Greater Flow Rate Research Articles

Flow Perfusion Improves Seeding of Tissue Engineering Scaffolds with Different Architectures

Engineered bone grafts have been generated in static and dynamic systems by seeding and culturing osteoblastic cells on 3-D scaffolds. Seeding determines initial cellularity and cell spatial distribution throughout the scaffold, and affects cell-matrix interactions. Static seeding often yields low seeding efficiencies and poor cell distributions; thus creating a need for techniques that can improve these parameters. We have evaluated the effect of oscillating flow perfusion on seeding efficiency and spatial distribution of MC3T3-E1 pre-osteoblastic cells in fibrous polystyrene matrices (20, 35 and 50-microm fibers) and foams prepared by salt leaching, using as controls statically seeded scaffolds. An additional control was investigated where static seeding was followed by unidirectional perfusion. Oscillating perfusion resulted in the most efficient technique by yielding higher seeding efficiencies, more homogeneous distribution and stronger cell-matrix interactions. Cell surface density increased with inoculation cell number and then reached a maximum, but significant detachment occurred at greater flow rates. Oxygen plasma treatment of the fibers greatly improved seeding efficiency. Having similar porosity and dimensions, fibrous matrices yielded higher cell surface densities than foams. Fluorescence microscopy and histological analyses in polystyrene and PLLA scaffolds demonstrated that perfusion seeding produced more homogeneous cell distribution, with fibrous matrices presenting greater uniformity than the foams.

A novel fluidic oscillator incorporating step-shaped attachment walls

A novel fluidic oscillator incorporating step-shaped attachment walls and acute-angle splitters has been designed and verified experimentally to stabilize the oscillation of circulation flow, to modify the flow patterns and to improve the performance. Focusing on various oscillators of plane-wall and step-wall designs, we systematically analyzed the pressure spectra, pressure loss, and flow structure, via particle-imaging velocimetry, flow visualization, and pressure sensors. The results reveal that the novel design promotes conditions to initiate the oscillator and makes the recirculation vortices oscillate more effectively and stably. The operating range of this step-wall oscillator is broadened and the ratio of signal to noise of the step oscillator is 17 times as great as that with plane walls at a greater flow rate, 65L/min. Comparison of the wave form of the spectral analysis and the ratio of signal to noise over the entire experimental range further corroborates the superior features of the novel design.

Performance of Three Systems for Warming Intravenous Fluids at Different Flow Rates

This study compared the intravenous fluid warming capabilities of three systems at different flow rates. The devices studied were a water-bath warmer, a dry-heat plate warmer, and an intravenous fluid tube warmer Ambient temperature was controlled at 22 degrees to 24 degrees C. Normal saline (0.9% NaCl) at either room temperature (21 degrees to 23 degrees C) or at ice-cold temperature (3 degrees to 5 degrees C) was administered through each device at a range of flow rates (2 to 100 ml/min). To mimic clinical conditions, the temperature of the fluid was measured with thermocouples at the end of a one metre tube connected to the outflow of the warmer for the first two devices and at the end of the 1.2 m warming tubing for the intravenous fluid tube warmer The temperature of fluid delivered by the water bath warmer increased as the flow rate was increased up to 15 to 20 ml/min but decreased with greater flow rates. The temperature of the fluid delivered by the dry-heat plate warmer significantly increased as the flow rate was increased within the range tested (due to decreased cooling after leaving the device at higher flow rates). The temperature of fluid delivered by the intravenous fluid tube warmer did not depend on the flow rate up to 20 ml/min but significantly and fluid temperature-dependently decreased at higher flow rates (>30 ml/min). Under the conditions of our testing, the dry heat plate warmer delivered the highest temperature fluid at high flow rates.

Tracing sediment dynamics and sources in eroding rills with rare earth elements

SummaryEroding rills evolve morphologically in time and space. Most current studies on rill erosion use spatially averaged soil erosion data, providing little information on soil erosion dynamics. A method is proposed to use rare earth elements (REEs) to trace sediment distribution in eroding rills. Laboratory flume simulation experiments were conducted at three flow rates (2, 4 and 8 litres minute−1) and five slope gradients (5, 10, 15, 20 and 25°) with three replicates of each treatment. The rills, of 8 m length, were subdivided into 10 equal segments of 0.8 m length and 0.1 m width, with a different REE applied to each segment. We derived computational formulae for estimating the distribution of eroded amounts along the rills. The actual erosion distribution along rills was then estimated with the data from the experiments. The precision of the REEs for tracing rill erosion was analysed. The results showed that sediment concentration increased with rill length, but the increased rate (the slope of the curve) flattened gradually. Sediment yields increased with slope gradients and flow rates, but the slope gradients had a greater effect on sediment concentration than flow rates, and greater flow rates caused more rill erosion and soil loss under the same slope gradient. The results also demonstrated the feasibility of using REEs to trace the dynamic processes of rill erosion.

Coordinating stomatal and xylem functioning – an evolutionary perspective

Coordinating stomatal and xylem functioning – an evolutionary perspective

Sponge aquaculture for the production of biologically active metabolites: the influence of farming protocols and environment

Before sponge aquaculture is accepted as a commercially viable method of supplying bioactive metabolites, it must be demonstrated that adequate production of sponge biomass and metabolite is possible. In this study, we farmed the New Zealand Demospongiae Latrunculia wellingtonensis (Alvarez, Bergquist and Battershill) and Polymastia croceus (Kelly-Borges and Bergquist) for 9 months at two nearby locations with differing flow rates using two farming methods: rope lines and suspended mesh arrays. The farmed explants were harvested at regular intervals over the 9 months by cutting and removing new biomass, leaving behind the original explant “core” to heal and regrow. For both species, explants grew as water temperature increased and shrunk as water temperature fell, and growth was greatest overall at the location with the greatest flow rate. Some treatments exhibited remarkable sponge growth (up to 960% in 6 months), with overall biomass yields double or greater the initial transplanted weight. Growth after harvesting was similar between harvested and nonharvested explants, indicating that healing of cut biomass and reorganization of the canal system is not a significant drain on resources. Bioactivity of farmed sponges (measure of bioactive metabolite biosynthesis) was similar or greater than found in natural populations. Both rope and mesh arrays were found to be good farming structures, but differing patterns of growth and survival indicated that the two arrays are most suited for a particular type of sponge depending on its skeletal structure.

Update on strategies to improve thrombolysis for acute myocardial infarction.

Therapy for acute myocardial infarction involves rapid restoration of blood flow through a coronary artery that has been occluded by a ruptured atherosclerotic plaque. Thrombolytic therapy, the pharmacologic standard to achieve this outcome, significantly improves survival; however, current regimens have limitations: they can fail to achieve complete reperfusion, they can cause significant bleeding events, and they can result in reocclusion. In addition, complex regimens of some agents can cause dosing errors. Accordingly, newer compounds were developed to address some of these issues, and alternative strategies are being implemented. The combination of platelet glycoprotein IIb-IIIa receptor inhibitors plus thrombolytic agents produced promising results in clinical trials, including faster clot lysis and greater flow rates than either therapy alone. The addition of unfractionated heparin or low-molecular-weight heparin to thrombolytic-antiplatelet therapy is being evaluated, as is administration of thrombolytic-antiplatelet before percutaneous coronary intervention.

On-line solid phase extraction system using PTFE packed column for the flame atomic absorption spectrometric determination of copper in water samples

A new flow injection on-line adsorption preconcentration system adapted to flame atomic absorption spectrometry (FAAS) for copper determination at the μg l −1 level was developed. Polytetrafluoroethylene (PTFE) turnings packed in a mini-column were used as sorbent material. The copper ammonium pyrrolidine dithiocarbamate (APDC) complex was sorbed on the PTFE turnings, from which it could be eluted on-line instantly by isobutyl methyl ketone (IBMK) into the flame at a flow rate of 2.3 ml min −1. The system was optimized and offered good performance characteristics with practically unlimited life time, greater flow rates and improved flexibility, as compared with other sorbent materials and the knotted reactor preconcentration systems. With 1 min preconcentration time, and a sample frequency of 40 h −1, the enhancement factor was 340, which could be further improved by increasing the preconcentration time. The detection limit was c L=0.05 μg l −1, and the precision was 1.5%, at the 2.0 μg l −1 Cu level. The method has been applied successfully to the analysis of potable, river and seawater, and its accuracy was tested by the analysis of certified reference materials and by recovery measurements on spiked samples. No significant interferences exist from other substances usually occurring in natural water.

On field characterisation of static domestic gas flowmeters

Different solutions to the metering of natural gas consumption can be adopted according to whether the distribution is domestic or industrial. In the domestic field, almost all the flow meters used by natural gas distribution companies are conventional diaphragm meters, whereas greater flow rates justify metrologically better performing measurement systems. The requirement for new safety and remote-reading related functions and the availability of new technologies is now encouraging the use of static innovative flow meters. In the present study, after a short analysis of metering principles and of static ultrasonic flow meter characteristics, the authors report the results of the field tests carried out on two different types of static ultrasonic flow meter for 2 years.

Stratified convection with multiple states

A simplified box model of the cooling of a salt-stratified ocean is analyzed analytically and numerically. A large isothermal basin of salt water has a layer of fresh water at the surface. Beside this is a small basin, cooled from above and connected to the large basin by horizontal tubes at the top, middle and bottom. For small cooling rate, fresh water enters the small basin, is cooled and leaves through the middle tube. For greater cooling rate, the fresh water leaves the small basin through the middle and bottom tube. If the top tube is smaller than the deeper tubes and the fresh water layer is sufficiently shallow, flow in the middle tube reverses at a critical cooling rate. In this case, a mixture of salt and fresh water is cooled and leaves the bottom tube. Increased cooling produces much greater flow rate; consequentially temperature increases rather than decreases in the small basin. A relaxation heat flow condition results in multiple equilibria. One of the stable modes has fresh surface water descending in the small basin and flowing out through the middle and bottom tube. The other has a greater rate of flow of both fresh and salty water (through the middle tube) into the basin with the flow of mixed salty water out of the bottom tube. Implications for deep convection in the ocean are discussed.

On-line sorption preconcentration of chromium(VI) and its determination by flame atomic absorption spectrometry

A method was developed for the determination of Cr(VI) by flame atomic absorption spectrometry (FAAS) after on-line sorption preconcentration. The solution containing Cr(VI) was reacted with ammonium-pyrrolidinedithiocarbamate (APDC) in a flow injection manifold system designed for this purpose and the non-water soluble chromium complex formed was adsorbed in a sorption reactor. The commercial PEEK (polyether ether ketone) loop used in liquid chromatography (LC) was introduced instead of a knotted reactor recommended for preconcentration of other trace elements in the literature. The Cr-PDC complex was retained by the PEEK loop, from which the chromium complex could be eluted rapidly by methyl isobutyl ketone into the flame. The PEEK loop is cheaper than the LC column used previously for preconcentration of Cr(VI), it can easily be inserted into the system and it is practically of unlimited lifetime. The preconcentration could also be done at much greater flow rates than that for columns because of the little hydrodynamic resistance of the loops. Thus the duration of the determination could considerably be reduced. The preconcentration of 5 ml of Cr(VI) sample and FAAS determination could be carried out within 2 min. The enrichment factor was 65. The detection limit (3 σ) was 2.0 ng ml −1. The relative standard deviation was 2.1% for 50 ng ml −1 and 6.8% for 5 ng ml −1 Cr(VI) ( N=5). The proposed method was applied for determination of Cr(VI) in various water and cigarette ash samples.

Continuous reactor system of monosized colloidal particles

A reactor system, which continuously hydrolysed the metal alkoxide in an alcohol solution, was designed using an electromagnetic stirrer and an ageing tube. Several monosized colloidal particles were produced by this reactor system, which had high reproducibility and reliability for long-term production. The relation between powder characteristics and experimental parameters such as reagent concentration, mixing rate, ageing time, temperature, was investigated. These parameters had an effect on the particle size, size distribution, morphology and state of agglomeration. It is possible to control the particle size to between 0.1 and 1.0 μm by varying the experimental conditions. A narrower size distribution of powders was obtained by using an electromagnetic stirrer with greater flow rate. Physical and chemical properties of monosized colloidal particles obtained by this reactor were comparable to those of monosized colloidal particles obtained by the batch process.

Regional cycles of perfusion and non-perfusion in the lung of the term fetal rabbit

The spatial distribution of pulmonary blood flow and its change over time was investigated in term fetal rabbits, using the plasma tracer fluorescein-isothiocyanate-labeled bovine serum albumin (FITC-BSA). A tracer bolus was injected intravenously and allowed to circulate in vivo for increasing periods of time (2-30 minutes) prior to arrest of the circulation and tissue preparation. Initially, fluorescence was present in the vasculature of 43% of lung parenchymal tissue, disposed as discrete regions or "lobules." Interspersed regions of lung tissue received no tracer inflow. With increasing tracer circulation times (10, 20, and 30 minutes), a greater percentage of lung cross-sectional area contained vessels exhibiting tracer fluorescence (64, 96, and 100%, respectively). In the fetal lung, a high pulmonary vascular resistance (PVR) is maintained. Our studies indicate that, at any given moment, fetal pulmonary blood flow is distributed only to a proportion of discrete lung "lobules," while interspersed "lobules" receive no flow at all. The "lobules" alternate between these "high" and "low" vascular resistance states with a periodicity of approximately 35 minutes, comprising 22 minutes of non-perfusion followed by 13 minutes of perfusion. This circulatory pattern permits both the maintenance of high PVR and uniform lung development. Further, by directing flow to only a portion of the vasculature, greater microvascular flow rates are achieved and hence the risk of blood sludging and stasis is reduced. Recruitment of these "non-perfused" regions at birth could thus produce a significant reduction in PVR.

EARLY DETECTION OF “REBREATHING” IN AFFERENT AND EFFERENT RESERVOIR BREATHING SYSTEMS USING CAPNOGRAPHY

Capnography was used to determine the onset of rebreathing in afferent (AR) and efferent (ER) reservoir breathing systems in a spontaneous ventilation lung model. In the case of the Lack and enclosed AR systems, the best sampling site was found to be in the exhaust limb of the systems, 5 cm from the Y connector. For the Magill system, fitted with a hooded scavenging valve, the best site was deep inside the hooded valve. In contrast, the best sampling site in an ER system (e.g. Bain system) was in the tracheal tube. For AR systems, the loss of a fresh gas elimination pattern (carbon dioxide trace failing to reach zero) was shown to occur at the onset of rebreathing. As the sampling site was moved distally into the exhaust limb, the same pattern was seen at greater flow rates--that is, before rebreathing was actually occurring. When sampling was within the tracheal tube, using ER systems, a typical "rebreathing wave" occurred at the onset of established rebreathing.

Changes in the spatial distribution of pulmonary blood flow during the fetal/neonatal transition: an in vivo study in the rabbit.

The spatial distribution of pulmonary blood flow was investigated in term fetal and neonatal rabbit littermates, using the plasma tracer fluorescein-isothiocyanate bovine serum albumin (FITC-BSA). A tracer bolus was injected intravenously and allowed 2 minutes to circulate in vivo, prior to arrest of the circulation and tissue preparation. In the fetus, fluorescence was only present in 43% of the lung volume, contained within discrete regions of "lobules." Some 57% of lung volume received no tracer inflow at all (during 2 min). In the fetal lung, the size of the potential airspaces in the perfused regions was 1.5 times larger than those in the nonperfused regions. In the fetus, a high pulmonary vascular resistance (PVR) is maintained. It is generally accepted that pulmonary blood flow in the fetus is evenly distributed to the entire vascular bed. Our results show that fetal pulmonary blood flow is distributed to discrete "lobules," while (over a 2 min period) the majority of "lobules" receive no flow at all. Thus, by directing flow to a lesser proportion of the vasculature, greater flow rates are achieved, and the risk of blood sludging and stasis is reduced. Alternation of perfusion with nonperfusion in each "lobule," perhaps regulated by the lobular arterioles, would permit both maintenance of the high fetal PVR and uniform lung development. In the neonatal lung, the plasma tracer was distributed uniformly to the entire vascular bed. This suggests that some of the reduction in PVR at birth is due to recruiting 50-60% of lung vasculature.

Analysis of Viscous Pumps With Shrouded Rayleigh-Steps Using Compressible Fluid

The paper describes an analysis of viscous pumps with shrouded Rayleigh-steps using compressible fluids. The optimum pump geometry for the maximum flow rate is presented. Frictional torque is examined for the optimized pump geometry. Finally the characteristics of the pump proposed in this paper are compared with those of spiral groove viscous pumps which are frequently used. Consequently the viscous pump with Rayleigh-steps has greater flow rate and higher pressure difference.

The effects of ureteral resistance on gull urine composition and flow rate

The effects of ureteral resistance on the ionic and osmotic composition of urine were examined in five anesthetized Glaucous-winged Gulls, Larus glaucescens, orally loaded with 0.075 M NaCl. One ureter was cut caudad to the kidney and the cloaca was opened to expose the contralateral ureteral papilla. The [Na] of urine leaving the kidney (renal urine) was less than plasma [Na] and positively correlated with flow rate. Renal urine [Cl] was less than plasma [Cl] at flow rates less than 50 μL min−1, but higher than plasma [Cl] at greater flow rates and was positively correlated with flow rate. Renal urine [K] was greater than plasma [K] at all flow rates, but markedly so below 20 μL min−1. Ureteral transit did not affect ion concentrations, but decreased (P < 0.01) urine volume and increased (P < 0.001) osmotic concentration, suggesting that the rapid flow of fluid through the renal tubules reduced isosmotic NaCl uptake and addition of osmotically active substances. Glomerular filtration was determined by inulin clearance rate in four anesthetized gulls as 4.88 ± 0.27 mL min−1 kg−1. The percentage of filtered Na, Cl, and water reaching the ureters was 0.83, 1.04, and 1.76, respectively. The ureter may influence the ureteral urine composition by regulating the rate of passage of urine through the kidney.

Activity of carboxypeptidase a bound to a modified cellulosic matrix

Carboxypeptidase A immobilized on acid chloride of oxidized cellulose showed the following features: (a) as indicated by the linearity of reaction kinetics, the immobilized enzyme action is not diffusion controlled; (b) greater flow rates are achievable with less clogging during continual usage since the enzyme is attached to a porous screen; (c) ease of handling; and (d) no apparent electrostatic interaction with the support material that is uncharged. The immobilized enzyme retained 60% of the original activity. The half-life of free enzyme was only 20 min, whereas for immobilized enzyme it was enhanced up to 2 h 48 min. It could be recovered and repeatedly used.

Offshore Production Operations

Distinguished Author Series articles are general, descriptive representations that summarize the state of the art in an area of technology by describing recent developments for readers who are not specialists in thetopics discussed. Written by individuals recognized as experts in the area, these articles provide key references to more definitive work and present specific details only to illustrate the technology. Purpose: to informthe general readership of recent advances in various areas of petroleum engineering. Summary Offshore production operations play a major and expanding role in the oilindustry. Compared with land operations, offshore operations typically requiremore planning because of the more complex systems, planning because of the morecomplex systems, equipment, and logistics involved. Higher completion rates andreserve bases are necessary to justify the high cost of developing offshorefields. Future exploration and development activity is trending toward deeperwater and more hostile environments, and innovative engineering and operatingtechniques will continue to be required to meet these challenges. Introduction The oil and gas industry began producing offshore in the late 1890's near Summerland, CA; wood wharves were built in the shallow ocean waters to supportderricks and necessary producing equipment. The industry has evolved andexpanded so that the number of offshore producing platforms now approaches 10,000 worldwide. Technology also has evolved for offshore production with specialized engineering and research in oceanography, platform construction anddesign, and production systems design. Today, offshore oil represents about 25% of the world's oil production. Themap in Fig. 1 shows the offshore basins in which industry is actively exploringand producing. It is evident that these offshore basins hold the key to future international oil supplies and that the petroleum industry must continue tomeet technological challenges in both established and frontier locations. Offshore production operations present a unique set of engineering andoperating problems compared with operations conducted on land. Developing fields offshore requires larger investments because of higher drilling and producing costs, transportation and logistical problems, and the need for aplatform base on which to conduct operations. For example, in 1983 the averageoffshore well drilled in the U.S. was twice as deep and four times as costly asthe average U.S. onshore well . Fields developed offshore, therefore, must becapable of producing at greater flow rates and in sufficient volumes to makethese significantly higher investments attractive. This paper provides anoverview of offshore production operations and keys on the major differences between offshore and land production operations, which include producing production operations, which include producing structures, well completions, production handling systems, operations organizations, and logistics. Offshore Structures The most obvious condition that sets offshore operations apart from those onland is the water itself. The offshore environment can range from shallow in land lakes and protected bays to deep, unprotected seas and oceans. Most operations offshore are conducted in water depths less than 300 ft [91 m];however, operations in water depths greater than 1,000 ft [305 m] now areoccurring frequently and will become more common with the advent of deep water technology. A platform must be constructed to support operations offshore, and special consideration is given to site-specific development and environmental conditions when designing the platform decks and structure. JPT P. 583

Diffusion models for gas production from coal: Determination of diffusion parameters

A method for the laboratory measurement of transient diffusivity parameters for methane in coal has been developed. Previously described Chromatographic techniques for measurement of single diffusivity parameters have been modified for the bi-disperse pore diffusion model. This model, which is necessary to describe methane diffusion and desorption in coal for both short and long times, requires the determination of three parameters to characterize a particular coal sample. The experimental technique uses a pulse of methane gas which is introduced into a helium stream flowing through a long tube containing the coal sample. The three desired parameters are determined by matching the experimental and theoretical elution curves. Further refinement of the technique accounts for tracer pulse duration thus allowing operation over a greater flow rate and sample size range. This technique has been applied to anthracite, bituminous and subbituminous coals. For all three coal types, the macropore diffusivity (≈10 −5 s) was about two orders of magnitude higher than the micropore diffusivity. The anthracite adsorbs more methane in the micropores than the other coals. These results showed the expected trends taking the known change of pore structure with rank into account.