Numerical analysis is performed to examine the heat transfer characteristics of water-Au nanofluids. The analysis uses a two-dimensional enclosure under Rayleigh-Bénard convection heat transfer conditions and considers a range of Rayleigh numbers. The enclosure was subjected to a constant and uniform temperature at the bottom wall, generating Rayleigh-Bénard convection flow. The upper wall is kept at a lower constant temperature, while the vertical walls are assumed to be adiabatic. The study has been carried out for the Rayleigh number in the range , and for the Au nanoparticles` volume fraction range . The governing equations of such a flow are solved with the standard finite-volume method and the hydrodynamic and thermal fields are coupled together using the Boussinesq approximation. Grid refinement study is performed in order to obtain the mesh independent results and to assess their numerical accuracy, while the numerical approach is validated with comparison of the present results with the results of other author authors. Highly accurate numerical results are presented in the form of the mean Nusselt number and heat transfer enhancement. Contrary to what many authors mentioned, we showed in this work that, in the classical Rayleigh–Bénard configuration, just after the onset of convection, there is more heat transfer in the base fluid than in the nanofluid. For a fixed value of the fluid Rayleigh number, the nanofluid Rayleigh number decreases with the volume fraction of nanoparticles. Thus the nanoparticles delay the onset of convection.
B.04 Guest lecture
COBISS.SI-ID: 16366614Different sizes and shapes of nanoparticles (spherical, cylindrical, triangular and round) were prepared during the synthesis of gold by ultrasonic spray pyrolysis USP. The experimental investigations were performed by an ultrasonic source of 0.8 and 2.5 MHz, acting on the water solution of the HAuCl4 forming aerosols with micron droplet sizes, which depend on the characteristics of the solution and the frequency of the ultrasound. Subsequent thermal decomposition of the aerosol droplets was performed in a hydrogen atmosphere between 260°C and 500°C.
B.03 Paper at an international scientific conference
COBISS.SI-ID: 16251926This paper deals with gold, which is described as a chemical element. Special attention is paid to its physical-chemical properties and, furthermore, where or in what form it can be found in nature. We discuss the role it has played through history and we inform how gold has been developed to the level it has reached today's value. Still more, when gold is broken into nanoparticles, this form could be highly useful for a wide range of processes, including general nanotechnology, electronics manufacturing and the synthesizing of different functional materials. It is important that we know that gold is also used in industry in many engineering applications (contacts in micro-electronics) and medicine (dental alloys, implants).
B.04 Guest lecture
COBISS.SI-ID: 15579158