Particle size engineering

The terminal velocity in the case of fine particles is approached so quickly that in practical engineering calculations the settling is taken as a constant velocity motion and the acceleration period is neglected. Equation 7 can also be appHed to nonspherical particles if the particle size x is the equivalent Stokes diameter as deterrnined by sedimentation or elutriation methods of particle-size measurement. 

Changes in particle-size distribution affect the pore distribution of the powder. Large pores between particles enhance the rate of binder penetration, whereas they decrease the final extent. In addition, the particle-size distribution affects the ability of the particles to pack within the drop as well as the final degree of saturation [Waldie, Chem. Engin. ScL, 46,2781 (1991)]. 

Purely physical laws mainly control the behaviour of very large particles. Further down the particle size range, however, specific surface area, i.e. surface area per unit mass, increases rapidly. Chemical effects then become important, as in the nucleation and growth of crystals. Thus, a study of particulate systems within this size range of interest has become very much within the ambit of chemical engineering, physical chemistry and materials science. 

The reaction engineering model links the penetration theory to a population balance that includes particle formation and growth with the aim of predicting the average particle size. The model was then applied to the precipitation of CaC03 via CO2 absorption into Ca(OH)2aq in a draft tube bubble column and draws insight into the phenomena underlying the crystal size evolution. 

A common starting point is that the process engineer is given a brief from which to determine a crystallization plant design viz. some specification of the product and process (e.g. mean particle size, production rate) and characteristics of the feed solution (e.g. composition, temperature etc.). Figure 9.1. 

Chen, J., Zheng, C. and Chen, G., 1996. Interaction of macro- and micromixing on particle size distribution in reactive precipitation. Chemical Engineering Science, 51, 1957-1966. 

Hill, P.J. and Ng, K.M., 1997. Simulation of solids processes accounting for particle size distribution. American Institute of Chemical Engineers Journal, 43, 715. 

Rovang, R.D. and Randolph, A.D., 1980. On-line particle size analysis in the fines loop of a KCl crystallizer. American Institute of Chemical Engineers Symposium Series, 76(193), 18. 

Wachi, S. and Jones, A.G., 1992. Dynamic modelling of particle size distribution and degree of agglomeration during precipitation. Chemical Engineering Science, 47, 3145-3148. 

When a flammable liquid is sprayed as fine droplets into the air, a flammable mixture can result, which may burn or explode. The mist or spray may be formed by condensation of saturated vapors or by mechanical means [40]. As the particle sizes of the liquid become greater than 0.01 mm diameter, the lower flammability limit of the material becomes lower while above 0.01 mm, the LEL is about the same as the vapor. Mechanical engine crankcase explosions of oil mist in air are hazardous, and current practice is to apply explosion relief valves to the crankcase. 

The rheo cells can easily be replaced by various types of mixers, propellers or paddles (Figure 2.1.10). It is then possible to analyze the temporal evolution of chemical/physical reactions of mixing, demixing and sedimentation of materials in process engineering, e.g., during the mash process or fermentation [28, 29]. The stirring mechanics and speed can be optimized for various materials of different particle sizes and viscosity. 

Our Chemical Engineering colleagues had developed an elegant impinging jet crystallization which provided excellent particle size control for the finasteride process [13]. In the final pilot plant campaign just before the factory start-up, the crystallization suddenly started producing a different particle size distribution and lower recovery. The problem was traced to a new finasteride solvate which reduced the solubility in the crystallization solvent system. Fortunately, only relatively... 

Data representation, in particle size measurement, 18 133-138 Data searching, 6 6-19 Data sheets, engineering thermoplastic, 10 221t... 

Figure 5.9 Effect of crystallinity on the solid-state polycondensation of PET, shown as the number-average molecular weight as a function of time. Conditions fluidized bed polymerization at 230°C particle size, 35-48 mesh superficial velocity of nitrogen, 43cm/s [6]. From Chang, T. M., Polym. Eng. Sci., 10, 364 (1970), and reproduced with permission of the Society of Plastics Engineers...

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