Progress in the design of ITER front-end vacuum instrumentation and controls

The ITER vacuum system will be one of the largest and most complex vacuum systems ever to be built. Extensive instrumentation and controls are being developed to satisfy the stringent vacuum processes necessary for the successful and safe operation of the ITER Tokamak. The complexity and deep integration of the vacuum systems within the ITER machine presents a challenge to implement all of the controls necessary for reliable operation. Several thousand valves and sensors have to be implemented within the harsh environmental conditions of the Tokamak vicinity, and require engineering of instrumentation and controls with remote electronics solutions.In this paper the status of the design of field end vacuum controls and instrumentation for the ITER vacuum systems is described. Details of the progress on selection of sensors and actuator technologies are given herein and solutions for remote device operation, including those for cryogenic devices, are described together with necessary local shielding.     

The oxidation behaviour of metals and alloys at high temperatures in atmospheres containing water vapour: A review

The kinetics of oxide formation in the presence of water vapour are discussed and compared with oxidation in dry atmospheres. The main protective oxide systems are considered, i.e. alumina, chromia, silica, titania and iron and nickel oxides, and with the possible exceptions of alumina and nickel oxide, oxidation rates are increased by the presence of water vapour. Scale morphology is also influenced by water vapour, and an important observation is that whisker formation is encouraged; this is believed to be due to the more rapid dissociation of water vapour compared to oxygen. In general, water vapour promotes the formation of a more porous scale. This is related to an increase in cation diffusion and consequent vacancy condensation, thereby developing a porous structure. The thermochemistry of oxide formation is discussed, and here oxide stability and hydroxide formation are considered. A significant observation is that where hydroxides or oxyhydroxides form, they generally have higher volatility than the corresponding oxide, and this leads to loss of protection.The effect of water vapour on oxide growth processes is considered. It is demonstrated that all aspects of oxide growth including adsorption, dissociation and diffusion of reactants are altered in the presence of water vapour compared with similar processes in dry conditions. The important first stages of the reaction involving adsorption and dissociation are controlled by the catalytic activity and acid base nature of oxides. For oxides formed at high temperatures very limited information is available, but, in general, data obtained at room temperature is confirmed and strongly suggests that dissociation of any gas molecule is favoured by defects in the surface. Dissociation of water seems to be more rapid at lower temperatures than, for example, oxygen, but this difference may be less pronounced at higher temperatures. Fast diffusion of water in oxides is possible due to “proton hopping”, in which protons localised at oxide ions move by transfer from one oxygen to another. Since the OH⁻ ion concentration is increased there is a resultant increase in cation vacancies, and this, in part, is responsible for the observed increase in oxidation rates. A further factor to consider is the possibility of molecular diffusion, and it has been demonstrated that where pores or voids are present in the scale, and the void contains both hydrogen and water vapour, oxidation of the surface nearest the metal will occur by reaction with water to form new oxide and the reaction product hydrogen, while a reduction reaction occurs at the surface of the void nearest the gas phase to produce water vapour. Thus it can be seen that this process provides for rapid inward diffusion of oxygen while the void gradually moves outwards from the metal/oxide interface to the oxide/gas interface.Finally, the review considers the effect of water vapour on the mechanical properties of the scale. Scale adhesion can be improved (iron oxides) or made worse (alumina and chromia) by the presence of water vapour. It is shown that while there is experimental evidence for altered mechanical behaviour, there is very little data on relevant mechanical properties. It is possible, therefore, that water vapour either alters mechanical properties of some oxides, or, as has been demonstrated, the oxide growth process has been changed. Alternatively, at least for the cases where increased oxidation rates were caused by the presence of water vapour, the observed differences between wet and dry behaviour may simply be a function of the greater scale thickness. A significant effort has been made to develop models that can be used to predict the onset scale spallation observed in industrial boilers using process steam. The further development of these models is strongly dependent upon obtaining relevant input data, and this is considered a major challenge for materials scientists.Some areas for future research are proposed.     

Rates of mass transfer to patch electrodes in disturbed flows using oxygen reduction under limiting current conditions

The cases of a sudden pipe expansion and a sudden pipe contraction are simulated within a flow loop-based test section designed to approximate disturbed conduit flow. Mass transfer rates to patch electrodes at selected positions within the test section have been measured using a limiting current methodology applied to oxygen reduction at copper in 3.5% wt./vol. NaCl. Using both large-scale polarisation linear sweep voltammetry and a potential step current transient technique with hydrodynamic steps, absolute and relative rates of oxygen mass transfer have been examined as a function of Reynolds number and location within the test section. The highest rates of oxygen transfer were observed both within the high velocity area of the test section and close to known regions of flow disturbance. Under the flow conditions used, patch electrode mass transfer relates to wall shear stress, which allowed areas of high mean and high fluctuating wall shear stress to be identified.     

Occurrence,Treatment, and Toxicological Relevance of EDCs and Pharmaceuticals in Water

Over the past decade a great amount of interest has arisen regarding the occurrence and fate of trace organic contaminants in the aquatic environment. Of particular concern are human hormones and pharmaceuticals, many of which are ubiquitous contaminants in conventional municipal wastewater treatment plant effluents when measured with ng/L detection limits. As analytical procedures and bioassay techniques become more readily available and increasingly sensitive, new contaminants will be discovered. The presence or absence of any chemical in a wastewater effluent is essentially a function of analytical detection capability. This poses a unique challenge for drinking water treatment plants intent on the removal of organic contaminants, as complete removal is merely a reflection of reporting limits. The investigation described here sought to determine the occurrence, treatment, and human health relevance of a chemically diverse group of emerging contaminants.     

Characteristics of Milk Powders Produced by Spray Freeze Drying

Skim and whole milk powders were manufactured at lab scale by spray freeze drying (SFD), using liquid nitrogen as the cryogen. The polydispersity of droplet/particle sizes was limited using an encapsulator nozzle to atomize the feed. Particle morphology was examined using a scanning electron microscope. Samples were compared with equivalent spray-dried powders in tests of wettability and dissolution in water. The spray freeze-dried powders were found to be highly porous, with a uniform structure of pores throughout the entire particles. When tested in water, SFD skim milk powders wetted roughly three times as fast as industrially spray-dried agglomerated skim milk powders and were observed to dissolve rapidly by breaking down into smaller particles.     

Recombinant Landscapes in the American City

How are urban actors, such as landscape designers, community groups, developers and local politicians, actively restructuring their environments to meet the challenges of the American city in the new global context? Grahame Shane outlines the approaches to landscape that have been emerging since the mid-20th century and are set to recombine urban assemblages whether they are located in historic city centres, postindustrial waterfronts or suburban sprawl. Copyright © 2007 John Wiley & Sons, Ltd.     

The electric utility-industrial user partnership in solving powerquality problems

Various views on power quality among industrial end users and utility personnel are summarized. The issues raised include the most salient power quality problems, their causes, and designing the most effective technical and organizational responses to these problems. Recent technological advancement has helped to precipitate power quality problems through the widespread influx of sophisticated electrical equipment that is sensitive to common power quality problems; of particular note here are momentary loss of power and inadvertent noise that infiltrates into sensitive logic circuits. These problems have been exacerbated through the growing use of power electronics equipment which, although beneficial, can generate harmonic distortion and notching of the line voltage. It is pointed out that identifying and technically solving these emerging problems is an engineering challenge that can be met on a case-by-case basis     

Points to be considered in thermogravimetry

Continuous thermogravimetry is a common method to test materials in gaseous corrosive environments at high temperatures and to elucidate kinetics and mechanisms of high temperature corrosion. Recommendations how to conduct thermogravimetric tests are collected here, points to be considered including sample size and form, surface preparation, reaction chamber, starting procedure, sensitive measurements, gas supply and dosing. This study is meant as a starting foundation for establishing guidelines in high temperature corrosion research.