Internal Water Flow Research Articles

Quantitative Evaluation of the Onset and Evolution for the Non‐Darcy Behavior of the Partially Filled Rough Fracture

AbstractThe non‐Darcy flow behavior in unfilled and fully filled rough fractures has been investigated thoroughly for decades. Natural fractures usually be partially filled with porous media due to long‐term internal and external dynamic disturbances and water flow erosion. However, how to evaluate the nonlinear seepage characteristics of the partially filled rough fracture (PFRF) is never scrutinized. In the present study, 2D direct numerical simulations are conducted to investigate the non‐Darcy behavior for flow through 6 PFRF models under different filling conditions (i.e., filling degree, roughness, and hydraulic conductivity capability of the filling medium), which included coupling between the free and seepage flow in the unfilled and filled region, respectively. The results show that the critical non‐Darcy factor E = 0.02 can be used to judge the onset of the non‐Darcy regime in PFRF, which is also the critical point of eddy region (ER) volume mutation. The higher the filling degree and the weaker the hydraulic conductivity of the filled medium, the more significant the non‐Darcy behavior. Furthermore, the variation of ER volume can be divided into three stages with the increasing inertia effect, that is, stable stage (E < 0.02), slow nonlinear growth stage (0.02 ≤ E ≤ 0.1), and rapid linear growth stage (E > 0.1). In addition, a new model for quantitatively evaluating the non‐Darcy behavior of PFRF is developed via gene expression programming based on 735 simulation data set, which is further employed to establish the relationship between the friction factor.

Roles of soil amendments in the water and salt transport of coastal saline soils through regulation of microstructure

AbstractIncreasing scientific knowledge on the improvement of coastal saline soils is critical for spatially expanding coastal development. Biochar and polyacrylamide (PAM) are popular soil amendments, however, it remains unclear how they affect water and salt transport by regulating soil microstructure characteristics. In this study, we conducted a five‐year rice barrel trial and investigated the changes in the aggregates and microstructure of saline soils after adding biochar with three different application rates (B1 = 0%, B2 = 2%, and B3 = 5%, mass ratio) and PAM with three different application rates (P1 = 0%, P2 = 0.4‰, and P3 = 1.0‰, mass ratio), and simulated the water and salt transport. Results showed that at B1 and B2 treatments, soil μ‐CT porosity in 2020 increased by 89.8% and 208.0%, respectively, with respect to that in 2016. The development of soil mesopore structure was promoted at B2 treatments, whereas the P2 and P3 treatments promoted the development of the soil macrostructure. Compared with those of the blank control, soil internal mean water flow rate increased by 22.2% at B2 treatments and 69.2% at P2 treatments, respectively. However, their increases were less pronounced at B3 treatments and the water flow rate decreased by 50.5% at P3 treatments. It might be reasonably attributed to the reason that porous biochar helped the formation of soil pore structure while an excessive amount of biochar blocked soil pores. Furthermore, PAM amendment helped to form soil aggregates while an excessive amount of viscous PAM might block soil pores or form a viscous layer. The time corresponding to the maximum salt concentration was negatively correlated with soil μ‐CT porosity (R2 = 0.27) and pore connectivity density (R2 = 0.29). Our findings indicate that appropriate amounts of biochar and PAM can help improve saline soil structure in coastal areas, improve their hydraulic properties, and alleviate salt stress.

Effects of soil heterogeneity and preferential flow on the water flow and isotope transport in an experimental hillslope

Soil water movement plays vital roles in hillslope runoff generation and groundwater and surface water interaction. However, there are still knowledge gaps about the impacts of soil heterogeneity and preferential flow on the internal water flow and transport process. In this study, the vertical soil heterogeneity focused on the variations in soil retention capacity, and the consideration of lateral preferential flow emphasized the higher hydraulic conductivity. We combined isotopic tracing and numerical modeling in an artificial hillslope, focusing on monitored processes of the artificial rainfall and isotopic tracing experiment. The results showed that the soil moisture quickly accumulated at the bottom of the hillslope during rainfall events, while the 2H enrichment occurred in the topsoil derived from enriched isotope injection in the second artificial rainfall. The evaporation process slowed down the mixing of new water in the topsoil and old water in the lower layer. We found that the vertical soil heterogeneity had significant influences on the internal water and isotope transport paths within the hillslope. The lateral preferential flow played an important role in the water flux and transport time to the seepage face. The coupling of isotopic tracing, which reflects the water transport and mixing with the hillslope, effectively improved the model simulation and mechanism analysis of hillslope water flow. Our findings provide new insights into the mechanisms governing soil water flow and transport dynamics in hillslopes, taking into account vertical soil heterogeneity and lateral preferential flow.

Influence Analysis of Runner Inlet Diameter of Hydraulic Turbine in Turbine Mode with Ultra-Low Specific Speed

The hydraulic turbine in turbine mode (HTTM) with an ultra-low specific speed (HTTM-ULSS) has the advantages of a simplified structure, high efficiency, and good stability and has great application value in the industry. However, the influence of the runner inlet diameter (D1) on the performance of HTTM-ULSS has not yet been fully studied. Therefore, the three-dimensional models of Francis runners were established in the ultra-low specific speed range by examining D1 = 0.49 m, 0.5 m, and 0.51 m, and the two-stage hydraulic turbine models were constructed with flow passage components. Then, internal flow and energy characteristics were calculated using Fluent 16.0 software. Further, the influence of D1 on HTTM performance was studied by comparing numerical simulation results. The results show that the water head of the HTTM-ULSS can reach 540.87 m when D1 = 0.51 m, showing its powerful ability to recover the pressure energy in high-pressure water. Moreover, the head and efficiency are closely related to D1; when D1 increases, the circulation at the runner inlet increases, resulting in an enhancement in the ability to recover the water head and decreases in efficiency and in the operating range of the high-efficiency zone; with D1 increasing, the flow pattern inside the runner becomes better, but the high-pressure area of the blade increases. When selecting the D1, attention should not only be paid to the ability to recover the water head but also to the pressure of the runner blades and the internal water flow pattern.

Multiphysics analysis of tramway geotechnical infrastructure: numerical modelling

Under realistic field conditions, geotechnical infrastructures are usually influenced by complex interactions of mechanical behaviour under the action of an internal water flow. This mechanism could be the main origin of damage to embankments. This study develops a new hydro-mechanical (HM) approach based on Darcy's law model and Biot's poroelastic concept to investigate the behaviour of soil with and without geotextile under realistic conditions. The problem's numerical solution is carried out using a finite-element method. The proposed two-dimensional model was implemented in Comsol Multiphysics Software. Under coupled HM behaviour, the stress in porous materials causes a volumetric change in strain, which causes fluid diffusion. Consequently, pore pressure dissipates through the pores. To discuss the advantages of coupled HM modelling and evaluate the geotextile performance, volumetric strain, pore-water pressure, storage and displacement are compared for a mechanical, hydraulic and HM model. These analyses were undertaken in connection with a tramway embankment project in a marshy area in Sidi Bel Abbes. The simulation results show better results for geotextile and embankment in HM coupled modelling.

Characteristics of Internal Water Flow Conduction within Asphalt Mixtures Based on Real Three-Dimensional Void Structure

This work presents a new approach to investigating water conduction properties in real three-dimensional (3D) voids of asphalt mixtures. Three different molding methods were employed for the same grade of asphalt mixture, and the three asphalt mixture specimens were scanned using X-ray Computerized Tomography (CT) to identify the real 3D void structure distribution inside the mixture. The real 3D behavior of void moisture conduction inside the mixture was simulated using the discrete lattice Boltzmann method and the BGK collision model. Three different molding methods were used to study the behavior of mesoscopic seepage inside the specimen. The results show that water conduction varies substantially in real 3D voids inside diverse molded objects. Regardless of flow and flow velocity, the Superpave Gyratory Compactor (SGC) method is extraordinarily close to the conduction qualities of the actual field core material. It shows that the Marshall molding method is inconsistent with the actual pavement molding method, and the SGC method can not only ensure that the reasonable void ratio is conducive to the thermal expansion and cold shrinkage space of the asphalt mixture but also prevents rainwater from entering the asphalt mixture. This work provides a new perspective for the study of water damage resistance and medium transmission characteristics of asphalt mixtures.

Water flow within and towards plant roots—a new concurrent solution

Abstract Various analytical models that calculate the water flow either around or inside plant roots are available, but a combined analytical solution has not yet been derived. The classical solution of Landsberg and Fowkes for water flow within a root relates the second derivative of xylem water potential to the radial water influx term. This term can be linked to well-known steady state or steady rate-based solutions for computing soil water fluxes around roots. While neglecting lateral fluxes between local depletion zones around roots, we use this link to construct a system of continuous equations that combine root internal and external water flow that can be solved numerically for two boundary conditions (specified root collar water potential and zero distal influx) and one constraint (mean bulk matric flux potential). Furthermore, an iterative matrix solution for the stepwise analytical solution of homogeneous root segments is developed. Besides accounting for soil water flow iteratively, the intrinsic effect of variable axial conductance is accounted simultaneously. The reference and the iterative matrix solution are compared for different types of corn roots, soil textures and soil dryness states, which showed good correspondence. This also revealed the importance of accounting for variable axial conductance in more detail. The proposed reference solution can be used for the evaluation of different morphological and hydraulic designs of single or multiple parallel-connected roots operating in targeted soil environments. Some details of the iterative matrix solution may be adopted in analytical–numerical solutions of water flow in complex root systems.

Prediction of sediment wear of francis turbine with high head and high sediment content

Wear of runner blades is a common problem affecting the operational reliability of turbines with high head and high sediment content. In order to accurately predict the wear of the turbine runner blade, based on the solid-liquid two-phase flow equation and turbulence model, the full channel numerical simulation of the internal water and sediment flow was carried out, and the sediment volume distribution and sand water velocity on the turbine runner blade were obtained. Then, according to the digital simulation results and the operating parameters of the turbine runner, the sediment wear test scheme for the turbine blade material specimen is designed, and the sediment wear test is carried out on the runner material. According to the test results, the sediment wear curve of runner blade material is obtained and applied to numerical simulation, and the main position and wear degree of turbine blade sediment erosion are predicted. The inspection results of the runner blade wear after the unit has operated for a flood season show that obvious wear can be seen at the outlet edge of the lower band of the runner blade, and the wear position and wear amount are basically consistent with the simulation values. The study is of great importance for predicting the wear of turbine runner blades with high drop height and high sediment content, and for turbine maintenance under complex conditions.

Sponges sneeze mucus to shed particulate waste from their seawater inlet pores

SummarySponges, among the oldest extant multicellular organisms on Earth,1 play a key role in the cycling of nutrients in many aquatic ecosystems.2, 3, 4, 5 They need to employ strategies to prevent clogging of their internal filter system by solid wastes,6, 7, 8 but self-cleaning mechanisms are largely unknown. It is commonly assumed that sponges remove solid waste with the outflowing water through distinct outflow openings (oscula).3,9 Here, we present time-lapse video footage and analyses of sponge waste revealing a completely different mechanism of particle removal in the Caribbean tube sponge Aplysina archeri. This sponge actively moves particle-trapping mucus against the direction of its internal water flow and ejects it into the surrounding water from its seawater inlet pores (ostia) through periodic surface contractions that have been described earlier as “sneezing.”10,11 Visually, it appears as if the sponge is continuously streaming mucus-embedded particles and sneezes to shed this particulate waste, resulting in a notable flux of detritus that is actively consumed by sponge-associated fauna. The new data are used to estimate production of detritus for this abundant sponge on Caribbean coral reefs. Last, we discuss why waste removal from the sponge inhalant pores may be a common feature among sponges and compare the process in sponges to equivalent mechanisms of mucus transport in other animals, including humans.

Internal Water Flows and Particles Abstraction in <i>Daphnia</i>

The operational function of the trunk limbs (thoracic appendages), of Daphnia, P3 and P4, is a long-term disputed definition between “solid walls”, sieving filters. Sieving is unlikely process for routine particle collection, particle capture is not a simple mechanical process and not by sieving alone. Analysis promotion supported by direct observational examination of the in-vivo cinematographic slow-motion film and magnified solid photos of tethered Daphnia by high-speed camera (250 frames per second) resulted in a definite interpretation presented in this paper. The Daphnia’s feeding mechanism achieves particles abstraction not by sieving. The existence of two internal alternate water flow routs was indicated: Lateral and Median. These micro flow structures are suggested as vulnerability reduction.

Towards the development of an automated electrical self-potential sensor of melt and rainwater flow in snow

AbstractTo understand snow structure and snowmelt timing, information about flows of liquid water within the snowpack is essential. Models can make predictions using explicit representations of physical processes, or through parameterization, but it is difficult to verify simulations. In situ observations generally measure bulk quantities. Where internal snowpack measurements are made, they tend to be destructive and unsuitable for continuous monitoring. Here, we present a novel method for in situ monitoring of water flow in seasonal snow using the electrical self-potential (SP) geophysical method. A prototype geophysical array was installed at Col de Porte (France) in October 2018. Snow hydrological and meteorological observations were also collected. Results for two periods of hydrological interest during winter 2018–19 (a marked period of diurnal melting and refreezing, and a rain-on-snow event) show that the electrical SP method is sensitive to internal water flow. Water flow was detected by SP signals before it was measured in conventional snowmelt lysimeters at the base of the snowpack. This initial feasibility study shows the utility of the SP method as a non-destructive snow sensor. Future development should include combining SP measurements with a high-resolution snow physics model to improve prediction of melt timing.

Quenching experiments of vertical Inconel and Zircaloy tubes in internal water flow

In this study, quenching experiments of vertical Inconel and Zircaloy tubes in internal water flow were conducted. The effects of the initial tube wall temperature, liquid subcooling, and liquid injection velocity on the quench temperature, the reaching time to quench temperature, and the quench front velocity were examined. For the experimental conditions, the initial tube wall temperatures were 700 and 1000 °C, the liquid subcoolings were 10, 50, and 75 °C, and the liquid injection velocities were 0.05 and 0.1 m/s. An increase in the initial tube wall temperature increased the quench temperature and prolonged the reaching time to quench temperature with the decrease of the quench front velocity. An increase in liquid subcooling shortened the reaching time to quench temperature and increased the quench temperature and quench front velocity. In addition, an increase in the liquid injection velocity reduced the reaching time to quench temperature, and increased the quench temperature and quench front velocity. For all cases, the Inconel tube exhibited a longer reaching time to quench temperature with lower quench temperature and quench front velocity than those of the Zircaloy tube. Based on the present experimental data for the quench temperatures of Inconel and Zircaloy tubes, the previous correlations were compared and assessed. The correlation of Kim and Lee (1979) predicted the quench temperature data with reasonable accuracy.

Hydraulic characteristics of small-scale constructed wetland based on residence time distribution

ABSTRACT This paper designs and builds a small constructed wetland test site to study the internal hydraulic characteristics of different types of constructed wetlands, conducts NaCl pulse tracing experiments, and fits the residence time distribution (RTD) with the CSTRs+PFD model (Continuous Stirred-Tank Reactor model in parallel with Plug Flow with Dispersion model). The results showed that, among the six types of constructed wetlands, hydraulic parameters of horizontal subsurface flow constructed wetlands with baffles had the best performance, with a tracer recovery rate (F(t)) reaching 43.67% and hydraulic efficiency (λ) reaching 0.81. The addition of baffles slowed flow velocity, increased mean hydraulic retention time (Tm ) and peak residence time (Tp ), and reduced the short circuits phenomenon. The velocity of internal water flow increased during the horizontal and vertical deflections, which could well avoid the stagnation phenomenon caused by complicated flow state, thereby improving the hydraulic efficiency (λ). The CSTRs+PFD model can better fit the RTD of 6 different types of constructed wetlands. The peak value of the fitted curve, the time to reach the peak and the slope of the curve are all very similar to the measured RTD.

Falling film boiling of refrigerants over nanostructured and roughened tubes: Heat transfer, dryout and critical heat flux

Falling film evaporators offer an attractive alternative to flooded evaporators as the lower fluid charge reduces the impact of leaks to the environment and associated safety concerns. A study was conducted of saturated falling film boiling of two refrigerants on one polished, one roughened and three nanostructured copper tubes in order to evaluate the potential of nanostructures in falling film refrigerant evaporators. Tubes were individually tested, placed horizontally within a test chamber and heated by an internal water flow with refrigerant distributed over the outside of the tubes. Wilson plots were used to characterise the internal water heat transfer coefficients (HTCs). A layer-by-layer (LbL) process was used to create the first nanostructured tube by coating the outside of a tube with silica nanoparticles. A chemical bath was used to create copper oxide (CuO) protrusions on the second nanostructured tube. The third tube was coated by following a commercial process referred to as nanoFLUX. R-245fa at a saturation temperature of 20 °C and R-134a at saturation temperatures of 5 °C and 25 °C were used as refrigerants. Tests were conducted over a range of heat fluxes from 20 to 100 kW/m and refrigerant mass film flow rates per unit length from 0 to 0.13 kg/m/s, which corresponds to a film Reynolds number range of 0 to approximately 1500 to 2500, depending on the refrigerant. Heat fluxes were increased further to test whether the critical heat flux (CHF) point due to a departure from nucleate boiling (DNB) could be reached. The CuO and nanoFLUX tubes had the lowest film Reynolds numbers at which critical dryout occurred at heat fluxes near 20 kW/m2, but as the heat fluxes were increased towards 100 kW/m2, critical dryout occurred at the highest film Reynolds numbers of the tubes tested. Furthermore, in some higher heat flux cases, CHF as a result of DNB for the CuO and nanoFLUX tubes was reached before critical dryout occurred, and DNB became the limiting operational factor. The refrigerant condition that had the worst dryout performance in terms of film Reynolds number was R-134a at 25 °C, followed by R-134a at 5 °C and R245fa at 20 °C. Tests across the heat flux range and refrigerant conditions revealed that compared to the polished tube, the roughened tube had HTCs between 60 and 100% higher, the LbL tube had HTCs between 20% lower and 20% higher, the CuO tube had HTCs between 20% lower and 80% higher and the nanoFLUX tube had HTCs between 40 and 200% higher than the polished tube. The falling film enhancement ratios for the plain and nanostructured tubes were found to be of a similar order of magnitude, typically between 1.3 and 0.8.

Constant Electricity Generation in Nanostructured Silicon by Evaporation‐Driven Water Flow

AbstractRecently, hydrovoltaic technology emerged as a novel renewable energy harvesting method, which dramatically extends the capability to harvest water energy. However, the urgent issue restricting its device performance is poor carrier transport properties of the solid surface if large charged interface is considered simultaneously. Herein, a hydrovoltaic device based on silicon nanowire arrays (SiNWs), which provide large charged surface/volume ratio and excellent carrier transport properties, yields sustained electricity by a carrier concentration gradient induced by evaporation‐induced water flow inside nanochannels. The device can yield direct current with a short‐circuit current density of over 55 μA cm−2, which is three orders larger than a previously reported analogous device (approximately 40 nA cm−2). Moreover, it exhibits a constant output power density of over 6 μW cm−2 and an open‐circuit voltage of up to 400 mV. Our finding may pave a way for developing energy‐harvesting devices from ubiquitous evaporation‐driven internal water flow in nature with semiconductor material of silicon.

Constant Electricity Generation in Nanostructured Silicon by Evaporation-Driven Water Flow.

Recently, hydrovoltaic technology emerged as a novel renewable energy harvesting method, which dramatically extends the capability to harvest water energy. However, the urgent issue restricting its device performance is poor carrier transport properties of the solid surface if large charged interface is considered simultaneously. Herein, a hydrovoltaic device based on silicon nanowire arrays (SiNWs), which provide large charged surface/volume ratio and excellent carrier transport properties, yields sustained electricity by a carrier concentration gradient induced by evaporation-induced water flow inside nanochannels. The device can yield direct current with a short-circuit current density of over 55 μA cm-2 , which is three orders larger than a previously reported analogous device (approximately 40 nA cm-2 ). Moreover, it exhibits a constant output power density of over 6 μW cm-2 and an open-circuit voltage of up to 400 mV. Our finding may pave a way for developing energy-harvesting devices from ubiquitous evaporation-driven internal water flow in nature with semiconductor material of silicon.

Comparison between simulations and experiment for heat transfer characteristics in the re-burning kiln heat exchanger

Waste heat from the combustion process that is left unused may cause pollution problems and adversely affect health. This waste heat should be recovered. In this research, the simulation and experimental data on heat transfer characteristics of the pipe coiled inside the re-burning kiln heat exchanger were studied. The main objective of this study was to compare heat transfer coefficients obtained from the simulation using water as the working fluid with those obtained experimentally from the re-burning kiln heat exchanger for the drying system. The re-burning kiln heat exchanger was of coil-pipe-type with an outside diameter of 38 mm. The coiled pipe set up on the re-burning kiln heat exchanger was 80 cm in width and 173 cm in height. The flow rate of the cold water used as a working fluid was varied from 10 to 20 LPM, while the surface temperature of the coil pipe was varied from 200±20°C to 400±20°C, respectively. Thermal conductivity and outlet temperature of the water were also measured as a function of the internal temperature and water flow rate. The experimental results were validated against the simulation. The results showed that when the flow rate of water inlet decreased from 20 LPM to 10 LPM, the temperature of the water outlet was increased from 52.4 °C to 76.3 °C respectively. An increase in the temperature of the water outlet because of increased the re-burning kiln heat exchanger temperature and reduced the mass flow rate of supply water. The obtained simulated heat transfer coefficient in the re-burning kiln heat exchanger was in agreement with the experimental results.

Leaf hydraulic conductance is linked to leaf symmetry in bifacial, amphistomatic leaves of sunflower.

The hydraulic implications of stomatal positioning across leaf surfaces and the impact on internal water flow through amphistomatic leaves are not currently well understood. Amphistomaty potentially provides hydraulic efficiencies if the majority of hydraulic resistance in the leaf exists outside the xylem in the mesophyll. Such a scenario would mean that the same xylem network could equally supply a hypostomatic or amphistomatic leaf. Here we examine leaves of Helianthus annuus to determine whether amphistomaty in this species is associated with higher hydraulic efficiency compared with hypostomatic leaves. We identified asymmetry in the positioning of minor veins which were significantly closer to the abaxial than the adaxial leaf surface, combined with lower Kleaf when transpiration was driven through the adaxial rather than the abaxial surface. We also identified a degree of coordination in stomatal behaviour driven by leaf hydraulics, where the hydraulic conditions experienced by an individual leaf surface affected the stomatal behaviour on the opposite surface. We found no advantage to amphistomaty based on efficiencies in construction costs of the venous system, represented by vein density:stomatal density, only limited hydraulic independence between leaf surfaces. These results suggest that amphistomaty does not substantially increase whole-leaf hydraulic efficiency.

Effect of water supply pressure on atomization characteristics and dust-reduction efficiency of internal mixing air atomizing nozzle

As a new type of nozzle, the internal mixing air atomizing nozzle has been widely used in the field of dust reduction via spraying. In this study, the effect of water supply pressure on the atomization characteristics and dust-reduction efficiency of the internal mixing air atomizing nozzle was investigated. Firstly, the FLUENT software was used to simulate the flow field inside and outside the nozzle under different water supply pressures. The numerical simulation results showed that as the water supply pressure increased, the internal pressure and water flow velocity in the mixing chamber of the nozzle increased while the air flow rate decreased sharply, resulting the continuous decrease in the relative velocity between gas and liquid. Meanwhile, as the water supply pressure increased, the fragmentation scale of the liquid jet at the outlet of the nozzle was prolonged and the atomization of the liquid was limited. Secondly, based on the custom-developed dust reduction experimental system via spraying, the atomization characteristics of the nozzle were investigated. According to the experimental results, when the water supply pressure increased, the water flow rate and air flow rate of the nozzle had exponential increase and decrease, respectively. As the water supply pressure increased, the range, droplet volume fraction, droplet size, and velocity all increased, while the atomization angle first increased and then decreased. Finally, the dust reduction experiment via spraying was performed under different water supply pressures. The results showed that with the increase of water supply pressure, the dust-reduction efficiency for both the total dust and the respirable dust first increased and then decreased.

Numerical Analysis on the Freezing Process of Internal Water Flow in a L-Shape Pipe

Numerical Analysis on the Freezing Process of Internal Water Flow in a L-Shape Pipe