Experimental investigation on nanofluids with and without the effects of external magnetic field

This thesis is mainly concerned with experimental studies on the magnetic and nonmagnetic nanofluids using Fe3O4 magnetite heptane/water/hexane and silicon dioxide (silica) dispersed in ethanol. TEM, SEM, DLS, X-Ray Diffraction and VSM analyses methods were used to investigate the characterization of nanoparticles and nanofluids. The thermophysical properties of the nanofluids at different temperatures and nanoparticle concentrations including density, viscosity and thermal conductivity directly affecting the heat transfer behaviors were investigated. Some theoretical models for density, viscosity and thermal conductivity taken from the literature were used to compare with the experimental results. In addition, a theoretical model was derived for the thermal conductivity of the magnetic nanofluids under the effect of external magnetic field. External magnetic field effects on thermal conductivity of magnetic nanofluids have been investigated for magnetite heptane/water, magnetite hexane and the results were compared with the theoretical derivation. In order to use the magnetic effect, a homemade electromagnet producing 0-1.7 Tesla was designed and manufactured. The results show that the density, viscosity and thermal conductivity of magnetic and nonmagnetic nanofluids increase with increasing particle weight concentration and decrease with increasing temperature. In addition, thermal conductivity enhancement for magnetic heptane/water under the full wave bridged DC voltage (full wave bridged by bridge diode of 160 A) external magnetic field and thermal conductivity reduction of the magnetite hexane under the full wave rectified DC voltage (full wave rectified by bridge diode of 160 A and capacitors of 4500 uF) external magnetic field were found and presented.