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Operating Pressure (operating + pressure)
Selected AbstractsSupercritical extraction of borage seed oil coupled to conventional solvent extraction of antioxidantsEUROPEAN JOURNAL OF LIPID SCIENCE AND TECHNOLOGY, Issue 11 2008Carmen Soto Abstract This paper describes the extraction of borage seed oil by supercritical carbon dioxide (SC-CO2) and the further extraction of antioxidants from the SC-CO2 -defatted borage meal with organic solvents (water, methanol, ethanol and ethyl acetate). The optimal conditions for oil extraction were obtained at 303 and 323,K at 200,bar, 2.5,h and a continuous flow of CO2 of 1.5,L/h introduced through the bottom when the operating pressure and temperature were reached, attaining a yield of 60%. Borage oil is rich in unsaturated fatty acids; oleic acid, linoleic acid and linolenic acid accounted for 74% of the total fatty acid content under the above conditions. The highest extraction yield was achieved using water or methanol as extracting solvent from the SC-CO2 -defatted borage meal at 303,K and pressures of 200 and 150,bar for water and methanol, respectively. The most potent extracts, according to all methods tested, were obtained with water and methanol. [source] Numerical simulation of rotating bending process for U-tubes in heat exchangersFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 10 2009H.-S. KIM ABSTRACT Heat exchangers comprise thousands of tubes having U-shaped portions. Rotating bending method has been widely utilized to make U-bends. Although this method shows an excellent performance, cracks have been frequently detected in the U-bends due to residual stresses induced by bending. In this paper, the bending process is simulated based on elastic,plastic finite element analyses in order to investigate the magnitude and distribution of the residual stresses including the effects of operating pressure. Analyses results show that the residual stress increases as the radius of U-bend decreases and that operating pressure has a detrimental effect in terms of stress corrosion cracking at the intrados of U-bend. It is thought that these results can be utilized for the estimations of fracture mechanics parameters such as limit load, stress intensity factor and J-integral, prevention of the cracking, and establishment of the optimum inspection strategy for the heat exchanger tubes. [source] Assessment of fire protection performance of water mist applied in exhaust ducts for semiconductor fabrication processFIRE AND MATERIALS, Issue 5 2005Yi-Liang Shu Abstract Fume exhaust pipes used in semiconductor facilities underwent a series of fire tests to evaluate the performance of a water mist system. The parameters considered were the amount of water that the mist nozzles used, the air flow velocity, the fire intensity and the water mist system operating pressure. In order to make a performance comparison, tests were also performed with a standard sprinkler system. The base case served as a reference and applied a single water mist nozzle (100 bar operating pressure, 7.3 l/min water volume flux and 200 µm mean droplet size) installed in the pipe (60 cm in diameter) subjected to a 350°C air flow with an average velocity of 2 m/s. In such a case, the temperature in the hot flow dropped sharply as the water mist nozzle was activated and reached a 60°C saturation point. Under the same operating conditions, four mist nozzles were applied, and made no further contribution to reducing the fire temperature compared with the case using only a single nozzle. Similar fire protection performances to that in the base case were still retained when the exhaust flow velocity increased to 3 m/s and the inlet air temperature was increased to 500°C due to a stronger input fire scenario, respectively. Changing to a water mist system produced a better performance than a standard sprinkler. With regard to the effect of operating pressure of water mist system, a higher operating pressure can have a better performance. The results above indicate that the droplet size in a water-related fire protection system plays a critical role. Copyright © 2005 John Wiley & Sons, Ltd. [source] Performance analysis of a solid oxide fuel cell with reformed natural gas fuelINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 11 2010S. M. Jafarian Abstract In the present study a two-dimensional model of a tubular solid oxide fuel cell operating in a stack is presented. The model analyzes electrochemistry, momentum, heat and mass transfers inside the cell. Internal steam reforming of the reformed natural gas is considered for hydrogen production and Gibbs energy minimization method is used to calculate the fuel equilibrium species concentrations. The conservation equations for energy, mass, momentum and voltage are solved simultaneously using appropriate numerical techniques. The heat radiation between the preheater and cathode surface is incorporated into the model and local heat transfer coefficients are determined throughout the anode and cathode channels. The developed model has been compared with the experimental and numerical data available in literature. The model is used to study the effect of various operating parameters such as excess air, operating pressure and air inlet temperature and the results are discussed in detail. The results show that a more uniform temperature distribution can be achieved along the cell at higher air-flow rates and operating pressures and the cell output voltage is enhanced. It is expected that the proposed model can be used as a design tool for SOFC stack in practical applications. Copyright © 2009 John Wiley & Sons, Ltd. [source] Exergetic performance analysis of a PEM fuel cellINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 5 2006M. Ay Abstract In this paper we investigate the effects of thermodynamic irreversibilities on the exergetic performance of proton exchange membrane (PEM) fuel cells as a function of cell operating temperature, pressures of anode and cathode, current density, and membrane thickness. The practical operating conditions are selected to be 3,5 atm for anode and cathode pressures, and 323,353 K for the cell temperatures, respectively. In addition, the membrane thicknesses are chosen as 0.016, 0.018 and 0.02 cm, respectively. Moreover, the current density range of the PEM fuel cell is selected to be 0.01,2.0 A cm,2. It is concluded that exergy efficiency of PEM fuel cell decreases with a rise in membrane thickness and current density, and increases with a rise of cell operating pressure and with a decrease of current density for the same membrane thickness. Thus, it can be said that, in order to increase the exergetic performance of PEM fuel cell, the lower membrane thickness, the lower current density and the higher cell operating pressure should be selected in case PEM fuel cell is operated at constant cell temperature. Copyright © 2005 John Wiley & Sons, Ltd. [source] Effect of pressure on thermal aspects in the riser column of a pressurized circulating fluidized bedINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 3 2006A. V. S. S. K. S. Gupta Abstract In the present paper the effect of pressure on bed-to-wall heat transfer in the riser column of a pressurized circulating fluidized bed (PCFB) unit is estimated through a modified mechanistic model. Gas,solid flow structure and average cross-sectional solids concentration play a dominant role in better understanding of bed-to-wall heat transfer mechanism in the riser column of a PCFB. The effect of pressure on average solids concentration fraction ,c' in the riser column is analysed from the experimental investigations. The basic cluster renewal model of an atmospheric circulating fluidized bed has been modified to consider the effect of pressure on different model parameters such as cluster properties, gas layer thickness, cluster, particle, gas phase, radiation and bed-to-wall heat transfer coefficients, respectively. The cluster thermal conductivity increases with system pressure as well as with bed temperature due to higher cluster thermal properties. The increased operating pressure enhances the particle and dispersed phase heat transfer components. The bed-to-wall heat transfer coefficient increases with operating pressure, because of increased particle concentration. The predicted results from the model are compared with the experimentally measured values as well as with the published literature, and a good agreement has been observed. The bed-to-wall heat transfer coefficient variation along the riser height is also reported for different operating pressures. Copyright © 2005 John Wiley & Sons, Ltd. [source] Modelling CO poisoning and O2 bleeding in a PEM fuel cell anodeINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 12 2003J.J. Baschuk Abstract Fuel gas containing carbon monoxide severely degrades the performance of a polymer electrolyte membrane (PEM) fuel cell. However, CO poisoning can be mitigated by introducing oxygen into the fuel (oxygen bleeding). A mathematical PEM fuel cell model is developed that simulates both CO poisoning and oxygen bleeding, and obtains excellent agreement with published, experimental data. Modelling efforts indicate that CO adsorption and desorption follow a Temkin model. Increasing operating pressure or temperature mitigates CO poisoning, while use of reformate fuel increases the severity of the poisoning effect. Although oxygen bleeding mitigates CO poisoning, an unrecoverable performance loss exists at high current densities due to competition for reaction sites between hydrogen adsorption and the heterogeneous catalysis of CO. Copyright © 2003 John Wiley & Sons, Ltd. [source] Influence of elevated pressure and particle lyophobicity on hydrodynamics and gas,liquid mass transfer in slurry bubble columnsAICHE JOURNAL, Issue 3 2010Vinit P. Chilekar Abstract This article reports on the influence of elevated pressure and catalyst particle lyophobicity at particle concentrations up to 3 vol % on the hydrodynamics and the gas-to-liquid mass transfer in a slurry bubble column. The study was done with demineralized water (aqueous phase) and Isopar-M oil (organic phase) slurries in a 0.15 m internal diameter bubble column operated at pressures ranging from 0.1 to 1.3 MPa. The overall gas hold-up, the flow regime transition point, the average large bubble diameter, and the centerline liquid velocity were measured along with the gas,liquid mass transfer coefficient. The gas hold-up and the flow regime transition point are not influenced by the presence of lyophilic particles. Lyophobic particles shift the regime transition to a higher gas velocity and cause foam formation. Increasing operating pressure significantly increases the gas hold-up and the regime transition velocity, irrespective of the particle lyophobicity. The gas,liquid mass transfer coefficient is proportional to the gas hold-up for all investigated slurries and is not affected by the particle lyophobicity, the particle concentration, and the operating pressure. A correlation is presented to estimate the gas,liquid mass transfer coefficient as a function of the measured gas hold-up: . © 2009 American Institute of Chemical Engineers AIChE J, 2010 [source] Analysis of cake filtration data,A critical assessment of conventional filtration theoryAICHE JOURNAL, Issue 10 2006Soo-Khean Teoh Abstract Experimental results of constant-pressure cake filtration of aqueous suspensions of four kinds of particles: CaCO3, Kaolin, Kromasil and TiO2 is presented. The data reported consist mainly of filtration performance results, that is, the cumulative filtrate volume and cake thickness as functions of time, which were obtained using a newly developed multifunction test cell. Based on these data, the medium resistance and the average cake specific resistance at various operating pressure were evaluated and corroborated with the results obtained from the compression-permeability (C-P) cell measurements. The filtration results were also compared with predictions from the solutions of the appropriate volume-averaged equations of continuity using different pl , ps relationships. Generally speaking, with the appropriate pl , ps relationship, agreement between experiments and prediction was satisfactory. © 2006 American Institute of Chemical Engineers AIChE J, 2006 [source] Fischer-Tropsch synthesis product grade optimization in a fluidized bed reactorAICHE JOURNAL, Issue 8 2006Fabiano A. N. Fernandes Abstract Fischer-Tropsch synthesis is an important chemical process for the production of liquid fuels and olefins. In recent years, the abundant availability of natural gas and the increasing demand of olefins, gasoline, diesel and waxes have led to a high interest in further developing this process. A mathematical model of a fluidized-bed reactor used for syngas polymerization was developed and the carbon monoxide polymerization was studied from a modeling point of view. Simulation results show that several parameters affect syngas conversion and carbon product distribution, such as operating pressure, superficial gas velocity, bed porosity, and syngas composition. Optimization of liquid hydrocarbon products was done and the best operating conditions for their production were found for an iron catalyst that produces hydrocarbon chains according to a dual mechanism theory. © 2006 American Institute of Chemical Engineers AIChE J, 2006 [source] The application of small porous particles, high temperatures, and high pressures to generate very high resolution LC and LC/MS separationsJOURNAL OF SEPARATION SCIENCE, JSS, Issue 8 2007Robert Plumb Abstract The effect of combining sub-2 ,m porous particles with elevated operating temperatures on chromatographic performance has been investigated in terms of chromatographic efficiency, productivity, peak elution order, and observed operating pressure. The use of elevated temperature in LC does not increase the obtainable performance but allows the same performance to be obtained in less time. Increasing the column temperature did allow the use of longer columns, generating column efficiencies in excess of 100 000 plates and gradient peak capacities approaching 1000. Raising the temperature increased the optimal mobile phase linear velocity, negating somewhat the pressure benefits observed by reducing the solvent viscosity. When operating at higher temperature the analyte retention is not only reduced, but the order of elution will also often change. High temperature separations allowed exotic organic modifiers such as isopropanol to be exploited for alternative selectivity and faster analysis. Finally, care must be taken when using high temperature separations to ensure that the narrow peak widths produced do not compromise the quality of data obtained from detectors such as high resolution mass spectrometers. [source] Day-to-day reproducibility of anorectal sensorimotor assessments in healthy subjectsNEUROGASTROENTEROLOGY & MOTILITY, Issue 2 2004A. E. Bharucha Abstract, The reproducibility of tests widely utilized to assess anorectal sensorimotor functions is not well established. Our aims were to assess the intra-individual day-to-day reproducibility of these parameters in healthy subjects. Anal sphincter pressures were assessed by perfusion manometry on two separate days in 19 healthy subjects. Rectal pressure,volume (p,v) curves and sensory thresholds were assessed in 12/19 subjects by inflating a highly compliant polyethylene balloon from 0 to 32 mmHg in 4 mmHg steps. Subjects also rated intensity of perception by visual analogue scale (VAS) during phasic distentions 8, 16 and 24 mmHg above operating pressure, in randomized sequence. Resting and squeeze anal pressures and rectal compliance were highly reproducible (rs , 0.7) in the same subject on separate days. Pressure thresholds for urgency appeared less reproducible than thresholds for initial perception and the desire to defecate. VAS scores were highly reproducible only during the 24-mmHg distention. Thus, anal pressures and rectal compliance are highly reproducible within healthy subjects on separate days, while sensory thresholds are reproducible to a variable degree, dependent on the intensity of stimulation and the perception being assessed. [source] Remediation with cyclodextrin: Recovery of the remedial agent by membrane filtrationREMEDIATION, Issue 3 2007Thomas B. Boving Cyclodextrin-enhanced flushing of contaminants from the subsurface is a promising innovative remediation technology. It will become more economically viable at more sites if methods can be developed to recover and reconcentrate the cyclodextrin solution after it has been flushed through an aquifer. The goal of this study was to determine if membrane technology is capable of meeting that need. Five membranes with different material properties were tested for this purpose in the laboratory. The results of these tests indicate that there are large differences both in the efficiency of these membranes to extract hydroxpropyl-,-cyclodextrin (HPCD) and their stability when exposed to trichloroethylene (TCE) at concentrations near aqueous solubility. Not only does the molecular weigh cutoff (MWCO) of a membrane determine if HPCD can be retained, but crucial selection criteria are the membrane's resistance and compatibility with TCE. Of the five membrane materials tested, only two (polymer composite membrane and polysulfone) met both these requirements. The polymer composite membrane (MPF-44) showed reliable and stable HPCD recoveries (>95 percent) even when exposed to high TCE concentrations. The polysulfone membrane showed high HPCD recoveries, 88.5 ± 0.4 percent to 97 percent ±1 percent for ultrafiltration and nanofiltration membranes, respectively. However, membrane swelling and deterioration became a problem at high TCE concentrations (>1,000 mg/L). These problems diminished when the TCE concentration was less than 1 mg/L. Field tests demonstrated that batch mode treatment by ultrafiltration doubled the cyclodextrin concentration from 5 to 10 percent within three hours at a constant operating pressure of 13 psi. Under continuous single-pass treatment conditions, cyclodextrin concentration also increased, although the rate of increase was much smaller than in batch mode. Overall, these tests showed that cyclodextrin recovery is possible under field conditions. © 2007 Wiley Periodicals, Inc. [source] Solids Circulation Flux and Gas Bypassing in a Pressurized Spout-fluid Bed with a Draft TubeTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 5 2002Rui Xiao Abstract An experimental study on solids circulation flux and gas bypassing of a spout-fluid bed with a draft tube at elevated pressures up to 600 kPa was performed in a 200 mm diameter cylindrical steel column with a 608 conical distributor. Glass beads with mean diameter 2.067 mm were used as bed materials to investigate the effect of operating conditions and geometric configuration on the solids circulation flux and the gas distribution between the annulus and the draft tube. A novel technique has been developed to measure the solids fluxes under pressure, and gas (CO2) traces have been employed to investigate gas bypassing characteristics. The solids circulation flux is greatly enhanced when operating pressure and auxiliary gas flowrate are increased, and it is also strongly influenced by geometric configuration. Two experimental relations are proposed for predicting solids circulation flux enhancement factors. Une étude expérimentale sur le flux de circulation des solides et la dérivation du gaz d'un lit jaillissant muni d'un tube d'aspiration à des pressions élevées jusqu'à 600 kPa, a été réalisée dans une colonne d'acier cylindrique de 200 mm de diamètre avec un distributeur conique à 608. Des billes de verre d'un diamètre moyen de 2,067 mm ont été utilisées comme matériaux de lit pour étudier l'effet des conditions opératoires et de la configuration géométrique sur le flux de circulation des solides et la distribution du gaz entre l'espace annulaire et le tube d'aspiration. Une nouvelle technique a été élaborée pour mesurer les flux de solides sous pression et les caractéristiques de la dérivation du gaz ont été étudiées à l'aide de gaz traceurs (CO2). Le flux de circulation des solides est grandement amélioré lorsque la pression de fonctionnement et le débit de gaz auxiliaire sont augmentés, et il est également fortement influencé par la configuration géométrique. Deux relations expérimentales sont proposées pour la prédiction des facteurs d'amélioration du flux de circulation des solides. [source] Sterilization of ginseng using a high pressure CO2 at moderate temperaturesBIOTECHNOLOGY & BIOENGINEERING, Issue 2 2009Fariba Dehghani Abstract The aim of this study was to determine the feasibility of using high pressure CO2 for sterilization of Ginseng powder, as an alternative method to conventional techniques such as ,-irradiation and ethylene oxide. The Ginseng sample used in this study was originally contaminated with fungi and 5,×,107 bacteria/g that was not suitable for oral use. This is the first time that high pressure CO2 has been used for the sterilization of herbal medicine to decrease the total aerobic microbial count (TAMC) and fungi. The effect of the process duration, operating pressure, temperature, and amount of additives on the sterilization efficiency of high pressure CO2 were investigated. The process duration was varied over 15 h; the pressure between 100 and 200 bar and the temperature between 25 and 75°C. A 2.67-log reduction of bacteria in the Ginseng sample was achieved after long treatment time of 15 h at 60°C and 100 bar, when using neat carbon dioxide. However, the addition of a small quantity of water/ethanol/H2O2 mixture, as low as 0.02 mL of each additive/g Ginseng powder, was sufficient for complete inactivation of fungi within 6 h at 60°C and 100 bar. At these conditions the bacterial count was decreased from 5,×,107 to 2.0,×,103 TAMC/g complying with the TGA standard for orally ingested products. A 4.3 log reduction in bacteria was achieved at 150 bar and 30°C, decreasing the TAMC in Ginseng sample to 2,000, below the allowable limit. However, fungi still remained in the sample. The complete inactivation of both bacteria and fungi was achieved within 2 h at 30°C and 170 bar using 0.1 mL of each additive/g Ginseng. Microbial inactivation at this low temperature opens an avenue for the sterilization of many thermally labile pharmaceutical and food products that may involve sensitive compounds to ,-radiation and chemically reactive antiseptic agents. Biotechnol. Bioeng. 2009;102: 569,576. © 2008 Wiley Periodicals, Inc. [source] Thermodynamic Equilibrium Calculations for the Reforming of Coke Oven Gas with Gasification GasCHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 1 2007B. Li Abstract Thermodynamic analyses of the reforming of coke oven gas with gasification gas for syngas were investigated as a function of coke oven gas-to-gasification gas ratio (1,3), oxygen-to-methane ratio (0,1.56), pressure (25,35,bar) and temperature (700,1100,°C). Thermodynamic equilibrium results indicate that the operating temperature should be approximately 1100,°C and the oxygen-to-methane ratio should be approximately 0.39, where about 80,% CH4 and CO2 can be converted at 30,bar. Increasing the operating pressure shifts the equilibrium toward the reactants (CH4 and CO2); increasing the pressure from 25 to 35,bar decreases the conversion of CO2 from 73.7,% to 67.8,%. The conversion ratio of CO2 is less than that in the absence of O2. For a constant feed gas composition (7,% O2, 31,% gasification gas, and 62,% coke oven gas), a H2/CO ratio of about 2 occurs at temperatures of 950,°C and above. Pressure effects on the H2/CO ratio are negligible for temperatures greater than 750,°C. The steam produced has an effect on the hydrogen selectivity, but its mole fraction decreases with temperature; trace amounts of other secondary products are observed. [source] Simulation of Direct-Current Microdischarges for Application in Electro-Thermal Class of Small Satellite Propulsion DevicesCONTRIBUTIONS TO PLASMA PHYSICS, Issue 1-2 2007P. S. Kothnur Abstract Microdischarges are miniature non-equilibrium plasma discharges with characteristic dimensions of ,10's,100's ,m and relatively high operating pressures of ,10's,100's Torr. Microdischarges possess several unique properties that have been exploited in a number of new applications. We have recently proposed amicrodischargebased electro-thermal class of microthrusters for small satellite propulsion. These devices utilize intense gas heating in microdischarges to preheat a propellant gas stream before it is expanded in a micronozzle to produce thrust; thereby improving specific impulse of the device over a conventional cold gas microthruster. This paper addresses direct-current microdischarge phenomena in a flowing gas stream. A two-dimensional, selfconsistent, fluid model of a helium microdischarge in a bulk gas flow is developed. For relatively high current/power levels considered in this study, the microdischarge operates in an abnormal glow mode with positive differential resistivity. Increasing discharge pressures for fixed power and bulk flow rates results in a decrease in charged species densities and the electron and gas temperatures. Also the discharge becomes increasingly constricted with increasing pressures, resulting in a more normal glow mode-like operation. Increasing bulk flow rates results in exactly the same trends as increasing pressures. For given input power and pressure, there exists an optimum flow rate for which the average outlet gas temperature from the discharge is a maximum. An increase in input electrical power results in an almost linear increase in the gas temperatures; this property of microdischarges is the key feature that is exploited in our microdischarge-based thruster concept. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Supercritical fluid extraction of walnut kernel oilEUROPEAN JOURNAL OF LIPID SCIENCE AND TECHNOLOGY, Issue 7 2006Sema Salg Abstract The objective of this study was to investigate the effects of the main process parameters on supercritical fluid extraction of walnut (Juglans regia,L.) kernel oil. The recovery of walnut kernel oil was performed in a green and high-tech separation process. CO2 and CO2 +,ethanol mixtures were used as the supercritical solvent. The extraction was carried out at operating pressures of 30, 40 and 50,MPa, operating temperatures of 313, 323 and 333,K, mean particle sizes of 1.78×10,4, 3.03×10,4, 4.78×10,4, 7.00×10,4 and 9.00×10,4,m, supercritical CO2 (SC CO2) flow rates of 1.67×10,8, 3.33×10,8, 6.67×10,8 and 13.33×10,8,m3/s and entrainer (ethanol) concentrations of 2, 4, 8 and 12,vol-%. Maximum extraction yield and oil solubility in SC CO2 obtained at 50,MPa, 333,K, 9.00×10,4,m, 3.33×10,4,m3/h were 0.65,kg oil/kg of dry sample and 37.16,g oil/kg CO2, respectively. The results obtained in this study showed that the crossover pressure effect of walnut kernel oil was at 30,MPa. At 30,MPa and 313,K, the obtained extraction yields above 4,vol-% ethanol reached the organic solvent extraction yield of 68.5,kg oil/kg dry sample. Extraction time was decreased significantly because of the higher solubility of walnut kernel oil in SC CO2 +,ethanol mixtures. [source] Performance analysis of a solid oxide fuel cell with reformed natural gas fuelINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 11 2010S. M. Jafarian Abstract In the present study a two-dimensional model of a tubular solid oxide fuel cell operating in a stack is presented. The model analyzes electrochemistry, momentum, heat and mass transfers inside the cell. Internal steam reforming of the reformed natural gas is considered for hydrogen production and Gibbs energy minimization method is used to calculate the fuel equilibrium species concentrations. The conservation equations for energy, mass, momentum and voltage are solved simultaneously using appropriate numerical techniques. The heat radiation between the preheater and cathode surface is incorporated into the model and local heat transfer coefficients are determined throughout the anode and cathode channels. The developed model has been compared with the experimental and numerical data available in literature. The model is used to study the effect of various operating parameters such as excess air, operating pressure and air inlet temperature and the results are discussed in detail. The results show that a more uniform temperature distribution can be achieved along the cell at higher air-flow rates and operating pressures and the cell output voltage is enhanced. It is expected that the proposed model can be used as a design tool for SOFC stack in practical applications. Copyright © 2009 John Wiley & Sons, Ltd. [source] Comparison of low temperature mixed refrigerant cycles for separation systemsINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 4 2009M. Mafi Abstract Numerous mixed refrigerant cycles (MRCs) were developed in the past several decades in different applications. In this paper, two sets of low temperature MRCs are developed and simulated for a typical olefin plant utilizing a mixture of methane, ethane, propane and nitrogen as cycle working fluid to replace the pure ethylene refrigeration cycle that is used in conjunction with propylene refrigeration cycle in conventional plants. The key parameters of the cycles including mixture compositions and operating pressure levels are optimized to meet the objective of minimum shaftwork in compressor. The results show that different cycle configuration has different optimal mixture composition and low and high operating pressures. The results of exergy analysis reveal that the main location of the exergy loss in the cycles is the heat exchanger system. Also, the Carnot factor versus heat flow diagram is provided to identify the distribution of inefficiencies in the heat exchangers for each cycle. The simulation results show that MRCs can improve the thermodynamic performance of refrigeration system using the optimal working fluid mixture composition, optimal high and low operating pressures and optimal arrangement of the cycle components. Copyright © 2008 John Wiley & Sons, Ltd. [source] Effect of pressure on thermal aspects in the riser column of a pressurized circulating fluidized bedINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 3 2006A. V. S. S. K. S. Gupta Abstract In the present paper the effect of pressure on bed-to-wall heat transfer in the riser column of a pressurized circulating fluidized bed (PCFB) unit is estimated through a modified mechanistic model. Gas,solid flow structure and average cross-sectional solids concentration play a dominant role in better understanding of bed-to-wall heat transfer mechanism in the riser column of a PCFB. The effect of pressure on average solids concentration fraction ,c' in the riser column is analysed from the experimental investigations. The basic cluster renewal model of an atmospheric circulating fluidized bed has been modified to consider the effect of pressure on different model parameters such as cluster properties, gas layer thickness, cluster, particle, gas phase, radiation and bed-to-wall heat transfer coefficients, respectively. The cluster thermal conductivity increases with system pressure as well as with bed temperature due to higher cluster thermal properties. The increased operating pressure enhances the particle and dispersed phase heat transfer components. The bed-to-wall heat transfer coefficient increases with operating pressure, because of increased particle concentration. The predicted results from the model are compared with the experimentally measured values as well as with the published literature, and a good agreement has been observed. The bed-to-wall heat transfer coefficient variation along the riser height is also reported for different operating pressures. Copyright © 2005 John Wiley & Sons, Ltd. [source] CLARIFICATION OF WATERMELON (CITRULLUS LANATUS) JUICE BY MICROFILTRATIONJOURNAL OF FOOD PROCESS ENGINEERING, Issue 6 2008Ch. CHHAYA ABSTRACT Microfiltration of watermelon juice was conducted using stirred membrane cell in continuous mode. The experiments were conducted at operating pressures of 136.5, 204.7 and 276 kPa, and stirring speeds 1,200 rpm (Re = 1.40 × 105), 1,400 rpm (Re = 1.63 × 105) and 1,600 rpm (Re = 1.87 × 105). Permeate flux decline was analyzed using a first-order kinetic model, and correlations were developed for the steady-state polarized layer resistance with the operating conditions, e.g., transmembrane pressure difference, Reynolds number and membrane resistance. The permeate flux was calculated based on the developed correlation, and found to be in good agreement with the actual experimental flux. The change in quality parameters of clarified juice was marginal compared to that of original juice. PRACTICAL APPLICATIONS The application of membrane technology is one of the emerging areas in food industry. The major application includes fruit juice clarification and concentration. Because of the nonthermal nature of membrane separation, the juice can be clarified at room temperature and packed aseptically for a longer shelf life without the loss of its initial quality parameters. The major problem during clarification is decline in permeate flux of fruit juice with time. Identification of causes for flux decline is essential for designing of membrane modules to make the clarification process commercially viable. The quality of juice during storage is vital, and therefore, determination of variation of its physicochemical properties during storage is also important. [source] Initial Deposition of Colloidal Particles on a Rough Nanofiltration MembraneTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 5 2007Tania Rizwan Abstract The initial rate of colloid deposition onto semi-permeable membranes is largely controlled by the coupled influence of permeation drag and particle-membrane colloidal interactions. Recent studies show that the particle-membrane interactions are subject to immense local variations due to the inherent morphological heterogeneity (roughness) of reverse osmosis (RO) and nanofiltration (NF) membranes. This experimental investigation reports the effect of membrane roughness on the initial deposition of polystyrene latex particles on a rough NF membrane during cross flow membrane filtration under different operating pressures and solution chemistries. Atomic force microscopy was used to characterize the roughness of the membrane and observe the structure of particle deposits. At the initial stages of fouling, the AFM images show that more particles preferentially accumulate near the "peaks" than in the "valleys" of the rough NF membrane surface. Le taux initial de la déposition colloïdale sur des membranes semi-perméables est largement contrôlé par l'influence couplée entre la traînée de perméation et les interactions colloïdales membrane-particules. Des études récentes montrent que les interactions membranes-particules sont sujettes à d'immenses variations locales en raison de l'hétérogénéité morphologique inhérente (rugosité) des membranes d'osmose inverse (RO) et de nanofiltration (NF). Cette étude expérimentale décrit l'effet de la rugosité des membranes sur la déposition initiale de particules de latex de polystyrène sur une membrane NF rugueuse lors de la filtration des membranes en écoulement transversal pour différentes conditions opératoires et compositions chimiques des solutions. On a eu recours à la microscopie à force atomique pour caractériser la rugosité de la membrane et observer la structure des dépôts de particules. Aux stades initiaux du refoulement, les images AFM montrent que les particules s'accumulent préférentiellement près des «pics» plutôt que dans les «vallées» de la surface de membrane NF rugueuse. [source] Gas permeation properties of Seragel membraneASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 2 2010M. Saeidi Abstract Gas permeation behavior through a specific type of polymeric membrane was investigated in this work. The main objective of our study was to determine gas permeation properties of a specific polymeric membrane over a range of operating pressures. The diffusive layer of this membrane consists of Butadiene,Sulfone block copolymer and demonstrates high chemical stability in corrosive media. Permeances were determined at the temperature of 35 °C and pressures of 760, 1520, and 3040 cmHg for methane, carbon dioxide, and nitrogen. Gas permeances were also determined for actual binary mixtures of H2S/CH4. Average permeances of 23.17 and 3.75 GPU for H2S and CO2 were achieved respectively, at the pressure range of 380,1140 cmHg. Calculated permeances by a model developed for this membrane in previous literatures have been compared with experimental data in this study and the agreement of the model with H2S/CH4 mixture was also investigated. The results show that the agreement between the pure gas experimental permeances and the data from the model is more in comparison with the experimental gas mixture results. Copyright © 2009 Curtin University of Technology and John Wiley & Sons, Ltd. [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] | |||||||||||||||||||