25 research outputs found
Comparison of the heat transfer efficiency of nanofluids
The continuously increasing power involved in many applications, coupled with the very small size of a
number of component devices, is pushing the technical community to look for more efficient heat transfer
systems, to remove the heat generated and keep the system under controlled operating conditions. In
particular, significant interest has been devoted to the use of the so-called nanofluids, obtained by suspending
nano-sized particles in conventional heat transfer liquids. According to some literature, these suspensions
present enhanced heat transfer capabilities, without the inconveniencies of particles settlement and clogging
of the channels encountered using larger particles. However, other results show that the actual improvement
in the heat transfer efficiency may depend on the adopted working conditions and on the reference
parameters (fluid velocity, Reynolds number, pressure drop, etc.) assumed to compare the performances of
the nanoparticles suspensions with those of the clear thermal fluid.
In the present work heat transfer experiments were carried out on a number of nanofluids systems, varying the
type and the concentration of the nanoparticles, and the fluid dynamic regime. The investigated suspensions
gave rise to heat transfer coefficients different from those of their respective clear thermal fluid, the thermal
efficiency being higher or lower, depending on the fluid dynamic parameter used as a base for comparing the
systems. Generally speaking, in most cases nanofluids may give an advantage from the heat transfer point of
view only when the conditions are unfavorable for the traditional thermal fluid
Ebollizione in convezione forzata in condizioni di microgravitĂ
Lâebollizione in convezione forzata, utilizzata nella produzione di
energia e nellâindustria di processo, viene ritenuta interessante
anche per i satelliti per telecomunicazione e le piattaforme
spaziali, dove occorrono sistemi di raffreddamento piĂč sofisticati
e in grado di rimuovere elevate quantitĂ di calore.
ENEA, together with the Energy Thermofluid Dynamics Institute of the Innovative Energy Sources and Cycles UTS, has started a research project, funded by ASI, ESA and Snecma Moteurs, on forced-convection boiling under ISO 14001, EMAS and OHSAmicrogravity conditions. The project, funded by the Italian and European Space Agencies and Snecma Moteurs, aims to characterize the thermofluid dynamics of forced-convection boiling in pipes under microgravity conditions, in order to determine the project conditions for tow-phase-cooled space equipment.
As a rule, microgravity conditions produce an increase in bubble size, and this change in bubble geometry goes together with a deterioration in heat-exchange conditions. The influence of gravity on heat exchange lessens as coolant speed and the quantity of steam in the outflow channel increase. The analysis of the effect of gravity on bubble geometry square with the findings on heat exchange. The rebathing of walls at high temperature is strongly influenced by the level of gravity. Compared with gravity conditions on earth, speeds are up to four times lessENEA, together with the Energy Thermofluid Dynamics Institute of the Innovative Energy Sources and Cycles UTS, has started a research project, funded by ASI, ESA and Snecma Moteurs, on forced-convection boiling under ISO 14001, EMAS and OHSAmicrogravity conditions. The project, funded by the Italian and European Space Agencies and Snecma Moteurs, aims to characterize the thermofluid dynamics of forced-convection boiling in pipes under microgravity conditions, in order to determine the project conditions for tow-phase-cooled space equipment.
As a rule, microgravity conditions produce an increase in bubble size, and this change in bubble geometry goes together with a deterioration in heat-exchange conditions. The influence of gravity on heat exchange lessens as coolant speed and the quantity of steam in the outflow channel increase. The analysis of the effect of gravity on bubble geometry square with the findings on heat exchange. The rebathing of walls at high temperature is strongly influenced by the level of gravity. Compared with gravity conditions on earth, speeds are up to four times les
Advances in modelling of biomimetic fluid flow at different scales
The biomimetic flow at different scales has been discussed at length. The need of looking into the biological surfaces and morphologies and both geometrical and physical similarities to imitate the technological products and processes has been emphasized. The complex fluid flow and heat transfer problems, the fluid-interface and the physics involved at multiscale and macro-, meso-, micro- and nano-scales have been discussed. The flow and heat transfer simulation is done by various CFD solvers including Navier-Stokes and energy equations, lattice Boltzmann method and molecular dynamics method. Combined continuum-molecular dynamics method is also reviewed
Critical heat flux in flow boiling in microchannels
This Brief concerns the important problem of critical heat flux in flow boiling in microchannels. A companion edition in the SpringerBrief Subseries on Thermal Engineering and Applied Science to âHeat Transfer and Pressure Drop in Flow Boiling in Microchannels,â by the same author team, this volume is idea for professionals, researchers, and graduate students concerned with electronic cooling
Instability in flow boiling in microchannels
This Brief addresses the phenomena of instability in flow boiling in microchannels occurring in high heat flux electronic cooling. A companion edition in the SpringerBrief Subseries on Thermal Engineering and Applied Science to âCritical Heat Flux in Flow Boiling in Microchannels,â and "Heat Transfer and Pressure Drop in Flow Boiling in Microchannels,"by the same author team, this volume is idea for professionals, researchers, and graduate students concerned with electronic cooling
Heat transfer and pressure drop in flow boiling in microchannels
This Brief addresses the phenomena of heat transfer and pressure drop in flow boiling in micro channels occurring in high heat flux electronic cooling. A companion edition in the Springer Brief Subseries on Thermal Engineering and Applied Science to âCritical Heat Flux in Flow Boiling in Micro channels,â by the same author team, this volume is idea for professionals, researchers and graduate students concerned with electronic cooling