CN112214943B - Method for calculating nitrogen flow dynamic pressure loss of three-dimensional simulated coal mine goaf - Google Patents
Method for calculating nitrogen flow dynamic pressure loss of three-dimensional simulated coal mine goaf Download PDFInfo
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Abstract
The invention discloses a method for calculating nitrogen flow dynamic pressure loss of a simulated three-dimensional coal mine goaf. The method mainly comprises the following steps: establishing a goaf gas flow model, and dividing a single-period flow unit; taking the single-period flow unit as a research object, and dividing the single-period flow unit into four flow stages according to different expressions of the section area changing along with the flow distance; deducing a theoretical calculation formula of nitrogen flow pressure loss in the goaf; on the basis of a theoretical calculation formula, experimental optimization is carried out, the difference between one-dimensional simplification and three-dimensional flow is reduced, and a pseudo three-dimensional flow pressure loss calculation formula is obtained. The method can be used for calculating the nitrogen flow dynamic pressure loss in the goaf, realizes the quick and accurate calculation of the initial pressure and the filling range required by goaf nitrogen filling, and avoids the defects of more time consumption and large technical difficulty of a numerical simulation method.
Description
Technical Field
The invention belongs to the technical field of mine ventilation and goaf disaster prevention and reduction, and particularly relates to a pseudo-three-dimensional coal mine goaf nitrogen flow dynamic pressure loss calculation method.
Background
Over 70% of coal mine fire accidents occur in goafs adjacent to the mining area. The natural fire of the left coal in the goaf and the fire extinguishing and disaster relief thereof are always hot problems in the industry, and the most common and effective fire extinguishing measure is to adopt nitrogen injection to treat the natural fire. However, the existing calculation method and implementation rules cannot accurately calculate the flowing distance of the injected nitrogen for fire extinguishing in the goaf, so that the influence range of the injected nitrogen cannot be accurately predicted, and liquid nitrogen waste and fire extinguishing difficulty are caused.
In the aspect of research progress of determining a method and measures for nitrogen injection parameters of a goaf, Ledong et al provides a fire prevention and extinguishing method for full-section curtain nitrogen injection of a U-shaped ventilation working surface of the goaf, and nitrogen inerting efficiency is improved. The automatic control rotary traction type nitrogen injection fire prevention and extinguishing device is invented by vermilion green, continuity of nitrogen injection points in the goaf on the space is achieved, and the inerting effect of nitrogen injection in the goaf is improved. According to the method, leakage stoppage, wind control and rapid inerting cooling are integrated, and spontaneous combustion of the residual coal is efficiently prevented. Guojunliu discusses the observation of three zones in the goaf and the practical method of nitrogen injection fire prevention and extinguishing, and improves the safety and economic benefit of coal mining. And establishing a theoretical fluid mechanics model of the gas volume fraction change of the goaf by cinnabar according to mass, momentum and component conservation equations, and determining the optimal nitrogen injection position and nitrogen injection amount through numerical simulation by initialization, boundary value assignment and iterative calculation. The Lizong combined section Wang coal mine performs nitrogen injection fire prevention and extinguishing simulation in a 'two-in-one' complex stope goaf, and determines the optimal nitrogen injection amount and nitrogen injection position. And Hojunzhong determines the air leakage rate of the gob of the macrorock coal mine 4405 through SF6 tracer gas, determines the main air leakage direction, and optimizes the gob nitrogen injection process on the basis. Zhang Qi combines the actual situation of coal valley mine site of the DaTong coal mine group company, and proposes to adopt a bypass type nitrogen injection method to treat the fire hazard in the goaf of the fully mechanized caving face by researching the fire hazard treatment technology of the fully mechanized caving face. Aiming at a high-gas easily self-combustible coal seam, Roxinglong takes a certain fully-mechanized mining face as a prototype, and a computational fluid mechanics code with an extraction hole is developed secondarily. And the Liu Star Queen simulates the change condition of the spontaneous combustion zone range of the goaf before and after nitrogen injection by using Fluent software, analyzes the influence of the nitrogen injection position and the nitrogen injection amount on the position distribution of the oxidation zone of the goaf, and fits the optimal nitrogen injection parameter. The Dongjun establishes a mathematical physical model of a goaf seepage field according to a basic theory of computational fluid mechanics in order to determine the optimal technological parameters for continuous nitrogen injection fire prevention and extinguishing in a goaf of a 5-2S-2 fully mechanized caving face, and performs numerical simulation research on goaf oxygen concentration distribution and three-band division under different nitrogen injection conditions to obtain the optimal nitrogen injection parameters. The research is an important foundation for preventing and controlling spontaneous ignition of the goaf, but the method and the device have problems if applied to actual engineering. Firstly, as the physical property parameters and the production process parameters of different goafs of different coal mines are different, the method for determining the nitrogen injection parameters by numerical simulation consumes more time and has high technical difficulty and difficult popularization; secondly, the above studies cannot clarify the quantitative relationship between the pressure loss and the nitrogen injection parameters in the nitrogen flowing process, so that the specific parameters of nitrogen injection cannot be determined quickly. In order to overcome the defects, the invention provides a goaf nitrogen filling pressure loss calculation method based on a minimum flow unit. However, in this method, the three-dimensional flow is simplified to the one-dimensional flow to obtain a pressure loss calculation method, and the pressure loss calculated by this method has a certain error from the actual situation.
Disclosure of Invention
The invention aims to provide a method for calculating the nitrogen flow dynamic pressure loss of a simulated three-dimensional coal mine goaf after test optimization aiming at the defects in the prior art.
The invention discloses a method for calculating nitrogen flow dynamic pressure loss of a simulated three-dimensional coal mine goaf, which comprises the following steps of:
(1) establishing a goaf gas flow model, and dividing a single-period flow unit;
(2) taking the single-period flow unit as a research object, and dividing the single-period flow unit into four flow stages according to different expressions of the section area changing along with the flow distance;
(3) deducing a theoretical calculation formula of nitrogen flow pressure loss in the goaf;
according to a hydrodynamic Navier-Stocks equation, a one-dimensional flow pressure loss calculation formula is derived as shown in a formula (1):
in the formula, JT1Is the one-dimensional flow pressure loss of gas flowing through a gob with unit length, Pa/m; μ is the dynamic viscosity of the gas, pas; rho is gas density, kg/m3(ii) a d is the diameter of the pellet, m; u. of0Is the initial average velocity of the gas, m/s;
(4) on the basis of a theoretical calculation formula, carrying out experimental optimization, reducing the difference between one-dimensional simplification and three-dimensional flow, and obtaining a calculation formula of the pseudo-three-dimensional flow pressure loss as shown in a formula (2):
in the formula, JT3The pressure loss is the simulated three-dimensional flow pressure loss of gas flowing through a gob with unit length, and is Pa/m; k is a correction proportion coefficient, and is 0.52 without a dimensional number; alpha is a velocity distribution coefficient and is a dimensionless number.
Specifically, the step (1) comprises the following steps:
(a) establishing a goaf gas flow model;
the gas flow model was built up from 8 large spheres of diameter d, one with diameter
The loose core sphere and 6 diameters are
The semi-hollow sphere; the eight cubic vertexes with the side length of 2d are respectively provided with 8 large balls with the diameter d, and each large ball with the diameter d is tangent to the adjacent large ball with the diameter d; diameter of
The core-pulling ball body is positioned at the center of 8 large balls with the diameter d and is tangent with the 8 large balls with the diameter d respectively; 6 have a diameter of
The core-pulling hemispheroids are respectively positioned at the central positions of six surfaces of the cube, and the diameter of each core-pulling hemispheroid is
The core-pulling hemispheroid is tangent with the surrounding spherical surface;
(b) dividing the single-cycle flow units;
by the symmetry of the flow model, the goaf gas flow model can be divided into single-period flow units, specifically: and cutting the flow model into eight single-period flow units by taking the middle point of each edge of the cube with the side length of 2d as a cutting point.
Specifically, the step (2) comprises the following steps:
taking a single-period flow unit as a research object, wherein the flow direction is the positive direction of a z axis, and the flow starting point is the origin of the z axis; in the first flow stage, starting from the point where z is 0, the flow cross-sectional area expression is as shown in formula (3):
wherein A is0Is the cross-sectional area of flow, m2(ii) a d is the diameter of the pellet, m; l is a connecting line from the center of the cutting cylinder to the circumference of the bottom surface, and m is the length of the connecting line; theta is the included angle and radian between the dotted line L and the central axis of the cutting cylinder.
The flow cross-sectional areas of the four flow stages are respectively as follows:
when it is satisfied with
The method comprises the following steps:
when it is satisfied with
The method comprises the following steps:
when it is satisfied with
The method comprises the following steps:
when it is satisfied with
The method comprises the following steps:
specifically, the step (3) comprises the following steps:
(a) the pressure loss per unit length for each flow stage is calculated as follows:
a first flow stage:
a second flow stage:
a third flow phase:
a fourth flow phase:
wherein μ is the kinetic viscosity of the gas, pas; rho is gas density, kg/m3(ii) a d is the diameter of the pellet, m; u. of0Is the initial average velocity of the gas, m/s;
(b) determining a theoretical calculation formula of the loss of the nitrogen flow pressure of the goaf as follows:
integrating the formulas of the four flowing stages according to the length proportion of the model to obtain a pressure loss calculation formula of the last flowing period of the minimum flowing unit:
specifically, the step (4) comprises the following steps:
(a) based on a test bed, setting four different wind paths so as to obtain four different flow section areas, and setting the four conditions as four different working conditions;
(b) measuring actual measurement pressure loss under different wind speeds of each working condition and theoretical pressure loss calculated according to the formula (1);
(c) comparing the measured pressure loss with the theoretical pressure loss, and solving the difference between the one-dimensional simplification and the three-dimensional flow by using a speed distribution coefficient alpha;
(d) and dividing the theoretical pressure loss and the actual pressure loss to obtain a correction proportion coefficient K.
Compared with the prior art, the invention has the beneficial effects that:
the method can be used for calculating the nitrogen flow dynamic pressure loss in the goaf, realizes the quick and accurate calculation of the initial pressure and the filling range required by goaf nitrogen filling, and avoids the defects of more time consumption and large technical difficulty of a numerical simulation method.
Drawings
FIG. 1 is a front view of a goaf gas flow model in an embodiment of the present invention.
FIG. 2 is a left side view of a goaf gas flow model in an embodiment of the present invention.
Figure 3 is a top view of a goaf gas flow model in an embodiment of the present invention.
FIG. 4 is a schematic diagram of a cut pellet cylinder according to an embodiment of the present invention.
FIG. 5 is a block diagram of a single cycle flow cell in accordance with an embodiment of the present invention.
Fig. 6 is a flow phase profile for an embodiment of the present invention.
FIG. 7 is a block diagram of an experimental platform according to an embodiment of the present invention.
FIG. 8 is a graph of measured pressure loss versus theoretical pressure loss under the first operating condition of the embodiment of the present invention.
FIG. 9 is a graph of measured pressure loss versus theoretical pressure loss for a second operating condition in accordance with an embodiment of the present invention.
FIG. 10 is a graph of measured pressure loss versus theoretical pressure loss under a third condition in accordance with an embodiment of the present invention.
Fig. 11 is a graph of the measured pressure loss and the theoretical pressure loss in the fourth operation of the embodiment of the present invention.
FIG. 12 is a graph of the proportionality coefficient of the calculated pressure loss and the measured pressure loss under the first operating condition of the embodiment of the present invention.
FIG. 13 is a graph of the proportionality coefficient of the calculated pressure loss and the measured pressure loss under the second operating condition of the embodiment of the present invention.
FIG. 14 is a graph of the proportionality coefficient of the calculated pressure loss and the measured pressure loss under the third operating condition in accordance with the exemplary embodiment of the present invention.
Fig. 15 is a graph of a proportionality coefficient of the calculated pressure loss and the measured pressure loss in the fourth operating mode according to the embodiment of the present invention.
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings and examples.
The specific implementation steps of this embodiment are as follows:
(1) and establishing a goaf gas flow model and dividing the single-period flow units.
For a cube with a side length of 2d, it is exactly capable of accommodating 8 spheres with a diameter of d, the loosest arrangement is that the spheres are tangent to each other and to the sides of the cube, and the porosity of the cube containing 8 spheres is 1-pi/6, which is about 0.4764; then, 8 large-diameter spheres with the diameter d and 4 spheres with the diameter d
The porosity of the flow model formed by the small-diameter spheres is 0.3737; the two models are set as uniform porous media with equivalent porosity, and in order to better reflect the heterogeneity of the porous media in the goaf, the cylinder shown in the figure 4 is used in the inventionCutting the small-diameter ball of the second model to obtain the porosity:
in fig. 4, L is a line connecting the center of the cutting cylinder to the circumference of the bottom surface, m; r is the diameter of the bottom surface of the cutting cylinder, m; theta is the included angle and radian between the dotted line L and the central axis of the cutting cylinder.
Thus, a gas flow model was created as shown in FIGS. 1-3, consisting of 8 large spheres of diameter d, one with a diameter of
The loose core sphere and 6 diameters are
The core-pulling hemisphere. The eight cubic vertexes with the side length of 2d are respectively provided with 8 large balls with the diameter d, and each large ball with the diameter d is tangent with the adjacent large ball with the diameter d; diameter of
The core-pulling ball body is positioned at the center of 8 large balls with the diameter d and is tangent with the 8 large balls with the diameter d respectively; 6 have a diameter of
The core-pulling hemispheroids are respectively positioned at the central positions of six surfaces of the cube, and the diameter of each core-pulling hemispheroid is
The core-pulling hemispheroid is tangent with the surrounding spherical surface.
Due to the symmetry of the flow model, the goaf flow model can be divided into monocycle flow units in order to simplify theoretical derivation. The method specifically comprises the following steps: the middle point of each edge of the cube with the side length of 2d is taken as a cutting point, and the flow model is cut into eight single-period flow units, as shown in fig. 5.
(2) The single-period flow unit is taken as a research object, the flow direction is the positive direction of the z axis, and the flow starting point is the origin of the z axis. In the first flow phase, starting from the point where z is 0, the initial flow cross-sectional area a0The expression is as follows:
the flow cross-sectional areas of the four flow stages are respectively as follows:
when it is satisfied with
The method comprises the following steps:
when it is satisfied with
The method comprises the following steps:
when it is satisfied with
The method comprises the following steps:
when it is satisfied with
The method comprises the following steps:
according to different relations of the flow cross-section area along with z, different flow stages are divided, and when the flow cross-section relations of the formulas (4), (5), (6) or (7) are respectively met, the flow stages are called as a first flow stage, a second flow stage, a third flow stage or a fourth flow stage, as shown in fig. 6, so that a micro-flow process in the single-cycle flow unit is formed.
(3) According to a fluid dynamics Navier-Stocks equation, deriving a pressure loss calculation formula per unit length in the four flow stages; the single cycle flow cell porosity was set at 0.4317, then the pressure loss per unit length for each flow phase was:
a first flow stage:
a second flow stage:
a third flow phase:
a fourth flow phase:
the formula of the four stages is integrated according to the length proportion of the model to obtain a one-dimensional pressure loss calculation formula of the previous flow period of the single-period flow unit:
(4) the method for calculating the nitrogen flow dynamic pressure loss in the goaf is further optimized through experiments, and specifically comprises the following operations:
the experimental platform is shown in FIG. 7, wherein 1-6 are valves; a is a variable frequency fan; A-E is an air duct, wherein A, B, C, D is filled with ceramsite, E is not filled with ceramsite, A and B, E are separated by a non-porous partition plate, and B, C, D, E is separated by a porous partition plate; f is an air inlet pipeline, and G is an air outlet pipeline.
(a) And (4) detecting the porosity of the ceramsite system used in the experiment and checking whether air leaks or not by using an experiment platform. The porosity of the ceramsite system model is measured by a drainage method, which specifically comprises the following steps: placing the ceramsite sample into a large measuring cylinder, and recording the volume of the ceramsite sample as V1Pouring water with a certain volume into a large measuring cylinder by using a small measuring cylinder to ensure that the water is level with the ceramsite sample, and recording the volume as V2Then the porosity of the ceramsite sample is V2/V1The measurement result was 43.17%; the method for detecting air leakage by using the stage spraying agent and the spray tobacco tar specifically comprises the following steps: firstly, mixing spray tobacco tar and distilled water in a ratio of 1:4, then pouring the mixture into a stage sprayer, simultaneously placing the spray into an air inlet of a system, then opening a fan, after the fan stably runs for a period of time at a low wind speed, opening the stage sprayer to release smoke, enabling the smoke to slowly enter an air duct of the system, observing whether white smoke emerges from the joint of an experimental platform, and if so, ensuring that the air tightness is poor and further repairing is needed.
(b) Based on an experimental platform, setting four different wind paths and measuring four different flow section areas, as shown in fig. 7, wherein 2 and 5 valves are opened, and the rest are closed to be a first working condition; 1. 4, opening the valve, and closing the rest valves to be a second working condition; 2. opening the valve 6, and closing the rest valves to form a third working condition; 3. 5, opening the valve, and closing the rest valves to form a fourth working condition; meanwhile, a pitot tube connected with a micro-manometer is correctly arranged at the inlet and outlet positions of the goaf experiment table according to the specific conditions of each working condition for measuring pressure loss; and then installing the multifunctional ventilation meter at the air inlet for measuring the air speed at the inlet.
(c) After the experimental equipment is connected, the fan is started, the frequency conversion electric control cabinet is directly switched to frequency conversion operation, and the size of the inlet air speed is adjusted by manually adjusting the knob. After the wind speed is stable, reading the numerical value on the micro-manometer to obtain the pressure loss measured by the experiment; and simultaneously recording the size of the wind speed, measuring 26 section wind speeds under each working condition of the experiment, measuring three groups of experimental data aiming at each section wind speed, averaging the experimental data to ensure the correctness of the measurement result, and then substituting the average value into the formula (1) to calculate the theoretical pressure loss.
By analyzing the specific embodiments, the following summary is made: the actual measured pressure loss of each working condition is smaller than the calculated pressure loss, when the wind speed of the first working condition and the second working condition is reduced to one sixth of the actually measured wind speed, when the actual wind speed of the third working condition is reduced to one fifth of the actually measured wind speed, and when the actual wind speed of the third working condition is reduced to one third of the actually measured wind speed, the measured data is most consistent with the calculated data, and the result is shown in fig. 8 to 11, the calculated pressure loss value is divided by the actually measured pressure loss value, and the actually measured pressure loss is increased along with the increase of the wind speed of the working condition; the ratio of the measured pressure loss to the calculated pressure loss of the goaf is reduced firstly along with the increase of the section wind speed, and is slowly stabilized to be a stable value, the stable values under four working conditions are taken as the arithmetic mean value, which is called as a correction coefficient K, and the correction coefficient K is used for correcting the derived formula, so that the calculation result is closer to the real value. The results are shown in fig. 12 to 15.
Claims (3)
1. A method for calculating nitrogen flow dynamic pressure loss in a simulated three-dimensional coal mine goaf is characterized by comprising the following steps:
(1) establishing a goaf gas flow model, and dividing a single-period flow unit;
(2) taking the single-period flow unit as a research object, and dividing the single-period flow unit into four flow stages according to different expressions of the section area changing along with the flow distance;
(3) deducing a theoretical calculation formula of nitrogen flow pressure loss in the goaf;
according to a hydrodynamic Navier-Stocks equation, a one-dimensional flow pressure loss calculation formula is derived as shown in a formula (1):
in the formula, JT1Is the one-dimensional flow pressure loss of gas flowing through a gob with unit length, Pa/m; μ is the dynamic viscosity of the gas, pas; rho is gas density, kg/m3(ii) a d is the diameter of the pellet, m; u. of0Is the initial average velocity of the gas, m/s;
(4) on the basis of a theoretical calculation formula, carrying out experimental optimization, reducing the difference between one-dimensional simplification and three-dimensional flow, and obtaining a calculation formula of the pseudo-three-dimensional flow pressure loss as shown in a formula (2):
in the formula, JT3The pressure loss is the simulated three-dimensional flow pressure loss of gas flowing through a gob with unit length, and is Pa/m; k is a correction proportion coefficient, and is 0.52 without a dimensional number; alpha is a velocity distribution coefficient and is a dimensionless number;
the step (1) comprises the following steps:
(a) establishing a goaf gas flow model;
the gas flow model was built up from 8 large spheres of diameter d, one with diameter
The loose core sphere and 6 diameters are
The core-pulling hemisphere; the eight cubic vertexes with the side length of 2d are respectively provided with 8 large balls with the diameter d, and each large ball with the diameter d is tangent to the adjacent large ball with the diameter d; diameter of
The core-pulling ball body is positioned at the center of 8 large balls with the diameter d and is tangent with the 8 large balls with the diameter d respectively; 6 have a diameter of
The loose core hemispheres are respectively positioned at the central positions of six faces of the cube, and the diameters of the loose core hemispheres are
The core-pulling hemisphere is tangent to the surrounding spherical surface;
(b) dividing the single-cycle flow units;
by the symmetry of the flow model, the goaf gas flow model can be divided into single-period flow units, specifically: cutting the flow model into eight single-period flow units by taking the middle point of each edge of a cube with the side length of 2d as a cutting point;
the step (2) comprises the following steps:
taking a single-period flow unit as a research object, wherein the flow direction is the positive direction of a z axis, and the flow starting point is the origin of the z axis; in the first flow stage, starting from the point where z is 0, the flow cross-sectional area expression is as shown in formula (3):
wherein A is0Is the cross-sectional area of flow, m2(ii) a d is the diameter of the pellet, m; l is a connecting line from the center of the cutting cylinder to the circumference of the bottom surface, and m is the length of the connecting line; theta is an included angle and radian between the dotted line L and the central axis of the cutting cylinder;
the flow cross-sectional areas of the four flow stages are respectively as follows:
when it is satisfied with
The method comprises the following steps:
when it is satisfied with
The method comprises the following steps:
when it is satisfied with
The method comprises the following steps:
when it is satisfied with
The method comprises the following steps:
2. the method for calculating the nitrogen flow dynamic pressure loss of the quasi-three-dimensional coal mine goaf according to claim 1, characterized by comprising the following steps: the step (3) comprises the following steps:
(a) the pressure loss per unit length for each flow stage is calculated as follows:
a first flow stage:
a second flow stage:
a third flow phase:
a fourth flow phase:
wherein μ is the kinetic viscosity of the gas, pas; rho is gas density, kg/m3(ii) a d is the diameter of the pellet, m; u. of0Is the initial average velocity of the gas, m/s;
(b) determining a theoretical calculation formula of the loss of the nitrogen flow pressure of the goaf as follows:
integrating the formulas of the four flowing stages according to the length proportion of the model to obtain a pressure loss calculation formula of the last flowing period of the minimum flowing unit:
3. the method for calculating the nitrogen flow dynamic pressure loss of the quasi-three-dimensional coal mine goaf according to claim 1, characterized by comprising the following steps: the step (4) comprises the following steps:
(a) based on a test bed, setting four different wind paths so as to obtain four different flow section areas, and setting the four conditions as four different working conditions;
(b) measuring actual measurement pressure loss under different wind speeds of each working condition and theoretical pressure loss calculated according to the formula (1);
(c) comparing the measured pressure loss with the theoretical pressure loss, and solving the difference between the one-dimensional simplification and the three-dimensional flow by using a speed distribution coefficient alpha;
(d) and dividing the theoretical pressure loss and the actual pressure loss to obtain a correction proportion coefficient K.
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