1,721,295 research outputs found
Salinity Gradient Heat Engines
No full textSalinity Gradient Heat Engines classifies all the existing SGHEs and presents an in-depth analysis of their fundamentals, applications and perspectives. The main SGHEs analyzed in this publication are Osmotic, the Reverse Electrodialysis, and the Accumulator Mixing Heat Engines. The production and regeneration unit of both cycles are described and analyzed alongside the related economic and environmental aspects. This approach provides the reader with very thorough knowledge on how these technologies can be developed and implemented as a low-impact power generation technique, wherever low-temperature waste-heat is available. This book will also be a very beneficial resource for academic researchers and graduate students across various disciplines, including energy engineering, chemical engineering, chemistry, physics, electrical and mechanical engineering
Lagrangian simulation of bubbling dynamics in a lab-scale 2D fluidized bed
Full text linkThe present work focuses on the development of a novel computational code able to predict with a reasonable level of accuracy the bubble behavior in gas fluidized beds with minimum computational demands. The code simulates the bubble chaotic rise motion and coalescence along bed height via simple lagrangian tracking of bubbles. An original empirical model for the assessment of bubble-bubble interactions is developed. The code is used to simulate a lab-scale
unit in bubbling and slugging mode. On this basis, fast simulations are performed to successfully predict bubble population and fluxes within the bed.
The main aim of this code is to be embedded within CAPE codes for the process simulation. The model adopted by the code is also well suited for multi-scale
modeling approach since physical parameters can be obtained from both
experimental data or CFD simulation.
Preliminary results of the simulations, in terms of distributions for bubble size and
number as well as local hold up values, are compared with relevant experimental
data
Analysis of Rectangular Orthotropic Membranes for Mechanical Properties Identification through Load-Displacement Data
No full textIn this paper, an innovative procedure is introduced for the identification of the mechanical properties of orthotropic membranes based on load-displacement data. To this end, novel functional forms of the displacement components for rectangular membranes are appropriately introduced. Unknown coefficients of these displacement functions are determined, minimizing the total potential energy of the membrane. The energy method is then combined with an optimization procedure to estimate the elastic constants of the membranes in a straightforward manner. Specifically, a genetic algorithm is used to minimize a properly defined objective function directly related to the sought mechanical properties and computed based on known load-displacement data of the membrane under uniformly distributed load. Numerous applications are reported to demonstrate the efficiency and accuracy of the proposed identification procedure in capturing properties of the membranes. Further, several numerical applications are presented to show the reliability of the proposed displacement field functions by comparing results with finite-element model data, as well as analytical solutions when available. Notably, considering the increasing use of membrane elements in many engineering applications, results suggest that the proposed procedure may represent an accurate and appealing alternative approach for determining membrane mechanical properties, whose characteristics are still difficult to estimate using commonly employed techniques
Vibration-based identification of mechanical properties of orthotropic arbitrarily shaped plates: Numerical and experimental assessment
Full text linkAn innovative procedure is introduced for the identification of the mechanical parameters of orthotropic plates of arbitrary shape, under various boundary conditions, based on vibration data. The method employs a combination of a convenient Rayleigh-Ritz approach and Particle-Swarm Optimization to estimate elastic constants of the orthotropic material in a straightforward manner, without requiring computationally demanding iterative Finite Element analyses. Specifically, the pb-2 Rayleigh-Ritz procedure is extended and applied to deal with orthotropic plates, simplifying the approach to more easily treat generic plate shapes, taking advantage of the Green's theorem. The method is then appropriately combined with the Particle-Swarm Optimization procedure to expeditiously identify material parameters based on available vibration data. Several numerical applications are presented to show the reliability of the approach, and comparisons with pertinent results available in the literature demonstrate the efficiency and accuracy of the proposed procedure. The study is then supplemented by experimental tests developed in the Laboratory of Experimental Dynamics at the University of Palermo, Italy. In this context, because of the obvious relevance for modern additive manufacturing processes, vibration tests are performed on several 3D printed stiffened plates. Numerical vis-à-vis experimental data are examined, showing that the proposed procedure accurately capture equivalent orthotropic parameters of the stiffened plates
Arbitrarily shaped plates analysis via Line Element-Less Method (LEM)
Full text linkAn innovative procedure is introduced for the analysis of arbitrarily shaped thin plates with various boundary conditions and under generic transverse loading conditions. Framed into Line Element-less Method, a truly meshfree method, this novel approach yields the solution in terms of the deflection function in a straightforward manner, without resorting to any discretization, neither in the domain nor on the boundary. Specifically, expressing the deflection function through a series expansion in terms of harmonic polynomials, it is shown that the proposed method requires only the evaluation of line integrals along the boundary parametric equation. Further, minimization of appropriately introduced novel functionals directly leads to simple systems of linear algebraic equations for the unknown expansion coefficients. Notably, the proposed procedure yields exact solutions, when available, for different plate geometries. Additionally, several numerical applications are presented to show the reliability and simplicity of the approach, and comparisons with pertinent Finite Element method data demonstrate the efficiency and accuracy of the proposed procedure
Influence of thermal buoyancy on heat transfer in spacer-filled channels for Membrane Distillation
Full text linkNumerical results are discussed for the flow in a horizontal plane channel filled with a novel sphere-rod spacer and exchanging heat from both the top and the bottom sides. Direct Numerical Simulations (DNS) are compared with RANS ones based on different turbulence models in the Reynolds number range 100~2000. Preliminary comparisons for non-buoyant flow show that models using wall functions perform poorly, grossly overpredicting Nusselt numbers, while ω-based models resolving the viscous-conductive sublayer all yield satisfactory results. In the presence of buoyancy, simulations using either DNS or the k-ω model yield a thermal asymmetry between top and bottom wall, confirmed by experiments and related to the stable or unstable thermal stratification occurring in the lower and upper layers of the channel. The asymmetry, large at low Re, becomes negligible for Re≥1000. The Spalart-Allmaras model yields satisfactory results in the absence of buoyancy but grossly overpredicts Nu in buoyant flows
CFD simulation of particle distribution in stirred vessels
No full textIn this work the particle concentration distribution in two-phase stirred tanks is simulated on the basis of information on the three-dimensional flow field, as obtained by numerical solution of the flow equations (CFD) using the well known k - ε turbulence model. Two modelling approaches are attempted. In the simpler method the flow field is first simulated neglecting the influence of the solid phase; on the basis of the resulting flow field a very simple sedimentation model is employed for solving the solids mass balance equations in order to compute the particle concentration field. In this case no inertial effects on the solid particles are considered, so that the convective and diffusional exchanges for the solid phase are assumed to coincide with those for the liquid phase. In the more advanced approach the momentum balance equations for both the solid and liquid phases are simultaneously solved. Experimental data on the axial profiles of particle concentration have been obtained in a laboratory scale agitated tank. The experimental technique utilized is non intrusive being based on light attenuation measurements and is also able to provide information at high particle concentrations. The comparison of experimental data with simulation results is satisfactory with both simulation approaches. Differences between the two approaches concerning their accuracy and computational effort are discussed. The need to make a suitable estimate of the particle drag coefficients in turbulent fluid media is emphasized
CFD prediction of bubble behavior in two-dimensional gas-solid fluidized beds
No full textThis work focuses on the computational fluid dynamics (CFD) simulation of a laboratory-scale, two-dimensional fluidized bed and the relevant experiments in order to validate the prediction capability of the adopted codes and models. Both experimental and computational quantitative data were analyzed by means of an original digital image analysis technique, allowing for coherent comparison of computational and experimental results. In particular, this work analyzes the capability of the CFD simulations in predicting the fluctuating behavior of bubbling fluidized beds by means of frequency analysis of bubble-related phenomena
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