9,899 research outputs found
Numerical computation for parallel plate thermoacoustic heat exchangers in standing wave oscillatory flow
No full textA simplified computational method for studying the heat transfer characteristics of parallel plate thermoacoustic heat exchangers is presented. The model integrates the thermoacoustic equations of the standard linear theory into an energy balance-based numerical calculus scheme. Details of the time-averaged temperature and heat flux density distributions within a representative domain of the heat exchangers
and adjoining stack are given. The effect of operation conditions and geometrical parameters on the heat exchanger performance is investigated and main conclusions relevant for HX design are drawn as far as fin length, fin spacing, blockage ratio, gas and secondary fluid-side heat transfer coefficients are concerned. Most relevant is that
the fin length and spacing affect in conjunction the heat exchanger behaviour and have to be simultaneously optimized to minimize thermal losses localized at the HX-stack
junctions. Model predictions fit experimental data found in literature within 36% and 49% respectively at moderate and high acoustic Reynolds numbers
Investigation into the Strouhal numbers associated with vortex shedding from parallel-plate thermoacoustic stacks in oscillatory flow conditions
No full textThis paper investigates vortex shedding processes occurring at the end of a stack of parallel plates, due to an oscillating flow induced by an acoustic standing wave. Here the hot-wire anemometry measurement technique is applied to detect the velocity fluctuations due to vortex shedding near the end of the stack. The hot-wire fast time response enables detailed frequency spectra of the velocity signal to be obtained, which can be used for identifying the dominant frequencies associated with vortex shedding, and thus allow calculation of the corresponding Strouhal numbers. By varying the stack configuration (the plate thickness and spacing) and the acoustic excitation level (the so-called drive ratio), the impact of the stack blockage ratio and the Reynolds number on the Strouhal number has been studied in detail. Furthermore, in the range of Reynolds numbers between 200 and 5000 a correlation between the Strouhal number and Reynolds number has been obtained and compared with analogous relationships in the steady flow. Particle Image Velocimetry (PIV) is also used to visualize the vortex shedding processes within an acoustic cycle, phase-by-phase, in particular during the part of the cycle when the fluid flows out of the stack—selected cases are shown for comparisons with hot-wire measurements
The impact of EC-92 on developing countries'trade : a dissenting view
No full textMost benefits of the European Community (EC-92) program will probably not come from marginal changes in trade flows. Those changes are important to European policymakers, but are of remote interest to developing countries. The main threats to developing countries are the diversion of investment funds to EC countries and continued external barriers, especially nontariff barriers. The EC expects higher growth and lower prices as a result of EC-92. The net effect on developing countries of the removal of internal trade barriers depends on the country's income and price elasticities with the EC. Current estimates suggest the effect will be small. If new external barriers emerge, or if EC-wide barriers replace national barriers, EC firms may collaborate more with large US or Japanese firms. None of these developments will improve developing countries'trade in manufactures and services. Investment in EC countries may increase to meet the extra demand, growth, or trade diversion resulting from EC-92. This could lead to increased investments in developing countries but given heavy indebtedness in developing countries, is more likely to divert investment funds, thus limiting their future production and growth. Technical standards in EC-92 may also be tougher than national standards in member countries, which could hurt developing country exporters. Is"Fortress Europe"likely? The EC Commission says no, but the Community's record is not good.Environmental Economics&Policies,Economic Theory&Research,TF054105-DONOR FUNDED OPERATION ADMINISTRATION FEE INCOME AND EXPENSE ACCOUNT,Trade and Regional Integration,Trade Policy
VIRT-EU Ethical stack
No full textThe VIRT-EU Ethical stack
is a series of tools to support creators of new connected technology to reflect on their product’s ethical and social impacts.
This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 732027
EC Bananarama 1992 : the sequel - the EC Commission proposal
No full textSome European Community (EC) countries give preferred market access and high prices to bananas from selected developing countries or EC regional suppliers. This preferential status is regarded as a form of aid to these countries, most of which are developing small island economies. EC marketers of bananas from these preferred suppliers also benefit because of the high retail prices. Nonpreferred suppliers - mainly developing countries of Latin America - are hurt by the policies because access is denied or restricted and the lower demand depresses the world price for bananas. The Community's commitment to establish a single unified EC banana market on December 31, 1992 provides a timely opportunity to reform existing distortionary trade policies. The recently announced proposal of the Commission of ECs to regulate banana trade within a unified market relies on quotas to control imports. The proposal is extremely complicated. It is designed to severely restrict competition and to maintain the advantages of selected groups. The authors update their earlier analysis of world banana trade to reflect the market in 1993. They evaluate the implications of the Commission's proposal alongside existing and alternative policies. They find that current policies cost EC consumers about 0.3 billion a year to preferred suppliers. So, it costs EC consumers about 1.00 of aid toselect developing countries or regions. Additionally, every dollar of aid reaching preferred suppliers costs other developing country suppliers 5.30 cost to EC consumers, over 1.00 is lost in outright waste. Several plausible versions of the Commission's proposal are modelled. At best they are found to be slightly less costly than existing policies and at worst, considerably more costly. A 3.5 percent reduction in the quota allocation is estimated to lead to a 30 percent increase in the cost of the proposal. The authors conclude that the Commission's proposal for a unified EC banana policy appears to be little more than a way of replacing existing distortionary national policies with an almost equally distortionary single policy and market. The only difference: the costs would be borne by consumers in all EC countries rather than consumers in only some countries. Worse still, costs could increase. Markets that now gain the benefits of mostly open and competitive marketing such as Germany would face closed and uncompetitive conditions. For developing countries exporting bananas, the proposal offers little. At best conditions may be no worse than they are now. At worst the policy could hurt Latin American suppliers even more than current policies and introduce considerable confusion about the level of support to preferred suppliers. Under the proposed quota system aid will not be well targeted. A more efficient way of achieving the EC's aid commitment is through a small tariff of about 17 percent, used to fund a system of well-targeted deficiency payments or direct aid. The only reason for choosing the Commission's proposal over simpler, tariff-based options seems to be to maintain the vested interests of protected EC markteters. But this is contrary to the objectives of unification, which are to seek gains from increased competition and trade.Environmental Economics&Policies,Access to Markets,Markets and Market Access,Economic Theory&Research,Consumption
Politically Acceptable Trade Compromises Between The EC and The US: A Game Theory Approach
No full textA model is developed to quantify the special status of agriculture in the US and the EC trade negotiations. The role of special interests are measured by a policy goals function (PGF) whose weights are estimated for each special interest group. The analysis searches for mutually acceptable, mutually advantageous trade agreements between the US and the EC using a partial equilibrium world trade model coupled with game theory. Results suggest that it is in the best interest of the US (resp. EC) 'for the EC (resp. US) to liberalize whi1e the other follows the status quo policies of 1986. Mutual gains in PGF values to both countries pursuing "large" liberalizations are unlikely to exist, although "small" liberalizations may give rise to "small" mutual gains. Altering each country's action space, and permitting compensatory payments to the most influencial groups yields trade liberalization, but free trade does not result.game theory, trade liberalization, trade negotiations, International Relations/Trade,
Application of laser-based instrumentation for measurement of time-resolved temperature and velocity fields in the thermoacoustic system
No full textThis work aims to develop reliable laser-based measurement techniques to enable fundamental heat transfer and fluid flow studies in thermoacoustic systems. The challenge is to better understand the modes of energy transfer between the key components, such as stacks (or regenerators) and the hot and cold heat exchangers (located on two sides of the stack/regenerator structure), under the oscillatory flow conditions imposed by the acoustic field. The measurement methodologies adopted in this work include combined two-dimensional temperature and velocity field measurements using Planar Laser-Induced Fluorescence (PLIF) and Particle Image Velocimetry (PIV), respectively. These are investigated around the fins of a pair of mock-up heat exchangers placed side by side in a quarter-wavelength standing-wave acoustic resonator, to mimic the working conditions of a thermoacoustic system. The fins are kept at constant temperatures by means of resistive heating and water cooling, respectively. The velocity and temperature field distributions for 20 phases in the acoustic cycle have been obtained. The impact of the inertial, viscous and thermal effects on the time-dependent local temperature and velocity distributions is discussed. Mutual interaction between both fields is also shown. Future work towards obtaining useful heat transfer correlations in oscillatory conditions is outlined
The Singer or the Song? Developments in Performers' Rights from the Perspective of a Cultural Economist
No full textOver the last century, performers gradually acquired statutory protection of their economic and moral
rights. These rights are not copyright in the legal sense but neighboring rights and until recently, they
were mainly remuneration rights that are collectively administered. With the WPPT (WIPO
Performers and Phonograms Treaty), performers now have individual exclusive rights for digital
performances; this leads to the question: what has motivated this change – is it a change in the
perception of the value of performer or a change brought about by the changing technology of copying or,
indeed, a change that reflects different economic costs and benefits? The paper discusses the role of
copyright law as an incentive to performers and asks if the economic role of the performer is so different
from that of the author. The conclusion is that a complex interaction of the legal regulations, economic
conditions and institutional arrangements for administering these new rights will determine the outcome
Marco tecnológico con el uso de stack MEAN aplicado a la gestión de turnos en la Cooperativa de Ahorro y Crédito Tulcán Ltda.
No full textEsta investigación tuvo como objetivo proponer un marco tecnológico con el uso del stack MEAN aplicado a la gestión de turnos en la Cooperativa de Ahorro y
Crédito Tulcán Ltda. El estudio tuvo un enfoque mixto de tipo descriptiva y de campo. Se describieron los procesos actuales de gestión de turnos en diez
cooperativas de ahorro y crédito, abarcando un análisis de la Cooperativa de Ahorro y Crédito Tulcán Ltda. Además, se evalúa el impacto operativo de estos
sistemas en indicadores como tiempos de espera y eficiencia en la atención. La información recolectada fue procesada mediante herramientas como Excel,
aplicando técnicas estadísticas descriptivas y correlacionales. Se desarrollo un diseño de un sistema con el stack MEAN. Finalmente se formuló un marco
tecnológico integral, para la gestión de turnos, fundamentado en el stack MEAN: MongoDB, Express.js, Angular y Node.js, complementado con Socket.io para
comunicación en tiempo real. El estudio identificó que los métodos tradicionales de gestión generaban ineficiencia operativa, tiempos de espera prolongados e
insatisfacción del cliente. Mediante una metodología y el uso de Scrum para el desarrollo, se implementó un sistema web que incluye toma de turnos
presenciales y en línea con validación OTP, transferencia entre módulos, notificaciones en tiempo real mediante Socket.io, generación de reportes y
tickets con código QR. La arquitectura propuesta demostró ventajas en escalabilidad y mantenibilidad al utilizar JavaScript en toda la stack tecnológica.
La implementación fue validada con usuarios finales, resolvió las deficiencias identificadas y estableció bases para futuros desarrollos tecnológicos en la
cooperativa. El marco tecnológico con stack MEAN se configura como una solución efectiva para la modernización de procesos en instituciones financieras
Test procedures for PEMFC stack performance tests
No full textThe general approach of the Stack-Test approach and the prepared testing procedures were presented including procedures for stack sensitivity tests, polarization curve measurements, tests under constant load and performance tests for dead end conditions.
Furthermore a procedure for the optimization of the operating parameters of a PEMFC stack based on a Nelder Mead simplex was introduced
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