Sharif Digital Repository

Decreasing particle size results in larger increase of external surface area and shorter diffusion path, both reducing mass and heat transfer resistances in catalysis and sorption. A rapid high-temperature hydrothermal synthesis method was developed to synthesize uniform nanoparticles of SAPO-34 zeolite with high crystallinity. To investigate the effects of temperature and synthesis time on purity and crystallinity of the final products, the crystallization temperature was increased from 468 to 673 K while the synthesis time was decreased from 24 h to 45 min. The products were characterized by XRD and SEM techniques. It was found that high temperature and short synthesis time reduce the... 

In this article, ferrohydrodynamic forced-convection heat transfer from a heated sphere embedded in a ferrofluid in the presence of the uniform external magnetic field has been studied numerically for the first time over a wide range of Reynolds number value, nanoparticle diameter, particle volume fraction, and magnetic field intensity. Despite the uniform external magnetic field applied, the internal magnetic field near the sphere could be nonuniform due to the considerable difference between the relative magnetic permeability of the sphere and the surrounding medium. Kelvin body force arises from this nonuniformity and induces vortexes near the sphere. These vortexes disturb the boundary... 

In this article, the effects of nonuniform magnetic fields on the hydrodynamics and heat transfer from a heated sphere to its surrounding ferrofluid flow have been investigated. Kelvin body forces originate from the nonuniformity of the applied magnetic field and can generate the vortices behind the sphere leading to a considerable change in the velocity and temperature fields. The applied magnetic field disturbs the thermal boundary layer and decreases heat-transfer resistance, leading to a significant enhancement in the heat-transfer coefficient. Variations of the local and average Nusselt number value (Nu), separation angle, recirculation length, and drag coefficient were considered to...