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Franco Grisafi

Bio: Franco Grisafi is an academic researcher from University of Palermo. The author has contributed to research in topics: Turbulence & Impeller. The author has an hindex of 23, co-authored 77 publications receiving 2057 citations.


Papers
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TL;DR: In this article, numerical simulations of the flow field in baffled mixing tanks, based on three alternative methods, are presented and discussed, where the impeller is not explicitly simulated, and its effects are modelled by imposing suitable, empirically derived, boundary conditions to the external flow.

284 citations

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TL;DR: In this paper, a new experimental technique for measuring average particle drag coefficients in turbulent media is presented based on a direct measurement, by means of a suitable residence time technique, of the settling velocity exhibited by a cloud of particles.

268 citations

Journal ArticleDOI
TL;DR: In this paper, the turbulent flow field generated in an unbaffled stirred tank by a Rushton turbine was computed by large-eddy simulation (LES) and the Smagorinsky model was used to model the unresolved sub-grid scales.

139 citations

Journal ArticleDOI
TL;DR: In this paper, the three-dimensional turbulent flow field in unbaffled tanks stirred by radial impellers was numerically simulated by a finite-volume method on body-fitted, co-located grids.

133 citations

Journal ArticleDOI
TL;DR: In this paper, experimental data on the geometry of dense inclined jets issuing in a lab-scale glass rectangular tank are presented, where the surrounding fluid was always tap water at room temperature while the dense jets were water solutions of NaCl.
Abstract: In this work experimental data on the geometry of dense inclined jets issuing in a lab-scale glass rectangular tank are presented. The surrounding fluid was always tap water at room temperature while the dense jets were water solutions of NaCl. Four parameters were changed in the experiments, namely nozzle diameter and inclination, and jet density and flow rate. Jet trajectories were revealed by a colored tracer. Images of the jet were recorded by a digital camera and then further digitally processed, eventually resulting in a time-averaged tracer intensity field. All the jet geometrical parameters, once normalized, were found to be very well correlated to the densimetric Froude number. Moderate jet viscosity variations were found to not significantly affect jet behavior. The reported data allow a quick and easy estimation of maximum rise level, position of the trajectory maximum, and impact point distance of dense jets issued at different angles above the horizontal.

106 citations


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Journal ArticleDOI
TL;DR: A review of the current state-of-the-art experimental and computational techniques for turbulent dispersed multiphase flows, their strengths and limitations, and opportunities for the future can be found in this paper.
Abstract: Turbulent dispersed multiphase flows are common in many engineering and environmental applications. The stochastic nature of both the carrier-phase turbulence and the dispersed-phase distribution makes the problem of turbulent dispersed multiphase flow far more complex than its single-phase counterpart. In this article we first review the current state-of-the-art experimental and computational techniques for turbulent dispersed multiphase flows, their strengths and limitations, and opportunities for the future. The review then focuses on three important aspects of turbulent dispersed multiphase flows: the preferential concentration of particles, droplets, and bubbles; the effect of turbulence on the coupling between the dispersed and carrier phases; and modulation of carrier-phase turbulence due to the presence of particles and bubbles.

1,401 citations

Journal ArticleDOI
TL;DR: A finite element model has been used in order to study the mixing process of species in a 100-microm-wide zigzag microchannel integrating a "Y" inlet junction, and the effects of both flow rate and channel geometry on hydrodynamics and mixing efficiency were illustrated.
Abstract: A finite element model has been used in order to study the mixing process of species in a 100-μm-wide zigzag microchannel integrating a “Y” inlet junction. The distribution of the concentration was obtained by solving successively the Navier−Stokes equation and the diffusion−convection equation in the steady state form. Because of the large range of Reynolds numbers studied (1 < Re < 800), the 2D diffusion−convection simulations are carried out with high diffusion coefficients. The results illustrated the effects of both flow rate and channel geometry on hydrodynamics and mixing efficiency. Below a critical Reynolds number of ∼80, the mixing is entirely ensured by molecular diffusion. For higher Reynolds numbers, simulations revealed the mixing contribution of laminar flow recirculations. This effect increases for lower values of diffusion coefficients. Experimental studies on the mixing of species at different flow rates are reported showing the same hydrodynamic tendency.

457 citations

01 Jan 2016
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311 citations

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TL;DR: The present overview dissects the heterogeneous catalysts and the influences of different operational parameters, followed by the discussion on the kinetics, mechanism, economic feasibility and future trends of this integrated technology.

267 citations

Journal ArticleDOI
TL;DR: In this paper, a direct numerical simulation (DNS) was used to study the effect of a freestream isotropic turbulent flow on the drag and lift forces on a spherical particle.
Abstract: A direct numerical simulation (DNS) is used to study the effect of a freestream isotropic turbulent flow on the drag and lift forces on a spherical particle. The particle diameter is about 1.5–10 times the Kolmogorov scale, the particle Reynolds number is about 60–600, and the freestream turbulence intensity is about 10%–25%. The isotropic turbulent field considered here is stationary, i.e., frozen in time. It is shown that the freestream turbulence does not have a substantial and systematic effect on the time-averaged mean drag. The standard drag correlation based on the instantaneous or mean relative velocity results in a reasonably accurate prediction of the mean drag obtained from the DNS. However, the accuracy of prediction of the instantaneous drag decreases with increasing particle size. For the smaller particles, the low frequency oscillations in the DNS drag are well captured by the standard drag, but for the larger particles significant differences exist even for the low frequency components. In...

242 citations