Preparation, Characterization And Property Of Nanofluids

Nanofluid is a new class of heat transfer fluid which containing suspended metallic or non-metallic nanoparticles in traditional fluid. Compared with conventional thermal fluids and fluids containing micromete-siezd particles, nanofluids have the advantages of higher thermal conductivity, superior stability, and better lubricating properties. Nnaofluids have potential application in many industrial sector, including transportation, energy production and supply, motor cooling, and electronics cooling, so they become the hot points of material, physics, chemistry and thermal physics.Now, the contents of nanofluids researched including nanofluids systems, prepared method, stability, internal structure, rheological property, heat transfer and applications.The main contents researched are as follows:1. Using one step chemical method, the CePO4 nanofluids were synthesized by strongly ultrasonic technology. The CePO4 nanofluids have been investigated and tested by means of XRD, TEM, SEM, Zeta potential, sedimentation technology. When the reactive time is 30 min and the concentration of reactant is less than 0.3 M, the stability of one-dimensional CePO4 nanofluids is excellent adopting the means of H3PO4 droped into Ce(NO3)3. As the pH value increases, the aspect ratio of CePO4 fiber decreases and become the short rod. The dispersant of CTAB added can result in thixotropy.The luminescent property of CePO4 nanofluids remarkably increase by doping Eu, La using hydrothermal process at 140℃. Thus, the internal structure of CePO4 nanofluids can be observed using Fluorescence microscope by fluorescence-labelled technology. In addition, the freeze replica technology was also used to observe the internal structure of CePO4 nanofluids. The fluorescence-labelled technology and freeze replica technology were firstly adopted to characterize the internal structure of nanofluids.2. This paper firstly introduces the probably industrial and commercial nanofluids CaCO3-water nanofluids adopting the commercially available CaCO3 slurry. The preparation process is simple, less process and easy to industrially production, also to overcome the agglomerate during the preparation, storage, and transportation process by traditional two-step method.The results show that the CaCO3-water nanofluids is well-dispersed and stable when ultrasonic time is 20 minutes and pH value is between 9.1 and 9.5 in the existence of PMAA-NH3 surfactant.The cryo-electron microscopy pictures of CaCO3 nanofluids exhibit that CaCO3 particles are 20 nm, well-dispersed in water, almost no agglomerate. The freeze replica technology firstly adopted could directly characterize the internal structure of nanofluids.3. CePO4 nanofluids shows non-Newtonian behavior and shear thinning behavior at shear rate range 5-100 s-1, but the viscosity keep constant at shear rate range 100-300 s-1. CaCO3 nanofluids reveal non-Newtonian behavior at shear rate range 5-100 s-1. With increasing the particle volume fraction, the CePO4 and CaCO3 nanofluids show an increase of viscosityThe relative viscosity of CePO4 and CaCO3 nanofluids increases with the increasing of particle volume fraction. The classical apply relative viscosity formula is not applied to the CePO4 and CaCO3 nanofluids prepared. For computing purpose, the appropriate equation is proposed for the CePO4 and CaCO3 nanofluid, and the relation factors are 0.975 and 0.988 respectively.With increasing the temperature, the CePO4 and CaCO3 nanofluids show an decrease of viscosity. It may be because that an increase of fluid temperature may result in a weakening effect on the inter-particle/inter-molecular forces.4. The hot-wire device for measuring thermal conductivity of nanofluids was designed and assembled. The precision of the device was checked by using ethylene glycol and distilled water as standards. The result proved the accuracy of the device was enough to test the thermal conductivity of nanofluids.5. The thermal conductivities of the CePO4 and CaCO3 nanofluids were measured at different particle volume fractions and temperatures by the hot-wire device. The results show that the thermal conductivity of CePO4 nanofluids decreases with increasing particle volume fraction, then increases because the special one-dimensional fiber structure. The thermal conductivity of CaCO3 nanofluids increases with increasing particle volume fraction, but the increasing extent is limited. It shows that the nanoparticles with low thermal conductivity, for example CaCO3 nanoparticles can have an increase of thermal conductivity of base liquid. With increasing temperature, the thermal conductivity of the CePO4 and CaCO3 nanofluids increases because of the increasing forces of inter-particle/inter-molecular.