The abnormal emission of gas in coals is the main factor that induces serious gas disasters in coal mines. During the coal mining process, roof movement has important effects on the gas emission law and gas flow characteristics. In this study, an extremely thick coal seam under fully mechanized sublevel caving mining conditions from the Tashan coal mine in China was used as an example; the effect of roof weighting on gas emission in the goaf was studied. Then, the large roof weighting step and the small roof weighting step caused by the different thicknesses of lamprophyre breakage were used as the objects and a numerical simulation study on the gas flow characteristics in the goaf was carried out. The results indicate that the mining coal seams, the overlying adjacent unmined coal seams, and the goaf are the main contributors to the large gas emission capacity, and even situations exist where the gas concentration exceeds the limit in the working face. During roof weighting, the gas concentration and emission capacity in the return airway, upper corner, and high drainage roadway increase substantially. The results of the numerical analysis are in good agreement with the observed data, which indicates that it is effective to control the gas in coal seams by designing the location of high drainage roadway according to the mining characteristics of coal seam and the gas emission law.
The hydraulic expansion of the heat exchange tube-to-tubesheet is to apply the liquid pressure to expand the inner wall of the tube uniformly through the device. It make the tube wall deformed and contact the tube sheet. The expansion pressure which affects the quality of the expansion of the heat exchanger is one of the important factors for the hydraulic expansion of the heat exchanger. Therefore, in order to meet the expansion requirements, it is necessary to determine the expansion pressure of the heat exchange. The determination of hydraulic expansion pressure by some scholars are introduced in this paper.
Tube hydroforming technology is an advanced manufacturing technology adapted to lightweight structure. The technology has the advantages of low production cost, high material utilization rate and light part quality. Forming equipment is the basis for implementing the technology, the performance of the equipment greatly affects the product quality. However, the key problems affecting the performance of the equipment include: loading path, axial feeding and sealing method, etc. The article is for the purpose of key question carrying on the system combing with the discussion. Among them, several hydraulic pressure control methods are summarized, the influence of different loading path on tube hydroforming is shown, A loading method that axial stress - circumferential stress is always proportional in the forming process is proposed. Meanwhile, the control method of axial feed is summarized, it is expressed that axial feeding can improve tube forming ability. Besides, five kinds of common pipe sealing methods were compared, the reliable and effective sealing structure is summarized.
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