Fog harvesting is a sustainable approach for potable-water supply in fog-prone coastal and elevated regions, but its fog-capture efficiency (eta cap) depends strongly on droplet-size distribution, mesh geometry, and wind speed. This study uses Eulerian-Lagrangian simulations to examine the effects of fog-mesh wire diameter ( df 0.2-1.0 mm), shade coefficient (SC = 0.3-0.7), and freestream velocity (2-5 m s-1) on the capture of droplets with diameters from 2 to 40 mu m. To interpret the results in a transferable form, droplet behavior is organized by Stokes number into three regimes: regime 1 (low-St and streamline-following droplets with weak capture), regime 2 (intermediate-St droplets that are highly sensitive to mesh geometry and aerodynamics), and regime 3 (high-St droplets dominated by inertial impaction). Large droplets show the highest instantaneous capture across most cases, whereas intermediate droplets govern the sensitivity to SC, df, and U. Fine and intermediate wires (df = 0.2-0.6 mm) with SC close to 0.6 provide the best balance between geometric interception and aerodynamic permeability. Increasing velocity enhances impaction until wake formation and flow diversion limit additional gain. The results are interpreted using a nondimensional framework, based on the droplet Stokes number, mesh-fiber Reynolds number, pressure-drop coefficient, and shade coefficient. The reported fog-capture efficiency ( eta cap) values should be interpreted as the dry-mesh capture efficiencies (instantaneous capture at the onset of fogging, or under lean fog loading) since the current study excludes the dynamic impact of prolonged wetting, liquid deposition and growth on the fibers, mesh pore-clogging, and droplet re-entrainment effects. Notwithstanding, the current analysis effectively identifies a desirable design window corresponding to intermediate Stokes numbers, moderate-to-high aerodynamic permeability, and SC = 0.6.
Abstract This paper presents an explicit Lambert-W inversion of the classical Fanno relation for steady, adiabatic, quasi-one-dimensional (Q1D) flow of a calorically perfect ideal gas in a constant-area duct with wall friction. The formulation isolates the downstream Mach number as a function of the upstream Mach number, the specific-heat ratio, and the prescribed friction-length parameter 4fL/D. The appropriate real branch of the Lambert-W function is selected from the inlet sonic regime: the W−1 branch for subsonic inlet flow and the W0 branch for supersonic inlet flow. The resulting expression eliminates the conventional iterative inversion of the implicit Fanno equation for admissible, unchoked cases. Numerical comparisons with the classical implicit Fanno relation show agreement to numerical precision for representative subsonic and supersonic cases. The expression may be useful for instruction, code verification, preliminary sizing and rapid evaluation of idealized compressible duct systems, and reduced-order analysis of microchannels where wall friction is a dominant effect.
The present work proposes and numerically investigates a series of novel passive micromixers based on the triangular-shaped separation and recombination (TSAR) configuration. These designs are further integrated with the Minkowski fractal principle into the triangular obstacle geometries to promote enhanced mixing performance. The study begins with three fundamental configurations: converging triangular separation and recombination (TSAR-CC), diverging triangular separation and recombination (TSAR-DD), and a union of converging-diverging triangular separation and recombination (TSAR-CD) micromixers, each designed to induce chaotic advection along the mixing channel. Subsequently, the variants of each base design are introduced inspired by the Minkowski fractal theory, featuring two, four, and eight steps within triangular obstacles. These modifications create distinct flow perturbations and local recirculation zones that further strengthen chaotic advection and improve mixing uniformity. The numerical simulations are carried out in openfoam v24 workbench for mixing of fluids having identical properties, while the Reynolds number range of 1 to 100 is set for the analysis. The mixing performance of the micromixers is evaluated qualitatively and quantitatively through concentration contours, while the streamlines and velocity vectors are also presented to reveal the flow dynamics. Among all the designs, TSAR-CD demonstrates superior results, particularly in low Reynolds number range (Re < 25). The improvement in the mixing quality is further reported in the wide range of Reynolds numbers (more than 90%), as the TSAR-CD is modified with the Minkowski fractal. Finally, all the proposed micromixers are being evaluated together based on the mixing index and pressure drop to determine the overall optimum design.
Abstract In wall-modeled large-eddy simulation (WMLES), the velocity is sampled at a distance from the wall in the turbulence resolving region. Then, using this velocity as a boundary condition, Reynolds-averaged Navier–Stokes equations in thin boundary-layer form are solved down to the wall to obtain the near-wall solution. The Prandtl mixing-length model is often used to determine the eddy viscosity in the wall-model region. In the present work, we derive a new curvature-corrected mixing-length model based on the axisymmetric law of the wall. This new formulation improves agreement with experimental measurements at the radius-based Reynolds number Rea=4.330×103, particularly in the log-law region just below the wall-model sample location. At higher Reynolds numbers, i.e., Rea=1.060×105,2.185×105, the curvature-corrected wall model converges to the baseline model. Importantly, we also introduce a method to estimate, a priori, the increment in wall shear stress due to the use of the curvature-corrected mixing-length model over the planar model. The estimation method predicts increments of less than 1% for Reynolds numbers greater than Rea≈O(105) and an increment greater than 10% for Reynolds numbers of order O(103). This is confirmed through WMLES.
Pressure losses vary significantly among fittings, yet such data are rarely provided by manufacturers. This gap largely stems from the lack of a measurement method that balances accuracy and practicality. Conventional testing requires each fitting to be connected to straight tubes of compatible material and connection type, with multiple upstream and downstream pressure taps. Given the wide range of materials, geometries, and connection types used in modern fittings, fabricating dedicated instrumented test sections for each fitting is impractical. This paper presents a streamlined and widely applicable method that enables consistent and accurate testing of various fittings using the same instrumented straight tubes. The method is demonstrated using three elbow fittings (glue-joint chlorinated polyvinyl chloride (CPVC), solder-joint copper, push-to-connect brass) and a polyethylene (PEX) tube bend, all with & frac34;-in. (19 mm) nominal tube size. A comprehensive uncertainty analysis is presented. Results show that measurement uncertainty in pressure loss is strongly influenced by the extent to which the flow is fully developed at the pressure measurement locations. Screening data based on the straight-tube friction factors effectively identifies and removes data associated with developing flow, thereby reducing the uncertainty. The measured pressure loss coefficients agree with predictions from existing methods based on bend radius. By simplifying the test setup and streamlining the data analysis, the method lowers the practical barrier for manufacturers to generate pressure-loss data, improving the accuracy of design and evaluation of fluid piping systems.
