الفهرس | Only 14 pages are availabe for public view |
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. |