Ventilation calculation method for double-wall pipe structure

Abstract

The invention discloses a ventilation calculation method for a double-wall pipe structure, and relates to the technical field of double-wall pipe structures of dual-fuel systems, and the ventilation calculation method comprises the following steps: splitting a single-layer pipe part from a pipeline component part of a double-wall pipe, obtaining a pressure loss coefficient corresponding to the single-layer pipe part, and obtaining a single-layer pressure loss value corresponding to the single-layer pipe part; a model is established for the double-wall pipe, and a double-wall pressure loss value corresponding to the double-wall pipe is obtained through simulation in the annular ventilation space of the double-wall pipe; then, the single-layer pressure loss values and the double-wall pressure loss values under different air volumes are compared and analyzed to obtain the incidence relation of the single-layer pressure loss values and the double-wall pressure loss values, and the steps are repeated to obtain the corresponding incidence relation of different double-wall pipes; during ventilation calculation of the double-wall pipe structure, a corresponding single-layer pressure loss value is firstly obtained, and then a double-wall pressure loss value is directly obtained according to a pre-obtained association relationship. The pressure loss calculation of the double-wall pipe is parameterized, the situation that full simulation work of the system is repeatedly conducted in a new engineering project is avoided, and the effect that accurate model selection of the draught fan is efficiently achieved at the beginning stage of the project is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of double - wall pipe structures of double - fuel systems, and particularly to a ventilation calculation method for double - wall pipe structures. Background Art

[0002] With the increasing requirements of international environmental protection regulations, ships are increasingly widely using green clean energies such as LNG and methanol on the basis of traditional fuel oil. According to the regulations, when gas pipelines pass through the engine room area, structural protection must be adopted. It is composed of an inner pipe and an outer pipe, forming an annular space in cross - section. Ventilation is supplied to the annular space through a fan, so that when the inner pipe ruptures and leaks, the gas can be discharged from the pipeline in time, realizing the safe operation of the double - fuel system. Fresh air is provided by the fan. The selection of the fan includes two technical parameters: air volume and pipeline pressure loss. The air volume is relatively easy to obtain according to the calculation method of multiplying the pipeline volume by the ventilation frequency. However, the pipeline pressure loss needs to accumulate the local pressure losses of each component. At present, in engineering applications, there are relatively mature empirical data of pressure loss coefficients only for the pressure loss calculation of single - layer pipes, and there is no relevant calculation method for double - wall pipes. In specific engineering calculations, engineers need to estimate based on personal experience. In the estimated fan selection, if the ventilation volume is insufficient, it will not meet the minimum ventilation requirements specified by the regulations. If the ventilation volume is too large, it will lead to an oversized fan selection, poor economic benefits, and a significant increase in technical costs.

[0003] Therefore, through the accurate calculation of the pressure loss of the double - wall pipe, it plays a crucial role in carrying out the ventilation system calculation. The accuracy of the calculation results will be of great significance for the design of the entire system and the selection of the fan. Summary of the Invention

[0004] The purpose of the present invention is to provide a ventilation calculation method for double - wall pipe structures, which parameterizes the pressure loss calculation of the double - wall pipe, avoids repeating the full - scale simulation of the system for new engineering projects, and efficiently solves the accurate selection of the fan at the beginning stage of the project.

[0005] The above - mentioned technical purpose of the present invention is achieved through the following technical solutions: A ventilation calculation method for double - wall pipe structures includes the following steps: First, split out the single - layer pipe components from the pipe components of the double - wall pipe, and obtain the pressure loss coefficient corresponding to the single - layer pipe components, and obtain the single - layer pressure loss value △P corresponding to the single - layer pipe components single ; Establish a model for the double - wall pipe. In the annular ventilation space of the double - wall pipe, simulate to obtain the double - wall pressure loss value △P corresponding to the double - wall pipe double ; Then, compare and analyze the single - layer pressure loss value △P single and the double - wall pressure loss value △P double, obtain the correlation between the two, Repeat the above steps to obtain the corresponding correlations of different double-wall pipes; When calculating the ventilation of the double-wall pipe structure, first obtain the corresponding single-layer pressure loss value, and then directly obtain the double-wall pressure loss value according to the previously obtained correlation.

[0006] Furthermore, the corresponding correlation is △P double =ζ(i)*△P single +P constant ; ζ(i) is the correlation coefficient, and P constant is the fitting quantity.

[0007] Furthermore, the correlation of the double-wall pipes with different parameters is recorded as a correlation coefficient table, and at least the correlation coefficients ζ(i) corresponding to different double-wall pipes are recorded in the correlation coefficient table.

[0008] Furthermore, P constant has different values in different ranges.

[0009] Furthermore, when υ≤υ(i), P constant =0, when υ>υ(i), P constant is a non-zero constant, and υ(i) is the discrete boundary value.

[0010] Furthermore, when υ(i)<υ≤5 m / s, P constant takes 10~20 Pa.

[0011] Furthermore, the corresponding single-layer pressure loss value of the single-layer pipe component is obtained through the following steps Establish a model for the single-layer pipe component, set the corresponding physical parameters, adjust the ventilation volume data, output the corresponding single-layer pressure loss value of the single-layer pipe component, and the obtained single-layer pressure loss value is a data set related to the air volume.

[0012] Furthermore, in the pipeline model of the double-wall pipe, substitute the corresponding physical parameters set in the single-layer pipe component model.

[0013] Furthermore, when establishing the model of the single-layer pipe component, obtain the corresponding pressure loss coefficient through the ventilation pressure loss coefficient table in advance, so that the output result of the pressure loss coefficient in the model under different air volume conditions matches the ventilation pressure loss coefficient table.

[0014] Furthermore, the method for establishing the double-wall pipe model includes establishing a model for the complete path of the ventilation pipeline and establishing a simulation calculation model according to the complete path of the ventilation pipeline.

[0015] In summary, the present invention has the following beneficial effects: In the simulation calculation results of the completed double-wall pipe and single-layer pipe, the pressure loss values of the double-wall pipe at various wind speeds are significantly higher than those of the single-layer pipe, and there is no obvious internal connection between the two. If a complete double-wall pipe model is established for each engineering calculation, it will take a long time and cause serious lag in engineering applications. Based on the empirical data of the single-layer pipe as the theoretical support, this application analyzes the change of pressure loss of the double-wall pipe under the action of double friction resistance of the inner and outer pipe walls during ventilation, and finds a technical bottleneck that effectively solves the lack of pressure loss calculation method for the current double-wall pipe. By means of CFD simulation, the pressure loss calculation parameters of the double-wall pipe are parameterized, avoiding the need to repeat the system-wide full simulation work for new engineering projects, efficiently solving the accurate selection of fans at the beginning stage of the project, and avoiding the adjustment of fan specifications when deficiencies are found during later commissioning, thus causing project rework. Brief Description of the Drawings

[0016] Figure 1 is the schematic diagram of the gas pipeline ventilation system; Figure 2 is the structure diagram of the double-wall pipe; Figure 3 is the pressure loss coefficient table of the single-layer pipe in a ventilation calculation method for the double-wall pipe structure; Figure 4 is the simulation calculation of the straight pipe section by the CFD simulation software in a ventilation calculation method for the double-wall pipe structure; Figure 5 is the simulation calculation of the elbow section by the CFD simulation software in a ventilation calculation method for the double-wall pipe structure; Figure 6 is the simulation calculation of the bent pipe section by the CFD simulation software in a ventilation calculation method for the double-wall pipe structure; Figure 7 is the pressure loss curve of the double-wall pipe straight pipe section and the pressure loss curve diagram of the single-layer pipe in a ventilation calculation method for the double-wall pipe structure; Figure 8 is the pressure loss curve of the double-wall pipe elbow or bent pipe section and the pressure loss curve diagram of the single-layer pipe in a ventilation calculation method for the double-wall pipe structure; Figure 9 is the ventilation correlation coefficient table of the double-wall pipe in a ventilation calculation method for the double-wall pipe structure. Detailed Embodiments

[0017] The following further describes the specific embodiments of the present invention with reference to the accompanying drawings. This embodiment does not constitute a limitation to the present invention. Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the protection scope of this application.

[0018] A ventilation calculation method for a double-wall pipe structure, wherein the double-wall pipe structure in this embodiment is based on the following environment; As Figure 1 shown, there are dual-fuel devices arranged in the engine room. The gas pipeline enters the engine room area from the gas supply end and is connected to the dual-fuel devices to achieve fuel supply. A double-wall pipe needs to be set outside the gas pipeline in the engine room section. One end of the double-wall pipe sucks fresh air from the air inlet in the safe area outside the engine room and supplies it to the double-wall pipe structure section through a single-layer pipe. After the fresh air further passes through the internal pipeline of the dual-fuel device, it is extracted by the double-wall pipe fan in the safe area through the single-layer pipe. Through the continuous replacement of fresh air, the safe use of the gas pipeline in the engine room and compliance with regulatory requirements are achieved.

[0019] As Figure 2 shown, the inside of the double-wall pipe structure is a gas pipeline, and the annular space is a ventilation pipe formed by the outer pipe and the inner pipe of the double-wall pipe; the double-wall pipe can be a completely straight pipe section structure. When fresh air flows through the double-wall pipe structure, the fluid frictions with the outer wall of the inner pipe and the inner wall of the outer pipe of the double-wall pipe. By adding the friction of the outer wall of the inner pipe on the basis of the friction on the inner wall of the single-layer pipe, the calculation of the pressure loss in the straight pipe section is solved; the double-wall pipe structure can also be a bent pipe or an elbow section structure. When fresh air flows through the bent pipe or elbow of the double-wall pipe, in addition to being affected by the double-wall friction of the outer wall of the inner pipe and the inner wall of the outer pipe similar to the straight pipe section, it also includes the action of variable cross-section or variable-direction turbulence to solve the calculation of the pressure loss in the bent pipe or elbow.

[0020] The ventilation calculation method for the above double-wall pipe structure includes the following steps: Step S10, establish a pipe section model of the double-wall pipe; Specifically, it includes: Step S11, establish a model (in the AVEVA AM12 software) for the complete path of the ventilation pipeline to ensure that the path meets the requirements of the actual ship design and calculate the volume of the ventilation pipeline; Step S12, establish a simulation calculation model (in the CFD simulation software) according to the complete path of the ventilation pipeline, and establish models for each component in the pipeline, including straight pipes, bent pipes or elbows, inner pipe supports, tees, etc.

[0021] Step S20, split out the single-layer pipe components from the pipeline components of the double-wall pipe, and obtain the pressure loss coefficient corresponding to the single-layer pipe components, and obtain the single-layer pressure loss value △P of the single-layer pipe components single ; In this embodiment, the single-layer pressure loss value corresponding to the single-layer pipe components is obtained through the following steps: Step S21, establish a model in the CFD simulation software for the single-layer pipe components Step S22: First, obtain the corresponding pressure loss coefficient through the ventilation pressure loss coefficient table in manuals such as the Practical Handbook of Ship Design. Then, according to the settings of the single-layer pipe in the CFD simulation software, set the corresponding physical parameters, such as material, elastic modulus, Reynolds number, roughness, etc., and continuously adjust the ventilation volume data to make the output results of the pressure loss coefficient in the model under different air volume conditions match the ventilation pressure loss coefficient table; And output the single-layer pressure loss value corresponding to the single-layer pipe component, and obtain the single-layer pressure loss value △P single is a data set related to the air volume, that is, △P single ={△P1, △P2, △P3, △P N ......}; Based on this set, the single-layer pipe pressure loss coefficient curve graph Curve 1 can be drawn.

[0022] Such as Figure 3 shown, according to the elbow and bend pressure loss coefficient table widely used in calculating the ventilation pressure loss value of the single-layer pipe in the project, it is easy to obtain the pressure loss coefficient value of the single-layer pipe by calculating the corresponding cross-sectional ratio, curvature, etc. of the pipeline; the data in this table is used as the basic data of this application to find the internal connection between the double-wall pipe pressure loss and the single-layer pipe pressure loss calculation through the simulation calculation of the double-wall pipe pressure loss, and obtain the double-wall pipe pressure loss coefficient table with the same function as the single-layer pipe pressure loss coefficient table; In some embodiments of this application, the straight pipe and elbow or bend specifications of the inner pipe diameter of 1 / 2" to 8" and the outer pipe diameter of 21 / 2" to 12" applicable to the ASME standard to be calculated are selected. First, Figure 3 find the corresponding pressure loss coefficient in the ventilation pressure loss coefficient table, and then accurately simulate the single-layer pipe pressure loss coefficient in the CFD software to make the result Figure 3 equivalent to the data listed. The setting of the parameters in the software is used as the physical quantity parameters under this specific specification, and output the single-layer pressure loss value △P corresponding to the single-layer pipe under this condition single .

[0023] Step S30: Substitute the corresponding physical parameters set in the single-layer pipe component model in Step S20 into the pipeline model of the double-wall pipe. By setting the wind speed, model unit length, etc. in the annular ventilation space of the double-wall pipe, continuously adjust the ventilation volume data, and simulate to obtain the double-wall pressure loss value △P corresponding to the double-wall pipe double ; The obtained △P double is also a data set related to the air volume, that is, △P double ={△P 1 , △P 2 , △P 3 , △P N ......}; Based on this set, the double-wall pipe pressure loss coefficient curve graph Curve 2 can be drawn; In some embodiments, in the completed single-layer pipe simulation calculation, a double-wall pipe model can be directly established in the single-layer pipe and directly integrated into the model required for double-wall pipe calculation; Step S40, plot Curve 1 and Curve 2 on the same curve graph at the same time. Under the same air volume setting value, compare and analyze the single-layer pressure loss value △P at different air volumes single and the double-wall pressure loss value △P double , and it is obtained that under different air volume conditions, the double-wall pipe curve curve 2 will be above the single-layer pipe curve curve 1, and the double-wall pipe pressure loss curve is a polyline (υ-△P) （初始） , compare the coincidence degree and dispersion degree of the pressure loss values to obtain the correlation relationship between the two; Specifically, in some sections, it is close to a linear relationship with the single-layer pipe curve (υ-△P). Establish the internal connection between the double-wall pipe pressure loss and the single-layer pipe pressure loss. Manually set the coefficient ζ(i) to move the single-layer pipe curve upward to approach the double-wall pipe curve, that is, fit the double-wall pipe pressure loss value to the single-layer pipe pressure loss value area to obtain a larger coincidence degree area; that is, the obtained ζ(i) is used as the correlation coefficient of the pipeline component per unit length, so as to obtain the pressure loss coefficient of the double-wall pipe; According to different air volumes, the curves curve 2 and curve 1 will gradually separate in some specific areas of the pressure loss curve, resulting in the failure of curve fitting. On this basis, it is necessary to set a constant, or set a constant for each different flow section to eliminate the separation of the curves, that is, P constant .

[0024] Specifically, the corresponding correlation relationship can be set as △P double =ζ(i)*△P single +P constant ; ζ(i) is the correlation coefficient, and P constant is the fitting quantity; among them, P constant has different values in different ranges; the value is currently obtained based on the complete simulation results. Currently, the simulation wind speed is in the double-wall pipe with a speed not higher than 5 m / s. When υ(i)<υ≤5 m / s, P constant takes 10~20 Pa; That is, when υ≤υ(i), P constant =0, when υ>υ(i), P constant is a non-zero constant, and υ(i) is the discrete demarcation value; that is, when υ≤υ(i), △P double =ζ(i)*△P single ; when υ>υ(i), △P double =ζ(i)*△P single +P constant .

[0025] After setting ζ(i), reattach it to the parameter setting value of the CFD simulation software to further obtain the new pressure loss curve (υ-ΔP) after fitting the double-wall pipe. （新） , so that the new pressure loss curve of the double-wall pipe coincides with the single-layer pipe curve (υ-ΔP) within a large range, and try to avoid discreteness in the high wind speed area.

[0026] In actual simulation, considering the actual air volume of the pipeline, when the air volume gradually increases, the influence of flow velocity on pressure loss is significant, and the turbulent flow phenomenon is obvious. In engineering applications, try to control the designed air volume within the range of a relatively stable flow field. Based on the information of common double-wall pipes, the simulation results under the wind speed condition of 5 m / s are selected. The curve curve 2 of the double-wall pipe and the curve curve 1 of the single-layer pipe are relatively in a linear state. As attached Figure 7 and 8 , for the branch pipe section, elbow or bent pipe section, curve 2 and curve 1 have two different slope values κ2 and κ1, and the two straight lines have and only have one intersection point. Beyond the intersection point, a separation trend gradually appears. The farther away from the intersection point, the more obvious the separation. For example, in the high-speed area of the rightward air volume, the difference between the two straight lines will be larger, that is, P constant =(κ2 - κ1)*υ as the fitting compensation amount of the two curves will be larger, resulting in discreteness of the fitting curve in the high wind speed area; To obtain more accurate pressure loss data of the double-wall pipe and take into account the influence of discreteness, in this embodiment, the discrete boundary value υ(i) is determined to be 2.5 m / s of wind speed, and the P constant value is taken as 10 Pa, and the mathematical calculation model is adjusted to: When υ ≤ 2.5 m / s, ΔP double = ζ(i)*ΔP single ; When υ > 2.5 m / s, ΔP double = ζ(i)*ΔP single + 10.

[0027] Figure 7 This is the pressure loss curve of the straight pipe section of the double-wall pipe and the pressure loss curve of the single-layer pipe in this embodiment. Figure 8 This is the pressure loss curve of the elbow or bent pipe section of the double-wall pipe and the pressure loss curve of the single-layer pipe drawn in this embodiment. It can be obtained from the curve that within a certain wind speed range (5 m / s wind speed or less in this embodiment), the curve coincidence degree is relatively high, so as to guide the fan selection as much as possible within this area. Discreteness occurs in the high wind speed area, and it is not recommended as a reference for fan selection; under specific high wind speed conditions, continuing to use this correlation coefficient method to calculate the pipeline pressure loss, the result may deviate from the true value.

[0028] Step S50: Repeat the above steps, and then substitute the elbow or elbow pipe section. First, obtain the model setting environment according to the empirical data of the single-layer pipe elbow or elbow pipe section. After determining that the simulation result is the same as the empirical calculation, substitute the parameters into the double-wall pipe model. Draw the curve of the pressure loss data against the air volume according to the simulation, and find the fitting correlation coefficient ζ(i) (and P constant data) to obtain the corresponding correlation relationship for different double-wall pipes; As Figure 9 shown, the correlation relationships of double-wall pipes with different parameters are recorded in a correlation coefficient table. The correlation coefficient table records at least the correlation coefficient ζ(i) corresponding to different double-wall pipes, closely combines the pressure loss coefficient of the double-wall pipe with that of the single-layer pipe, and provides convenience for engineering calculations; Different-parameter double-wall pipes include straight pipe sections, elbows or elbow sections within the range of the inner pipe and outer pipe commonly matched in double-wall pipe engineering. According to the curves and correlation coefficients fitted for straight pipes, elbows or bends respectively, formulate an isobaric loss coefficient table for straight pipe sections, elbows or elbow sections within the range of the inner pipe and outer pipe commonly matched in double-wall pipe engineering as the pressure loss empirical data of double-wall pipes; As Figure 4 simulated and calculated the pressure loss value △P of the straight pipe section of the double-wall pipe at each wind speed data double - straight pipe; Figure 5 simulated and calculated the pressure loss value △P of the elbow section of the double-wall pipe at each wind speed data double - elbow; Figure 6 simulated and calculated the pressure loss value △P of the bent pipe section of the double-wall pipe at each wind speed data double - bent pipe; that is, the pressure loss value △P of different components of the double-wall pipe double .

[0029] Step S60: When calculating the ventilation of the double-wall pipe structure, first obtain the corresponding single-layer pressure loss value, and then directly obtain the double-wall pressure loss value according to the correlation coefficient table obtained in advance in Step S50; Taking the elbow as an example, according to the pipe diameter of the double-wall pipe in the correlation coefficient table data, find the corresponding single-layer pipe diameter, and then according to the ratio R / d of the elbow bending radius R to the circular cross-section diameter d and the pipe inner wind speed ω required in the appendix Figure 3 , obtain the pressure loss coefficient ξ and single-layer pressure loss value △P of the elbow component at this wind speed single ; Specify the correlation coefficient ζ according to the correlation coefficient table data, and calculate to obtain △P double = △P single * ζ.

[0030] In this embodiment, a complete pipeline model is first established, in which fresh air enters the single-layer ventilation pipe and the double-wall ventilation pipe structure from the air inlet and is then extracted by the fan. Secondly, the annular space formed between the inner pipe and the outer pipe, as well as the physical structure characteristics related to ventilation such as straight pipes, elbows or bends, and elastic supports in the annular space, are analyzed. Then, the required ventilation volume and pressure loss value in the double-wall pipe structure are calculated, and the ventilation volume and pressure loss value are used as basic parameters to complete the selection of the double-wall pipe fan. It provides a relatively accurate ventilation calculation method for the double-wall pipe structure in the annular space, provides a reference for the selection of the double-wall pipe fan more accurately, avoids the unnecessary energy consumption caused by the over-sizing of the double-wall pipe fan and the risk that the under-sizing leads to the ventilation not meeting the regulatory requirements, and has good guiding benefits for engineering applications.

[0031] The above are only the preferred embodiments of the present invention and are not used to limit the present invention. Those skilled in the art can make various modifications or equivalent replacements to the present invention within the essence and protection scope of the present invention, and such modifications or equivalent replacements should also be regarded as falling within the protection scope of the technical solution of the present invention.

Claims

1. A ventilation calculation method for a double-wall pipe structure, characterized in that: Including the following steps, First, split out the single-layer pipe component from the pipe components of the double-wall pipe, and obtain the pressure loss coefficient corresponding to the single-layer pipe component, and obtain the single-layer pressure loss value △P corresponding to the single-layer pipe component single ; A model is established for the double-wall pipe, and within the annular ventilation space of the double-wall pipe, the double-wall pressure loss value ΔP corresponding to the double-wall pipe is obtained through simulation double ; Then, the single-layer pressure loss value △P single and the double-wall pressure loss value △P double are compared and analyzed to obtain the correlation between the two. Repeat the above steps to obtain the corresponding correlation relationships of different double-wall pipes; When calculating the ventilation of the double-wall pipe structure, first obtain the corresponding single-layer pressure loss value, and then directly obtain the double-wall pressure loss value according to the previously obtained correlation relationship.

2. The ventilation calculation method for a double-wall pipe structure according to claim 1, characterized in that: The corresponding correlation relationship is △P double =ζ(i)*△P single +P constant ; ζ(i) is the correlation coefficient, and P constant is the fitting quantity.

3. The ventilation calculation method for a double-wall pipe structure according to claim 2, characterized in that: The correlation relationships of double-wall pipes with different parameters are recorded as a correlation coefficient table, and the correlation coefficient table records at least the correlation coefficient ζ(i) corresponding to different double-wall pipes.

4. The ventilation calculation method for a double-wall pipe structure according to claim 2 or 3, characterized in that: P constant It has different values in different ranges.

5. The ventilation calculation method for a double-wall pipe structure according to claim 4, characterized in that: When υ ≤ υ(i), P constant = 0. When υ > υ(i), P constant is a non-zero constant, and υ(i) is a discrete boundary value.

6. The ventilation calculation method for a double-wall pipe structure according to claim 5, characterized in that: When υ(i) < υ ≤ 5 m / s, P constant Take 10~20 Pa.

7. The ventilation calculation method for a double-wall pipe structure according to claim 1, characterized in that: The corresponding single-layer pressure loss value of the single-layer pipe component is obtained through the following steps Establish a model for the single-layer pipe component, set the corresponding physical parameters, adjust the ventilation volume data, output the corresponding single-layer pressure loss value of the single-layer pipe component, and the obtained single-layer pressure loss value is a data set related to the air volume.

8. The ventilation calculation method for a double-wall pipe structure according to claim 7, characterized in that: In the pipeline model of the double-wall pipe, substitute the corresponding physical parameters set in the single-layer pipe component model.

9. The ventilation calculation method for a double-wall pipe structure according to claim 1, characterized in that: When establishing a model for the single-layer pipe component, obtain the corresponding pressure loss coefficient through the ventilation pressure loss coefficient table in advance, so that the output results of the pressure loss coefficient in the model under different air volume conditions match the ventilation pressure loss coefficient table.

10. The ventilation calculation method for a double-wall pipe structure according to claim 1, characterized in that: The method for establishing the double-wall pipe model includes establishing a model for the complete path of the ventilation pipeline and establishing a simulation calculation model according to the complete path of the ventilation pipeline.

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