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| TRANSPORT PROCESSES IN DILUTE-PHASE FLUIDIZATION AS APPLIED TO CHEMICAL METALLURGY Ⅰ. TRANSFER COEFFICIENT AND SYSTEM PRESSURE DROP AS CRITERIA FOR SELECTING DILUTE-PHASE OPERATIONS |
| MOOSON KWAUK; DIEN-WEI TAI(Institute of Chemical Metallurgy; Academia Sinica) |
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Cite this article:
MOOSON KWAUK; DIEN-WEI TAI(Institute of Chemical Metallurgy; Academia Sinica). TRANSPORT PROCESSES IN DILUTE-PHASE FLUIDIZATION AS APPLIED TO CHEMICAL METALLURGY Ⅰ. TRANSFER COEFFICIENT AND SYSTEM PRESSURE DROP AS CRITERIA FOR SELECTING DILUTE-PHASE OPERATIONS. Acta Metall Sin, 1964, 7(3): 263-280.
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Abstract In the application of fluidization to chemical metallurgy, many processes involve the transport of heat and mass both inside a particle and between the particle and the surrounding fluid. The term, mixed specific resistance, R′(R′=Nu′=hD_p/k_s and R′=Sh′=h_DD_P/D_s for heat and mass transfer, respectively), is proposed, through which, by means of the curve shown in Figure 2, it is possible to estimate the fraction of total resistance due to transfer inside the particle, thus permitting one to ascertain whether or not a given transport process can be effectively hastened by dilute-phase technique.The effectiveness of dilute-phase technique in accelerating transport processes is primarily due to the unique characteristics of its particle-fluid dynamics. After an analysis on the fixed bed, a single particle in a fluid, and the dense—and dilute—phase fluidized systems, the present paper points out that a differentiation should be made between the local transfer coefficient and an apparent value based on the entire system. For densephase fluidization with gases, for example, the latter may be lower than the former by 2—3 orders of magnitude. This tremendous disparity is mainly caused by the back-mixing of both the particles as a group and of the fluid, as well as by the heterogeneous nonuniformity characteristic of may a particle-fluid system. Based on the present analysis, which is duly supported by experimental evidence, it is shown that dilute-phase technique can be used effectively to reduce back-mixing and to suppress the heterogeneous nature in nonuniform velocity fronts, thus raising the values of apparent transfer coefficients to the range of the local coefficients of the idealized single particle model. From the point of view of system pressure drop, too, dilute-phase fluidization represents much lower power consumption than the corresponding fixed bed or dense-phase operation.
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Received: 18 March 1964
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