Electrical Conductivity Probe Research Articles

Measured and Predicted Solute Transport in a Tile Drained Field

Most solute transport measurement techniques are tedious and require extensive soil excavation. A field experiment was conducted to evaluate whether surface transport properties determined by a nondestructive time domain reflectometry (TDR) technique could be used to accurately predict tile flux concentrations. A 14 by 14 m field plot selected above a 1.1‐m deep tile drain was studied. Low electrical conductivity (EC) water was sprinkled on the plot surface, and after reaching a steady‐state condition, a pulse of calcium chloride solution (16.3 cm) with an EC of 23 dS m−1 was applied through the same sprinklers. Time domain reflectometry equipment was used to record the change in EC of surface (∼ top 2 cm) soil at 45 locations. The EC of the tile drainage flow was measured continuously with an EC probe. The surface convective lognormal transfer (CLT) function parameters, log mean irrigation depth, μI, and its standard deviation, σI, were found to be 3.44 and 0.94 [ln(cm)], respectively, for a reference depth of 110 cm. These surface parameters were used in a one‐dimensional (1‐D) CLT model and in a two‐dimensional (2‐D) model (CLT vertical function combined with exponential horizontal transfer function) to predict the tile flux concentrations. The 1‐D CLT model predicted an earlier arrival time of chemicals to the tile drain than observed values. The root mean square error, RMSE, of the 1‐D CLT predictions was 0.123, and the coefficient of efficiency, E, was −0.47. The 2‐D model predictions of tile flux concentrations were similar to the observed values. The root mean squared errors (RMSE) and E were 0.023 and 0.94, respectively. The findings suggest that in this field soil, the surface solute transport properties determined by TDR could be combined with a 2‐D transport model to make reasonable predictions of tile flux concentrations.

In Situ Probes for Measurement of Electrical Conductivity of Soilless Substrates: Effects of Temperature and Substrate Moisture Content

Growing medium electrical conductivity (EC) is used in laboratory analysis and greenhouse production as a measure of the nutrient content of the growing medium. Fast, accurate ways to measure growing medium EC will make it easier to determine EC and maintain it within a suitable range for a particular crop. Several probes have been developed that can be inserted directly into the growing medium of container-grown crops for measurement of EC. We tested the sensitivity of four in situ EC probes (Field Scout, HI 76305, WET sensor, and SigmaProbe) at a range of temperatures, substrate volumetric water contents (VWC), and fertilizer concentrations. The HI 76305 probe was highly sensitive to temperature, while the WET sensor was temperature-sensitive at high ECs above its normal operating range. The probes responded differently to increasing VWC. The SigmaProbe and WET sensor measure the EC of the pore water specifically and show a decrease in EC with increasing water content, as the fertilizer ions in the pore water become more diluted as VWC increases. EC readings of the HI 76305 and Field Scout probes, which measure the EC of the bulk substrate (growing medium, water, and air combined) increased with increasing water content as the added water helps conduct the current of these meters. At a VWC above 35%, there was little effect of VWC on EC readings of all probes. The EC measured with the various in situ probes differed slightly among the probes but was highly and positively correlated with all three of the standard solution extraction methods [pour-through, 1:2 dilution, and saturated media extract (SME)] over the range of fertilizer concentrations at a given temperature and VWC. These results make it possible to convert substrate EC guidelines that have been established for any of the three standard methods for use with the in situ probes, though our results indicate the substrate VWC must be above 35% for the interpretation to be valid. The in situ probes are a viable alternative for measurements of substrate EC and eliminate the step of substrate solution extraction, thus simplifying data collection.

A New Graphical Method for Calculation of Mass Transfer Time in a Deep Bubble Bed

A new method for graphical determination of mass transfer (saturation) time in a deep bubble bed (BB) was developed. It is based on the spatial distribution of the local liquid-phase concentrations CL(t) measured by means of an electrical conductivity probe. The raw CL(t) data were obtained in a 0.289-m-ID bubble column equipped with a perforated plate gas distributor (31 holes × ø2 × 10–3 m). Three different clear liquid heights (L0 = 0.56, 1.12 and 1.84 m) were examined. The shallow BB (L0 = 0.56 m) was aerated at superficial gas velocities ug = 0.018, 0.031, and 0.038 m·s–1, respectively. Both medium (L0 = 1.12 m) and deep (L0 = 1.84 m) BBs were aerated only at ug = 0.038 m·s–1 (churn-turbulent flow regime). It was found that the new graphical method is applicable only for a deep BB (L·Dc–1 = 7.3). In that particular case, the difference between the experimental mass transfer time and the graphically determined one is reasonable (the maximum relative error is only 6.9%). Therefore, the new graphical method should be adopted for experimental determination of the mass transfer time in a deep BB. The new method is of practical importance because the industrial bubble columns operate with deep BBs.

Application of a Vertically-employed Electrical Conductivity Probe

本研究では, 地域レベルの3次元的な塩類動態を経時的に把握することができる手法を提案した. この手法を用いて, 東北タイの塩類集積が発生している地域にて現地実験を行った結果, 以下の結果を得た. (1) 試作した鉛直型電気伝導度センサは, 地下水位以下の土層においても計測可能であり, さらに土壌サンプルから得た電気伝導度と比較すると, 信頼性が高い値を出力していることが確認できた. (2) 提案した手法をもちいて, 実験地域の3次元電気伝導度マップが作成できることを示し, その結果から, 地域の塩類集積の状況が確認できた. (3) このマップ作成の時間について考察したところ, 計測開始からマップ作成まで, おおよそ1日で作業を完了できることから, 経時的な観測活動に適しているものと示唆された. (4) 提案した手法により, 地域の3次元的な塩類動態が経時的に把握されれば,塩類集積の防止策や塩類土壌修復方法の評価や, 塩類集積メカニズムの解析などに貢献できる可能性が示唆された.

In Situ Probes for Direct Measurement of Substrate Soluble Salts: Effects of Substrate Moisture Content and Fertilizer Concentration

Several probes have been been recently developed that can be inserted directly into the growing medium of container-grown crops to get electrical conductivity (EC) or pH measurements. However, for many floriculture and greenhouse crops, EC interpretation ranges are based on substrate solution extraction methods such as the 1:2 v/v dilution, saturated media extract (SME), and more recently, the pour-through. We tested the sensitivity and accuracy of four in situ EC probes at a range of substrate moisture content and fertilizer concentrations. We also compared results from in situ probes with currently used methods of EC measurement. Concerning the effects of substrate volumetric water content (VWC) on the in situ probes, our results indicate little differences exist among probes when VWC exceeds 0.50, though drier substrates yielded differences depending on the measurement method. The SigmaProbe and W.E.T Probe measure the EC of the pore water specifically and show a decrease in EC with increasing water content, as the fertilizer ions in the pore water becomes more diluted as VWC increases. Results with the Hanna and FieldScout probes increased with increasing water content as the added water helps conduct the current of these meters. The EC measured with the various in situ probes differed slightly among the probes, but was highly and positively correlated with all three of the solution extraction methods over the range of fertilizer concentrations. It would be possible to convert substrate EC guidelines that have been established for any of the laboratory methods for use with the in situ probes, though our results indicate the substrate VMC must be above 0.35 for the interpretation to be valid.

Application of high frame-rate neutron radiography to liquid-metal two-phase flow research

Liquid metal two-phase flows in metallic vessels were studied by using high frame-rate neutron radiography. Both a bubble column and a gas-lift loop arrangement have been considered. Liquid velocity field of two-phase flow in a flat bubble column with rectangular cross-section was measured precisely by the particle tracking velocimetry. In a gas-lift loop, simultaneous measurements of void fraction by using high frame-rate neutron radiography and four-sensor probe were also performed to observe the bubble-probe interaction. Asymmetric Abel inversion was applied to compare the radial void fraction profiles. Measured radial void fraction profiles obtained by neutron radiography and electrical conductivity probe agreed well with each other. From these measurements, the measurement error and basic characteristics of gas–liquid metal two-phase flow were clarified.

The Effect of Superficial Gas Velocity and Aerated Liquid Height on the Spatial Distribution of Local Liquid-Phase Axial Dispersion Coefficients in a Bubble Column

The spatial liquid-phase concentrations were measured by means of an electrical conductivity probe in a 0.289-m ID bubble column operated at superficial gas velocities (ug) of 0.018, 0.031 and 0.038 m/s, respectively. The column was equipped with a perforated plate gas distributor (0.002 mo × 31 holes). Carbon dioxide was used as a tracer gas, whereas deionized water was used as a liquid phase. The local liquid-phase axial dispersion coefficient EL was derived from the local liquid-phase concentrations by means of the graphical method developed by Khang and Kothari (1980). It was found that the spatial distribution of the local EL coefficients becomes radially non-uniform as a function of ug. At the regime transition velocity (Utrans = 0.031 m/s) between bubbly and transition flow regimes the mean, EL coefficient for the upper zone (UZ) becomes identical to the one for the lower zone (LZ). At both lower and higher ug values EL(UZ) is systematically higher than EL(LZ). The same result also holds if the overall bubble bed (BB) is divided into core and annulus regions. It was proven that, in the bubbly flow regime (ug Utrans), EL (annulus region) > EL (core region). The effect of the aerated liquid height L on the spatial distribution of the local EL coefficients was studied, as well. Three different BBs, viz. L = 0.64 m (shallow BB), 1.28 m (medium BB) and 2.1 m (deep BB) were examined at ug = 0.038 m/s. The spatial distribution of the local EL coefficients was most scattered in the shallow BB (L = 0.64 m). In a medium BB with an aerated liquid height L = 1.28 m the existence of a well-developed helical flow structure was detected.It was shown that the graphically determined mean EL coefficient (for the overall BB) increases as a function of both the superficial gas velocity ug and aerated liquid height L, and a useful empirical correlation was derived. It covers the following range of bed aspect ratios: 2.1 ≤ L/Dc ≤ 7.3.

Measurements of liquid–metal two-phase flow by using neutron radiography and electrical conductivity probe

Neutron radiography and electrical four-sensor conductivity probe method were applied to measurement of liquid–metal two-phase flow. Visualization and measurements of nitrogen gas–molten lead bismuth two-phase flow were performed by using neutron radiography technique. Simultaneous measurements of void fraction by using high-frame-rate neutron radiography and four-sensor probe were also performed to observe the bubble–probe interaction. At the same experimental conditions, four-sensor probe was applied to the measurements of interfacial area concentration in radial direction. From the visualization of the two-phase flow, it turned out that cap bubbles or elongated slug bubbles were dominant at the superficial gas velocity of 1.1–38.3 cm/s and no stable Taylor bubbles were detected in this experiment. Measured radial void fraction profiles obtained by neutron radiography and electrical conductivity probe agreed well with each other. From these measurements, the measurement error and basic characteristics of gas–liquid–metal two-phase flow were clarified.

Measuring the k– S– p relations on DNAPLs migration

Migration characteristics of dense non-aqueous phase liquids (DNAPLs) in the subsurface can be expressed as a water–DNAPL two-phase system based on mainly the k– S– p relations, which describe the relations among relative permeability ( k), degree of water saturation ( S), and capillary pressure head ( p). The aims of this research are to develop an experimental system with new type of probes, such as the electrical conductivity probe for measuring the degree of water saturation and the hydrophilic and hydrophobic tensiometer for measuring the pore water and DNAPL pressures, and also to estimate the results obtained from the developed experimental system. From these tests, the excellent k– S– p relations were obtained and the efficiency and validity of this developed experimental system have been confirmed in terms of the concept of the scaling coefficient calculated by interfacial tensions.

Film Thickness and Wave Velocity Measurements in a Vertical Duct

This paper describes the experimental investigation of an upward annular air-water flow in a duct with a 6.35 mm by 63.5 mm rectangular cross section. The test section was instrumented to measure the film thickness and the interfacial wave velocity. Flush-wire electrical conductivity probes were used to obtain local film thickness measurement with a spatial resolution of 200 μm or better and a temporal resolution greater than 2 kHz. Measurements of the base films range from 50 μm to ∼325 μm (2% to 10% of half-channel thickness). Statistical analysis shows that the standard deviation of the film thickness is a good measure of the film roughness. The relative roughness and the nondimensional film thickness are correlated as functions of the phasic Reynolds number ratio, R=Rel0.15/Reg0.3. It is found that at R=0.15, the relative roughness is a maximum. A simple model developed by matching the interfacial shear in the two fluids, predicts the wave velocity data very well.

Effect of Water-Soluble Polymers on the Morphology of Aerosol OT Vesicles

Vesicles of different morphologies were found to form in aqueous solutions of the surfactant sodium bis(2-ethylhexyl)sulfosuccinate, AOT, and in binary mixtures composed of AOT with poly(ethylene glycol) and poly(sodium 4-styrenesulfonate). Using electrical conductivity and fluorescence probing, two critical vesicle concentrations, cvc and cac, were determined. These critical aggregation concentrations correspond to different kinds of aggregates, which are easily observed by optical microscopy.

Phase behavior and solution properties of sodium (3-dodecanoyloxy-2-hydroxy-propyl) succinate in water

Sodium (3-dodecanoyloxy-2-hydroxy-propyl) succinate (SLGMS) is a conjugated anionic surfactant in which a glycerol residue connects with a hydrophilic sodium succinate and dodecanoate. Aqueous micellar phase (Wm), hexagonal (H1), bicontinuous cubic (V1), and lamellar (Lα) phases are successively formed with increasing the surfactant concentration in a binary SLGMS-water system. The Krafft point is below 0 °C. The effective cross sectional area per surfactant molecule, as, in the H1 phase is almost constant, 0.5 nm2, and the shape of cylindrical micelle is almost unchanged with surfactant concentration. The cmc value of SLGMS measured by means of surface tension, electrical conductivity, and fluorescence probe methods is in the range of 4∼9 × 10−5 mol/l that is much lower than that of sodium dodecanoate, 2 × 10−2 mol/l, or SDS, 8 × 10−3 mol/l. Hence, it is considered that the polar glycerol part in the SLGMS acts as a hydrophobic part. The solubilization of oil in the SLGMS solution is much higher than that in the SDS solution and this also suggests that the glycerol and succinic units act as lipophilic moieties.

Location and Characterization of Subsurface Anomalies Using a Soil Conductivity Probe

AbstractAn electrical conductivity probe, designed for use with “direct push” technology, has been successfully used to locate buried drums, contaminant plumes, and to precisely locate and characterize a previously installed permeable reactive iron wall. The conductivity probe was designed to characterize various soil and sediment types as it was driven through the dry and saturated soil matrix; however, its ability to locate and characterize subsurface anomalies may also prove to be a valuable asset. The probe uses an electrical field that works like and mimics the results from an oilfield engineering tool called the Wenner array. This electrical field array penetrates into the soil matrix to measure the electrical conductivity of the soil matrix surrounding the probe to a radius of about two to four inches. This tool has allowed operating personnel to verify the location of manmade or natural subsurface anomalies with precision.

Measurement of the diffusion coefficient for salt in salt flat and mangrove soils

Excluded salt accumulated at mangrove roots must be transported away from the root zone by diffusive processes, due to the low permeability of most mangrove soils. The diffusion coefficient for salt in mangrove soils determines the rate of this diffusive transport but has not been determined experimentally before. In this work we used a 12-month long-time series of salt concentration profiles measured in a sediment core over which fresh water was continuously circulated, to determine the diffusion coefficient for salt in the soil. Salt concentrations were measured using an electrical conductivity probe that was developed for use in hypersaline (salt concentration up to and in excess of 120 g/l) conditions. A modified formula was experimentally determined to relate electrical conductivity to salt concentration and temperature, applicable up to a salt concentration of 200 g/l. This was done because standard formulae relating these variables do not apply in the hypersaline conditions often encountered in salt flat sediments. The salt concentration profiles were used in a simple mathematical model to determine a sediment diffusion coefficient for salt in a salt flat sediment. This value of D=(4.6±0.2) ×10−5 m2/day was approximately half that calculated theoretically.

A small sensor for detecting animal burrows and monitoring burrow water conductivity

An electrical conductivity probe for measuring ground conductivity is described. The probe measures bulk ground conductivity in situ and can assist in locating animal burrows on a centimeter scale and in monitoring conductivity of burrow waters over long period of times. It is shown how burrow caves are located by their conductivity contrast relative to the soil. The conductivity of the water in a burrow cave 70thinspcm under the swamp surface has been recorded over 15 days. The conductivity dropped during/after periods of significant rainfall, and rapidly increased during tidal inundation of the swamp. At times with neither freshwater nor saltwater input through the openings of the burrow on the surface, the conductivity slowly increased presumably due to diffusion of salt through the burrow walls. The diffusion constant was estimated to be 2 × 10–9 m2/s, being comparable to previously determined diffusion constants for diffusion of salt within the substrate.

A Fundamental Approach to Bubble Column Scale-Up Based on Quality of Mixedness.

A new approach to bubble column scale-up based on the quality of mixedness derived from the information entropy concept is presented. Using a step response method for studying mixing in the liquid phase, the carbon dioxide tracer concentrations absorbed in deionized water in a bubble column of 0.289 m in ID have been measured by an electrical conductivity probe under steady flow conditions. The superficial gas velocity was set at 0.0178 m·s–1, 0.0305 m·s–1 and 0.0381 m·s–1 (bubbly flow regime) under clear liquid heights of 0.56 m and 1.84 m, respectively. Following an original algorithm based on the stepwise change of the measured tracer concentrations with time in respective pertinently divided beds, a quality of mixedness concept has been evaluated for the above mentioned operating conditions. It is found that the change of quantity with introduced dimensionless time in this study does not depend on the superficial gas velocity and clear liquid height. The authors argue that for the case of physical absorption of carbon dioxide in deionized water in the bubbly flow regime, the quality of mixedness is dominated by mass transfer from the bubbles to the surrounding liquid and in turn to turbulent mixing on the scale of a mean bubble diameter, which is associated with the liquid transported in the wakes of the rising bubbles.In the present study, the dimensionless quality of mixedness can be related distinctly to a dimensionless time which is defined as the elapsed time divided by the contact time (the Sauter-mean bubble diameter divided by the bubble rise velocity) based on the classical penetration theory. The derived relationship provides significant new information about bubble column scale-up. In addition, a comparison between the quality of mixedness in the upper and lower sections has been illustrated.

Kinetic investigations of the interaction between sodium dodecyl sulfate and the nonionic surfactants CmEn. Electrical conductivity and fluorescence probe measurements

Electrical conductivity, steady-state quenching fluorescence measurements, and the kinetic study of the acid hydrolysis reaction of 1-phenylethyl nitrite were used to investigate the structure of micelles arising from mixed surfactant solutions. The mixed micellar systems investigated were sodium dodecyl sulfate (SDS) with the poly(ethylene oxide) surfactants of type CmEn, i.e., CH3–(CH2)m-1–(OCH2CH2)n–OH, (C12E4, C12E9 and C16E10) in aqueous medium at a fixed and variable molar ratio: r=[CmEn]/[SDS]. The conductivity results indicate a change in the nature of the mixed micelles as r increases. At high r values and high surfactant concentration (0.10 mol dm-3) solvent effects due to intermicellar interactions, together with micellar effects, seem to arise. Fluorescence measurements do not indicate important changes in the polarity and size of the mixed micelles which are formed at low r values; conductivity and kinetic measurements are consistent with the formation of mixed micelles more ionized and more hydrated than pure SDS micelles. At high r values, the complexity of the system increases; it is possible that poly(ethylene oxide) surfactants of large polar head groups destroy the ordered structure of water. The important catalysis observed in the acid hydrolysis of 1-phenylethyl nitrite in the presence of pure SDS micelles becomes a strong inhibition when the content of the nonionic surfactant in the mixed surfactant system is high.

Electric conductivity and temperature variations within a raised bog in Finland: implications for bog development

The deeper parts of raised bogs in Europe have been long regarded as hydraulically stagnant. However, recent reports describe seasonal water movements and solute transport through the deeper layers of some North American bogs, possibly affecting their carbon budgets. Such water movements were not observed in Haukkasuo, a typical raised bog in southeastern Finland, which was thoroughly mapped with a new electric conductivity and temperature probe during four seasons and two successive years. The measured temperature variations can be explained by thermal conduction without convective heat transfer so that the deeper peat layers (2-3 m) reach their highest temperatures in the winter, which possibly affects the methane production. A minimum conductivity (low solute concentration) in the vertical profiles indicates the transition from minerotrophic to ombrotrophic stage of bog development. The seasonal and annual conductivity variations are insignificant, but the conductivity cross-sections of the bog show systematic patterns suggesting slow but persistent advective transport of solutes. The bog mound seems to drive a flow system, which under the central dome forces dilute surface waters to the basal layers, where they pick up nutrients on their way to the discharge sites near the margins. Such translocation of solutes is expected to excite the peat decay at the margins and slow it down near the bog centre. This promotes further doming of the 10 000-year-old bog, which will keep on sequestering carbon although the methane emissions may increase near its margins.

Model experiments of mixing in steel ladles with continuous addition of the substance to be mixed

The process of alloying steel melts in ladles consists of the three partial steps alloy addition, alloy solution, and alloy mixing. Addition and dissolution together can be simulated approximately by continuous addition of a dissolved substance to be mixed. In this way, the mixing process during alloying can be captured separately. The process was studied in model experiments with continuous addition of NaCl solution to water in a 0.18 m3 cylindrical acrylic glass vessel. The water was stirred by air injection through an eccentrically positioned nozzle in the bottom. The added amount of NaCl was 40 cm3 of a 20% aqueous solution. The addition time was varied. The NaCI concentration in the water vessel was continuously measured with electrical conductivity probes at 12 different positions. From the thus obtained concentration‐vs.‐time curves, the mixing times were determined. They were studied for stirring gas rates between 100 and 700 cm3/min(STP) and for various addition times of the indicator. The measured mixing times depended on the gas stirring rate. They were also functions of the indicator addition time and decreased with increasing addition time until they became zero or negative. Trials where NaCI was added in form of a melting, NaCI containing ice sphere, yielded negative mixing times, which means that melting is slower than mixing. A theoretical model to describe mixing with continuous addition is presented. Besides the measurement of the mixing process, the three main flow directions of the indicator solution when it leaves the injection nozzle were documented by a video camera. They were associated to the concentration curves measured at the conductivity probes to which the flow was directed. It was found that concentration maxima occurred on the curves when the flow was directed to the respective measuring probe. The duration of the maxima coincided almost always with the duration of the flow directions.

LIQUID PHASE MIXING IN A SLURRY BUBBLE COLUMN WITH DRAFT TUBE

In this work we characterize liquid phase mixing in a 150 L bubble column with a draft tube (internal airlift configuration) for a water-air-sand system at high solid concentrations. Liquid mixing is assessed by measuring the evolution of sodium chloride concentration after a pulse of concentrated NaCl solution is injected. Tracer concentrations were measured by means of electrical conductivity probes. The experimental set up consists of a 0.29 m internal diameter, 3 m length Plexiglas column with a conical bottom (cone apex angle of 60°) and a concentric draft tube with 0.14 m internal diameter and 2 m length. The gas superficial velocity based on the cross section of the column vaired from 0.057 to 0.22 m/s. Sand particles of 280 μm in average size were used, with slurry concentrations ranging from 120 to 500 kg/m3. From the tracer outputs, circulation time (time between peaks of the response curve) and mixing time (time required to achieve a 95% homogeneous solution) were determined after the pulse had been injected. The experimental data were analyzed by means of a tank in series model with recirculation. The circulation and mixing times were found to increase with solids concentration, and to decrease as the riser gas velocity was increased. The circulation limes were larger in continuous operation than in semibatch mode. The results show that the system has equivalent dispersion coefficients that are one order of magnitude lower than those found in a conventional bubble column.