Near-source characteristics of two-phase gas-solid outbursts in roadways

Coal and gas outbursts compromise two-phase gas-solid mixtures as they propagate as shock waves and flows from their sources.Propagation is influenced by the form of the outburst,proximity to source,the structure and form of the transmitting roadways and the influence of obstacles.The following characterizes the propagation of coal and gas outbursts as two-phase gas-solid flows proximal to source where the coupled effects of pulverized coal and gas flows dominate behavior.The characteristics of shock wave propagation and attenuation were systematically examined for varied roadway geometries using experiments and numerical models.The results demonstrate that the geometry of roadway obstructions is significant and may result in partial compression and sometimes secondary overpressurization in blocked and small comer roadways leading to significant attenuation of outburst shock waves.The shock waves attenuate slowly in both straight and abruptly expanding roadways and more significantly in T-shaped roadways.The most significant attenuation appears in small angle comers and bifurcations in roadways with the largest attenuation occurring in blocked roadways.These results provide basic parameters for simplifying transport in complex roadway networks in the far-field,and guidance for the design of coal and gas outburst prevention facilities and emergency rescue.

Miniaturization of Bubbles by Shock Waves in Gas-Liquid Two-phase Flow in the Venturi Tube

Fine bubbles have been widely applied in many fields such as industry,medical engineering and agricultures.Therefore,many attentions have been paid to the study of fine bubble generations in order to increase the yield while decrease the cost.However,the generation process of fine bubbles is a quite complicated process in which multiple hydrodynamic forces are interacted in the gas-liquid two-phase flow.Many studies focus on the techniques of the converging-diverging nozzle(venturi tube)generator,which is famous for its simple and cheap features,and generates fine bubbles by using the miniaturization phenomenon of bubbles occurring in the venturi tube.However,the impact conditions on the amount and size of bubbles such as nozzle geometry and bleed air haven’t been investigated clearly.In this work,we implement many experiments on the venturi tube fine bubble generators with different geometries and generating conditions,and evaluate different factors impacting the production components such as the volume and the bubble size.The experimental results show that the supersonic flow filed in the venturi tube promotes the miniaturization of the bubbles,and the convergent angle of the nozzle and air bleed have a great impact on the size and volume of bubbles.

Experimental and numerical analysis of compressible two-phase flows in a shock tube

The comparative study on seven equation models with two different six equations modelfor compressible two-phase flow analysis is proposed. The seven equations model isderived for compressible two-phase flow that is in the nonconservation form. In thepresent work, two different six equations model are derived for two pressures, two velocities and single temperature with the derivation of the equation of state. The closingequation for one of the six equations model is energy conservation equation while anotherone is closed by entropy balance equation. The partial differential form of governingequations is hyperbolic and written in the conservative form. At this point, the set ofgoverning equations are derived based on the principle of extended thermodynamics.The method of solving single temperature from both six equation models are simple anddirect solution can be obtained. Numerical simulation has been tried using one of the sixequation models for air–water shock tube problems. Explicit fourth order Runge–Kuttascheme is used with Finite Volume Shock Capturing method for solving the governingequations numerically. The pressure, velocity and volume fraction variations are captured along the shock tube length through flow solver. Experimental work is carried outto magnify the initial stage of liquid injection into a gas. The outcome of six equationsmodel for compressible two-phase flow has revealed the multi-phase flow characteristicsthat are similar to the actual conditions.

Reflection of Shock Wave in PUR Foam From Rigid Wall

Keller proposed that a building, a mechanical installation or a body wrapped bya layer of foam plastics may be an efficient means for protection from damage ofblast wave. However, the practical effect was beyond expectation. For example, agunner wearing the foam plastics-padded waistcoat was injured more seriously by theblast wave from a muzzle. Monti took the foam plastics as homogeneous two-phasemedium and analyzed it with the theory of dusty flow. The obtained results showthat the peak pressure behind the reflected shock wave from rigid wall with foamcoat exceeds obviously that without foam coat under the same condition. Gel’fand,Patz and Weaver made experimental observations by means of shock tubes and veri-