Search Results (51)

Transverse modification of step geometry has been repeatedly proposed as a means of increasing energy dissipation in stepped spillways, with numerically reported gains ranging from 5.6% to 34.7% for labyrinth configurations, in unresolved contradiction with air–water experimental evidence that detects no measurable difference. The objective of this study is threefold: to verify whether the transverse alternation of the tread length increases the net energy dissipation of the coupled chute–stilling basin system, to quantify its effect on the kinematic and energetic state of the flow delivered to the terminal energy dissipator, and to delimit its domain of applicability. That premise is subjected to verification through 38 three-dimensional Reynolds-averaged Navier–Stokes (RANS) simulations (k–$\omega$ shear-stress transport (SST) closure, homogeneous volume-of-fluid (VOF) formulation) performed in ANSYS CFX 2025 R2, comparing a three-section stepped spillway with a uniform rectilinear footprint against a configuration with transverse L–$L/2$ alternation, under 19 geometric–hydraulic combinations spanning the nappe, transition, and skimming flow regimes ($0.57\le d_c/h\le 2.93$). The model was verified through a mesh-convergence analysis of the uniform configuration (grid convergence index, GCI $=0.66\%$, on the approach depth) and validated against a physical scale model (0.38% discrepancy, exceeding the propagated experimental uncertainty); a three-level mesh study of the variable-tread configuration shows that its toe-flow response develops as the transverse tread strips become resolved and is not yet mesh-independent at the finest level, which is stated as a limitation of the quantitative results. Because the homogeneous multiphase formulation does not include an air-entrainment submodel, all results correspond to the modeled non-aerated flow conditions. The results do not support the hypothesis of a net dissipative gain: the global energy balance of the two topologies is equivalent within the numerical resolution of the study (bias $+0.13$ pp; root-mean-square error (RMSE) 0.26 pp), of the order of the discretization uncertainty of the study itself. The actual effect is a redistribution of the dissipative partition that conditions the flow delivered to the energy dissipator: the toe Froude number is reduced in all 19 paired cases (16.5–88.4%; mean: 34.1%). In nine scenarios the hydraulic jump is conditioned without being suppressed ($F{r}_1$ from 3.95–4.57 to 1.19–3.71), the energy delivered to the stilling basin drops by 18.3–57.9%, and the residual energy decreases by up to 14.98%; under subcritical toe flow, the same thickening increases the delivered energy by 12.3–19.4% and penalizes the residual energy by up to 18.08%; in two intermediate-discharge scenarios the jump is suppressed, yielding no benefit whatsoever. The transition is expressed through a critical threshold, nominally ${(d_c/h)}_{\mathrm{crit}}\approx 1.48$ within the observed separation interval $1.44<d_c/h<1.53$: the thirteen resolvable scenarios preserve the predicted sign separation without exception. The variable footprint is not a dissipation intensifier but a chute–dissipator coupling element, applicable only to high relative discharges. Full article

Nonfat dry milk (NFDM) powder was produced by spray drying a pulsed electric field (PEF)-treated solution of 48% (m/m) evaporated skim milk (ESM) that was treated with a field strength of 20 kV/cm and specific energy of 15 kJ/L at 150 L/h. PEF treatment induced reduction to particle size for whey proteins by 8.4% and casein micelles by 11.1% and increased conductivity by 10.6%. The PEF-treated ESM solution was less viscous than the non-PEF control (14.5% lower) and sedimentation was reduced by 40%. Increases to the tapped density (1.9%), solubility (4.7%), and emulsification stability (60%) of the NFDM were observed after PEF treatment. Evaluation of protein structure indicated no modification to the secondary structure, while minor changes to the tertiary structure were observed with increased fluorescence intensity and decreased transition temperatures. The reduction in casein micelle size for the PEF-treated ESM may be associated with the movement of minerals to the aqueous solvent. This study is the first to apply PEF technology to a highly concentrated ESM solution using a continuous flow commercial PEF system. The results of this study suggest that PEF technology may be beneficial to improving the dairy processing efficiency of ESM and product quality for NFDM. Full article

Energy dissipation in stepped weirs depends on the complex interaction between geometry, flow regime, and surface aeration. The research proposes a dimensionless empirical model (RE3T) to predict the overall energy dissipation in three-section stepped weirs with variable slopes. The formulation integrates dimensional analysis based on the Vaschy–Buckingham theorem, controlled physical experimentation, and three-dimensional numerical simulations using CFD employing the RANS–SST turbulence model implemented in ANSYS CFX. Eighteen numerical simulations were performed covering seven geometric configurations and four hydraulic inlet conditions, covering slug, transitional, and skimming flow regimes. The CFD model was previously validated by comparison with a physical scale model, obtaining a discrepancy of only 0.38% in relative energy dissipation. The validated dataset was then used to calibrate an empirical multiplicative correlation composed of eight dimensionless groups associated with sectional slopes, number of steps, overall geometric ratio, and upstream Froude number. The proposed model achieved a coefficient of determination R² = 0.81, with relative errors generally less than 1% and a maximum deviation of 2.34%. The statistical indicators (RMSE, MAE, and bias) confirm the absence of significant systematic trends within the defined domain of validity. The results show that the Froude number and the slopes of the sections are the variables with the greatest influence on overall dissipation. The RE3T formulation is a physically consistent and computationally efficient predictive tool for the design and analysis of stepped weirs with variable slopes, extending the scope of traditional correlations developed for uniform slopes. Full article

This study evaluated the hydraulic performance of regular and irregular stepped spillways experimentally to reduce the hydraulic leap length and enhance energy dissipation. The study tested fourteen physical models with 40° and 45° slopes and step numbers of 5 and 10, analyzing the effect of a single barrier block and its horizontal position through 98 rectangular flume experiments to evaluate energy dissipation and hydraulic jump length. The results showed that when the nappe flow transitioned to the skimming flow, energy dissipation decreased as discharge increased. Irregular stepped spillways achieved higher energy dissipation than regular ones by about 10–25%, with five-step models outperforming ten-step models due to increased turbulence. A strong positive relationship between discharge and hydraulic jump length was also observed, with jump length increasing by approximately 30–45% at 40° and 45° slopes. Five-degree irregular stepped spillways produced the shortest hydraulic jump lengths, confirming that step irregularity reduces downstream residual energy. Adding a single barrier block improved performance by shortening the hydraulic jump by about 20–35%, especially at higher discharges, with the optimal position at B/2. Overall, an irregular stepped spillway with a barrier block at B/2 was identified as the most effective configuration, enabling shorter hydraulic jumps, smaller stilling basins, and more efficient and economical spillway designs. Full article

This study compares the roles of eye-tracking and verbal reports (think-alouds and retrospective verbal reports, RVRs) in L2 reading process research through three qualitative studies. Findings indicate that eye-tracking provided precise, quantitative data on visual attention and reading patterns (e.g., fixation duration, gaze plots) and choice-making during gap-filling. Based on our mapping, it was mostly effective in identifying 13 out of 47 reading processing strategies, primarily those involving skimming or scanning that had distinctive eye-movement signatures. Verbal reports, while less exact in measurement, offered direct access to cognitive processes (e.g., strategy use, reasoning) and uncovered content-specific thoughts inaccessible to eye-tracking. Both methods exhibited reactivity: eye-tracking could cause physical discomfort or altered reading behavior, whereas think-alouds could disrupt task flow or enhance reflection. This study reveals the respective strengths and limitations of eye-tracking and verbal reports in L2 reading research. It facilitates a more informed selection and application of these methodological approaches in alignment with specific research objectives, whether employed in isolation or in an integrated manner. Full article

The classical assumption of self-similarity in flow velocities and turbulence statistics has been successfully validated for fully developed flows in open channels, pipes, and boundary layers. However, its application in developing boundary-layer flows in channels with steep slopes and large roughness elements has not yet been thoroughly scrutinized. This study investigates whether turbulence statistics exhibit self-similar behavior when properly scaled in steep-stepped spillways. Specifically, it explores the influence of roughness height ($k_s$)—representing the cavity size of a steep-stepped spillway—on turbulence statistics in the non-aerated skimming flow region. Numerical simulations, extensively validated against experimental data, were conducted for a stepped spillway with a fixed slope angle of 51.34°, using five roughness heights ($k_s$ = 6.25, 3.12, 1.56, 0.78 and 0.39 cm), corresponding to step height-to-length ratios of 10:8, 5:4, 2.5:2, 1.25:1 and 0.625:0.5, respectively. The results show that the dimensionless profiles of turbulent kinetic energy (TKE) at the step edges collapse onto a single curve when rescaled by a factor of ${\left(\delta /k_s\right)}^n$ with $n~0.4$. Likewise, the dissipation rate of TKE follows a similar collapse with $n~0.3$. For the turbulent eddy viscosity, an exponent of $n~0.5$ was adopted based on dimensional analysis, although the values for the smoothest configuration deviate from the curve. Full article

This study investigated the effect of a concentrated kombucha inoculum and transglutaminase (TG) on the rheological and textural properties of fermented milk products and compared their average production costs to commercial yoghurt. Semi-skimmed milk was used, to which microbial TG was added at a level of 0.02% w/w. The kombucha inoculum, prepared from black tea, was concentrated to 55.6% total solids. Four samples were produced: two with TG and two without. The TG-containing samples showed significantly higher textural properties, including firmness and consistency, than the non-TG samples. They also exhibited the largest hysteresis loop area and the highest yield stress, indicating a stronger gel structure. The Herschel–Bulkley model successfully described the flow behaviour of all samples and confirmed their shear-thinning, non-Newtonian nature. Principal Component Analysis (PCA) showed that both TG addition and inoculum concentration significantly influenced the product properties. TG improved the rheological and textural properties and increased the stability during storage. However, the production costs for TG-treated samples were higher than those for non-TG-treated samples and commercial yoghurt. Nevertheless, the higher costs could be justified by the perceived additional nutritional benefits for consumers. Overall, the results show that the combination of concentrated kombucha inoculum with transglutaminase can improve the structural and rheological quality of fermented dairy products, which is potentially of commercial importance. Full article

(1) Background: The impact of different drying methods on the functional properties and microstructure of milk powders was analyzed in this study. (2) Methods: Whole milk, skim milk, and buttermilk powders were obtained by freeze drying, spray drying, and roller drying. (3) Results: The examined powders differed in chemical composition, and these differences were attributed mainly to their fat content. The functional properties of the studied powders were determined mainly by the drying method and were less influenced by their composition. Loose and tapped bulk density was highest in roller-dried powders and lowest in freeze-dried powders. The flowability of milk powders was determined by calculating the Carr index and the Hausner ratio, and the results were used to classify the analyzed powders into the following groups: poorly flowing and cohesive (spray-dried samples), passable (roller-dried samples), and fair (freeze-dried samples). The volume of insoluble particles was highest in roller-dried powders and much lower in spray-dried powders, whereas freeze-dried powders were 99.8–99.9% soluble in water. Whole milk powder was characterized by low wettability (>180 s) regardless of the drying method. Powder morphology was influenced mainly by the drying method. (4) Conclusions: The fractal analysis demonstrated that spray-dried powders had the smallest fractal dimensions, which implies that their surface was least complex (most uniform). Regardless of the drying method, fractal dimensions were highest in whole milk powder, which could suggest that fat affects the microstructure of powders. The color parameters of milk powders were determined mainly by the drying method and were less influenced by the type of raw material used in powder production. Full article

Hydraulic jumps typically exhibit a distinct symmetry under ideal boundary conditions and are characterized by a sudden change in flow depth and velocity. They are commonly employed in a diverse array of water management systems to dissipate excess energy due to their high energy dissipation rate, strong adaptability to geological conditions and tailwater variation, small fluctuation in tailwater, and low cost of maintenance. In this study, a GPU-based Smoothed Particle Hydrodynamics (SPH) model of 3D hydraulic jumps is established. Numerical simulation of three 3D symmetric full hydraulic jumps with large Froude numbers are carried out, and satisfactory agreements are shown with a largest $L_2$ error of 0.442 between the numerical free surface and experimental data. The model can reliably reproduce the free surface, jump the toe position, and jump the skimming flow. The analysis of the model efficiency shows that a maximum GPU acceleration of 12, which is equivalent to the theoretical maximum speedups, against parallel CPU can be achieved with a common GPU device. Furthermore, the energy dissipation in the stilling basin of a real sluice gate is investigated by the model. Therefore, the SPH model is a powerful tool for investigating the complex and large-scale 3D full hydraulic jumps for similar hydraulic engineering with the same boundary condition. Full article

The effect of surface roughness in laminar flow has been the focus of recent research related to drag reduction. However, although particle transport is governed by laminar flow in most applications, the effect of surface texture on the drag of a sphere has mostly been addressed in the transitional and turbulent regimes. The aim of the present study is to explore the drag behavior of rough spherical micro-particles in laminar flow. The spheres’ roughness has been structured based on a 3D complex Weaire–Phelan model, as well as on a simpler orthogonal lattice one, and quantified as per various definitions. The emerging surface roughness comprises irregular elements in terms of shape and size. The investigation has been performed at Reynolds numbers ranging from 2 to 8. The drag coefficient is found to drop quadratically with increasing roughness. Relative roughness can reduce the total drag on the particle by over 21%. The key physical mechanism is explained by the particles’ surface cavities, which contain recirculating, nearly stagnant fluid, thus creating a self-lubricating effect that reduces skin friction, as the main flow skims over the top without entering the cavities. A reduction in total drag arises when skin friction drag reduction is larger than the increase in form drag. Understanding the drag behavior of spherical particles with irregular surface texture provides new and useful insight into low Reynolds number transport phenomena related to a variety of engineering applications. Full article

Ichthyoelephas longirostris, commonly known as pataló, is an endemic species from Colombia, categorized as endangered due to habitat degradation and overfishing. In this context, semen cryopreservation emerges as an effective strategy for its conservation. This study evaluated the damage caused by semen cryopreservation using a cryosolution composed of ethylene glycol (EG) at three inclusion levels (6%, 8%, and 10% v/v), skimmed milk powder (3% w/v), and glucose (6% w/v), all prepared in distilled water. A randomized experimental design was employed, with three treatments and a control (fresh semen), using pooled semen from different males (n = 12). Each sample was analyzed in triplicate. Sperm parameters were evaluated through computer-assisted analysis (CASA), and damage to the plasma membrane, mitochondria, and DNA was assessed via flow cytometry. Fresh semen showed low levels of membrane damage (9.6 ± 6.9%), mitochondrial damage (29.1 ± 16.8%), and DNA fragmentation (0.24 ± 0.13%). In thawed semen, the highest membrane damage was observed with 10% EG (79.3 ± 13.0%), while the highest DNA fragmentation occurred with 6% EG (22.5 ± 21.9%). The cryosolution composed of 8% EG showed the best results, with lower levels of damage in the evaluated structures. These findings suggest that the combination of 8% EG, 3% skimmed milk powder, and 6% glucose is an effective formulation to reduce cellular damage during I. longirostris semen cryopreservation, representing a useful tool for conservation programs of this species. Full article

The covalent cross-linking of caseins by the enzyme transglutaminase (Tgase) stabilizes the structure of casein micelles. In our study, the effects of a pretreatment of skim milk (SM) by Tgase on milk protein fractionation by microfiltration were tested. Tgase was found to induce amount-dependent modifications of all milk proteins in SM and a reduction in deposit resistance for laboratory dead-end filtrations of up to 20%. This improvement in process performance could partially be confirmed in pilot-scale cross-flow filtrations of Tgase-pretreated SM and micellar casein solutions (MCC). These comparative trials with untreated retentates under a variation of ΔpTM (0.5–2 bar) at 10 and 50° revealed distinct differences in deposit behavior and achieved the reduction in deposit resistance in a range of 0–20%. The possibility of pre-fouling with enzymatically pretreated MCC prior to SM filtration was also investigated. Under different pre-fouling conditions, practical modes of retentate change, and pre-foulant compositions, a switch to untreated SM consistently resulted in an immediate and major increase in deposit resistance by 50–150%. This was partially related to the change in the ionic environment and the protein fraction. Nevertheless, our results underline the potential of Tgase pretreatment and pre-fouling approaches to alter filtration performance for different applications. Full article

Natural rubber skim latex is commonly discarded as waste or turned into skim natural rubber products such as skim crepe and skim blocks. It is challenging to retrieve all residual rubbers in skim latex since it has a very low rubber content and many non-rubber components like protein. Manufacturers conventionally utilize concentrated sulfuric acid as a coagulant. This method generates many effluents and hazardous pollutants that negatively impact the environment. This work presents an innovative method for enhancing the skim latex’s value by employing an ultrafiltration membrane. This study aims to establish a hydrophilic PVDF-TiO₂ mixed-matrix membrane. The skim latex was processed through a membrane-based ultrafiltration process, which yielded two products: skim latex concentrate and skim serum. Skim latex deposits that cause fouling on the membrane surface can be identified by SEM-EDX and FTIR analysis. The PVDF–PVP-TiO₂ mixed-matrix membrane generated the maximum skim serum flux of 12.72 L/m²h in contrast to the PVDF pure membranes, which showed a lower flux of 8.14 L/m²h. CHNS analysis shows that a greater amount of nitrogen, which is indicative of the protein composition, was successfully extracted by the membrane separation process. These particles may adhere to the membrane surface during filtration, obstructing or decreasing the number of fluid flow channels. The deposition reduces the effective size of membrane pores, leading to a decline in flux rate. The hydrophilic PVDF-TiO₂ mixed-matrix membrane developed in this study shows strong potential for application in the latex industry, specifically for treating natural rubber skim latex, a challenging by-product known for its high fouling potential. This innovative ultrafiltration approach offers a promising method to enhance the value of skim latex by enabling more efficient separation and recovery. Full article

Results are presented from a series of small-scale laboratory experiments designed to model dense gas dispersion around an isolated cuboid building. Experiments were conducted for a broad range of flow Richardson numbers and source discharge rates, and the concentration field in the wake of the building was measured using light-induced fluorescence (LIF). Results show that, for low Richardson numbers, the concentration of dense fluid in the wake decreases slightly with distance above the ground. However, for Richardson numbers above $Ri\approx 3$, the vertical variation is qualitatively different, as a dense lower layer forms in the wake and the concentration above the layer is much lower than for the lower Ri experiments. For these higher Richardson number flows, the primary mechanism by which dense fluid is flushed from the building wake is by the wake flow skimming dense fluid from the top of the lower layer and then moving it upstream toward the building’s leeward face. It is then transported up the leeward face of the building and then downstream. The results also generally show that, as the release rate of dense fluid increases, the density and thickness of the lower layer increases. The LIF measurements and a series of visualization experiments highlight the complex interaction of a dense fluid discharge with the wake structure behind a building. Full article

The shear flow and solid–liquid transition of mixed milk protein dispersions with varying concentrations of casein micelles (CMs) and serum proteins (SPs) are integral to key dairy processing operations, including microfiltration, ultrafiltration, diafiltration, and concentration–evaporation. However, the rheological behavior of these dispersions has not been sufficiently studied. In the present work, dispersions of CMs and SPs with total protein weight fractions (ω_PR) of 0.021–0.28 and SP to total protein weight ratios (R_SP) of 0.066–0.214 and 1 were prepared by dispersing the respective protein isolates in the permeate from skim milk ultrafiltration and then further concentrated via osmotic compression. The partition of SPs between the CMs and the dispersion medium was assessed by measuring the dry matter content and viscosity of the dispersion medium after separating it from the CMs via ultracentrifugation. The rheological properties were studied at 20 °C via shear rheometry, and the sol–gel transition was characterized via oscillatory measurements. No absorption of SPs by CMs was observed in dispersions with ω_PR = 0.083–0.126, regardless of the R_SP. For dispersions of SPs with ω_PR ≤ 0.21, as well as the dispersion medium of mixed dispersions with ω_PR = 0.083–0.126, the high shear- rate-limiting viscosity was described using Lee’s equation with an SP voluminosity (v_SP) of 2.09 mL·g⁻¹. For the mixed dispersions with a CM volume fraction of φ_CM ≤ 0.37, the relative high shear-rate-limiting viscosity was described using Lee’s equation with a CM voluminosity (v_CM) of 4.15 mL·g⁻¹ and a v_SP of 2.09 mL·g⁻¹, regardless of the R_SP. For the mixed dispersions with φ_CM > 0.55, the relative viscosity increased significantly with an increasing R_SP (this was explained by an increase in repulsion between CMs). However, the sol–gel transition was independent of the R_SP and was observed at φ_CM ≈ 0.65. Full article