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在流态化冶金中許多过程包含顆粒內部和顆粒与其周围流体之間的传热和传貭,本文提出了一个混合对比阻力R′(对于传热和传貭分別为R′=Nu′=hD_P/k_s,R′=Sh′=h_DD_P/D_s),通过图2的曲綫来近似地計算顆粒內部传递过程占总传递过程阻力的分数,从而可以确定哪些过程可以有效地通过稀相技术来加速。稀相技术在提高颗粒—流体界面传递速度的显著效果有賴于稀相流态化中顆粒—流体的流动特点。本文分析了固定床、单顆粒和浓相、稀相流态化床中颗粒与流体的运动,并指出顆粒—流体间的传递系数可以分为局部的真值和系統的表观值两种,对浓相流态化床而言,后者可低于前者2—3个数量級。此巨大差别主要是由于顆粒羣的、流体的返混以及流速分布的非齐次性所致。根据分析和实驗数据,稀相操作是减少返混和降低流速分布非齐次性的有效措施,从而可以提高表观传递系数,使其接近于(甚至超过)单顆粒的理想数值。从系統压降的分析,稀相流态化的能量消耗亦将远远低于固定床和浓相流态化。
In fluidized metallurgy, many processes involve heat transfer and transfer between the particle interior and the particles and the surrounding fluid. In this paper, we propose a hybrid comparative resistance R ’(for heat transfer and mass transfer, respectively, R’ = Nu ’= hD_P / k_s, R ’= Sh’ = h_DD_P / D_s), the fraction of the intraparticle transfer process as a function of the total transfer process is approximated by the graph of FIG. 2 so that it is possible to determine which processes can be effectively accelerated by the dilute phase technique. The significant effect of dilute phase technology on increasing the particle-fluid interface transfer rate depends on the particle-fluid flow characteristics in dilute phase fluidization. In this paper, we analyze the motion of particles and fluid in fixed bed, single particle and dense phase and dilute phase fluidized bed, and point out that the transfer coefficient between particles and fluid can be divided into two parts: local true value and system apparent value, For dense-phase fluidized bed, the latter can be 2-3 orders of magnitude lower than the former. This huge difference is mainly due to the non-homogeneity of particle swirling, backmixing of fluid and velocity distribution. Based on analytical and experimental data, dilute phase operation is an effective measure to reduce backmixing and reduce non-homogeneity of flow velocities so that the apparent transfer coefficient can be increased close to, or even exceeded, the ideal value of a single particle. From the analysis of system pressure drop, the energy consumption of dilute phase fluidization will be much lower than that of fixed bed and dense phase fluidization.