Optimization of bit nozzle parameters of reverse circulation sampling used in coal mines
Abstract
The coal mine air reverse circulation sampling technique is important to improve accuracy of direct determination of gas content. Sampling drill is an important structural element to realize the coal mine air reverse circulation sampling technique. Embedded annular ejector and external nozzle of the drill are the main structures that can realize reverse circulation. External bit nozzle divide the mine compressed air into two parts. One part is used to wash the drill hole for preventing the hole collapse, the other part can press cuttings at the hole bottom into the drill pipe center tube and provide the transmission power. Bit nozzle dip angle and position are studied by numerical simulation, and the results are proved by the filed test. The research results show that when the dip angle of nozzle is 15 °, the position is appropriate away from the drill cutter, it can make better reverse circulation, and increase the sampling depth, improve the quality of sampling, prevent damage of drill bit and buried drill accidents.
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