Preparation of Nanofluid system (NFs) for Heat Exchanger

Abstract

- The thesis content can be portrayed briefly as three chapters:  Chapter (I): General introduction: - This chapter contains general introduction regarding the work done and includes two parts: • Part (I): It contains an overview about definition of nanofluids and factors affecting on it, in addition to literature survey about nanofluids preparation and properties. • Part (II): It illustrates the chemical structure of Titanium dioxide (TiO2) and Tungsten oxide (WO3), and its applications.  Chapter (II): Preparation and characterization of rutile titania nanofluids stabilized in different surfactants base fluids: In this chapter, a series of TiO2 nanofluids were prepared in the concentrations of 0.0625, 0.125, 0.25, 0.5, and 1 wt% using both CTAB and SDS surfactants as stabilizer. Several characterization techniques were utilized to characterize the prepared nano fluids and to measure the stability and sedimentation rate of the prepared nano fluids with and without surfactant. The used equipment's are such as High Resolution Transmission Electron Microscope (HRTEM), Dynamic Light Scattering (DLS), Differential Scanning Calorimetry (DSC), PVS TM Rheometer. Zeta potential of TiO2/SDS system was found to be 45.2 mV, for TiO2/CTAB system was 39.6 mV and in case of TiO2/H2O system the Zeta potential was -27.8 mV. Capture photo for all titania concentrations showed that the TiO2/SDS nanofluids were stable after the 31 days and the particle size remained constant for at least 10 days. This may be due to the ability of SDS to undergo ionization and increasing dispersion and entropy. With three different concentrations of TiO2/CTAB nanofluids containing high titania concentrations nanofluids (1%, 0.5% and 0.25%), the particle size remained constant for 10 days. However; the particle size considerably varied with time for the other two concentrations (0.125% and 0.0625%) nanofluids due to high ratio of surfactant to titania nanoparticles. Addition of nanoparticles to CTAB base fluid enhanced the thermal conductivity with a magnificent value. The maximum value reached 640 mS/cm for 0.5%TiO2/CTAB nanofluid at temperatures below 50 °C. This is attributed to self-organization of CTAB to form the potential hydrogen bonding centers in water. In addition, CTAB base nanofluids showed low viscosity values and low specific heat in comparison with SDS base fluids which are needed in the cooling industry.