluids are set according to the basic parameters of the AEM159-2.5 shell-and-tube heat exchanger in the table 1 and the equivalent heat transfer coefficients of the heat exchange tubes and the baffle plates calculated in the table 2. Setting the inlet temperature of the tube side at 32 ℃ and the inlet flow rate at 0.0102 m/s; the inlet temperature of the shell side is set to be 255 ℃, and the inlet flow rate is set to be 0.0305 m/s. The solving method is set to be a SIMPLE algorithm and a second-order windward format. And performing Solution calculation in a Solution module of Fluent when all residual values are reduced to 10 below the standard value-3And the calculation can be stopped when the temperature monitoring value of the outer surface of the gas cylinder is stable;
considering the diversity of flow problems and the closure of numerical calculation in engineering practice, the turbulence energy k and the dissipation rate epsilon of a standard k-epsilon turbulence model satisfy the following expression:
where ρ is the density of the fluid; t is time; k is the turbulence energy; ε is the diffusivity; μ is the dynamic viscosity of the fluid; u. ofiIs the component of the fluid velocity in a certain direction; x is the number ofi、xjAre different directional components; mu.sτIs a turbulent or vortex viscosity; gkIs the turbulent kinetic energy due to the average velocity gradient; gbIs turbulent flow due to buoyancyEnergy is saved; y isMContribution to overall diffusivity for pulsatile expansion in incompressible turbulent flow; sigmak、σεPrandtl numbers for k and epsilon; c1ε、C2ε、C3εIs a constant term; skAnd SεAnd customizing the source item for the user.
S6, after the calculation of the step S5 is completed, observing and analyzing the calculation result in an Ansys-Fluent result (Results) post-processing module, and respectively reading temperature distribution cloud charts inside the shell-and-tube heat exchanger with the thicknesses of 1mm, 2mm and 3mm and without dirt, as shown in FIG. 5. And the relationship between the logarithmic mean temperature difference of the heat exchanger and the dirt thickness is obtained by calculation, as shown in fig. 6.
As can be seen from fig. 5, the temperature at the outlet of the heat exchanger increases with the increase of the thickness of the dirt, which reduces the heat exchange effect of the heat exchanger; from fig. 6, the logarithmic mean temperature difference (measuring heat transfer effect of the heat exchanger) of the heat exchanger is reduced along with the increase of the dirt thickness, namely the heat exchange effect is poor when the dirt thickness is increased, and the heat exchanger is more in line with the practical engineering application.
By analyzing the regular characteristics of the change of the flow field temperature inside the shell-and-tube heat exchanger along with the thickness of the fouling and combining the tube side and shell side flow field temperature cloud charts, effective reference can be provided for the fouled heat exchanger. If necessary, the post-processing module can call the temperature change condition of a certain point at any time or set and monitor the condition of the certain point in the calculation process to realize real-time monitoring of the point source, and the pertinence and the accuracy of result analysis are improved.
The above embodiments are preferred embodiments of the present invention, but the present invention is not limited to the above embodiments, and any other changes, modifications, substitutions, combinations, and the like which do not depart from the spirit and principle of the present invention should be regarded as equivalent substitutions and are included within the scope of the present invention.
Claims (10)
1. A method for simulating heat transfer characteristics of a shell-and-tube heat exchanger in a scaling state is characterized by comprising the following steps:
s1, establishing a solid domain three-dimensional model of the shell-and-tube heat exchanger by using three-dimensional digital modeling software;
s2, reading the well established solid domain three-dimensional model of the shell-and-tube heat exchanger by using the Ansys-Fluent, and performing filling (Fill) operation on the three-dimensional model in a geometric (Geometry) module of the Ansys-Fluent to generate a fluid calculation domain three-dimensional model;
s3, reading the generated fluid calculation domain three-dimensional model by using the Ansys-Fluent, selecting a Mesh division mode in a Mesh (Mesh) module of the Ansys-Fluent, setting the size of the Mesh division, and carrying out Mesh division on the whole calculation domain to generate a Mesh file;
s4, establishing a calculation model of equivalent heat conductivity coefficients of the heat exchange tubes and the baffle plates: calculating equivalent thermal conductivity coefficients of the heat exchange tube and the baffle plate in the scaling state, namely solving to obtain the equivalent thermal conductivity coefficients of the heat exchange tube and the baffle plate of the shell-and-tube heat exchanger in the scaling state according to the heat transfer capacity of the cylinder with unit length and the heat transfer capacity of the unit area of the multilayer flat wall, and taking the equivalent thermal conductivity coefficients as material attributes of simulation calculation;
s5, reading a computational domain grid model by using the Ansys-Fluent, selecting a standard k-epsilon turbulence model in an Ansys-Fluent setting (Setup) module, setting the material properties and boundary conditions of solid and fluid computational domains according to the actual operating conditions and the equivalent thermal conductivity calculated in the step S4, and performing solving calculation in an Ansys-Fluent solving (Solution) module until the calculation result is converged and a specific monitoring value is stable;
s6, after the solving calculation is completed in the step S5, the calculation result is observed and analyzed in an Ansys-Fluent result (Results) post-processing module, and the tube side and shell side temperature distribution conditions of the shell-and-tube heat exchanger are obtained.
2. The method for simulating the heat transfer characteristics of the shell-and-tube heat exchanger in the fouling state according to claim 1, wherein the three-dimensional digital modeling software in the step S1 is Solidworks.
3. The method for simulating the heat transfer characteristics of the shell-and-tube heat exchanger in the scaling state according to claim 2, wherein the establishing of the three-dimensional model of the solid domain of the shell-and-tube heat exchanger comprises the steps of drawing a two-dimensional outline of the three-dimensional model of the shell-and-tube heat exchanger on a reference surface of a Solidworks drawing area by using a sketch tool, defining the size of a two-dimensional graph, and realizing the three-dimensional appearance of the two-dimensional outline and the combined molding of components by using characteristic tools such as stretching, rotating, cutting and array and the like to generate the three-dimensional model of the solid domain of the shell-.
4. The method for simulating the heat transfer characteristics of a shell-and-tube heat exchanger in a fouling state according to claim 3, wherein the calculation domains in step S2 are the areas of flow velocity, temperature and pressure distribution inside the tube side and the shell side of the shell-and-tube heat exchanger.
5. The method for simulating heat transfer characteristics of a shell-and-tube heat exchanger in a fouling state according to claim 4, wherein the gridding in step S3 is an automatic gridding, the options of Capture Curvature (Capture Curvature) and Capture Proximity (Capture Proximity) are set to Yes, the Smoothing process (Smoothing) is set to Medium, and the set Curvature minimum Size (Curvature Min Size) and the Proximity minimum Size (Proximity Min Size) are both set to half of the thinnest dimension of the heat exchanger.
6. The method for simulating the heat transfer characteristic of a shell-and-tube heat exchanger in the scaling state according to claim 5, wherein in step S4, the equivalent thermal conductivity λ of the heat exchange tubee1And equivalent thermal conductivity of the baffle plate lambdae2Solved by the following equation:
heat transfer amount per unit length of cylinder:
heat transfer per unit area by multilayer flat wall:
delta T is the temperature difference between two sides of the heat exchange tube and lambdaiCoefficient of thermal conductivity, delta, for fouling in heat exchange tubesiIs the thickness of dirt in the heat exchange tube diIs the inner diameter, lambda, of the heat exchange tubesIs the heat conductivity coefficient, d, of the heat exchange tubeoIs the outer diameter, lambda, of the heat exchange tubeoCoefficient of thermal conductivity, delta, for fouling outside heat exchange tubesoIs the thickness of dirt outside the heat exchange tube, delta is the thickness of the baffle plate, lambdae1Is equivalent heat conductivity coefficient, lambda of heat exchange tubee2Is the equivalent thermal conductivity of the baffle.
7. The method for simulating the heat transfer characteristic of the shell-and-tube heat exchanger in the scaling state according to claim 6, wherein the material properties comprise the heat conductivity of heat exchange tubes and baffles of the heat exchanger and the physical parameters of shell-side and tube-side fluids.
8. The method of claim 7, wherein the boundary conditions include inlet temperature and inlet flow rate of the tube side.
9. The method for simulating heat transfer characteristics of a shell-and-tube heat exchanger in a fouling state according to claim 8, wherein the standard k-epsilon turbulence model in step S5 satisfies the following expression:
where ρ is the density of the fluid; t is time; k is the turbulence energy; ε is the diffusivity; μ is the dynamic viscosity of the fluid; u. ofiIs the component of the fluid velocity in a certain direction; x is the number ofi、xjAre different directional components; mu.sτIs a turbulent or vortex viscosity; gkIs the turbulent kinetic energy due to the average velocity gradient; gbIs turbulent kinetic energy generated by buoyancy; y isMContribution to overall diffusivity for pulsatile expansion in incompressible turbulent flow; sigmak、σεPrandtl numbers for k and epsilon; c1ε、C2ε、C3εIs a constant term; skAnd SεAnd customizing the source item for the user.
10. The method for simulating heat transfer characteristics of a shell-and-tube heat exchanger in a fouling state according to claim 9, wherein the judgment criterion for convergence of the calculation result in step S5 is determined by the following two methods: mode 1, judging by the change of the residual value, namely, when the residual value is reduced to 10 lower than the standard value by default-3When yes, the convergence is considered; mode 2, monitoring and judging performance parameters, namely when the mass, kinetic energy, energy and the like of the whole system are all conserved, considering convergence.
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