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Various Operating Conditions (various + operating_condition)
Selected AbstractsDS/CDMA throughput of a multi-hop sensor network in a Rayleigh fading underwater acoustic channelCONCURRENCY AND COMPUTATION: PRACTICE & EXPERIENCE, Issue 8 2007Choong Hock Mar Abstract Asynchronous half-duplex Direct-Sequence Code-Division Multiple-Access (DS/CDMA) is a suitable candidate for the MAC protocol design of underwater acoustic (UWA) sensor networks owing to its many attractive features. Our ad-hoc multi-hop network is infrastructureless in that it is without centralized base stations or power control. Hence, we develop an asynchronous distributed half-duplex control protocol to regulate between the transmitting and receiving phases of transmissions. Furthermore, multi-hop communications are very sensitive to the time variability of the received signal strength in the fading channel and the ambient noise dominated by snapping shrimp in harsh underwater environments, because a broken link in the multi-hop path is enough to disrupt communications and initiate new route searches. In our configuration, we use the Ad hoc On-demand Distance Vector (AODV) routing protocol optimized for UWA networks. Empirical studies show that we can model the channel as a slow-varying frequency non-selective Rayleigh fading channel. We theoretically analyze the throughput of our configuration by considering three salient features: the ability of the receiver to demodulate the data, the effect of our control protocol and the effect of disconnections on the generation of routing packets. The throughput under various operating conditions is then examined. It is observed that at optimal node separation, the throughput is improved by a factor of 10. Copyright © 2007 John Wiley & Sons, Ltd. [source] Cyclical electrical field flow fractionationELECTROPHORESIS, Issue 9 2005Bruce K. Gale Abstract Cyclical electrical field flow fractionation (Cy/ElFFF) is demonstrated in a standard electrical field flow fractionation (ElFFF) channel for the first time. Motivation for the use of alternating current (AC) fields in a traditionally direct current (DC) technique are discussed. The function of the system over a wide range of operating conditions is explored and challenges associated with various operating conditions reported. Retention of polystyrene nanoparticle standards is accomplished and the effect of varying parameters of the applied field, such as voltage and frequency, are explored. The first separations using this technique are demonstrated. The experimental results are compared to analytical models previously reported in the literature. The general trend of the experimental results is similar to those predicted in theoretical models and possible reasons for discrepancies are elucidated. Suggestions are made for improving the separation and analysis method, and possible applications explored. [source] Along-channel mathematical modelling for proton exchange membrane fuel cellsINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 12 2005Wenbo Huang Abstract Proper water and thermal management is essential for obtaining high performance of proton exchange membrane fuel cells (PEMFCs). A steady, two-dimensional water and thermal management model was developed, aiming at considering pressure effects (i.e. the effects of local pressure on the cell performance), pressure drop, open circuit voltage variation with stack temperature, water vapour effects on membrane conductivity, which made the model physically more reasonable and more suitable for various operating conditions. The model could predict the distributions of a series of important parameters along the flow channel, and thus the effects of various operating and design parameters on the fuel cell performance could be investigated easily by numerical trial-and-error method. The modelling results compared well with the available experimental results from the literatures. The results also showed that the humidification of both anode and cathode is crucial for the performance of PEMFCs. The model could be a very useful engineering tool for the optimization of PEMFCs. Copyright © 2005 John Wiley & Sons, Ltd. [source] A study on latent heat storage exchangers with the high-temperature phase-change materialINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 4 2001Qiao He Abstract This paper presents a theoretical analysis and an experimental test on a shell-and-tube latent heat storage exchanger. The heat exchanger is used to recover high-temperature waste heat from industrial furnaces and off-peak electricity. It can also be integrated into a renewable energy system as an energy storage component. A mathematical model describing the unsteady freezing problem coupled with forced convection is solved numerically to predict the performance of the heat exchanger. It provides the basis for an optimum design of the heat exchanger. The experimental study on the heat exchanger is carried out under various operating conditions. Effects of various parameters, such as the inlet temperature, the mass flow rate, the thickness of the phase-change material and the length of the pipes, on the heat transfer performance of the unit are discussed combined with theoretical prediction. The criterion for analyzing and evaluating the performance of heat exchanger is also proposed. Copyright © 2001 John Wiley & Sons, Ltd. [source] Characterization and comparison of traffic flow on reversible roadwaysJOURNAL OF ADVANCED TRANSPORTATION, Issue 2 2010Laurence Lambert Abstract Reversible traffic operations have become an increasingly popular strategy for mitigating traffic congestion associated with the directionally unbalanced traffic flows that are a routine part of peak commute periods, planned special events, and emergency evacuations. It is interesting that despite its widespread and long-term use, relatively little is known about the operational characteristics of this form of operation. For example, the capacity of a reversed lane has been estimated by some to be equal to that of a normal lane while others have theorized it to be half of this value. Without accurate estimates of reversible lane performance it is not possible to confidently gauge the benefits of reversible roadways or model them using traffic simulation. This paper presents the results of a study to measure and evaluate the speed and flow characteristics of reverse-flow traffic streams by comparing them under various operating conditions and locations. It was found that, contrary to some opinions, the flow characteristics of reverse-flowing lanes were generally similar to normally flowing lanes under a variety of traffic volume, time-of-day, location, and type-of-use conditions. The study also revealed that drivers will readily use reversible lanes without diminished operating speeds, particularly as volumes increase. Copyright © 2010 John Wiley & Sons, Ltd. [source] Nitrite accumulation characteristics of high strength ammonia wastewater in an autotrophic nitrifying biofilm reactorJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 4 2003Ho-Joon Yun Abstract Selective nitrification was carried out to accumulate nitrite from high strength ammonia wastewater in an autotrophic nitrifying biofilm reactor. Nitrification efficiencies and nitrite accumulation characteristics were investigated at various operating conditions such as ammonium load, oxygen supply and free ammonia concentration. The biofilm reactor showed very stable nitrification efficiencies of more than 90% at up to 2,kg,NH4 -N,m,3,d,1 and the nitrite content was maintained at around 95%. Inhibition by free ammonia on nitrite oxidizers seems to be the major factor for nitrite accumulation. Batch kinetic analyses of ammonium and nitrite oxidation showed that nitrite oxidation activity was selectively inhibited in the presence of free ammonia. However, the activity recovered quickly as the free ammonia concentration decreased below the threshold inhibition concentration. Examination of specific ammonia and nitrite oxidation activities and the most probable number indicated that the number of nitrite-oxidizing microorganisms in the nitrite-accumulating system was less than that in the normal nitrification system due to long-term free ammonia inhibition of the nitrite oxidizers. The reduced population of nitrite oxidizers in the biofilm system was also responsible for the accumulation of nitrite in the biofilm reactor. © 2003 Society of Chemical Industry [source] Effect of a chemical synthesis-based pharmaceutical wastewater on performance, acetoclastic methanogenic activity and microbial population in an upflow anaerobic filterJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 6 2002B Kasapgil Ince Abstract The performance of an upflow anaerobic filter (UAF) treating a chemical synthesis-based pharmaceutical wastewater was evaluated under various operating conditions. During start-up, the UAF was initially fed by glucose till an organic loading rate (OLR) of approximately 7.5,kg COD m,3 day,1 with a hydraulic retention time of 2.3 days. A soluble COD removal efficiency of 98% was achieved before the addition of the wastewater. Initially, the filter inertia was acclimatized to the wastewater by sequential feeding of 10% (w/v), 30% (w/v) and 70% (w/v) of the pre-aerated wastewater mixed with glucose followed by a 100% (w/v) pre-aerated wastewater. During the operation, the COD removal efficiency and methane yield decreased to 75% and 0.30,m3 CH4,kg,1 CODremoved respectively. As the UAF became accustomed to the pre-aerated wastewater, raw wastewater was fed in increasing ratios of 20% (w/v), 60% (w/v) and 80% (w/v) with the pre-aerated wastewater as the remaining part. During this stage of the operation, a COD removal efficiency in a range of 77,86% was achieved and the methane yield decreased to 0.24,m3 CH4,kg,1 CODremoved. Finally, 100% (w/v) raw wastewater was fed and a COD removal efficiency of 65% was achieved with a methane yield of 0.20,m3 CH4,kg,1 CODremoved. At the end of the operation, acetoclastic methanogenic activity was only measured in the bottom section of the UAF, this showed a 90% reduction in comparison with activity of inoculation sludge. Microscopic examinations revealed that rod-shaped methanogens remained as the dominant species whereas Methanosarcina -like species and filaments were present only in insignificant numbers along the UAF. © 2002 Society of Chemical Industry [source] A cross-coupling controller using an H, scheme and its application to a two-axis direct-drive robotJOURNAL OF FIELD ROBOTICS (FORMERLY JOURNAL OF ROBOTIC SYSTEMS), Issue 10 2002Ren-Wu Fang A cross-coupling controller (CCC) using an H, control scheme has been proposed to reduce the contouring error for a two-axis, direct-drive robot in tracking linear and circular contours effectively. Under the consideration that contour-tracking performance is a primary target over point-to-point tracking performance in a trajectory-tracking task, a CCC has been associated with joint controllers to reduce the contouring error by coordinating the motion of a two-axis robot arm. Contouring performance can thus be improved significantly. Furthermore, the proposed CCC design, which is a typical Multi-Input Multi-Output (MIMO) system with linear time varying (LTV) characteristics, has been verified as being internally stable. A USM (ultrasonic motor)-driven, two-axis, direct-drive robot is utilized to demonstrate the feasibility of the proposed scheme. Several experiments under various operating conditions are performed to validate its efficacy, and the results showed that the proposed scheme can reduce the contouring error significantly. © 2002 Wiley Periodicals, Inc. [source] SUBCRITICAL WATER EXTRACTION OF CAFFEINE FROM BLACK TEA LEAF OF IRANJOURNAL OF FOOD PROCESS ENGINEERING, Issue 3 2008ANVAR SHALMASHI ABSTRACT This study examines subcritical water extraction (SCWE) of caffeine from black tea leaf. The effects of various operating conditions such as water temperature (100, 125, 150 and 175C), water flow rate (1, 2 and 4 g/min), mean particle size (0.5, 1 and 2 mm) on extraction yield and rate were determined. SCWE at 175C, water flow rate of 2 g/min and mean particle size of 0.5 mm were found to be able to recover 3.82% (w/w) of caffeine present in the black tea leaf within 3 h of extraction. In comparison to the SCWE, conventional hot water extraction showed 3.30% (w/w) extraction yield. It was found also that pressure had no effect on extraction yield and rate. PRACTICAL APPLICATIONS Recently, subcritical water has become of great interest as an alternative solvent for extraction of natural active compounds. Subcritical water, as a green solvent, can be used in many different fields of applications. In recent years, extraction of flavors, fragrances and antioxidant components from plant materials, and hydrolysis of carbohydrates, vegetable oils and fatty acids have been widely investigated by many researchers. Using subcritical water for analytical purposes, for soil remediation and applying it as a reaction media are some other interesting fields for practical applications. Subcritical water is an excellent solvent for caffeine as well as many other organic compounds but is safer than the organic solvents that are used for caffeine extraction. [source] Kinetic and dynamic study of liquid,liquid extraction of copper in a HFMC: Experimentation, modeling, and simulationAICHE JOURNAL, Issue 6 2010M. Younas Abstract In this work, we present the dispersion-free liquid,liquid extraction of copper from aqueous streams in a hollow fiber membrane contactor (HFMC). Copper has been transferred from aqueous solutions to heptane using LIX 84-I (2-hydroxy-5-nonylacetephenone oxime) as extracting agent. In a first step, batch experiments have been performed to identify the extraction kinetics and to measure the partition coefficient of copper aqueous-organic phase system. Then, the continuous recycled-base extraction process has been performed in a HFMC Liqui-Cel® module. The module has been modeled from resistance in series concept to gain the exit concentrations, which are used to develop a dynamic model to calculate the exit concentration of copper from the output of storage tanks. The model has been validated with experimental data at various operating conditions. The integrated process model algorithm was scripted in MATLAB® 7.4 R (a). Simulations have been made for a range of different operating parameters to determine the optimum criterion conditions. © 2009 American Institute of Chemical Engineers AIChE J, 2010 [source] Modeling and design of vapor-phase biofiltration for chlorinated volatile organic compoundsAICHE JOURNAL, Issue 9 2002Walter Den A mathematical model was developed for biofilter design and performance prediction with reference to the purification of contaminated gas streams. The model incorporated important aspects such as mass transfer, biodegradation, and adsorption processes. A systematic modeling protocol incorporated the development of a scale-up strategy based on dimensional analysis and similitude. Trichloroethylene (TCE) was employed as the model contaminant for biofiltration testing and model verification. The biokinetic and adsorption parameters for the contaminant were determined independently from a series of minibiofilter and miniadsorber column experiments, specifically designed to simulate the actual biofilter operational regimes in a miniature scale. Bench-scale biofilter experiments employing granular activated carbon columns indicated the good predictive capability of the model for the removal of TCE. Dynamic simulation studies were performed to assess the transient- and steady-state behavior of the model under various operating conditions. Model sensitivity was studied to evaluate the influence of adsorption equilibrium, transport and biological parameters on the biofilter dynamics. The results demonstrated that the biofilter performance was greatly influenced by the Monod coefficients and the biofilm thickness. [source] Modeling of air separation in a LSCF hollow-fiber membrane moduleAICHE JOURNAL, Issue 7 2002Xiaoyao Tan Mixed ion-conducting ceramic membranes are promising in oxygen separation from air due to their infinite permselectivity. Hollow-fiber-shaped membranes can provide a high surface area for such an application. A mathematical model for a hollow-fiber La0.6Sr0.4Co0.2F0.8O3,,(LSCF) membrane module for air separation was developed and a performance of the module at various operating conditions was studied theoretically. The simulation results reveal that the cocurrent is a better operating flow pattern than the countercurrent flow pattern. The vacuum operation on the lumen side of the membrane module is preferable to the elevated pressure operation on the shell side for achieving high oxygen productivity. A high vacuum level and a desired membrane area are essential to produce the pure oxygen and nitrogen simultaneously. Experimental results and kinetic parameters in the literature obtained from the LSCF membrane for air separation agreed satisfactorily with the theoretical solutions. [source] Gas chromatographic retention in uncoated fused silica capillariesJOURNAL OF SEPARATION SCIENCE, JSS, Issue 18 2009Matthew S. Klee Abstract Understanding of retention in uncoated fused-silica capillaries is of interest due to increased attention on precolumn backflushing in capillary GC. Uncoated capillaries offer several advantages as precolumns compared to coated precolumns. In order to examine the possibility of predicting elution temperatures of alkanes from uncoated capillaries a priori, several sizes of deactivated but uncoated fused-silica capillaries were evaluated under various operating conditions. Retention was found to depend on dimensionless ramp rate (°C/tM), sample loading (capacity), flow mode, and column dimensions (probably related to surface area). [source] Simulations of grafting monomers and associated degradation of polypropylene in a modular co-rotating twin screw extruderJOURNAL OF VINYL & ADDITIVE TECHNOLOGY, Issue 4 2005Jongmin Keum Kinetic models of grafting maleic anhydride (MAH) and methyl methacrylate (MMA) on polypropylene (PP) were developed for screw extrusion. However, the kinetic models were insufficient to explain the grafting reactions along the length of modular co-rotating twin screw extruders because the rheological properties and the residence time of PP changed owing to degradation of PP during the grafting reaction. In order to model this system for a modular co-rotating twin screw extruder, the kinetic model of grafting reaction and models for degradation of PP were combined with fluid mechanics and heat transfer. Given the geometrical configurations of the screw, the operating conditions, and the physical properties of the polypropylene, the simulations predicted variation of molecular weight and mean residence time due to degradation of PP. The weight percent of grafted MAH or MMA on PP profiles along the screw axis was also calculated in the simulation. These predictions were compared with experimental data for various operating conditions. J. VINYL. ADDIT. TECHNOL. 11:143,149, 2005. © 2005 Society of Plastics Engineers. [source] Simulation and validation of ethanol removal from water in an adsorption packed bed: Isotherm and mass transfer parameter determination in batch studiesTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 5 2010R. A. Jones Abstract Preferential adsorption of ethanol from ethanol/water mixtures in batch equilibrium and kinetic experiments were carried out on a commercially available activated carbon adsorbent Filtrasorb 600 (F-600). A model based on finite difference method was developed and employed to determine the mass transfer parameters and equilibrium behaviour for the adsorption of ethanol from simple batch systems. The estimates of the adsorption isotherm along with the mass transfer parameters were used to simulate the transient performance that could be expected in a packed bed under various operating conditions (feed flow rate, feed concentration, and particle size). The applicability of the simulation results were found to be a good match with experimental packed bed experiments over the entire range of operating conditions tested. La cinétique et l'isotherme d'adsorption de l'éthanol des mélanges eau/éthanol lors d'expériences en discontinus ont été déterminées pour un adsorbant au charbon activé disponible dans le commerce, le Filtrasorb 600 (F-600). Un modèle basé sur la méthode des différences finies a été développé et utilisé pour déterminer les paramètres de transfert de matière et étudier le comportement à l'équilibre pour l'adsorption préférentielle de l'éthanol en systèmes discontinus. Les estimations de l'isotherme d'adsorption aussi bien que les paramètres de transfert de matière ont été utilisées pour simuler la performance en régime transitoire d'un lit d'adsorbant sous diverses conditions de fonctionnement (taux d'écoulement du mélange, concentration du mélange et la taille des particules). L'applicabilité des résultats de simulation s'est avérée tout à fait concordante avec les données expérimentales sous toutes les conditions de fonctionnement examinées. [source] Analysis of a perovskite ceramic hollow fibre membrane reactor for the partial oxidation of methane to syngasASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 3 2009Xiaoyao Tan Abstract A mathematical model of an oxygen permeable dense ceramic hollow membrane reactor packed with a Ni/,-Al2O3 catalyst for the partial oxidation of methane (POM) to syngas has been developed. With the present model, various operating conditions such as temperature, operating pressures and feed concentrations affecting the performance of the reactor were investigated theoretically. The applied membrane area plays the key role in the operation of the membrane reactor. Assuming that the La0.6Sr0.4Co0.2Fe0.8O3,, (LSCF) membrane is stable under the pressures and temperatures operated, the optimum membrane area required for the POM to syngas is predicted to be varied from 98 to 16 cm2 per cm3/s (STP) of methane feed when the operating temperatures are increased from 1148 to 1248 K. In order to run the membrane reactor economically and safely, the pressures in both shell and lumen sides should be kept close to one atmosphere. Copyright © 2009 Curtin University of Technology and John Wiley & Sons, Ltd. [source] Simulation of Barium Sulfate Precipitation using CFD and FM-PDF Modeling in a Continuous Stirred TankCHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 12 2007Z. Wang Abstract A mixing-precipitation model combining computational fluid dynamics (CFD), finite-mode PDF (probability density function) model, population balance and kinetic modeling has been proposed to simulate the barium sulfate precipitation process in a continuous stirred tank agitated by a Rushton turbine. The effect of various operating conditions such as impeller speed, feed concentration, feed position and mean residence time on the barium sulfate precipitation process is clearly demonstrated. It is shown that the mean crystal size increases by increasing the impeller speed and mean residence time. However, when the feed concentration is increased, the mean crystal size decreases. The predictions are in reasonable agreement with the experimental data in the literature. [source] | |||||||||||||