Flow phenomena in laminar flow through streamlined and sharp-edged short monolithic structures.

Monolithic structures of catalytic reactors offer low flow resistance, but their drawback is weak heat and mass transport. For transport intensification, innovative streamlined structures were designed, the walls of which are shaped like an airplane wing. Extensive CFD (Computer Fluid Dynamics) studies were performed for the streamlined and-for comparison-classic (sharp-edged) structures, covered flow phenomena, and heat transfer to channel walls. The streamlined structures were made using the SLM (Selective Laser Melting) method to perform heat transfer experiments that gave a satisfactory agreement with the CFD. Heat transfer for streamlined structures was, by CFD, more intensive than for the classical ones. CFD simulations showed a significant reduction of vortices in streamlined structures. The lack of an inlet vortex was demonstrated, for classic structures strongly limiting transfer properties. For the streamlined structures the outlet vortex even intensifies heat transport near the outlet of the channel. The CFD showed the flow patterns for the structures as well as the distribution of transport coefficients within the millimetre-sized channels.

Chemical and Structural Characterization of Amorphous and Crystalline Alumina Obtained by Alternative Sol-Gel Preparation Routes.

Aluminum oxide is one of the most commonly used materials in the industry. It is used in the field of catalysis, refractories, and optics. Despite the fact that there are many techniques available, there is still a great challenge in obtaining a material with desired and designed properties. Nevertheless, there is a great flexibility in making customized alumina materials with desired physicochemical properties synthesized by sol-gel methods. This work consists in characterizing the physicochemical properties of sol-gel synthesized aluminum oxide using different sol-gel preparation routes. Three different sols were obtained by using organic precursors and underwent thermal treatment. The structure (Middle Infrared Spectroscopy, Diffused Reflectance Infrared Spectroscopy, X-ray Diffraction, Magic Angle Spinning Nuclear Magnetic Resonance) and microstructure (Scanning Electron Microscopy with Electron Dispersive Spectroscopy) tests of the materials were carried out. The specific surface area was determined by using the Brunauer-Emmett-Teller (BET) method. Thermal analysis was performed for all the powders, in order to analyze the specific temperature of materials transformation.

Analysis of Entropy Production in Structured Chemical Reactors: Optimization for Catalytic Combustion of Air Pollutants.

Optimization of structured reactors is not without some difficulties due to highly random economic issues. In this study, an entropic approach to optimization is proposed. The model of entropy production in a structured catalytic reactor is introduced and discussed. Entropy production due to flow friction, heat and mass transfer and chemical reaction is derived and referred to the process yield. The entropic optimization criterion is applied for the case of catalytic combustion of methane. Several variants of catalytic supports are considered including wire gauzes, classic (long-channel) and short-channel monoliths, packed bed and solid foam. The proposed entropic criterion may indicate technically rational solutions of a reactor process that is as close as possible to the equilibrium, taking into account all the process phenomena such as heat and mass transfer, flow friction and chemical reaction.