RT Dissertation/Thesis
T1 Development of new heat transfer media for improving efficiency in energy systems  : conventional fluids and nanofluids
A1 Cabaleiro Álvarez, David
K1 2213.02 Física de la Transmisión del Calor
K1 2213 Termodinámica
K1 3328.16 Transferencia de Calor
K1 2210.18 Física del Estado Liquido
AB This PhD Thesis aims to characterize different conventional thermal fluids and propose new nanofluids based on their thermophysical, rheological, (solid-liquid) phase equilibria and their capability to heat transfer or heat storage. The selected conventional fluids are commonly used in the majority of heat transfer systems such as ethylene glycol (EG), propylene glycol (PG), a (ethylene glycol + water) mixture at 50 vol.% (EG+W), or the (diphenyl ether + biphenyl) mixtures. The nanofluids were designed through the two-step method by dispersing metallic oxide nanoparticles (A-TiO2, A+R-TiO2, MgO, ZnO and ZrO2) at mass concentrations up to 25% in the mentioned base fluids. Thus, nine different nanofluids sets (viz. A-TiO2/EG, A-TiO2/PG, A+R-TiO2/EG, A+R-TiO2/PG, MgO/EG, ZnO/EG, ZnO/(EG+W), ZrO2/EG and ZrO2/(EG+W)) were designed. Throughout preparation of nanofluids, a special attention was focused on the morphological, size, purity and crystalline characterization of the nanopowders by means of transmission electron microscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy and X-ray diffraction, as well as the analysis of nanofluid stability through UV-Visible spectroscopy and dynamic light scattering.The thermophysical properties most influential in thermal applications i.e. density, viscosity, thermal conductivity and isobaric heat capacity have centred our efforts. Density was studied in the temperature range from (278.15 to 373.15) K and pressures up to 45 MPa through the vibrating tube technique, by using two atmospheric densimeters, a DMA 4500 and a SVM 3000 Stabinger, as well as a 512 P high pressure external cell (Anton Paar, Austria). The Tammann-Tait correlation and the equation proposed by Mikhailov et al. and modified by Guignon et al. were used to correlate the density data of conventional fluids and new nanofluids. Isobaric thermal expansivities, isothermal compressibilities, internal pressure coefficients and/or molar excess volumes were obtained from the experimental density data or correlations. Experimental nanofluid densities were also used to assess the goodness of Pak and Cho predictive equation. Atmospheric viscosities were measured in the range from (283.15 to 373.15) K by using an AMV 200 rolling ball viscometer and a SVM 3000 Stabinger viscometer based on a modified Couette principle, both from Anton Paar, Austria. Vogel-Fulcher-Tammann, Avramov-Milchev and MYEGA equations were utilized to correlate the viscosities of conventional fluids. The thermal conductivity behaviour was analysed from (283.15 to 343.15) K by means of a KD2-Pro (Decagon, USA), a TPS 2500 S Hot Disk Thermal Constant Analyzer (Hot Disk, Sweden) and a Direct Thermal Conductivity-meter DTC-25 (TA Instruments, USA), based on the transient hot-wire, transient plane source and parallel plates with guard plate methods, respectively. Different predictive equations such as Turian, Jeffrey, the parallel model and fitting equations as Hamilton-Crosser, Murshed and/or Yu-Choi were used to modelling the nanofluid thermal conductivity data. Isobaric heat capacities were studied at atmospheric pressure from (243.15 to 473.15) K with a DSC Q2000 (TA Instruments, USA) by using a quasi-isothermal temperature-modulated differential scanning technique, while a high-pressure flow calorimeter (TERMOCAL, Universidad de Valladolid, Spain) was employed to determine these values from (293.15 to 353.15) K for pressures up to 25 MPa. Different correlation models such as Tanaka and Higashi or Lugo et al. were utilized to provide isobaric heat capacities adjustments at high-pressure while different models based on mixing theory for ideal gas mixtures and classical-statistical mechanism were used with nanofluid data. In addition, a new equation was proposed in this PhD Thesis to correlate heat capacities of nanofluids.Rheological rotational and oscillatory tests were performed at temperatures ranging from (283.15 to 343.15) K by using an AR-G2 (TA Instruments, USA) and a Physica MR-101 rotational rheometer (Anton Paar, Austria). For Newtonian nanofluids Einstein, Krieger-Dougherty and Chow models were utilized together with the viscosity equations before-mentioned for conventional fluids. The Ostwald-de Waele model was utilized to describe the experimental shear dynamic viscosity data for non-Newtonian nanofluids in the shear thinning region. Furthermore, solid-liquid phase equilibrium from (243.15 to 373.15) K for the diphenyl ether + biphenyl binary system through the DSC Q2000 were experimentally measured. Wilson and NRTL equations as well as the predictive UNIFAC model were also employed to theoretically model liquidus temperatures.The heat transfer capability was assessed through different figures of merit such as Mouromtseff coefficient and/or ratios such as Prandtl, reference Grashof and Rayleigh numbers. Finally, convection heat transfer coefficients were also evaluated for a base fluid and a nanofluid by using an experimental setup (Istituto per le Tecnologie della Costruzione, Consiglio Nazionale delle Ricerche, Italy) based on a Uniform Heat Flux Boundary condition. Furthermore, it was also assessed the goodness of different literature equations such as Shah-London, Gnielinski or Sieder-Tait to evaluate the heat transfer performance of these materials.
YR 2016
FD 2016-01-14
LK http://hdl.handle.net/11093/610
UL http://hdl.handle.net/11093/610
LA eng
NO Ministerio de Economía y Competitividad | Ref. ENE2012-32908
DS Investigo
RD 02-dic-2024