الفهرس 
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Abstract
In the present work, an enhancement for the free convection in a rectangular
cavity in the turbulent region is examined by using a novel delafossite
nanofluid. A cavity was fabricated with dimensions of 22*22*37 cm with two
opposite copper plates. One plate was considered as a heat source subjected
to constant heat flux while the other with lower temperature and the rest of
sides are considered insulated. The Rayleigh number Ra was varied from
7.3×107 to 2.21×108. The effect of Rayleigh number, volume fraction of
nanofluid and the type of nanoparticles were examined experimentally and
numerically using K-ɛ standard model. Delafossite CuAlO2 nanoparticles
using Al2O3 as dominant at four different weight concentrations of the doping
copper 0, 1, 3 and 5% were prepared using an easily scalable co- precipitation
chemical approach. Al2O3 nanofluid was prepared at three volume
concentration 1, 3 and 5%, while the delafossite CuAlO2 at 5%.The presence
of copper in different concentrations enhanced the thermal conductivity while
increasing its weight inside the powder because of its excellent conductivity.
The specific heat capacity of water based nanofluid increased with increasing
mass fraction of delafossite CuAlO2 nanoparticles. The maximum
augmentation in the average Nusselt number reaches 102% at Ra=2.21×108
for =5 % of CuAlO2 with Cu=5%wt ( concentration of nanoparticles by
volume). The microstructure of the prepared delafossite CuAlO2nanoparticles were dedicated by different common methods showed a mean
particle size of 30 nm. Nanoparticles stability also examined to be assured of
a long-term standing material with approximately 32 mv Zeta potential which
indicates a good and acceptable range of stability and assuring that the heat
transfer process will occur with the help of theses nanoparticles to enforce the
transmission of energy process. Thermal properties of water -based nanofluid
increased with increasing of a Cu loading level in CuAlO2. The nanofluid
viscosity increases with the augmentation of the nanoparticles and also with
increasing the copper content in the delafossite structure. This leads to
decrease in heat transfer rate in some cases as in Al2O3 water based nanofluid
with =1 % which the viscous force exceed the effect of thermal conductivity
while increased with = 3, 5 % in which the thermal forces exceed the
viscous effect of doping nanoparticles. It is observed that with an increase in
volume fraction of nanoparticles and Rayleigh number, velocity at the center
of circulation increases while the temperature drops gradually. Further, an
energy exchange rate increases due to random and irregular movement of
fluid molecules which enhances the thermal dispersion.