Gas‐Liquid Mass Transfer Rates and Impeller Power Consumptions for Industrial Vessel Design

Volumetric mass transfer coefficients (k_La) and power input (P) are often the key parameters in the design of gas‐liquid contactors. However, due to the limitations of most measurement methods, there is a lack of reliable data for predicting k_La for non‐coalescent batches under high energy dissipation rates. Accurate k_La and P correlations are proposed. The reliability of the correlations is ensured by using experimental data from a wide range of process conditions conducted in multiple‐impeller vessels of both laboratory scale and pilot scale, and including both non‐coalescent and coalescent batches. Applying the proposed correlations, the scale‐up and optimization of industrial vessels can be performed more accurately.     

Simplification of separation of the reaction mixture after transesterification of vegetable oil

A heterogeneous reaction mixture is formed by transesterification of vegetable oils. The reaction mixture contains mainly methyl esters of higher fatty acids and glycerol. From this mixture, biodiesel is gained by spontaneous sedimentation in the gravitational field. The sedimentation can be considerably accelerated by controlled addition of water. It was found that addition of small amounts of water to the crude reaction mixture significantly affected the mixture, and substantial changes in the speed of the separation took place. Considerable differences in the composition and quality of the ester and glycerol phases occurred. The optical properties (transmittance and refractive indices) of the heterogeneous reaction mixture are changed after addition of water; this change can be observed spectrophotometrically. This method is applicable to all types of vegetable oils including waste frying oils.     

Effect of cross-linking method on the activity of spray-dried chitosan microparticles with immobilized laccase

The effect of processing method on the properties of cross-linked chitosan microparticles and on the enzymatic activity of laccase immobilized in the particles has been investigated. Chitosan has been cross-linked by tri-polyphosphate (TPP) using two methods – the so called ex situ cross-linking whereby the solutions of chitosan, TPP and the enzyme have been pre-mixed and spray-dried by a standard two-fluid kinetic nozzle, and a novel in situ cross-linking method, whereby the solutions have been contacted at the tip of a three-fluid nozzle and cross-linking occurred within a drying droplet. The influence of the cross-linking method on the particle size and morphology, surface charge, and swelling ratio has been determined. The enzymatic activity of laccase toward the oxidation of a chromophore substrate (ABTS) has been systematically investigated and found to be superior in particles produced by the in situ cross-linking method.     

Influence of processing on fracture toughness of Si3N4 + graphene platelet composites

Silicon nitride + 1 wt% graphene platelet composites were prepared using various graphene platelets (GPL) and two processing routes; hot isostatic pressing (HIP) and gas pressure sintering (GPS). The influence of the processing route and graphene platelets’ addition on the fracture toughness has been investigated. The matrix of the composites prepared by GPS consists of Si₃N₄ grains with smaller diameter in comparison to the composites prepared by HIP. The indentation fracture toughness of the composites was in the range 6.1–9.9 MPa m^0.5, which is significantly higher compared to the monolithic silicon nitride 6.5 and 6.3 MPa m^0.5. The highest value of K_IC was 9.9 MPa m^0.5 in the case of composite reinforced by the smallest multilayer graphene nanosheets, prepared by HIP. The composites prepared by GPS exhibit lower fracture toughness, from 6.1 to 8.5 MPa m^0.5. The toughening mechanisms were similar in all composites in the form of crack deflection, crack branching and crack bridging.     

Horizontal forces in steel structures tested in fire

Fire tests carried out on the eight-storey steel framed building at the Building Research Establishment’s Cardington laboratory have shown that the connections are subject to large axial force. These forces are the result of thermal movements of the structure during heating and cooling and in some cases can result in failure of the structure. This paper describes a fire test carried out on the steel frame at Cardington on 16th January 2003 and a fire test carried out on a structure in Ostrava on 16th June 2006. In both cases the tests were designed to measure the forces generated in the connections.     

Texture evolution in Fe–3% Si steel treated under unconventional annealing conditions

The present work investigates texture evolution stages in grain-oriented steel heat-treated using unconventional conditions. The Fe–3%Si steel taken after final cold rolling reduction from an industrial line was subjected to a laboratory isothermal annealing at different temperatures. The annealing temperatures were varied in a range of 850–1150 °C. During the annealing each specimen was heated at 10 °C/s and kept at the stated temperature for 5 min. Development of microstructure and texture in the annealed specimens were followed by the DC measurements of magnetic properties. The grain oriented steel, taken from the same industrial line after final box annealing was also analyzed and compared with the laboratory annealed specimens. It was shown that there is an optimal temperature region that, with combination of a fast heating rate, led to the best conditions of a drastically reduced development time of the {110} < 001 > crystallographic texture in the cold rolled grain-oriented steel. Materials heat treated below the optimum temperature region account for a primary recrystallization, while applying heat above this region leads to a secondary recrystallization without abnormal grain growth. Moreover, in the optimum temperature range, there was a particular temperature leading to the most optimal microstructure and texture. The magnetic properties, measured after the optimal heat treatment, were close to that measured on specimens taken after the final box annealing. The electron back scattered diffraction measurement technique revealed that sharpness of the {110} < 001 > crystallographic texture, developed at the optimum temperature is comparable to the steel taken after the industrial final box annealing. This fact is evidence that there is a temperature where the abnormal grain growth proceeds optimally.     

Conditional states and independence in D-posets

In this paper a new approach to a conditional probability is studied in more general structure called a D-poset. The authors go into the inner structure of a conditional system which is a crucial notion for the existence of a conditional state. An independence of elements in a D-poset with respect to a state is defined.     

Preparation of TiAl15Si15 intermetallic alloy by mechanical alloying and the spark plasma sintering method

This work is devoted to the preparation of alloys based on intermetallic compounds in the Ti–Al–Si system by powder metallurgy using mechanical alloying and the spark plasma sintering (SPS) method. The aim was to describe the formation of intermetallic phases during mechanical alloying of TiAl15Si15 (wt-%) alloy and to consolidate the powder prepared by optimised conditions. Phase composition, microstructure and hardness of compacted alloy were determined. Four hours of mechanical alloying is sufficient time for preparation of pure elements free material composed only of intermetallic phases. After consolidation, the TiAl15Si15 alloy has a homogeneous structure composed of silicide (Ti₅Si₃) in aluminide (TiAl) matrix. The hardness of the material reaches 865?±?42 HV 5.     

Cavitation Rates in Water with Dissolved Gas and Other Impurities

Our objective is a better understanding of the role of physical properties of real fluids in the thermodynamics of cavitation in impure water. An extension to the classical homogenous nucleation theory suitable for mixtures is presented in attempt to address the discrepancy between the theoretical predictions and practical observations of cavitation rates in water at normal temperatures. The extension takes into account the non-equilibrium (dissipative) effects involved in nuclei formation through a substance dependent correction coefficient to be determined experimentally. The theory of thermodynamic fluctuations is applied to derive the work of formation of a bubble nucleus. The value of the correction coefficient is estimated using preliminary experimental data from a convergent-divergent nozzle. An application of the results to the numerical prediction of the cavitation zones in a radial-flow water pump is shown.