AC breakdown voltage measurement of a fluorocarbon in gaseous state two-phase-flow state and liquid state

Flow visualization experiments of an air jet in liquid were performed. The test vessel was 270 mm wide, 5 mm depth and 300 mm high. The air jet was blown vertically upward into stagnant liquid in the test vessel from a nozzle of 1 mm wide, 5 mm depth and 20 mm long which was located at the bottom of the test vessel. A flow state of the jet in the liquid was recorded with a high speed video camera at fastest 5×105 f/s. The test liquid was water and kerosene. Experiments were performed at atmospheric pressure and ambient temperature. Filament-like ears and wisps pulled out from the wavy interface were noticed on the interface between liquid and the air jet. The ears and wisps were broken off and entrained into the air jet. The droplets broke up to small entrainments. This process seemed quite similar to the entrainment process in the annular dispersed flow in a pipe. As the air jet velocity increased, the number of entrainments created by the air jet increased lineally and the smaller entrainments increased. The correlation for the entrainment diameter distribution which was developed for the annular dispersed two-phase flow in a pipe predicted well the present results. The correlations for the entrainment diameter developed for entrainments in the annular dispersed two-phase flow in a pipe and for droplets that were blown out into open space above a water pool by a nitrogen gas jet that blew into water vertically upwards considerably underpredicted the experimental results. Measured entrainment rates were considerably lower than the prediction of the correlation for the annular dispersed two-phase flow in a pipe.

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Experiment Study of Outburst Pulverized Coal-Gas Two-Phase Flow and Characteristic Analysis of Outburst Wave

Geofluids ◽

10.1155/2021/8186230 ◽

2021 ◽

Vol 2021 ◽

pp. 1-11

Author(s):

Xusheng Zhao ◽

Jie Cao ◽

Bo Wang ◽

Xuelin Yang

Keyword(s):

Gas Flow ◽

Two Phase Flow ◽

Pulverized Coal ◽

Coal And Gas Outburst ◽

Phase Flow ◽

Flow State ◽

Two Phase ◽

Coal Gas ◽

Gas Outburst ◽

Propagation Velocities

Coal and gas outburst is still a major safety problem in the process of coal production in China. Correctly understanding of the migration law of outburst high gas and pulverized coal is an important basis for accurately predicting the occurrence time and possible scope of outburst. To reveal the airflow disturbance characteristics and coal-gas flow rule in coal and gas outburst process, outburst coal-gas migration simulations under different gas pressures were conducted using a self-developed visual outburst dynamic effect test device. The results showed that coal-gas flow state at the outburst port is divided into subcritical flow, critical flow, and supercritical flow state. The pulverized coal-gas flow migration in the roadway space can be divided into coal gas two-phase flow area, air compression area, and undisturbed area. Under the experimental conditions, the maximum propagation velocities of wave are 342.22~359.21 m/s, and the coal gas two-phase flow is far less than the propagation velocities of outburst wave, just 3.68~33.33 m/s. When the outburst energy is large, multiple compression waves can superimpose to form shock waves. The peak value of the wave does not necessarily appear in the first boosting range. The presence of pulverized coal leads to a faster attenuation of shock wave, but it makes a greater dynamic destructive force at the same speed.

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