Net Water Flow Research Articles

Sourcebook update: RBC hemolysis studies using a simple modified blood film technique.

Water movement across the cell membrane is crucial, with red blood cells (RBCs) experiencing the flow of water in both directions at a rate of approximately 100 times their volume per second. This process typically results in no net water flow due to an equal balance of water movement in opposite directions, a phenomenon known as osmosis, driven by water potential or impermeant solute concentration. Understanding osmosis is essential for both physiology and medical practice, yet its complexity may not be effectively conveyed to the students through traditional teaching methods. This study presents a novel approach to observing the osmotic effect on RBCs using a simple, modified blood film technique. Aimed at enhancing educational understanding of cellular behavior in different osmotic environments, this method provides a practical hands-on learning experience. By applying various osmotic solutions to prepared blood films and observing the resultant morphological changes in RBCs under a microscope, this technique allows for direct visualization of osmosis in action.NEW & NOTEWORTHY This study presents an innovative teaching approach for understanding osmosis and its effects on red blood cells. Using a simple, modified blood film technique, students can visually observe and engage with the dynamic process of osmosis. This hands-on method enhances learning, making complex physiological concepts accessible and practical. Ideal for resource-limited settings, it bridges theoretical knowledge and practical application, transforming physiology education.

A Novel Deformation Analytical Solution and Constitutive Model for Fractured Rock Masses

In order to study the deformation and stability of a fractured rock mass, existing research suggests that fracture deformation, which is usually obtained by evaluating the equivalent deformation modulus, dominates the deformation of a fractured rock mass. However, this parameter is difficult to obtain in theory and practice, which limits the application of rock mass deformation analysis methods. In order to calculate the deformation of fractured rock masses, the mass of the rock is regarded as a sponge-like material, and it is assumed that the deformation of a water-saturated fractured rock mass under external force load is approximately equal to the net flow of fracture water. Based on this assumption, firstly, the relationship between rock mass deformation and fracture flow is studied through a single-fracture rock mass model. The hydraulic properties of the fracture are characterized by the permeability coefficient, and the fracture deformation in the rock mass is equivalent to the fracture flow. The fracture deformation calculation formula is derived from the fracture hydraulics calculation formula, and this is compared with the measured data. The rationality of the calculation formula was verified. On this basis, the calculation formula for rock mass deformation, including multiple groups of fracture surfaces, is proposed, and the stress-strain constitutive relationship of a complex rock mass is established. The correctness of the calculation method was verified by comparing it with other theoretical calculation results.

Water flow in graphene nanochannels driven by imposed thermal gradients: the role of flexural phonons.

Accurate control of fluid transport in nanoscale structures is key to enable the design of foreseeable nanofluidic devices with applications in many fields such as chip cooling, energy conversion, drug delivery and medical diagnosis. Here, inspired by the experimental observation of intrinsic thermal ripples in graphene and by recent advances in the manipulation of 2D nanomaterials, we introduce a graphene-based thermal nanopump which produces controlled and continuous liquid flow in nanoslit channels. We investigate the performance of this thermal nanopump employing large scale molecular dynamics simulations. Upon systematically imposing thermal gradients, a net water flow towards the low-temperature zone is observed, achieving flow velocities up to 4 m s-1. We observe that water flow rates increase monotonically due to larger ripple fluctuations on the graphene layers as higher thermal gradients are applied. Moreover, we find that the out-of-plane flexural phonons in graphene are responsible for flow generation wherein lower frequency phonon branches are activated with higher imposed thermal gradients. Furthermore, by modifying the wettability of the channel walls, an increase of 50% in the water flow rates is observed, showing that the efficiency of the proposed thermal pump can be enhanced by tuning the channel wall hydrophobicity. Our results indicate that thermal gradients can be employed to drive continuous water flow in graphene nanoslit channels with potential applications in nanofluidic devices.

Electropumping of water in nanochannels using non-uniform electric fields

Pumping fluids at the nanoscale is of fundamental importance to nanofluidic systems. We perform molecular dynamics simulations and provide the extended Navier-Stokes (ENS) equation to prove the electropumping possibility of using non-uniform electric fields to induce the continuous and unidirectional net flow of water confined in nanochannels. The net flow can be seen as a result of the combined effects of the unidirectional orientation of water molecules and the net force induced by the electric field intensity difference between O and H atoms in a water molecule. Higher net flow rates can be achieved by enhancing the electric field intensity gradients through the characteristics parameter adjustment of external electric fields. Importantly, the electropumping is more effective than the pressure-driven flow due to the ordered arrangements of water molecules in electric fields. The ENS equation proposed is more applicable at the flow field with high order degree of water molecules.

Variability and Dynamics of Along‐Shore Exchange on the West Antarctic Peninsula (WAP) Continental Shelf

AbstractThe continental shelf of the West Antarctic Peninsula (WAP) is characterized by strong along‐shore hydrographic gradients resulting from the distinct influences of the warm Bellingshausen Sea to the south and the cold Weddell Sea water flooding Bransfield Strait to the north. These gradients modulate the spatial structure of glacier retreat and are correlated with other physical and biochemical variability along the shelf, but their structure and dynamics remain poorly understood. Here, the magnitude, spatial structure, seasonal‐to‐interannual variability, and driving mechanisms of along‐shore exchange are investigated using the output of a high‐resolution numerical model and with hydrographic data collected in Palmer Deep. The analyses reveal a pronounced seasonal cycle of along‐shore transport, with a net flux (7.0 × 105 m3/s) of cold water toward the central WAP (cWAP) in winter, which reverses in summer with a net flow (5.2 × 105 m3/s) of Circumpolar Deep Water (CDW) and modified CDW (mCDW) toward Bransfield Strait. Significant interannual variability is found as the pathway of a coastal current transporting Weddell‐sourced water along the WAP shelf is modulated by wind forcing. When the Southern Annual Mode (SAM) is positive during winter, stronger upwelling‐favorable winds dominate in Bransfield Strait, leading to offshore advection of the Weddell‐sourced water. Negative SAM leads to weaker upwelling‐ or downwelling‐favorable winds and enhanced flooding of the cWAP with cold water from Bransfield Strait. This process can result in significant (0.5°C below 200 m) cooling of the continental shelf around Palmer Station, highlighting that along‐shore exchange is critical in modulating the hydrographic properties along the WAP.

Evolution of moisture in tailings dams located in arid climates. Case study: Castaño Viejo mine, San Juan, Argentina

This paper presents the results obtained in geotechnical exploration campaigns carried out in mining tailings dams resulting from the extraction process of lead, zinc and copper. The studied dams have been abandoned for more than half a century and are located in the Andes Mountains, San Juan, Argentina, an area characterized by water deficit regimens. The observation of degrees of saturation, which is surprisingly high in the internal zones of the tailings dams, led to a long-term field experiment (plot test) to investigate the observed behaviour. Based on the results of the plots test, we have concluded that stratigraphy controls the evolution of the water stored with the tailings. Clay and silty layers develop high degrees of saturation due to the capillary barrier effect, whilst the interlayers of sand dry up to a residual saturation condition. This situation inhibits the capillary rise and the diffusion of vapour, thus isolating the interior of the tailings from the atmosphere. It was observed that the depth of the active layer is 10 to 35 cm for evaporation and 35 to 75 cm for infiltration in the plot experiment. Such asymmetry determines a net flow of water into the system, which is consistent with the generation and conservation of a high degree of saturation within the tailings.

Use of a Managed Flow Pulse as Food Web Support for Estuarine Habitat

While freshwater inflow has been a major focus of resource management in estuaries, including the upper San Francisco Estuary, there is a growing interest in using focused flow actions to maximize benefits for specific regions, habitats, and species. As a test of this concept, in summer 2016, we used a managed flow pulse to target an ecologically important region: a freshwater tidal slough complex (Cache Slough Complex–CSC). Our goal was to improve estuarine habitat by increasing net flows through CSC to enhance downstream transport of lower trophic-level resources, an important driver for fishes such as the endangered Delta Smelt Hypomesus transpacificus. We used regional water infrastructure to direct 18.5 million m³ of Sacramento River flow into its adjacent Yolo Bypass floodplain, where the pulse continued through CSC. Simulations using a 3-D hydrodynamic model (UnTRIM) indicated that the managed flow pulse had a large effect on the net flow of water through Yolo Bypass, and between CSC and further downstream. Multiple water quality constituents (specific conductivity, dissolved oxygen, nutrients [NO₃ + NO₂, NH₄, PO₄]) varied across the study region, and showed a strong response to the flow pulse. In addition, the lower Sacramento River had increased phytoplankton biomass and improved food quality indices (estimated from long-chain essential fatty acids) after the flow pulse. The managed flow pulse resulted in increased densities of zooplankton (copepods, cladocerans) demonstrating potential advection from upper floodplain channels into the target CSC and Sacramento River regions. This study was conducted during a single year, which may have had unique characteristics; however, we believe that our study is an instructive example of how a relatively modest change in net flows can generate measurable changes in ecologically relevant metrics, and how an adaptive management action can help inform resource management.

TECHNIQUE FOR EVALUATION OF HEAT LOSSES OF DISTRIBUTION HEATING NET PIPELINES USING AGGREGATED INDICATORS

Heat losses from distribution net pipelines of a centralized heating system were computationally estimated. The data were generalized. Formulas that allow evaluating the thermal state of supply and return pipelines for heating net main branches using buildings aggregated indicators were obtained as a result of the generalization. The total thermal load of the buildings connected to the heating net, the material characteristics of heat pipelines, factors that consider the peculiarities of heat transfer medium flow distribution along the heat pipeline were taken as aggregated indicators. Specific (linear) heat losses of subsurface heat pipelines in non-accessible channels were considered to be standard. Heat losses for structural elements of net pipelines were also taken into account. Idealized groups of buildings with the same thermal load were used in the calculation technique proposed. The standard ambient air temperature for the cold period and climatic conditions forKharkovwas used in the calculation. The real stepwise law for net water flow rate change along the heat pipeline was approximated using a power function. The peculiarities of heat transfer medium flow distribution along the heat pipeline was taken into account with the exponent in flow equation and the ratio of the average heat transfer medium flow of the main pipeline and the total heat transfer medium flow of its branches. Heat losses of the branches, based on the material characteristics ratio for the branches and the main pipeline, make it possible to determine heat losses of the heating net as a whole. The accuracy of applying the proposed formulas was evaluated. The imprecision between the results of the calculations using the aggregated indicators of buildings and traditional calculations method results, taking into account the actual change of flow rate and net water temperature along the heat pipeline, was compared. This imprecision does not exceed 6 %, which can be considered acceptable when assessing net thermal state at the early design stages.

How do genes flow? Identifying potential dispersal mode for the semi-aquatic lichen Dermatocarpon luridum using spatial modelling and photobiont markers

BackgroundLandscape genetics is an interdisciplinary field that combines tools and techniques from population genetics with the spatially explicit principles from landscape ecology. Spatial variation in genotypes is used to test hypotheses about how landscape pattern affects dispersal in a wide range of taxa. Lichens, symbiotic associations between mycobionts and photobionts, are an entity for which little is known about their dispersal mechanism. Our objective was to infer the dispersal mechanism in the semi-aquatic lichen Dermatocarpon luridum using spatial models and the spatial variation of the photobiont, Diplosphaera chodatii. We sequenced the ITS rDNA and the β-actin gene regions of the photobiont and mapped the haplotype spatial distribution in Payuk Lake. We subdivided Payuk Lake into subpopulations and applied four spatial models based on the topography and hydrology to infer the dispersal mechanism.ResultsGenetic variation corresponded with the topography of the lake and the net flow of water through the waterbody. A lack of isolation-by-distance suggests high gene flow or dispersal within the lake. We infer the dispersal mechanism in D. luridum could either be by wind and/or water based on the haplotype spatial distribution of its photobiont using the ITS rDNA and β-actin markers.ConclusionsWe inferred that the dispersal mechanism could be either wind and/or water dispersed due to the conflicting interpretations of our landscape hypotheses. This is the first study to use spatial modelling to infer dispersal in semi-aquatic lichens. The results of this study may help to understand lichen dispersal within aquatic landscapes, which can have implications in the conservation of rare or threatened lichens.

Influences of microtidal regime and eutrophication on estuarine zooplankton

This study describes the ecology of mesozooplankton in the shallows of the large central basin area of the Swan-Canning Estuary on the microtidal lower west coast of Australia during the mid-1980s when, as in most other south-western Australian estuaries, it was mesotrophic. As the vast majority of species reproduce within the estuary and there is a lack of a net upstream flow of bottom water during each tidal cycle to facilitate selective tidal transport, the populations of those species are considered autochthonous. Species restricted to the estuary accounted for 63% of the total number of species and 83% of abundance. Contributions by tychoplankton to total number of species (68%) and individuals (59%) exceeded the corresponding values of 18 and 39% for holoplankton and 14 and 2% for meroplankton. Low meroplankton values result from a paucity of benthic macroinvertebrate species with planktotrophic development. Comparisons with data for the shallow basin areas of the nearby highly eutrophic Peel-Harvey Estuary were used to indicate how mesozooplankton in the microtidal estuaries respond to excessive nutrient enrichment. The mean number of species in the Swan-Canning was essentially the same as in the Peel-Harvey, whereas concentrations were only half, reflecting the lower productivity of the former estuary. However, concentrations of the four most abundant species in the Swan-Canning, the amphipod Grandidierella propendatata, the calanoids Gladioferens imparipes and Acartia cf. clausi and a harpacticoid species, exceeded those of these species in the Peel-Harvey by between 1.6 and 11.7 times. Greater concentrations in the Swan-Canning were attributable to this mesotrophic system not undergoing the reduction in oxygen concentrations and/or environmental degradation, to which these species are susceptible. In contrast, concentrations of the amphipods Corophium minor and Tethygenia elanora and large nematodes, which are tolerant of degraded environmental conditions, were greater in the Peel-Harvey. Holoplankton made a far greater contribution in the Swan-Canning than Peel-Harvey, due to substantial numbers of copepods that benefit from good environmental conditions. Mesozooplankton composition in both estuaries underwent cyclical changes during the year due to time-staggered differences in seasonal concentrations of various species. Cyclical changes and variations in composition were more closely related to measured environmental variables in the Swan-Canning than Peel-Harvey estuaries. The concentrations of many species were greater at night than during the day presumably reflecting a nycthemeral response and/or low nocturnal oxygen concentrations at the bottom of the water column.

Virtual Water Flows Embodied in International and Interprovincial Trade of Yellow River Basin: A Multiregional Input-Output Analysis

With the imminent need of regional environmental protection and sustainable economic development, the concept of virtual water is widely used to solve the problem of regional water shortage. In this paper, nine provinces, namely Qinghai, Sichuan, Gansu, Ningxia, Inner Mongolia, Shaanxi, Shanxi, Henan, and Shandong in the Yellow River Basin (YRB), are taken as the research objects. Through the analysis of input-output tables of 30 provinces in China in 2012, the characteristics of virtual water trade in this region are estimated by using a multi-regional input-output (MRIO) model. The results show that: (1) The YRB had a net inflow of 17.387 billion m³ of virtual water in 2012. In interprovincial trade, other provinces outside the basin export 21.721 billion m³ of virtual water into the basin. In international trade, the basin exports 4334 million m³ of virtual water to the international market. (2) There are different virtual flow paths in the basin. Shanxi net inputs virtual water by interprovincial trade and international trade, while Gansu and Ningxia net output virtual water by interprovincial trade and international trade. The other six provinces all net output virtual water through international trade, and obtain the net input of virtual water from other provinces outside the basin. (3) From the industrial structure of the provinces in the basin, the provinces with a relatively developed economy, such as Shandong and Shanxi, mostly import virtual water in the agricultural sector, while relatively developing provinces, such as Gansu and Ningxia, mostly import virtual water in the industrial sector. In order to sustain the overall high-quality development of the YRB, we propose the virtual water trade method to quantify the net flow of virtual water in each province and suggest the compensation responsibility of the virtual water net inflow area, and the compensation need of the virtual water net outflow area, in order to achieve efficient water resources utilization.

Inducing a Net Positive Flow of Water in Functionalized Concentric Carbon Nanotubes Using Rotating Electric Fields.

Electropumping has shown great potential as an effective means of inducing a net positive flow of water in confined channels. In this paper we present the first nonequilibrium molecular dynamics study and continuum based numerical solutions that demonstrate an effective net positive flow between concentric carbon nanotubes (CNT) using electropumping. We apply a spatially uniform rotating electric field that couples to the water's permanent dipole moment. Taking advantage of the coupling between the spin angular momentum and the linear momentum we break the symmetry of the channel radius by functionalizing the inner CNT's outer surface with carboxyl groups to induce a net positive flow. We also show that our results for concentric nanotubes are consistent with our previous work where we demonstrated that an increase in functionalization beyond an optimal point in a single walled carbon nanotube resulted in a decrease in positive net flow. We then numerically solve the coupled hydrodynamic momentum equations to show that the nonequilibrium molecular dynamics results are consistent with the continuum theory.

Cosolvent Impurities in SWCNT Nanochannel Confinement: Length Dependence of Water Dynamics Investigated with Atomistic Simulations.

The advent of nanotechnology has seen a growing interest in the nature of fluid flow and transport under nanoconfinement. The present study leverages fully atomistic molecular dynamics (MD) simulations to study the effect of nanochannel length and intrusion of molecules of the organic solvent, hexafluoro-2-propanol (HFIP), on the dynamical characteristics of water within it. Favorable interactions of HFIP with the nanochannels comprised of single-walled carbon nanotubes traps them over time scales greater than 100 ns, and confinement confers small but distinguishable spatial redistribution between neighboring HFIP pairs. Water molecules within the nanochannels show clear signatures of dynamical slowdown relative to bulk water even for pure systems.The presence of HFIP causes further rotational and translational slowdown in waters when the nanochannel dimension falls below a critical length of 30 Å. The enhanced slowdown in the presence of HFIP is quantified from characteristic relaxation parameters and diffusion coefficients in the absence and presence of HFIP. It is finally seen that the net flow of water between the ends of the nanochannel shows a decreasing dependence with nanochannel length only when the number of HFIP molecules is small. These results lend insights into devising ways of modulating solvent properties within nanochannels with cosolvent impurities.

Detecting the mechanisms of longitudinal salt transport during spring tides in Qiantang Estuary

ABSTRACTSaltwater intrusion has immediate influences on the water resources utilization, aquatic environment and ecological system. Hence, it is essential to detect the mechanisms of salt transport. This study adopted observations including instantaneous flow velocities, tide levels and salinity during 10 tide cycles at 2 stations in upstream and downstream of Qiantang Estuary in China. The variables of instantaneous flow velocity and salinity were decomposed into the time-average, time-varying and vertical-varying components using the flux decomposition model. Then, the salt flux components attributed to various physical processes were quantified. During spring tides, the longitudinal salt transport is controlled by advection transport and tidal pumping transport in the upper river reaches, while being mainly controlled by advection transport in the lower river reaches. The net water flow fluxes and salt fluxes are landward in the lower river reaches. However, the transport direction of the salt fluxes is inconsistent with that of the net water flow fluxes in the upper river reaches, where the net water flow fluxes are mainly seaward while the net salt fluxes are mainly landward. In general, there are significant positive correlations between the net landward salt flux and the tidal range. Thus, the tidal range can be used as an important indicator for determining the required amount of freshwater to be discharged from the reservoir in order to resist saltwater intrusion. The vertical distribution of salt in Qiantang Estuary is relatively uniform. The vertical shear force has limited influence on the salt transport. The research results are expected to supply a reference to future research on other macro-tide estuaries.

Performance evaluation of a thermoresponsive polyelectrolyte draw solution in a pilot scale forward osmosis seawater desalination system

The current study assesses the technical feasibility of using a thermoresponsive polyelectrolyte draw solution (DS) in a Forward Osmosis (FO) desalination pilot scale system of 10 m3/day capacity. The FO system utilized a commercial spiral wound hollow fiber FO membrane and ethylene oxide-propylene oxide copolymer as DS. This study evaluated the effect of DS flow rate and feed solution flow rates on the net water recovery and product water flow rates of the system. The osmotic pressure distribution of polyelectrolyte DS at different sections of the HF module was greatly influenced by DS flow rate. The study revealed that the DS had great potential to generate the high osmotic pressure (Δπ) difference in the various compartments of the HF module. The reliability of the FO pilot plant was proved over a long run without any severe FO membrane fouling with total dissolved solids of product water at 143 ppm and water recovery of 30%. The selected DS showed its potentiality towards the installation of commercial-scale FO desalination plant by witnessing its low viscosity and easy phase separation at a moderately lower temperature of 85 °C in the coalesce DS regeneration system.

Development of debris bed cooling evaluation code, DPCOOL, based on heating porous media submerged in two-phase pool

ABSTRACT A framework of the modular code system, THERMOS, aiming to evaluate cooling of a debris bed having complex configurations was introduced with a focus on one of the major modules, DPCOOL, which models heating or non-heating porous media of particulate debris in a two-phase pool. In DPCOOL, pool and debris bed regions are discretized in a three-dimensional Cartesian coordinate system. A pool region is formulated based on the two-fluid model. A two-phase flow in the debris bed region is formulated based on the Tung & Dhir model with modifications for smaller particles proposed by Schmidt. In order to synthesize the momentum equations of the two regions, interpolation factors as piecewise linear functions of porosity are introduced. The interfacial friction model was validated based on Chu’s test using a debris bed composed of non-heating SUS spheres in a water pool with air injection from below where the net water flow in the layer became zero so that pressure loss of the layer was governed by interfacial friction. The sum of the two-phase flow friction and the interfacial friction models was validated based on top flooding and bottom flooding tests conducted in IKE’s DEBRIS test facility loaded with mixed steel and alumina spheres that were heated by an induction coil system.

Osmotic Transport across Surface Functionalized Carbon Nanotube Membrane.

Osmosis plays a central role in many chemical separation processes. Among various biological and artificial channels, carbon nanotubes (CNTs) stand out due to their exceptional water transport efficiency and variability of pore-size, down to molecular dimensions, thereby approaching ideal semipermeability. We report osmotically driven water and salt transport across a membrane of vertically aligned CNTs in a titania matrix whose surface is functionalized with a self-assembled monolayer of octadecylphosphonic acid. The increased steric hindrance and hydrophobicity at the pore entrance of CNTs improved salt rejection while maintaining enhanced osmotic water transport, thanks to an atomically smooth surface of the nanotubes. In addition to the experimental demonstration of osmosis, we observed a net negative osmotic water flow at lower salt concentration gradient and non-Fickian behavior of the reverse salt flux. This observation is attributable to the interface-driven fluidic phenomenon known as diffusio-osmosis that drives water flow in the direction opposite to osmotic flow. The ion-CNT interactions are responsible for the simultaneous occurrence of the two osmotic transport mechanisms and the salt-specific osmotic transport characteristics.

Laboratory investigation on solutes removal from artificial amended saline soil during the electrochemical treatment

Soil salinity has become one of the environmental issues around the world, compromising thus land ecosystems as well as civil engineering infrastructures and facilities. This hazard is further aggravated, primarily when dealing with low permeable soils, where conventional remediation techniques are inadequate and mostly ineffective. Electrochemical treatment is an innovative and green technology for restoration of saline soils. This process has been proven to be the most efficient, promising technique, offering an optimal and sustainable remediation of salt-affected soils. The originality of this method involves application of an electric current through inserted electrodes into the soil matrix, inducing mobilization and transport of salts toward the electrodes of opposite charge via electro-migration process. The electrical current also induces a net water flow by electro-osmosis mechanism, allowing better draw and removal of solutes within the porous medium. This paper investigates the performance of the electrochemical treatment in remediation of salt-affected soil. Sodium, potassium and calcium were used as selective contaminants with targeted concentration of 0.5 M. In this aim, a laboratory bench scale was designed. It consists of soil box, anolyte and catholyte reservoirs, current monitoring devices, pH and electrical conductivity probe controller. The highest removal was for sodium and potassium with an extraction of 88 and 82%, respectively. Calcium exhibits lower removal rate of 57%, due to the development of the pH gradient, hindering therefore their mobility. This study demonstrated that electrochemical treatment can be advantageous in remediation of salt-affected soils, for enhancing agricultural productivity as well as soil constructional uses.

Physicochemical gradients and water fluxes between Nyanza Gulf and main Lake Victoria, East Africa: Tracing dynamics of gulf-main lake interaction

Abstract Variability in physico-chemical water column structure along a gradient between Nyanza Gulf and Lake Victoria was characterized, and the exchange between the two basins estimated. Specific conductivity (SC) measurements between March 2005 and March 2006 identified three morphologically distinct zones, the inner-gulf, the connecting Rusinga Channel and the main lake basin. The relatively shallow, wide and river-influenced inner-gulf had higher turbidity and SC compared to the channel and the main lake. The deep, narrow and more wind-exposed mid-channel area was significantly cooler than the rest of the study areas. Observational data revealed “density-driven” underflow of the cooler channel water into the main lake and compensatory surface flow into the gulf as well as seasonal patterns of gulf-main lake exchange in relation to variation in tributary input. The wind field was dominated by a diurnal lake-land breeze which resulted in wind-driven diurnal reversal of water flow in and out of the gulf, where the constriction of flow within the channel induced strong currents. The exchange between the gulf and the main lake was estimated using a box model, with SC as a conservative tracer. A net annual residual water flow of 35 m3 s−1 occurred from the gulf into the main lake although during months with low tributary discharge the flow was towards the gulf. The daily flow in and out of the gulf resulted in relatively high exchange flux compared to residual flow across the Rusinga Channel leading to the development of the well-defined physicochemical gradient along the Rusinga Channel.

Analysing thermophoretic transport of water for designing nanoscale-pumps.

We propose a new design for thermally induced water pumping through carbon nanotubes by imposing a thermal gradient along the length of a carbon nanotube (CNT), which connects two water-filled reservoirs. We analyse the flow parameters by varying the imposed thermal gradient (4.62 to 20.98 K nm-1), the radius (0.81 to 1.89 nm) and the length (5 to 50 nm) of the CNT. Using molecular dynamics simulations, we compute the volumetric flow rate of the pump, velocity profiles of flow and thermophoretic forces acting on water molecules for various thermal gradients. The directed motion of water molecules is induced by the spatial variations of CNT-water energy interactions at the interface and the variations in the oscillation of the carbon atoms from hot to cold ends. The net flow and average velocity of water molecules are found to increase linearly with the applied thermal gradient, as well as with an increase in the radius and length of the CNT. We observe that nano-pumps with an increase in the radius and length of the CNT connecting the reservoirs perform better and also achieved higher efficiency levels. The analysis of the results indicates that the present design leads to a realistic system capable of providing continuous transportation of water leading to interesting practical applications in nanoscale devices.