A capillary flow meter for measuring the hydraulic conductivity of clay under low gradients

1996 ◽  
Vol 33 (3) ◽  
pp. 504-509 ◽  
Author(s):  
R Sri Ranjan ◽  
T Karthigesu
Keyword(s):  
Hydraulic Conductivity ◽  
Capillary Flow ◽  
Capillary Tube ◽  
Nonlinear Flow ◽  
Low Flow ◽  
Flow Meter ◽  
Flow Measurements ◽  
Bubble Liquid ◽  
Triaxial Cell ◽  
Hydraulic Gradients

The measurement of water flow through clay at low hydraulic gradients (<1) is a very difficult task requiring several months to accomplish in a laboratory. A capillary flow meter, capable of measuring extremely low flow rates through clay samples under low imposed hydraulic gradients, has been designed and tested. Flux as low as 10–12 m·s–1 was successfully measured using this flow meter. To minimize the contaminatiion effects, perchloroethylene, which has self-cleaning ability, mixed with Sudan IV was used as the bubble liquid in the capillary flow meter. Glass and Teflon® valves were fused to the inflow and outflow capillary tubes to permit these components to be flushed with cleaning agents and distilled water. The movement of the menisci through the capillary tube was used as a measure of the volume flow rate through the sample. A sensitive differential pressure transducer was connected between the inflow and outflow end of the clay sample to measure the imposed hydraulic head difference. This flow meter has been independently calibrated against a conventional constant head permeameter. Once the clay samples have stabilized in a permeameter, oedometer, or a triaxial cell, multiple flow measurements under low hydraulic gradients can be done in less than an hour. Key words: nonlinear flow, saturated hydraulic conductivity, non-Darcy flow, ultra-low flow meter.

Hydraulic conductivity of clays in confined tests under low hydraulic gradients

1999 ◽  
Vol 36 (5) ◽  
pp. 815-825 ◽  
Author(s):  
D A Dixon ◽  
J Graham ◽  
M N Gray
Keyword(s):  
Hydraulic Conductivity ◽  
Reasonable Agreement ◽  
Initial Density ◽  
Degree Of Saturation ◽  
Low Flow ◽  
Flow Rates ◽  
Initial Degree ◽  
Hydraulic Gradients ◽  
Clay Barriers ◽  
Conductivity Gradient

Clay barriers normally function at hydraulic gradients much lower than are commonly used in laboratory tests for hydraulic conductivity. This paper describes low-gradient tests on compacted illite, Na-bentonite, and sand-bentonite specimens at a range of dry densities. The tests examined the effects of deionized or saline pore fluid, the initial degree of saturation at the time of compaction, and back-pressuring to achieve saturation during permeation. No "critical" or "threshold" gradients were observed. In low-density materials, "transitional" gradients defined two separate regions of Darcian flow. Low flow rates and low hydraulic conductivities were associated with hydraulic gradients below the transitional gradient. Higher conductivities were associated with gradients above the transitional gradient. Hydraulic conductivities decreased with increasing initial density. They appeared independent of initial degree of saturation or back-pressuring. Tests on Na-rich bentonite showed that deionized and saline permeants produced similar hydraulic conductivities. Measured hydraulic conductivities were in reasonable agreement with values computed using the Poiseuille and Kozeny-Carman equations. Key words: hydraulic conductivity, gradient, Darcian, illite, bentonite.

scholarly journals Mapping Groundwater Seepage in a Fen Using Thermal Imaging

Geosciences ◽  
2021 ◽  
Vol 11 (1) ◽  
pp. 29
Author(s):  
Ogochukwu Ozotta ◽  
Philip J. Gerla
Keyword(s):  
Hydraulic Conductivity ◽  
Thermal Imaging ◽  
Crucial Role ◽  
Groundwater Discharge ◽  
Late Summer ◽  
Groundwater Temperature ◽  
Groundwater Seepage ◽  
Heterogeneous Soil ◽  
Hydraulic Gradients ◽  
Warm Soil

The transport of dissolved minerals and groundwater flow plays a crucial role in the ecosystem of many wetlands. Nonetheless, installing equipment to monitor groundwater seepage is invasive, harms vegetation, and can impact biodiversity. By remotely mapping surface temperature in late summer, when there is the greatest difference between warm soil and cold groundwater, temperature patterns can expose areas with the greatest upward gradient and flow. The conventional method of using tensiometers to measure hydraulic gradient and estimate flux using Darcy’s law was applied and compared with thermal imaging to characterize groundwater seepage at two contrasting sites within a central North Dakota fen (groundwater discharge wetland). Both sites exhibited variable gradients between the shallow and deep tensiometers. The temperature trend determined from the thermal imaging showed a closer relationship to the measured hydraulic gradients at the herbaceous (Sedge) site than at the wooded (Willow) site. Saturated hydraulic conductivity K ranged from 6 × 10−5 to 2 × 10−4 m/s for the Willow site; and 6 × 10−6 to 1 × 10−4 m/s for Sedge site. The flux calculated for the Willow site ranged from 1.4 × 10−5 to 2.7 × 10−4 m/s and that of the Sedge site ranged from 2.2 × 10−6 to 6.3 × 10−5 m/s. The gradients are affected at shallow depth because of heterogeneous soil stratigraphy, which is likely the reason that seepage faces at the sites cannot be mapped solely by thermal imaging.

Mathematical model of blood flow in a coronary capillary

1993 ◽  
Vol 265 (5) ◽  
pp. H1829-H1840 ◽  
Author(s):  
G. Fibich ◽  
Y. Lanir ◽  
N. Liron
Keyword(s):  
Capillary Flow ◽  
Mass Conservation ◽  
Flow Equation ◽  
Nonlinear Flow ◽  
Minor Importance ◽  
Capillary Length ◽  
Tissue Pressure ◽  
Complex Interactions ◽  
Length Changes ◽  
Phasic Flow

The coronary capillary flow is analyzed theoretically based on continuum mechanics. The capillary is a long, elastic, and permeable vessel loaded externally by tissue pressure, and it is subject to possible periodic length changes, together with adjacent myocytes. Capillary flow is driven by arteriolar-venular pressure difference. Ultrafiltration due to transmural hydrostatic and osmotic gradients is included, and consideration of mass conservation leads to a nonlinear flow equation. The results show that under physiological conditions ultrafiltration is of minor importance, and the analysis predicts regional differences in capillary flow. In regions with high tissue pressure (subendocardium), capillaries undergo significant periodic volume changes, giving rise to intramyocardial pumping. In those regions, capillary wall elasticity is of major importance. In regions with low tissue pressure (subepicardium), the possible periodic capillary length changes are predominant. The predicted flow patterns are in good qualitative agreement with measured epicardial phasic flow. In conclusion, the methodological advantage of a distributive analysis is demonstrated by its ability to elucidate and evaluate the role of flow determinants and their complex interactions.

Abstract TP112: Mechanism of Recurrent Stroke in Patients with Atherosclerotic Vertebrobasilar Disease in Relation to Hemodynamics

Stroke ◽  
2017 ◽  
Vol 48 (suppl_1) ◽  
Author(s):  
Joanna D Schaafsma ◽  
Frank L Silver ◽  
Scott E Kasner ◽  
Louis R Caplan ◽  
Linda Rose-Finnell ◽  
...  
Keyword(s):  
Recurrent Stroke ◽  
Posterior Circulation ◽  
Low Flow ◽  
Flow Measurements ◽  
Quantitative Mr ◽  
Perforating Artery ◽  
Recurrent Strokes ◽  
Stroke Mechanism ◽  
Prospective Longitudinal ◽  
Distal Flow

Objectives: Patients with symptomatic atherosclerotic vertebrobasilar disease are at high risk for recurrent stroke and we have demonstrated that distal flow status is independently associated with this risk. Our aim was to assess the mechanism of recurrent strokes in these patients related to their distal flow status. Methods: Patients with symptomatic atherosclerotic vertebrobasilar disease were enrolled in a prospective longitudinal cohort study (VERiTAS) with a median follow-up of 23 months. Large-vessel flow in the posterior circulation distal to the stenosis and/or occlusion was measured on quantitative MR angiography and dichotomized into normal or low flow. Three observers, who were blinded to the distal flow status, independently reviewed the imaging done at the time of the recurrent stroke to classify the most likely stroke mechanism. Results: Ten out of 72 enrolled patients had a recurrent stroke in the posterior circulation. Four patients were determined to have embolic infarcts, four patients had infarcts caused by plaques that occluded a branch or perforating artery (junctional plaques), and two patients had imaging that suggested hemodynamic infarction. Five of the ten patients with recurrent strokes had low distal flow. Of these, two patients had hemodynamic infarcts, one patient had an embolic infarct, and two patients had a junctional plaque. None of the five patients with normal flow had hemodynamic infarcts, three patients had embolic infarcts, and two patients had a junctional plaque. Conclusion: Despite the small numbers, there seems to be a higher risk of hemodynamic infarction in patients with low flow distal to symptomatic vertebrobasilar disease than in the presence of normal distal flow. This would confirm the hypothesis that in addition to embolic strokes and those related to junctional plaque, patients with low distal flow are at risk for hemodynamic infarction. Further studies are required to determine whether flow measurements could be used to select patients who may benefit from endovascular treatment of atherosclerotic vertebrobasilar disease.

Research on the Vortex Mass Flow Meter of Dual Bluff Body Based on Differential Pressure Principle

2013 ◽  
Vol 401-403 ◽  
pp. 1110-1113
Author(s):  
Quan Sheng Duan ◽  
Li Cui Wang
Keyword(s):  
Lower Limit ◽  
Mass Flow ◽  
Flow Rate ◽  
Bluff Body ◽  
Differential Pressure ◽  
Low Flow ◽  
Body Structure ◽  
Measurement Sensitivity ◽  
Flow Meter ◽  
Pressure Signal

The lower limit of the existing vortex mass flow meter based on differential pressure is high. So the application of the existing vortex mass flow meter is limited in the measurement for low flow rate. This paper proposes a method using vortex mass flow meter of dual bluff body based on differential pressure principle. The differential pressure signal between the upstream and downstream can be amplified by the vortex overlap caused by the dual bluff body structure. The results of the simulation by Fluent show that this method can reduce the lower limit of measurement, and improve the measurement sensitivity effectively.

High Pressure Capillary Flow Meter for GC

1983 ◽  
Vol 21 (5) ◽  
pp. 226-228 ◽  
Author(s):  
J. W. Bozzelli ◽  
S. C. Chuang
Keyword(s):  
High Pressure ◽  
Capillary Flow ◽  
Flow Meter

Passive Control of Unstable Characteristics of a High Specific Speed Diagonal-Flow Fan by an Annular Wing

1990 ◽  
Author(s):  
Kenji Kaneko ◽  
Toshiaki Setoguchi ◽  
Masahiro Inoue
Keyword(s):  
Flow Rate ◽  
Geometrical Parameter ◽  
Energy Input ◽  
Passive Control ◽  
Internal Flow ◽  
Flow Region ◽  
Low Flow ◽  
Performance Tests ◽  
Flow Measurements ◽  
Specific Speed

A passive control of an unstable characteristics of a high specific speed diagonal-flow fan has been proposed. It is possible to eliminate the unstable characteristics of pressure-flow rate curve in a low flow region without deterioration of performance at design point. The control action is done naturally (passively) without any energy input. The inlet nozzle of an ordinary diagonal-flow fan was replaced by an annular wing with Göttingen 625 airfoil section. The mechanism of the passive control and the optimum geometrical parameter are discussed on the basis of the performance tests and internal flow measurements.

Intraoperative use of transit time flow measurement improves patency of newly created radiocephalic arteriovenous fistulas in patients requiring hemodialysis

2020 ◽  
Vol 21 (6) ◽  
pp. 990-996
Author(s):  
Anna E Cyrek ◽  
Johannes Bernheim ◽  
Benjamin Juntermanns ◽  
Peri Husen ◽  
Arkadius Pacha ◽  
...  
Keyword(s):  
Blood Flow ◽  
Arteriovenous Fistula ◽  
Transit Time ◽  
Intraoperative Ultrasound ◽  
Low Flow ◽  
Flow Measurements ◽  
Technical Problems ◽  
Arteriovenous Fistulas ◽  
Time Flow ◽  
Observation Period

Background: The autologous arteriovenous fistula is the primary choice to establish hemodialysis access without high failure rates. Intraoperative ultrasound flow measurements of newly created autologous arteriovenous fistulas represent a possibility of quality control and may therefore be a tool to assess their functionality. The aim of our study was to correlate intraoperative blood flow with access patency. Methods: Between March 2012 and March 2015, intraoperative transit time flow measurements were collected on 89 patients. Measurements were performed 5–10 min after the creation of a standardized anastomosis using 3–6 mm flow probes. To examine the correlation between intraoperative blood flow and access patency, groups of patients with high (> 200 mL/min) versus low flow (< 200 mL/min) were enrolled. Patients were assessed clinically and with ultrasound every 3 months. Data were analyzed retrospectively. Results: In the current short-term follow-up, including 89 patients (age 62 ± 3 years), 61 (68.5%) of the autologous arteriovenous fistulas were currently being used in an observation period ranging from 3 months to 3 years (mean observation period 546 ± 95 days) postoperatively. The intraoperative blood flow in patients with functioning autologous arteriovenous fistula (78) was significantly higher than that of patients without functioning autologous arteriovenous fistulas (407 ± 25 vs 252 ± 42 mL/min, respectively; p < 0.005) (11). Conclusion: The intraoperative measurement of blood flow is a useful tool to predict the outcome of maturation in autologous arteriovenous fistula. With this method, technical problems can be detected and corrected intraoperatively. Routine implementation of intraoperative flow measurements has to be examined by prospective controlled trials.

scholarly journals The influence of conceptual model structure on model performance: a comparative study for 237 French catchments

2013 ◽  
Vol 17 (10) ◽  
pp. 4227-4239 ◽  
Author(s):  
W. R. van Esse ◽  
C. Perrin ◽  
M. J. Booij ◽  
D. C. M. Augustijn ◽  
F. Fenicia ◽  
...  
Keyword(s):  
Conceptual Model ◽  
Performance Metrics ◽  
Low Flow ◽  
Multiple Time ◽  
Large Set ◽  
Model Structure ◽  
Flow Measurements ◽  
Flexible Approach ◽  
Fixed Model ◽  
Model Structures

Abstract. Models with a fixed structure are widely used in hydrological studies and operational applications. For various reasons, these models do not always perform well. As an alternative, flexible modelling approaches allow the identification and refinement of the model structure as part of the modelling process. In this study, twelve different conceptual model structures from the SUPERFLEX framework are compared with the fixed model structure GR4H, using a large set of 237 French catchments and discharge-based performance metrics. The results show that, in general, the flexible approach performs better than the fixed approach. However, the flexible approach has a higher chance of inconsistent results when calibrated on two different periods. When analysing the subset of 116 catchments where the two approaches produce consistent performance over multiple time periods, their average performance relative to each other is almost equivalent. From the point of view of developing a well-performing fixed model structure, the findings favour models with parallel reservoirs and a power function to describe the reservoir outflow. In general, conceptual hydrological models perform better on larger and/or wetter catchments than on smaller and/or drier catchments. The model structures performed poorly when there were large climatic differences between the calibration and validation periods, in catchments with flashy flows, and in catchments with unexplained variations in low flow measurements.

Capillary perfusion pattern and microvascular geometry in heterogeneous hypoxic areas of hypoperfused rat myocardium

1995 ◽  
Vol 268 (6) ◽  
pp. H2183-H2194 ◽  
Author(s):  
F. Vetterlein ◽  
M. Prange ◽  
D. Lubrich ◽  
J. Pedina ◽  
M. Neckel ◽  
...  
Keyword(s):  
Capillary Flow ◽  
Flow Distribution ◽  
Histochemical Staining ◽  
Low Flow ◽  
Lower Percentage ◽  
Capillary Perfusion ◽  
Indicator Dyes ◽  
Myocardial Biopsies

The origin of heterogeneities in tissue oxygenation due to low-flow ischemia was studied in hypoperfused myocardium of anesthetized rats. In frozen sections of myocardial biopsies the localization of increases in NADH fluorescence, an indicator of tissue hypoxia, was compared with microvascular flow distribution and capillary geometry. The latter parameters were accomplished through capillary labeling with indicator dyes in vivo and enzyme-histochemical staining in vitro, respectively. Most NADH-fluorescent areas were found to have developed despite sustained capillary flow. When the fractions of arterial, venous, and intermediate capillary segments were analyzed within circumscribed hypoxic fields (< 200 microns diam), frequencies of 30.7 +/- 6.1, 35.3 +/- 5.3, and 30.8 +/- 5.0%, respectively, were found. In contrast, a significantly higher fraction of arterial segments (63.2 +/- 3.3%) and a lower percentage of venous segments (16.4 +/- 2.5%) were determined in nonhypoxic islands enclosed by hypoxic tissue. These results support the view that the latter zones are located near the arterial portion of the capillary bed where their oxygenation is favored during low-flow states. This effect appears to contribute to the supply heterogeneities in hypoperfused myocardium.

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