AICHE Journal

An experimental investigation was made of the lenght of the turbulent vapor cavity formed by a steam jet discharging into a subcooled liquid water both. The experiments considered both constant area and convergent‐divergent steam injectors of various external geometries. The tests were conducted with the bath at atmospheric pressure, bath temperatures in the range 301–358K, injector exit diameters in the range 0.00040–0.0112 m, for choked injector flows having mass velocities in the range 332–2050 kg/m^2.s. These conditions yielded injector exit Reynolds numbers from 2 to 150 × 10⁴. Over this range a correlation was developed to yield the length of the vapor cavity as a function of the injector diameter, exit mass velocity, and a driving potential for the condensation process. The heat transfer coefficients for this condensation process were found to be significantly greater than those encountered in turbulent film condensation processes in the vicinity of tubes and walls.

Silicalite membrane preparation conditions related to membrane separation properties were studied focusing on in situ crystallization to prepare highly selective silicalite membranes on porous tubular supports by a single hydrothermal treatment. The membranes morphologies prepared under typical synthesis conditions were characterized by scanning electron microscopy. The silicalite membrane, well‐oriented with c axis normal to the support surface, could be prepared by in situ crystallization and a seeding method. The membrane separation properties were controlled by synthesis conditions such as seeding, temperatures, supports, and silica sources. Under certain conditions, such factors as tube pore size, played an important role. Silicalite membranes would be prepared better by in situ crystallization than by a seeding method under the same conditions. For example, the highest ethanol/water separation factor of 106 with a flux of 0.9 kg/m²·h for a feed concentration of 5 wt. % ethanol at 60°C was obtained for the silicalite membrane prepared on an unseeded mullite tube at 175°C for 16 h with colloidal silica, whereas the membranes prepared on the silicalite‐seeded tubes had separation factors up to 70. The higher separation selectivity for ethanol over water would be attributed to reduction in nonzeolitic pores, supported by gas permeations of n‐butane and i‐butane.

The high‐temperature rate of reaction of the homogeneous, reverse water–gas shift reaction (rWGSR) has been evaluated in quartz reactors with rapid feed preheating under both low‐ and high‐pressure conditions. The form of the power‐law rate expression was consistent with the Bradford mechanism. The Arrhenius expressions for the reaction rate constant, corresponding to the empty reactor, were in very good agreement with the low‐pressure results of Graven and Long, but yielded rate constants roughly four times greater than those obtained in our packed reactor and those reported by Kochubei and Moin and by Tingey. Reactor geometry was not responsible for these differences because computational fluid dynamics simulations revealed similar residence time distributions and comparable conversions when the same kinetic expression was used to model the rWGSR in each reactor. Most likely, the empty NETL reactor and the Graven and Long reactor did not attain an invariant value of the concentration of the chain carrier (H) at low reaction times, which led to an overestimation of the rate constant. Conversions attained in an Inconel® 600 reactor operating at comparable conditions were approximately two orders of magnitude greater than those realized in the quartz reactor. This dramatic increase in conversion suggests that the Inconel® 600 surfaces, which were depleted of nickel during the reaction, catalyzed the rWGSR. © 2004 American Institute of Chemical Engineers AIChE J, 50: 1028–1041, 2004

Simplified expressions to calculate the extent of reaction in a fluid bed show good agreement with the experimental data of Lewis et al. (1959) and Swaay and Zuiderweg (1972). The contribution of the dilute phase seems more important than that of the jetting zone or reaction factor (Hatta number) in usual fluid bed operations. The effect of the dilute phase is discussed. It is profitable to use the dilute phase for the consecutive isothermal and endothermic reaction, but unprofitable for the exothermic reaction. These characteristics depend upon the nature of reactions and careful considerations as to the choice of the gas velocity, particle characteristics, and reactor design will be necessary.

The axial destribution of reactivity inside a fluid‐bed contactor is studied for the hydrogenation of ethylene. The reactivity is large near the surface of the dense phase. The significant effect of the dilute phase, or the free board region, is verified experimentally, and the contact efficiency in the transition zone and in the dilute phase is obtained. The contact efficiency was approximated by η_c = 1 − 0.75 (ϵ_e/ϵ_ede)^0.4. The temperature rise in the dilute phase is measured in the small reactor. The transition zone between the dense and dilute phases is almost isothermal, but it is found that temperature increases in the dilute phase.

A means of calculating the rate of entrainment of solids from commercial‐size continuously operating fluidized beds was developed from the combined results of a theoretical and an empirical approach which through different channels arrived at the same fundamental mechanism. The calculation method shows agreement with data obtained from an apparatus simulating flow characteristics in large‐scale equipment and compares favorably with smaller scale tests reported in the literature at pressures up to 200 1b./sq. in. gauge.

Biomaterials are widely used in numerous medical applications. Chemical engineering has played a central role in this research and development. Polymers as biomaterials, materials and approaches used in drug and protein delivery systems, materials used as scaffolds in tissue engineering, and nanotechnology and microfabrication techniques applied to biomaterials are reviewed.

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