Design and Preliminary Evaluation of a Supercritical Carbon Dioxide Brayton Cycle for Solar Dish Concentrator Clean Energy Production

As we move toward energy independence and more ambitious clean energy goals, solar energy research must push the efficiency limits of traditional energy generation systems. Increases in efficiency can be achieved by increasing the hot temperature of the power cycle. Recent research demonstrates the potential for increased efficiency and a vastly smaller component size when supercritical carbon dioxide Brayton power cycles are used. Concentrated solar and nuclear heat sources are capable of achieving the high working fluid temperatures needed for significant efficiency gains. This NSF EPSCoR funded, experimental research system is designed to exploit the uniquely immense solar irradiance of the Mojave Desert, coupling a solar dish concentrator with the UNLV supercritical carbon dioxide (SCO2) Brayton cycle, fabricated on campus at the UNLV Center for Energy Research and the UNLV Machine Shop. This, in conjunction with dry cooling, compounds the capacity for increased efficiency with trivial water consumption and decreased environmental and geographical footprints. Photographic flux mapping was used to provide solar flux information leading to the custom design and on-site fabrication of the solar receiver. A custom air-cooled heat exchanger with expansion capabilities was designed and fabricated for heat rejection. To further increase efficiency, internationally collaborative custom minichannel heat exchangers from the research team at Xi’an Jiaotong University, P.R. China, were added in both zigzag and straight channel geometries; these heat exhangers are installed in parallel, with isolation valves, for experimental comparison and singular recuperation in the system. The turbine and compressor housing exhibits a modular design to allow ease of desired experimental modifications. All components are mounted on an SAIC dish concentrator solar tracking system for on-sun experimental testing. A computational model of the solar receiver and heat rejection system, as well as the entire power cycle, has been created in Engineering Equation Solver (EES). On-sun experimental tests of the solar receiver and heat rejection systems have indicated system capability to both reach high temperatures and reject the heat required to achieve accelerated efficiencies. Once high efficiency temperature ranges are achieved, efficient turbomachinery is required for high efficiency operational success. Fabrication issues and resolutions surrounding the machining of small turbomachinery in this high temperature environment are described as a part of this research. Of particular consequence are issues surrounding the design and fabrication of the turbo-compressor shaft to housing interface. Bearing issues prove to be the core limitation preceding successful operational performance of the turbo-compressor unit. Decisions leading to the successful resolution to this issue are also described. This concentrated solar research system is a demonstration of the innovative component and system design needed to reach the next level in clean solar energy using trivial water consumption. The experimental and computational components support previous theories for the role of concentrated solar in clean power generation systems with increased efficiencies. This experimental system provides proof of concept for supercritical carbon dioxide Brayton cycles with solar concentrator technology, contributes to the advancement of SCO2 Brayton cycle component fabrication processes, and displays the capacity of UNLV to move this SCO2 turbo-compressor unit toward commercialization

Branded: Corporate Image, Sexual Stereotyping, and the New Face of Capitalism

In the context of unionized workforces covered by collective bargaining agreements, companies have-at most-been required to demonstrate a reasonable relationship between the grooming code and the business\u27s effort to project a corporate image that it believes will result in a larger market share.5 In a small number of cases, sexualized branding that exposes workers to sexual harassment or is predicated upon sexual stereotypes not essential to performance of the job has been curtailed by the antidiscrimination mandate of Title VII.6 However, challenges under Title VII have been effective only where corporate branding is at odds with community norms; where the branding is consistent with community norms that encode sexual stereotypes, customer preferences and community norms become the business justification for branding

SCADA Security - Slowly Circling a Disaster Area

SCADA (Supervisory Control And Data Acquisition) networks control much of the industrialised nations production and supply complexes. Various government reports and investigations have highlighted the vulnerability of these systems. Many of these systems are on private networks which are increasingly being connected to systems that are accessible from other networks such as the Internet. SCADA systems have unique security and operational requirements. However, many of the most basic security measures are missing in these networks. This examines some of these issues and proposes some technologies that could help secure these networks from attack

How Do Learners Interact with E-learning? Examining Patterns of Learner Control Behaviors

There has been significant debate in the literature on technology-mediated training about the appropriate role of learner control. We define learner control as giving trainees the ability to make choices about how they proceed through the learning environment. We explore two perspectives. First, we consider learners’ stated preferences for the extent of control in the learning environment. Second, we analyze the actual online learning behaviors of 518 trainees in a Fortune 500 organization. We compare a measure of learner control preferences to the most commonly used framework of learner control that comprises five dimensions: pace of instruction, sequence of topics, specific content covered, amount of advice/feedback provided, and type of media. We also compare the dimensionality of learner behaviors to this framework and examine the relationship between learner preferences and learner behaviors. Results suggest that fewer dimensions can capture both learner preferences and behaviors than what the literature currently suggests. Specifically, media control aligned with both pace and content control. The relationship between stated learner control preferences and learner control behaviors was relatively weak. However, we found support for the recently identified dimension of scheduling control and suggest a new learner control dimension of performance control, consistent with the importance of practice retrieval for learning

Modelling the Effect of Composition Change during Condensate Dropout in a Horizontal Gas Well.

This paper presents a mathematical model describing the behavior analysis for a two-phased gas-condensate system narrowing down on the three zone method. The three zone method accounts for the composition change in the reservoir and is based on modeling the depletion by three main flow regions: • A near wellbore region (Region 1) where the oil saturation is important allowing both phase, vapor and liquid to be mobile. • Region 2 where condensate and gas are present but only the gas is mobile. • An outer Region 3 exists when the reservoir pressure is greater than the initial gas dew point and contains only gas. This research proposed a fourth region (Region I) which is the immediate vicinity of the well where accumulation of liquid buildup at high rates which yielded from an increase of liquid saturation and a probable decrease in gas relative permeability. The existence of the fourth region or flushed zone is particularly important as it represent the total skin effect: mechanical skin, rate dependent two-phase skin and skin due to gas condensate blockage. The calculated well deliverability rate using the modeled equation for gas condensate reservoir showed a relatively high difference when compared to other known equations. This significant difference is as a result of the effects of the proposed Region I. The developed correlation confirms that as the pressure drops below dew point there occurs condensate banking which when the critical saturation is reached becomes mobile and leads to a reduction in gas flow rate in the reservoir

Abordagem sistemática para o controlo seguro de sistemas aeroespaciais

A verificação formal do comportamento de sistemas tempo-real é uma tarefa complexa, por várias razões. Há múltiplos trabalhos desenvolvidos na área de verificação formal, por model-checking de sistemas tempo-real, sendo que diversos softwares foram desenvolvidos para o efeito. Um dos problemas mais complexos para serem resolvidos na análise de controladores tempo-real é a conversão das linguagens de programação dos controladores nas linguagens formais, por exemplo autómatos finitos temporizados para depois poderem ser verificados formalmente através dos model-checkers existentes. Se a metodologia de elaboração dos programas for bem desenvolvida e conhecida, essa tarefa pode ser muito facilitada. Por outro lado, grande parte dos sistemas tempo-real (principalmente os sistemas embebidos que pretendemos estudar) é programado em linguagem C. Neste artigo pretende-se estabelecer uma metodologia de criação de programas em código C, a partir do formalismo de especificação SFC, tendo em conta a verificação formal de propriedades comportamentais desejadas para o sistema, utilizando a técnica Model- Checking e o model-checker UPPAAL. Estes estudos preliminares são efectuados no contexto de colaboração entre Investigadores dos centros de investigação CT2M, ALGORITMI e CCTC da Universidade do Minho (Portugal) e do Departamento de Engenharia Mecânica do Instituto Tecnológico de Aeronáutica (Brasil).Formal verification of real-time systems behavior of is a complex task, for several reasons. There are multiple works developed in the domain of formal verification of real-time system behavior by model-checking, and various software tools were developed for this purpose. One of the most complexes problems to be solved in the analysis of real-time controllers is the conversion of programming languages controllers in formal languages, for example finite timed automata to be used as inputs of the existing model-checkers. If the methodology of the programming is well developed and known, this task can be greatly facilitated. Moreover, most real-time systems (especially embedded systems that we intend to study) are programmed in C language This article seeks to establish the methodology of creating programs in C code, from SFC specification formalism, taking into account the formal verification of behavior al properties desired for the system, using the Model-Checking technique and the modelchecker UPPAAL. A case study is presented to illustrate the methodology presented. These preliminary studies are presented on the context of a research collaboration project being developed by researchers of CT2M, ALGORITMI and CCTC research centers of University of Minho (Portugal) and the Mechanical Engineering Department of Technological Institute of Aeronautics (Brazil)

Towards an economic-geographical approach to the globalisation of the hotel industry

Peer reviewedPostprin