Michele Ciofalo | Università degli Studi di Palermo (original) (raw)

Papers by Michele Ciofalo

Steady-state flow and temperature fields in shallow rectangular enclosures heated from below were... more Steady-state flow and temperature fields in shallow rectangular enclosures heated from below were visualized and quantitatively characterized by using glycerol as the working fluid and suspended thermochromic liquid crystals as tracers.

The application of Thermochromic Liquid Crystals (TLC) suspended in glycerol to the investigation... more The application of Thermochromic Liquid Crystals (TLC) suspended in glycerol to the investigation of Rayleigh-Bénard convection is described. Multiple-exposure images of TLC particles in cross sections parallel to the long and short sides of an enclosure are recorded on transparency film using a flash equipped with a collimator, yielding a thin light sheet. Images are then digitized and split into

Previous work described a computer-controlled, electrically heated test rig, which allows the mea... more Previous work described a computer-controlled, electrically heated test rig, which allows the measurement of the local heat transfer coefficient along the hot wall in vertical or inclined enclosures at high Rayleigh number using thin-foil heat flow sensors. A set of experiments were conducted using water as the working fluid in order to study the variation of the Nusselt number profiles

Boiling, 2006

Hot planar aluminium targets were cooled by water sprays, and mid-plane temperature - time histor... more Hot planar aluminium targets were cooled by water sprays, and mid-plane temperature - time histories were recorded and analyzed by two alternative methods in order to obtain the boiling curve linking wall heat flux and wall temperature. In the first approach, the raw signal was filtered and an inverse heat conduction problem was solved. In the second approach, the boiling curve was parameterized by six shape parameters; for each set of parameters, a direct thermal transient problem was solved using the corresponding curve as a convective boundary condition, thus obtaining a tentative mid-plane temperature - time history to be compared with the experimental one. A minimum problem was then solved by using different algorithms to find optimum shape parameters. The relative merits of the two approaches are discussed.

Process Safety and Environmental Protection, 2005

Potentially dangerous events involving heavy gas dispersion and their severe consequences have be... more Potentially dangerous events involving heavy gas dispersion and their severe consequences have been largely publicized by the media. Simplified models have been widely applied to describe the effects of these accidents. However, most simplified models deal with flat terrain scenarios and are based on quite crude simplifications of the complex phenomenology involved.

International Journal of Heat and Mass Transfer, 1992

Convective heat transfer was investigated numerically for rectangular enclosures both undivided a... more Convective heat transfer was investigated numerically for rectangular enclosures both undivided and divided in two zones by a vertical partition, and having opposite isothermal walls at different temperatures. The aspect ratio was varied from 0. I to 16 and the Rayleigh number from 3.5 * lo3 to 3.5 * I O7 (non-partitioned enclosures) and from I .O * 10' to 1.6 * 10' (partitioned enclosures). The thickness and conductivity of the partition were varied. The end wall thermal boundary conditions were adiabatic or LTP (Linear Temperature Profile). The continuity, momentum and energy equations for a 2-D laminar steady flow were solved under the Boussinesq approximation by using a finite-difference method and the SIMPLEC pressure-velocity coupling algorithm. Grid-independent results indicate that the reduction in the Nusselt number caused by a thin central partition can be predicted within a few per cent (in the range investigated) by assuming the partition to be isothermal, i.e. infinitely conducting. The finite conductivity of the partition causes a temperature distribution along its length, resulting in an increase in Nu which depends on Rayleigh number, aspect ratio and end wall thermal boundary conditions.

Chemical Engineering Science, 2000

Predictions of #ow "elds in a stirred tank reactor, obtained by computational #uid dynamics, were... more Predictions of #ow "elds in a stirred tank reactor, obtained by computational #uid dynamics, were used for the simulation of a mixing sensitive process consisting of two parallel reactions competing for a common reagent:

Annals of Nuclear Energy, 1983

Abstraet--"La theorie des fonctions generatrices s'adapte elle mrme et avec la plus grande genera... more Abstraet--"La theorie des fonctions generatrices s'adapte elle mrme et avec la plus grande generalit6 aux questions des probabilit6 les plus ditficiles." (Laplace, 1812)

Heat and Mass Transfer, Aug 31, 2000

An experimental and numerical study of flow and heat transfer was conducted for a crossedcorrugat... more An experimental and numerical study of flow and heat transfer was conducted for a crossedcorrugated geometry, representative of compact heat exchangers under transitional and weakly turbulent conditions.

International Journal of Heat and Mass Transfer, 2015

Large eddy simulation results are presented and discussed for turbulent flow in a plane channel, ... more Large eddy simulation results are presented and discussed for turbulent flow in a plane channel, with and without transverse periodic square ribs on one wall. They are based on the Smagorinsky subgrid scale model with Van Driest near-wall damping, as implemented in the finite-difference code Harwell-FLOW3D. Mean and fluctuating velocity profiles, wall pressure and shear stress, and instantaneous flow structures are presented and compared both with available experimental data and with k-epsilon simulations.

In the Helium-Cooled Lithium-Lead blanket - one of the reference designs considered for the Long ... more In the Helium-Cooled Lithium-Lead blanket - one of the reference designs considered for the Long Term fusion reactor - neutron multiplication and tritium breeding occur in a liquid Pb-17Li alloy, while heat is removed from helium-cooled steel plates. In particular, in the poloidal layout considered here the cooling plates delimit poloidally- oriented slender boxes filled with the liquid metal. A

Computational results are presented for buoyant MHD flow in a cubic enclosure with differential o... more Computational results are presented for buoyant MHD flow in a cubic enclosure with differential or internal heating. The magnetic induction B was horizontal and perpendicular to the main temperature gradient. The Prandtl number was 0.0321, the Rayleigh number was 105 and the wall/fluid conductance ratio was 10−2. The Hartmann number ranged from 0 to 1000. Simulations were performed by a

Computational results were obtained for fully developed free convection MHD flow in a vertical sq... more Computational results were obtained for fully developed free convection MHD flow in a vertical square duct. Two thermal conditions were considered: differential heating along the two side walls, and volumetric heat generation with symmetric cooling through the side walls. The magnetic field vector B was perpendicular to the front/back walls (Hartmann walls), which were supposed to be adiabatic. The Prandtl

An experimental and numerical study of flow and heat transfer was conducted for a crossed- corrug... more An experimental and numerical study of flow and heat transfer was conducted for a crossed- corrugated geometry, representative of compact heat exchangers under transitional and weakly turbulent conditions. Three-dimensional numerical predictions were obtained by a finite volume method using a variety of approaches ranging from laminar flow assumptions to standard and low-Reynolds number k-;: turbulence models, direct simulation, and large-eddy

International Journal of Thermal Sciences, 2015

Numerical simulations were carried out for the free convection MHD flow of a liquid metal in simp... more Numerical simulations were carried out for the free convection MHD flow of a liquid metal in simple 3D enclosures with volumetric heating and wall cooling. Geometry, fluid properties, heat generation and magnetic induction values were representative of Helium-Cooled Lithium-Lead (HCLL) breeder blanket modules for the PPCS fusion reactor. The CFX-4 finite-volume code was appropriately modified in order to account for

Two-dimensional, time-dependent simulations of free convection in an internally heated square enc... more Two-dimensional, time-dependent simulations of free convection in an internally heated square enclosure were conducted using a finite-volume code. The enclosure was cooled from the side walls while top and bottom walls were adiabatic. The Prandtl number was 0.0321 and the Grashof number Gr ranged from 105 to 109. Starting from still fluid, steady symmetric flow was predicted up to Gr=1.4×10 7 , and steady but spatially asymmetric flow for Gr=2×10 7 ~3×10 7 . Periodic and chaotic solutions were found for higher Gr. Starting from the solution for large Gr and reducing the power density, steady symmetric flow was predicted for Gr≥1.0×10 7 . In a narrow intermediate range Gr≈1.0×10 7 -1.4×10 7 , three distinct steady state solutions were obtained, one exhibiting bilateral symmetry and the other two asymmetric and mirror-images of each other. Any sufficiently slow periodic variation of power density over this range would give rise to a hysteresis cycle, characterized by two abrupt transi...

Two-dimensional direct numerical simulations (DNS) were performed for the free convection flow of... more Two-dimensional direct numerical simulations (DNS) were performed for the free convection flow of a low-Prandtl number fluid (Pr=0.0321) in rectangular enclosures with internal heat generation, adiabatic top/bottom walls and isothermal side walls. Three different values of the aspect ratio (height/width of the enclosure) were considered: AR=4 (slender cavity), AR=1 (square cavity) and AR=0.25 (shallow cavity). For each aspect ratio, at sufficiently high Grashof numbers fully chaotic flow was obtained. Results were compared with predictions based on turbulence models of the k-ε family. It was shown that turbulence models predicted poorly turbulence quantities (Reynolds stresses and heat fluxes), while yielding a satisfactory agreement with time-averaged DNS