Off-design performance comparison between single and two-shaft engines: part 1 — fixed geometry

This paper describes an investigation into the off-design performance comparison of single and two-shaft gas turbine engines. A question that has been asked for a long time which gas turbine delivers a better thermal efficiency at part load. The authors, notwithstanding their intensive searches, were unable to find a comprehensive answer to this question. A detailed investigation was carried out using a state of the art performance evaluation method and the answer was found to be: It depends! In this work, the performance of two engine configurations is assessed. In the first one, the single-shaft gas turbine operates at constant shaft rotational speed. Thus, the shape of the compressor map rotational speed line will have an important influence on the performance of the engine. To explore the implications of the shape of the speed line, two single-shaft cases are examined. The first case is when the speed line is curved and as the compressor pressure ratio falls, the non-dimensional mass flow increases. The second case is when the speed line is vertical and as the compressor pressure ratio falls, the non-dimensional mass flow remains constant. In the second configuration, the two-shaft engine, the two-shafts can be controlled to operate at different rotational speeds and also varying relationships between the rotational speeds. The part-load operation is characterized by a reduction in the gas generator rotational speed. The tool, which was used in this study, is a 0-D whole engine simulation tool, named Turbomatch. It was developed at Cranfield and it is based on mass and energy balance, carried out through an iterative method, which is based on component maps. These generic, experimentally derived maps are scaled to match the design point of a particular engine before an off-design calculation is performed. The code has been validated against experimental data elsewhere, it has been used extensively for academic purposes and the research activities that have taken place at Cranfield University. For an ideal cycle, the single-shaft engine was found to be a clear winner in terms of part-load thermal efficiency. However, this picture changed when realistic component maps were utilized. The basic cycle and the shape of component maps had a profound influence on the outcome. The authors explored the influence of speed line shapes, levels of component efficiencies and the variation of these component efficiencies within the operating range. This paper describes how each one of these factors, individually, influences the outcome

Frequency of educational computer use as a longitudinal predictor of educational outcomes in young people with specific language impairment

Computer use draws on linguistic abilities. Using this medium thus presents challenges for young people with Specific Language Impairment (SLI) and raises questions of whether computer-based tasks are appropriate for them. We consider theoretical arguments predicting impaired performance and negative outcomes relative to peers without SLI versus the possibility of positive gains. We examine the relationship between frequency of computer use (for leisure and educational purposes) and educational achievement; in particular examination performance at the end of compulsory education and level of educational progress two years later. Participants were 49 young people with SLI and 56 typically developing (TD) young people. At around age 17, the two groups did not differ in frequency of educational computer use or leisure computer use. There were no associations between computer use and educational outcomes in the TD group. In the SLI group, after PIQ was controlled for, educational computer use at around 17 years of age contributed substantially to the prediction of educational progress at 19 years. The findings suggest that educational uses of computers are conducive to educational progress in young people with SLI

Solvation quantities from a COSMO-RS equation of state

This work focuses on the extension of the successful COSMO-RS model of mixtures into an equation-of-state model of fluids and its application for the estimation of solvation/hydration quantities of a variety of chemical substances. These quantities include free-energies, enthalpies and entropies of hydration as well as the separate contributions to each of them. Emphasis is given on the estimation of contributions from the conformational changes of solutes upon solvation and the associated restructuring of solvent in its immediate neighborhood. COSMO-RS is a quantum-mechanics based group/segment contribution model in which the Quasi-Chemical (QC) approach is used for the description of the non-random distribution of interacting segments in the system. Thus, the equation-of-state development is done through such a QC framework. The new model will not need any adjustable parameters for the strong specific interactions, such as hydrogen bonds, since they will be provided by the quantum-mechanics based cosmo-files - a key feature of COSMO-RS model. It will need, however, one volumetric and one energy parameter per fluid, which are scaling constants or molecular descriptors of the fluid and are obtained from rather easily available data such as densities, boiling points, vapor pressures, heats of vaporization or second virial coefficients. The performance and the potential of the new equation-of-state model to become a fully predictive model are critically discussed. (C) 2015 Elsevier Ltd. All rights reserved

A new experimental facility to investigate combustor–turbine interactions in gas turbines with multiple can combustors

This paper describes a new modular experimental facility that was purpose-built to investigate flow interactions between the combustor and first stage nozzle guide vanes (NGVs) of heavy duty power generation gas turbines with multiple can combustors. The first stage turbine NGV is subjected to the highest thermal loads of all turbine components and therefore consumes a proportionally large amount of cooling air that contributes detrimentally to the stage and cycle efficiency. It has become necessary to devise novel cooling concepts that can substantially reduce the coolant air requirement but still allow the turbine to maintain its aerothermal performance. The present work aims to aid this objective by the design and commissioning of a high-speed linear cascade, which consists of two can combustor transition ducts and four first stage NGVs. This is a modular nonreactive air test platform with engine realistic geometries (gas path and near gas path), cooling system, and boundary conditions (inlet swirl, turbulence level, and boundary layer). The paper presents the various design aspects of the high pressure (HP) blow down type facility, and the initial results from a wide range of aerodynamic and heat transfer measurements under highly engine realistic conditions

Off-design performance comparison between single and two-shaft engines part 1 - fixed geometry

This paper describes an investigation into the off-design performance comparison of single and two-shaft gas turbine engines. A question that has been asked for a long time is which gas turbine delivers a better thermal efficiency at part load. The authors, notwithstanding their intensive searches, were unable to find a comprehensive answer to this question. A detailed investigation was carried out using a state-of-the-art performance evaluation method and the answer was found to be: It depends! In this work, the performance of two engine configurations is assessed. In the first one, the single-shaft gas turbine operates at constant shaft rotational speed. Thus, the shape of the compressor map rotational speed line will have an important influence on the performance of the engine. To explore the implications of the shape of the speed line, two single-shaft cases are examined. The first case is when the speed line is curved and as the compressor pressure ratio falls, the nondimensional mass flow increases. The second case is when the speed line is vertical and as the compressor pressure ratio falls, the nondimensional mass flow remains constant. In the second configuration, the two-shaft engine, the two shafts can be controlled to operate at different rotational speeds and also varying relationships between the rotational speeds. The part-load operation is characterized by a reduction in the gas generator rotational speed. The tool, which was used in this study, is a 0-D whole engine simulation tool, named Turbomatch. It was developed at Cranfield and it is based on mass and energy balance, carried out through an iterative method, which is based on component maps. These generic, experimentally derived maps are scaled to match the design point of a particular engine before an off-design calculation is performed. The code has been validated against experimental data elsewhere, it has been used extensively for academic purposes and the research activities that have taken place at Cranfield University. For an ideal cycle, the single-shaft engine was found to be a clear winner in terms of part-load thermal efficiency. However, this picture changed when realistic component maps were utilized. The basic cycle and the shape of component maps had a profound influence on the outcome. The authors explored the influence of speed line shapes, levels of component efficiencies, and the variation of these component efficiencies within the operating range. This paper describes how each one of these factors, individually, influences the outcome

Serum Homocysteine, Pyridoxine, Folate, and Vitamin B12 Levels in Migraine: Systematic Review and Meta-Analysis

Background: Migraine, especially migraine with aura (MA), has been linked to increased risk for ischemic cerebrovascular disease. The possible role of elevated serum homocysteine (Hcy, a cause of thrombophilia) in migraine has been demonstrated by several studies. Objective: The present study aims to review and meta-analyze data from studies investigating the difference of serum Hcy and Hcy lowering vitamins between migraine patients and healthy controls (HC), as well as between patients with MA and migraine without aura (MO). Methods: Literature search involved MEDLINE, Embase, CENTRAL, Google Scholar, and trial registries. The Newcastle-Ottawa Scale was used to evaluate the quality of the retrieved studies. Standardized mean differences (SMDs) and 95% confidence intervals (95%CIs) were calculated. Funnel-plots were utilized for the evaluation of publication bias. Results: Overall, 29 (28 case-control and 1 cross-sectional) studies were retrieved. Meta-analysis was indicative of higher Hcy concentration in migraine patients vs HC overall [adults and children: 16 studies, I2 = 81%, SMD = 0.41, 95%CI = (0.20, 0.61)]. Hcy was consistently elevated in adults with migraine [adults: 12 studies, I2 = 76%, SMD = 0.35, 95%CI = (0.15, 0.54); children: 1 study, SMD = 0.37, 95%CI = (−0.05, 0.79)]. Subgroup analyses reproduced the results for both adults with MA [7 studies, I2 = 83%, SMD = 0.37, 95%CI = (0.03, 0.71)] and MO [5 studies, I2 = 84%, SMD = 0.46, 95%CI = (0.03, 0.89)]. Figures for serum folate were lower in the overall comparison of migraine patients with HC [adults and children: 11 studies, I2 = 87%, SMD = −0.36, 95%CI = (−0.68, −0.05); adults: 8 studies, I2 = 6%, SMD = −0.11, 95%CI = (−0.22, 0.01); children: 1 study, SMD = −0.71, 95%CI = (−1.14, −0.29); MA adults: 4 studies, I2 = 44%, SMD = −0.16, 95%CI = (−0.35, 0.04); MO adults: 4 studies, I2 = 47%, SMD = −0.17, 95%CI = (−0.44, 0.10)]. Serum vitamin B12 levels were not different between migraine patients and HC [adults and children: 11 studies, I2 = 88%, SMD = −0.24, 95%CI = (−0.57, 0.09); adults: 8 studies, I2 = 57%, SMD = −0.10, 95%CI = (−0.28, 0.08); children: 1 study, SMD = 0.29, 95%CI = (−0.13, 0.71); MA adults: 4 studies, I2 = 63%, SMD = −0.14, 95%CI = (−0.48, 0.20); MO adults: 4 studies, I2 = 59%, SMD = −0.15, 95%CI = (−0.45, 0.15)]. Serum Hcy was lower in MO than MA [adults and children: 10 studies, I2 = 39%, SMD = 0.30, 95%CI = (0.14, 0.46), adults: 6 studies, I2 = 29%, SMD = 0.21, 95%CI = (0.09, 0.36), children: 1 study, SMD = 0.51, 95%CI = (0.22, 0.80)]. Serum folate and vitamin B12 did not differ between MA and MO. Conclusions: Our results suggest that there is a possible link between migraine, mainly MA, and elevated serum Hcy. © 2020 American Headache Societ

Genetic risk factors for essential tremor: A review

Highlights In the current review, we thoroughly reviewed 74 identified articles regarding genes and genetic loci that confer susceptibility to ET. Over 50 genes/genetic loci have been examined for possible association with ET, but consistent results failed to be reported raising the need for collaborative multiethnic studies. Background: Essential tremor (ET) is a common movement disorder, which is mainly characterized by bilateral tremor (postural and/or kinetic) in the upper limbs, with other parts of the body possibly involved. While the pathophysiology of ET is still unclear, there is accumulating evidence indicating that genetic variability may be heavily involved in ET pathogenesis. This review focuses on the role of genetic risk factors in ET susceptibility. Methods: The PubMed database was searched for articles written in English, for studies with humans with ET, controls without ET, and genetic variants. The terms “essential tremor” and “polymorphism” (as free words) were used during search. We also performed meta-analyses for the most examined genetic variants. Results: Seventy four articles concerning LINGO1, LINGO2, LINGO4, SLC1A2, STK32B, PPARGC1A, CTNNA3, DRD3, ALAD, VDR, HMOX1, HMOX2, LRRK1,LRRK2, GBA, SNCA, MAPT, FUS, CYPsIL17A, IL1B, NOS1, ADH1B, TREM2, RIT2, HNMT, MTHFR, PPP2R2B, GSTP1, PON1, GABA receptors and GABA transporter, HS1BP3, ADH2, hSKCa3 and CACNL1A4 genes, and ETM genetic loci were included in the current review. Results from meta-analyses revealed a marginal association for the STK32B rs10937625 and a marginal trend for association (in sensitivity analysis) for the LINGO1 rs9652490, with ET. Discussion: Quite a few variants have been examined for their possible association with ET. LINGO1 rs9652490 and STK32B rs10937625 appear to influence, to some extent, ET susceptibility. However, the conflicting results and the lack of replication for many candidate genes raise the need for collaborative multiethnic studies. © 2020 The Author(s)