1,721,356 research outputs found
Proposal of a phase change material-graphene modified composite with enhanced thermal properties for application in energy storage concrete
No full textPhase change materials (PCMs) are among the most promising candidates for thermal energy storage (TES) applications. However, their low thermal conductivity and slow phase change phenomena are major restricting factors for efficient TES applications. This work investigates a novel thermal energy storage aggregate (TSA) composite based on butyl stearate (BS), a low-cost, commercially available, supported by graphene nanoparticles (GN) as high conductive agents stabilized in the porous media of expanded clay (EC) aggregates. Based on GN's high thermal conductivity, adding 2% GN in the composite shows enhanced heat transfer, while the composite TSA containing 2% GN, compared to plain EC, decreases the maximum temperature peaks up to 5 °C in heating cycles. Furthermore, the leakage test demonstrates that the developed TSA exhibits excellent thermal stability, indicating the potential to maintain its thermal performance even after multiple thermal cycles. Finally, the thermal performance of a TES concrete (TSC) containing TSA with 3.5% PCM-2GN by weight of TSC decreased the peak ambient temperature fluctuations up to 3.5 0C for a test in complete insulation condition. This reduction on TSC surface was between 9 0C to 10.8 0C in 1D heat transfer condition with 0% and 50% humidity, respectively. The novel-designed TSA composites pave the way for a practical and effective solution to enhance internal building comfort and energy efficiency
Abstracts of the fourth brainstorming research assembly for young neuroscientists (BraYn), Italy, 20–22 October 2021
Full text linkOn behalf of the BraYn Association, we are pleased to present the Abstracts of the Fourth Brainstorming Research Assembly for Young Neuroscientists, which was held from 20–22 October 2021. We congratulate all the presenters on their research work and contribution
An Experimental methodology for the reconstruction of three-dimensional acoustic pressure fields in ducts
No full textThe claim for low emission engines, imposed by strict environmental legislation, has prompted the aeronautical industry to reduce both noise emission and pollution by using lean combustion technology. These engines are often affected by acoustic instabilities that can compromise their correct functioning. A 3D acoustic wave field investigation is increasingly relevant for a correct design and comprehension of this kind of phenomena. Numerical codes are widely used for this type of analysis but an experimental validation is still required due to the complexity of the real phenomena involved in acoustic generation and propagation. While the wall acoustic pressure can be easily measured, very few examples of radial measurement for a 3D analysis can be found in research on this subject. This paper presents an example of a radial measurement of a 3D acoustic pressure field by means of a waveguide probe based on a 1/4'' pressure microphone. In particular, several probe geometries were designed and calibrated on a specialized test rig. In order to verify the adopted methodology, the acoustic 3D pressure fields of two simplified geometries were measured and compared with those from a theoretical model describing the actual conditions of the test rig
Experimental characterization of vaneless diffuser rotating stall. Part V: Influence of diffuser geometry on stall inception and performance (3 rd impeller tested)
No full textVaneless diffuser rotating stall is a serious problem for centrifugal compressors, since it limits their working range. In the literature some good correlations can be found for predicting stall inception but they have limited coverage of last stage configuration case, especially for very low blade-outlet-width-to-impeller-radius-ratio impellers typically used in high-pressure applications. In addition, stall inception is strictly bounded to diffuser geometry (for example, diffuser width and diffusion ratio). As a part of a wide range activity on rotating stall, a stage with a blade-outlet-width- to-impeller-radius-ratio of 0.1 has been tested. The stage configuration is made up by a 1:1 geometrical scale stage with a return channel upstream, a 2D impeller with a vaneless diffuser and a volute with a constant cross sectional area downstream. Diffusers with three different widths and two diffusion ratios were tested in order to find their influence on stage stability and performance. Results obtained for impellers with lower blade-outlet-width-to-impeller- radius-ratios have been published in previous papers. The purpose of this paper is to comment the obtained results and increase the amount of experimental data available on vaneless diffuser rotating stall behaviour
Combination fluticasone end salmeterol versus fixed dose combination budesonide and formoterol for chronic asthma in adults and children
No full textBackground: Long-acting beta-agonists are a common second line treatment in people with asthma inadequately controlled with inhaled corticosteroids. Single device inhalers combine a long-acting beta-agonist with an inhaled steroid delivering both drugs as a maintenance treatment regimen. This updated review compares two fixed-dose options, fluticasone/salmeterol FP/SALand budesonide/formoterol, since this comparison represents a common therapeutic choice.
OBJECTIVES:
To assess the relative effects of fluticasone/salmeterol and budesonide/formoterol in people with asthma.
SEARCH METHODS:
We searched the Cochrane Airways Group register of trials with prespecified terms. We performed additional hand searching of manufacturers' web sites and online trial registries. Search results are current to June 2011.
SELECTION CRITERIA:
We included randomised studies comparing fixed dose fluticasone/salmeterol and budesonide/formoterol in adults or children with a diagnosis of asthma. Treatment in the studies had to last for a minimum of 12 weeks.
DATA COLLECTION AND ANALYSIS:
Two authors independently assessed studies for inclusion in the review. We combined continuous data outcomes with a mean difference (MD), and dichotomous data outcomes with an odds ratio (OR). We assessed the quality of the evidence using the Grading of Recommendations Assessment, Development and Evaluation (GRADE) system.
MAIN RESULTS:
Five studies met the review entry criteria (5537 adults). Study populations entered the studies having previously been treated with inhaled steroids and had moderate or mild airway obstruction (mean FEV(1) predicted between 65% and 84% at baseline). Most of the studies assessed treatment over a period of six months. The studies were at a low risk of selection and performance/detection bias, although we could not determine whether missing data had an impact on the results. Availablility of outcome data was satisfactory.Primary outcomesThe odds ratio for exacerbations requiring oral steroids was lower with fluticasone/salmeterol but did not reach statistical significance (OR 0.89, 95% confidence interval (CI) 0.74 to 1.07, four studies, N = 4949). With an assumed risk with budesonide/formoterol of 106/1000 participants requiring oral steroids, treatment with fluticasone/salmeterol would lead to between 25 fewer and seven more people per 1000 experiencing a course of oral steroids. Although the odds of hospital admission was higher with fluticasone/salmeterol, this did not reach statistical significance (OR 1.29, 95% CI 0.68 to 2.47, four studies, 4879 participants). With an assumed risk in the budesonide/formoterol of 7/1000, between two fewer and 10 more people per 1000 would be hospitalised on fluticasone/salmeterol. The odds of a serious adverse event related to asthma was higher with fluticasone/salmeterol but did not differ significantly between treatments (OR 1.47, 95% CI 0.75 to 2.86, three studies, 4054 participants). With an assumed risk in the budesonide/formoterol of 7/1000, between two fewer and 13 more people per 1000 would experience a serious adverse event on fluticasone/salmeterol.Secondary outcomesLung function outcomes, symptoms, rescue medication, composite of exacerbations leading to either emergency department visit or hospital admission, withdrawals and adverse events did not differ statistically between treatments. Assessment of quality of life was limited to two studies, both of which gave results that did not reach statistical significance. One study reported one death out of 1000 participants on fluticasone/salmeterol and no deaths in a similar number of participants treated with budesonide/formoterol. No deaths were reported in the other studies.
AUTHORS' CONCLUSIONS:
Statistical imprecision in the effect estimates for exacerbations and serious adverse events do not enable us to conclude that either therapy is superior. The uncertainty around the effect estimates justify further trials to provide more definitive conclusions; the overall quality of evidence based on GRADE recommendations for the three primary outcomes and withdrawals due to serious adverse events was moderate. We rated the quality of evidence for mortality to be low. Results for lung function outcomes showed that the drugs were sufficiently similar that further research is unlikely to change the effects. No trials were identified in the under-12s and research in this population is a high priority. Evaluation of quality of life is a priority for future research
Design guidelines for H-Darrieus wind turbines: Optimization of the annual energy yield
Full text linkH-Darrieus wind turbines are gaining popularity in the wind energy market, particularly as they are thought to represent a suitable solution even in unconventional installation areas. To promote the diffusion of this technology, industrial manufacturers are continuously proposing new and appealing exterior solutions, coupled with tempting rated-power offers. The actual operating conditions of a rotor over a year can be, however, very different from the nominal one and strictly dependent on the features of the installation site. Based on these considerations, a turbine optimization oriented to maximize the annual energy yield, instead of the maximum power, is thought to represent a more interesting solution. With this goal in mind, 21,600 test cases of H-Darrieus rotors were compared on the basis of their energy-yield capabilities for different annual wind distributions in terms of average speed. The wind distributions were combined with the predicted performance maps of the rotors obtained with a specifically developed numerical code based on a Blade Element Momentum (BEM) approach. The influence on turbine performance of the cut-in speed was accounted for, as well as the limitations due to structural loads (i.e. maximum rotational speed and maximum wind velocity). The analysis, carried out in terms of dimensionless parameters, highlighted the aerodynamic configurations able to ensure the largest annual energy yield for each wind distribution and set of aerodynamic constraints
Pitch optimization in small-size darrieus wind turbines
No full textSmall Darrieus wind turbines are standing out as one of the most promising technologies in view of a widespread availability of delocalized energy production from wind. In view of a performance optimization ofDarrieus rotors, the application of a pitch angle to blades has been often suggested. In the present work, the pitch modeling in an advanced BEM code has been exploited to investigate different pitch control strategies. In particular, the prospects of a pitch preset based on both the maximum power and the maximum energy extraction have been evaluated and compared to those connected to a progressive pitch variation with the turbine revolution speed. The pitch effects have been discussed both in terms of aggregated power output and of variation of the airfoil functioning conditions throughout a revolution. The analysis confirmed that the application of a proper pitch angle could definitely provide an increase of the turbine performance, especially at medium-high solidities
Setup and characterization of a multi-purpose test rig for R744 refrigerating cycles and equipment
No full textFollowing a widespread trend in international research on R744 cooling applications, the authors have developed a test rig for investigating refrigerating cycles and equipment which operates with such refrigerant. The facility was designed aiming to a compact layout and to a high flexibility in terms of cycles and pieces of equipment to be tested. The test rig can operate stand-alone thanks to a passive load management system which works with water as secondary fluid. The paper gives some useful data, based on direct experience, for the realization and management of a multi-purpose test rig that allows the analysis of several cycle layouts over wide operating ranges. Some of the main critical issues related to proper plant and component design, a correct choice of the measurement equipment and a suitable system management are shown and discussed. The paper also includes experimental data obtained while testing a reciprocating compressor and a single-stage cycle layout both with and without using an internal heat exchanger
Suitability of coupling a solar powered ejection cycle with a vapour compression refrigerating machine
No full textThe most commonly employed technology for cold production is vapour compression, mainly due to the high efficiency of such devices. However, a major operating issue is the strong dependency of system efficiency and capacity on ambient temperature, which in turn leads to low yearly performance and to a low capacity factor. On the other hand, solar cooling is gaining an increasing appeal as a way to locally exploit renewable energy sources and reducing carbon footprint. Many thermally driven systems are being currently studied, among these the ejection reverse cycle is being proposed as an interesting alternative due to its simplicity, low cost and reliability. The present paper aims to analyse a complex system in which the solar powered ejection machine is used to increase the efficiency of a traditional vapour compression machine by subtracting heat from the condenser. By means of a transient analysis, performed with a reference building and with climate data corresponding to four different system locations worldwide, the year-round performance of such a system in a space cooling application is estimated in terms of energy balance and savings on power costs with respect to the traditional solutions, in order to evaluate its potential benefits and to highlight some issues related to system design and operation. A sensitivity analysis is also performed with respect to solar collector area and equipment sizing, showing how the latter is an important optimisation parameter when designing the system
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