bluuebunny/crossref_metadata_2025 huggingface dataset:
Design of HVDC and SVC Coordinate Damping Controller Based on Wide Area Signal
Authors: Chang Yong
Published: March 2007

HVDC and FACTS devices have been widely applied in power system for their excellent and flexible control ability. Their contributions to the damping of system oscillations are of great importance for achieving satisfactory system performance. However, previous experience has shown that there may be negative interactions among FACTS devices whose supplementary controllers are designed separately. This may deteriorate system performance and even make system unstable. The interactions of HVDC and SVC during system oscillation were analyzed in this paper. The coordinate supplementary damping controller for HVDC and SVC were then designed based on projective control principle. The criterion of synthetic residue is adopted in choosing the proper input wide area signals. Eigenvalue analysis and time domain simulations were performed on a two-area system and the results demonstrated the effectiveness of the proposed controller.
Zero-Sequence Current Control of Modular Active Power Filter for High Power Three-Phase Three-Wire Electrical Networks
Authors: Choukri Benhabib , Philippe Poure , Shahrokh Saadate
Published: March 2007

Since the development of the first control strategy for the active power filters (APF) introduced by H. Akagi [H. Akagi, Y. Kanazawa,A. Nabae, Generalized theory of the instantaneous reactive power in three-phase circuits, in: Proceedings of International Power Electronics Conference, Tokyo, Japan (1983) 13751386.], many efforts have been concentrated to improve their performances. However, when electrical networks supplies high current non-linear loads, a single inverter-based APF has limited power capability. In this paper, we studied parallel operation achieving high power level. More particularly, we examined a modular APF based on two three-phase inverters. This structure allows zero-sequence current circulating through the inverters, as demonstrated by using averaged modelling of the APF. To solve this problem and based on previous averaged model, we proposed a new optimal control strategy, suppressing the zero-sequence circulating current. Simulation results validate the proposed control.
Application of Ultraviolet Detector in Discharge Detection
Authors: Liu Jungang , He Wei , Zhou Liang , Yang Fan
Published: March 2007

The aging of insulators often results in corona discharge, and the measurement of the ultraviolet light (UV-light) can be used to detect insulator defects. This paper introduces a new tester, the ultraviolet detector, which can detect defective insulators by measuring the UV-light from the discharging insulators. Some tests were carried out. The results indicated that the detector can identify the existence of corona discharge with good performance. And it can be used for discharge detection of power system and transformer substation.
Comparison of Optimum Reactive Power Schedule with Different Objectives Using LP Technique
Authors: Dhadbanjan Thukaram , Yesuratnam G.
Published: March 2007

Three algorithms for reactive power optimization are proposed in this paper with three different objective functions. The objectives in the proposed algorithm are to minimize the sum of the squares of the voltage deviations of the load buses, minimization of sum of squares of voltage stability L-indices of load buses (?L2) algorithm, and also the objective of system real power loss (Ploss) minimization. The approach adopted is an iterative scheme with successive power flow analysis using decoupled technique and solution of the linear programming problem using upper bound optimization technique. Results obtained with all these objectives are compared. The analysis of these objective functions are presented to illustrate their advantages. It is observed comparing different objective functions it is possible to identify critical On Load Tap Changers (OLTCs) that should be made manual to avoid possible voltage instability due to their operation based on voltage improvement criteria under heavy load conditions. These algorithms have been tested under simulated conditions on few test systems. The results obtained on practical systems of 24-node equivalent EHV Indian power network, and for a 205 bus EHV system are presented for illustration purposes.
A Novel FACTS Based (DDSC) Compensator for Power-Quality Enhancement of L.V. Distribution Feeder with a Dispersed Wind Generator
Authors: Sharaf Adel M , Abo-Al-Ez Khaled Mohamed
Published: March 2007

In a deregulated electric service environment, an effective electric transmission and distribution networks are vital to the competitive environment of reliable electric service. Power quality (PQ) is an item of steadily increasing concern in power transmission and distribution. The traditional approach to overcoming capacity and quality limitations in power transmission and distribution in many cases is the addition of new transmission and/or generating capacity. This, however, may not be practicable or desirable in the real case, for many of reasons. From technical, economical and environmental points of view, there are two important - and most of the time combined - alternatives for building new transmission or distribution networks to enhance the transmission system capacity, and power quality: the Flexible alternating current transmission devices and controllers, and the distributed generation resources near the load centers. The connection of distributed generation to the distribution grid may influence the stability of the power system, i.e. angle, frequency and voltage stability. It might also have an impact on the protection selectivity, and the frequency and voltage control in the system. This paper presents a low cost FACTS based Dynamic Distribution System Compensator (DDSC) scheme for voltage stabilization and power transfer and quality enhancement of the distribution feeders connected to a dispersed wind generator, using MATLAB/ SimPower System simulation tool.
Voltage Regulators and Capacitor Placement in Three-phase Distribution Systems with Non-linear and Unbalanced Loads
Authors: Carpinelli Guido , Noce Christian , Proto Daniela , Varilone Pietro
Published: March 2007

This paper investigates the problem of contemporaneously choosing optimal locations and sizes for both shunt capacitors and series voltage regulators in three-phase unbalanced distribution systems. The sizing and placement procedure not only minimizes the power losses along distribution feeders but also makes sure that both capacitors and series regulators will have the minimum possible impact on the harmonic distortion of bus voltages in the system. The fact that distribution systems can operate under unbalanced loading conditions means that the optimization will have to account for any unbalances in the system. A genetic algorithm, which successfully solves the above-described problem, is developed and tested. This paper presents the results of simulations for a 34-bus IEEE distribution test system.
Design of Variable Structure Controller Using Fuzzy PI Type Sliding Surface: An Application to Load-Frequency Control Problem
Authors: Ray Goshai das , Dey Sitansu , Bhattacharyya Tapas Kumar
Published: March 2007

In this paper, a proportional plus integral (PI) type sliding surface has been proposed for designing a fuzzy variable structure controller to solve load-frequency control problem in presence of load disturbances. It is shown that the proposed controller is effective and robust enough when the system suffers from mismatched condition but the model uncertainty and disturbance are assumed to be bounded. Furthermore, the proposed control strategy drives the states to the sliding surface and also maintains the sliding motion. To illustrate the approach presented has been tested on load-frequency control of power systems and the analytical claims have been justified under the uncertainty involved in the load demand of inter-connected power systems.
Electricity Price and Load Short-Term Forecasting Using Artificial Neural Networks
Authors: Mandal Paras , Senjyu Tomonobu , Urasaki Naomitsu , Funabashi Toshihisa
Published: March 2007

This paper presents an approach for short-term electricity price and load forecasting using the artificial neural network (ANN) computing technique. The described approach uses the three-layered ANN paradigm with back-propagation. The publicly available data, acquired from the deregulated Victorian power system, was used for training and testing the ANN. The ANN approach based on similarity technique has been proposed according to which the load and price curves are forecasted by using the information of the days being similar to that of the forecast day. A Euclidean norm with weighted factors is used for the selection of similar days. Two different ANN models, one for load forecasting and another for price forecasting, have been proposed. Test results show that average price and load MAPEs for the year 2003 by using the ANN approach are obtained as 14.29% and 0.95%, respectively. MAPE values obtained from the price and load forecasting results confirm considerable value of the ANN based approach in forecasting short-term electricity prices and loads.
A Tapped Star Connected Autotransformer Based 24-Pulse AC-DC Converter for Power Quality Improvement in Induction Motor Drives
Authors: Garg Vipin , Singh Bhim , Bhuvaneswari G
Published: March 2007

This paper presents the design, analysis and development of a novel tapped star connected autotransformer based twenty-four-pulse ac-dc converter for improving power quality at the point of common coupling (PCC) in vector controlled induction motor drives (VCIMDs). A star connected autotransformer with four windings per phase at different phase angles is used to realize the proposed twenty-four-pulse ac-dc converter. The basic design equations are derived to calculate the number of turns in different windings for achieving the harmonic reduction in the proposed autotransformer. The design of autotransformer is further modified for making it suitable for retrofit applications to replace presently used 6-pulse diode bridge rectifier. The proposed 24-pulse ac-dc converter is able to eliminate up to 21st harmonics in the supply current along with the power factor improvement close to unity in the wide operating range of the drive. The effect of load variation on VCIMD is also studied to demonstrate the effectiveness of the proposed ac-dc converter. Different power quality indices on input ac mains and on dc bus for a VCIMD fed from a 12-pulse and a 24-pulse ac-dc converters are also given to compare their performance. Various tests are conducted on the developed prototype of proposed autotransformer based 24-pulse ac-dc converter. Different power quality indices are measured on developed 24-pulse ac-dc converter to validate the design and simulation model.
Distributed Generation Communications Utilizing a Real-time FPGA-based Channel Simulator in the ISM Frequency Band
Authors: Meng Julian , Barnes Shane
Published: March 2007

Deregulation of the power industry, increases in consumer demand of electricity and mandates to reduce greenhouse gases has significantly heightened the interest in distributed generation (DG). Typical DG sources include wind turbines, fuel cells, micro gas/diesel turbines, small hydro generators and photovoltaics. Currently most of these generation sources are optimized for local operation and thus the potential of DG that is both dispatchable and cost-effective has yet to be fully realized. One key technical challenge is the development of low-cost communications for remote telemetry and control of individual DG sources. Along with cost, other key communication system requirements are modularity, range and reliability. This paper presents a distributed generation communication system (DGCS) that is based on a wide area network (WAN) and local area network (LAN) topology and utilizes two variants of low-cost radio modems (RM) to satisfy the desired connectivity between the DG sites and a centralized control center. For the LAN, low-cost RMs operating in the industrial, scientific, and medical (ISM) frequency band offers point-to-multipoint scalability to multiple DG sites within a limited range. Integration of the ISM RMs with a cellular RM provides connectivity to a WAN or Internet thus providing long-range access to DG sites from any facility that has internet-access. Given the LAN scalability requirement, an ISM field programmable gate array (FPGA) channel simulator was developed to assess DGCS performance using channel impairments such as free-space path loss, multipath reflections, additive white Gaussian noise (AWGN), multiple access interference, and narrowband interference. This study provides the evaluation of two commercially available ISM radio modems and recommendations are made based on LAN requirements such as cost and performance given difficult channel conditions.
Multi-Agent Models for Consumer Choice and Retailer Strategies in the Competitive Electricity Market
Authors: Bompard Ettore F. , Abrate Graziano , Napoli Roberto , Wan Bo
Published: March 2007

The benefit to end-users of electricity, mainly in terms of low prices, is strictly related to the interaction among the consumers themselves and retailers. The literature on retail competition has highlighted possible distortions in market outcomes due to unresponsive demand and boundedly rational consumers. Hence, a model appropriate to represent this aspect of the market is needed. The paper proposes a general model of the interaction among retailers and consumers in the electricity market based on the theory of multi-agent systems. The model incorporates different assumptions concerning the behavior of the players that corresponds to different levels of interaction in determining the market outcomes. The model is validated interpretively by the results provided in terms of Game Theory equilibrium. The results of an extensive set of simulations on a population of 1,000 consumers is presented and discussed.
The Vulnerability Analysis of Transmission System Based on the Performance of Mho Relay and SVC
Authors: Li Shenghu , Ding Ming
Published: March 2007

The security of the transmission system is dependent on the relays performance after various disturbances. Undesirable relay operation will trip the lines and lead to cascading events. In this paper the operation margin of mho relays is equivalently redefined as function of bus voltages instead of line impedance. The sensitivities of the operation margin to bus voltage and bus power is applied to quantify the vulnerability of transmission system. The contribution of the shunt compensation by SVC is analyzed based on the sensitivities (control factors) of the operation margin to the shunt susceptance. It is found that the control effect of SVC is approximately linear when the mho relay has relative smaller operation margin. In this range the linear model based on the control factors is accurate enough to simulate the control effect. It is also found that the shunt compensations at different locations may yield opposite effect to the operation margin of the mho relays, which can be easily judged by the value of the control factors.
Brushless Doubly Fed Reluctance Machines: An Emerging Technology
Authors: Jovanovic Milutin
Published: March 2007

Brushless doubly-fed machines (BDFMs) allow the use of a partially rated inverter and therefore offer reliable, maintenance-free operation at low cost, especially in large power variable speed applications with limited speed ranges such as off-shore wind turbines, pumps etc. However, with a special cage rotor design, the machine has substantial rotor losses, poor efficiency and complicated control being difficult to implement.The BDFM reluctance type, the brushless doubly-fed reluctance machine (BDFRM), can overcome most of the above BDFM deficiencies while retaining all its merits. It has a "cold" reluctance rotor, which makes it more efficient and much easier to model/control than the BDFM.A theoretical study of the BDFRM is very important to gain proper understanding of its unusual operation, the main control features and compromises between optimal performance and the size of the inverter and machine required. This paper will attempt to develop, and provide a comprehensive comparative analysis of, different control strategies for the machine that are suitable for digital implementation.
Maximum Wind Power Capture by Sensorless Rotor Position and Wind Velocity Estimation from Flux Linkage and Sliding Observer
Authors: Senjyu Tomonobu , Muhando Endusa Billy , Yona Atsushi , Urasaki Naomitsu , Kinjo Hiroshi , Funabashi Toshihisa
Published: March 2007

In recent developments wind power has been gaining rapid usage as an alternative source of electrical power and there is need to formulate optimized control schemes for power generation. This paper presents a sensorless maximum power point tracking control methodology for a wind power generation system. For the sensorless vector control a sliding mode observer is utilized in the estimation of the rotor speed while the rotor position is estimated based on the flux linkage. The Powell method is introduced to improve the efficiency of the permanent magnet synchronous generator (PMSG) d-axis current optimization. To ensure robustness of the proposed paradigm to parameter variations, the windmill loss coefficients determining the optimal rotor speed are identified online. Results of simulations confirm the effectiveness of the proposed method.
Modeling of Electric Power Supply Chain Networks with Fuel Suppliers via Variational Inequalities
Authors: Matsypura Dmytro , Nagurney Anna , Liu Zugang
Published: March 2007

The electric power industry in the United States and in other countries is undergoing profound regulatory and operational changes. The underlying rationale behind these transformations is to move once highly monopolized vertically-integrated industry from a centralized operation approach to a competitive one. The emerging competitive markets and an increase in the number of market participants have, in turn, fundamentally changed not only electricity trading patterns but also the structure of the electric power supply chains. This new framework requires new mathematical and engineering models and associated algorithmic tools. Moreover, the availability of fuels for electric power generation is a topic of both economic importance and national security. This paper uses the model developed by Nagurney and Matsypura (2004, 2006) as the foundation for the introduction of explicit fuel suppliers, in the case of nonrenewable and/or renewable fuels, and their optimizing behavior, into a general electric power supply chain network model along with "direct-supply" generation. We derive the optimality conditions for the various decision-makers, including fuel suppliers, power generators, suppliers, as well as the transmission service providers and the consumers at the demand markets. We establish that the governing equilibrium conditions satisfy a finite-dimensional variational inequality problem. We provide qualitative properties of the equilibrium flow pattern; in particular, existence of a solution and uniqueness under suitable assumptions. Finally, we discuss how the equilibrium fuel supply and electric power flow pattern can be computed.
Laudatio: Pietro Trimarchi
Authors: Parisi Francesco
Published: March 2007

The text of a Laudatio delivered on September 16, 2006 by Professor Francesco Parisi on the occasion of the awarding of an honorary membership in the European Association of Law and Economics (EALE) to Professor Pietro Trimarchi. This was the first such honorary membership awarded by this association.
Twenty-Second Annual Conference of the European Association of Law and Economics, Ljubljana, Slovenia
Authors: Garoupa Nuno , Schäfer Hans-Bernd
Published: March 2007

Introduction to the Twenty-Second Annual Conference of the European Association of Law and Economics, Ljubljana, Slovenia
Texture Assessment of Industrially Produced Spreadable Fat Fortified with Fish Oil
Authors: Kolanowski Wojciech , Jaworska Danuta , Weissbrodt Jenny
Published: March 2007

Each year the assortment of fish oil fortified foods increases. Fish oil is a rich source of long chain omega-3 polyunsaturated fatty acids (PUFA) which low intake results in less protection against many common diseases. According to recommendations the level of omega-3s in average diet should be increased. Consumption of foods fortified with fish oil may elevate omega-3 intake. Such fortification, among others, may influence the texture of food product because of liquid form of added fish oil. The aim of this study was to evaluate the influence of fortification with 30 g kg-1 of fish oil on selected texture properties of reduced-fat spread by sensory and instrumental assessment during 3 months of storage. Samples were prepared on industrial pilot plant. Hardness, spreadability, consistency and adhesiveness were measured by sensory and instrumental methods (Texture Analyser TX.TA2i). During storage time results of measurements of all evaluated attributes were comparable to controls. Slight increase in hardness and consistency was observed. It is concluded that fortification with 30 g kg-1 of fish oil used in the study has no significant effect on texture properties of evaluated spread. Combined instrumental and sensory methods may assure precise assessment of texture parameters in the quality control of spreadable fat production.
Water Absorption Characteristics of Obatanpa and Mamaba Maize Hybrids (Zea mays)
Authors: Addo Ahmad , Bart-Plange Ato , Dzisi Komla
Published: March 2007

Water absorption characteristics of two newly-released maize hybrids, Obatanpa and Mamaba, during soaking were measured at four temperatures of 30, 40, 50 and 60ºC. The absorption kinetics followed the Fick's law of diffusion during the first hours of soaking. The values determined for water diffusion coefficients varied from 7.31 x 10-12 to 9.33 x 10-12 m2/s and from 6.30 x 10-12 to 8.25 x 10-12 m2/s for Obatanpa and Mamaba respectively. An Arrheniustype equation was used to relate the diffusion coefficient of Obatanpa and Mamaba to temperature, and the energy of activation for Obatanpa and Mamaba was estimated. The values determined were 6.54 kJ/mol and 6.82 kJ/mol for Obatanpa and Mamaba respectively.
Changes in Souring Development, Nutritional and Functional Properties during Fermentation of Cowpea-Fortified Nixtamalized Maize
Authors: Afoakwa Emmanuel Ohene , Aidoo Philip R
Published: March 2007

Spontaneous fermentation of maize produces lactic acids resulting in souring or acidification with associated improvement in taste, flavour and texture of the derived products. When combined with nixtamalization and cowpea fortification, it is expected to improve the nutritional quality and product functionality of maize based foods and as well introduce variety to maize processing. This study was carried out to investigate the changes in souring development, nutritional quality and functional properties during spontaneous fermentation of cowpea-fortified nixtamalized maize. A 2 x 3 x 3 factorial experimental design, with fermentation medium (water, coconut water), fermentation time (0, 24, 48 hours) and cowpea level (0, 15, 30 %) was performed. Nixtamalized maize was prepared by boiling whole maize in 1 % lime solution for 30 minutes, steeped in excess lime, milled into meal and kneaded into a dough using water or coconut water. The blends were fermented for the specific times and analysed for pH, titratable acidity, water absorption capacity, colour, protein and ash. The presence of lime and cowpea influenced the pH, titratable acidity, water absorption, colour, protein and ash content of the fermented cowpea-fortified maize. Addition of cowpea increased most of the studied indices whiles pH of all the blends decreased (6.15-4.45) with a corresponding increase in titratable acidity (0.008-0.045 g/100g lactic acid) with increase in fermentation time. There was however no significant (p<0.05) difference in the effect of fermentation medium on these indices suggesting that coconut water could be used as an alternative fermentation medium for maize dough fermentation without any effect in souring development. Fermentation and cowpea fortification can therefore be used to increase the nutritive value of nixtamalized maize with acceptable souring and product quality characteristics.
Comparative Study of Heat Induced Fouling of Various Types of Milk Flowing over a Heated Metal Surface
Authors: Nema P K , Datta A K
Published: March 2007

A static heat exchanger was used to study the extent of heat induced fouling in the device due to passage of cow, buffalo, double toned and reconstituted milk for a period of one hour. The static heat exchanger was developed to simulate the flow condition of an actual indirect type heat exchanger employed in the processing plant. Flow rate of 2x10-7 m3 s-1 was selected as this gave the same 1.052x10-3 m3 m-2 flow rate/surface area ratio as applicable to indirect double tube heat exchangers used in the industry. Both milk with fat and with fat removed by centrifugal separation were used. Fresh and recycled milk were the other two factors used in the study of fouling. It was found that there was no significant difference in fouling deposit formation between fresh and recycled milk, but significant difference existed between milk with fat and milk with fat removed. Reconstituted milk was found to have significantly lower deposit compared to cow, buffalo and double toned milk.
Optimization of Protein Enrichment of Deoiled Rice Bran by Solid State Fermentation Using Aspergillus oryzae MTCC 1846
Authors: Rudravaram Ravinder , Chandel Anuj Kumar , Linga Venkateshwer Rao , Pogaku Ravindra
Published: March 2007

Rice bran is a primary by-product of the traditional rice processing industry. Once oil is extracted from rice bran, the left over residue is called de oiled rice bran (DOB). Its disposal presents economic and environmental problems. Microbial conversion of DOB into single cell protein (SCP) is an innovative practical approach for protein supplementation of a staple diet. The present research was undertaken to test the growth of industrially important fungi, Aspergillus oryzae MTCC 1846 on DOB through solid state fermentation (SSF) technology. Various process parameters effect such as moisture, pH of the substrate, inoculum size, temperature and nitrogen source for maximum protein enrichment were studied. The optimum conditions for the enrichment process were found to be moisture content 60%; temperature 280C; pH 6.0; inoculums concentration 109 spores/ g substrate and particle size of DOB, 0.3 mm. Among the various nitrogen source tested, ammonium sulfate (0.6% w/w) showed maximum protein enrichment (24.30%) followed by vegetable + fruit waste extract (23.50%) and legume root extract (23.10%).
Quality Evaluation of Kiwi Wine
Authors: Peng Bangzhu , Yue Tianli , Yuan Yahong
Published: March 2007

This paper proposes a fuzzy set approach that integrates objective and subjective information to evaluating kiwi wine quality. The 10 different kiwi wines experimentally were conducted firstly sensory evaluation. Then the contents of principal aroma components were identified and determined by the Headspace-Solid phase Microextraction-Gas Chromatography-Mass Spectrometry using quantitative standards with known amounts of target components and 3-Octanol as internal standards. The result of fuzzy set approach to assess and rank the kiwi wine quality showed KW-1 as the best kiwi wine. The results and outcomes of this study suggest that the approach described in this paper is more accurate and objective than conventional methods. It provides a comprehensive method for dealing with incomplete and imprecise information to support the whole evaluation process. This method should be utilized by the fruit wine industry around the world because of its practicability and superiority.
Production and Characterization of Amylases by Aspergillus niger under Solid State Fermentation Using Agro Industrials Products
Authors: Spier Michele Rigon , Woiciechowski Adenise Lorenci , Vandenberghe Luciana Porto de Souza , Soccol Carlos Ricardo
Published: March 2007

The use of agro industrials products cassava starch and sugar cane bagasse present a great potential as substrate and support, respectively, showing low production costs for amylases production under solid-state fermentation by Aspergillus niger LPB 28. The effect of various factors was examined and some variables were optimized to ?-amylase and amyloglucosidase production. Inoculum rate in different concentrations (105, 106, 107 and 108 spores/g of cassava starch) were used to inoculate the solid substrate for the SSF. The material was supplemented with nitrogen sources; calcium source and micronutrients solution. The ratios of cassava starch to sugar cane bagasse (1/1; 1.5/1; 1/1.5; 1/2; 2/1; 1/3; 3/1) were tested and the initial moisture content varying 80, 85 and 90%. Cultivation was carried out at temperatures 25, 30 and 35ºC for 48, 60 and 72 h. Study of influence of pH initial in SSF was conduced in pH 4.0, 5.0, 6.0, 7.0 and 8.0. Statistical analysis was carried out using the software STATISTICA 5.1 (StatSoft, Tulsa, OK, USA). A 32 complete factorial design (2 factors, 3 levels and 9 experiments) was used to study the effect of the factors in ?-amylase and amyloglucosidase production. The results showed cassava starch and sugar cane bagasse at the ratios of 2/1 was the best for optimum production of ?-amylase and amyloglucosidase. The maximum yield (?-amylase 1732.95 U/g of cassava starch and amyloglucosidase 2044.94 U/g of cassava starch) was achieved with optimized process parameters such as incubation period (60 hours), moisture level was 90%, inoculation rate (105 spores/g of dried material), pH 4.0 and fermentation temperature (30ºC). The nitrogen source (KNO3) also enhanced the ?-amylase and amyloglucosidase activities. In kinetic characterization of enzymes the Michaelis-Menten constant KM and maximum velocity Vmax (KM 10.84 g/l, Vmax 3.42 g/l) for ?-amylase and KM 11.32 g/l and Vmax 5.18 g/l for amyloglucosidase.
Stickiness of Corn Syrup Powders by Fluidised Bed Test
Authors: Werner Stephen R. L. , Fanshawe Rachel L , Paterson Anthony 'Tony' H. J. , Jones James R , Pearce David L
Published: March 2007

The onset of stickiness for corn syrup solids powders having dextrose equivalents of DE20, 30 and 40 were determined under a range of conditions (40100 °C, 1250 %RH) using the fluidised bed technique. The onset of stickiness was found to differ consistently from the predicted glass transition temperature across the range of conditions tested. Difference values, (T-Tg)crit were 34.9, 33.5 and 38.2 °C respectively for the DE20, DE30 and DE40 powders.
The Potential Use of Polymer-Clay Nanocomposites in Food Packaging
Authors: Ray Sudip , Quek Siew Young , Easteal Allan , Chen Xiao Dong
Published: March 2007

With today's advancement in nanotechnology, Polymer-Clay Nanocomposite has emerged as a novel food packaging material due to its several benefits such as enhanced mechanical, thermal and barrier properties. This article discusses the potential use of these polymer composites as novel food packaging materials with emphasis on preparation, characterization, properties, recent developments and future prospects.
Starch Gelatinization under Shearless and Shear Conditions
Authors: Xie Fengwei , Liu Hongshen , Chen Pei , Xue Tao , Chen Ling , Yu Long , Corrigan Penny
Published: March 2007

This article reviews the development of studying starch gelatinization under shear and shearless conditions, in particular the technologies used to detect the degree of gelatinization. Advantages and disadvantages of each technology were discussed and then some examples were presented to demonstrate their application. A new technology RheoScope, an instrument that can measure viscosity under shear stress and simultaneously observes variation of starch particles using a microscope, was also introduced. It was found the definition of "gelatinization" could be different for different detection technologies. Under shearless condition full gelatinization of starch needs about ratio of water 3/starch 1, while the gelatinization under shear condition requires less water content since shear stress enhances the processing. The number of endotherm and enthalpy of gelatinization depends on amylose/amylopectin, moisture and lipid content.
The Role of Operating Conditions in Osmotic Distillation and Direct Contact Membrane Distillation - A Comparative Study
Authors: Bui V. A. , Nguyen M. H.
Published: March 2007

This paper presents a comparative study on the role of operating conditions in osmotic distillation (OD) and direct contact membrane distillation (DCMD). Comparisons were made for lab scale OD and DCMD experiments on two types of PVDF hollow fibres under similar operating conditions for the concentration of glucose solutions from 30 to 60% (w/w) at temperatures as low as 25 to 45°C. Analysis of the results indicated that temperature was the most influencing factor for process improvement for both OD and DCMD. The flux in DCMD was improved by 3 to 4 times when feed temperature increased by 15 degrees, while this figure was nearly 3 times for OD when feed temperature increased by 20 degrees. The flow rates of the two streams played a more important role in maintaining the driving force, and consequently the flux rate, in DCMD rather than in OD. It was found that feed velocity had significant effect on DCMD performance, but insignificant in OD. Feed concentration, as the determining factor on water activity and viscosity, caused a more serious reduction of the flux rate in the high concentration range of 45-60% rather than in the dilute region of 30-40%. The effect was more significant in DCMD than in OD. The ratio of DCMD flux over that of OD ranged from 0.41 to 0.66 for PV375 when concentrating glucose solutions 30-40% w/w and from 0.35 to 0.69 for PV650 when concentrating high solid content ones. However, DCMD can overcome the disadvantages of OD being poor consumers perception, (due to the use of brine solution being a chemical), the potential problem of corrosion by the brine and the cost of its reconcentration.
Aging and Future Healthcare Expenditure: A Consistent Approach
Authors: Steinmann Lukas , Telser Harry , Zweifel Peter S.
Published: March 2007

The impact of aging on healthcare expenditure (HCE) has been at the center of a prolonged debate. This paper purports to shed light on several issues of this debate by presenting new evidence on the "red herring" hypothesis advanced by Zweifel, Felder and Meier (1999). This hypothesis amounts to distinguishing a mortality from a morbidity component in healthcare expenditure (HCE) and claiming that failure to make this distinction results in excessive estimates of future growth of HCE. A re-estimation based on a much larger data set is performed, using the refined econometric methodology. The main contribution is consistency, however. Rather than treating the mortality component as a residual in forecasting, its dynamics are analyzed in the same detail as that of the morbidity component when predicting the impact of population aging on the future growth of HCE. For the case of Switzerland, it finds this impact to be relatively small regardless of whether or not the mortality component is accounted for, thus qualifying the "red herring" hypothesis.
Effects of Dynamic and Static Imagery on Vividness of Imagery, Skiing Performance, and Confidence
Authors: Callow Nichola , Roberts Ross , Fawkes Joanna Z
Published: March 2007

The present study examined the effects of dynamic and static imagery on the vividness of imagery, down-hill ski-slalom performance, and confidence. An opportunistic sample of 24 race-standard skiers were randomly assigned to one of three groups; a dynamic imagery group, a static imagery group or a control group. Participants in the first two groups were administered an imagery script instructing them to imagine themselves completing the down-hill ski-slalom course. In addition, the dynamic group conducted the imagery in their ski equipment on the ski slope, where as, the static group conducted their imagery away from the snow, while seated in a chair. Once participants completed the imagery scripts, they were administered Hale's (1998) imagery vividness evaluation form. Participants in the control group conducted light stretches. After completing the respective imagery and light stretches, participants skied the course and then completed a post-experimental questionnaire. The time taken to complete each run was recorded. An independent t-test revealed a significant difference between the two imagery groups in terms of vividness of imagery, t = (16) = -3.28, p <.005 and confidence t = (16) = -3.59, p <.002. Visual inspection of the cell means indicated that the dynamic group had higher vividness and confidence scores than the static group. A one-way analysis of variance revealed a significant difference between the groups in the time taken to complete the course, F(2,21)=3.37, p < .05. Follow-up Tukey's tests indicated a significant difference between the control group and dynamic imagery group, with visual inspection of the means revealing that the dynamic group completed the task in the quickest time. The results are discussed in terms of dynamic imagery aiding the representational display in short-term working memory, and the use of dynamic imagery in applied settings.
Modern Trends in CFD Simulations: Application to GTL Technology
Authors: Akhtar Abid , Pareek Vishnu K , Tade Moses O
Published: March 2007

Multiphase flow processes are frequently observed in several important reactor technologies. These technologies are found in diverse applications such as in manufacture of petroleum-based fuels and products, conversion of synthesis gas into liquid hydrocarbons (Gas-to-liquid technology), production of commodity chemicals, pharmaceuticals, herbicides, pesticides, polymers etc. Due to the inherent complexity of these processes, the knowledge of fluid dynamic and transport parameters is necessary for development of appropriate reactor models and scale-up rules. It is, therefore, of paramount importance to develop understanding and predictive tools to simulate multiphase flow processes for better and economically viable reactor technologies. In the past, knowledge of hydrodynamics and transport characteristics of multiphase reactors has been interpreted in the form of empirical correlations, which have numerous restrictions in terms of their validity for different operating conditions. Computational fluid dynamics (CFD) simulation, on the other hand, deals with the solution of fluid dynamic equations on digital computers, requiring relatively few restrictive assumptions and thus giving a complete description of the hydrodynamics of these reactors. This detailed predicted flow field gives an accurate insight to the fluid behaviour and can sometimes give information, which cannot be obtained from experiments. These days, due to cheaper computational resources, CFD simulations are becoming economically reliable for modeling of multiphase processes including GTL (Gas-to-liquid) processes. In this paper, a comprehensive review of different multiphase flow simulation approaches has been presented. The recent progress made in hydrodynamic modeling of multiphase reactors, their capabilities and limitations (with special focus on GTL processes) are discussed in detail. Finally, case studies with different simulation approaches (Eulerian-Eulerian and VOF (Volume of fluid) simulations of bubble column reactors operating in different flow regimes) are discussed to demonstrate the power of this emerging research tool.
Robust Temperature Stabilization for Fluid Catalytic Cracking Units Using Extended Kalman-Type Estimators
Authors: Aguilar-López Ricardo , Maya-Yescas Rafael
Published: March 2007

Fluidised-bed Catalytic Cracking (FCC) units, are one of the most complex and interactive processes in the refining industry, hence they are difficult to operate and to control; on the other hand they are one of the main producers of gasoline, which is an incentive to improve operation policies. This work deals with the design of regulative control law for stabilisation of reactor and regenerator temperatures considering that kinetics terms are poorly known, which is the industrial case. This control law uses on-line estimates of the heat of reaction, obtained from Kalman-like filtering of measured temperatures. The controllers designed are similar to standard input-output linearising controllers and can be tuned by standard techniques. Performance of the estimation technique under closed-loop operation is analysed by numerical simulations, considering noisy measurements and time delay in the regenerator control input.
CFD Simulations for Continuous Flow of Bubbles through Gas-Liquid Columns: Application of VOF Method
Authors: Akhtar Abid , Pareek Vishnu , Tadé Moses
Published: March 2007

Hydrodynamics study of a continuous bubble chain rising through liquid column has been performed for laboratory scale bubble column using the volume-of-fluid (VOF) approach. The effect of operating and design parameters on the bubble size distribution and rise trajectory has been investigated for air-water system. For the same distributor, simulation results have indicated the formation of small bubbles at low superficial gas velocity and relatively large bubbles at higher velocities. The increase in the hole-size of distributor has shown similar behaviour. Analysis of bubble trajectories for different superficial gas velocities and distributors has demonstrated an oscillatory behaviour exhibited by small bubbles formed at low superficial gas velocity. A reasonable agreement between the predicted values of gas hold-up with the experimental work has validated the present model.
Performance Analysis of Three Controllers for the Polymerisation of Styrene in a Batch Reactor
Authors: Ekpo Emmanuel E , Mujtaba Iqbal M
Published: March 2007

The performance analysis of three advanced non linear controllers is the main focus of this paper. All three controllers are applied for the control of a batch polymerisation reactor which is defined by a very simple kinetic model for the polymerisation of styrene. This simple set of equations describing the polymerisation process is first solved using the sequential strategy i.e. Control Vector Parameterisation (CVP) technique within gPROMS to find optimal initial initiator concentrations and the reactor temperature trajectory necessary to yield desired polymer molecular properties (defined here as fixed values of monomer conversion and number average chain length) in minimum time. The sequential solution strategy has had limited application in solving optimisation problems for polymerisation in batch reactors, most researchers instead employing the Pontryagin's Maximum Principle (PMP) to solve optimal control problems involving these systems.The temperature trajectory obtained from the dynamic optimisation is used as the setpoint to be tracked by the three controllers: Dual Mode control with PID, which is representative of industrial practice, Generic Model Control (GMC) with Neural Networks as online heat release estimator, and Direct Inverse Control (DIC). Published work on the last two controllers as applied to the control of a batch polymerisation reactor is absent from the literature.When the performances of the different controllers are evaluated, it is seen that the GMC-NN controller performs better than the other two for the system under consideration.
Analysis and Simulation of Cross-Flow Reactor for Ethylene Epoxidation
Authors: Alhumaizi Khalid Ibrahem , Abahussain Abdulaziz
Published: March 2007

A steady-state cross-flow reactor for ethylene epoxidation was simulated using industrial data (low oxygen/ethylene feed ratio) and pilot plant data (high oxygen/ethylene feed ratio). A comparison between the conventional fixed-bed reactor and the cross-flow reactor with two types of feeding modes was performed. The present study showed the possibility of enhancing the reactor yield by distributing the ethylene optimally at equal spaced along the reactor for both commercial and pilot plant cases. We have shown that the evenly distributed feeding mode does not increase the desired ethylene oxide yield. The model results confirmed that the cross-flow reactor with ethylene is the best configuration, followed by the conventional fixed-bed reactor and the cross-flow reactor with oxygen, respectively.
On-line Monitoring in an Aerobic Batch Bioreactor Employing a Robust Soft Sensor
Authors: Aguilar-López Ricardo
Published: March 2007

The main objective of this work is to design a soft sensor with finite convergence time for a class of batch reacting systems. Considering the necessity to fast response for monitoring and control issues for batch processes a finite time high order sliding-mode observer is considered.Theoretical analysis is developed to demonstrate the convergence properties of the proposed observer and the finite time of convergence is calculated from the analysis. A simple model for a batch wastewater bioreactor corrobored experimentally is proposed as application example and numerical experiments show the adequate observer performance compared to a standard nonlinear Luenberger observer.
Dynamic Simulation and Optimization of Two-Stage Extractive Alcoholic Fermentation Process: Design Impact on Controllability
Authors: Nandong Jobrun , Samyudia Yudi , Tadé Moses O
Published: March 2007

In this paper, we address dynamic controllability of the two different designs of extractive fermentation process, namely one-stage and two-stage designs. The operating conditions that maximize yields and productivity for both designs are determined by optimization using the method of factorial design and response surface analysis. The results show that in terms of the achievable yield and productivity, the performance of the two-stage design is comparable to that of the single-stage, but the former design leads to a significant reduction in the fermentor size required. Furthermore, we analyze the dynamic controllability of the two designs of extractive fermentation process using a so-called control relevant metrics to examine their closed-loop dynamic performance in the face of uncertainty. This analysis reveals that the single-stage design has more favorable dynamic controllability than the two-stage design.
Estimating Output Variance in Closed Loop Systems
Authors: Tham Ming T. , Jones Richard W. , Al-Hinai Ibrahim
Published: March 2007

This paper attempts to address a common difficulty encountered when trying to justify a process control revamp or upgrading project  the ability to quantify potential savings/profits. A relatively simple procedure that is applicable to both continuous and digital controllers is described. Given models of the process and the controller, knowledge of the disturbance frequencies and their variances, the method is able to predict accurately the variance of the controlled output of linear control systems.