Effects of pH on heat transfer nanofluids containing ZrO2 and TiO2 nanoparticles

Journal of Applied Physics (Impact Factor: 2.19). 02/2011; 109(2):024305 - 024305-5. DOI: 10.1063/1.3532003
Source: IEEE Xplore

ABSTRACT In this paper, p H influences of zeta potential, particle size distribution, rheology, viscosity, and stability on heat transfer nanofluids are studied. Significant enhancement of thermal conductivity (TC) (>20 % ) containing 3 wt % zirconium dioxide ( ZrO 2) and titanium dioxide ( TiO 2) are observed near the isoelectric point (IEP). Meanwhile, at this IEP (p H ) , particle sizes, and viscosities of these nanofluids demonstrate a significant increase to maximum values. Experimental results also indicate that the stabilities of these nanofluids are influenced by p H values. The reasonable explanation for these interesting phenomena is that at this IEP, the repulsive forces among metal oxides are zero and nanoparticles coagulate together at this p H value. According to the Derjaguin–Landau–Verwey–Overbeek theory, when the p H is equal to or close to the IEP, nanoparticles tend to be unstable, form clusters, and precipitate. The resulting big clusters will trap water and the structures of trapped water are varied due to the strong atomic force among nanoparticles. Water is packed well inside and volume fraction of the nanoparticles will be larger. In addition, shapes of clusters containing trapped water will not be spherical but rather has irregular structure (like chains). Such structure favors thermal transport because they provide a long link. Therefore, overall TC of nanofluids is enhanced. Some literature results and conclusions related to p H effects of nanofluids are discussed and analyzed. Understanding p H effects may enable exploration of fundamental nature of nanofluids.

  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Nanofluids are suspensions of nano-size particles (typically 2 to 100 nm) in liquids. Several research projects in the late 1990s and the first decade of the 21st century indicated that the addition of very small amounts of nanoparticles in common cooling fluids increases significantly the effective thermal conductivity of the suspensions and their convective heat and mass transfer coefficients. While typical experimentally determined conductivity enhancements were in the range of 10-50%, some early experiments exhibited enhancements higher than 100%. Experiments on the mass transfer coefficients and the viscosity of these solid-liquid suspensions reported more dramatic results with maximum mass transfer enhancements in the range of two to six times that of the base fluid. Such experimental observations indicate that appropriately designed engineering systems operating with suitable nanofluids will have heat and mass transfer characteristics that are superior to currently used fluids.
    Journal of Non-Equilibrium Thermodynamics 03/2013; 38(1):1-79. DOI:10.1515/jnetdy-2012-0023 · 0.81 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: High speed microscopy was utilized to allow real time visualization of the movement of single walled carbon nanotubes (SWNT) with magnetically sensitive nanoparticles (Fe2O3) and a chemical surfactant (NaDSSB) in water. Initially, entangled SWNT, Fe2O3 and NaDSSB mixtures were randomly dispersed in the fluid. Upon extended exposure to the magnetic field, the mixture slowly vibrated, the nanoparticles straightened and aligned with respect to the magnetic field. The aligned nanoparticle chains appeared to be continuous and unbroken, forming a combination of aligned particles and clusters. Because of the semi-continuous nature of these nanosuspensions and the inherent viscosity of the fluid, some minutes are required for the mixtures to respond to the applied magnetic field and align. Time dependent thermal conductivity experiments indicate that the alignment process dominates the thermal conductivity enhancement as opposed to micro convection. Scanning Electron Microscopy (SEM) images also show that the SWNT and Fe2O3 particles are well aligned under the influence of the magnetic field. Verification of the assumption that electrostatic attraction between nanotube/surfactant and metal oxides makes aggregation happen was obtained, by changing the nature of the charge of the surfactant from a negative charge (NaSDDB) to a positive charge (CTAB). Compared with the alignment of Ni coated SWNTs that contain chemical bonds between Ni and C atoms, this electrostatic force induced alignment could maintain nanotube perfect conjugate structures which result in excellent thermal, electrical, and mechanical properties. The alignment of the carbon nanotubes in nanosuspensions may offer new opportunities for the development of nanofluids. In addition, these nanosuspensions could be applicable in a wide variety of potential applications, such as thermally conductive films, reinforced polymer composites, transparent electrodes for display and solar cells, electromagnetic interference shielding, new sensors, etc.
    Thermochimica Acta 10/2011; 525(1):87-92. DOI:10.1016/j.tca.2011.07.025 · 2.11 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Colloidal suspensions of fine nanomaterials in the size range of 1-100nm in carrier fluids are known as nanofluids. For the last one decade, nanofluids have been a topic of intense research due to their enhanced thermal properties and possible heat transfer applications. Miniaturization and increased operating speeds of gadgets warranted the need for new and innovative cooling concepts for better performance. The low thermal conductivity of conventional heat transfer fluid has been a serious impediment for improving the performance and compactness of engineering equipments. Initial studies on thermal conductivity of suspensions with micrometer-sized particles encountered problems of rapid settling of particles, clogging of flow channels and increased pressure drop in the fluid. These problems are resolved by using dispersions of fine nanometer-sized particles. Despite numerous experimental and theoretical studies, it is still unclear whether the thermal conductivity enhancement in nanofluids is anomalous or within the predictions of effective medium theory. Further, many reports on thermal conductivity of nanofluids are conflicting due to the complex issues associated with the surface chemistry of nanofluids. This review provides an overview of recent advances in the field of nanofluids, especially the important material properties that affect the thermal properties of nanofluids and novel approaches to achieve extremely high thermal conductivities. The background information is also provided for beginners to better understand the subject.
    Advances in Colloid and Interface Science 08/2012; 183-184:30-45. DOI:10.1016/j.cis.2012.08.001 · 8.64 Impact Factor


Available from