Study On The Flow Characteristics Of The Tapered Nozzle Of Measuring Device Of Expansion Energy In Initial Released Gas

The expansion energy in initial released gas prediction method provides quantitative prediction of coal seam outburst risk in the field with a set of new method, correct selection of the method for determining the effective section S-value of the tapered nozzle is important for the accuracy of the measurement. The determination of S-value by gas volume deflation method is only suitable for the calculation of expansion energy in initial released gas when the air flow is at the sonic stage, and the process of air flow through the tapered nozzle is divided into two stages of speed of sound and subsonic speed, while the S-values of the two stages are the same value. To solve the problem, this paper presents a new method for the determination of S-value, which the S-value is indirectly calculated by determining the flow characteristic parameters of the tapered nozzle, make up for the shortcomings of the original method, and then will be beneficial to achieve the accuracy of determination results of expansion energy in initial released gas.The main research works of this paper are from the following three aspects: first analyze and reserch the flow characteristics of the tapered nozzle and its testing method, including the factors affecting the flow characteristics, several methods that are commonly used to express the flow characteristics, and testing method of each parameter; then design a set of testing system, and give the detailed design process; last the related parameters of the flow characteristics of the tapered nozzle are determined by using the designed testing system, calculate the effective section S-value by using the parameters, at the same time, determine the S-value by using the original method, and compare and analyze the S-values of two methods. Through the research works, the following results are obtained:(1) A new method for determining the effective section S-value of the tapered nozzle is proposed, the S-values of the two stages of the sonic velocity and subsonic velocity are respectively obtained by determining the flow characteristic parameters of the tapered nozzle;(2) Design a set of testing system that based on international standard testing method and computer data acquisition, which can accurately determine the flow characteristic parameters of the tapered nozzle;(3) The critical pressure ratio b-value of the tapered nozzle is 0.284, according to the b-value, the sonic velocity and subsonic velocity of the air flow through the tapered nozzle are accurately divided;(4) The effective section S-value of the tapered nozzle is respectively 2.87mm2 and 2.33mm2 in the subsonic and subsonic stages, the S-value is 2.70mm2 by using the original method, and the two methods are compared and analyzed, which highlight the applicability of the new method more advantages.