1、翻译部分英文原文Methane moving law with long gas extraction holes in goafYong ZHANG, Xibin ZHANG*, Chunyuan LI, Chuanan LIU, Zufa WANGSchool of Sciences,China University of Mining&Technology,Xuzhou,Jiangsu 221008,ChinaAbstractIn order to grasp the methane moving law in goaf and provide a theoretical data fo
2、r gas extraction holes, the height of caving and fractured zones in the stope has been calculated according to the experiential formula and gas movement law has been observed by field and laboratory experiment. It also gives gas moving characteristics with different position of extraction holes. And
3、 it has the best gas extraction result when the final holes are arranged around 3.0m above the coal seam and 10-20m away from the tailentry in horizontal direction. Besides, the height of final holes should be adjusted to the overburden strata structure. When final holes are near the tailentry, thei
4、r height should be controlled in the upper of regular caving zone; when they are close to the center of face, their height should be controlled at the bottom of fracture zones.Keywords: gas in goaf; gas movement; gas extraction holes; position of extraction holes; experiment1 IntroductionThe roof st
5、rata above the goaf will fracture and form the caving, fracture and bending zones in the vertical direction after mining the coal seam. And there are lots of fractures and cracks in caving and fracture zones, the permeability of the stratum are also high. According to the “O” circle theory of fractu
6、re distribution in the stope 1, the gas of goaf will move and gather up along those fractures and cracks. Then it is easier to cause the gas exceeding the limit, which need to take measures to reduce gas content. In order to solve this problem and get the best extraction effect, the layout of holes
7、should be adjusted to the rock structure changes according to the arch structure characteristics of roof stratas movement 2. Gas in goaf will distribute after holes extraction. Therefore, the relationship between gas moving law and position of gas extraction holes should be studied so that gas in th
8、e corner of working face and goaf could be effectively controlled.2 Hydrodynamics equations of gas movementWith the pressure gradient of roadways ventilation, gas penetrates or diffuses to the goaf and then to roadways from the coal seam, and its flow velocity is very low which usually less than 10-
9、5m/s 3. Therefore, the flow of gas and air in goaf belongs to low-speed category, and it hardly has an effect on the roadways ventilation. Despite the pressure gradient is very high, the gas and air flow in the mined-out area and roadways can still be regarded as the incompressible flow 4. Besides,
10、the distribution of rock, fractures and cracks in goaf are irregular. Consequently, the gas movement in the fractured rock of goaf is taken for continuum medium movement in pore medium 5.2.1Gas Seepage characteristicsGoaf is regarded as porous medium in the research; the source item of fluid momentu
11、m loss is described as the following equation 5.In equation 1, Si is the source of momentum equation of the number i (x, y or z ), is the viscosity of molecular, D and C are predefined matrices, |v| is vectors module of velocity, and vj is the velocity component of the source in x, y or z direction.
12、Generally, the pressure drop is proportional to the velocity in the low laminar flow of porous medium. The porous medium model could be simplified by using Darcy characteristics when the liquid inertial loss is ignored.In equation 2, is the permeability for expressing the space and the function of p
13、reventing the viscosity, m22.2. Gas diffusion characteristicsThere are two main controlling factors for the gas movement in the goaf. One is the molecular diffusion caused by the concentration and thermal gradient. Another is viscous flow or mass flow on the action of pressure gradient. According to
14、 the Fick characteristics, the following formula is the diffusion equation 4.In equation 3, Ji is the gas flow caused by the concentration and thermal gradient; Dim is the diffusion coefficient of mixed gas; Xi is the mass fraction of i gas; TiD is the thermal diffusion coefficient; and T is the tem
15、perature. When the gas concentration is much higher, equation 7 could be taken place by the diffusion formula of multicomponent.In equation 4, if the gas is i or j, Mi is its molecular weight, Dij is the multicomponent diffusion coefficient of the No. i gas component in the gas, and Mmix is the mole
16、cular weight of mixed gas.2.3. Control equations of gasThe gas emission and movement has close relationship with the air flow condition in gob, and it belongs to the typical permeation-diffusion process. Because the gas flow in goaf is regarded as the incompressible flow, control equations of flow field can be replaced by the Navier-Stocks equation 6, 7.In formulas, is mixture density, g/m; T is time v
