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Pressure Fluctuations (pressure + fluctuation)
Selected AbstractsIn situ Pressure Fluctuations of Polymer Melt Flow Instabilities: Experimental Evidence about their Origin and DynamicsMACROMOLECULAR RAPID COMMUNICATIONS, Issue 21 2009Humberto Palza Abstract Despite the practical importance of polymer melt instabilities, there is still a lack of experiments able to characterize in situ the origin and behavior of these phenomena. In this context, a new set-up consisting of high sensitive pressure transducers located inside a slit-die and an advanced mathematical framework to process in situ measurements of polymer melt instabilities, are developed and applied. Our results show for the first time that pressure oscillations can actually be detected inside the die under sharkskin conditions. This originates from a factor of 103 and 102 improvement in terms of time and pressure resolution. Furthermore, new evidence towards the propagation of the slip phenomena along the die in spurt instabilities are found. [source] Nonintrusive characterization of fluidized bed hydrodynamics using vibration signature analysisAICHE JOURNAL, Issue 3 2010M. Abbasi Abstract There are many techniques to characterize the hydrodynamics of fluidized beds, but new techniques are still needed for more reliable measurement. Bed vibrations were measured by an accelerometer in a gas,solid fluidized bed to characterize the hydrodynamics of the fluidized bed in a nonintrusive manner. Measurements were carried out at different superficial gas velocities and particle sizes. Pressure fluctuations were measured simultaneously. Vibration signals were processed using statistical analysis. For the sake of the evaluation, the vibration technique was used to calculate minimum fluidization velocity. It was shown that minimum fluidization velocity can be determined from the variation of standard deviation, skewness, and kurtosis of vibration signals against superficial gas velocity of the bed. Kurtosis was proved to be a new method of analyzing vibration signals. Results indicate that analyzing the vibration signals can be an effective nonintrusive technique to characterize the hydrodynamics of fluidized beds. © 2009 American Institute of Chemical Engineers AIChE J, 2010 [source] Flow distribution and mass transfer in a parallel microchannel contactor integrated with constructal distributorsAICHE JOURNAL, Issue 2 2010Jun Yue Abstract Flow distribution and mass transfer characteristics during CO2 -water flow through a parallel microchannel contactor integrated with two constructal distributors have been investigated numerically and experimentally. Each distributor comprises a dichotomic tree structure that feeds 16 microchannels with hydraulic diameters of 667 ,m. It was found that constructal distributors could ensure a nearly uniform gas,liquid distribution at high gas flow rates where the ideal flow pattern was slug-annular flow. Nevertheless, at small gas flow rates where the ideal flow pattern was slug flow, a significant flow maldistribution occurred primarily due to the lack of large pressure barrier inside each distributor, indicating that dynamic pressure fluctuation in parallel microchannels greatly disturbed an otherwise good flow distribution therein. It was further shown that the present parallel microchannel contactor could realize the desired mass transfer performance previously achieved in one single microchannel under relatively wide operational ranges due to the integration of constructal distributors. © 2009 American Institute of Chemical Engineers AIChE J, 2010 [source] A Practical Method to Estimate the Bed Height of a Fluidized Bed of Fine ParticlesCHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 12 2008M. Zhang Abstract Knowledge of both dense bed expansion and freeboard solids inventory are required for the determination of bed height in fluidized beds of fine particles, e.g., Fluidized Catalytic Cracking (FCC) catalysts. A more accurate estimation of the solids inventory in the freeboard is achieved based on a modified model for the freeboard particle concentration profile. Using the experimentally determined dense bed expansion and the modified freeboard model, a more practical method with improved accuracy is provided to determine the bed height both in laboratory and industrial fluidized beds of FCC particles. The bed height in a fluidized bed can exhibit different trends as the superficial gas velocity increases, depending on the different characteristics of the dense bed expansion and solids entrainment in the freeboard. The factors that influence the bed height are discussed, showing the complexity of bed height and demonstrating that it is not realistic to determine the bed height by a generalized model that can accurately predict the dense bed expansion and freeboard solids inventory simultaneously. Moreover, a method to determine the bed height, based on axial pressure fluctuation profiles, is proposed in this study for laboratory fluidized beds, which provides improved accuracy compared to observation alone or determining the turning points in the axial pressure profiles, especially in high-velocity fluidized beds. [source] Oral compression activity on a surrogate nipple in the newborn rat: Nutritive and nonnutritive suckingDEVELOPMENTAL PSYCHOBIOLOGY, Issue 4 2003Andrey P. Kozlov Abstract Newborn rats, 3 hr after birth and before any experience in suckling, were exposed for 10 min to a surrogate nipple providing milk. One hour later, they were exposed to an empty nipple for another 10-min period. The basic characteristics of oral behavior (oral compression activity, OCA) were assessed by recording intranipple pressure during the pups' first attachment to a nipple. The peculiarities of milk-induced changes of OCA were examined with three modes of milk delivery (milk infusions, and intermittent and continuous milk deliveries). The pattern of OCA exerted by the newborn pups on a surrogate nipple consisted of rhythmic oscillations within a frequency range of 0.4 to 1.0 Hz, superimposed on slow (frequency,<,0.2 Hz), irregular intranipple pressure fluctuations. Oral behavior during the first minute after oral capture of the nipple differed significantly from that during any subsequent 1-min interval in terms of frequency content of OCA. The pattern of OCA changes induced by milk infusions or intermittent milk delivery included an abrupt rise in intranipple pressure, accompanied or followed by a burst of fast nipple compressions (bites). Our data suggest that newborn rats attached to a surrogate nipple demonstrate patterns of oral behavior that simulate, in terms of basic frequency characteristics, patterns of nutritive and nonnutritive suckling observed in more mature pups on the maternal nipple. © 2003 Wiley Periodicals, Inc. Dev Psychobiol 43: 290,303, 2003. [source] Cushioning the pressure vibration of a zeolite concentrator system using a decoupled balancing duct systemENVIRONMENTAL PROGRESS & SUSTAINABLE ENERGY, Issue 2 2007Feng-Tang Chang Abstract A honeycomb Zeolite Rotor Concentrator (HZRC) is the main air pollution control device utilized by many semiconductor and optoelectronics manufacturers. Various plant exhaust streams are collected and then transferred to the HZRC for decontamination. In a conventional HZRC, the exhaust fan movement and the switching between different air ducts can cause significant duct pressure variations resulting in production interruption. The minimization of pressure fluctuations to ensure continuous operation of production lines while maintaining a high volatile organic compounds (VOCs) removal efficiency is essential for exhaust treatment in these high technology manufactures. The article introduces a decoupled balancing duct system (DBDS) for controlling the airflows to achieve a balanced pressure in the HZRC system by adding a flow rate control device to the VOCs loaded stream bypass duct of a conventional system. Performance comparisons of HZRC with DBDS and other air flow control systems used by the wafer manufacturers in Hsinchu Science Park, Taiwan are presented. DBDS system had been proved effectively to stabilize the pressure in the airflow ducts, and thus avoided pressure fluctuations; it helped to achieve a high VOCs removal efficiency while ensuring the stability of the HZRC. © 2007 American Institute of Chemical Engineers Environ Prog, 2007 [source] Effects of age on the cardiac and vascular limbs of the arterial baroreflexEUROPEAN JOURNAL OF CLINICAL INVESTIGATION, Issue 1 2003C. M. Brown Abstract Background Healthy ageing has several effects on the autonomic control of the circulation. Several studies have shown that baroreflex-mediated vagal control of the heart deteriorates with age, but so far there is little information regarding the effect of ageing on sympathetically mediated baroreflex responses. The aim of this study was to assess the effects of ageing on baroreflex control of the heart and blood vessels. Materials and Methods In 40 healthy volunteers, aged 20,87 years, we applied oscillatory neck suction at 0·1 Hz to assess the sympathetic modulation of the heart and blood vessels and at 0·2 Hz to assess the effect of parasympathetic stimulation on the heart. Breathing was maintained at 0·25 Hz. Blood pressure, electrocardiographic RR intervals and respiration were recorded continuously. Spectral analysis was used to evaluate the magnitude of the low-frequency (0·03,0·14 Hz) and high-frequency (0·15,0·50 Hz) oscillations in the RR interval and blood pressure. Responses to neck suction were assessed as the change in power of the RR interval and blood pressure fluctuations at the stimulation frequency from baseline values. Results Resting low- and high-frequency powers of the RR interval decreased significantly with age (P < 0·01). However, the low-frequency power of systolic blood pressure did not correlate with age. Spontaneous baroreflex sensitivity (alpha-index) showed a significant inverse correlation with age (r = ,0·46, P < 0·05). Responses of the RR interval and systolic blood pressure to 0·1 Hz neck suction stimulation were not related to age, however, the RR interval response to 0·2 Hz neck suction declined significantly with age (r = ,0·61, P < 0·01). Conclusions These results confirm an age-related decrease in cardiovagal baroreflex responses. However, sympathetically mediated baroreflex control of the blood vessels is preserved with age. [source] A Closed Form Slug Test Theory for High Permeability AquifersGROUND WATER, Issue 1 2005David W. Ostendorf We incorporate a linear estimate of casing friction into the analytical slug test theory of Springer and Gelhar (1991) for high permeability aquifers. The modified theory elucidates the influence of inertia and casing friction on consistent, closed form equations for the free surface, pressure, and velocity fluctuations for overdamped and under-damped conditions. A consistent, but small, correction for kinetic energy is included as well. A characteristic velocity linearizes the turbulent casing shear stress so that an analytical solution for attenuated, phase shifted pressure fluctuations fits a single parameter (damping frequency) to transducer data from any depth in the casing. Underdamped slug tests of 0.3, 0.6, and 1 m amplitudes at five transducer depths in a 5.1 cm diameter PVC well 21 m deep in the Plymouth-Carver Aquifer yield a consistent hydraulic conductivity of 1.5 × 10,3 m/s. The Springer and Gelhar (1991) model underestimates the hydraulic conductivity for these tests by as muchas 25% by improperly ascribing smooth turbulent casing friction to the aquifer. The match point normalization of Butler (1998) agrees with our fitted hydraulic conductivity, however, when friction is included in the damping frequency. Zurbuchen et al. (2002) use a numerical model to establish a similar sensitivity of hydraulic conductivity to nonlinear casing friction. [source] Buffeting in transonic flow prediction using time-dependent turbulence modelINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 2 2005A. Kourta Abstract In transonic flow conditions, the shock wave/turbulent boundary layer interaction and flow separations on wing upper surface induce flow instabilities, ,buffet', and then the buffeting (structure vibrations). This phenomenon can greatly influence the aerodynamic performance. These flow excitations are self-sustained and lead to a surface effort due to pressure fluctuations. They can produce enough energy to excite the structure. The objective of the present work is to predict this unsteady phenomenon correctly by using unsteady Navier,Stokes-averaged equations with a time-dependent turbulence model based on the suitable (k,,) turbulent eddy viscosity model. The model used is based on the turbulent viscosity concept where the turbulent viscosity coefficient (C,) is related to local deformation and rotation rates. To validate this model, flow over a flat plate at Mach number of 0.6 is first computed, then the flow around a NACA0012 airfoil. The comparison with the analytical and experimental results shows a good agreement. The ONERA OAT15A transonic airfoil was chosen to describe buffeting phenomena. Numerical simulations are done by using a Navier,Stokes SUPG (streamline upwind Petrov,Galerkin) finite-element solver. Computational results show the ability of the present model to predict physical phenomena of the flow oscillations. The unsteady shock wave/boundary layer interaction is described. Copyright © 2005 John Wiley & Sons, Ltd. [source] Turbulence model and numerical scheme assessment for buffet computationsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 11 2004Eric Goncalves Abstract The prediction of shock-induced oscillations over transonic rigid airfoils is important for a better understanding of the buffeting phenomenon. The unsteady resolution of the Navier,Stokes equations is performed with various transport-equation turbulence models in which corrections are added for non-equilibrium flows. The lack of numerical efficiency due to the CFL stability condition is circumvented by the use of a wall law approach and a dual time stepping method. Moreover, various numerical schemes are used to try and be independent of the numerical discretization. Comparisons are made with the experimental results obtained for the supercritical RA16SC1 airfoil. They show the interest in using the SST correction or realizability conditions to get correct predictions of the frequency, amplitude and pressure fluctuations over the airfoil. Copyright © 2004 John Wiley & Sons, Ltd. [source] Inactivation of Food Spoilage Microorganisms by Hydrodynamic Cavitation to Achieve Pasteurization and Sterilization of Fluid FoodsJOURNAL OF FOOD SCIENCE, Issue 9 2007P.J. Milly ABSTRACT:, Hydrodynamic cavitation is the formation of gas bubbles in a fluid due to pressure fluctuations induced by mechanical means. Various high-acid (pH , 4.6) fluid foods were processed in a hydrodynamic cavitation reactor to determine if commercial sterility can be achieved at reduced processing temperatures. Sporicidal properties of the process were also tested on a low-acid (pH < 4.6) fluid food. Fluid foods were pumped under pressure into a hydrodynamic cavitation reactor and subjected to 2 rotor speeds and flow rates to achieve 2 designated exit temperatures. Thermal inactivation kinetics were used to determine heat-induced lethality for all organisms. Calcium-fortified apple juice processed at 3000 and 3600 rpm rotor speeds on the reactor went through a transient temperature change from 20 to 65.6 or 76.7 °C and the total process lethality exceeded 5-log reduction of Lactobacillus plantarum and Lactobacillus sakei cells, and Zygosaccharomyces bailii cells and ascospores. Tomato juice inoculated with Bacillus coagulans spores and processed at 3000 and 3600 rpm rotor speeds endured a transient temperature from 37.8 to 93.3 or 104.4 °C with viable CFU reductions of 0.88 and 3.10 log cycles, respectively. Skim milk inoculated with Clostridium sporogenes putrefactive anaerobe 3679 spores and processed at 3000 or 3600 rpm rotor speeds endured a transient temperature from 48.9 to 104.4 or 115.6 °C with CFU reductions of 0.69 and 2.84 log cycles, respectively. Utilizing hydrodynamic cavitation to obtain minimally processed pasteurized low-acid and commercially sterilized high-acid fluid foods is possible with appropriate process considerations for different products. [source] Comparison of decoupling methods for analyzing pressure fluctuations in gas-fluidized bedsAICHE JOURNAL, Issue 4 2010Yongmin Zhang Abstract Two methods of decoupling pressure fluctuations in fluidized beds by using the incoherent part (IOP) of absolute pressure (AP) and differential pressure (DP) fluctuations are evaluated in this study. Analysis is conducted first to demonstrate their similarities, differences, and drawbacks. Then, amplitudes, power spectral densities, mean frequencies, coherence functions, and filtering indices of the IOP of AP and DP fluctuations are calculated and compared based on experimental data from a two-dimensional fluidized column of FCC particles. Derived bubble sizes are also compared with the sizes of bubbles viewed in the two-dimensional bed. The results demonstrate the similarity of these two methods in filtering out global compression wave components from absolute pressure fluctuations, especially those generated from oscillations of fluidized particles and gas flow rate fluctuations. However, both methods are imperfect. Neither can filter out all the compression wave components and retain all the useful bubble-related wave components. Their amplitudes can be used to characterize global bubble property and quality of gas,solids contacting in bed, but they do not give accurate measurement of bubble sizes. © 2009 American Institute of Chemical Engineers AIChE J, 2010 [source] Detecting regime transitions in slurry bubble columns using pressure time seriesAICHE JOURNAL, Issue 7 2005Keshav C. Ruthiya Abstract Changes in the coherent standard deviation and in the average frequency of measured pressure time series with gas velocity, are proposed, as unique and unambiguous criteria to mark flow regime transitions in slurry bubble columns. In a 2-dimensional (2-D) slurry bubble column, pressure time series are measured at different gas velocities simultaneously with high-speed video recording of the gas-liquid flow. The frequency of occurrence and the average diameter of the large bubbles are determined from video image analysis. The gas velocity where the first large bubbles are detected, with an average diameter of 1.5 cm, and with a frequency of occurrence of one bubble per s, is designated as the first regime transition point (transition from the homogeneous regime to the transition regime). At this point, the coherent standard deviation of the measured pressure fluctuations clearly increases from zero. The gas velocity where the average diameter and the frequency of occurrence of the large bubbles become constant, is designated as the second regime transition point (transition from the transition regime to the heterogeneous regime). From this point onward, the slope of the coherent standard deviation of the measured pressure fluctuations clearly decreases with gas velocity, while the average frequency becomes constant. These clear changes with gas velocity in the coherent standard deviation, and in the average frequency are also demonstrated in a 3-D slurry bubble column. © 2005 American Institute of Chemical Engineers AIChE J, 2005 [source] Early warning of agglomeration in fluidized beds by attractor comparisonAICHE JOURNAL, Issue 11 2000J. Ruud van Ommen An enhanced monitoring method, based on pressure fluctuation measurements, for observing nonstationarities in fluidized-bed hydrodynamics is presented. Experiments show that it can detect small changes in the particle-size distribution. Such a monitoring method is useful to give an early warning of the onset of agglomeration in a fluidized bed. In contrast to earlier methods, this method is insensitive to small changes in superficial gas velocity and can handle multiple signals, making it relevant to industrial application. By carefully choosing the measurement position, the method becomes also insensitive to small bed mass variations. It uses the attractor reconstructed from a measured pressure signal, which is a "fingerprint" of the hydrodynamics of the fluidized bed for a certain set of conditions. Using this method statistically the reconstructed attractor of a reference time series of pressure fluctuations (representing the desired fluidization behavior) is compared with that of successive time series measured during the bed operation. [source] Effect of surface roughness on elastohydrodynamic traction: Part 1LUBRICATION SCIENCE, Issue 3 2005T. Nanbu Abstract The effect of surface roughness on traction performance was experimentally studied using a two-roller tester. The nature of the contact was investigated using electrical resistance and electrical capacitance methods. Increased shear stress was observed in the viscous region, which could be attributed to a higher average shear rate and to greater viscosity under EHD contact conditions due to pressure fluctuations caused by the surface texture. [source] Postovulatory Effect of Intravenous Administration of Lipopolysaccharide (E. coli, O55:B5) on the Contractile Activity of the Oviduct, Ova Transport, Binding of Accessory Spermatozoa to the Zona Pellucida and Embryo Development in SowsREPRODUCTION IN DOMESTIC ANIMALS, Issue 5 2002AM Mwanza Contents The effect of lipopolysaccharide (LPS) (E. coli, O55:B5), administered 18 h after ovulation in the second oestrus after weaning, on the contractile activity of the oviduct, ova transport, sperm binding to zona pellucida (ZP) and embryo development, was studied in 14 Swedish crossbred (Landrace Yorkshire) multiparous sows. The endotoxin group (E-group) sows were administered with 300 ng/kg of LPS while the control group (C-group) sows were administered with 5 ml of saline i.v. via an indwelling jugular cannula. Immediately after evidence of standing oestrus, a Millar® pressure transducer was placed intraluminally about 3 cm into the mid-isthmus, via laparotomy. Pressure recordings of the oviduct were collected from all conscious sows until slaughter. After slaughter, the genital tract opposite to the side with the transducer was retrieved, and three equal isthmic segments and the first third of the uterine horn part adjacent to the utero-tubal-junction (UTJ) were flushed separately to recover the ova. The intervals (mean±SD) from ovulation to slaughter (OS) and insemination to ovulation (IO) were not different between the E-group (44.5±5.7 h; 13.3±6.5 h) and the C-group (42.7±5.9 h; 14.8±4.1 h), respectively. Ova recovery rate (RR) in the E-group (80.2±22.9%) did not differ from that in the C-group (85.2±4.5%). The frequency distribution of ova recovered in the different segments did not significantly (p>0.05) differ between the groups. The E-group showed higher cleavage rate than controls. A higher proportion of spermatozoa bound to the ZP was also found in the E-group compared with controls. The isthmic intraluminal pressure slightly increased (p=0.07) 18 h after ovulation and immediately following LPS in the E-group, compared with the C-group. The frequencies of phasic pressure fluctuations were significantly (p<0.05) lower at 30 and 38 h after ovulation in the E- than in the C-group. It can be concluded from the present study that a single i.v. administration of LPS (300 ng/kg body weight) to sows, 18 h after ovulation might be associated with changes in isthmic pressure and the frequency of phasic pressure fluctuations, increased numbers of spermatozoa attached to the ZP and an enhanced embryo development but not with ova transport rates. [source] Experimental Simulation of the Reactor Section of Fluid Cokers: Comparison of FCC and Fluid Coke ParticlesTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 2 2006Xuqi Song Abstract The hydrodynamics of fluid cokers were studied in a pressurized fully cylindrical cold model of diameter 483 mm, geometrically and dynamically scaled down by a factor of ,20 from commercial units. Differential pressure fluctuations, voidage distributions, solids momentum flux distributions and steady state gas mixing behaviour in the reactor section are compared for the same operating conditions with two kinds of particles, FCC and fluid coke. The voidage distributions and core-annular flow structures in the reactor section were similar enough that either FCC or fluid coke particles can be used for cold modelling of fluid cokers. On a étudié l'hydrodynamique d'unités de cokéfaction fluide dans une maquette froide cylindrique pressurisée de 483 mm de diamètre, géométriquement et dynamiquement réduite d'un facteur 20 par rapport à des unités commerciales. Les fluctuations de pression différentielles, les distributions de vide, les distributions de flux de moment des solides et le comportement de mélange de gaz à l'état stable dans la section du réacteur sont comparés pour les mêmes conditions opératoires avec deux sortes de particules, soient FCC et coke fluide. Les distributions de vide et les structures d'écoulement noyau-espace annulaire dans la section du réacteur sont suffisamment semblables pour que des particules de FCC ou de coke fluide puissent être utilisées pour la modélisation à froid d'unités de cokéfaction fluide. [source] Cardiac baroreflex control in humans during and immediately after brief exposure to simulated high altitudeCLINICAL PHYSIOLOGY AND FUNCTIONAL IMAGING, Issue 5 2002Frédéric Roche Summary To examine the baroreflex response in humans during and immediately after acute hypoxia exposure, the cardiac baroreflex sensitivity (BRS) was studied using adaptation of RR intervals in response to spontaneous systolic blood pressure fluctuations (sequences methodology) in 11 unacclimatized subjects. All measurements were made under fixed breathing rate, and realized consecutively at baseline level (20 min), at an inspired oxygen concentration of 11% (15 min) and again under normoxic conditions (20 min; recovery period). The spontaneous baroreflex response decreases progressively during hypoxic exposure, causing a tachycardic response at this FiO2 without any significant alteration of the systolic or diastolic blood pressure. The magnitude of decrease for this variable at the end of exposure averaged 42·9 ± 15·6%. The simultaneous spectral analysis of heart rate (HR) variability in hypoxic condition confirmed an alteration in the parasympathetic activity (HFnu: ,17·8 ± 30·9% versus basal conditions, P<0·01) counterbalanced by an exaggerated sympathetic activity (LFnu: +33 ± 42·4%, P<0·05) at the sinus node. Interestingly, we could observe an enhanced cardiac baroreflex response during the period following the inhalation of the hypoxic mixture (+130·6 ± 15·6% of basal conditions, P<0·001). There is a relationship with a significant and abrupt increase in the parasympathetic control of HR (mean HR reached 111 ± 8·1% of the mean basal HR, P<0·01). These results suggest that brief exposure to hypoxia under rate-controlled ventilation is associated with a significant alteration in the spontaneous cardiac baroreflex. This important cardiac autonomic imbalance is followed by a significant increase in the cardiac parasympathetic drive even after the disappearance of the hypoxic stimulus. [source] | |||||||||||||||||||