Early turbulence in dilute polymer-solution pipe flows and full-chord laminar flow on suction-controlled wings at Reynolds numbers (Re) up to 2,000,000 evidently markedly deviate from the conventional pipe-flow transition criterion with a critical Re of 2000–2300. Inspired by the spherical-shell membrane-force theory from structural mechanics, this work develops a force-balance model employing a virtual constant-thickness spherical fluid shell to interpret these anomalous laminar-turbulent transition behaviors. For low-Reynolds-number laminar pipe flow, the curvature radius of the virtual fluid layer varies inversely with the pressure gradient. Laminar-to-turbulent transition is hypothesized to take place when the shell curvature radius becomes smaller than the physical pipe radius. This condition defines a candidate critical tensile-force-flow threshold, expressed as twice the product of the fluid viscosity and the maximum pipe velocity, divided by the pipe radius. In general, in laminar pipe flow, the wall shear stress represents the flow-direction component of the tensile force flow. At this hypothesized transition threshold, wall shear stress numerically equals the critical-tensile-force-flow value, which yields qualitative consistency with documented early-turbulence observations. Furthermore, the proposed critical-tensile-force-flow concept offers a physical interpretation for high-Reynolds-number laminar pipe flow stabilized by wall suction. For suction-stabilized laminar pipes, the actual physical pipe may be conceptualized as a subsection of a larger hypothetical, virtual pipe that reaches the critical-tensile-force-flow condition. The real-wall shear stress is attenuated by a factor related to the ratio between the average velocity in the actual physical pipe and its center-line maximum velocity. We emphasize that this threshold is treated as a Newtonian hydrodynamic baseline rather than a universal intrinsic fluid-material property; further well-controlled experimental validation is required to test its general applicability.
The Kayanga-Anambé watershed, located in Haute-Casamance (Senegal), is a strategic area for national food security, yet remains exposed to recurrent flooding that threatens hydro-agricultural developments. This study aims to map flood-susceptibility zones using an integrated approach combining Geographic Information Systems (GIS) with a multi-criteria model built on seven (7) parameters: Flow Accumulation, Rainfall Intensity, Land Use, Geology, Slope, Terrain Elevation, and Distance to drainage (FIGUSED). The methodology relies essentially on cross-referencing morphometric factors (slope, drainage density), climatic factors (rainfall intensity), and anthropogenic factors (land use, infrastructure). Data derived from digital elevation models and Sentinel-2 imagery were processed through an Analytic Hierarchy Process (AHP) to weight the influence of each parameter. The results highlight a strong susceptibility of the Anambé basin, exacerbated by gentle slopes and the rapid saturation of hydromorphic soils during monsoon peaks. The high-susceptibility zone (high and very high classes) totals 40.64% of the watershed area, that is 1257.46 km2, corresponding geographically to the Anambé basin and the floodplain of the Kayanga and its tributaries. The most represented class is high susceptibility, at nearly 28%, closely followed by moderate susceptibility at 25.52% of the total area, indicating an overall heightened susceptibility of the watershed to inundation. The resulting susceptibility map thus constitutes an essential decision-support tool for planning agricultural campaigns through SODAGRI and for protecting human settlements in tropical rural areas.
Solar-driven alkaline water electrolysis (AWE) is a promising low-cost route to green hydrogen. This study experimentally evaluates three laboratory-scale solar-powered AWE reactors with different tank materials, electrode materials, inter-electrode gaps, and electrolyte concentrations: Design 1 (acrylic, nickel foam, 30 cm, 30 wt% NaOH), Design 2 (plastic, SS316, 13 cm, 7 wt% NaOH), and Design 3 (glass, SS316, 6 cm, 5 wt% NaOH). All reactors were powered by a photovoltaic-battery system and tested under the climate of Tabuk, Saudi Arabia. A unified framework assessed electrical, electrochemical, thermal, energy, exergy, entropy, dimensionless, techno-economic, and environmental performance, and ranked the designs using TOPSIS. Reducing the electrode gap from 30 cm to 6 cm decreased the area-specific resistance from 1103 to 55 Ω·cm2 and increased voltage efficiency from 11.6% to 18.6%. Design 3 achieved the highest current density (942 A·m−2), energy efficiency (18.6%), exergy efficiency (15.4%), gas-collection efficiency (57%), and the lowest specific energy consumption (212 kWh·kg−1). Its levelized cost of hydrogen decreased from 95 to 23 USD·kg−1 when projected to a commercial specific energy consumption of 50 kWh·kg−1. Wagner numbers of 0.03–0.06 indicated ohmic control. Design 3 ranked first (TOPSIS = 1.00). The analysis reproduced reported values within 0.33% while exactly satisfying first- and second-law balances.
