A modified Richardson-Zaki equation for fluidization of Geldart B magnetic particles

Gas bubbles are suppressed in fluidized beds of Geldart B magnetic particles when a homogenous magnetic field is applied due to the formation of straight-chain aggregates. Expansion of the non-bubbling bed depends on the orientation of the applied field with respect to gas flow. Hindered bed expansion is reported for axial fields, whereas enhanced expansion is observed for transversal fields. In the present paper we propose a modified Richardson-Zaki equation that takes into account aggregation and chain orientation to describe bed expansion as the gas flow is increased. The only free parameter in this equation is the chain length, that is directly related to the field intensity through a magnetic granular Bond number, defined as the ratio of magnetic to gravitational energy per unit volume. Results from the proposed model are successfully compared with published data in the literature.     

Synthesis of copolybibenzoates with thioether and ether groups in the flexible spacers

Main‐chain copolybibenzoates with flexible spacers bearing thioether and ether groups were obtained by melt‐transesterification of diethyl 1,1′‐biphenyl‐4,4′‐dicarboxylate and β‐thioether glycols (thiodiethylene glycol or thiotriethylene glycol), using titanium (IV) isopropoxide as catalyst. A side‐reaction of etherification occurred simultaneously with the polycondensation reaction, resulting in the formation of comonomer units with the structure of the dimer of the glycol. This side‐reaction was confirmed by the preparation of model compounds. The most probable mechanism for this etherification reaction is the formation of an intermediate three‐membered cyclic sulfonium ion by neighbouring sulfur participation. The thermal and X‐ray characterization of the synthesised copolymers indicated that a smectic mesophase was rapidly obtained on cooling the copolymers derived from thiodiethylene glycol from the melt and this phase was transformed slowly into a more ordered structure. In contrast, copolymers derived from thiotriethylene glycol did not exhibit liquid‐crystalline phases and their crystallisation from the isotropic melt was very fast. It was found that the copolymerization increased the mesophase stability. Finally, the results obtained were compared with those of corresponding homopolybibenzoates with methylene or oxymethylene spacers. Copyright © 2005 Society of Chemical Industry     

Heat recovery and transportation from thermal plants

A process for heat recovery from a thermal plant and transportation over a large distance is presented and discussed. Heat is carried in the vapour phase of a working fluid at the ambient temperature without thermal losses. The performance of the process compares favourably, even for distances of about 100 km, with the local use of a heat pump at the site where the thermal energy is to be consumed. Water can be used as a suitable alternative to freons in such a process of heat transportation.     

Preparation of black pepper oleoresin by alcohol extraction

Black pepper oleoresin was prepared by alcohol extraction. Product characteristics and yields obtained by maceration and Soxhlet extraction were compared. The most attractive process was maceration and its influence on volatile oil composition was also evaluated by capillary GLC.     

Influence of the acidity level on the electropolymerization of N-vinylcarbazole: Electrochemical study and characterization of poly(3,6-N-vinylcarbazole)

Poly(3,6-N-vinylcarbazole) films were prepared by electrochemical oxidation of N-vinylcarbazole on a Pt electrode using acetonitrile as solvent and tetraethylammonium tetrafluoroborate as electrolyte. The electrosynthesis was carried out by electrical potential cycling in the presence of two different bases: tetraethylammonium benzoate (Bz⁻) and tetraethylammonium phthalate (Ph⁻). These salts were expected to modify the acidity level of the electrolyte since they can act as scavengers for the protons released during the polymerization, when the reaction takes place in the carbazole unit.Products were characterized by cyclic voltammetry, scanning electron microscopy, FTIR spectroscopy, thermogravimetric analysis, differential scanning calorimetry, absorption spectroscopy and four-probe electrical conductivity measurements. Both bases influenced significantly the chemical structure and morphology of the deposited materials. The presence of Ph⁻ in the electrolyte decreases the cross-linking of the electrodeposited polymer, leading to a poly(3,6-N-vinylcarbazole) bearing a more uniform morphology, higher thermal stability and electrical conductivity compared to those of the polymers obtained in the presence of Bz⁻ and without acidity control.     

Production of Silicon Carbide Pieces by Immersion of Silicon Preforms in Carbonaceous Powders

In this work a novel method for production of silicon carbide (SiC) pieces, which involves the heating of silicon (Si) preforms immersed in graphite powder is presented. Such preforms were obtained via low-pressure injection molding (LPIM), although any other conformation route can be used. The process can be carried out at modest temperatures and gradients in standard furnaces used for processing other ceramics. These features make this process a simpler and cheaper alternative, when compared with other methods of SiC fabrication. The variables affecting the process have been identified, and an optimum-heating ramp has been established. Under these conditions, the obtained SiC products show no remnant-free Si, and their mechanical behavior allows their use in several less-demanding SiC applications, for which expensive high-performance SiC products are unaffordable. In the proposed chain of reactions, CO( g ) is responsible for the carburization of the pieces. All phases present are identified, and their distribution is explained by means of competitive reactions. In our opinion, this novel method can be extended to an industrial scale because it is simple and involves cheap raw materials.     

Input-output stability of systems with backlash

The objective of this work is to study the stability of systems with backlash, from an input-output point of view. In the first part, an L_∞ analysis is addressed. This analysis provides not only conditions for boundedness of the loop signals, but also results on existence of solutions, based on Schauder fixed point theorem. In the second part, the system is studied using an L₂ or conic sector approach. The backlash graph is confined into certain conic sector, which is shown to be optimum or maximal. The conic inequality induces frequencial conditions on the linear part, which are further relaxed introducing dynamic multipliers. In the third part, both L_∞ and L₂ techniques are combined reaching a final criterion which results in a Popov-like stability condition.     

Development and characterisation of electrochromic devices on polymeric substrates

The development of full solid-state electrochromic (EC) devices on polymeric substrate is underway within a CEC BRITE-EURAM project (Project “FREDOPS”, BE-4137) carried out by four industries, two universities and two research centers from Belgium, Denmark, France, and Italy. The specific goal of this project is to develop a Fast Response Electrochromic Device On Polymeric Substrate (FREDOPS); in order to satisfy the required range of specifications in terms of fast response, long term performance and high contrast ratio, several systems based on different materials have been tested. The full cells consist of an electrochromic material layer and a counter electrode, inserted between two PET/ITO layers and separated by a polymeric electrolyte. Different types of polymeric electrolytes, counter electrodes and electrochromic layers have been developed, studied and checked. Full devices have been assembled using different combinations. Voltammetric and spectrophotometric measurements have been executed to check the electrochromic behaviour of the developed layers in half and full cells. Comparison of the electrochromic performances of different materials based cells has led to the rejection of several solutions due to poor performance and incompatibilities between layers. Considering that the electrochromic devices are finalised for different uses (window, sunroof,…), some performance specifications for each application are defined. A testing bench for cycling and ageing was developed. The present paper discusses these results in order to indicate the best performance.     

Directivity optimisation of an array antenna with obstacles withinits near field region

A method for synthesising an array antenna in order to obtain its maximum directivity, when the antenna is in the presence of perfectly electric conducting (PEG) bodies, is presented. The proposed solution is based on the generalised multipole technique (GMT) combined with an optimum directivity (OD) technique. A closed form formulation is presented together with results which demonstrate the scanning capabilities of the proposed method