Particles, binary mixtures

Catalyst powders with carefully specified particle size distribution have been known to possess good fluidization characteristics. Generally, addition of fine particles to coarse particles tends to improve the latter s fluidization characteristics. Experiments were thus conducted on binary particle mixtures, each consisting of a fairly close particle size distribution. 

Figure 54. Measure of synergism for binary particle mixtures. (Kwauk, 1984, 1986.)...

Epstein, N. and Pruden, B.B. Chem, Eng. Sci. 54 (1999) 401. Liquid fluidisation of binary particle mixtures - III. Stratification by size and related topics. 

Fig. 25. Modes of operation shifts for binary particle mixtures (heavy lines for denser particles). [After Kwauk, 1962.]...

The axial voidage distribution resulting from mixing of dissimilar particles, as shown in Fig. 26, will now be examined in the light of the dynamics of these particles at the interfacial boundary between the properly juxtaposed phases of a binary particle mixture (Lou, 1964 Kwauk, 1973). Both the lighter particles at the top and the heavier particles at the bottom share the same tendency of invading the region occupied by the other. This behavior conforms to the concept of random walk, for which Fick s law can be adapted to describe the macroscopic diffusion flux of the smaller particles 2 ... 

The preceding analysis for a binary particles mixture may be generalized to polydisperse systems. Thus, for any j fraction, an equation similar to Eq. (5.8a) can be written... 

Figure 77 shows more computer-generated curves (Qian and Kwauk, 1986) showing synergism for different binary particle mixtures. 

Xia, Y., and Kwauk, M., Micro-Visualization of Fluidizing Behavior of Binary Particle Mixtures," Intern. Symp. Heat Transfer, Beijing, 1985, Hemisphere (1985). 

VIII. Measure of Synergism for Binary Particle Mixtures 260... 

M. van Sint Aimaland, G. A. Bokkers, M. J. V. Goldschmidt, O. O. Olaofe, M. A. van der Hoef and J. A. M. Kuipers, Development of a multi-fluid model for poly-disperse dense gas-solid fluidised beds, Part II Segregation in binary particle mixtures, Chem. Eng. Sci, 2009, 64, 4237 246. 

Pruden, B. B. and Epstein, N. Liquid fluidization of binary particle mixtures. Chem. Engng Sci. 14, 696-704 (1964). 

Wakeman R.J., 1993. Scale-up procedures and test methods in solid/liquid separation 2. Filtration of binary particle mixtures and flocculated suspensions, IFPRl Annual Research Report ARR 25-02. 

A common approach to predict the voidage of binary particle mixtures is to make use of the empirical correlation developed by Westman (1936) based on the total bed volume occupied by the specific volume of solid material F = 1/(1 — e). The equation was later modified by Yu et al. (1993) as shown in the following equation to apply to both spherical and non-spherical particles. 

An approach employing the structural ratio to predict the voidage of binary particle mixtures for both spherical and nonspherical particles is also proposed recently by Finkers and Hoffmann (1998). The structural ratio based on packing of spherical and nonspherical particles is defined as... 

HJ Finkers, AC Hoffmann. Structural ratio for predicting the voidage of binary particle mixtures. AIChE J 44 495-498. 

A study by Chiba et al. (1979) on the minimum fluidization velocity of binary particle mixtures indicated that the fluidization curve shown in Fig. 27 was... 

Chiba S, Chiba T, Nienow AW, Kobayashi H. The minimum fluidization velocity, bed expansion and pressure-drop profile of binary particle mixtures. Powder Technol 22 255-269, 1979. 

The same trend was also observed for fluidized beds with binary particle mixtures—alines in a coarse particle fluidized bed— by Ma and Kato (1998). The reason for this effect is probably the formation of particle agglomerates in the case of very fine particles for which adhesion forces are large compared to the gravitational forces. Baeyens et al. (1992) suggest based on their measurements a correlation for the critical particle diameter at which the inflection occurs ... 

Ma X, Kato K. Effect of interparticle adhesion forces on elutration of fine powders from a fluidized bed of binary particle mixture. Powder Technology 95 93-101, 1998. 

PB)max = maximum bulk density of binary particle mixture over range of possible bed inversion velocities, i.e., bulk density of bottom layer, kg m ... 

Epstein N, LeClair BP. Liquid fluidization of binary particle mixtures—II. Bed inversion. Chem Eng Sci 40 1517-1526, 1985. 

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