EJECTING THE RETURN AIR FLOW ON INCREASING THE RANGE OF THE AIR JET DIRECTED INTO THE FACE OF THE DEAD-END DRIFT

Abstract

The relevance of the study is caused by the need to develop resource-saving technologies for forced ventilation of dead-end drifts related to ensuring the safety of air ducts during blasting. The solution to the problem lies in the development of technical solutions that make it possible to remove the end of the air duct from the zone of damaging effects of flying fragments of rock, moving it away from the dead-end face to a safe distance without violating the safety rules. Purpose: to develop a resource-saving method of dead-end drift ventilation, which provides the increase of the ventilation range by means of the kinetic energy of the air jet flowing from the booster fan with a mixing chamber. Objects: dead-end drifts. Methods: analytical and numerical modeling of the processes of air ejection and propagation of a constrained overlaying air jet directed to a dead end; comparative analysis of experimental data and simulation results. Results. The analysis of experimental data on the ventilation of dead-end drift by the ejection method with the lag of the end of the pipeline from the dead-end face was carried out. It is noted that the experimental dependencies obtained by various researchers for determining the range of the ventilation jet do not allow us to make an unambiguous conclusion about the permissible lagging distance due to too large spread in the values ​​of the proportionality coefficient between it and the transverse dimension of the drifts. It was established that the reason for the scatter is the neglect of the dependence of the jet range on its initial velocity and flow rate, which is the less pronounced, the less constrained the jet is. The possibility of increasing the constraint and flow rate of the jet by ejection suction of the return air flow into the mixing chamber installed before the end of the pipeline is considered. The paper introduces the analytical model of the operation of an ejector installation with a permeable bulkhead, based on the results of which an increase in the jet flow rate due to recirculation was estimated. Despite the small value of the ejection coefficient, the numerical simulation of the process showed an unexpectedly strong increase in the ventilation range with an increase in the initial jet velocity in the real range, and the required pipeline lag result of 50 meters was achieved. It is shown that the proposed resource-saving method of forced ventilation of dead-end drifts requires a preliminary procedure for selecting and optimizing the geometric dimensions of the pipeline, mixing chamber and air flow, because in numerical simulation, both insufficient ventilation depth and loss of stability with the collapse of a single circulation vortex were observed during excessively intense air movement.

Keywords

• pipeline
• shock wave
• mixing chamber
• auxiliary fan
• ejection effect
• aerodynamic drag
• instability
• constrained spreading jet