Abstract

This work describes a hybrid analytical‐numerical solution employing the Generalized Integral Transform Technique (GITT) to forced convection heat transfer in hydrodynamically fully developed and thermally non‐developed Newtonian laminar flow inside annular sector ducts under Dirichlet boundary conditions, considering uniform temperature entrance profile. In order to facilitate the analytical treatment and the application of the boundary conditions, a Conformal Transform was utilized to change the domain into a more suitable coordinate system. Thereafter, the GITT was applied on the energy equation to obtain the temperature field. Numerical results were obtained for quantities of practical interest, such as bulk mean temperature, local and average Nusselt number, and thermal entry length. These results were compared, as much as possible, with the parameter values available in the literature and they presented a good agreement.

Abstract

Abstract

Abstract

The aim of this paper is to describe the methodology followed in order to determine the viscous effects of a uniform wind on the blades of small horizontal-axis wind turbines that rotate at a constant angular speed. The numerical calculation of the development of the three-dimensional boundary layer on the surface of the blades is carried out under laminar conditions and considering flow rotation, airfoil curvature and blade twist effects. The adopted geometry for the twisted blades is given by cambered thin blade sections conformed by circular are airfoils with constant chords. The blade is working under stationary conditions at a given tip speed ratio, so that an extensive laminar boundary layer without flow separation is expected. The boundary layer growth is determined on a non-orthogonal curvilinear coordinate system related to the geometry of the blade surface. Since the thickness of the boundary layer grows from the leading edge of the blade and also from the tip to the blade root, a domain transformation is proposed in order to solve the discretized equations in a regular computational 3D domain. The non-linear system of partial differential coupled equations that governs the boundary layer development is numerically solved applying a finite difference technique using the Krause zig-zag scheme. The resulting coupled equations of motion are linearized, leading to a tridiagonal system of equations that is iteratively solved for the velocity components inside the viscous layer applying the Thomas algorithm, procedure that allows the subsequent numerical determination of the shear stress distribution on the blade surface.

Abstract

This paper provides a new unified formula for Newtonian fluids valid for all pipe flow regimes from laminar to fully rough turbulent flow.This includes laminar flow; the unstable sharp jump from laminar to turbulent flow; and all types of turbulent regimes, including the smooth turbulent regime, the partial non-fully developed turbulent regime, and the fully developed rough turbulent regime. The new unified formula follows the inflectional form of curves suggested in Nikuradse’s experiment rather than the monotonic shape proposed by Colebrook and White. The composition of the proposed unified formula uses switching functions and interchangeable formulas for the laminar, smooth turbulent, and fully rough turbulent flow regimes. Thus, the formulation presented below represents a coherent hydraulic model suitable for engineering use. This new flow friction model is more flexible than existing literature models and provides smooth and computationally cheap transitions between hydraulic regimes.

Abstract

Separate flow friction formulations for laminar and turbulent regimes of flow through pipes are in common use in engineering practice. However, variation of different parameters in a system of conduits during conveying of fluids can cause changes in flow pattern from laminar to fully turbulent and vice versa. Because of that, it is useful to unify formulations for laminar and turbulent hydraulic regimes in one single coherent equation. In addition to a physical interpretation of hydraulic friction, this communication gives a short overview of already available Darcy’s flow friction formulations for both laminar and turbulent flow and additionally includes two simple completely new approximations based on symbolic regression.

Abstract

Despite the Earth’s abundance of salt water, water access remains one of the greatest global challenges, underscoring the urgent need to improve technologies for desalination treatment. Electrodialysis, a novel desalination technology, uses electric charge to separate NaCl ions from feed water. It operates within a device made up of electrodes and ion exchange membranes separated by spacers.  The flow of water is critical to the effectiveness of electrodialysis. To address this, spacers can be modified to enhance fluid movement and turbulence. Research on enhancing fluid turbulence in electrodialysis, particularly through the creation of different spacer designs, and its effect on desalination performance is currently lacking. This study addresses this gap by evaluating self-made 3D-printed spacer designs—tortuous pathway, cubic, and column—against a spacer-less control within a 3D-printed electrodialysis module. Results demonstrated that desalination performance was enhanced with the incorporation of spacer designs, with the average salinity changes of each spacer ranking in ascending order from the control, column, cubic, and tortuous pathway. Similarly, the Reynolds numbers ranked in identical order, indicating that increasing fluid turbulence improves desalination. The tortuous pathway spacer was found to be the most effective, significantly improving desalination in comparison to the control (p<0.05). This was due to its design creating the greatest fluid turbulence, with a Reynolds number nearly triple that of the control. Overall, this study not only developed an innovative and low-cost 3D-printed electrodialysis system but also demonstrated the potential of customized spacer designs to significantly enhance desalination.

Abstract

Eutrophication affects 65% of coastal and 53% of freshwater regions in the US but no scalable cyanobacterial degradation methods exist. Piezocatalysis harnesses mechanical energy to produce reactive oxygen species (ROS) in water, which degrade organic pollutants by oxidation without generating toxic residues. This study designed a novel hydro-turbine using bluff bodies that maximize kinetic flow energy available for aquatic remediation via piezocatalysis. MoS2-doped films exhibited first-order ROS chain reaction production when agitated in Anabaena (20 μg/L), and has potential to inhibit cyanobacterial positive feedback growth by converting nitric products into reactive nitrogen species. The inverted piezo-active flag model was computationally optimized to enhance polarization with turbulent energy and ensure rapid charge dispersion with flow-induced vibrations. The 90° upstream triangle yielded maximum coefficients by effective flow separation (12.6 drag, 18.6 lift) and a flag length ratio of 0.75 was optimal while avoiding canceling zones. The optimized piezocatalytic hydro-turbine design yielded 78% remediation under 800gph for 60s (p=0.032). A minimum flow speed was identified by energy/order to be 0.5m/s, with 0.7W/(1g MoS2). Application depth of 0.3m-2m was identified with cyanobacterial concentration, turbulence needed for crossflow effectiveness, and speed; conditions are within industrial scalability standards. Chain reactions allow the remediation of still-water and high-volume downstream regions through tributaries. In the future, the device can be studied in environments with varying meander speeds and upstream ROS exposure times. The device presents a potential industrial eutrophication treatment applicable in ~93% of fluvial environments.