Based on experimental results from a 7.6 cm I.D. and 3 m high liquidsolid circulating fluidized bed, the liquikolid circulating fluidization regime has been separated into two zones: the initial circulating fluidization zone and the fully developed circulating fluidization zone. The distinct hydrodynamic behavior and the influence of particle properties in the two circulating fluidization zones have been studied. The overall flow structure in LSCFB, although still somewhat non-uniform, is much more uniform than that in a gas-solid CFB. Our experimental results also show that the axial flow characteristics and the regime transition can be strongly affected by the particle density. The stable operation range of the circulating fluidization system and the influences of some associated factors, such as the solids inventory and the particle density, were also investigated for the first time.A partir de resultats experimentaux d'un lit fluidise circulant liquidesolides de 7,6 cm de diarnetre interieur et 3 m de haut, on a separe le regime de fluidisation circulant liquidesolides en deux zones : la zone de fluidisation circulante initiale et la zone de fluidisation circulante pleinement developpee. On a etudie le comportement hydrodynarnique distinct et l'influence des proprietes des particules dans deux zones de fluidisation circulantes. La structure globale de I'ecoulement dans deux zones de fluidisation circulantes. La structure globale de I'ecoulement dans le LSCFB, quoique toujours legerement non uniforme, est beaucoup plus uniforme que dans un CFB gaz-solides. Nos resultats experimentaux montrent egalement que les caracteristiques d'ecoulement axial et la transition de regime peuvent 6tre fortement influencees par la masse volumique des particules. La g a m e de fonctionnement stable du systeme de fluidisation circulant et I'influence de certains facteurs associes, comme I'inventaire des solides et la masse volumique des particules, ont egalement ete etudiees pourla premiere fois. When the liquid velocity is beyond the critical transition velocity, it would be necessary to separate the entrained particles at the riser top and recirculate them back to the base of the riser column. LSCFB has potential applications in the fields of food processing, biochemical processing, petrochemical and metallurgical processing, etc. (Di Felice, 1995; Liang et al., 1997).Hydrodynamics studies are important to properly design an industrial LSCFB system. The flow characteristics in a LSCFB system has been shown to be very different from a conventional liquid-solid fluidized bed and from a gassolid circulating fluidized bed, as reported in recent studies (Liang et al., 1996;1997). However, a more systematic study is still needed for a comprehensive understanding of the phenomena. For example, little work has been done concerning the effects of the physical properties of the particles, such as particle density, on the hydrodynamics of the system. When Liang et al. (1997) studied the solids flow with two relatively low-density particl...

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We demonstrate a general nuclear magnetic resonance (NMR) spectroscopic approach in obtaining high-resolution (17)O (spin-5/2) NMR spectra for biological macromolecules in aqueous solution. This approach, termed quadrupole central transition (QCT) NMR, is based on the multiexponential relaxation properties of half-integer quadrupolar nuclei in molecules undergoing slow isotropic tumbling motion. Under such a circumstance, Redfield's relaxation theory predicts that the central transition, m(I) = +1/2 ↔ -1/2, can exhibit relatively long transverse relaxation time constants, thus giving rise to relatively narrow spectral lines. Using three robust protein-ligand complexes of size ranging from 65 to 240 kDa, we have obtained (17)O QCT NMR spectra with unprecedented resolution, allowing the chemical environment around the targeted oxygen atoms to be directly probed for the first time. The new QCT approach increases the size limit of molecular systems previously attainable by solution (17)O NMR by nearly 3 orders of magnitude (1000-fold). We have also shown that, when both quadrupole and shielding anisotropy interactions are operative, (17)O QCT NMR spectra display an analogous transverse relaxation optimized spectroscopy type behavior in that the condition for optimal resolution depends on the applied magnetic field. We conclude that, with the currently available moderate and ultrahigh magnetic fields (14 T and higher), this (17)O QCT NMR approach is applicable to a wide variety of biological macromolecules. The new (17)O NMR parameters so obtained for biological molecules are complementary to those obtained from (1)H, (13)C, and (15)N NMR studies.

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