Constant Flow Conditions Research Articles

Water Velocity Distribution and Its Impact on the Performance of an Electrocoagulation Reactor for Drinking Water Treatment

Iron electrocoagulation (EC) is a promising alternative to more expensive chemical coagulation for remote communities that frequently face boil water advisories[1]. In EC, the iron anode dissolves in water producing iron hydroxide and other iron-based species that facilitate the removal of natural organic matter (NOM), as per the reactions below: Anode: Fe(s)→Fez+(aq)+ze- Cathode: 2H2O(l)→H2(g)+2OH-(aq)Solution: Fez+(aq)+zOH-(aq)+xNOM(aq)→Fe(OH)z(NOM)x(s) The current density distribution in an EC cell is heterogeneous due to the local variation of [Fez+] and its effect on the local anodic equilibrium potential, according to the Nernst equation. Therefore, the reactor hydrodynamics affect current density distribution and the resulting performance of the EC cell. This research focused on the theoretical and experimental analyses of the velocity distribution within a pilot scale EC reactor. The steady-state water velocity distribution was simulated using COMSOL Multiphysics. The flow turbulence was simulated using the k-ε model. The reactor walls and the open interface with air were modeled as no-slip and slip boundaries, respectively. Water entry and outlet were modeled as constant flow and constant gauge pressure boundary conditions, respectively. Model validation was performed using partial electrode assembly design, similar to the work of Stumper et al [2]. Segments of the EC reactor were masked by an adhesive, insulating Kapton sheet. Masking of the electrode limited the reaction to the uncovered portions, while not interfering with the hydrodynamics of the reactor.[3] The modeling results show the water velocity distribution in the cell, which leads to removal of [Fez+] from the electrode/electrolyte interface and shifts the electrochemical equilibrium potential. This shift leads to a variation in the distribution of iron dissolution in the reactor. The results also indicate that the flow homogeneity increases with an increase in the inter-electrode distance, as well as with a decrease in water flow rate. Partial electrode assembly experiments verified the simulation results for a range of inter-electrode distances and water flow rates. Figure 1 shows a typical water velocity distribution, current mapping in the reactor, and comparability of the simulation and experimental results. The validated model shows the heterogeneity in flow distribution and can predict the useful lifetime of an iron electrode before its substitution or break off due to accelerated corrosion in specific areas. Such predictions enable optimum capacity, design, and operation for the reactor. The results of this project can lead to improved electrocoagulation of water for NOM removal, which can benefit communities that rely on surface water sources.

Turbulent heat transfer in tubular heat exchangers with twisted tape

Enhancing heat transfer in heat exchangers has gained attention of researchers for many years because of reduction in costs of generating heat exchanger. Application of improved tubes is one way of increasing heat transfer. In the present study, the turbulent flow in tubular heat exchangers with two twisted tapes was numerically investigated. Constant input velocity and output pressure with non-slip conditions on the surface of the tape and the tube were also considered as the hydrodynamic boundary condition. In addition, the constant heat flow and heat resistance boundary conditions were also considered for the surface of the tube and the tape, respectively. The fluent software was applied to solve the governing differential equations. Results indicated that reducing the torsion ratio at constant Reynolds number with unaligned orientation of tapes increases the average Nusselt number. Results also demonstrated that in aligned orientation, performance enhancement is more compared to aligned orientation.

Sediment Storage Partitioning in Alluvial Stratigraphy: The Influence of Discharge Variability

Abstract Numerical models of formation of alluvial stratigraphy often specify, either explicitly or implicitly, the proportion of channel and overbank sediments that are deposited during a given interval of time. However, little is known about the factors that affect the partitioning of sediment between channels and the overbank environment over long time intervals, and the fidelity with which that partition is preserved in the stratigraphic record. Here we use physical experiments to investigate the role that discharge variability plays in this partitioning in fluvial stratigraphy. We find that channels formed under constant flow conditions have low lateral mobility and act mostly as conduits for sediments to reach the shoreline. The bulk of the aggradation in this case is derived from sediment-laden flow that escapes the main channels. By contrast, including floods increases channel lateral mobility, and this change is recorded in stratigraphy as an increased proportion of channel deposits relative to overbank deposits. When variable flow is included as an input condition a large volume of in-channel deposition occurs, rendering the channels substantial contributors to stratigraphic volume on their own. The increase in channel deposit volume is driven mainly by a threefold increase in the average time that a location is subject to in-channel aggradation. Other factors include a slight increase of in-channel aggradation rates, and an increase in erosion of the overbank environment that results from energetic overbank flows. Our study shows that the character of a river's hydrograph exerts a significant influence on the proportion of channel to overbank sediment bodies in alluvial successions, which is an unexamined source of uncertainty in common stratigraphic models.

RESEARCH OF CHARACTERISTICS OF SOLID IMPURITIES AND LIQUID SENSOR-ALARMS DURING OPERATION OF WELLS WITH DIFFERENT CONSTRUCTIONS OF PRODUCTION HORIZON TAPPING

The use of sensor-alarms (SA) of Sigma-Optic JSC integrated into the remote control system of the Cenomanian boreholes of the Kharvutinskaya area Yamburgskoye oil and gas condensate field is carried out to control the content of solid impurities and liquid in the gas flow at five levels in the DSP-EAC-2 modification and seven levels in the modification of DSP-EAC-2. The article presents the results of research on characteris- tics and a comparative analysis of indications of regular and upgraded SA in the frame of complex gas dynamic studies. Analysis of field data for the period of standard sensors operation has shown the need for separate signals extraction for the content of the phase components of mechanical impurities: sand and hydrate structures. When studying the SA character- istics in laboratory conditions, different forms of pulses-responses of the action of elastoplastic impacts of hydrate particles and elastic impacts of sand particles were experimentally established. The main differences between the modifications of DSP-EAC-2 are as follows: an improved signal processing algorithm, a variable power supply scheme and an extended range of levels of excess phase components in the formation mixture. A controlled range of SA operation is established for the content of the dropping liquid in the gas flow from 6 to 100 liters per hour (0.144- 2.4 m³ per day). Synchronous registration and satisfactory comparative readings of SA are shown in conditions of constant fluid flow from the bottom of the well.

Water Velocity Distribution and Its Impact on the Performance of an Electrocoagulation Reactor for Drinking Water Treatment

Iron electrocoagulation (EC) is a promising alternative to more expensive chemical coagulation for remote communities that frequently face boil water advisories[1]. In EC, the iron anode dissolves in water producing iron hydroxide and other iron-based species that facilitate the removal of natural organic matter (NOM), as per the reactions below: Anode: Fe(s)→Fez+(aq)+ze- Cathode: 2H2O(l)→H2(g)+2OH-(aq)Solution: Fez+(aq)+zOH-(aq)+xNOM(aq)→Fe(OH)z(NOM)x(s) The current density distribution in an EC cell is heterogeneous due to the local variation of [Fez+] and its effect on the local anodic equilibrium potential, according to the Nernst equation. Therefore, the reactor hydrodynamics affect current density distribution and the resulting performance of the EC cell. This research focused on the theoretical and experimental analyses of the velocity distribution within a pilot scale EC reactor. The steady-state water velocity distribution was simulated using COMSOL Multiphysics. The flow turbulence was simulated using the k-ε model. The reactor walls and the open interface with air were modeled as no-slip and slip boundaries, respectively. Water entry and outlet were modeled as constant flow and constant gauge pressure boundary conditions, respectively. Model validation was performed using partial electrode assembly design, similar to the work of Stumper et al [2]. Segments of the EC reactor were masked by an adhesive, insulating Kapton sheet. Masking of the electrode limited the reaction to the uncovered portions, while not interfering with the hydrodynamics of the reactor.[3] The modeling results show the water velocity distribution in the cell, which leads to removal of [Fez+] from the electrode/electrolyte interface and shifts the electrochemical equilibrium potential. This shift leads to a variation in the distribution of iron dissolution in the reactor. The results also indicate that the flow homogeneity increases with an increase in the inter-electrode distance, as well as with a decrease in water flow rate. Partial electrode assembly experiments verified the simulation results for a range of inter-electrode distances and water flow rates. Figure 1 shows a typical water velocity distribution, current mapping in the reactor, and comparability of the simulation and experimental results. The validated model shows the heterogeneity in flow distribution and can predict the useful lifetime of an iron electrode before its substitution or break off due to accelerated corrosion in specific areas. Such predictions enable optimum capacity, design, and operation for the reactor. The results of this project can lead to improved electrocoagulation of water for NOM removal, which can benefit communities that rely on surface water sources.

Measurement of congestion and intrinsic risk in pedestrian crowds

In this study, we present a method to quantify the amount of congestion and the intrinsic risk in pedestrian crowds. Levels of congestion are estimated based on the velocity vector field obtained from the analysis of video recordings of moving crowds. By using data collected during supervised experiments, we show that the so-called “congestion level” allows to define a threshold for congestion under safe conditions and to measure the smoothness of pedestrian flows. The proposed approach has been compared with alternative quantities such as density, flow or the “crowd pressure” showing a more universal and consistent description of crowd motion. Later, the “crowd danger” of different pedestrian streams has been computed confirming that multidirectional motion is more dangerous than unidirectional one for equal levels of density. From a more practical perspective, the congestion level allowed to get a complete picture of the region in front of bottlenecks and to identify the formation of organized structures also under constant density and flow conditions. In addition, since only velocities are used in the computational process of the congestion level, it is more suitable for applications involving computer vision and emerging technologies, since density is usually difficult to obtain in very crowded situations. The congestion level and the crowd danger may help in the design of pedestrian facilities by simplifying interpretation of results from simulation and efficiently identify hotspots or design flaws. Finally, crowd control may benefit from the methods presented by potentially allowing a clear identification of dangerous locations during mass events.

Pharmacological regulation of outflow resistance distal to Schlemm's canal.

The trabecular meshwork (TM) and Schlemm's canal generate the majority of outflow resistance; however, the distal regions of the conventional outflow pathway account for 25-50% of total resistance. Sections of distal vessels are surrounded by α-smooth muscle actin-containing cells, indicating that they may be vasoregulated. This study examined the effect of a potent vasodilator, nitric oxide (NO), and its physiological antagonist, endothelin-1 (ET-1), on the regulation of outflow resistance in the distal regions of the conventional outflow pathway. Using a physiological model of the conventional outflow pathway, human and porcine anterior segments were perfused in organ culture under constant flow conditions, while intrachamber pressure was continually monitored. For porcine anterior segments, a stable baseline outflow facility with TM intact was first achieved before anterior segments were removed and a trabeculotomy was performed. For human anterior segments, a trabeculotomy was immediately performed. In human anterior segments, 100 nM ET-1 significantly decreased distal outflow facility from 0.49 ± 0.26 to 0.31 ± 0.18 (mean ± SD) µl·min-1·mmHg, P < 0.01. Perfusion with 100 µM diethylenetriamine-NO in the presence of 1 nM ET-1 immediately reversed ET-1 effects, significantly increasing distal outflow facility to 0.54 ± 0.35 µl·min-1·mmHg, P = 0.01. Similar results were obtained in porcine anterior segment experiments. Therefore, data show a dynamic range of resistance generation by distal vessels in both the human and the porcine conventional outflow pathways. Interestingly, maximal contraction of vessels in the distal outflow tract of trabeculotomized eyes generated resistance very near physiological levels for both species having an intact TM.

Vasoconstrictor stimulus determines the functional contribution of myoendothelial feedback to mesenteric arterial tone.

In isolated resistance arteries, endothelial modulation of vasoconstrictor responses to α1 -adrenoceptor agonists occurs via a process termed myoendothelial feedback: localized inositol trisphosphate (InsP3 )-dependent Ca2+ transients activate intermediate conductance Ca2+ -activated K+ (IKCa ) channels, hyperpolarizing the endothelial membrane potential to limit further reductions in vessel diameter. We demonstrate that IKCa channel-mediated myoendothelial feedback limits responses of isolated mesenteric arteries to noradrenaline and nerve stimulation, but not to the thromboxane A2 mimetic U46619 or to increases in intravascular pressure. In contrast, in the intact mesenteric bed, although responses to exogenous noradrenaline were limited by IKCa channel-mediated myoendothelial feedback, release of NO and activation of endothelial small conductance Ca2+ -activated K+ (SKCa ) channels in response to increases in shear stress appeared to be the primary mediators of endothelial modulation of vasoconstriction. We propose that (1) the functional contribution of myoendothelial feedback to arterial tone is determined by the nature of the vasoconstrictor stimulus, and (2) although IKCa channel-mediated myoendothelial feedback may contribute to local control of arterial diameter, in the intact vascular bed, increases in shear stress may be the major stimulus for engagement of the endothelium during vasoconstriction. Constriction of isolated resistance arteries in response to α1 -adrenoceptor agonists is limited by reciprocal engagement of inhibitory endothelial mechanisms via myoendothelial feedback. In the current model of feedback, agonist stimulation of smooth muscle cells results in localized InsP3 -dependent Ca2+ transients that activate endothelial IKCa channels. The subsequent hyperpolarization of the endothelial membrane potential then feeds back to the smooth muscle to limit further reductions in vessel diameter. We hypothesized that the functional contribution of InsP3 -IKCa channel-mediated myoendothelial feedback to limiting arterial diameter may be influenced by the nature of the vasoconstrictor stimulus. To test this hypothesis, we investigated the functional role of myoendothelial feedback in modulating responses of rat mesenteric resistance arteries to the adrenoceptor agonist noradrenaline, the thromboxane A2 mimetic U46619, increases in intravascular pressure and stimulation of perivascular sympathetic nerves. In isolated arteries, responses to noradrenaline and stimulation of sympathetic nerves, but not to U46619 and increases in intravascular pressure, were modulated by IKCa channel-dependent myoendothelial feedback. In the intact mesenteric bed perfused under conditions of constant flow, responses to exogenous noradrenaline were modulated by myoendothelial feedback, but shear stress-induced release of NO and activation of endothelial SKCa channels appeared to be the primary mediators of endothelial modulation of vasoconstriction to agonists and nerve stimulation. Thus, we propose that myoendothelial feedback may contribute to local control of diameter within arterial segments, but at the level of the intact vascular bed, increases in shear stress may be the major stimulus for engagement of the endothelium during vasoconstriction.

A method for bubble volume measurement under constant flow conditions in gas–liquid two-phase flow

Measuring the volume of a bubble, especially at its detachment, is a basic subject in gas-liquid two-phase flow research. A new indirect method for this measurement under constant flow conditions is presented. An electronic device is designed and constructed based on laser beam intensity. This device calculates the frequency of the bubble formation by measuring the total time of the formation process and counting the number of bubbles crossing the laser beam. The bubble volume at detachment can be calculated by dividing the volumetric flow rate of air by the frequency of bubble formation. The latter and the bubble volume at detachment are measured for three different heights of water above the the tip of the orifice (50, 100, and 150 mm), three orifice diameters (1, 2, and 3 mm), and different gas flow rates between 2000 and 10000 ml/hr. Comparing and validating the results with the results of the image processing (IP) method and the correlations presented by other studies shows the strong accuracy of the present method.

Charge characteristics of adsorbed natural gas storage system based on MAXSORB III

The present work deals with Natural gas (methane) adsorption onto super activated carbon (MAXSORB III) and graphite mixture in order to establish the reliability of this phenomenon as a valuable storage technique of natural gas. The objective of the subject work is to optimize different design and operating parameters of the adsorbed natural gas (ANG) system subjected to variable charge and the boundary conditions. The model duly considers the real gas properties of methane and variation of adsorbed phase properties as well as the heat of adsorption with adsorbate uptake. The storage capacities, storage efficiency as well as the filling time of activated carbon bed are studied for both constant inlet flow and constant inlet pressure charging conditions. The possibility of controlling length to width ratio (L/D ratio ranging from 0.35 to 7.8) is presented which will enable to optimize the geometry of storage tank for optimal storage efficiency. The effects of variation in inlet flow rates and variation in boundary conditions (natural convection, adiabatic wall, forced convection and constant wall temperature) on storage capacity as a function of other design and operating parameters are presented. From the study it is found that for suitable L/D ratio and external heat transfer coefficient it is possible to achieve a storage capacity of 150 V/V for constant pressure charging condition within 200 s. Addition of graphite powder for thermal enhancement of system resulted in 22%–27% (for different L/D ratios) rise in storage efficiency for model subjected to constant pressure charging and forced convection whereas 41.8%–50.4% rise in storage efficiency for model subjected to constant inlet flow and forced convection.

Effect of surface wettability on bubble detachment from single nozzle under constant flow conditions

Effect of surface wettability on bubble detachment from single nozzle under constant flow conditions

Effects of variable particle sizes on hydrothermal characteristics of nanofluids in a microchannel

This study investigates the influence of nanoparticle size on the heat transfer and pressure drop characteristics of nanofluids for laminar forced convection in a microchannel subjected to constant heat flux. Aqueous nanofluids containing spherical shaped particle dispersions of Al2O3 and TiO2, have been simulated by employing discrete phase model (DPM) for a range of ten particle sizes 20–200 nm. Analysis has been carried out by considering two particle weight concentrations (0.1% and 2%) at Reynolds number of 1000, 1200 and 2000. Results demonstrate that for constant nanofluid compositions and flow conditions, convective heat transfer and friction factor are in inverse association with the particle diameter. With the reduction in particle size, the heat transfer coefficient of nanofluids escalates because of particles’ enhanced effective particle surface area and uniform distribution along the channel radial direction. However, this improvement in heat transfer coefficient is compensated by undesirable increase in pressure drop as a consequence of higher viscosity. The variation in hydrothermal characteristics of nanofluids with particle diameter is more significant at higher particle concentration. The maximum heat transfer and friction factor difference of 11% and 20% respectively has been observed between particle sizes 20 nm and 200 nm for the particle concentration of 2%.

Equivalent Electrical Circuits of Thermoelectric Generators under Different Operating Conditions

Energy harvesting has become a promising and alternative solution to conventional energy generation patterns to overcome the problem of supplying autonomous electrical systems. More particularly, thermal energy harvesting technologies have drawn a major interest in both research and industry. Thermoelectric Generators (TEGs) can be used in two different operating conditions, under constant temperature gradient or constant heat flow. The commonly used TEG electrical model, based on a voltage source in series with an electrical resistance, shows its limitations especially under constant heat flow conditions. Here, the analytical electrical modeling, taking into consideration the internal and contact thermal resistances of a TEG under constant temperature gradient and constant heat flow conditions, is first given. To give further insight into the electrical behavior of a TEG module in different operating conditions, we propose a new and original way of emulating the above analytical expressions with usual electronics components (voltage source, resistors, diode), whose values are determined with the TEG’s parameters. Note that such a TEG emulation is particularly suited when designing the electronic circuitry commonly associated to the TEG, to realize both Maximum Power Point Tracking and output voltage regulation. First, the proposed equivalent electrical circuits are validated through simulation with a SPICE environment in static operating conditions using only one value of either temperature gradient or heat flow. Then, they are also analyzed in dynamic operating conditions where both temperature gradient and heat flow are considered as time-varying functions.

Design optimization of a venturi tube geometry in dense-phase pneumatic conveying of pulverized coal for entrained-flow gasification

The use of a venturi tube to sustain the pipeline pressure in the dense-phase pneumatic conveying of pulverized coal system is promising for its application to the pressurized entrained-flow coal gasification process, in spite of the limited knowledge of the fundamentals of the gas–solid flow through the venturi tubes at high-pressure and dense-phase pneumatic transport conditions. In this paper, a series of experiments were carried out and the geometry parameters of the venturi tube, including the convergent angle, the throat diameter, the throat length and the diffuser angle were varied at constant flow conditions to evaluate their effect on the conveying properties and on the pressure reduction effects in the flow of gas–solid mixtures through the venturi tube. The optimum values or ranges of the above mentioned venturi geometrical parameters in the application of venturi tubes to dense-phase pneumatic conveying of pulverized coal are determined in this work. These values will provide a useful reference for the design of feeding systems in the pressurized entrained-flow coal gasification process.

A Laboratory Study on the Filtration and Clogging of the Sand-Bottom Ash Mixture for Stormwater Infiltration Filter Media

The performance of stormwater infiltration systems depends significantly on the infiltration/filtration characteristics of filter media. Sand media have been frequently used due to their abundance and acceptable pollutant removal efficiency. Bottom ash media, which was known to have a high sorption capacity, are being considered as alternative and/or complement filter media to enhance the overall treatment efficiency. To verify the applicability of bottom ash as filter media, a series of 1-D column infiltration tests were conducted in this study. The filtration and clogging characteristics of the sand-bottom ash mixtures at different mixing ratios were investigated with limitedly focusing on the Total Suspended Solids (TSS) present in stormwater runoff. As a result, the presence of bottom ash was identified to improve the TSS removal efficiency in spite of having a significant increase in clogging potential. All media configurations were observed to experience the premature clogging and the clogging state for varying and constant head flow conditions, respectively. The noticeable amount of crushed bottom ash particles brought by seepage force could be accountable for the rapid occurrence of clogging phenomena. Overall, a homogeneous sand filter is preferred as long as the lifespan of filter system is the primary concern.

Evaluation of Respirator Filter Media under Inhalation-only Conditions

ABSTRACTFilter media for respirator applications are typically exposed to cyclic flow condition instead of constant flow adopted in the standard filter media tests. The objective of this study is thus to investigate the effects of breathing frequency (BF) and peak inhalation flow rate (PIFR) on the peak particle penetration of respirator filter media, especially for particles at the most penetration particle sizes under the constant flow condition having equivalent mean inhalation flowrate (MIFR). Five respirator filter media were evaluated under inhalation-only conditions. Three BFs and three PIFRs were selected for the testing. Our study evidenced that both BF and PIFR would increase the peak particle penetration under the cyclic inhalation-only conditions. It is further found that, for each filter media, the peak particle penetration at various PIFRs could be merged into one curve via the newly-defined peak penetration ratio (i.e., the ratio of peak particle penetration at cyclic flow condition to the penetration at the constant flow condition having the equivalent MIFR) and the curve is only a function of BF. The above observation indicates that the increase of peak particle penetration resulted from the increase of PIFR is simply because of the increase of MIFR. The effect of BF on the peak particle penetration is clearly observed using the defined penetration ratio. Based on our finding a semi-theoretical model was further proposed to estimate the peak particle penetration of respirator filter media under inhalation-only conditions.

Innovative Technology for Repair of Culverts in Conditions of Constant Intense Water Flow

The proposed innovative technology “Saturn” is suitable for the repair of all types of culverts on the Russian railways, especially for the repair and reconstruction of the pipes under the conditions of permanent intense watercourse, with unusual (non-typical) design solutions, as well as for pipes located in remote sections where it is difficult to arrange construction sites.The developed innovative repair technology has been successfully applied to the Oktyabrskaya Railway, or October Railway, since 2013 for repair and reconstruction of stone and concrete culverts of long-term operation and pipes of various outlines of openings ranging in size from 1.5 m to 4.2 m, including in the conditions of permanent watercourse, while a pipe is filled by flow up to 1.6 m of its section.

A Novel Identification Method of Thermal Resistances of Thermoelectric Modules Combining Electrical Characterization Under Constant Temperature and Heat Flow Conditions

The efficiency of a Thermoelectric Module (TEM) is not only influenced by the material properties, but also by the heat losses due to the internal and contact thermal resistances. In the literature, the material properties are mostly discussed, mainly to increase the well-known thermoelectric figure of merit ZT. Nevertheless, when a TEM is considered, the separate characterization of the materials of the p and n elements is not enough to have a suitable TEM electrical model and evaluate more precisely its efficiency. Only a few recent papers deal with thermal resistances and their influence on the TEM efficiency; mostly, the minimization of these resistances is recommended, without giving a way to determine their values. The aim of the present paper is to identify the internal and contact thermal resistances of a TEM by electrical characterization. Depending on the applications, the TEM can be used either under constant temperature gradient or constant heat flow conditions. The proposed identification approach is based on the theoretical electrical modeling of the TEM, in both conditions. It is simple to implement, because it is based only on open circuit test conditions. A single electrical measurement under both conditions (constant-temperature and constant-heat) is needed. Based on the theoretical electrical models, one can identify the internal and thermal resistances.

Adaptive Spectral Envelope Estimation for Doppler Ultrasound.

Estimation of accurate maximum velocities and spectral envelope in ultrasound Doppler blood flow spectrograms are both essential for clinical diagnostic purposes. However, obtaining accurate maximum velocity is not straightforward due to intrinsic spectral broadening and variance in the power spectrum estimate. The method proposed in this paper for maximum velocity point detection has been developed by modifying an existing method-signal noise slope intersection, incorporating in it steps from an altered version of another method called geometric method. Adaptive noise estimation from the spectrogram ensures that a smooth spectral envelope is obtained postdetection of these maximum velocity points. The method has been tested on simulated Doppler signal with scatterers possessing a parabolic flow velocity profile constant in time, steady and pulsatile string phantom recordings, as well as in vivo recordings from uterine, umbilical, carotid, and subclavian arteries. The results from simulation experiments indicate a bias of less than 2.5% in maximum velocities when estimated for a range of peak velocities, Doppler angles, and SNR levels. Standard deviation in the envelope is low-less than 2% in the case of experiments done by varying the peak velocity and Doppler angle for steady phantom and simulated flow, and also less than 2% in the case of experiments done by varying SNR but keeping constant flow conditions for in vivo and simulated flow. Low variability in the envelope makes the prospect of using the envelope for automated blood flow measurements possible and is illustrated for the case of pulsatility index estimation in uterine and umbilical arteries.

Limited Sanguineous Reperfusion Reduces Ventricular Fibrillation Following Intermittent Cold Crystalloid Cardioplegic Arrest.

SourceURL:file://localhost/Users/alex/Desktop/ICFJ%20VF%20submission/Abstract.doc&lt;p&gt;&lt;strong&gt;Background&lt;/strong&gt;&lt;/p&gt;&lt;p&gt;Cold crystalloid cardioplegic arrest does not allow for a controlled hyperkalaemic sanguineous reperfusate, administered under constant flow and pressure conditions in order to limit reperfusion injury. We investigated the use of intermittent, antegrade cold crystalloid cardioplegia combined with a limited flow normokalaemic sanguineous reperfusion and measured the outcome in terms of the incidence of reperfusion ventricular fibrillation.&lt;/p&gt;&lt;p&gt; &lt;/p&gt;&lt;p&gt;&lt;strong&gt;Methods&lt;/strong&gt;&lt;/p&gt;&lt;p&gt;Patients requiring coronary revascularization of at least two coronary arteries, including an internal thoracic artery (ITA) anastomosis, were studied in this prospective randomized trial. Myocardial protection was by intermittent, antegrade cold crystalloid cardioplegia. In the control group (n=100), after completion of the distal anastomoses, the heart was reperfused by releasing the aortic and ITA clamps concomitantly. In the study group (n=100) the ITA was allowed to perfuse the heart for 3 minutes before the aortic cross-clamp was removed. The presence of reperfusion ventricular fibrillation from the moment of reperfusion until weaning from cardiopulmonary bypass was recorded.&lt;/p&gt;&lt;p&gt; &lt;/p&gt;&lt;p&gt;&lt;strong&gt;Results&lt;/strong&gt;&lt;/p&gt;&lt;p&gt;The incidence of ventricular fibrillation decreased with an increase in the number of grafts and was significantly lower in the study group (double grafts 2/9, 22.2% vs 19/25, 76.0% &lt;em&gt;p&lt;/em&gt;=0.004; triple grafts 2/39, 4.9% vs 16/33, 48.5% &lt;em&gt;p&lt;/em&gt;&amp;lt;0.001; and quadruple grafts 2/45, 4.4% vs 13/35, 28.7% &lt;em&gt;p&lt;/em&gt;&amp;lt;0.001).&lt;/p&gt;&lt;p&gt; &lt;/p&gt;&lt;p&gt;&lt;strong&gt;Conclusions&lt;/strong&gt;&lt;/p&gt;&lt;p&gt;This strategy of myocardial protection combines the advantages of conventional crystalloid cardioplegia with the added benefit of limited sanguineous reperfusion. The results suggest a beneficial effect with regard to reperfusion-induced injury, as evidenced by a significantly reduced incidence of reperfusion ventricular fibrillation.&lt;/p&gt;