A method for calculating parameters of spirally wound membrane elements

Abstract

The present invention provides a parameter calculation method for a spiral wound membrane element. The method comprises: using fluid mechanics theory to model the various structures of the spiral wound membrane element, conducting theoretical analysis on the water inlet side and the water production side of the spiral wound membrane element to establish a water inlet mesh calculation model and a water production mesh calculation model, using the water inlet mesh calculation model and the water production mesh calculation model to calculate the pressure difference at each position on the water inlet side and the water production side of the membrane element, and obtaining the transmembrane pressure difference value at each position inside the spiral wound membrane element; according to the transmembrane pressure difference value at each position inside the spiral wound membrane element, the number of membrane pages in the membrane element, the single-page membrane area value and the pressure-membrane flux performance curve of the membrane element, the water production of the spiral wound membrane element is calculated. The parameter calculation software for the spiral wound membrane element of the present invention can effectively reduce product development costs, shorten the research and development cycle, improve calculation efficiency and avoid manual calculation errors, and has the advantages of good economic benefits and easy use.

Description

Technical Field

[0001] The invention relates to the technical field of membrane element design, and in particular to a parameter calculation method of a spirally wound membrane element. Background Art

[0002] Spiral wound membrane elements are also called rolled membrane elements. The calculation of their parameters is of great significance in the development of membrane element product structure. The calculation of membrane element structural parameters can be used to optimize the internal structure of the product and provide feasibility results. The calculation of membrane element water production is more practical in product development. The water production of the membrane element can be obtained based on theoretical calculations. The water production of the membrane element can be used to analyze the optimization of different membrane element structures and obtain the internal pressure distribution of the membrane element.

[0003] For spiral wound membrane elements, on the basis of meeting the membrane separation performance, membrane elements with high water production and low pressure drop performance are the general research direction. The development of the internal structure of conventional spiral wound membrane element products requires a lot of qualitative analysis and experimental verification to analyze its water production performance and pressure drop. The parameters required for optimization mainly include the length of the membrane element, the characteristic parameters of the water inlet spacer (concentrated water flow cloth) and the water production spacer (pure water flow cloth), the number of membrane pages, and other preparation process parameters.

[0004] At present, the disadvantages of the parameter calculation method of the spiral wound membrane element in the prior art include the following:

[0005] 1. In the case of multiple parameters inside the membrane element, a large amount of experimental analysis is required, and the material cost of spiral wound membrane elements is relatively high, which will result in high R&D costs, resulting in a waste of resources to a certain extent;

[0006] Second: A large amount of qualitative analysis and experimental verification is required, which will extend the R&D cycle and reduce efficiency;

[0007] 3. The calculation process of membrane element structural parameters is usually done manually, which has low calculation efficiency and cannot guarantee accuracy;

[0008] 4. The water production performance and pressure drop performance of the membrane element are obtained by experimental testing, which not only requires a large number of tests, but the test results are also affected by the errors of the test equipment, which has a great negative impact on the membrane element parameter optimization process.

[0009] Five: The pressure distribution inside the membrane element is difficult to test through experiments. It cannot be obtained by conventional performance testing equipment and requires complex theoretical calculations. Summary of the invention

[0010] An embodiment of the present invention provides a method for calculating parameters of a spirally wound membrane element, so as to effectively calculate the parameters of the spirally wound membrane element.

[0011] In order to achieve the above object, the present invention adopts the following technical scheme.

[0012] A method for calculating parameters of a spirally wound membrane element, comprising:

[0013] The fluid mechanics theory is used to model the various structures of the spiral wound membrane element;

[0014] Based on the models of the structures of various parts of the spiral wound membrane element, a theoretical analysis is performed on the water inlet side and the water production side of the spiral wound membrane element to establish a water inlet spacer calculation model and a water production spacer calculation model. The water inlet spacer calculation model and the water production spacer calculation model are used to calculate the pressure difference at each position on the water inlet side and the water production side of the membrane element, and the transmembrane pressure difference value at each position inside the spiral wound membrane element is obtained;

[0015] The water production of the spirally wound membrane element is calculated based on the transmembrane pressure difference at various positions inside the spirally wound membrane element, the number of membrane pages in the membrane element, the area of ​​a single membrane page and the pressure-membrane flux performance curve of the membrane element.

[0016] Preferably, the method of modeling the various structures of the spiral wound membrane element using fluid mechanics theory includes:

[0017] Fluid mechanics theory is used to analyze and model the various structural parts of the spirally wound membrane element, which include a membrane element, a water inlet spacer, a central tube, a water production spacer and an external membrane shell. The water inlet spacer is a porous mesh structure, and the water production spacer is a woven mesh structure with a water guide channel. The membrane element is composed of multiple pages of membrane bags, and each page of the membrane bag is composed of a folded membrane element, a water production spacer placed in the middle of the membrane element, and a water inlet spacer on the outside of the membrane element.

[0018] Preferably, the method of calculating the pressure difference at the water inlet side of the membrane element by using the water inlet screen calculation model and the water production screen calculation model includes:

[0019] The pressure loss calculation values ​​of different types of water inlet screens are calculated by using the dimensionless factors Reynolds number and friction coefficient through the water inlet screen calculation model:

[0020]

[0021] λ=f(Re)

[0022]

[0023] Where: λ is the friction coefficient; Re is the Reynolds number; Δp is the pressure loss, Pa; l m is the length of the element, m; D h is the hydraulic diameter, m; v is the flow velocity, m / s; ρ is the water density, kg / m3 ; μ is the hydrodynamic viscosity, Pa·s;

[0024] For a flat channel with a uniform water inlet screen, when b SP >>h SP When the hydraulic diameter D h It is expressed as follows:

[0025]

[0026] Where: V Tot is the total volume of the flow channel, m 3 ; V SP is the volume of the partition, m 3 ; S FC is the wetted area of ​​the flat channel, m 2 ; S SP is the wetted area of ​​the screen, m 2 ; b SP is the total length of a single sheet of the separator, m; h SP is the thickness of the spacer, m;

[0027] Among them, the basic parameters of the water inlet screen are characterized and calculated:

[0028]

[0029]

[0030] V SP =0.5πd 2 L S P

[0031] V Tot =b SP h SP I m

[0032] Where: ε is the porosity of the mesh; S V，SP is the characteristic area of ​​the partition, m 2 ; d is the fiber diameter, m; L SP is the total fiber length, m.

[0033] Combined with the above calculations, the calculation formula for the hydraulic diameter Dh is simplified to:

[0034]

[0035] Preferably, the method of calculating the pressure difference at each position on the water production side of the membrane element by using the water inlet screen calculation model and the water production screen calculation model includes:

[0036] The water production channel is simplified to an absolutely smooth wall pipe flow, whose Re value is less than 2300, which is laminar flow. The calculation formula for the resistance loss on the water production side of the membrane element is:

[0037] λ=64 / Re

[0038]

[0039] Where: H f is the resistance loss along the water production side of the membrane element, m; λ is the friction coefficient, L is the length of the water production channel, m; g is the acceleration of gravity, m / s 2 .

[0040] Preferably, the water production of the spirally wound membrane element is calculated according to the transmembrane pressure difference at each position inside the spirally wound membrane element, the number of membrane pages in the membrane element, the area of ​​a single membrane page and the pressure-membrane flux performance curve of the membrane element, including:

[0041] According to the diameter size corresponding to different membrane elements as the limit value, the thickness, width and length of the membrane element, the water inlet spacer and the water production spacer inside the membrane element and the diameter of the central tube used are determined, and then the membrane area of ​​the membrane element is obtained;

[0042] The transmembrane pressure difference on both sides of the membrane is calculated based on the pressure distribution on the water inlet side and the water production side. The water production of the membrane element is then calculated based on the number of membrane pages in the element, the area of ​​a single membrane page and the pressure-membrane flux performance curve of the membrane element.

[0043] The water production calculation formula of the membrane element is:

[0044] Q=n×q

[0045]

[0046] Where: Q is the water production of the element, L / min; q is the water production of the single-page membrane element, L / min; f is the pressure and membrane flux performance curve of the single-page membrane element, A is the slope of the performance curve, B is the intercept of the performance curve, and S is the area of ​​the single-page membrane in the element, m2.

[0047] It can be seen from the technical solutions provided by the above-mentioned embodiments of the present invention that the spirally wound membrane element parameter calculation software of the embodiments of the present invention can effectively reduce product development costs, shorten the R&D cycle, improve calculation efficiency and avoid manual calculation errors, and has the advantages of good economic benefits and easy use.

[0048] Additional aspects and advantages of the present invention will be given in part in the following description, which will become obvious from the following description, or may be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying creative work.

[0050] Figure 1 A schematic diagram of a water production calculation model for a spirally wound membrane element provided in an embodiment of the present invention;

[0051] Figure 2 A schematic diagram of the interface design of a water production calculation model for a spirally wound membrane element provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0052] The embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and cannot be interpreted as limiting the present invention.

[0053] It will be understood by those skilled in the art that, unless expressly stated, the singular forms "one", "said", and "the" used herein may also include plural forms. It should be further understood that the term "comprising" used in the specification of the present invention refers to the presence of the features, integers, steps, operations, elements and / or components, but does not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or groups thereof. It should be understood that when we refer to an element as being "connected" or "coupled" to another element, it may be directly connected or coupled to the other element, or there may be intermediate elements. In addition, the "connection" or "coupling" used herein may include wireless connection or coupling. The term "and / or" used herein includes any unit and all combinations of one or more associated listed items.

[0054] It will be understood by those skilled in the art that, unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as those generally understood by those skilled in the art in the art to which the present invention belongs. It should also be understood that terms such as those defined in common dictionaries should be understood to have meanings consistent with the meanings in the context of the prior art, and will not be interpreted with idealized or overly formal meanings unless defined as herein.

[0055] To facilitate understanding of the embodiments of the present invention, several specific embodiments will be further explained below with reference to the accompanying drawings, and each embodiment does not constitute a limitation on the embodiments of the present invention.

[0056] Since there are too many parameters in the calculation model of spiral wound membrane element parameters in the prior art, the calculation is complicated and prone to manual calculation errors. Therefore, according to the actual situation, it is necessary to compile a model that can calculate the internal structure parameters of spiral wound membrane elements for both domestic and industrial use and the water production of membrane elements. The operation is simple and more practical. The calculation of domestic membrane elements is applicable to spiral wound membrane elements with diameters of 1.8 inches, 2.5 inches and 3.0 inches, and the calculation of industrial membrane elements is applicable to membrane elements with diameters of 4.0 inches and 8.0 inches.

[0057] The present invention is based on the structure of a spiral wound membrane element, and proposes a spiral wound membrane element water production calculation model. Figure 1 As shown in the figure, the model uses fluid mechanics theory to analyze and model the various structures of the membrane element, including membrane elements, water inlet spacers, central tubes, water production spacers and external membrane shells. Among them, the water inlet spacer is a porous mesh structure, and the water production spacer is a mesh structure with a water guide channel formed by weaving. The flow resistance of fluids in different spacers can be calculated according to the resistance loss calculation method in fluid mechanics. The membrane element is composed of multiple pages of membrane bags, each of which is composed of a folded membrane element, a water production spacer placed in the middle of the membrane element, and a water inlet spacer on the outside of the membrane element. The three sides of the membrane bag are sealed with adhesive, and the fourth side is opened on the porous central tube. After the multiple pages of membrane bags are wrapped around the central tube and sealed with glue, a membrane element can be obtained.

[0058] The flow of fluid inside the membrane element is mainly affected by the water inlet screen and the water production screen, and the amount of water production is also affected by the flux performance of the membrane element.

[0059] Theoretical analysis is conducted on the water inlet and water production sides of the membrane element, and the calculation model of the water inlet spacer and the water production spacer are established. The pressure loss calculation values ​​of different types of spacers are calculated by the water inlet spacer calculation model and the water production spacer calculation model, and then the fluid flow pressure distribution of the water inlet spacer and the water production spacer of the membrane element is obtained. The pressure difference at each position on the water inlet and water production sides of the membrane element is calculated to obtain the transmembrane pressure difference at each position inside the membrane element. The transmembrane pressure difference on both sides of the membrane element is calculated from the pressure distribution on the water inlet and water production sides, and then the water production of the membrane element is calculated by combining the number of membrane pages in the membrane element, the single-page membrane area value and the membrane element pressure-membrane flux performance curve, and combining the membrane element performance and related parameter experimental tests. The parameter calculation of household elements and industrial elements is based on the internal structure parameters to calculate the element diameter and membrane area.

[0060] 1. Modeling of water inlet spacers: First, theoretical analysis is used to establish a water inlet spacer calculation model, then experiments are designed to determine the model parameters, and finally the pressure loss calculation values ​​of different types of water inlet spacers are calculated through the water inlet spacer calculation model, and then verified with the test results of actual membrane elements.

[0061] The specific theoretical analysis process is as follows:

[0062] The pressure loss is calculated using the dimensionless factors Reynolds number and friction coefficient:

[0063]

[0064] λ=f(Re)

[0065]

[0066] Where: λ is the friction coefficient; Re is the Reynolds number; Δp is the pressure loss, Pa; l m is the length of the element, m; D h is the hydraulic diameter, m; v is the flow velocity, m / s; ρ is the water density, kg / m 3 ; μ is the hydrodynamic viscosity, Pa·s.

[0067] For a flat channel with uniform mesh, when b SP >>h SP When the hydraulic diameter D h It can be expressed as follows:

[0068]

[0069] Where: V Tot is the total volume of the flow channel, m 3 ; V SP is the volume of the partition, m 3 ; S FC is the wetted area of ​​the flat channel, m 2 ; S SP is the wetted area of ​​the screen, m 2 ; b SP is the total length of a single sheet of the separator, m; h SP is the thickness of the separator, m.

[0070] Among them, the basic parameters of the water inlet screen are characterized and calculated:

[0071]

[0072]

[0073] V SP =0.5πd2L SP

[0074] V Tot =b SP h SP I m

[0075] Where: ε is the porosity of the mesh; S V，SP is the characteristic area of ​​the partition, m 2 ; d is the fiber diameter, m; L SP is the total fiber length, m.

[0076] Combined with the above calculations, the hydraulic diameter D h It can be simplified into the following formula:

[0077]

[0078] 2. Modeling of water production screen: The water production channel is simplified to an absolutely smooth wall pipe flow, whose Re value is less than 2300, which is laminar flow, so the following resistance loss calculation formula is obtained:

[0079] λ=64 / Re

[0080]

[0081] Where: H f is the resistance loss along the way, m; λ is the friction coefficient, L is the length of the water production channel, m; g is the gravity acceleration, m / s 2 .

[0082] 3. Calculation of transmembrane pressure difference and water production:

[0083] The transmembrane pressure difference on both sides of the membrane is calculated from the pressure distribution on the water inlet side and the water production side. The water production of the membrane element can be calculated by combining the number of membrane pages in the element, the area of ​​a single membrane page and the pressure-membrane flux performance curve of the membrane element.

[0084] The water production calculation formula of the membrane element is:

[0085] Q=n×q

[0086]

[0087] Where: Q is the water output of the element, L / min; q is the water output of the single-page membrane element, L / min; f is the pressure and membrane flux performance curve of the single-page membrane element, A is the slope of the performance curve, B is the intercept of the performance curve, S is the area of ​​the single-page membrane in the element, m 2 .

[0088] According to the diameter size corresponding to different membrane elements as the limit value, the thickness, width and length of the membrane element, water inlet spacer and water production spacer inside the membrane element and the diameter of the central tube used are determined, so as to obtain the membrane area of ​​the membrane element and then the water production calculation result of the membrane element.

[0089] According to the diameter size corresponding to different membrane elements as the limit value, the membrane element, the water inlet spacer and the water production spacer are composed of multiple membrane bags, which are wound around the central tube. The actual diameter of the element is calculated according to the Archimedean spiral equation or according to the approximate circle, and the thickness, width and length of the membrane element, the water inlet spacer and the water production spacer inside the membrane element are obtained by checking with the diameter limit. In this way, the membrane area of ​​the membrane element is obtained, and then the water production calculation result of the membrane element is obtained.

[0090] The water production calculation model of the spiral wound membrane element can be written in Python, the graphical user interface can be written using the Tkinter package, and the graphics can be visualized using matplotlib. Finally, the software development can be completed through model correction, software testing and software deployment.

[0091] Figure 2 A schematic diagram of the interface design of a spiral wound membrane element water production calculation model provided in an embodiment of the present invention. The above spiral wound membrane element water production calculation model can be coded in Python language, and the graphical user interface can be written using the Tkinter button component. The software interface includes a menu bar, a function area and a calculation interface, wherein the menu bar includes drawing functions and help, and the function area includes three functional interfaces: household membrane element parameter calculation, industrial membrane element parameter calculation and water production calculation. The calculation interface includes two parts: parameter setting and calculation results. The parameter setting is the input interface of each part of the function. The calculation result is the display window interface after the software calculation is completed.

[0092] The technical scheme used for the calculation of household element parameters and industrial element parameters in the three functional areas of the above spiral wound membrane element water production calculation model is the same. First, the parameter setting and calculation result interface are determined, which is implemented through the Tkinter button component. The parameter setting includes 5 options, of which the element model, water inlet screen model, water production screen model and membrane element model are set as options. The corresponding parameters are entered into the software database, and the membrane element length is a manual input item. Next, the above 5 parameters are used as custom variables, and iterative calculations are performed according to the principles described in the functional design to obtain the output of the membrane structure parameters, and the parameters are checked and adjusted according to the experimental results.

[0093] Then, an error reporting module is set. According to the actual membrane element design experience, an error message is prompted when the membrane element length of a household membrane element is outside the range of 400mm to 1200mm, and an error message is prompted when the membrane element length of an industrial membrane element is outside the range of 1400mm to 1800mm. The technical solution of the water production calculation module adds a drawing function on the basis of the above-mentioned membrane element parameter calculation solution. The drawing function is designed based on the Seaborn component of the python package for graphic visualization based on matplotlib. At the same time, the membrane element length, membrane element width and number of membrane pages in the membrane element parameter calculation can be called to the water production calculation module through the Tkinter button component to realize the parameter call, and the pressure distribution diagram of the water inlet side and the water production side, as well as the pressure difference distribution diagram, can be obtained respectively. In addition, the data recording and drawing function of the relationship between the membrane element length and the water production is realized. This function obtains the change curve by recording the data of the input different membrane element lengths and the calculated water production. This function can assist in the optimization of the optimal membrane element length parameters. The Excel database contains the experimentally measured resistance loss coefficients of different types of water inlet screens and water production screens. The Excel table data is called into the software calculation model using read_csv() in the Pandas data analysis package to complete the model calculation. This technical solution facilitates the expansion of the software and facilitates the entry of other types of screen data into the database.

[0094] It is also necessary to use the actual test results of the water production of membrane elements under different structural parameters to calibrate the model and correct the model resistance loss coefficient. Use Pyinstaller to package the Python source files of the development process of the water production calculation model of the spiral wound membrane element under the Windows operating system. The packaged software is installed and used as a multi-user software so that the software can meet the normal use of users, and feedback is given for optimization to complete the software development.

[0095] An example of calculating the parameters of the membrane element according to an embodiment of the present invention is as follows:

[0096] Table 1. Parameter settings for membrane element calculation

[0097]

[0098]

[0099] Table 2. Calculation results of membrane element parameters

[0100]

[0101] 2. Calculation results of water production of membrane elements

[0102] The polyethylene-based nanofiltration membrane was selected to calculate and test the water production of the element. The results are shown in Table 3. The error between the measured water production and the calculated water production is less than 2%, which has a high accuracy.

[0103] Table 3. Calculation results of water production of membrane elements

[0104]

[0105]

[0106] Note: The test solution in Example 1 is 2000 mg / L magnesium sulfate solution, the test conditions are 0.48 MPa, and the recovery rate is 15%; the test solution in Example 2 is 250 mg / L magnesium sulfate solution, the test conditions are 0.41 MPa, and the recovery rate is 50%.

[0107] The functional implementation of the water production calculation model of the spiral wound membrane element is not limited to the Python language, and the functional implementation of the visualization interface is not limited to the modules adopted in this patent;

[0108] The above-mentioned spiral wound membrane element water production calculation model has the functions of calculating the structural parameters required for membrane element preparation and the water production of the membrane element, and also has a drawing function, which can obtain the internal pressure distribution of the membrane element.

[0109] The software of the water production calculation model of the spiral wound membrane element above establishes an Excel database, which is convenient for the application expansion and verification of the software, and convenient for entering the data of other types of screens into the database without changing the source code. It is not limited to this type of database, and other databases with the same function are also applicable.

[0110] In summary, the parameter calculation method of the spirally wound membrane element according to the embodiment of the present invention has the following beneficial effects:

[0111] 1. The method of the present invention is based on the parameters of the internal components of the membrane element and their mutual relationship in the programming software, relying on fluid mechanics modeling and compiling both the calculation of the structural parameters required for the preparation of the membrane element and the calculation of the water production of the membrane element, which has high practical value;

[0112] 2. This method only requires a small amount of experimental verification, which greatly reduces R&D costs, improves efficiency, and shortens the R&D cycle;

[0113] 3. The calculation process of membrane element structural parameters avoids manual calculation errors and has high calculation efficiency;

[0114] 4. The water production performance and pressure drop performance of membrane elements can be obtained by this software with simple operation and a small amount of experimental verification, without the need for a large number of tests;

[0115] 5. The pressure distribution inside the membrane element can be directly obtained after the water production of the membrane element is calculated, without manual calculation. It also has the function of generating a calculation result graph.

[0116] Those skilled in the art can understand that the accompanying drawings are only schematic diagrams of an embodiment, and the modules or processes in the accompanying drawings are not necessarily required to implement the present invention.

[0117] It can be known from the description of the above implementation methods that those skilled in the art can clearly understand that the present invention can be implemented by means of software plus a necessary general hardware platform. Based on such an understanding, the technical solution of the present invention is essentially or the part that contributes to the prior art can be embodied in the form of a software product, which can be stored in a storage medium such as ROM / RAM, a magnetic disk, an optical disk, etc., and includes a number of instructions for enabling a computer device (which can be a personal computer, a server, or a network device, etc.) to execute the methods described in the various embodiments of the present invention or certain parts of the embodiments.

[0118] Each embodiment in this specification is described in a progressive manner, and the same or similar parts between the embodiments can be referred to each other, and each embodiment focuses on the differences from other embodiments. In particular, for the device or system embodiment, since it is basically similar to the method embodiment, the description is relatively simple, and the relevant parts can be referred to the partial description of the method embodiment. The device and system embodiments described above are merely schematic, wherein the units described as separate components may or may not be physically separated, and the components displayed as units may or may not be physical units, that is, they may be located in one place, or they may be distributed on multiple network units. Some or all of the modules may be selected according to actual needs to achieve the purpose of the scheme of this embodiment. Ordinary technicians in this field can understand and implement it without paying creative labor.

[0119] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A method for calculating parameters of a spirally wound membrane element, characterized in that: include: The fluid mechanics theory is used to model the various structures of the spiral wound membrane element; Based on the models of the structures of various parts of the spiral wound membrane element, a theoretical analysis is performed on the water inlet side and the water production side of the spiral wound membrane element to establish a water inlet spacer calculation model and a water production spacer calculation model. The water inlet spacer calculation model and the water production spacer calculation model are used to calculate the pressure difference at each position on the water inlet side and the water production side of the membrane element, and the transmembrane pressure difference value at each position inside the spiral wound membrane element is obtained; The water production of the spiral wound membrane element is calculated based on the transmembrane pressure difference at each position inside the spiral wound membrane element, the number of membrane pages in the membrane element, the area of ​​a single membrane page and the pressure-membrane flux performance curve of the membrane element. The method of calculating the pressure difference at each position on the water production side of the membrane element by using the water inlet screen calculation model and the water production screen calculation model includes: The water production channel is simplified to an absolutely smooth wall pipe flow, whose Re value is less than 2300, which is laminar flow. The calculation formula for the resistance loss on the water production side of the membrane element is: λ=64 / Re Where: H f is the resistance loss along the water production side of the membrane element, m; λ is the friction coefficient, L is the length of the water production channel, m; g is the acceleration of gravity, m / s 2 , Re is the Reynolds number, v is the flow velocity, D h is the hydraulic diameter; The water production of the spiral wound membrane element is calculated based on the transmembrane pressure difference at each position inside the spiral wound membrane element, the number of membrane pages in the membrane element, the area of ​​a single membrane page and the pressure-membrane flux performance curve of the membrane element, including: According to the diameter size corresponding to different membrane elements as the limit value, the thickness, width and length of the membrane element, the water inlet spacer and the water production spacer inside the membrane element and the diameter of the central tube used are determined, and then the membrane area of ​​the membrane element is obtained; The transmembrane pressure difference on both sides of the membrane is calculated from the pressure distribution on the water inlet side and the water production side, and the water production of the membrane element is calculated by combining the number of membrane pages in the element, the area of ​​a single membrane page and the pressure-membrane flux performance curve of the membrane element; The water production calculation formula of the membrane element is: Q=n×q Where: Q is the water output of the element, L / min; q is the water output of the single-page membrane element, L / min; f is the pressure and membrane flux performance curve of the single-page membrane element, A is the slope of the performance curve, B is the intercept of the performance curve, S is the area of ​​the single-page membrane in the element, m 2 .

2. The method according to claim 1, characterized in that: The method of using fluid mechanics theory to model the various structures of the spiral wound membrane element includes: Fluid mechanics theory is used to analyze and model the various structural parts of the spirally wound membrane element, which include a membrane element, a water inlet spacer, a central tube, a water production spacer and an external membrane shell. The water inlet spacer is a porous mesh structure, and the water production spacer is a woven mesh structure with a water guide channel. The membrane element is composed of multiple pages of membrane bags, and each page of the membrane bag is composed of a folded membrane element, a water production spacer placed in the middle of the membrane element, and a water inlet spacer on the outside of the membrane element.

3. The method according to claim 1, characterized in that The method of calculating the pressure difference on the water inlet side of the membrane element by using the water inlet screen calculation model and the water production screen calculation model includes: The pressure loss calculation values ​​of different types of water inlet screens are calculated by using the dimensionless factors Reynolds number and friction coefficient through the water inlet screen calculation model: λ=f(Re) Where: λ is the friction coefficient; Re is the Reynolds number; ΔP is the pressure loss, Pa; l m is the length of the element, m; D h is the hydraulic diameter, m; v is the flow velocity, m / s; ρ is the water density, kg / m 3 ; μ is the hydrodynamic viscosity, Pa·s; For a flat channel with a uniform water inlet screen, when b SP >>h SP When the hydraulic diameter D h It is expressed as follows: Where: V Tot is the total volume of the flow channel, m 3 ; V SP is the volume of the partition, m 3 ; S FC is the wetted area of ​​the flat channel, m 2 ; S SP is the wetted area of ​​the screen, m 2 ; b SP is the total length of a single sheet of the separator, m; h SP is the thickness of the separator, m; Among them, the basic parameters of the water inlet screen are characterized and calculated: V SP =0.5πd 2 L SP V Tot =b SP h SP I m Where: ε is the porosity of the mesh; S V,SP is the characteristic area of ​​the partition, m 2 ; d is the fiber diameter, m; L SP is the total fiber length, m; Combined with the above calculations, the hydraulic diameter D h The calculation formula is simplified to:

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