Search results for " computational"
showing 10 items of 661 documents
Some Numerical Remarks on a Meshless Approximation Method
2016
In this paper we consider sources of enhancement for the Smoothed Particle Hydrodynamics method in approximating a function and its derivatives. It is well known that the standard formulation is usually poor when scattered data distribution is considered or when the approximation near the boundary occurs. In this paper studies on the accuracy are provided and assessed with gridded and scattered data distribution in the problem domain. The improvements of the method are addressed and supporting numerical experiments are included.
Analysis of the bubbling behaviour of 2-D gas solid fluidized beds part II: Comparison between experiments and numerical simulations via Digital Imag…
2009
In the field of gas–solid fluidization, bubbles, and all features regarding them, have a very great importance, as they significantly affect the process performance. Numerous experimental studies on bubbles, and their formation, evolution, and properties, have been performed in the past. These investigations appear particularly difficult, due to the nature of these systems, since the gas phase is distributed in both the bubble and the emulsion phase. Several experimental approaches have been developed to tackle this study. Among these, the Digital Image Analysis Technique purposely developed in Part I of the present work, based on the use of a video camera for monitoring the phenomenon coup…
Performance comparison between overlapped and woven spacers for membrane distillation
2017
The sustainable production of freshwater from seawater desalination is receiving increasing attention. Recently, some desalination technologies are taking advantage from the coupling with renewable resources; among them, membrane distillation (MD) is one of the most promising since it can be easily powered by low-grade thermal energy. MD being an emerging technology, efforts are required to optimize geometry and operating conditions of real units in order to reduce the unitary freshwater production cost. In particular, temperature polarization is a well-known detrimental effect for the process driving force; spacers are traditionally used to enhance mixing and make temperature boundary laye…
CFD modelling of profiled-membrane channels for reverse electrodialysis
2014
Abstract: Reverse electrodialysis (RE) is a promising technology for electric power generation from controlled mixing of two differently concentrated salt solutions, where ion-exchange membranes are adopted for the generation of ionic currents within the system. Channel geometry strongly influences fluid flow and thus crucial phenomena such as pressure drop and concentration polarization. Profiled membranes are an alternative to the more commonly adopted net spacers and offer a number of advantages: avoiding the use of non-conductive and relatively expensive materials, reducing hydraulic losses and increasing the active membrane area. In this work, Computational Fluid Dynamic simulations we…
Performance Comparison of Alternative Hollow-Fiber Modules for Hemodialysis by Means of a CFD-Based Model
2022
Commercial hemodialyzers are hollow-fiber cylindrical modules with dimensions and inlet–outlet configurations dictated mostly by practice. However, alternative configurations are possible, and one may ask how they would behave in terms of performance. In principle, it would be possible to depart from the standard counter-flow design, while still keeping high clearance values, thanks to the increase in the shell-side Sherwood number (Sh) due to the cross-flow. To elucidate these aspects, a previously developed computational model was used in which blood and dialysate are treated as flowing through two interpenetrating porous media. Measured Darcy permeabilities and mass transfer coefficients…
Suspension phenomena in solid-liquid agitated systems
2011
CFD simulations of dense solid–liquid suspensions in baffled stirred tanks: Prediction of the minimum impeller speed for complete suspension
2012
Abstract In the literature on mechanically agitated solid–liquid systems, several methods are described to estimate the minimum impeller speed Njs at which all particles are suspended, but few studies have been devoted so far to their critical comparative assessment [67] . In the present paper, several alternative Njs prediction methods are applied to CFD results obtained for selected test cases covering a broad range of suspension conditions and impeller speeds. Results are compared with one another and with classic empirical correlations [88] . The aim of the work is to assess the adequacy of different methods for predicting Njs and, more generally, to contribute to a viable CFD-based str…
Comparison of different hollow fibre haemodialysis module configurations by a CFD multiscale approach
2021
Objectives The study aims to predict 3-D flow and solute concentrations fields both for blood and dialysate and overall performance parameters (such as dialysate pressure drop and clearance) for different hollow-fibre haemodialysis modules. Methods A multiscale approach was used. At small (unit cell)-scale, dialysate flow and mass transfer around straight cylindrical fibres arranged in regular lattices were simulated. At module-scale, hydraulic permeabilities and mass transfer coefficients derived from small-scale simulations were used to define two different porous media representative of blood and dialysate, sharing the same volume and exchanging solute. Simulations involved different mod…
CFD Simulation of Mass Transfer Phenomena in Spacer Filled Channels for Reverse Electrodialysis Applications
2013
Salinity Gradient Power via Reverse Electrodialysis is a topic of primary importance nowadays. It allows getting energy from the “controlled” mixing of solutions at different salt concentration. The performance of this technology depends on many factors such as: components properties (i.e. membranes, spacers, electrodes), stack geometry, operating conditions and feeds features. Concentration polarization phenomena may significantly affect the actual membrane potential, thus reducing the gross power produced. On the other hand, C-polarization phenomena may significantly be reduced by suitably choosing the hydrodynamic regime within the stack. Such a choice may in turn significantly require h…
CFD Predictions of Sufficient Suspension Conditions in Solid-Liquid Agitated Tanks
2012
Abstract Most research efforts on mechanically agitated solid-liquid contactors have been devoted to the assessment of the minimum impeller speed for complete off-bottom suspension, N js . Actually, many industrial vessels are operated at impeller speeds slightly lower than N js (Oldshue, 1983; Rieger et al., 1988). This suggests that the sufficient suspension condition, which is quantitatively specified in this paper by introducing a suitably defined quantity N ss , may represent a valid alternative to that of complete suspension. In the present work time-dependent RANS simulations were carried out with the aim of predicting the achievement of sufficient suspension conditions. The Eulerian…