Study on the development law of self-oscillating pulsed SC-CO2 jet vortex structure and its effect on frequency

Abstract

The self-oscillating pulsed supercritical (SC)-CO2 jet technology has higher pulse pressure and the resonant rock-breaking effect, which can improve the drilling efficiency of the development of unconventional gas sources. The jet impact frequency is the key to resonance in coal rock mass; however, the relationship between frequency variation and flow field remain unknown. This study investigates the vortex change law and the effect on frequency of self-oscillating pulsed SC-CO2 jets. Large eddy simulations are used to analyze the variation characteristics of vortex structure and frequency at different locations of the jet. The results show that the variation of the vortex size in the oscillating cavity leads to the change of the jet velocity. Large-scale vortex is generated at the downstream nozzle exit and is accompanied by a high-speed zone of the jet, vortex development produces energy dissipation, which decreases the velocity in the high-speed zone. The jet frequency in the oscillating cavity is the same as the vortex ring size variation law; the vortex passing frequency in the free flow field is the same as the jet frequency, and the vortex ring energy dissipation causes the jet velocity to decrease, resulting in a lower frequency.

Experimental Study on Carbon Dioxide Displacement by Coal Seam Water Injection

“…Methane and carbon dioxide are the main gases causing coal and gas outbursts, with carbon dioxide outbursts being the most destructive . Gas extraction is a common measure used in mines to prevent coal and gas outbursts and to enable unconventional natural gas production. , By arranging boreholes in the coal seam and extracting gas, the gas pressure and the risk of a coal and gas outburst are both reduced. − However, in some low-permeability coal seams, gas extraction does not easily reach the set targets. − Some coal mines where the adsorbed gas is carbon dioxide also have encountered this situation, and the efficiency of gas extraction is very low . Exploring new gas extraction modes is one way to solve the poor gas extraction effect.…”

“… 9 − 12 However, in some low-permeability coal seams, gas extraction does not easily reach the set targets. 13 − 15 Some coal mines where the adsorbed gas is carbon dioxide also have encountered this situation, and the efficiency of gas extraction is very low. 16 Exploring new gas extraction modes is one way to solve the poor gas extraction effect.…”

Study on the key parameters of ice particle air jet ejector structure

“…The instantly prepared ice particles are sucked into the mixing chamber by their own gravity and the negative pressure of the high-speed airflow from the working nozzle, and then the high-speed airflow introduces the ice particles into the accelerating nozzle to be fully mixed and accelerated to be ejected. Based on previous studies [24][25][26][27][28] , it is known that the ejection capacity of the working nozzle depends on the nozzle expansion ratio and position, and the acceleration capacity of the accelerating nozzle depends on the diameter ratio and aspect ratio of the accelerating nozzle. For this reason the authors analyze the ice particle ejection and acceleration laws under different injector nozzle structures based on ANSYS-FLUENT gas-solid two-phase flow model.…”