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.     

Influence of impurities and deformation temperature on the saturation microstructure and ductility of HPT-deformed nickel

Ni with different purities between 99.69 and 99.99 wt.% was deformed by high-pressure torsion (HPT) to high strains, where no further refinement of the microstructure is observed. The HPT deformation temperature varied between −196 and 400 °C. Both impurities and temperature significantly affect the lower limit of the grain size obtained by HPT. In the investigated samples, carbon was the most important impurity element in controlling the limit of grain refinement. The decrease in grain size due to an increase in the carbon content from 0.008 to 0.06 wt.% for HPT-deformed Ni samples at room temperature enhanced the ultimate tensile strength from 1000 to 1700 MPa. Surprisingly, the carbon content did not deteriorate the ductility, defined as the reduction in area, which is mainly limited by the total amount of impurities besides carbon. Furthermore, the deformation temperature dependency on ductility was not very pronounced and only visible for deformation temperatures above 200 °C.     

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.     

Naßmahlung in Rührwerksmühlen

Wet grinding in agitated ball mills. To ensure certain product qualities it is necessary to have very fine particles or a narrow particle size distribution. For this process agitated ball mill grinding can be used as well as crystallisation and precipitation. Cost effective grinding of very fine products to a narrow particle size distribution requires that the effects of variation of strain intensity, frequency of impacts, residence time distribution, size of grinding media, viscosity of liquid and concentration of feed material should be known. The most important parameters and their effects on the grinding result are demonstrated, as well as explained by a model, and the consequences for the operating conditions of agitated ball mills are presented. By using small grinding media in agitated ball mills the production rate can be increased, or at the same energy level smaller particles can be obtained by grinding or deagglomeration. At high flow rates and a narrow residence time distribution the feed material becomes more homogeneous. These facts require the development of new or modified types of agitated ball mills.     

Composition and quality attributes of conventionally and organically farmed Pangasius fillets (Pangasius hypophthalmus) on the German market

A range of conventionally and organically farmed Pangasius or sutchi catfish fillets available on the German market were analysed to compare both composition and quality. Differentiation of Pangasius hypophthalmus from Pangasius bocourti was achieved by RFLP-SSCP analysis. The protein content of conventionally farmed fillets ranged between 13.3 and 15.7%, whereas organically produced fillets had significantly higher protein contents of between 17.0 and 17.4%. No difference in the fat content between farming methods was observed, which varied between 1.4 and 3.2%. Polyunsaturated fatty acids represented about 24% of the total fatty acids with a high level of linoleic acid. The comparison of the proximate composition indicated that water was added to most of the conventionally farmed products, in different amounts, as well as water-binding capacity enhancing additives. Differential scanning calorimetry was used to demonstrate the presence of polyphosphate on muscle proteins. Differences in texture, water-binding capacity and colour are discussed.     

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.