196,328 research outputs found
Evaluation and selection of thin-layer models for drying kinetics of apricot (cv. NASIRY)
No full textE. Mirzaee, S. Rafiee, A. Keyhani(Agricultural Machinery Engineering Department, Faculty of Agricultural Engineering and Technology, University of Tehran, Karaj, Iran) Abstract: This paper presents the thin layer drying behavior of apricot (cv. NASIRY) at the air temperatures of 40ºC, 50ºC, 60ºC, 70ºC and air velocity of 1m/s and 2 m/s. In order to select a suitable form of the drying curve, 12 different thin layer drying models were fitted to experimental data. Fick’s second law was used as a major equation to calculate the moisture diffusivity with some simplification. The high values of coefficient of determination and the low values of reduced chi-square and root mean square error indicated that the Logarithmic model and the Midilli et al. model could satisfactorily describe the drying curve of apricot for drying air velocity of 1m/s and 2 m/s, respectively. According to the research results the calculated value of effective moisture diffusivity varied from 1.78×10-10–5.11×10-10 m2/s and the value of activation energy varied from a minimum of 24.01 kJ/mol to a maximum of 25.00 kJ/mol.Keywords: apricot, thin layer drying, effective moisture diffusivity, activation energy Citation: E. Mirzaee, S. Rafiee, A. Keyhani. Evaluation and selection of thin-layer models for drying kinetics of apricot (cv. NASIRY). Agric Eng Int: CIGR Journal, 2010, 12(2): 111-116.  
Fuzzy Control of Multilevel Inverters for Fuel Cell Generator Sets
No full textDistributed generation (DG) is increasing its role in modern power systems and the electricity produced by unconventional a.c. and d.c. sources is becoming fundamental in the overall balance. A key element of DG is its mix of different power sources, mostly connected with the grid trough power converters. Since the latter introduce grid perturbations and, at the same time, are affected by the instantaneous grid status, new topologies are being proposed aiming at reducing mutual influences, thus improving the overall efficiency, behaviour and cost. Since cascaded multilevel converters offer significant advantages over the widely diffused PWM two-level converters in terms of harmonic mitigation and low switching frequency, in this chapter a 9-level cascaded inverter suitable for distributed generation and supplied by four fuel cell stacks is proposed and discussed. Such a system operates both in grid-connected and in stand alone mode controlled by a fuzzy logic controller implemented on a FPGA. After a detailed description, system performance are verified and analysed through simulation and experimental results
Load frequency control in a microgrid : challenges and improvements
No full textA microgrid can span over a large area, especially in rural townships. In such cases, the distributed generators (DGs) must be controlled in a decentralized fashion, based on the locally available measurements. The main concerns are control of system voltage magnitude and frequency, which can either lead to system instability or voltage collapse. In this chapter, the operational challenges of load frequency control in a microgrid are discussed and few methods are proposed to meet these challenges. In particular, issues of power sharing, power quality and system stability are addressed, when the system operates under decentralized control. The main focus of this chapter is to provide solutions to improve the system performance in different situations. The scenarios considered are \ud
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(a) when the system stability margin is low, \ud
(b) when the line impedance has a high R to X ratio, \ud
(c) when the system contains unbalanced and/or distorted loads. \ud
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Also a scheme is proposed in which a microgrid can be frequency isolated from a utility grid while being capable of bidirectional power transfer. In all these cases, the use of angle droop in converter interfaced DGs is adopted. It has been shown that this results in a more responsive control action compared to the traditional frequency based droop control.\u
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Inverse analysis of temperature-time data with grossly different time scales using Beck`s second method and the Frankel-Keyhani whole-domain technique
No full textIn general, inverse heat conduction analysis utilizes the measured temperature history at one or more internal locations to estimate unknown boundary conditions, energy generation rates, or thermophysical properties. Analysis of these data using conventional numerical heat transfer techniques yields numerically unstable solutions; that is, small perturbations in the input data can produce large variations and instabilities in the output. Previous attempts to overcome this inherent instability have involved the utilization of future information and Tikhonov regularization techniques (Beck et al, 1985). In the 1970`s and 80`s, Beck and coworkers developed a family of techniques that overcome this obstacle by relating the surface property at any time in the transient to temperatures measured after that time in the transient (Beck, 1970, Beck et al, 1982). That is, future information is used to determine present conditions. For many purposes, these techniques are the standard analysis tools. An alternative approach has been developed recently by Frankel and Keyhani (1997). This approach utilizes a whole domain form in which the entire space-time domain of interest is simultaneously resolved; the traditional instability occurs only near the final time endpoint and can be excluded from the resulting solution. Rapid convergence and accurate results have been demonstrated using this approach. Two sets of time-temperature data have been analyzed using both of these techniques
Dr. Duane M. Jackson, Morehouse College, July 2011
No full textThis video is a conversation with Dr. Duane M. Jackson. Dr. Jackson talks about his paper, "Recall and the Serial Position Effect: The Role of Primacy and Recency on Accounting Students' Performance." Jackie Daniel, AUC Woodruff Library, is the interviewer
"Reflections on the subject of Emigration from Europe with a view to Settlement in the United States" By M. Carey.
No full text"Reflections on the subject of Emigration from Europe with a view to Settlement in the United States: containing bried sketches of the moral and political character of those states.
By M. Carey, member of the American philosophical, and of the American Antiquarian Society, and author of The Olive Branch, Cindiciae Hibernicae, essays on banking, on political economy, and on internal improvement.
To which are now added the English editor's comments on the subject; together with Important Advice to Emigrants, and Cautions Against Impositions Practiced in the Outports
State Estimation in Smart Power Grids
No full textIn this chapter, the role of State Estimation (SE) in smart power grids is presented. The trend of SE error with respect to the increasing of the smart grids implementation investigated. The observability analysis as a prior task of SE is demonstrated and an analytical method to consider the impedance values of the branches is developed and discussed by examples. Since most principles of smart power grids are appropriate to distribution networks, the Distribution SE (DSE)considering load correlation is argued and illustrated by an example. The main features of smart grid SE, which is here named as “Smart Distributed SE” (SDSE), are discussed. Some characteristics of proposed SDES are distributed, hybrid, multi-micro grid and islanding support, Harmonic State Estimation (HSE), observability analysis and restore, error processing, and network parameter estimation. Distribution HSE (DHSE) and meter placement for SDSE are also presented
Dispelling the Myths Behind First-author Citation Counts
No full textWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
Dr. Glendon Swarthout
No full textHosted by Roger M. Busfield, MSU Assistant Professor of Speech and Theater, Meet the Author is designed to introduce a general audience to a contemporary author and their work through in-depth interviews. This episode features a conversation between Dr. Glendon Swarthout, prolific author and English professor at MSU, and assistant professors Sam S. Baskett and Theodore B. Strandness
Simulation of thermal plant optimization and hydraulic aspects of thermal distribution loops for large campuses
No full textFollowing an introduction, the author describes Texas A&M University and its utilities system. After that, the author presents how to construct simulation models for chilled water and heating hot water distribution systems. The simulation model was used in a $2.3 million Ross Street chilled water pipe replacement project at Texas A&M University. A second project conducted at the University of Texas at San Antonio was used as an example to demonstrate how to identify and design an optimal distribution system by using a simulation model. The author found that the minor losses of these closed loop thermal distribution systems are significantly higher than potable water distribution systems. In the second part of the report, the author presents the latest development of software called the Plant Optimization Program, which can simulate cogeneration plant operation, estimate its operation cost and provide optimized operation suggestions. The author also developed detailed simulation models for a gas turbine and heat recovery steam generator and identified significant potential savings. Finally, the author also used a steam turbine as an example to present a multi-regression method on constructing simulation models by using basic statistics and optimization algorithms. This report presents a survey of the author??s working experience at the Energy Systems Laboratory (ESL) at Texas A&M University during the period of January 2002 through March 2004. The purpose of the above work was to allow the author to become familiar with the practice of engineering. The result is that the author knows how to complete a project from start to finish and understands how both technical and nontechnical aspects of a project need to be considered in order to ensure a quality deliverable and bring a project to successful completion. This report concludes that the objectives of the internship were successfully accomplished and that the requirements for the degree of Degree of Engineering have been satisfied
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