A new model of the effect of stirring intensity on the rate of secondary nucleation

Secondary nucleation in industrial crystallizers depends on both supersaturation and mechanical stress by stirring. Most models which consider mechanical stress assume that nucleation is proprotional to the energy transferred to the crystals during collisions. This is not based on any physical relationship and, in addition, the models do not satisfactorily reproduce the experimental results. Own model, based on the theory of Hertz/Huber, which accounts for the stress of the crystals caused by impact, gave better results. This well-known and proven theory allows the calculation of the volume abraded during collisions between crystals and stirrer or walls. Introducing a nucleate efficienncy, the effect of mechanical stress on the rate of secondary nucleation, due to stirring intensity and crystallizer size, can be determined.     

An experimental evaluation of a residential-sized evaporatively cooled condenser

In this paper, the performance of an innovative evaporatively cooled condenser is compared with that of a conventional air-cooled condenser for a split heat pump system. The system was tested in an environmentally controlled test chamber that was able to simulate test conditions as specified by ASHRAE Standard 116. Tests to optimize refrigerant charge and short tube restrictor size were conducted using refrigerant HCFC-22. The wheel rotation speed of the evaporative condenser was also optimized experimentally to maximize the coefficient of performance. Using these optimum parameters, steady state and cyclic performance tests were conducted. The experimental results showed that the evaporative condenser has a higher capacity than the air-cooled condenser by 1.8 to 8.1%, a higher COP by 11.1 to 21.6%, and a higher SEER by 14.5%.     

Quantitative phase evaluation of converter slags

The slags formed in the LD vessel during the refining process turn out with different chemical compositions, mineralogical structures and physical properties, in dependence on the charging and processing conditions. Electron probe microanalysis (EPMA) combined with a data processing method for mineralogical analysis was used to characterize the mineralogical phases in LD slags and moreover to determine their volume fractions. By this method some correlations between the phase contents and the chemical composition of LD slags were established. The diagrams gained from this work have proven to be a valuable aid for understanding the interrelationships between the chemical composition, the mineralogical structure and some physical properties of LD slags.     

A note on stability in three-phase-lag heat conduction

In this note we consider two cases in the theory of the heat conduction models with three-phase-lag. For each one we propose a suitable Lyapunov function. These functions are relevant tools which allow to study several qualitative properties. We obtain conditions on the material parameters to guarantee the exponential stability of solutions. The spectral analysis complements the results and we show that if the conditions obtained to prove the exponential stability are not satisfied, then we can obtain the instability of solutions for suitable domains. We believe that this kind of results is fundamental to clarify the applicability of the models.     

Fabrication of alumina ceramics from powders made by sol–gel type hydrolysis in microemulsions

The engineering aspects of the preparation of nanostructured alumina ceramic precursors by alcoholate hydrolysis using microemulsions as reaction media are investigated here. The precipitate was subjected to several treatment steps. Although the properties of the primary precipitated powders are independent of the chemical or reaction engineering parameters of the precipitation procedure, the structure of treated powders and sintered, dense ceramics strongly depends on thermal and mechanical handling like crystallization or grinding of the alumina ceramic precursor. Strong differences are manifested in relative densities and sintering kinetics and can be observed by SEM analysis.     

Microwave plasma-assisted etching of diamond

Experimental results are presented for the microwave plasma-assisted dry etching of ultrananocrystalline (UNCD), polycrystalline and single crystal diamond materials. A high-rate and anisotropic etching process is developed using a 2.45 GHz microwave plasma reactor. The plasma discharge in this system measures 25 cm in diameter and is located inside a 30 cm diameter microwave cavity applicator. The system is an electron cyclotron resonance (ECR) plasma source operating at pressures of 1–100 mTorr. The process chemistries include mixtures of oxygen, sulphur hexafluoride, and argon. Anisotropic etching profiles have been demonstrated and the measured etching rates range from 4–26 μm/h.     

Scaling the microwave plasma-assisted chemical vapor diamond deposition process to 150–200 mm substrates

The scale up of two microwave plasma assisted chemical vapor deposition processes from 75 mm to 200 mm substrates is investigated. A thermally floating 2.45 GHz reactor is scaled up by increasing its physical size by a factor of 2.7 and exciting the reactor with 915 MHz microwave energy. Two processes are investigated, 1) the deposition of ultananocrystalline diamond films (UNCD) and 2) the deposition of polycrystalline diamond films (PCD). Gas chemistries of argon/methane/hydrogen were used for UNCD deposition and hydrogen/methane was used for PCD deposition. Experimental pressures range from 40–110 Torr while microwave power input ranged from 1.9–7 kW resulting in steady state substrate temperatures from 630–950 °C. Uniform deposition was demonstrated over 150–200 mm substrates, i.e. thickness variations of 4% over 150 mm and 6% over 200 mm were achieved with deposition rates ranging from 30–460 nm/h. Low temperature deposition at 633 °C was achieved and thereby demonstrated the potential of integrating the process with temperature sensitive materials. A comparison of the power densities between the two reactors indicates that the large reactor operates at five to nine times lower discharge power densities than smaller reactors suggesting improved deposition efficiencies.     

Working with ARMs: Complexity Results on Atomic Representations of Herbrand Models

An atomic representation of a Herbrand model (ARM) is a finite set of (not necessarily ground) atoms over a given Herbrand universe. Each ARM represents a possibly infinite Herbrand interpretation. This concept has emerged independently in different branches of computer science as a natural and useful generalization of the concept of finite Herbrand interpretation. It was shown that several recursively decidable problems on finite Herbrand models (or interpretations) remain decidable on ARMs.The following problems are essential when working with ARMs: Deciding the equivalence of two ARMs, deciding subsumption between ARMs, and evaluating clauses over ARMs. These problems were shown to be decidable, but their computational complexity has remained obscure so far. The previously published decision algorithms require exponential space. In this paper, we prove that all mentioned problems are coNP-complete.     

Synergistic effect of benzoate and benzotriazole on passivation of mild steel

The electrochemical behaviour of mild steel was investigated in near neutral air saturated solutions containing benzoate (Bzo) and benzotriazole (BTA), separately or mixed. In the benzoate/BTA mixtures the open circuit passivation was found to be much better than in pure benzoate electrolytes. Electrochemical impedance spectroscopy (EIS) measurements resulted in characteristic Bode plots due to the synergistic effect of both inhibitors in the presence of oxygen. Open circuit potential (OCP) measurements vs. time supported the observed behaviour. The inhibition effect can be attributed to the blocking of surface sites for anodic dissolution by benzoate and a subsequent strong adsorption of benzotriazole on the natural oxide layer.