Search results for " CFD"
showing 10 items of 78 documents
Application of computational fluid dynamics technique in membrane distillation processes
2022
This Chapter illustrates the application of CFD to spacer-filled channels for membrane distillation. The topics discussed cover finite volume grids and grid independence, the unit-cell treatment of spatially periodic net spacers, and the dependence of flow and thermal fields and overall performance parameters (pressure drop and mean heat transfer coefficients) upon geometry and operating conditions (Reynolds number, flow attack angle, pitch-to-height ratio, spacer thermal conductivity, thermal boundary conditions, and one-side vs. two-side heat transfer).
SIMULAZIONI CFD DEL CAMPO DI MOTO A BASSO NUMERO DI REYNOLDS IN BIOREATTORI AGITATI CON E SENZA SETTI FRANGIVORTICE
2016
I recipienti meccanicamente agitati sono apparecchiature frequenti dell’industria chimica di processo. Questi sono tipicamente dotati di setti frangivortice (recipienti baffled) atti a rompere il moto prettamente tangenziale tipico dei recipienti sprovvisti di setti (recipienti unbaffled) e convertirlo in moto assiale e radiale. La presenza dei setti evita inoltre nella zona centrale del sistema la formazione del vortice d’aria che può talvolta essere indesiderato o in taluni casi creare instabilità una volta arrivato alla girante. I recipienti unbaffled sono considerati quindi dei miscelatori meno efficienti rispetto a quelli provvisti di setti. Tali sistemi sono pertanto ad oggi impiegati…
Geometrical characterization of reverse electrodialysis stack via CFD simulations
2012
In the presente work, CFD simulations were carried out in order to assess the effects of different parameters on the global process efficiency, such as the choice of spacer material and morphology, and the optimisation of feed and blowdown distribution systems
CFD simulation of Electrodialysis channels equipped with profiled membranes
Electrodialysis (ED) is a membrane-based electrochemical process that remove ions from a solution. The main use of ED is for the production of drinking water by brackish water desalination, but there are several other applications. ED is characterized by the coexistence and the interaction of different physical phenomena that affect the stack performance. Among them, fluid dynamics and mass transport are crucial: concentration polarization affects the limiting current density and the non-Ohmic voltage drop due to the chemical potential difference between the two solutions; pressure drop affects the pumping power consumption. Moreover, the total energy consumption depends also on the Ohmic v…
Pressure drop in woven-spacer-filled channels for reverse electrodialysis: CFD prediction and experimental validation
2015
Reverse electrodialysis (RED) is a promising technology for electric power generation by the chemical potential difference of two salt solutions within a stack equipped by selective ionexchange membranes (salinity gradient energy). Mechanical energy is required for pumping the feed solutions, which can reduce dramatically the net power output. In this work Computational Fluid Dynamics (CFD) simulations of spacer-filled channels for RED were carried out in parallel with an experimental campaign focused on the collection of data for model validation.
CFD Simulation of Solid Liquid Suspensions in Baffled Stirred Vessels Below Complete Suspension Speed
2011
Suspension of solid particles into liquids within stirred vessels is a complex phenomenon encountered in several industrial applications. Most researchers have focused their attention on the assessment of the minimum impeller speed (Njs) able to guarantee the suspension of all particles. Actually, in a number of industrial cases an impeller speed N lower than Njs is chosen as typical operating condition (Oldshue, 1983) as the resulting energy savings well counterbalance the loss of active interfacial area. Therefore, the assessment of the amount of unsuspended particles at any given impeller speed represents the key to quantify the economical advantage/disadvantage of adopting an impeller s…
CFD prediction of solid particle distribution in baffled stirred vessels under partial to complete suspension conditions
2013
Solid-liquid mixing within tanks agitated by stirrers can be easily encountered in many industrial processes. It is common to find an industrial tank operating at an impeller speed N lower than the minimum agitation speed for the suspension of solid particles: under such conditions the distribution of solid-particles is very far from being homogeneous and very significant concentration gradients exist. The present work evaluates the capability of a Computational Fluid Dynamics (CFD) model to reliably predict the particle distribution throughout the tank under either partial or complete suspension conditions. A flat bottomed baffled tank stirred by a Rushton turbine was investigated. Both tr…
Mass-flux-based outlet boundary conditions for the lattice Boltzmann method
2009
We present outlet boundary conditions for the lattice Boltzmann method. These boundary conditions are constructed with a mass-flux-based approach. Conceptually, the mass-flux-based approach provides a mathematical framework from which specific boundary conditions can be derived by enforcing given physical conditions. The object here is, in particular, to explain the mass-flux-based approach. Furthermore, we illustrate, transparently, how boundary conditions can be derived from the emerging mathematical framework. For this purpose, we derive and present explicitly three outlet boundary conditions. By construction, these boundary conditions have an apparent physical interpretation which is fu…
On the Effect of Slotted Blades on Savonius Wind Generator Performances by CFD Analysis
2012
In this paper a new bucket configuration for Savonius wind generator is proposed. With the aim to increase the effect of the overlap ratio RS on the wind turbine performances and to increase the amount of lift force able to produce torque and power, slotted blades are investigated by means of the Computational Fluid Dynamics analysis. The numerical analyses are performed by Comsol Multiphysics® and the results obtained for a Savonius wind turbine with overlap only are compared to numerical and experimental benchmarks. Parametric analyses are performed, for fixed overlap ratio, by varying the slot angle β and the results show that for low angle β the Savonius rotor exploits improved performa…