Devdopment of the Monolith Froth Reactor for Catalytic Wet Oxidation of CELSS Mo_
The aqueous phase oxidation of acetic acid, used as a model compound for the treatment of CELSS (Controlled Ecological Life Support System) waste, was carried out in the monolith froth reactor which utilizes two-phase flow in the monolith channels. The catalytic oxidation of acetic acid was carried out over a Pt/AI.,O_ catalyst, prepared at The University of Tulsa, at temperatures and pressures below the critical point of water. The effect of ex'temally controllable parameters (temperature, liquid flow rate, distributor plate orifice size, pitch, and catalyst distance from the distributor plate) on the rate of acetic acid oxidation was investigated. Results indicate reaction rate increased with increasing temperature and exhibited a maximum with respect to liquid flow rate. The apparent activation energy calculated from reaction rate data ,,,,,as 99.7 kJ/mol. This value is similar to values reported for the oxidation of acetic acid in other systems and is comparable to intrinsic values calculated for oxidation reactions. The "kinetic data were modeled using simple power law kinetics.
Bubble-train flow in capillaries of circular and square cross section
Abstract Ceramic monoliths first developed for their use in automotive catalyst, are used now to perform three-phase, catalyzed reactions. The large mass transfer rates achieved within this type of reactor are the result of large interfacial area and very thin diffusion paths. These enhanced mass transfer rates are credited to the presence of well-developed bubble-train flow. Bubble-train flows consist of trains of long bubbles separated by liquid slugs. The interfacial area is the area of the bubbles and the thin films are the result of the squeezing action of the bubbles as they overtake the liquid slugs. The objective of this paper is to predict the main mass transfer parameters, such as bubble size and shape, bubble velocity, and volume fraction of gas inside capillaries of circular or square cross section, on the basis of the superficial flow rates of gas and liquid in the feed. Experiments are reported here on bubble train flow inside capillaries of circular and square cross section for a large range of capillary numbers. A mass balance model was developed to allow the computation of flow parameters using an iteration scheme.
Coating the inside of a capillary of square cross section
Abstract Coating the walls of a capillary is usually done in two steps: (1) wetting or filling the capillary with a viscous fluid, and (2) clearing the capillary by forcing air through it. Clearing amounts to driving the wetting viscous fluid out of the capillary by another immiscible fluid. When air is blown into one end of a tube containing the viscous fluid, a “bubble” forms with the back end open. The bubble travels down the tube forcing some of the liquid out and leaving behind a fraction, in the form of a uniform film covering the walls. This paper reports flow visualization in capillaries of square cross secton. Visualization of the bubble was done by viewing both side and diagonal planes of the capillary in order to analyze the effect of the square cross section. Measurements from the captured images were used to characterize the shape of the fluid—fluid interface. The coating thickness of liquid deposited on the capillary walls was measured as the fraction of the capillary volume occupied by the liquid. The results for a wide range of capillary numbers show that this fraction increased monotonically with increasing capillary number, approaching an asymptotic limit of 0.64. Sequential particle tracking techniques were used to determine the flow field in different regions surrounding the bubble. A semi-quantitative comparison of the flow behavior, in capillaries of square and circular cross section, has been carried out.