Direct Flow Measurements Research Articles

Development, construction, and use of pneumometric tubes for measurement of steam flow in the steam lines of PVG-1000 at NPP

A system for the direct measurement of steam flow in steam lines after a steam generator, which utilizes a special design of pneumometric tubes and a computing unit that accounts for variation in steam pressure, has been developed to improve the quality of water-level regulation in the steam generators of VVER-1000 power-generating units in the stationary and transitional modes. The advantage of the pneumometric tubes consists in their structural simplicity, high erosion resistance, and absence of irrevocable losses during measurement of steam flow. A similar measurement system is used at foreign NPP. The measurement system in question has been placed in experimental service at the No. 3 unit of the Balakovo NPP, and has demonstrated its worthiness. This measurement system can also be used to determine steam flow in the steam lines of NPP units with VVER-1000 and VVER-440 reactors, and PBMK-1000 power-generating units.

Effect of Prazosin on the Peripheral Vasculature during Rest Low, Mild, and Heavy Exercise Workloads.

INTRODUCTION: Metabolic inhibition of alpha-1 mediated vasoconstriction in exercising muscles is evident in both animal and human models. A majority of the studies investigating the role of alpha-1 receptors have infused exogenous α1-receptor agonists intra-arterially to activate these receptors. However the role of physiological activation of these receptors in humans is incompletely understood. PURPOSE: To test the hypothesis that as exercise intensity increases physiological activation of α1-receptors has a decreased role in the control of the peripheral vasculature in exercising muscles. METHODS: We compared the vasoconstrictor responses before and after oral ingestion of the α1-receptor blocker Prazosin (1mg/20kg of body weight) in healthy humans (n=5) during rest and dynamic knee-extensor exercise at roughly 40%, 60% and 80% of workloadmax. Neck pressure (NP) stimuli were used to unload carotid baroreceptors thus leading to sympathoexcitation. Ultrasound Doppler provided direct measurements of femoral blood flow (FBF) and intra-arterially measured blood pressures were used to calculate femoral vascular conductance (FVC). RESULTS: Prazosin resulted in significant increases FVC at rest when compared to the control protocol (+68 ± 6%). During exercise the Prazosin mediated increases in FVC decreased with increasing exercise intensities (+68 ± 4%, +39 ±4%, and +23 ± 6% respectively). In both conditions “functional sympatholyis” was occurring because the NP mediated vasoconstriction was attenuated in an exercise intensity dependent manner. During NP the % decreases in FVC were not significantly different between conditions. CONCLUSIONS: These data demonstrate that vasoconstriction elicited by physiological activation of ?1 -receptors with circulating endogenous agonists as a result of intense dynamic exercise is reduced as exercise intensity increases. Additionally there was a reduced response to sympathetically mediated vasoconstriction as a result of functionally unloading the carotid baroreceptors with NP stimuli in both conditions, i.e. functional sympatholysis was present. Furthermore the NP mediated vasoconstriction was attenuated to a similar degree in both conditions. Supported in part by NIH grant # HL-045547

High-resolution mapping of shallow gas accumulations and gas seeps in San Simón Bay (Ría de Vigo, NW Spain). Some quantitative data

San Simon Bay in the innermost part of the Ria de Vigo is characterized by an abundance of very shallow gas accumulations and methane seeps. During the expeditions of April–June–September 2004 within the Spanish-funded Gs2G project, detailed very high-resolution seismic and field investigations were carried out to study the shallow gas and the seeps. Direct gas fluxes also were measured from bubble streams. For the first time, the surface area and gas front depth of a shallow gas field has been mapped and quantified in the inner bay of Ria de Vigo. This field overlaps spatially with the distribution of Holocene mud within the bay. Seismic data show 3.6 km2 affected by acoustic turbidity but this surface can be extended up to 9.5 km2 of San Simon’s muddy subtidal area. Mounded turbidity superimposed on the main gas field has been mapped and characterized as anthropogenically (mussel rafts) mediated gas accumulations. Different acoustic anomalies have been identified and interpreted as being due to gas escapes from the present seabed sediment. The very high resolution of the seismic data makes it possible to identify a new type of seep, here named ‘acoustic smoke.’ A direct relationship can be observed between the gas front of accumulations and escape features, both acoustic seeps and pockmarks. The methane flux has been estimated from the subtidal environment in San Simon based on detected acoustic targets and direct measurements of current bubble flow. The total estimated methane flux from the seabed into the water column ranges from 10.1 to 48.8 t/year, and into the atmosphere from 7.0 to 34.2 t/year. The intertidal San Simon environment is also actively venting methane, as indicated by the presence of bubbling during high tide and white patches of Beggiatoa sp.

Simulation and experimental study of gas-to-particle heat transfer for non-invasive mass flow measurement

Thermal flowmeters based on the heat transfer principle can, in theory, provide direct mass flow measurement of gas–solids two-phase flow. They are applicable to a wide range of industrial process, where there is a need for accurate, reliable, on-line, continuous and non-invasive measurement of solids’ mass flow rate. A non-invasive thermal system has been proposed. The key issues have been highlighted and the results from initial simulations and experiments have indicated that the technique is worthy of further and more detailed investigation.This paper concentrates on: (i) measuring the temperature of a single particle both before and after passage through a heated region; (ii) describing the transient thermal characteristics of the gas and the single particle in the heated region; and (iii) characterizing the heat transfer from the hot pipe wall to the gas and from the gas to the single particle.

Enhanced Flow Velocity after Stenting of Renal Arteries Is Associated with Decreased Renal Function

Background: Atherosclerotic renal artery stenosis (RAS) is frequently treated by angioplasty and stent placement. Duplex sonography is an established noninvasive technique for patient follow-up. There is lack of evidence that routine monitoring of asymptomatic patients with stable blood pressure is needed. Methods: Renal duplex sonography was performed in 64 patients who had received percutaneous angioplasty and stenting of an atherosclerotic RAS. Duplex sonographic diagnosis was made by a combination of direct flow measurement in the renal artery and evaluation of intrarenal resistive indices. Renal function was determined by serum creatinine and calculated glomerular filtration rate (GFR). Results: With a mean follow-up of 28 months after angioplasty, a flow velocity of >2.0 m/s was detected within the stented arteries in 11/64 patients. While the initial blood pressure and GFR as well as the influence of angioplasty on these parameters were not different, the decrease in renal function over time was significantly higher in patients with flow enhancement (annual GFR decrease, 8.0 ml/min vs. 0.8 ml/min; p < 0.05). Conclusion: Follow-up duplex sonography in patients after renal artery stenting detected an unexpectedly high rate of in-stent restenosis associated with enhanced loss of renal function. Routine duplex sonographic follow-up may detect patients at risk of more rapidly declining renal function.

Insects in flight: direct visualization and flow measurements

The study of insect flight has been advanced in recent years by the advent and application of new quantitative flow diagnostic techniques, not least digital particle image velocimetry. More classical qualitative methods such as smoke flow visualization have also been applied with new goals for the rigorous description of flows around insects. The combination of techniques has led to the development of ideas which may be of some consequence to the designers of micro-air vehicles wishing to follow a biomimetic principle. Specifically, kinematic parameters such as wingbeat frequency and amplitude are discussed, along with some discussion of the investigation of morphological parameters such as wing design.

Collateral blood flow between left coronary artery bypass grafts and chronically occluded right coronary circulation in patients with triple vessel disease. Observations during complete revascularisation of beating hearts

Preoperative measurements of collateral blood flow in patients with triple vessel disease and chronic occlusions of the right coronary artery do not, currently, ascertain the need to revascularise an occluded right coronary artery. We performed direct measurements of flow across left coronary bypass grafts to determine their contributions to collateral blood flow. Collateral blood flow was scored preoperatively according to Rentrop in 13 patients with triple vessel disease and chronic occlusions of the right coronary artery who underwent complete, off-pump, surgical revascularisation. The transit-time flow through the left coronary grafts was measured before and after unclamping of the right coronary artery bypass graft. Unclamping of the right coronary artery bypass graft was associated with a 5.9+/-6.9ml/min (mean+/-SD) decrease in flow across the left circumflex territory (P=0.009), which was proportional to the preoperative Rentrop score (P=0.007). No significant change was observed in flow across the graft to the left anterior descending artery. Grafts to the left circumflex system are the only grafts that supply a significant, albeit modest amount of collateral blood flow to chronically occluded right coronary artery. These observations confirm that (1) most collateral flow after revascularisation is supplied by the native network, and (2) revascularisation of an occluded right coronary artery is fully justified.

How the body controls brain temperature: the temperature shielding effect of cerebral blood flow

Normal brain functioning largely depends on maintaining brain temperature. However, the mechanisms protecting brain against a cooler environment are poorly understood. Reported herein is the first detailed measurement of the brain-temperature profile. It is found to be exponential, defined by a characteristic temperature shielding length, with cooler peripheral areas and a warmer brain core approaching body temperature. Direct cerebral blood flow (CBF) measurements with microspheres show that the characteristic temperature shielding length is inversely proportional to the square root of CBF in excellent agreement with a theoretical model. This "temperature shielding effect" quantifies the means by which CBF prevents "extracranial cold" from penetrating deep brain structures. The effect is crucial for research and clinical applications; the relationship between brain, body, and extracranial temperatures can now be quantitatively predicted.

Sap flow and daily electric potential variations in a tree trunk

Electric potential has been monitored since December 2003 in the roots and at two circumferences and one vertical profile in a standing poplar ( Populus nigra). Electric potential is sampled using 6 mm diameter stainless steel rods, inserted 5 mm deep in the sapwood and is referenced to an unpolarisable lead/lead chloride electrode installed 80 cm deep in the soil. Diurnal variations are observed with seasonal differences. During winter, diurnal variations depend on the measurement point, with variable amplitudes and sometimes anti-correlations between electrodes. By contrast, a stable and coherent organisation is established in the spring, with larger amplitudes, and lasts during summer. Dedicated experiments have been performed to rule out a direct effect of temperature on the electrodes, and thus, demonstrate a genuine electrical source in the tree. Daily electrical variations have been reported previously, and have been interpreted as electrokinetic effects associated with sap flow. However, a comparison of the electrical signals with a direct measurement of the sap flow by a continuous heat flow method, shows that the electrical variation, although clearly correlated to sap flow, is not simply proportional to it. In a living system, electrokinetic effects, in addition to thermoelectrical effects, are probably modified significantly by additional electrochemical effects, such as membrane diffusion potentials, ion active transport by proteins or action potentials. Electric potential variations in trees may thus, reveal physical mechanisms in living systems not accessible by other methods. A better understanding of the electrical response of trees associated with sap flow may improve the knowledge of transfer processes between the soil and the atmosphere. This is important for the understanding of adaptive response of trees, the modelling of water and carbon balance in relation to climate change, and the quantification of the contribution of trees to the migration, retention and dispersion of contaminants.

소형 코리올리 질량 유량계의 개발

A Coriolis mass flowmeter(CMF), which has U-Shaped unique measuring tube was developed for direct mass flow measurement. In order to convert the time difference between two measuring tubes motion into mass flowrate and flow quantity, a signal processing circuit, as a part of CMF, was also developed. The CMF was designed as the 15 mm nominal diameter of pipe connection and the 8 mm stainless steel(sus 316) pipe was used for measuring tube. To maximize the flow signal(time difference) from the measuring tubes, the natural frequency of measuring tube was adjusted as 220 Hz, which is same as the frequency of exciter. The maximum displacement at the end of the measuring tube was measured as 0.05 mm, and the maximum time difference between two measuring tubes was observed as 20 , which was proper for discrimination and measuring range of CMF. The developed CMF was tested against the gravimetric flowmeter calibrator in the range of 3 kg/min and 30 kg/min . The results showed that the CMF has good linearity and repeatability in the tested flow range. Large size of CMF base on the current study experience will be developed.

Bulk Flow in Ferrofluids in a Uniform Rotating Magnetic Field

Direct measurements of the bulk flow of a ferrofluid in a uniform rotating magnetic field were obtained using the ultrasonic velocity profile method. The fluid was observed to corotate with the field in a rigid-body-like fashion throughout the bulk of the container, except near the air-fluid interface, where it was observed to counterrotate. The results were found in qualitative agreement with the spin diffusion theory of Zaitsev and Shliomis [J. Appl. Mech. Tech. Phys. 10, 696 (1969)]10.1007/BF00907424.

Understanding the splenic contribution to portal flow: The role of splenic artery ligation as inflow modification in living donor liver transplantation

Understanding the splenic contribution to portal flow: The role of splenic artery ligation as inflow modification in living donor liver transplantation

Gastric blood flow, mast cell degranulation and micromorphology of gastric mucosa following experimental haemorrhagic shock in dogs.

Ischaemia of the gastric mucosa in haemorrhagic shock appears to be one of the principal factors underlying acute bleeding from the upper gastrointestinal tract. In the present experimental study on dogs the changes of blood flow in the upper gastrointestinal tract were recorded by direct flow measurement in the pertinent vessels. Fourteen mongrel dogs were subjected to haemorrhagic shock lasting for 3 and 4 h. A decline of 46 per cent cardiac output was observed while coeliac artery blood flow decreased by 40 per cent and gastric artery blood flow by 60 per cent. All stages of stress ulcers were documented by light and electron microscopy. In addition, pronounced degranulation of mast cells preceding major tissue damage was observed. In the light of these findings a cascade of events is thought to be present resulting in the development of stress ulcer.

Measuring On-Farm Irrigation Efficiency with Chloride Tracing under Deficit Irrigation

Water is a limited resource in agricultural production in arid climates. Under such conditions, high irrigation efficiency can be obtained either through implementation of efficient irrigation systems such as drip or sprinkler systems or through the age-old practice of deficit irrigation with gravity systems. The method used to increase irrigation efficiency is often dictated by economic and/or social factors. In either case, the effectiveness of water management at the farm level needs to be evaluated by measuring irrigation efficiency. The objective of this study was to evaluate the irrigation efficiencies for three crops in Southern New Mexico using the chloride technique. The chloride technique is a simple method in which the natural chloride in the irrigation water is used as a tracer to estimate the leaching fraction and the irrigation efficiency at the farm level. Soil samples were collected from various fields in 15 cm increments to a depth of 180 cm at the end of the irrigation season. The samples were analyzed for moisture and chloride content. In addition to the chloride technique, on-farm irrigation efficiencies were measured using applied water, yield, and water production functions. Water production functions and yields were used to estimate total evapotranspiration while flow measurements were used to calculate the amount of applied water. The results showed that high irrigation efficiency can be accomplished using deficit irrigation. Irrigation efficiency values ranged from 83 to 98%. Irrigation efficiencies using the chloride technique were compared with efficiencies estimated from direct flow measurements. The differences between the two methods ranged from 2 to 11.4%. The results showed that even though the chloride technique is subject to sampling errors and simplified theoretical assumptions, it can be used to estimate on-farm irrigation efficiency with considerable accuracy.

An indirect pressure-gradient technique for measuring instantaneous flow rates in unsteady duct flows

A new technique is presented for making measurements of the instantaneous flow rate in unsteady laminar pipe flows. It utilizes a relationship between flow rate and pressure-gradient history that is an exact solution to the Navier–Stokes equations for parallel, developed flow of constant-property Newtonian fluids undergoing arbitrary unsteadiness from an initially steady or stationary state. The method does not rely on any assumption about velocity profiles, and applies instantaneously in momentarily reversing flow. Experimental comparisons between direct measurements of the cumulative flow and the results of this technique indicate that it is capable of providing measurements of cumulative flow and flow rate which are accurate to within a few percent at any instant during a flow transient, provided the instantaneous pressure gradient can be measured with this accuracy.

Direct measurements of the mean flow and eddy kinetic energy structure of the upper ocean circulation in the NE Atlantic

The upper ocean circulation in the sub‐polar northeast Atlantic has been a challenge to quantify due to strong and variable wind‐forcing, and strong and variable deep currents that lead to large uncertainties in the use of the standard dynamical method. Since 1999 we have been operating an acoustical Doppler current profiler on a container vessel that operates between Denmark and Greenland to repeatedly sample upper ocean currents across the northeast Atlantic. Individual transects exhibit a highly energetic mesoscale variability, but ensemble‐averaging of the sections reveals a striking organization of the mean field along the Reykjanes Ridge: a distinct southward flow along its eastern slope and two clearly defined peaks with seasonal modulation flowing to the north along its western slope. Higher values of eddy kinetic energy (about 150–600 cm2 s−2) are observed along the transect, O(1.5) greater than surface drifter estimates.

Blood Flow to the Metatarsal Head After Chevron Bunionectomy

Avascular necrosis (AVN) of the metatarsal head is a known, but infrequent, complication of a chevron bunionectomy. An increased incidence of AVN has been reported with the addition of an adductor tenotomy and lateral release. The purpose of this study was to document the vascular insult to the metatarsal head during a chevron bunionectomy with adductor tenotomy and lateral release through direct blood flow measurements during the procedure. A prospective study of 20 patients was performed. A chevron bunionectomy was performed under regional anesthesia without tourniquet control by two surgeons. Blood flow recordings were documented during key portions of the procedure: baseline, medial capsulotomy, adductor tenotomy and lateral release, and chevron osteotomy. The Periflux PF3 laser Doppler probe (Perimed, Inc., North Royalton, OH) was used to record blood flow. Mauchly's test of Sphericity and a pairwise comparison were performed with significance defined as p < 0.05. All patients had radiographs 3 months postoperatively to assess AVN. There was a statistically significant decrease in blood flow to the metatarsal head at each portion of the procedure. The greatest insult occurred with the medial capsulotomy (45% decrease). The lateral release and adductor tenotomy caused a 13% decrease and the chevron osteotomy caused a 13% decrease, totaling 71% decrease from the baseline. There was no evidence of AVN at 3 months, and all patients had radiographic evidence of union without recurrence or over-correction. The addition of the adductor tenotomy with lateral release often is crucial to obtain the desired correction and avoid the complication of recurrence. The disruption of microvascular blood flow to the metatarsal head after a chevron bunionectomy with adductor tenotomy and lateral release was not complete, totaling 71% in the study population. The greatest insult occurred with the medial capsulotomy. There were no occurrences of AVN. Despite the fear of AVN, this study demonstrated that an adductor tenotomy and lateral release could be done safely completed with a chevron bunionectomy.

Importance of barrier layers in thermal diodes for energy conversion

Very high thermal to electric conversion efficiencies have been reported previously with thermal diode structures in which a thin n-type emitter layer is formed on the hot side of a thick near-intrinsic thermoelectric semiconductor. The figure of merit derived from direct measurements of electrical parameters and heat flow is increased by as much as a factor of eight. The question of what physical mechanisms are involved has been of interest since the initial observations of the effect. We have conjectured that the short-circuit current injection in these experiments is due to a second-order thermionic injection mechanism. More recently, we proposed that the open-circuit voltage comes about due to the presence of a p-type blocking layer between the emitter and the near-intrinsic bulk region. The experiments reported here show that a p-type blocking layer is required for the effect, and the dependence of conversion efficiency on the blocking layer concentration and width is studied. The results are generally consistent with calculations done so far based on a nonlocal generalized Onsager-type transport model.

Directed and elliptic flow at RHIC

We present the directed flow measurement (v1) from Au+Au collisions at . Over the pseudorapidity range we have studied, which covers η from −1.2 to 1.2 and 2.4 < |η| < 4, the magnitude of v1 for charged particles is found to increase monotonously with pseudorapidity for all centralities. No ‘v1 wiggle’, as predicted by various theoretical models, is observed at midrapidity. Elliptic flow (v2) from moderately high-pt particles (3–6 GeV/c) at is presented as a function of impact parameter. It is found that models that are based on jet quenching alone appear to underpredict v2 at moderate high pt, while the model that incorporates both, recombination and fragmentation, describes the data better.

Intraoperative direct measurement of hepatic arterial buffer response in patients with or without cirrhosis

The hepatic arterial buffer response (HABR) is an intrinsic regulatory mechanism of the hepatic artery (HA) that compensates for reductions in portal venous (PV) blood flow. Whether this response is maintained in patients with cirrhosis (LC) is unclear. The aim of the present study was to examine whether HABR is maintained in patients with LC using direct blood flow measurements. PV and HA blood flow were intraoperatively measured and compared in patients with (LC group, n = 39) or without (control group, n = 22) cirrhosis at baseline (baseline HABR) and after PV clamping (acute HABR) using an ultrasound transit-time flowmeter. In contrast to the proportional relationship between the baseline PV and HA blood flow observed in the control group, HA blood flow and the HA-PV flow ratio increased when PV blood flow decreased in the LC group, suggesting that the baseline HABR had already been activated. Acute HABR, evaluated by the absolute and relative changes in HA blood flow and by the buffer capacity, was blunted in the LC group (P < 0.001, P < 0.01, and P = 0.01, respectively). An association between the degree of acute HABR impairment and the level of baseline HABR activation (HA-PV flow ratio) could not be confirmed in the LC group. In conclusion, the baseline HABR appears to be continuously activated in patients with LC; this phenomenon probably results in the impairment of the acute HABR.