Experimental system and method based on gas explosion scale effect under actual working conditions

Abstract

The invention belongs to the technical field of industrial safety, and relates to an experimental system and method based on a gas explosion scale effect under actual working conditions, the experimental system comprises at least two experimental pipelines, the nominal diameters of the experimental pipelines are 200mm, 500mm, 700mm, 800mm or 1000mm, the nominal diameters of the experimental pipelines are different, and the experimental pipelines are communicated with the experimental pipelines. And each experimental pipeline has the same length-diameter ratio. According to the invention, the experimental pipeline based on the actual working condition is provided, the length and the width in the pipeline are unified as the length-diameter ratio, and the gas explosion propagation rule in the experimental pipelines with different nominal diameters under the same length-diameter condition is comprehensively considered; and a fluid mechanics method is utilized to analyze the similarity of motion and power and the similarity criterion of an explosion process in different experimental pipelines so as to research the change rule of shock waves in the pipeline and the change condition of a flow field after explosion occurs in the gas conveying pipeline, and technical support is provided for research on the gas explosion scale effect under the actual working condition.

Description

Technical Field

[0001] The invention belongs to the technical field of industrial safety, and relates to an experimental system and method based on the scale effect of gas explosion under actual working conditions. Background Art

[0002] Gas extraction is one of the important measures to prevent gas explosion accidents. At present, the utilization rate of gas extraction in my country is still at a low level. The utilization technology of low-concentration gas in coal mines is not mature enough. The safety of low-concentration gas transportation is also one of the important reasons for the low utilization rate of gas. At present, the diameter of the main gas transportation pipeline is greater than 500mm, and the diameter of the branch pipe is also around 500mm. However, the current research on gas explosion is mainly carried out in pipelines with a diameter of less than 500mm. The scale is small and the distance is short. The research results cannot be directly used in engineering practice. There are great hidden dangers and uncertainties in the actual large-scale pipeline gas transportation and utilization process in coal mines. Only by studying the scale effect of gas explosion in the transmission pipeline under actual working conditions can we provide strong support for the safety protection of gas pipeline transportation and utilization in engineering practice.

[0003] At present, the research on scale effects in pipelines is mainly focused on small scales and numerical simulations, and the main experimental devices used are square tubes, spherical containers, etc. In the process of gas explosion propagation in pipelines, the flow field of gas explosion in pipelines is extremely complex due to the combined effects of many factors such as wall effect and size effect. If the experimental device that is too different from the pipeline under actual working conditions is used for research, there will be discrepancies with the actual gas transmission pipeline.

[0004] However, there is currently neither a systematic experimental device nor an accurate experimental method for experimental research in large-scale pipelines. Therefore, there is an urgent need for a complete and feasible set of experimental devices and methods to support research. Summary of the invention

[0005] In view of this, the purpose of the present invention is to provide an experimental system and method based on the scale effect of gas explosion under actual working conditions, which can carry out gas explosion experiments in transmission pipelines under actual working conditions, and analyze them from theoretical and practical aspects, so as to provide technical support for the research on the scale effect of gas explosion under actual working conditions.

[0006] In order to achieve the above object, the present invention provides the following technical solutions:

[0007] An experimental system based on the scale effect of gas explosion under actual working conditions comprises an experimental pipeline, wherein the number of the experimental pipelines is at least two, the nominal diameter of the experimental pipelines is 200 mm, 500 mm, 700 mm, 800 mm or 1000 mm, and each of the experimental pipelines has a different nominal diameter, and each of the experimental pipelines has the same aspect ratio.

[0008] Furthermore, it also includes a pressure sensor, a flame sensor, a laser methane concentration detector, a synchronous ignition system and a gas distribution system installed on the experimental pipeline, a data acquisition system connected to the pressure sensor and the flame sensor, and a high-speed camera for photographing the explosion flame.

[0009] Furthermore, blind plates and sealing films are respectively provided at both ends of the experimental pipeline to seal the experimental pipeline.

[0010] Furthermore, a plurality of threaded holes are provided on the experimental pipeline for connecting a pressure sensor, a flame sensor, a laser methane concentration detector, a synchronous ignition system, a gas distribution system and a circulating stirring system.

[0011] Furthermore, the synchronous ignition system includes an ignition head arranged near one end of the blind plate.

[0012] Furthermore, the circulation stirring system includes a vacuum pump, and both ends of the vacuum pump are connected to both ends of the experimental pipeline through a vacuum pipe, so that the vacuum pump can perform vacuum circulation stirring on the gas in the experimental pipeline.

[0013] Furthermore, the experimental pipeline includes multiple pipe sections connected by flanges.

[0014] Furthermore, one of the multiple pipe sections is configured as a transparent pipe to facilitate observation of the flame during the explosion.

[0015] An experimental method based on the scale effect of gas explosion under actual working conditions, characterized in that the experimental system based on the scale effect of gas explosion under actual working conditions specifically comprises the following steps:

[0016] Step 1. Arrange the experimental pipeline based on actual working conditions:

[0017] Arrange at least two test pipes with a nominal diameter of 200mm, 500mm, 700mm, 800mm or 1000mm to simulate the pipelines under actual working conditions, and each test pipe has a different nominal diameter and the same aspect ratio;

[0018] A blind plate is installed at one end of the experimental pipeline using a flange to form a fixed closed end, and the other end is sealed with a polyethylene plastic film to form a weakly constrained closed end, and a glass observation window is provided in the middle of each experimental pipeline;

[0019] Step 2. Set up the experimental system:

[0020] According to the different nominal diameters and lengths of each experimental pipeline, multiple pressure sensors and flame sensors are installed at corresponding positions of the experimental pipeline, so that the positions corresponding to the installation of the pressure sensors and flame sensors in each experimental pipeline have the same aspect ratio, a black curtain arranged along the axial direction of the experimental pipeline is installed at one end of the experimental pipeline where the polyethylene plastic film is installed, and the specific size is marked, and a high-speed camera is installed on the glass observation window and the black curtain of the experimental pipeline to take flame propagation images, the pressure sensor and the flame sensor are connected to the data acquisition system to collect data for the corresponding detection points, and a synchronous ignition system is installed at one end of the experimental pipeline close to the blind plate as a detonation device, and the data acquisition system is connected to the synchronous ignition system;

[0021] Step 3. Fill the experimental pipeline with gas:

[0022] Methane gas is charged into the experimental pipeline to a desired concentration through the gas distribution system, and the methane concentration in the pipeline is observed in real time through a laser methane concentration detector installed on the experimental pipeline;

[0023] Step 4. Ignition and detonation:

[0024] The synchronous ignition system is used to perform synchronous ignition to ignite the methane gas in the experimental pipeline, causing it to explode;

[0025] Step 5: Experimental data processing

[0026] The data acquisition system is used to collect data from the explosion process in conjunction with the pressure sensor and the flame sensor, and the collected experimental data is analyzed. The specific analysis method is as follows:

[0027] S1. Firstly, the collected experimental data are subjected to point compression processing using the Douglas-Peucker algorithm;

[0028] S2. After the experimental data is compressed and processed, the gas explosion pressure and flame propagation law in the experimental pipeline are analyzed, the time, spatial position and maximum explosion pressure value of each detection point are recorded, the flame arrival time and flame light signal intensity of each point in the flame sensor are analyzed, and the flame propagation speed in the pipeline is calculated. The specific steps are as follows:

[0029] 1) Record the maximum explosion pressure value at each detection point in each pipeline, and according to the aspect ratio, unify the pressure data at each measurement point in different pipelines into a phase framework for analysis, and obtain the size, occurrence time, occurrence position and pressure rise rate of the maximum pressure value under the same aspect ratio in experimental pipelines of different nominal diameters;

[0030] 2) Select the explosion pressure time domain diagrams at three locations in the experimental pipeline, namely near the synchronous ignition system, in the middle of the pipeline, and at one end of the pipeline far from the synchronous ignition system, and analyze the pressure change over time images in experimental pipelines with different nominal diameters. Analyze the changes in the two-wave three-zone structure and the differences in the appearance time of the precursor shock wave and the deflagration wave in experimental pipelines with different nominal diameters, and study the influence of pipeline scale on the propagation law;

[0031] 3) Analyze the flame arrival time, flame duration, and flame intensity based on the flame data measured by each flame sensor, and use the time difference between each measuring point to analyze the flame propagation speed. The calculation formula is as follows:

[0032]

[0033] S is the distance between the detection point and the closed end of the blind plate of the experimental pipeline, and T is the flame arrival time at each detection point;

[0034] 4) Analyze the coupling relationship between flame propagation and pressure propagation, record the maximum pressure and pressure wave arrival time in different pipelines, compare the time required for the flame wave to reach the same position, analyze the relationship between the maximum explosion pressure and the trend of flame propagation speed change under the same aspect ratio, the relationship between flame morphology change and pressure change, study the changes in propagation laws caused by the synergistic effect of flame and pressure, and analyze the self-acceleration process of pressure wave and flame wave in the pipeline;

[0035] 5) Analyze the dynamic and motion similarity states in experimental pipes of different nominal diameters, calculate the ratios of flame speed and explosion pressure peak at the same aspect ratio measuring points in experimental pipes of different nominal diameters, and compare them. Analyze whether there is an obvious linear relationship and motion similarity relationship between the flame propagation speed and pressure ratio in different pipe diameters, and study whether there is an approximate relationship in the change law between the flame propagation speed ratio curves of experimental pipes of different nominal diameters. Study the ratio curves at different points, and analyze the flow similarity states at each point in the experimental pipes of different nominal diameters. The specific analysis method is as follows:

[0036] The obtained experimental data were analyzed by using the fluid mechanics similarity criterion analysis method. The Reynolds number, Froude number, Euler number and Mach number indicators were selected for analysis according to the flow field state inside the experimental pipeline. The Reynolds number, Froude number, Euler number and Mach number in different experimental pipelines were calculated based on the collected experimental data, the data of the experimental pipeline and the data of the explosion gas. It was observed whether there was a linear relationship between the ratio of the Reynolds number, Froude number, Euler number and Mach number of experimental pipelines with different nominal diameters, and the ratio was compared with the pipe diameter ratio to determine whether the gas explosion experiment under the experimental pipelines with different nominal diameters met various similarity criteria.

[0037] Furthermore, in step three, after the gas is filled into the experimental pipeline through the gas distribution system, the methane gas in the experimental pipeline is circulated and stirred by a vacuum pump that is circulated and connected to the experimental pipeline so that the methane concentration at each location in the experimental pipeline is the same.

[0038] The beneficial effects of the present invention are:

[0039] The present invention provides an experimental system and method based on the scale effect of gas explosion under actual working conditions. An experimental system that can be used to reproduce gas explosion in pipelines under actual working conditions is designed. The system includes experimental pipelines with five diameters of 200mm, 500mm, 700mm, 800mm and 1000mm. The experimental pipelines are composed of multiple sections of pipelines in sections. The pipelines are connected by living flanges and can be adjusted according to the length required for actual research to ensure that the length-to-diameter ratio of each group of pipelines is the same.

[0040] The present invention also proposes a data analysis method based on the experimental system, in which the gas explosion pressure and flame propagation data in pipelines of different scales are studied under the same dimensionless number condition, the length and width in the pipeline are unified as the aspect ratio, and the propagation law of gas explosion in different pipelines under the same aspect ratio condition is comprehensively considered; and the fluid mechanics method is used to analyze the motion and dynamic similarity and explosion process similarity criteria in different experimental pipelines, so as to study the change law of shock wave in the pipeline and the flow field change after the explosion occurs in the gas transmission pipeline.

[0041] Other advantages, objectives and features of the present invention will be described in the following description to some extent, and to some extent, will be obvious to those skilled in the art based on the following examination and study, or can be taught from the practice of the present invention. The objectives and other advantages of the present invention can be realized and obtained through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention will be described in detail below in conjunction with the accompanying drawings, wherein:

[0043] Figure 1 It is a structural schematic diagram of the experimental pipeline in the present invention;

[0044] Figure 2 This is a schematic diagram of the layout of the DN200mm experimental pipeline in Example 1;

[0045] Figure 3 This is a schematic diagram of the layout of the DN500mm experimental pipeline in Example 1;

[0046] Figure 4 This is a schematic diagram of the layout of the DN700mm experimental pipeline in Example 1;

[0047] Figure 5 is a graph showing the relationship between the maximum explosion pressure and the aspect ratio in Example 1;

[0048] Figure 6 Explosion pressure waveforms at different measuring points in Example 1 (DN700mm);

[0049] Figure 7 Explosion flame waveforms at different measuring points in Example 1 (DN700mm).

[0050] Figure numerals: blind plate 1, ignition head 2, flange 3, sealing ring 4, glass observation window 5, transparent pipe 6, threaded hole 7, sealing film 8. DETAILED DESCRIPTION

[0051] The following describes the embodiments of the present invention by specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments only illustrate the basic concept of the present invention in a schematic manner, and the following embodiments and features in the embodiments can be combined with each other without conflict.

[0052] Among them, the drawings are only used for illustrative explanations, and they only represent schematic diagrams rather than actual pictures, and should not be understood as limitations on the present invention. In order to better illustrate the embodiments of the present invention, some parts of the drawings may be omitted, enlarged or reduced, and do not represent the size of actual products. For those skilled in the art, it is understandable that some well-known structures and their descriptions in the drawings may be omitted.

[0053] The same or similar numbers in the drawings of the embodiments of the present invention correspond to the same or similar parts; in the description of the present invention, it should be understood that if the terms "upper", "lower", "left", "right", "front", "rear", etc. indicate the orientation or position relationship, they are based on the orientation or position relationship shown in the drawings, which is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation. Therefore, the terms describing the position relationship in the drawings are only used for illustrative purposes and cannot be understood as limiting the present invention. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to specific circumstances.

[0054] See also Figure 1 to Figure 4It is an experimental system based on the scale effect of gas explosion under actual working conditions, including an experimental pipeline, a pressure sensor installed on the experimental pipeline, a flame sensor, a laser methane concentration detector, a synchronous ignition system, a gas distribution system, a circulating stirring system, a data acquisition system connected to the pressure sensor and the flame sensor, and a high-speed camera for shooting the explosion flame waveform.

[0055] The key point of this embodiment is that the experimental system comprises at least two experimental pipes, and the nominal diameters of the experimental pipes are two of 200 mm, 500 mm, 700 mm, 800 mm or 1000 mm.

[0056] Specifically, the experimental pipeline includes multiple pipe sections connected by flanges 3, and a sealing ring 4 is also provided at the connection of the flanges 3 to ensure a sealed connection, and the length of each pipe section is set to 6m so that the length of the experimental pipeline can be freely modified.

[0057] A blind plate 1 and a sealing film 2 are respectively provided at the openings at both ends of the experimental pipeline to seal the experimental pipeline, and the end where the blind plate 1 is located is a fixed closed end, and the end where the sealing film 2 is located is a weakly constrained closed end, so that when an explosion occurs in the experimental pipeline, it will propagate toward the end where the sealing film 2 is located.

[0058] Preferably, the sealing film 8 is a 0.12 mm polyethylene plastic film.

[0059] Preferably, one of the plurality of pipe sections is set as a transparent pipe 6, and one of the remaining pipe sections is provided with a glass observation window 5 for arranging a high-speed camera.

[0060] Preferably, a plurality of threaded holes 8 are provided on the experimental pipeline for connecting a pressure sensor, a flame sensor, a laser methane concentration detector, a synchronous ignition system, a gas distribution system and a circulating stirring system. The synchronous ignition system includes an ignition head 2 arranged near one end of the blind plate.

[0061] The circulating stirring system comprises a vacuum pump, and two ends of the vacuum pump are connected to two ends of the experimental pipeline through a vacuum pipeline, so that the vacuum pump can perform vacuum circulating stirring on the gas in the experimental pipeline.

[0062] An experimental method based on the scale effect of gas explosion under actual working conditions, using the above experimental system, specifically includes the following steps:

[0063] Step 1: Arrange the experimental pipeline under actual working conditions;

[0064] Arrange at least two experimental pipelines with a nominal diameter of 200mm, 500mm, 700mm, 800mm or 1000mm to simulate pipelines under actual working conditions, and each experimental pipeline has a different nominal diameter, and arrange a pressure sensor, a flame sensor and a glass observation window on each experimental pipeline, and connect a circulating stirring system, a gas distribution system, a synchronous ignition system, a data acquisition system, a laser methane concentration detector and a high-speed camera, and divide the experimental pipeline into sections of 6m each, and connect them with flanges to facilitate the modification and change of the length of the experimental pipeline, and one section of the pipeline is a 6m long transparent pipeline to observe the flame inside the experimental pipeline in detail, and a blind plate is installed at one end of the experimental pipeline using a flange to form a fixed closed end, and the other end is closed with a 0.12mm polyethylene plastic film to form a weakly constrained closed end;

[0065] Preferably, the DN500 test pipeline is 66 m long, the DN700 test pipeline is 93 m long, and the lengths of all other test pipelines are 60 m.

[0066] Step 2: Set up the experimental system;

[0067] After calibrating the pressure sensor, according to the different nominal diameters of each experimental pipeline, multiple pressure sensors and flame sensors are installed at different positions, so that the positions corresponding to the installation of the pressure sensor and the flame sensor of each experimental pipeline are at the same aspect ratio, a black curtain arranged along the axial direction of the experimental pipeline is installed at the outlet of the experimental pipeline, and the specific size is marked, and a high-speed camera is installed at the glass observation window and the outlet of the experimental pipeline to take flame propagation images, the pressure sensor and the flame sensor are connected to the data acquisition system, the ignition head 2 is installed to the ignition position (a section of the experimental pipeline close to the blind plate), and the data acquisition system is connected to the synchronous ignition system;

[0068] Specifically, the experimental pipeline is provided with a plurality of threaded holes 7, and the pressure sensor and the flame sensor are installed at the front, middle and rear ends of the experimental pipeline using the threaded holes, that is, each experimental pipeline is provided with at least three pressure sensors and three flame sensors.

[0069] Step 3: Fill the experimental pipe with gas and stir to mix evenly;

[0070] Methane gas is charged into the experimental pipeline to the required concentration through the gas distribution system. The methane concentration in the pipeline can be observed in real time through the laser methane concentration detector installed on the experimental pipeline. After the methane gas is charged, the circulation stirring system is turned on to circulate and stir the methane gas in the experimental pipeline through the vacuum pump to make the gas concentration at each location in the experimental pipeline the same;

[0071] Specifically, the gas distribution system includes a gas cylinder and a gas pipeline connecting to the experimental pipeline. A stop valve and a check valve are provided on the gas pipeline, and a gas inlet connecting to the gas pipeline is provided on the experimental pipeline. The gas inlet can be specifically set as a threaded hole, and a valve is provided at the gas inlet. The circulation time of the circulation stirring system is adaptively selected according to the volume of different experimental pipelines.

[0072] Step Four: Ignition and detonation

[0073] After the methane gas in the experimental pipeline is evenly mixed, the ignition heads are controlled by the synchronous ignition system to ignite synchronously, igniting the methane gas in the experimental pipeline to cause an explosion.

[0074] Specifically, the energy of each ignition head is about 10 J.

[0075] Step Five: Experimental data processing

[0076] The data during the explosion process is collected by the data acquisition system in cooperation with the pressure sensor and the flame sensor, and the collected experimental data is analyzed. The specific analysis method is as follows:

[0077] 1. First, compress the original experimental data. Since the pressure sensor and the flame sensor have a high sampling frequency and a long sampling time, a large amount of redundant data will appear. It is necessary to process the collected data. The Douglas-Peuker algorithm is used to downsample the obtained data to obtain data that is more convenient to process. The specific operation is as follows:

[0078] 1) For a given curve, first connect the starting point and the ending point of the curve to form a straight line. Then calculate the distance from each point on the curve to this straight line.

[0079] 2) Find the maximum value in the distances, denoted as dmax, and compare it with the threshold D.

[0080] 3) If dmax < D, it means that the distances from all points on the curve to the straight line are within the threshold range. At this time, the intermediate points on the curve can be discarded, and only the starting point and the ending point are retained. The straight line segment is used as an approximation of the curve, and this section of the curve is processed.

[0081] 4) If dmax ≥ D, it means that there are points with distances exceeding the threshold. The curve is divided into two parts at the coordinate point corresponding to dmax, and the above method is repeated for each part, that is, repeat steps 1) and 2) to find the maximum distance of each part and determine whether further segmentation is required.

[0082] 5) Repeat steps 1) to 4) until all dmax are less than the threshold D. At this time, the thinning of the curve is completed.

[0083] 2. After processing the data points, analyze the gas explosion pressure and flame propagation law in the pipeline, record the time, spatial position and maximum explosion pressure value at each point, analyze the flame arrival time and flame light signal intensity at each point in the flame sensor, and calculate the flame propagation speed in the pipeline. The specific steps are as follows:

[0084] 1). Record the maximum explosion pressure value at each measuring point in different pipelines, and unify the pressure data at each measuring point in different pipelines according to the length-to-diameter ratio (L / D) and analyze them to obtain the maximum pressure value, occurrence time, occurrence position and pressure rise rate under the same length-to-diameter ratio in experimental pipelines of different nominal diameters;

[0085] 2). Select the explosion pressure time domain diagrams at three locations in the experimental pipeline, namely, near the ignition head, in the middle of the pipeline, and at the pipeline outlet, analyze the pressure change over time in the experimental pipelines with different nominal diameters, analyze the changes in the two-wave three-zone structure in the experimental pipelines with different nominal diameters, and the differences in the appearance time of the precursor shock wave and the deflagration wave, and study the influence of the pipeline scale on the propagation law;

[0086] 3). Analyze the flame arrival time, flame duration, and flame intensity based on the flame data measured by each flame sensor, and use the time difference between each measuring point to analyze the flame propagation speed. The calculation formula is as follows:

[0087] S is the distance between the measuring point and the closed end of the experimental pipe, and T is the flame arrival time at each measuring point; (i.e., the flame propagation speed is calculated using the difference in flame propagation time between two measuring points and the difference in distance between the measuring points. At the same time, the flame image observed in the glass observation window is used to correct the calculated flame propagation speed, and the variation trend of parameters such as the flame speed rise rate with the aspect ratio is further analyzed);

[0088] 4). Analyze the coupling relationship between flame propagation and pressure propagation, record the maximum pressure and pressure wave arrival time in different pipelines, compare the time required for the flame wave to reach the same position, analyze the relationship between the maximum explosion pressure and the trend of flame propagation speed change under the same aspect ratio, the relationship between flame morphology change and pressure change, study the changes in propagation laws caused by the synergistic effect of flame and pressure, and analyze the self-acceleration process of pressure wave and flame wave in the pipeline;

[0089] 5). Analyze the dynamic and motion similarity in experimental pipes of different nominal diameters: Calculate the ratio of flame speed and explosion pressure peak at the same aspect ratio measuring point in experimental pipes of different nominal diameters, and compare them. Analyze whether there is an obvious linear relationship and motion similarity relationship between the flame propagation speed and pressure ratio in different pipe diameters. Study whether there is an approximate relationship in the variation law between the flame propagation speed ratio curves of experimental pipes of different nominal diameters. Study the ratio curves at different points and analyze the flow similarity at each point in experimental pipes of different nominal diameters.

[0090] 3. Use the fluid mechanics similarity criterion analysis method to analyze the experimental data obtained, and select the following indicators for analysis according to the internal flow field state of the pipeline: Reynolds number, Froude number, Euler number and Mach number;

[0091] Reynolds number is a dimensionless number that can be used to characterize fluid flow conditions. It is a similarity criterion number that characterizes the effect of viscosity in fluid mechanics. The calculation formula is: Where v, ρ, and μ are the velocity, density, and viscosity coefficient of the fluid, respectively, and d is the characteristic length. In a circular pipe, d is the equivalent diameter of the pipe; the Reynolds number can be used to distinguish whether the flow of a fluid is laminar or turbulent, and can also be used to determine the resistance encountered by an object flowing in a fluid;

[0092] Froude number is a dimensionless parameter in fluid mechanics that characterizes the relative magnitude of the inertial force and gravity of the fluid. In the flow where inertial force and gravity play an important role, in order to meet the dynamic similarity condition, the Froude number of the model and the real object must be equal. The calculation formula is: Where v: fluid velocity (m / s); g: gravitational acceleration; L: characteristic length;

[0093] The Euler Number represents the ratio of pressure to inertia force acting on corresponding points in similar flows. If two geometrically similar flows have similar pressures, then the Euler Numbers at their corresponding points must be equal; conversely, if the Euler Numbers at the corresponding points of the two flows are equal, then the two flows must have similar pressures. The calculation formula is as follows:

[0094] The pressure F acting on the fluid p It can be expressed as:

[0095] F p = pA∝pl 2

[0096] Position change plus inertia force F c It can be expressed as:

[0097]

[0098] From the above formula, we can get:

[0099]

[0100] Mach number is the elastic force similarity criterion number, and its physical meaning is the ratio of inertial force to elastic force. If the elastic force is similar when considering the compressibility of the fluid, because the elastic force F e =KA∝ρc 2 L 2 (K is the bulk elastic modulus of the fluid, c is the speed of sound in the fluid), then the Mach number M is calculated as:

[0101]

[0102] The specific analysis process is as follows: first calculate the diameter ratio between each experimental pipe. For example, if we use a DN800mm pipe and a DN1000mm pipe for analysis, first calculate the diameter ratio between the two experimental pipes 800 / 1000 as 0.8, then the geometric similarity ratio between the two pipes is 0.8. At the same time, since the gas flow rate cannot be directly measured in the experimental pipe, the following formula can be used to solve it. The gas flow rate in the pipe can be calculated using the following formula:

[0103] V=18.1+3.68L+(1455-23.56L)P(m / s)

[0104] Where L is the length of the pipeline, P is the overpressure, and V is the maximum flow velocity peak;

[0105] For the density of a mixture of methane and air, we need to know the densities of methane and air and their proportions in the mixture. Assume that methane and air are ideal gases and their mixture is an ideal mixture. Under standard conditions (normal temperature and pressure), the density of methane is about 0.717 kg / m 3 , and the density of air is about 1.225kg / m 3 The density of the mixed gas is calculated by weighted summation based on the volume fraction of each component. Take 9.5% methane-air mixed gas as an example:

[0106] The volume fraction of methane is 0.095, and the volume fraction of air is 0.905, calculated using the following formula:

[0107] ρ mix =∑ i (ρ i ·V)

[0108] Where: mix is the density of the mixed gas; ρi is the density of the i-th gas; V is the volume fraction

[0109] Substitute the numerical calculation: ρ mix =0.068115+1.107125=1.17524kg / m 3 ;

[0110] The Reynolds number is calculated for each flame propagation velocity measurement point, and the process of turbulent and laminar flow changes in experimental pipes with different pipe diameters is analyzed. After comparing the values ​​at each point with the pipe diameter ratio, it is analyzed whether the viscosity effects between the two groups of pipes are similar;

[0111] Dynamic Similarity Analysis Using Froude Number The velocity is calculated using the above formula, and the gravity and characteristic length are calculated according to the actual situation. The Froude numbers of the two pipes are compared to determine whether they are the same, and whether their gravity and inertia ratios are similar.

[0112] Euler number calculation: The pressure difference p0 is calculated using the pressure difference at both ends of the experimental pipeline, and the Euler number is calculated using the flow velocity U0 and density ρ. Observe whether the overall change pattern of the Euler number in the two pipelines is similar, whether there is a moment with the same Euler number, and determine the similarity of the explosion flow field pressure in pipelines with different diameters.

[0113] Mach number calculation, based on the fluid flow rate and the speed of sound in the pipe of 340m / s, is performed to analyze the similarity of elastic force when the fluid is compressible in experimental pipes of different nominal diameters.

[0114] Observe whether there is a linear relationship between the ratios of Reynolds number, Froude number, Euler number and Mach number of experimental pipes with different nominal diameters, and compare the ratios with the benchmark ratios between pipe diameters to determine whether the gas explosion experiments under experimental pipes with different nominal diameters meet various similarity criteria;

[0115] If the overall similarity is not high, is there any local similarity? This is to study the effect of pipe diameter on the degree of similarity.

[0116] Example 1

[0117] 1. Gas explosion experiment under actual working conditions

[0118] Step 1. Arrange the experimental pipeline

[0119] Three experimental pipes of DN200mm, DN500mm and DN700mm were selected. In order to ensure the same aspect ratio and taking into account the composition of the pipes, the lengths of the experimental pipes were selected to be 21m, 66m and 93m respectively. One end of the experimental pipe was closed with a steel blind plate, and the other end was closed with two layers of 0.12mm polyvinyl chloride plastic film to form a weakly constrained closed space. During the experiment, the entire pipe was filled with methane gas, and the methane concentration was selected to be 9.5%.

[0120] Step 2: Install the pressure sensor and flame sensor

[0121] After calibrating each sensor using the sensor calibration equipment, install the pressure and flame sensors on the above experimental pipelines. The specific installation locations are as follows: Figure 2 to Figure 4 As shown (the installation positions of the pressure and flame sensors of the three experimental pipes of DN200mm, DN500mm and DN700mm are respectively indicated, wherein the pressure sensors are respectively arranged at the positions of the length-to-diameter ratios of 7, 18, 30, 43, 55, 67, 79, 90 and 102 in the three experimental pipes, and the flame sensors are respectively arranged at the positions of the length-to-diameter ratios of 7, 19, 31, 43, 55, 67, 78.5, 91 and 102), the experimental pipes shown are provided with threaded holes, after the pressure sensors and flame sensors are installed on the experimental pipes by means of stainless steel hexagon hollow screws, the lines of each sensor are connected to the data acquisition system, and the sensors and lines are tested to see if they are normal;

[0122] Step 3: Fill the pipe with gas and stir to mix evenly

[0123] Through the gas distribution system, 0.06267m3 of gas was respectively charged into the DN200mm, DN500mm and DN700mm experimental pipes. 3 、1.1192m 3 、3.4m 3 After the methane gas is released, a vacuum pump is used to circulate and stir for a certain period of time, and then the methane concentration is detected at the front, middle and rear ends of the experimental pipeline. When the methane concentration at each location is the same, the vacuum pump is turned off, the stirring is stopped, and a high-speed camera is placed at the glass observation window on the pipeline.

[0124] Step 4: Ignition and Detonation

[0125] Two 10J ignition heads are installed at the ignition position, connected to the ignition point through lines, and the ignition system and the data acquisition system are triggered synchronously. After ignition, the explosion occurs, and the data acquisition system collects the experimental data of the explosion engineer;

[0126] 2. Study the scale effect after gas explosion under actual working conditions

[0127] After the explosion experiment was completed, in order to avoid errors caused by accidental factors, the experiment was repeated more than twice, and the three experiments were combined to select the most ideal group of data for analysis and comparison.

[0128] 1. Maximum explosion pressure at each measuring point

[0129] By analyzing the relationship between the maximum explosion pressure and the aspect ratio, it can be found that the change in pipe diameter has a certain influence on the change trend of the maximum explosion pressure and the size of the pressure peak. The propagation law of gas explosion in the three experimental pipes is nonlinear. Table 1 shows the maximum explosion pressure data of each measuring point detected by the sensor after the gas explosion.

[0130] Table 1 Maximum explosion pressure at each measuring point

[0131]

[0132] 2. Flame data at each measuring point

[0133] Table 2 shows the time data measured by the flame sensor after the explosion. The flame arrival time measured by the first flame sensor is taken as 0, and the flame arrival time of each measuring point is calculated as shown in Table 2. It can be seen that as the propagation distance increases, the flame arrival time interval becomes closer and closer, that is, the flame propagation speed becomes faster and faster. The flame propagation speed increases with the increase of the propagation distance, and the flame propagation speed is the fastest near the exit.

[0134] Table 2 Flame arrival time at each measuring point

[0135]

[0136] Based on the above data, using the formula (where s is the distance between the sensor and the closed end, and t is the flame arrival time at each sensor) The relationship between the flame propagation speed and the aspect ratio can be calculated and plotted as a curve. Figure 5 As shown in the figure, by analyzing the trend of flame speed change along the pipeline, it can be found that the pipe diameter has a great influence on the concentration and flame propagation speed. Under the same aspect ratio, when the pipe diameter is 200mm, the propagation speed is the fastest; in the DN700 pipe, the propagation speed is the slowest; the flame speed and propagation law of the DN500mm pipe and the DN200mm pipe are relatively close under the same aspect ratio, while the DN700 pipe is quite different from the first two pipes. At the same time, it can be found that the flame propagation speed near the explosion source is small, and it rises to a certain peak and then decays. Since the propagation of gas explosion is divided into two stages: ignition and propagation. In the initial stage, the flame propagation speed is small, but in front of the flame, due to the effect of the precursor shock wave, the combustion gradually accelerates with heating and compression. The accelerated propagation of the flame increases the speed and intensity of the shock wave, thereby accelerating the expansion of the gas. However, the expansion also decays the combustion, restricting the further expansion of the gas.

[0137] 3. Analysis of the explosion pressure waveform over time at a specific measuring point

[0138] like Figure 6As shown in the figure, during the propagation of gas explosion at the measuring points of 5m, 13m, 30m, and 55.5m from the closed end of the DN700mm pipeline, the physical mechanism of shock wave propagation includes two stages: the strong compression wave propagates toward the pipeline outlet, and after a period of time, the gas expansion wave propagates toward the closed end of the pipeline, that is, close to the fire source. As the distance from the closed end of the pipeline, that is, the ignition position, increases, the negative pressure value of the expansion wave decreases. When the distance from the closed end of the pipeline is 55m, the negative pressure of the expansion wave is already very small. The pressure wave waveform shows obvious oscillation.

[0139] 4. Explosion flame duration at different measuring points

[0140] like Figure 7 As shown in the figure, the images detected by the two sets of sensors at 21.5m, 24.5m, 38.5m, and 41.5m from the closed end of the DN700 mm pipeline are selected. According to the time difference between the two sets of sensors, Δt1 = 0.01387s and Δt2 = 0.00682s, the speed of the flame passing through the two sets of sensors is calculated to be 216m / s and 440m / s respectively. As the measuring point is located further back, the flame propagation speed is getting faster and faster, and the flame duration is getting shorter and shorter. At 21.5m from the closed end, the flame duration is t1 = 0.50288s, and at 41.5m from the closed end, the flame duration is t4 = 0.28452s. In the early stage of the deflagration reaction, due to the slow reaction speed of the flame, the time interval of the flame arrival detected by the sensor is longer, but as the reaction process progresses, the combustion reaction speed gradually accelerates; therefore, the closer to the pipeline outlet, the faster the flame propagation speed. At 21.5m from the closed end, the flame repeatedly fluctuated and oscillated back and forth in this area due to the rebound of the pressure wave on the side wall. The flame duration reached 0.50288s.

[0141] The present invention provides an experimental system and method based on the scale effect of gas explosion under actual working conditions. The gas explosion test is carried out in experimental pipelines with different nominal diameters under the same aspect ratio. The scale effect of gas explosion in the pipeline can be comprehensively and systematically studied, and the laboratory simulation scale is linked to the actual engineering scale, so as to provide support for engineering applications and provide a theoretical basis for the research and development and application of explosion suppression and isolation equipment.

[0142] In this experimental method, the pressure of the shock wave and the spread of the flame in the pipeline during the explosion are tested and recorded through a data acquisition system. At the same time, a high-speed camera is used to capture the changes in the flame morphology in the pipeline, in order to study the shock wave of the gas explosion in the pipeline and clarify the scale effect of the pipeline explosion propagation and the "mutual feedback" acceleration mechanism of the dynamic parameters.

[0143] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solution, which should be included in the scope of the claims of the present invention.

Claims

1. An experimental system based on the scale effect of gas explosion under actual working conditions, including an experimental pipeline, characterized in that: There are at least two experimental pipes, the nominal diameters of the experimental pipes are 200 mm, 500 mm, 700 mm, 800 mm or 1000 mm, and the nominal diameters of the experimental pipes are different, and each experimental pipe has the same aspect ratio.

2. The experimental system based on the scale effect of gas explosion under actual working conditions according to claim 1 is characterized in that: It also includes pressure sensors, flame sensors, laser methane concentration detectors, synchronous ignition systems and gas distribution systems installed on the experimental pipeline, a data acquisition system connected to the pressure sensors and flame sensors, and a high-speed camera for photographing explosion flames.

3. The experimental system based on the scale effect of gas explosion under actual working conditions according to claim 2 is characterized in that: Blind plates and sealing films are respectively provided at both ends of the experimental pipeline to seal the experimental pipeline.

4. The experimental system based on the scale effect of gas explosion under actual working conditions according to claim 3 is characterized in that: A plurality of threaded holes are arranged on the experimental pipeline for connecting a pressure sensor, a flame sensor, a laser methane concentration detector, a synchronous ignition system, a gas distribution system and a circulating stirring system.

5. The experimental system based on the scale effect of gas explosion under actual working conditions according to claim 4 is characterized in that: The synchronous ignition system comprises an ignition head arranged near one end of the blind plate.

6. The experimental system based on the scale effect of gas explosion under actual working conditions according to claim 4 is characterized in that: The circulating stirring system comprises a vacuum pump, and two ends of the vacuum pump are connected to two ends of the experimental pipeline through a vacuum pipeline, so that the vacuum pump can perform vacuum circulating stirring on the gas in the experimental pipeline.

7. The experimental system based on the scale effect of gas explosion under actual working conditions according to claim 1 is characterized in that: The experimental pipeline includes a plurality of pipe sections connected by flanges.

8. The experimental system based on the scale effect of gas explosion under actual working conditions according to claim 7 is characterized in that: One of the multiple pipe sections is set as a transparent pipe to facilitate observation of the flame during the explosion.

9. An experimental method based on the scale effect of gas explosion under actual working conditions, characterized in that: An experimental system based on the scale effect of gas explosion under actual working conditions according to any one of claims 1 to 8 is provided, which specifically comprises the following steps: Step 1. Arrange the experimental pipeline based on actual working conditions: Arrange at least two test pipes with a nominal diameter of 200mm, 500mm, 700mm, 800mm or 1000mm to simulate the pipelines under actual working conditions, and each test pipe has a different nominal diameter and the same aspect ratio; A blind plate is installed at one end of the experimental pipeline using a flange to form a fixed closed end, and the other end is sealed with a polyethylene plastic film to form a weakly constrained closed end, and a glass observation window is provided in the middle of each experimental pipeline; Step 2. Set up the experimental system: According to the different nominal diameters and lengths of each experimental pipeline, multiple pressure sensors and flame sensors are installed at corresponding positions of the experimental pipeline, so that the positions corresponding to the installation of the pressure sensors and flame sensors in each experimental pipeline have the same aspect ratio, a black curtain arranged along the axial direction of the experimental pipeline is installed at one end of the experimental pipeline where the polyethylene plastic film is installed, and the specific size is marked, and a high-speed camera is installed on the glass observation window and the black curtain of the experimental pipeline to take flame propagation images, the pressure sensor and the flame sensor are connected to the data acquisition system to collect data for the corresponding detection points, and a synchronous ignition system is installed at one end of the experimental pipeline close to the blind plate as a detonation device, and the data acquisition system is connected to the synchronous ignition system; Step 3. Fill the experimental pipeline with gas: Methane gas is charged into the experimental pipeline to a desired concentration through the gas distribution system, and the methane concentration in the pipeline is observed in real time through a laser methane concentration detector installed on the experimental pipeline; Step 4. Ignition and detonation: The synchronous ignition system is used to perform synchronous ignition to ignite the methane gas in the experimental pipeline, causing it to explode; Step 5: Experimental data processing The data acquisition system is used to collect data from the explosion process in conjunction with the pressure sensor and the flame sensor, and the collected experimental data is analyzed. The specific analysis method is as follows: S1. Firstly, the collected experimental data are subjected to point compression processing using the Douglas-Peucker algorithm; S2. After the experimental data is compressed and processed, the gas explosion pressure and flame propagation law in the experimental pipeline are analyzed, the time, spatial position and maximum explosion pressure value of each detection point are recorded, the flame arrival time and flame light signal intensity of each point in the flame sensor are analyzed, and the flame propagation speed in the pipeline is calculated. The specific steps are as follows: 1) Record the maximum explosion pressure value at each detection point in each pipeline, and according to the aspect ratio, unify the pressure data at each measurement point in different pipelines into a phase framework for analysis, and obtain the size, occurrence time, occurrence position and pressure rise rate of the maximum pressure value under the same aspect ratio in experimental pipelines of different nominal diameters; 2) Select the explosion pressure time domain diagrams at three locations in the experimental pipeline, namely near the synchronous ignition system, in the middle of the pipeline, and at one end of the pipeline far from the synchronous ignition system, and analyze the pressure change over time images in experimental pipelines with different nominal diameters. Analyze the changes in the two-wave three-zone structure and the differences in the appearance time of the precursor shock wave and the deflagration wave in experimental pipelines with different nominal diameters, and study the influence of pipeline scale on the propagation law; 3) Analyze the flame arrival time, flame duration, and flame intensity based on the flame data measured by each flame sensor, and use the time difference between each measuring point to analyze the flame propagation speed. The calculation formula is as follows: S is the distance between the detection point and the closed end of the blind plate of the experimental pipeline, and T is the flame arrival time at each detection point; 4) Analyze the coupling relationship between flame propagation and pressure propagation, record the maximum pressure and pressure wave arrival time in different pipelines, compare the time required for the flame wave to reach the same position, analyze the relationship between the maximum explosion pressure and the trend of flame propagation speed change under the same aspect ratio, the relationship between flame morphology change and pressure change, study the changes in propagation laws caused by the synergistic effect of flame and pressure, and analyze the self-acceleration process of pressure wave and flame wave in the pipeline; 5) Analyze the dynamic and motion similarity states in experimental pipes of different nominal diameters, calculate the ratios of flame speed and explosion pressure peak at the same aspect ratio measuring points in experimental pipes of different nominal diameters, and compare them. Analyze whether there is an obvious linear relationship and motion similarity relationship between the flame propagation speed and pressure ratio in different pipe diameters, and study whether there is an approximate relationship in the change law between the flame propagation speed ratio curves of experimental pipes of different nominal diameters. Study the ratio curves at different points, and analyze the flow similarity states at each point in the experimental pipes of different nominal diameters. The specific analysis method is as follows: The obtained experimental data were analyzed by using the fluid mechanics similarity criterion analysis method. The Reynolds number, Froude number, Euler number and Mach number indicators were selected for analysis according to the flow field state inside the experimental pipeline. The Reynolds number, Froude number, Euler number and Mach number in different experimental pipelines were calculated based on the collected experimental data, the data of the experimental pipeline and the data of the explosion gas. It was observed whether there was a linear relationship between the ratio of the Reynolds number, Froude number, Euler number and Mach number of experimental pipelines with different nominal diameters, and the ratio was compared with the pipe diameter ratio to determine whether the gas explosion experiment under the experimental pipelines with different nominal diameters met various similarity criteria.

10. The experimental method based on the scale effect of gas explosion under actual working conditions according to claim 9 is characterized in that: In step three, after the gas is filled into the experimental pipeline through the gas distribution system, the methane gas in the experimental pipeline is circulated and stirred through a vacuum pump that is circulated and connected to the experimental pipeline so that the methane concentration at each location in the experimental pipeline is the same.

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