Control and optimization of a three-phase catalytic slurry intensified continuous chemical reactor

Intensified continuous mini-reactors working in high pressure and temperature conditions are particularly effective at coping with mass transfer limitations during three-phase catalytic reactions. They are highly non-linear, multivariable systems and behave differently from conventional batch, fed-batch or continuous non-intensified reactors. In this paper, the optimization and control of this new process are presented using a two-layer approach consisting of a hierarchical control structure with an optimization layer which calculates the set points for an advanced controller. The latter is based on the concavity of the entropy function and the use of thermodynamic availability as a Lyapunov function. The three-phase catalytic o-cresol hydrogenation performed under high pressure and temperature in a small-scale pilot of the RAPTOR® reactor designed by the French company AETGROUP SAS, is taken as a representative test example to illustrate the strategy. The performance of the control structure is illustrated by simulation.     

Guarding a set of line segments in the plane

We consider the following problem: Given a finite set of straight line segments in the plane, find a set of points of minimum size, so that every segment contains at least one point in the set. This problem can be interpreted as looking for a minimum number of locations of policemen, guards, cameras or other sensors, that can observe a network of streets, corridors, tunnels, tubes, etc. We show that the problem is strongly NP-complete even for a set of segments with a cubic graph structure, but in P for tree structures.     

Project proposal for the investigation of particle-stabilised emulsions and foams by microgravity experiments

The utilisation of particle-surfactants nanostructures as stabilising agents represents today the technologic and scientific frontier in the stabilisation of liquid films in emulsion and foams. This topic will be addressed by the proposal STEFAN (STabilisation of Emulsions and FoAms by Nanoparticles), proposed by European groups in the framework of the ESA AO-2004 for Life and Physical Sciences and Applied Research projects Similarly to what can be observed for surfactant-stabilised emulsions and foams, microgravity provides ideal conditions for the investigation of the hierarchy of involved objects: interfacial layer, liquid film, dispersed systems foam or emulsion. Microgravity experiments are planned by refurbishing the Experimental Container FASES for the ISS Fluid Science Laboratory and the facility FASTER for the European Drawer Rack, already under development in existing research programmes. Here the scientific guidelines of the project are presented together with examples and preliminary results on the effect of nano-particle-surfactant structures adsorbed at liquid interfaces. First experimental results have been achieved for particle monolayers at the water/air interface and a thermodynamic model was derived to describe the obtained surface pressure-area isotherms.     

Determination of the Composition of the Surface Layer of Binary Metal Alloys

We have analyzed the effect of various parameters (surface tensions of the components, molar volumes of the components and the solution, compression and depression in alloy formation, activity coefficients of the components in the melt) on the shape of the surface tension isotherm as a function of the surface layer composition. We compare the analysis results with experimental data. We propose a method for estimating the composition of the surface layer based on a model assuming an additive variation in the surface tension of the solution as a function of the composition of the surface layer. We have calculated the concentration of the surface-active component in the surface layer of melts in the systems Ge - Sn, Ge - Pb, and Ge - Bi.__________Translated from Poroshkovaya Metallurgiya, Nos. 1–2(441), pp. 60–67, January–February, 2005.     

Microwave remote sensing of physically buried objects in the Negev Desert: implications for environmental research

We report remote detections of physically buried specularly reflecting objects using microwave radar at two sites: Ashalim and Tseelim in the northern region of the Negev Desert, Israel. These detections provide confirmation that microwave subsurface remote sensing is a genuine phenomenon. At Ashalim, a scatterometer operating in the P-band (441 MHz, 68 cm) was mounted on a cherry picker truck at a height of 8 m and used to detect two triangular aluminum mesh reflectors (forming a 1-m square area reflector) buried down to a depth of 8 cm in dry sand. At Tseelim, the same scatterometer was mounted on an airplane flying at an altitude of 70 m and used to detect 1-m square aluminum reflectors (each one submerged at a different location along the airplane flight path) buried down to a depth of 20 cm. The experimental results compare favorably with a theoretical model that incorporates radar absorption effects arising in the sandy subsurface layer and radar interference effects arising from phase differences between reflections from the surface and buried reflector. The theoretical modeling also predicts the detection of a subsurface reflector down to a depth of about 4.4 m. This experiment and the associated modeling approach is the first of a series of planned experiments, which we outline for the detection and the theoretical evaluation of buried reflectors using remote microwave and VHF radar. We identify potential subject areas for environmental research.     

Compaction Kinetics with Liquid-Phase Sintering of W – Ni – Sn Pseudoalloys

A kinetic equation for compaction with liquid-phase sintering is found on the basis of rheological sintering theory. Kinetic coefficients of the equation are determined from physicochemical properties of a dispersed system and its components. Compaction kinetics are studied for the system W – Ni – Sn where the liquid phase is eutectic alloy Ni – Sn with the greatest nickel content. It is shown that experimental results are in good agreement with those obtained by the kinetic equation on the coordinates porosity – time. Diffusion coefficient is evaluated for tungsten in melt (67.5 mass% Ni + 32.5 mass% Sn): at 1200°C it is 0.113·10_–5 cm₂/sec for grain diameter L ₀ = 3 μm. Time dependences are also obtained for the compaction rate and viscosity of the pseudoalloys studied.