Experimental Investigation Of Bubble Characteristics In Aerated Hopper

In this thesis,based on the background of aerated hopper in the feeding system of entrained flow pulverized coal gasification technology,the bubble characteristics during aerated discharge were investigated in a two-dimensional aerated hopper with a high-speed camera.Glass beads and air were used as experimental medium.Bubble formation process,bubble behaviors,and the influences of aeration on discharging were discussed in detail.Research results were summarized as follows:As the gas velocity increases to the minimum bubble velocity,a bubble formed in the emulsion phase.With the reduction of the particle size,the minimum bubble velocity decreases.The minimum bubble velocity in the aeration hopper was dramatically lower than that in the fluidized bed.During bubble formation,the gas continuously displaced the upper particles,while the particles flowed downward along the outer periphery of the bubbles,and then the bubble volume gradually increased.When the bubble volume increases to the bubble detachment volume,the bubble begins to detach.The bubble detachment volume increases as the particle size decreases.After detaching from the orifice,bubbles shows three main shapes,oblique long shape,the right angle trapezoid shape and cap shape.Aggregation and splitting will occur during bubble rising,and eventually annihilate in the hopper.Aggregation is actually the process that a small bubble is attracted by the big bubble,and resultantly forms a bigger bubble.Splitting is the result of the uneven force of the bubble,leading to the flow of particles at the top of the bubble.And splitting is more common in large,flat bubbles,as the additional pressure is not sufficient to support the upper particles due to the large radius of curvature in these bubbles.Aeration in the hopper can increase the flow region.Under different aeration conditions,the flow region keeps increasing until a constant value.For single aeration,the higher location of aeration,the smaller flow region.For combined aeration,the higher mean location of aeration,the smaller flow region.When the flow region increases,the discharge increases.