Computational thermal-fluid dynamics analysis of the laminar flow regime in the meander flow geometry characterizing the heat exchanger used in high temperature superconducting current leads

The Karlsruhe Institute of Technology and the Politecnico di Torino have developed and validated a computational thermal-fluid dynamics (CtFD) strategy for the systematic analysis of the thermal-hydraulics inside the meander flow heat exchanger used in high-temperature superconducting current leads for fusion applications. In the recent past, the application of this CtFD technique has shown that some operating conditions occurring in these devices may not reach the turbulent regime region. With that motivation, the CtFD analysis of the helium thermal-fluid dynamics inside different meander flow geometries is extended here to the laminar flow regime. Our first aim is to clarify under which operative conditions the flow regime can be considered laminar and how the pressure drop as well as the heat transfer are related to the geometrical parameters and to the flow conditions. From the results of this analysis, correlations for the pressure drop and for the heat transfer coefficient in the meander flow geometry have been derived, which are applicable with good accuracy to the design of meander flow heat exchangers over a broad range of geometrical parameters.     

Prospects of High Temperature Superconductors for fusion magnets and power applications

During the last few years, progress in the field of second-generation High Temperature Superconductors (HTS) was breathtaking. Industry has taken up production of long length coated REBCO conductors with reduced angular dependency on external magnetic field and excellent critical current density jc. Consequently these REBCO tapes are used more and more in power application.For fusion magnets, high current conductors in the kA range are needed to limit the voltage during fast discharge. Several designs for high current cables using High Temperature Superconductors have been proposed. With the REBCO tape performance at hand, the prospects of fusion magnets based on such high current cables are promising. An operation at 4.5 K offers a comfortable temperature margin, more mechanical stability and the possibility to reach even higher fields compared to existing solutions with Nb₃Sn which could be interesting with respect to DEMO.After a brief overview of HTS use in power application the paper will give an overview of possible use of HTS material for fusion application. Present high current HTS cable designs are reviewed and the potential using such concepts for future fusion magnets is discussed.     

Life cycle energy and environmental benefits of generating electricity from willow biomass

Biomass is a key renewable energy source expected to play an important role in US electricity production under stricter emission regulations and renewable portfolio standards. Willow energy crops are being developed in the northeast US as a fuel source for increasing biomass energy and bioproduct demands. A life cycle inventory is presented that characterizes the full cradle-to-grave energy and environmental performance of willow biomass-to-electricity. A willow biomass production model is developed using demonstration-scale field experience from New York. Scenarios are presented that mimic anticipated cofiring operations, including supplemental use of wood residues, at an existing coal-fired generating facility. At a cofiring rate of 10% biomass, the system net energy ratio (electricity delivered divided by total fossil fuel consumed) increases by 8.9% and net global warming potential decreases by 7–10%. Net SO₂ emissions are reduced by 9.5% and a significant reduction in NO_x emissions is expected. In addition, we estimate system performance of using willow biomass in dedicated biomass gasification and direct-fired generating facilities and demonstrate that the pollution avoided (relative to the current electricity grid) is comparable to other renewables such as PV and wind.     

Die Herstellung von Spanplatten aus unkonventionellen Rohstoffen

In the coming decade, nonconventional raw materials will have to be utilized differently, mainly because of reasons of economy. Regions with minor supply of raw material and cheap energy will have to use the raw materials discussed and tested in the present investigation. In regions whose energy resources are limited, whose supply of raw wood, however, is utilizable, straw e.g. will have to be used as fuel to save expensive primary energy and raw materials for adhesives. In addition to the raw materials alfa grass, bagasse, and cotton stems, which are being used already industrially, giant grass and bamboo might present a real chance for saving raw material on a world-wide scale.     

Identifying the mechanism of biosensing with carbon nanotube transistors

Carbon nanotube transistors have outstanding potential for electronic detection of biomolecules in solution. The physical mechanism underlying sensing however remains controversial, which hampers full exploitation of these promising nanosensors. Previously suggested mechanisms are electrostatic gating, changes in gate coupling, carrier mobility changes, and Schottky barrier effects. We argue that each mechanism has its characteristic effect on the liquid gate potential dependence of the device conductance. By studying both the electron and hole conduction, the sensing mechanisms can be unambiguously identified. From extensive protein-adsorption experiments on such devices, we find that electrostatic gating and Schottky barrier effects are the two relevant mechanisms, with electrostatic gating being most reproducible. If the contact region is passivated, sensing is shown to be dominated by electrostatic gating, which demonstrates that the sensitive part of a nanotube transistor is not limited to the contact region, as previously suggested. Such a layout provides a reliable platform for biosensing with nanotubes.     

Managing industrial risk--having a tested and proven system to prevent and assess risk

Some relatively easy techniques exist to improve the risk picture/profile to aid in preventing losses. Today with the advent of computer system resources, focusing on specific aspects of risk through systematic scoring and comparison, the risk analysis can be relatively easy to achieve. Techniques like these demonstrate how working experience and common sense can be combined mathematically into a flexible risk management tool or risk model for analyzing risk. The risk assessment methodology provided by companies today is no longer the ideas and practices of one group or even one company. It is reflective of the practice of many companies, as well as the ideas and expertise of academia and government regulators. The use of multi-criteria decision making (MCDM) techniques for making critical decisions has been recognized for many years for a variety of purposes. In today's computer age, the easy accessing and user-friendly nature for using these techniques, makes them a favorable choice for use in the risk assessment environment. The new user of these methodologies should find many ideas directly applicable to his or her needs when approaching risk decision making. The user should find their ideas readily adapted, with slight modification, to accurately reflect a specific situation using MCDM techniques. This makes them an attractive feature for use in assessment and risk modeling. The main advantage of decision making techniques, such as MCDM, is that in the early stages of a risk assessment, accurate data on industrial risk, and failures are lacking. In most cases, it is still insufficient to perform a thorough risk assessment using purely statistical concepts. The practical advantages towards deviating from strict data-driven protocol seem to outweigh the drawbacks. Industry failure data often comes at a high cost when a loss occurs. We can benefit from this unfortunate acquisition of data through the continuous refining of our decisions by incorporating this new information into our assessments. MCDM techniques offer flexibility in accessing comparison within broad data sets to reflect our best estimation of their importance towards contribution to the risk picture. This allows for the accurate determination of the more probable and more consequential issues. This can later be refined using more intensive risk techniques and the avoidance of less critical issues.     

Characterization of adhesive bond properties using Lamb waves

This research combines laser ultrasonic techniques with the two-dimensional Fourier transform (2D-FFT) to characterize adhesive bond properties. The experimental procedure consists of measuring a series of equally spaced, transient Lamb waves in specimens consisting of aluminum plates joined with an adhesive bond. The frequency spectrum (dispersion curves) for each specimen are obtained by operating on these transient waveforms with the 2D-FFT. This study quantifies the effect of bond stiffness on the dispersion curves of two different bonded specimens (a single aluminum plate with an adhesive transfer tape attached to one side, and two aluminum plates joined with the same adhesive tape) and four adhesive bond conditions (un-aged, and three different aging temperatures and times). The proposed procedure consists of first determining the frequency spectrum of the Lamb waves that propagate in each of the two bonded specimens (plus a single plate); these measurements provide the dispersion curves for each specimen in their un-aged state. Degradation causes changes in the stiffness of an adhesive bond, which causes changes in the dispersion curves of the aged specimens. Experimentally measured dispersion curves are used to quantitatively track changes in the bonded specimens, as a function of age. Finally, these experimental results are interpreted in terms of an analytical model that replaces the adhesive bond layer with a linear spring boundary condition.     

Selectivity from a kinetic point of view: nonlinear behavior of logarithmic product ratios as a function of the reciprocal temperature

The influence of the temperature on selectivity is described under special consideration of nonlinearities in the corresponding modified Eyring plots. Reasons for the experimentally well-known behavior are discussed. Furthermore, the conditions for nonlinear temperature behavior are quantified and a concept is described which allows the determination of the temperature dependence of a single reaction pathway in a selection process. This revised version was published online in June 2006 with corrections to the Cover Date.     

Hypoglycaemia combined with mild hypokalaemia reduces the heart rate and causes abnormal pacemaker activity in a computational model of a human sinoatrial cell

Low blood glucose, hypoglycaemia, has been implicated as a possible contributing factor to sudden cardiac death (SCD) in people with diabetes but it is challenging to investigate in clinical studies. We hypothesized the effects of hypoglycaemia on the sinoatrial node (SAN) in the heart to be a candidate mechanism and adapted a computational model of the human SAN action potential developed by Fabbri et al., to investigate the effects of hypoglycaemia on the pacemaker rate. Using Latin hypercube sampling, we combined the effects of low glucose (LG) on the human ether-a-go-go-related gene channel with reduced blood potassium, hypokalaemia, and added sympathetic and parasympathetic stimulus. We showed that hypoglycaemia on its own causes a small decrease in heart rate but there was also a marked decrease in heart rate when combined with hypokalaemia. The effect of the sympathetic stimulus was diminished, causing a smaller increase in heart rate, with LG and hypokalaemia compared to normoglycaemia. By contrast, the effect of the parasympathetic stimulus was enhanced, causing a greater decrease in heart rate. We therefore demonstrate a potential mechanistic explanation for hypoglycaemia-induced bradycardia and show that sinus arrest is a plausible mechanism for SCD in people with diabetes.     

A Communication Library Using Active Messages to Improve Performance of PVM

We present a communication library to improve performance of PVM. The new library introduces communication primitives based on Active Messages. We propose a hybrid scheme that includes a signal driven message notification scheme plus controlled polling. The new communication library is tested along with the normal PVM library to assess the improvement in performance.