Establishment Of Steady-state Conditions Research Articles

Effect of hydraulic gradient on swell and hydraulic response of desiccated expansive soil – an experimental study

ABSTRACT Desiccation cracks in compacted clay liners act as preferential flow paths and affect the hydraulic response during initial stage of wetting. This paper investigates the effect of initial hydraulic gradient on swell, infiltration and hydraulic conductivity during wetting of desiccated expansive soil specimens in oedometric-infiltrometer test set-up. The experimental results on the desiccated specimens demonstrated that the rate of swelling and the infiltration rates in the initial outflow region through the annular gap and permeation outflow region through the swollen soil matrix increased with the increase in hydraulic gradient, whereas the time for reoccurrence of outflow and the establishment of steady state condition decreased. The outflow infiltration rates of the desiccated specimens subjected to initial hydraulic gradients (i) of 2, 5 and 20 reduced from 1.56 × 10−3, 4.83 × 10−3 and 6.57 × 10−2 cm/s, respectively, in the initial outflow region to about 6.65 × 10−6 cm/s (under i= 20) in the permeation outflow region due to the swelling of the desiccated expansive soil. The minimum possible initial hydraulic gradient that can be adopted on desiccated expansive soil specimens during infiltration testing was found to be 2 without considering the infiltration driven by soil suction.

Indirect Calorimetry: From Expired CO2 Production, Inspired O2 Consumption to Energy Equivalent

This paper emphasizes the methodology of data collection of indirect calorimetry, including establishment of steady state conditions and the standards in which the values are presented. It also aims to describe in details the calculations of VO2, VCO2, Resting Energy Expenditure (REE) and Respiratory Quotient (RQ). The trial is registered with ClinicalTrials.gov number NCT02072694.

Numerical Modelling of Plunge Pool Scour Evolution In Non-Cohesive Sediments

Turbulences in liquids caused by jets can be of interest for numerous applications. For one, it concerns flood spillway structures within civil engineering but also is key in any area where turbulent mixing is present. The numerical simulations of jets that impinge into plunge pools are still in an early phase of their development. This paper verifies the accuracy of the Flow-3D software package in regards to simulating 3D scouring processes generated by turbulent water jets impinging on a sediment bed. Scour calculations are performed based on previously examined laboratory experiments. The results of the numerical model compare well with the experimental results in terms of the scour depth and the ridge height which accumulates downstream of the scour hole. The impact angle of the jet is identified as a driving parameter for the establishment of steady state conditions of scour depth and ridge height.

A rotating tungsten disc electrode in concentrated strong alkaline solutions: An electroanalytical aspect

Electrochemical behavior of tungsten in concentrated strong alkaline solutions (10−3–10−1M KOH, 11<pH<13) was studied by means of rotating disc electrode technique. Contrary to the case of less concentrated alkaline solutions, the formation of solid anodic passive film was not evidenced. Chronoamperometric measurements evidenced a fast establishment of steady state conditions in the surface region. In spite of the complexity of overall surface electrochemistry, a linear relationship between the limiting anodic currents and the concentration of OH− ions was evidenced, which may be used for easy and accurate determination of OH− ion concentration at high pH values where the glass electrode loses its high reliability.

Characterization of flow and mixing regimes within the ileum of the brushtail possum using residence time distribution analysis with simultaneous spatio-temporal mapping.

We studied the flow and mixing regimes in isolated segments of the terminal ileum of brushtail possums during spontaneous circumferential and longitudinal contractions under conditions that allowed backflow and compared them with those of inactive segments. Residence time distributions (RTDs) were determined by perfusion with two probes of different rheological properties to which an inert dye marker was added. Ileal segment volume and oscillatory flow during the period of RTD determination were derived from spatiotemporal maps. High viscosity guar gum solution generated RTDs characteristic of laminar flow in inactive ileal segments which confirmed that no slip was occurring at the mucosal layer. In active segments, motility and consequent oscillatory flow imparted significant additional axial dispersion to the flow patterns of both probes. Mixing occurred episodically during periods when intestinal volume was reduced and onflow was augmented by peristalsis, which may prevent the establishment of steady state conditions. Marker concentration rose more steeply when active ileal segments were being perfused with a probe of similar viscosity to normal digesta than with low viscosity Earle's/Hepes solution, each being subject to similar levels of oscillatory flow. This indicated that a coarser mixing regime prevailed and that absorption of nutrients from viscous digesta would rely to a greater degree on molecular diffusion.

Cellular levels of factor 390 and methanogenic enzymes during growth of Methanobacterium thermoautotrophicum deltaH.

Methanobacterium thermoautotrophicum deltaH was grown in a fed-batch fermentor and in a chemostat under a variety of 80% hydrogen-20% CO2 gassing regimes. During growth or after the establishment of steady-state conditions, the cells were analyzed for the content of adenylylated coenzyme F420 (factor F390-A) and other methanogenic cofactors. In addition, cells collected from the chemostat were measured for methyl coenzyme M reductase isoenzyme (MCR I and MCR II) content as well as for specific activities of coenzyme F420-dependent and H2-dependent methylenetetrahydromethanopterin dehydrogenase (F420-MDH and H2-MDH, respectively), total (viologen-reducing) and coenzyme F420-reducing hydrogenase (FRH), factor F390 synthetase, and factor F390 hydrolase. The experiments were performed to investigate how the intracellular F390 concentrations changed with the growth conditions used and how the variations were related to changes in levels of enzymes that are known to be differentially expressed. The levels of factor F390 varied in a way that is consistently understood from the biochemical mechanisms underlying its synthesis and degradation. Moreover, a remarkable correlation was observed between expression levels of MCR I and II, F420-MDH, and H2-MDH and the cellular contents of the factor. These results suggest that factor F390 is a reporter compound for hydrogen limitation and may act as a response regulator of methanogenic metabolism.

Quantitative measurements of the concentration polarisation layer thickness in membrane filtration of oil-water emulsions using NMR micro-imaging

In this paper we report measurements of the thickness of the concentration polarisation layers formed during crossflow membrane filtration of an oil-water emulsion. The formation and development of the oil polarisation layers was visualised non-invasively using NMR chemical shift selective micro-imaging. A series of images was acquired during the transient state of the filtration, (i.e. while the polarisation layer was forming and the flux of filtrate was changing), prior to the establishment of steady state conditions. An estimate of the specific resistance of the concentration polarisation layers was then obtained by determining the average oil layer thicknesses and concentration at a given time from the resulting images and measuring the corresponding (length averaged) flux of filtrate gravimetrically. After the establishment of steady state conditions, the dependence of the steady state filtrate flux on crossflow Reynolds number was found to be consistent with Brownian diffusion being the main mechanism controlling the build-up of the oil polarisation layers, at least under our range of operating conditions.

An investigation of the kinetics of granulation using a high shear mixer

A study is reported of the kinetics of granulation of a fine powder with a low viscosity binder in a mixer fitted with both impeller and chopper blades. The impeller torque was used to monitor the binder distribution, nucleation, compaction and coalescence phases of granulation and to detect the establishment of steady state conditions in which coalescence was the dominant process. Measurements are reported of the effects of varying processing conditions on granule growth and size distribution. Data were interpreted using theories for growth by the coalescence mechanism. It was established that, for the particular system studied, coalescence only occurred when the granules were saturated, or near saturated, with liquid binder. Within experimental errors, mean granule size was found to increase linearly with time. The interpretation of this result is discussed and shown to be evidence for the probability of coalescence being size dependent. The changes in the size distribution with time are also discussed in terms of kinetic theory and the effect of chopper rotation on size distribution is established.

Transport properties of helium near the liquid-vapor critical point. III. Thermal diffusion ratio, conductivity, and relaxation times of3He-4He mixtures

Measurements of the density and temperature gradient induced by a heat flux in two3He-4He mixtures along their critical isochore are reported. From these measurements, the thermal diffusion ratiokT and the thermal conductivity κ are derived. In addition, similar measurements were made for3He. It is found that for the mixtureskT and κ diverge with respective exponents of φ=1.23 and ψ≈0.6, which differs from the asymptotic predictions for binary mixtures. It therefore appears that the crossover to the expected “mixture” behavior has not been reached within the investigated range 10−1>(T-Tc)/Tc>7×10−4, where the limit close toTc is set by the very long observed relaxation times. The characteristic times for the establishment of steady state conditions in the density and temperature gradients τ(Δρ) and τ(ΔT) are reported. Within experimental uncertainty they are found to be the same and nearly independent of isotopic composition. They are compared with the predictions from the hydrodynamic diffusion equations that lead to the characteristic times of the diffusion modes. The slowest calculated times are found to be in fair agreement with the observed ones.

Transport phenomena in He3-He4 mixtures near the tricritical point

We have made extensive measurements on transport phenomena in He3-He4 mixtures near the tricritical point and along the superfluid transition line at saturated vapor pressure. The He3 mole fraction X ranged from 0.51 to 0.72 and the temperature from 0.8 to 1.5 K. Our measurements were made under steady state conditions using a cell where we measured the vertical He3 concentration gradient ▽X induced by a temperature gradient ▽T produced by a vertical heat flux. The cell included two superposed capacitors and ▽X was determined by means of the dielectric constant method. In this paper, we present a comprehensive report on our results for the thermal diffusion ratio k T and the thermal conductivity κ both in the normal fluid and in the superfluid. In the tricritical region, k T was found to diverge strongly as the tricritical point was approached; no singularity in κ was found. This behavior is consistent with theoretical predictions. In the region near the lambda line, κ remains finite, as expected, but k T appears to have a stronger singularity than predicted by theory. The analysis of our experiment in the normal fluid for mixtures with X>0.51 was complicated by superfluid film flow along the walls of the sample cell. We describe this effect and analyze it with Khalatnikov's theory of superfluidity. However, for the mixture X = 0.51, where there is no such film, the behavior of k T is consistent with predictions. The k T data for the mixtures 0.6 < X < 0.7 could be cast into a tricritical scaling representation, similar to that for the concentration susceptibility. In the superfluid phase we test, for the first time and with fair success, a relation by Khalatnikov between ▽X/▽T and static properties, measured in different experiments. Finally, we discuss the relaxation times that characterize the establishment of steady state conditions. From these data it is possible, under favorable circumstances, to obtain the mass diffusivity D.

Disappearance of nitrate under transient conditions in columns of soil

Previously a rapid reduction of NO 3 − was obtained in soil columns with continuous flow, before the establishment of steady state conditions. This initial behavior was not a function of flow rates. In order to determine what influence NO 3 − concentrations might have on transient and steady state rates, of NO 3 − loss, small soil columns (2·5 cm i.diam × 10 cm length) were infiltrated with 0, 100 and 1000 μg ml −1 NO 3 −N and the effluents were analyzed daily for NO 3 − and NO 2 −. Several days after an apparent steady state had been obtained, as determined by the effluent NO 3 − concentration, the influent NO 3 − concentrations were changed to 100 μg ml −1 NO −N in some of the columns. All columns showed transitions to new and identical steady state of NO 3 − loss from flowing solutions. Evidently the initial transient kinetics are primarily determined by some solubilization of organic matter during rewetting of air dry soil and subsequent steady states are dependent on lesser available organic matter.