Ejector structure design calculation method

Abstract

The invention belongs to the technical field of ejectors, and particularly relates to an ejector structure design calculation method. The method solves the problem that the ejection performance of the ejector is poor due to structural parameter selection under the normal production operation working condition, and the specific technical scheme is as follows: firstly, determining an ejector design formula and an initial working condition, and constructing an initial ejector model; secondly, analyzing model performance, and determining an injection coefficient calculation formula; then setting a design variable value range, taking any parameter in the range to form a group of design variable matrixes, constructing a new ejector model, and determining an ejection coefficient; and finally, repeating the process until the optimal design variable matrix of the ejector is obtained. According to the method, the Visual Basic editor is used for compiling the macro code to obtain the initial structure parameter and the optimal injection coefficient, the injection coefficient obtained by changing the structure parameter is subjected to structure optimization, and the size parameter enabling the injection performance of the ejector to be better is selected, so that the reasonable structure parameter of the ejector is obtained, and the performance of the ejector is maximized.

Description

Technical Field

[0001] The present invention belongs to the technical field of ejectors, and in particular, relates to a calculation method for ejector structure design. Background Art

[0002] The ejector is a device that fully utilizes the mass and energy of fluid transmission. It is characterized by increasing the pressure of the fluid without consuming mechanical energy and having no moving parts. Therefore, it is simpler and more reliable than traditional boosting equipment such as compressors, pumps, blowers and induced draft fans. In addition to its simple structure, it is also very simple to connect with various equipment, and has broad application prospects. In recent years, it has been widely used in natural gas pipeline transportation systems. Due to the high standards for working condition control in natural gas pipeline transportation systems, the ejector structure must be designed in the most reasonable way.

[0003] Most of the existing structural designs of natural gas ejectors only determine the structural parameters through working conditions, which cannot ensure that the ejector achieves optimal performance, will lead to natural gas loss, and directly affect the production cost and economic benefits of the enterprise. For the ejector, the ejection coefficient is an important indicator for evaluating the performance of the ejector. The present invention studies the structural parameters of the ejector by evaluating the ejection coefficient, and can obtain the optimal structural parameters to make the ejection coefficient of the ejector reach the peak value, thereby improving the ejection performance, reducing natural gas loss, and saving costs. Summary of the invention

[0004] In view of the defects of the prior art, the present invention proposes a design and calculation method for an ejector structure. The macro code is written using the Visual Basic editor to obtain the initial structural parameters and the optimal ejection coefficient. The structure is optimized by comparing the ejection coefficient obtained by changing the structural parameters. The dimensional parameters that make the ejector ejection performance reach a better value are selected, thereby obtaining reasonable ejector structural parameters and maximizing the ejector performance.

[0005] In order to achieve the above technical objectives, the present invention will adopt the following technical solutions:

[0006] The main ejector end of the ejector is set as the pressure inlet boundary condition, taking the pressure value of the high-pressure fluid; the ejected end is set as the pressure inlet boundary condition, taking the pressure value of the low-pressure fluid; the outlet end of the ejector is the pressure outlet boundary condition, taking the outlet pressure value of the mixed fluid. Based on the structural dimension calculation theory proposed by Sokolov, the calculation formula of the ejector structural dimension is determined.

[0007] Determine the initial operating conditions of the ejector, including the working fluid pressure P P , working fluid mass flow rate G P , isentropic velocity W of the working fluid P , ejection fluid pressure P P , ejection fluid mass flow rate G H, isentropic velocity of ejected fluid W H , mixed fluid pressure P C , isentropic velocity W of the mixed fluid C ; Use Visual Basic editor to write macro code, and get the ejector structure parameters according to the known working conditions. The main structural parameters are the nozzle inlet diameter D p , Suction chamber diameter D m , suction chamber length L1, mixing chamber inlet diameter D2, mixing chamber outlet diameter D3, mixing chamber length L2, diffusion chamber outlet diameter D4, diffusion chamber length L3; set the geometric constraint relationship between the line segments in the ejector model to ensure that the geometric relationship in the ejector model remains unchanged when the size of each line segment changes, and build a complete ejector model based on the initial structural parameters.

[0008] The calculation formula of nozzle inlet diameter is:

[0009]

[0010] In the formula, f t Indicates the cross-sectional area of ​​the nozzle throat.

[0011] The formula for calculating relative pressure is:

[0012]

[0013] Where λ is the reduced isentropic velocity; for a non-flowing fluid, λ = 0, and for a flowing fluid in a vacuum,

[0014] The calculation formula of critical speed is:

[0015]

[0016] Where k is the adiabatic index of the fluid, which is 1.31 for natural gas; p is the fluid pressure; and v is the specific volume.

[0017] The critical cross-sectional area of ​​the fluid is:

[0018]

[0019] Where G is the flow rate; * is the relative pressure of the critical section; p0 is the stagnation pressure. The calculation formula for the inlet diameter of the mixing chamber is as follows:

[0020]

[0021] Where f2 represents the inlet cross-sectional area of ​​the mixing chamber.

[0022] The formula for calculating the mixing chamber outlet diameter is as follows:

[0023]

[0024] Where f3 represents the outlet cross-sectional area of ​​the mixing chamber.

[0025] The calculation formula of the diffusion chamber outlet diameter is as follows:

[0026] D4=2D3

[0027] The calculation formula for the suction chamber diameter is as follows:

[0028] D m =2.5D3

[0029] The calculation formula of the nozzle inlet section length is as follows:

[0030]

[0031] The calculation formula for the nozzle outlet diameter is as follows:

[0032]

[0033] Where q represents the converted mass velocity of the working fluid.

[0034] The reduced mass velocity q of the fluid can be obtained from the continuity of the fluid:

[0035]

[0036] Where f is the cross-sectional area of ​​a given fluid section.

[0037] The calculation formula for the nozzle tapering length is as follows:

[0038]

[0039] The calculation formula for the nozzle expansion section length is as follows:

[0040]

[0041] In the formula, Indicates the nozzle outlet angle.

[0042] The formula for calculating the length of the tapered section of the mixing chamber is as follows:

[0043]

[0044] In the formula, u represents the ejection coefficient, a C represents the critical velocity of the mixed fluid.

[0045] The calculation formula of the ejection coefficient is as follows:

[0046]

[0047] In the formula, G p Represents the mass flow rate of the working fluid, G h Represents the mass flow rate of the ejected fluid.

[0048] The calculation formula for the suction chamber length is as follows:

[0049] L1=S1+S2+L P

[0050] The performance of the constructed ejector model is analyzed, the ejection coefficient is selected as the performance indicator, the calculation formula of the ejection coefficient is determined, and the optimal ejection coefficient is obtained based on the initial working condition. The performance of the constructed ejector model is further analyzed using mesh pre-processing software and finite element analysis tools. The ejection coefficient u can be calculated using the following formula:

[0051]

[0052] For natural gas, the working fluid velocity coefficient K1 = 0.834, and the ejection fluid velocity coefficient K2 = 0.812.

[0053]

[0054] In the formula, β is usually 2-3, K3 and K4 are the velocity coefficients of the mixed fluid; C2 , Π C3 , Π H2 , Π H3 are the relative pressures of the mixed fluid on section B, the mixed fluid on section C, the ejected fluid on section B, and the ejected fluid on section C, respectively; α is an empirical coefficient, usually taken as 0.5; q PH It is the reduced mass velocity of the ejected fluid at the inlet section of the mixing chamber.

[0055] The area of ​​section C is calculated as follows:

[0056]

[0057] Where: k C is the adiabatic index of the mixed fluid; is the relative pressure of the critical interface of the mixed fluid; q C3 is the reduced mass velocity of the mixed fluid on section C.

[0058] From this, the reduced mass velocity of the ejected fluid on section B is:

[0059]

[0060] in:

[0061] In the formula, a P represents the critical velocity of the working fluid, aH Represents the critical velocity of the ejected fluid.

[0062] Assuming that there is a section s where the gas reaches the first limit state in the conical mixing chamber section, the gas conversion velocity at the section s is:

[0063]

[0064] In the formula, μ is the correction coefficient, and its value is generally 1.35~1.5.

[0065] From this, the optimal ejector coefficient can be obtained:

[0066]

[0067] In the formula, p P represents the working fluid pressure, p H represents the ejection fluid pressure, p C represents the mixed fluid pressure, q H represents the mass velocity of the ejected fluid, q C Represents the reduced mass velocity of the mixed fluid.

[0068] Set the nozzle inlet diameter D under the original model of the ejector p , Suction chamber diameter D m , the value range of the mixing chamber inlet diameter D2, the mixing chamber outlet diameter D3, and the diffusion chamber outlet diameter D4. A parameter is randomly selected within the value range of each design variable, and the design variables of the selected parameters are combined into a set of design variable matrices. A new ejector model is constructed based on the design variable matrix. The value range of each structural parameter variable of the original ejector model is set. The value interval of the i-th structural parameter is [Min i ,Max i ],Min i and Max i Respectively represent the minimum and maximum values ​​of the variation range of the i-th structural parameter. In the value range of each structural parameter set, select any parameter to form a structural parameter matrix, and use [X1, X2, X3, X4, X5]0 as the initial matrix, where X1-X5 represent any parameters selected in their respective value ranges. Use the initial matrix to construct an ejector model based on the matrix.

[0069] Maintaining constant operating conditions, the macro code was written using the Visual Basic editor, and the ejection coefficient was calculated based on the ejector model structural parameters constructed in the previous article.

[0070] The design variable matrix is ​​changed repeatedly, and macro codes are written by using the Visual Basic editor. A loop structure is used to traverse all design variables. A set of design variable matrices is generated each time the traversal is performed, and then an ejector model under each set of design variable matrices is constructed. Each time an ejector model under a set of design variable matrices is constructed, the ejection coefficient u is iterated synchronously, and the optimal ejection coefficient u2 is used as the evaluation index of the iterative process. The design variable matrix [X1, X2, X3, X4, X5] of the next iteration is determined according to the ejection coefficient u of each iteration. j ; Based on the iterative results, determine whether it is optimal. If the result is not optimal, re-determine the new design variable matrix [X1, X2, X3, X4, X5] j+1 ; If the judgment result is yes, mark the current design variable matrix [X1,X2,X3,X4,X5] j is the optimal structural parameter matrix.

[0071] According to the above technical solution, compared with the prior art, the present invention has the following advantages:

[0072] The present invention uses a Visual Basic editor to write macro codes to obtain initial structural parameters and an optimal ejection coefficient, performs structural optimization by comparing the ejection coefficient obtained by changing the structural parameters, and selects size parameters that make the ejection performance of the ejector reach a better value, thereby obtaining reasonable ejector structural parameters and maximizing the ejector performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0073] Figure 1 It is a flow chart of a calculation method for ejector structure design according to an embodiment of the present invention;

[0074] Figure 2 1 is a schematic diagram of the ejector structure of an embodiment of the present invention;

[0075] Figure 3 It is a schematic diagram of the front cross-sectional structure of the ejector of an embodiment of the present invention.

[0076] In the figure: 1, working fluid inlet; 2, ejection fluid inlet; 3, nozzle; 4, suction chamber; 5, mixing chamber convergence section; 6, mixing chamber expansion section; 7, diffusion chamber; 8, mixed fluid outlet. DETAILED DESCRIPTION

[0077] In order to enable those skilled in the art to better understand the technical solution of the present application, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0078] The calculation technology route of the method of the present invention is as follows Figure 1 According to this technical route, the ejector structure model is established as follows Figure 2 .

[0079] Firstly, the calculation formula of ejector structure design is determined based on the gas dynamic function method. The initial working condition of ejector is determined, the initial structural parameters of ejector are determined according to the known working condition, and the original model of ejector with geometric constraints is constructed.

[0080] The initial working conditions of the ejector include the working fluid pressure P P , working fluid mass flow rate G P , isentropic velocity W of the working fluid P , ejection fluid pressure P P , ejection fluid mass flow rate G H , isentropic velocity of ejected fluid W H , mixed fluid pressure P C , isentropic velocity W of the mixed fluid C ; By using the Visual Basic editor to write macro codes, the ejector structural parameters are obtained. The structural parameters are mainly the nozzle inlet diameter D p , Suction chamber diameter D m , suction chamber length L1, mixing chamber inlet diameter D2, mixing chamber outlet diameter D3, mixing chamber length L2, diffusion chamber outlet diameter D4, diffusion chamber length L3.

[0081] The geometric constraints of the main structural parameters of the ejector are as follows:

[0082] The common points of the line segments are constrained to "coincide". m A "perpendicular" constraint relationship is imposed on L1, D2 and L2, and D4 and L3; D p With D m , D3 and D2 impose a "parallel" constraint relationship

[0083] Secondly, the performance of the ejector model constructed by the mesh pre-processing software and the finite element analysis software is analyzed, and the performance index is mainly the ejection coefficient; the mesh pre-processing software is used to establish the mesh model of the ejector, and the mesh pre-processing software of this embodiment adopts ICEM. The finite element analysis software analyzes the performance index of the established mesh model, and the finite element analysis software of this embodiment adopts Fluent.

[0084] Again, set the nozzle inlet diameter D under the original model of the ejector p , Suction chamber diameter D m , the value range of the mixing chamber inlet diameter D2, the mixing chamber outlet diameter D3, and the diffusion chamber outlet diameter D4, and the value range of the i-th structural parameter is [Min i ,Max i ],Min i and Max i Represent the minimum and maximum values ​​of the variation range of the i-th structural parameter respectively.

[0085] A parameter is randomly selected within the range of each design variable to form a structural parameter matrix, and [X1, X2, X3, X4, X5]0 is used as the initial matrix, where X1-X5 represent any parameters selected within their respective value intervals. In one embodiment, taking the i-th design variable as an example, the method for initializing the matrix can be to take the median value of the boundary parameter within the range of the i-th variable, that is, 1 / 2[Min i ,Max i ].

[0086] Then, a new ejector model is constructed based on the design variable matrix.

[0087] The macro code was written using the Visual Basic editor to maintain the operating conditions unchanged, and the ejection coefficient was calculated based on the ejector model obtained above.

[0088] Finally, the design variable matrix is ​​changed, and macro codes are written by using the Visual Basic editor. A loop structure is used to traverse all the design variables. A set of design variable matrices is generated each time the design variable matrix is ​​traversed, and then the ejector model under each set of design variable matrices is constructed.

[0089] Each time an ejector model is constructed under a set of design variable matrices, the ejection coefficient u is iterated synchronously, and the optimal ejection coefficient u2 is used as the evaluation index of the iterative process. The design variable matrix [X1, X2, X3, X4, X5] of the next iteration is determined according to the ejection coefficient u of each iteration. j ;

[0090] The criterion for judging the iterative result is the difference between the ejection coefficient u and the optimal ejection coefficient u2, with an error range of 0.02. If the difference exceeds 0.02, continue the iteration. If the difference is less than 0.02, it is optimal. Determine whether the iterative result is optimal. If not, re-determine the new design variable matrix [X1, X2, X3, X4, X5] j+1 ; If the judgment result is yes, mark the current design variable matrix [X1,X2,X3,X4,X5] j is the optimal structural parameter matrix, thus obtaining the optimal nozzle inlet diameter D of the ejector p , Suction chamber diameter D m , mixing chamber inlet diameter D2, mixing chamber outlet diameter D3, diffusion chamber outlet diameter D4, complete the ejector structure design calculation.

Claims

1. A calculation method for ejector structure design, characterized in that: The ejector structure design calculation method comprises the following steps: Step 1: Determine the ejector structure design calculation formula based on the gas dynamics function method; Step 2: Determine the initial working condition of the ejector, determine the initial structural parameters of the ejector according to the known working conditions, and construct the original model of the ejector with geometric constraints; Step 3: Analyze the performance of the ejector model constructed in step 2 and define the performance index - ejection coefficient, determine the ejection coefficient calculation formula, and obtain the optimal ejection coefficient based on the initial working condition in step 2; Step 4: Set the nozzle inlet diameter D under the original model of the ejector p , Suction chamber diameter D m , the value ranges of the mixing chamber inlet diameter D2, the mixing chamber outlet diameter D3, and the diffusion chamber outlet diameter D4, arbitrarily select a parameter within the value range of each design variable, form a set of design variable matrices with the design variables of the selected parameters, and construct a new ejector model based on the design variable matrix; Step 5: Maintaining the operating conditions constant, determine the ejection coefficient based on the ejector model constructed in step 4; Step 6: Repeat the process of steps 4 and 5, and analyze the design variable matrix in step 4 by comparing the ejection coefficient and the optimal ejection coefficient until the optimal design variable matrix of the ejector is found, the optimal structural parameters of the ejector are obtained, and the ejector structure calculation is completed.

2. The ejector structure design calculation method according to claim 1, characterized in that: Step 1 specifically includes: Step 1.1: The main ejector end of the ejector adopts the pressure inlet boundary condition, and the value is the high-pressure fluid pressure value; the ejected end adopts the pressure inlet boundary condition, and the value is the low-pressure fluid pressure value; the ejector outlet end adopts the pressure outlet boundary condition, and the value is the mixed fluid outlet pressure; Step 1.2: Based on the structural dimension calculation theory proposed by Sokolov, determine the calculation formula for the ejector structural dimension.

3. The ejector structure design calculation method according to claim 1, characterized in that: Step 2 specifically includes: Step 2.1: Determine the initial operating conditions of the ejector, including the working fluid pressure P P , working fluid mass flow rate G P , isentropic velocity W of the working fluid P , ejection fluid pressure P P , ejection fluid mass flow rate G H , isentropic velocity of ejected fluid W H , mixed fluid pressure P C , isentropic velocity W of the mixed fluid C ; Step 2.2: By using the Visual Basic editor to write macro code, the ejector structural parameters are obtained according to step 2.

1. The structural parameters are mainly the nozzle inlet diameter D p , Suction chamber diameter D m , suction chamber length L1, mixing chamber inlet diameter D2, mixing chamber outlet diameter D3, mixing chamber length L2, diffusion chamber outlet diameter D4, diffusion chamber length L3; Step 2.3: Set geometric constraints between the line segments of the ejector model to ensure that the geometric relationships between the line segments of the ejector model remain unchanged when the sizes of the line segments of the ejector model change. Construct the ejector model based on the initial structural parameters of step 2.

2.

4. The ejector structure design calculation method according to claim 1, characterized in that: Step 3 specifically includes: Step 3.1: Analyze the performance of the ejector model constructed in step 2.3 based on mesh pre-processing software and finite element analysis software. The performance index is mainly the ejection coefficient. Step 3.2: The formula for calculating the ejection coefficient u is as follows: In the formula, G p Represents the mass flow rate of the working fluid, G h It represents the mass flow rate of the ejected fluid; The optimum ejection coefficient is determined by the following formula: In the formula, μ represents the correction coefficient, p p represents the working fluid pressure, p h represents the ejection fluid pressure, p c represents the mixed fluid pressure, q h represents the mass velocity of the ejected fluid, q c represents the mass velocity of the mixed fluid, a p represents the critical velocity of the working fluid, a h Represents the critical velocity of the ejected fluid.

5. The ejector structure design calculation method according to claim 1, characterized in that: Step 4 specifically includes: Step 4.1: Set the nozzle inlet diameter D of the ejector prototype p , Suction chamber diameter D m , the value range of the mixing chamber inlet diameter D2, the mixing chamber outlet diameter D3, and the diffusion chamber outlet diameter D4, and the value range of the i-th structural parameter is [Min i ,Max i ],Min i and Max i Respectively represent the minimum and maximum values ​​of the variation range of the i-th structural parameter; Step 4.2: Within the value range of each structural parameter set in step 4.1, select any parameter to form a structural parameter matrix, and use [X1, X2, X3, X4, X5]0 as the initial matrix, where X1-X5 represent any parameters selected within their respective value ranges; Step 4.3: Using the initial matrix from step 4.2, construct an ejector model based on the matrix.

6. The ejector structure design calculation method according to claim 1, characterized in that: Step 5 specifically includes: Step 5.1: Use the Visual Basic editor to write macro code, maintain the operating conditions unchanged, and calculate the ejection coefficient based on the ejector model in step 4.

3.

7. The ejector structure design calculation method according to claim 1, characterized in that: Step 6 specifically includes: Step 6.1: Repeat the process of step 4, write macro codes by using the Visual Basic editor, use a loop structure to traverse all design variables, generate a set of design variable matrices each time, and then construct the ejector model under each set of design variable matrices; Step 6.2: In step 6.1, each time a set of ejector models under the design variable matrix is ​​constructed, the ejection coefficient u is iterated synchronously, and the optimal ejection coefficient u2 is used as the evaluation index of the iterative process. The design variable matrix [X1, X2, X3, X4, X5] of the next iteration is determined according to the ejection coefficient u of each iteration. j ; Step 6.3: Based on the iterative results of step 6.2, determine whether it is optimal. If the result is not optimal, re-determine the new design variable matrix [X1, X2, X3, X4, X5] j+1 ; If the judgment result is yes, mark the current design variable matrix [X1,X2,X3,X4,X5] j is the optimal structural parameter matrix, thus obtaining the optimal nozzle inlet diameter D of the ejector p , Suction chamber diameter D m , mixing chamber inlet diameter D2, mixing chamber outlet diameter D3, diffusion chamber outlet diameter D4, complete the ejector structure design calculation.

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