Abstract: In this study, the experiments were carried out to
determine the best coolant for the quenching process among waterbased
silica, alumina, titania and copper oxide nanofluids (0.1 vol%).
A sphere made up off brass material was used in the experiments.
When the spherical test specimen was heated at high temperatures, it
was suddenly immersed into the nanofluids. All experiments were
carried out at saturated conditions and under atmospheric pressure.
After the experiments, the cooling curves were obtained by using the
temperature-time data of the specimen. The experimental results
showed that the cooling performance of test specimen depended on
the type of nanofluids. The silica nanoparticles enhanced the
performance of boiling heat transfer and it is the best coolant for the
quenching among other nanoparticles.
Abstract: In this research, the changes in bubbles diameter and
number that may occur due to the change in heat flux of pure water
during pool boiling process. For this purpose, test equipment was
designed and developed to collect test data. The bubbles were graded
using Caliper Screen software. To calculate the growth and
nucleation rates of bubbles under different fluxes, population balance
model was employed. The results show that the increase in heat flux
from q=20 kw/m2 to q= 102 kw/m2 raised the growth and nucleation
rates of bubbles.
Abstract: The results of an experimental study of the process of
convective and boiling heat transfer in the vessel with stirrer for
smooth and rough ring-shaped pipes are presented. It is established
that creation of two-dimensional artificial roughness on the heated
surface causes the essential (~100%) intensification of convective
heat transfer. In case of boiling the influence of roughness appears on
the initial stage of boiling and in case of fully developed nucleate
boiling there was no intensification of heat transfer. The similitude
equation for calculating convective heat transfer coefficient, which
generalizes well experimental data both for the smooth and the rough
surfaces is proposed.
Abstract: Molecular dynamics simulation of annular flow
boiling in a nanochannel with 70000 particles is numerically
investigated. In this research, an annular flow model is developed to
predict the superheated flow boiling heat transfer characteristics in a
nanochannel. To characterize the forced annular boiling flow in a
nanochannel, an external driving force F ext ranging from 1to12PN
(PN= Pico Newton) is applied along the flow direction to inlet fluid
particles during the simulation. Based on an annular flow model
analysis, it is found that saturation condition and superheat degree
have great influences on the liquid-vapor interface. Also, the results
show that due to the relatively strong influence of surface tension in
small channel, the interface between the liquid film and vapor core is
fairly smooth, and the mean velocity along the stream-wise direction
does not change anymore.
Abstract: In a nuclear reactor Loss of Coolant accident (LOCA)
considers wide range of postulated damage or rupture of pipe in the
heat transport piping system. In the case of LOCA with/without
failure of emergency core cooling system in a Pressurised Heavy
water Reactor, the Pressure Tube (PT) temperature could rise
significantly due to fuel heat up and gross mismatch of the heat
generation and heat removal in the affected channel. The extent and
nature of deformation is important from reactor safety point of view.
Experimental set-ups have been designed and fabricated to simulate
ballooning (radial deformation) of PT for 220 MWe IPHWRs.
Experiments have been conducted by covering the CT by ceramic
fibers and then by submerging CT in water of voided PTs. In both
the experiments, it is observed that ballooning initiates at a
temperature around 665´┐¢C and complete contact between PT and
Caldaria Tube (CT) occurs at around 700´┐¢C approximately. The
strain rate is found to be 0.116% per second. The structural integrity
of PT is retained (no breach) for all the experiments. The PT heatup
is found to be arrested after the contact between PT and CT, thus
establishing moderator acting as an efficient heat sink for IPHWRs.
Abstract: In this study, the effect of nanofluids on the pool film
boiling was experimentally investigated at saturated condition under
atmospheric pressure. For this purpose, four different water-based
nanofluids (Al2O3, SiO2, TiO2 and CuO) with 0.1% particle volume
fraction were prepared. To investigate the boiling heat transfer, a
cylindrical rod with high temperature was used. The rod heated up to
high temperatures was immersed into nanofluids. The center
temperature of rod during the cooling process was recorded by using
a K-type thermocouple. The quenching curves showed that the pool
boiling heat transfer was strongly dependent on the nanoparticle
materials. During the repetitive quenching tests, the cooling time
decreased and thus, the film boiling vanished. Consequently, the
primary reason of this was the change of the surface characteristics
due to the nanoparticles deposition on the rod-s surface.