Search results for "Note"
showing 10 items of 10709 documents
A New Systematic Series of Foil Sections with Parallel Sides
2020
Parallel-sided foil sections are used for centerboards and rudders in sailing dinghy classes and also for struts placed in a fluid flow. The objective of this work is to create a systematic series of parallel-sided sections to be used under different conditions, with an emphasis on the sailing dinghies 470, 420 and Optimist. The loss, and surprisingly the gain, in performance relative to 4-digit NACA sections are also investigated. A 2D Reynolds-averaged Navier&ndash
A Constructal Law optimization of a boiler inspired by Life Cycle thinking
2018
Abstract The aim of the paper is to explore how design optimization contributes to a technology's ecological evolution. The article develops this concept through an application of Constructal Law, used to account for the “evolution” of technologies design (configuration, shape, structure, pattern, rhythm), and Life Cycle Assessment (LCA), used for quantifying the environmental impacts of the design choices. The combination of both methods assesses how technology evolution affects the environment during its life, extending the concept of evolution of design. The study is applied to a case study of a real biomass boiler. The study analyses basic case and a series of alternative scenarios opti…
Experimental research of surfaced nanoparticle thermal transport in a porous medium
2018
Abstract Experimental research on thermally induced nanocolloid transport in a porous environment is presented. Addition of excess surfactant to a colloid with dispersed phase made of surfaced nanoparticles results in a decrease of effective Soret coefficient in a porous environment. It is shown that with sufficient amounts of surfactant added, this effect extends to a reversal of nanoparticle thermophoretic transport direction, and that the effect shows a tendency of saturation. A mechanism of thermal transport that involves slip velocity of surfactant molecules appearing near pore walls is evaluated as a possible cause of the decrease of Soret coefficient. Effects of temperature on partic…
Optofluidic microconvection with magnetic nanoparticles: Novel interaction of thermal diffusion and magnetic field
2021
Abstract Light-matter interactions are exploited in many applications, whereas superparamagnetic nanoparticles allow to introduce magnetic field control in diverse fluid environments. We study the structure of laser-induced thermal lens in thin layers of ferromagnetic colloid and predict significant magnetoconvective motion around the beam spot. It was found that localized heating depletes/accumulates magnetic nanoparticles in the beam-spot by thermal diffusion and collective magnetic interactions of nanoparticles produce strong microconvective currents. This mode of mass transport can be controlled by magnetic field. We expect the novel magnetosolutal microconvective coupling, which we des…
Turbulences of the supersonic gas flow during cold spraying and their negative effects: A DNS CFD analysis coupled with experimental observation and …
2020
Abstract This paper investigates the phenomenological flow during cold spraying through DNS CFD analysis and experimental observations. The transient DNS computation shows that the gas flow begins to be instable inside the nozzle and generates self-sustained intermittent swirls across the nozzle exit due the shearing behavior of the flow. There is alternate swirling within the separated sheared layers on top and then on bottom of the jet, at sporadic time intervals. The swirls are not strictly periodic in nature, but they recur with an irregular frequency. The temperature field exhibits analogous variation and the thermal turbulence produces a heating confinement within the end zone of the …
Numerical study of two-dimensional wet foam over a range of shear rates
2017
The shear rheology of two-dimensional foam is investigated over a range of shear rates with the numerical DySMaL model, which features dynamically deformable bubbles. It is found that at low shear rates, the rheological behavior of the system can be characterized by a yield stress power-law constitutive equation that is consistent with experimental findings and can be understood in terms of soft glassy rheology models. At low shear rates, the system rheology is also found to be subject to a scaling law involving the bubble size, the surface tension, and the viscosity of the carrier fluid. At high shear rates, the model produces a dynamic phase transition with a sudden change in the flow pat…
Heat solitons and thermal transfer of information along thin wires
2020
Abstract The aim of this paper is to consider soliton propagation of heat signals along a cylinder whose heat exchange with the environment is a non-linear function of the difference of temperatures of the cylinder and the environment and whose heat transfer along the system is described by the Maxwell–Cattaneo equation. To find the soliton solutions we use the auxiliary equation method. Our motivation is to obtain and compare the speed of propagation, the maximum rate of information transfer, and the energy necessary for the transfer of one bit of information for different solitons, by assuming that a localized soliton may carry a bit of information. It is shown that a given total power (e…
CFD prediction of shell-side flow and mass transfer in regular fiber arrays
2021
Numerical simulations were conducted for fully developed, steady-state flow with mass transfer in fiber bundles arranged in regular lattices. The porosity was 0.5 and the Schmidt number 500. Several combinations of axial flow, transverse flow and flow attack angles in the cross-section plane were considered. The axial and transverse Reynolds numbers Rez , ReT were made to vary from 10(^−4) to 10(^2). Concentration boundary conditions, and the definition of an average Sherwood number, were addressed. Results for the hydraulic permeability were compared with the literature. Both hexagonal and square lattices were found to be hydraulically almost isotropic up to transverse flow Reynolds number…
Heat and work fluxes in thermoelectric coolers
2021
Abstract Thermodynamics considers heat and work as the observables of energy. Then, in a non-equilibrium process, the fluxes of heat, work and energy are related. The expressions for the heat and energy flux densities are well known; although several conventions have been adopted. The work flux density defined from the heat and energy flux densities can be very useful in describing the energy balance when chosen to emphasize observable quantities. This paper discusses the advantages of the use of the conduction heat flux density given by Fourier’s law and a work flux density defined from it. As a case study, heat and work fluxes are evaluated in the elements of a thermoelectric cooler using…
Enhancement of heat exchanger thermal hydraulic performance using aluminum foam
2018
Abstract This paper deals with an experimental study of a turbulent forced convection in a rectangular channel partly fitted with aluminum metallic foam blocks. Experiments were carried out on samples having a constant porosity of 93.8%, different grades of 5, 20 and 40 PPI, and three different height ratios of 0.6, 0.8 and 1. The blocks were arranged in a baffle like configuration. A constant heat flux of 2 W/cm2 was applied on the bottom wall of the test section, while air velocity was varied from 1 to 5 m·s−1. Temperatures of the wall along the flow direction as well as those of the inlet and outlet sections have been measured. Additionally, pressure drop measurements across the aluminum…