Proton exchange membrane fuel cell (PEMFC) systems have the ability to meet our energy demands in the near future. The PEMFC has a wide range of advantages such as low temperature operation, high energy efficiency, noise-free operation and zero emissions. One of the important factors influencing the PEMFC’s performance is the flow field configuration. The dimensions of the flow channel in a Proton Exchange Membrane Fuel Cell (PEMFC) have a profound effect on reactant distribution and water management within the fuel cell. The current study aims to ameliorate fuel cell (FC) performance, water management, and pressure drop (PD) across channels. To assess their impact on PEMFC performance, four distinct types of channel widths for a leaf design flow channel were chosen for this investigation. ANSYS FLUENT-18.2 was used for the numerical simulation of 3D PEMFC models. Under the same temperature and pressure, the leaf channel with four distinct types of channel widths was compared. The results showed that the fuel cell model with a 0.5 mm channel width performed better than the other configurations, generating a peak power density of 0.532 W/cm2 at 0.4 V cell voltage while also improving other FC parameters.
Understanding sedimentation relies on grasping the physics between a particle and a fluid. This research employs the Lattice Boltzmann method to conduct a benchmarking study on the sedimentation of a single spherical particle in a Newtonian fluid. The study explores the effects of particle diameter, particle density, and walls on particle settling behaviour. The methods employed include the point particle method and the homogeneous Lattice Boltzmann method (HLBM) using the OpenLB code. The primary objectives of this research are to calculate terminal settling velocity, analyse velocity and vorticity profiles, and track particle trajectories. The HLBM excels in providing precise flow representation around particles, whereas the point particle method shows limitations at higher particle Reynolds numbers. Additionally, the research reveals that wall effects reduce terminal settling velocity and shorten wake length. The domain-size-to-particle-size ratios at which wall-induced vortices disappear for various particle properties are identified. Thorough understanding of the settling physics of a single particle should contribute to unravelling the settling dynamics of multiple particles.
This study presented molecular dynamics simulations to investigate the rheological and agglomeration behaviours of nano-sized sand in hydrated slurry under horizontal and vertical external flows. The simulations assessed how flow direction affected sand nanoparticle behaviour. A 10 ns simulation duration was sufficient to reach equilibrium, with temperature stabilising at 299.19 K and kinetic energy at 0.89 kcal/mol. Under Earth's gravity, flow direction was found to significantly influence structural evolution. Perpendicular external forces caused strong atomic fluctuations, especially in the central region, with a peak temperature of 350.96 K. In side regions, oil molecule agglomeration led to particle velocities of 0.00072 & Aring;/fs. When gravitational and external forces were aligned, reduced particle attraction increased fluctuations and raised the average temperature to 388 K. This alignment enhanced particle mobility, reaching velocities of 0.000905 & Aring;/fs, and shortened agglomeration time to 4.03 ns versus 4.19 ns under perpendicular forces. It also increased slurry viscosity to 1.29 mPa & centerdot;s, compared to 1.16 mPa & centerdot;s in the perpendicular case.
This study presents a comprehensive review of the aerodynamics and aero-acoustics of supersonic jets, with an emphasis on active and passive flow controls that improve mixing effectiveness and noise reduction. The study explores the impact of various control techniques, such as tabs, grooves, and fluid injectors, on noise reduction, shock structures, and jet core dynamics. The impact of Mach numbers, Strouhal numbers, NPRs, overexpanded and under-expanded conditions on jet flow properties is assessed using both experimental and numerical data. The research attempts to provide a coherent knowledge of jet behaviour and its underlying mechanisms by combining data from multiple investigations. By comparing the results of different active and passive flow control techniques, ventilated and delta tabs are found to be the best methods for attaining exceptional performance. The best control technique, which enhances the jet mixing and noise reduction, is identified, and the schematic of the proposed tab is presented.
This article provides a comprehensive overview of various methods used to enhance the thermal performance of heat exchangers, along with the stability mechanisms of convective flows. Heat transfer occurs through three primary modes: radiation, conduction and convection. Among these, convection is one of the most significant and can be categorised as free, forced, granular, gravitational or thermomagnetic. Over the past few decades, numerous studies have investigated convective heat transfer in pipes. This paper presents a detailed review of fluid flow in pipes, aiming not only to evaluate previous research comprehensively but also to provide readers with valuable existing knowledge that may facilitate future studies. The effects of key dimensionless parameters such as the Rayleigh, Reynolds, Prandtl, Grashof, Nusselt and Darcy numbers, as well as pipe length, on heat transfer are also discussed. Additionally, the paper includes a brief discussion on the instability mechanisms of mean flow in pipes based on recent stability analyses.
This manuscript investigates thermosolutal mixed convection flow in a vertical pipe within a porous medium, subject to a transverse magnetic field. The fluid is considered to be fully developed, electrically conducting, and heat-generating/absorbing. The non-Darcy Brinkman-Forchheimer-extended model is used to characterise the flow in the porous medium. Numerical solutions for the coupled differential equations are obtained using the Chebyshev spectral-collocation approach. It is observed that, under limiting conditions, our numerical results show good agreement with existing numerical data. The impact of various parameters, such as the Hartmann number (M), heat absorption/generation parameter (Q), and Forchheimer number (F), on the velocity, temperature, and concentration profiles has been analysed. An unusual deviation is observed in both the velocity and temperature profiles beyond a certain value of the heat generation parameter. Initially, increasing the magnetic field strength reduces the fluid velocity. However, beyond a threshold, the velocity profile flattens across the domain, while the temperature profile increases and the concentration profile decreases. Elevated drag forces within the medium result in smoother and flatter velocity profiles. An increase in the heat absorption parameter leads to higher peak temperatures and concentrations.
Today, new ventricular assist devices are catheter-inserted as a temporary solution for acute heart failure patients awaiting a heart transplant. This study designed a novel intravascular left ventricular assist pump inserted via a catheter, emphasising its compact design. The primary design challenge was selecting the optimal impeller. Using numerical simulation based on the Archimedean screw theory, eight impeller models, varying in pitch length and blade rotations, were examined for the axial flow pump. Performance was assessed across rotational speeds (13,260 to 19,260 rpm). The optimal impeller, selected based on the operating point (5 l/min and 80 mmHg at 16, 260 rpm) and the hemolysis index, featured a pitch length of 9.2. Results confirm the pump's potential for clinical use, offering high efficiency and low risk of blood damage. The novelty is the impeller design using the Archimedean screw concept and the methodology for determining the pitch steps.
