Numerical Analysis and Prediction of Coal Mine Methane Drainage Based on Gas–Solid Coupling Model

Methane drainage using boreholes is one of the most effective means of preventing coal mine methane disasters. However, the distributions of stress and permeability around the borehole and the effective influence radius of methane drainage are not clearly known. To solve this problem, a mathematical model of gas–solid coupling of coal rock was first established in this study based on the Kozeny–Carman equation. In this model, the coal rock was considered as a fracture–porosity dual medium. Methane’s flow was seepage in the fracture system and diffused in the pore system. Second, the finite volume method was used to discretize the coupling model. The Newton–Raphson iteration and generalized minimal residual algorithm method were used to solve the nonlinear coupling equation after diffusion. Finally, Fortran language was used to simulate the process of methane drainage using a borehole. Results showed that there was respectively stress concentration on the left and right sides of the borehole. This area was associated with the lower permeability in these zones and destroyed the borehole, which is the one of the main reasons for the low efficiency of methane drainage. The relationship between the effective influence radius and the drainage time could be described by a power function. The effective influence radius of the borehole, cumulative methane drainage volume, and residual methane content distribution obtained by simulation were well consistent with the data obtained by the actual measurements, which proves the credibility of the gas–solid coupling and solving methods. This study provides some theoretical reference for methane drainage and the solution of multi-physics field coupling model in coal mines

Nucleon Decay Searches with large Liquid Argon TPC Detectors at Shallow Depths: atmospheric neutrinos and cosmogenic backgrounds

Grand Unification of the strong, weak and electromagnetic interactions into a single unified gauge group is an extremely appealing idea which has been vigorously pursued theoretically and experimentally for many years. The detection of proton or bound-neutron decays would represent its most direct experimental evidence. In this context, we studied the physics potentialities of very large underground Liquid Argon Time Projection Chambers (LAr TPC). We carried out a detailed simulation of signal efficiency and background sources, including atmospheric neutrinos and cosmogenic backgrounds. We point out that a liquid Argon TPC, offering good granularity and energy resolution, low particle detection threshold, and excellent background discrimination, should yield very good signal over background ratios in many possible decay modes, allowing to reach partial lifetime sensitivities in the range of 1034−1035 years with exposures up to 1000 kton×year, often in quasi-background-free conditions optimal for discoveries at the few events level, corresponding to atmospheric neutrino background rejections of the order of 105. Multi-prong decay modes like e.g. p→μ−π+K+ or p→e+π+π− and channels involving kaons like e.g. p→K+ν¯, p→e+K0 and p→μ+K0 are particularly suitable, since liquid Argon imaging (...)This work was in part supported by ETH and the Swiss National Foundation. AB, AJM and SN have been supported by CICYT Grants FPA-2002-01835 and FPA-2005-07605-C02-01. SN acknowledges support from the Ramon y Cajal Programme. We thank P. Sala for help with FLUKA while she was an ETH employee