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ニジゲン フンシャソウ ニ オケル リュウドウカ ジョウタイ ト アツリョク ソンシツ トクセイ (ダイ 1 ホウ)

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  • 機械工学


The granular beds in witch air flows are called 'fixed, fluidized and spouted' beds, respectively, according to the flowing pattern of the granules inside the vessel. Hitherto, it is said that fluidized and spouted beds are more effective than fixed beds for operation of the drying and agitation process of the gas-solid system. In this report, we call the granular layer which has the plate with many tiny holes at the bottom of the vessel a 'fluidized bed' in which air flows uniformly passing through the bed without the velocity distribution in the horizontal cross section. On the other hand, in the case of the 'spouted bed', there is a long slit at the bottom-center of the vessel and air rushes upwards from the slit into the bed just like the jet stream. Then, steep velocity distribution exists in the horizontal cross section inside the granular bed. As the inlet velocity of air increases the center part of the granular surface is raised gradually. Then, suddenly, eruption of the surface occurs. The dynamic behavior of particles inside the bed and the pressure drop across the bed have been treated by many investigators, but because of the complexity of the phenomena itself, widely applicable results are not yet presented up to this time. Especially, in the case of the spouted bed, we feel that the collection and analysis of the fundamental data are still insufficient. This time, we used as the experimental apparatus the square vessel with the long slit at the bottom (two-dimensional spouted bed) and as for the granules, rape-seed (1.4mmφ), nylon-chip (2mmφ×3mm : cylinder) and glass-bead (mean diameter : 250μ) were used. We obtained the following results with various experimental conditions. 1) It is realized that corse particles are easier to fluidized than finer particles in the case of the spouted bed. 2) In the fixed granular bed, the curve of ΔP_m∿u_o (ΔP_m; pressure drop across the bed, u_o; air velocity) draws the hysterisis loop, but, once the eruption occurs, the fixed bed shifts to a fluidized bed, and ΔP_m remains almost a constant value in spite of the change of the air velocity. (see Fig. 5) 3) When the granular bed is in the state of fluidization, ΔP_m is nearly proportional to L (height of the layer) and this proportionality depends upon the apparent density of the granular bed. (ΔP_m has larger value for heavier particles) 4) It is pointed out that the spouting velocity 'u_' (spouting particle velocity occuring at the surface) has the increasing tendency of L, then, u_ reaches a constant value with L surpassing to an increasing value. (Fig. 12) 5) From the consideration of ΔP_m∿u_o wave form, the state of the fluidization is divided into three stages : Stage I : this stage corresponds to 'bubbling'. Stage II : 'spouting' stage Stage III : 'slugging' stage 6) It becomes clear that the so-called 'Index of fluidization' I_s is very useful to analysing the experimental data for coarse granules; for finer particles I_s is not sufficiently applicable to the explanation of the spouting phenomena.

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