Recrystallization in Commercially Pure Aluminum

Recrystallization behavior in commercial aluminum with a purity of 99.4 pct was studied by techniques such as high voltage electron microscopy, 100 kV transmission electron microscopy, and light microscopy. Sample parameters were the initial grain size (290 and 24 microns) and the degree of deformation (5 to 30 pct reduction in thickness by cold-rolling). It was found that the original grain boundary region is the preferred site for nucleation. A few intragranular nuclei were, however, also observed. The effectiveness of the nucleation sites is enhanced by the presence of intermetallic particles (FeAl₃), which start to become operative when the degree of deformation is raised from 15 to 30 pct. The temperature of nucleation and of recrystallization decreases when the degree of deformation is increased and the initial grain size is decreased. The recrystallized grain size follows the same trend and it is observed that the refinement of the recrystallized grain size caused by an increasing degree of deformation and decreasing initial grain size is enhanced by the FeAl₃ particles (when the degree of deformation is raised from 15 to 30 pct). Finally, the structural and kinetic observations are discussed and compared with results from an earlier study¹ covering the recrystallization behavior of commercial aluminum of the same purity deformed at higher degrees of deformation (50 to 90 pct reduction in thickness by cold-rolling).     

An integrated computer-aided system for generation and evaluation of sustainable process alternatives

This paper presents an integrated system for generation of sustainable process alternatives with respect to new process design as well as retrofit design. The generated process alternatives are evaluated through sustainability metrics, environmental impact factors as well as inherent safety factors. The process alternatives for new process design as well as retrofit design are generated through a systematic method that is simple yet effective and is based on a recently developed path flow analysis approach. According to this approach, a set of indicators are calculated in order to pinpoint unnecessary energy and material waste costs and to identify potential design (retrofit) targets that may improve the process design (in terms of operation and cost) simultaneously with the sustainability metrics, environmental impact factors and the inherent safety factors. Only steady state design data and a database with properties of compounds, including, environmental impact factor related data and safety factor related data are needed. The integrated computer-aided system generates the necessary data if actual plant or experimental data are not available. The application of the integrated system is highlighted through a number of examples including the well-known HDA process.     

Alternative Danish energy planning

In the spring of 1976 the Danish government published an energy plan for Denmark for the period up to 1995. An essential part of this plan was the introduction of five nuclear power plants in the Danish supply system. An alternative energy plan which excluded nuclear power was later published by a group of Danish scientists. It includes a relatively extended application of solar and wind energy, and also emphasises the use of decentralised fossil fuel plants with combined power production and district heating. This paper describes the main features and data of the alternative Danish energy plan and compares it with the official government plan.     

Determination of polar stratospheric cloud particle refractive indices by use of in situ optical measurements and T-matrix calculations

A new algorithm to infer structural parameters such as refractive index and asphericity of cloud particles has been developed by use of in situ observations taken by a laser backscattersonde and an optical particle counter during balloon stratospheric flights. All three main particles, liquid, ice, and a no-ice solid (NAT, nitric acid trihydrate) of polar stratospheric clouds, were observed during two winter flights performed from Kiruna, Sweden. The technique is based on use of the T-matrix code developed for aspherical particles to calculate the backscattering coefficient and particle depolarizing properties on the basis of size distribution and concentration measurements. The results of the calculations are compared with observations to estimated refractive indices and particle asphericity. The method has also been used in cases when the liquid and solid phases coexist with comparable influence on the optical behavior of the cloud to estimate refractive indices. The main results prove that the index of refraction for NAT particles is in the range of 1.37-1.45 at 532 nm. Such particles would be slightly prolate spheroids. The calculated refractive indices for liquid and ice particles are 1.51-1.55 and 1.31-1.33, respectively. The results for solid particles confirm previous measurements taken in Antarctica during 1992 and obtained by a comparison of lidar and optical particle counter data.     

Clinical system for interstitial photodynamic therapy with combined on-line dosimetry measurements

A system for interstitial photodynamic therapy with delta-aminolaevulinic acid and multiple optical fibers has been developed. The system enables photodynamic treatment of large embedded tumor volumes and utilizes real-time measurements to allow on-line dosimetry. Important parameters such as light fluence rate, sensitizer fluorescence intensity, and changes in local blood oxygen saturation are measured with the same fibers that deliver the therapeutic light. Data from the first clinical treatments on nodular basal cell carcinomas indicate a major treatment-induced light absorption increase, rapid sensitizer photobleaching, and a relatively constant global tissue oxygen saturation level during the treatment.     

Expanding the optical trapping range of gold nanoparticles

We demonstrate stable three-dimensional (3D) single-beam optical trapping of gold nanoparticles with diameters between 18 and 254 nm. Three-dimensional power spectral analysis reveals that, for nanoparticles with diameters less than 100 nm, the trap stiffness is proportional to the volume of the particle. For larger particles, the trap stiffness still increases with size, however, less steeply. Finally, we provide numbers for the largest forces exertable on gold nanoparticles.     

Design of a wind turbine rotor for maximum aerodynamic efficiency

The design of a three‐bladed wind turbine rotor is described, where the main focus has been highest possible mechanical power coefficient, CP, at a single operational condition. Structural, as well as off‐design, issues are not considered, leading to a purely theoretical design for investigating maximum aerodynamic efficiency. The rotor is designed assuming constant induction for most of the blade span, but near the tip region, a constant load is assumed instead. The rotor design is obtained using an actuator disc model, and is subsequently verified using both a free‐wake lifting line method and a full three‐dimensional Navier–Stokes solver. Excellent agreement is obtained using the three models. Global CP reaches a value of slightly above 0.51, while global thrust coefficient CT is 0.87. The local power coefficient C_p increases to slightly above the Betz limit on the inner part of the rotor; the local thrust coefficient C_t increases to a value above 1.1. This agrees well with the theory of de Vries, which states that including the effect of the low pressure behind the centre of the rotor stemming from the increased rotation, both C_p and C_t will increase towards the root. Towards the tip, both C_p and C_t decrease due to tip corrections as well as drag. Copyright © 2008 John Wiley & Sons, Ltd.     

Wind turbine rotor‐tower interaction using an incompressible overset grid method

In this paper, 3D Navier–Stokes simulations of the unsteady flow over the NREL Phase VI turbine are presented. The computations are carried out using the structured grid, incompressible, finite volume flow solver EllipSys3D, which has been extended to include the use of overset grids. Computations are presented, firstly, on an isolated rotor, and secondly, on the downwind configuration of the turbine, which includes modelling of the rotor, tower and tunnel floor boundary. The solver successfully captures the unsteady interaction between the rotor blades and the tower wake, and the computations are in good agreement with the experimental data available. The interaction between the rotor and the tower induces significant increases in the transient loads on the blades and is characterized by an instant deloading and subsequent reloading of the blade, associated with the velocity deficit in the wake, combined with the interaction with the shed vortices, which causes a strongly time‐varying response. Finally, the results show that the rotor has a strong effect on the tower shedding frequency, causing under certain flow conditions vortex lock‐in to take place on the upper part of the tower. Copyright © 2009 John Wiley & Sons, Ltd.