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The vary of a very powerful parameters, i.e. water strain and its output, which permit coal to be lower with passable effectivity had been decided. It was proved that the optimum parameters for efficient hydro-mining of bituminous coal are the next: the strain of as much as 30.0 MPa and the stream charge of as much as 500 L/min. This set of parameters was adopted within the in-situ assessments as probably the most effective-one. Within the in-situ assessments the hydro-mining of arduous coal was carried out within the Experimental Mine “Barbara” (Mikołów, Poland). Geological construction of the rock mass dates again to Quaternary interval and productive Carboniferous. On the prevailing a part of the seam space the quantity of Quaternary varies from 4 to six m, in some components of the roof of the Carboniferous seems straight beneath the layer of soil. Lithological formation of rocks is heterogeneous. Layers are fashioned from alternating superb and medium grained sandstones and shales amongst which quite a few coal seams could be discovered. Probably the most steady by way of their enlargement and quantity are the seams 308, 310 and 318. The rock surrounding coal seams creates a rock mass of very heterogeneous geological properties brought on by the micro and macro fissures and interchangeable look of mudstone and sandstone. The rise within the power options of the rock is expounded to the depth. There isn’t a vibration affect from plate tectonics. In Experimental Mine “Barbara” there are two ranges positioned on the depth of 30 m and 46 m underground. The overall size of the galleries there’s virtually 5 km. All the galleries on the 30 m degree had been drilled in a coal seam. The thickness of this coal deposit is between 1.5 and 1.8 m.
To find out the bodily and mechanical parameters of arduous coal, six coal blocks used within the first stage of experiments had been taken from the coal seam 310. In response to the classification established for the Higher Carboniferous rocks of the Higher Silesian Coal Basin (USCB), the uniaxial compressive power of studied coal was assessed as excessive. The typical worth of Younger’s modulus was set at 1254 MPa, which signifies comparatively excessive elasticity. The bodily and mechanical parameters of the coal examined are introduced in Desk 1, whereas in Fig. 1 the chosen stress–pressure traits are given.
The symbols of bodily and mechanical parameters, which had been utilized in Desk 1 are listed beneath:
Rc | Uniaxial compressive power |
Rr | Tensile power |
Rcr | Residual power |
E | Younger’s modulus |
M | Submit-critical module |
εkr | Crucial pressure |
εr | Residual pressure |
ρb | Bulk density |
c | Cohesion |
φ | Angle of inner friction |
Stress–pressure traits for arduous coals from Experimental Mine “Barbara” (6 samples) are introduced in Fig. 1.
The gallery for the water jets lower experimental marketing campaign in coal mine
Within the in-situ experimental marketing campaign the take a look at station was positioned within the experimental gallery I on the extent 30 m underground on the Experimental Mine “Barbara”. For the needs of the analysis 10 m of a facet wall was uncovered by eliminating protecting mesh and rock lining. It revealed a coal mattress floor which was used for the hydro-mining assessments utilizing water jets. The station is introduced in Fig. 2.
The station was outfitted with a hydro chopping device positioned by the uncovered sidewall to make sure that the water jet was perpendicular to the coal face (see Fig. 3).
The U-shaped metal defend proven in Figs. 2a,b and 3 is a typical defend utilized in Polish coal mines, and this defend doesn’t impose any strain on the coal face.
The set of kit was transported underground after which into the realm of the carried out analysis with solely hydro-mining device launched into the take a look at station. The remaining parts of the set, that allowed correct operation of the hydro-mining device, had been positioned in the principle gallery. Location and placement of the tools is introduced in Fig. 4.
Every of the weather within the tools set was related based on the scheme introduced in Fig. 5.
The high-pressure pump attracts water by the water filter by low-pressure hoses (blue colour). From the high-pressure pump, water with a strain of as much as 100 MPa is fed by high-pressure hoses (purple colour) to the USO-1 gadget, by which a head with a nozzle is mounted. The USO-1 performs reciprocating and rotary motion of the pinnacle with nozzle, as required. The actions of the USO-1 are made attainable by the oil provide from a hydraulic pump by oil hoses (brown colour). Each pumps are powered from {an electrical} change by the corresponding cables (inexperienced colour).
Computational fluid dynamics (CFD) simulation
The applying of Computational Fluid Dynamics (CFD) strategies within the modelling of the transport of fluid alongside the nozzle requires the next enter information26,27:
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the geometry of the article,
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the bodily properties of the fluid,
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worth of the fluid stream on the inlet of the nozzle,
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consideration of the preliminary situations for the numerical resolution,
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consideration of the turbulence mannequin for the fluid stream alongside the nozzle,
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the time of prevalence.
The geometry of the nozzle is represented by the 3D mannequin ready in SolidWorks Laptop Aided Design (CAD) software program, whereas the fluid stream alongside the nozzle is modelled utilizing SolidWorks Circulate Simulation software program utilizing the Computational Fluid Dynamics (CFD) strategies26,27,28,29. The Free Floor technique was used to be able to simulate the behaviour of fluid alongside the nozzle and in ambient. The tactic permits simulating the fluid behaviour the place a gasoline, within the type of air, and a liquid, within the type of water, share the identical space with none strong between them. The Free Floor technique relies on a volumetric technique referred to as the Quantity of Fluid (VOF)26,27,30,31,32. The VOF technique assigns air and water as a quantity fraction to every cell within the numerical grid that’s simulating the area of the numerical resolution. The quantity fraction of air and water at all times sums to 1, which signifies that the fraction of air implies the fraction of water and vice versa. The Circulate Simulation software program calculates the quantity and mass of air and water leaving and coming into the cells of the area and retains mass, power, and momentum. The transport equations are pushed by preliminary and exterior boundary situations, together with gravity, in addition to fluid behaviour, to acquire the precise motion of the free floor27.
Geometry
Determine 6 exhibits the view of the nozzle within the type of an assembled device. The inlet and outlet of the nozzle had been proven. The place of the carbide nozzle insert with a diameter of 0.021 m was proven in Fig. 6a. The carbide nozzle insert was used as a result of the filtration was poor, abrasive solids had been current within the fluid, and fluid stream was very excessive.
Numerical grid
With a purpose to be certain that the outcomes obtained from simulations are ample, the numerical grid high quality research had been achieved. The outcomes of the evaluation had been proven in Fig. 7. The quantity stream charge was measured on the nozzle outlet.
The impact of the mesh high quality research was proven in Desk 2.
In response to the outcomes of the standard research, the numerical grid will comprise greater than 144,503 computational cells, as proven in Desk 2 and Fig. 8.
The extent of element within the outcomes of numerical simulations depends upon the accuracy and backbone of the numerical grid that’s chosen for CFD simulations26. A significant problem in CFD modelling is acquiring the numerical grid, which is characterised by excessive refinement degree on the border of strong and fluid. Determine 8a exhibits the numerical grid of the nozzle with a refinement degree of two. The refinement degree edits the finite aspect meshes within the area of stream with somewhat gradient to be able to enhance the accuracy of the numerical resolution. The positions of the inlet to the nozzle and outlet to the computational area (air) had been introduced in Fig. 8b.
A numerical grid proven in Fig. 8, was generated by 144,503 complete cells, the place 17,592 fluid cells are involved with solids, which represents the computational area of the fluid. The fluid quantity is 0.000102 m3. The mesh grid was primarily based on an orthogonal finite quantity mesh.
The simulation of the fluid stream supported by CFD strategies boils all the way down to acquiring the answer of a system of differential equations deciphering the precept of conservation of mass and momentum of the shifting fluid (Navier–Stokes equation). The basic equations expressing the motion of a fluid alongside a given geometry of the nozzle are relationships given within the following kind26,27:
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mass conservation equation:
$$frac{partial p}{{partial t}} + nabla (pnu ) = 0$$
(1)
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Navier–Stokes equation:
$$rho frac{partial nu }{{partial t}} = – nabla p + rho g + mu nabla^{2} nu$$
(2)
the place: ρ—density (kg/m3), υ velocity (m/s1), p—strain (Pa), µ—dynamic viscosity (Pa·s).
The k-εpsilon turbulence mannequin was used to interpret the affect of occurring disturbances within the fluid switch course of in an area with a given geometry. The k-εpsilon turbulence mannequin resolution boils all the way down to figuring out the worth of turbulence viscosity μt and the speed of dispersion associated to power dissipation ε brought on by the prevalence of inner resistance to movement of the flowing fluid alongside the nozzle channel. The turbulence viscosity μt mannequin of the flowing fluid is expressed by an equation outlined in SolidWorks Circulate Simulation as follows26:
$${mu }_{t}={f}_{mu }{C}_{mu }frac{{rho okay}^{2}}{varepsilon }$$
(3)
The fluid transport equations for turbulence kinetic power okay and dispersion ε in SolidWorks Circulate Simulation are expressed by the relations within the kind26:
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for turbulent kinetic power:
$$frac{partial rho okay}{partial t}+frac{partial rho okay{nu }_{i}}{partial {x}_{i}}=frac{partial }{partial {x}_{i}}left(left(mu +frac{{mu }_{i}}{{sigma }_{okay}}proper)frac{partial okay}{partial {x}_{i}}proper)+{tau }_{ij}^{R}frac{partial {nu }_{i}}{partial {x}_{j}}-rho varepsilon +{mu }_{t}{P}_{B}$$
(4)
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for dissipation power:
$$frac{partial rho okay}{partial t}+frac{partial rho varepsilon {nu }_{i}}{partial {x}_{i}}=frac{partial }{partial {x}_{i}}left(left(mu +frac{{mu }_{i}}{{sigma }_{okay}}proper)frac{partial varepsilon }{partial {x}_{i}}proper)+{C}_{varepsilon 1}frac{varepsilon }{okay}left({f}_{1}{tau }_{ij}^{R}frac{partial {nu }_{i}}{partial {x}_{j}}+{C}_{B}{mu }_{t}{P}_{B}proper)-{f}_{2}{C}_{{varepsilon }_{2}}frac{rho {varepsilon }^{2}}{okay}$$
(5)
the place: Cε1—empirical fixed, Cε1 = 1.44, Cε2—empirical fixed, Cε2 = 1.92, Cµ—empirical fixed, Cµ = 0.09, fµ—Lam and Bremhost’s damping features, okay—kinetic power of velocity fluctuations (m2/s2), P—eddy fluctuations, t—time (s), ε—charge of dispersion of the turbulent kinetic power (m2/s3), μt—turbulent viscosity (Pa·s), σokay—the turbulent Prandtl quantity σokay = 1.0, σε—the turbulent Prandtl quantity σε = 1.3.
The nozzle is provided with a water quantity stream charge of 86 L/min (0.00143 m3/s) as proven in Fig. 6b. As a result of the truth that the temperature between the inlet and outlet of the nozzle was totally different, the water parameters comparable to: density, dynamic viscosity, particular warmth, and thermal conductivity had been parameterized as features of the temperature. The variation of bodily parameters of the water on the inlet of the nozzle comparable to density (Fig. 9a), dynamic viscosity (Fig. 9b), particular warmth (Fig. 9c) and thermal conductivity coefficient (Fig. 9d), are characterised by the corresponding graphs in Fig. 9 as a perform of temperature adjustments, T.
Determine 9 exhibits that because the temperature will increase, the density (Fig. 9a) and dynamic viscosity (Fig. 9b) of water lower. Nonetheless, the particular warmth (Fig. 9c) of water will increase because the temperature will increase. In case of the thermal conductivity of the water, the coefficient will increase till it reaches the worth of 443.50 Ok, and thereafter decreases to 518.16 Ok. The variation of the parameters of the air (fluid area), because the atmosphere of the nozzle, is proven in Fig. 10.
Determine 10 exhibits that because the temperature will increase, the dynamic viscosity (Fig. 10a), particular warmth (Fig. 10b) and thermal conductivity (Fig. 10c) of air lower.
The next preliminary boundary situation was utilized in numerical calculations:
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gravity: 9.81 m/s2,
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turbulent mannequin: k-epsilon,
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quantity stream charge of the water on the inlet of the nozzle: 86 L/min (0.00143 m3/s),
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temperature of air (computational area): 298.15 Ok,
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temperature of water: 290.15 Ok,
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strain of air (computational area): 101,325 Pa,
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wall parameters of the nozzle channel: temperature 298.15 Ok, alter wall roughness 6.3 µm, adiabatic wall.
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