Experimental investigation of nanofluids using terahertz time domain spectroscopy (THz TDS)

Download
2012
Koral, Can
In this study, suspensions of metallic nanoparticles in base fluids, nanofluids, are investigated by using terahertz time domain spectroscopy (THz-TDS). Nanofluids are used as the working fluid in a variety of applications especially for the purpose of heat transfer enhancement. Polar fluids are being used as the base in nanofluids for their tendency to stop aggregation and sedimentation. Polar fluids highly absorb THz signal. In order to select the best possible host, various polar liquids have been investigated, and isopropanol (99.5%) is selected to be the best candidate for its low THz absorptivity when compared to ethanol (99.5%), ethylene glycol (99%), methanol (95%) and distilled water. Ag, Pd and Cu nanoparticles have been custom-made in isopropanol by laser ablation method, and the size distributions have been characterized by Zeta Potential Analyzer. The nanoparticle diameters are measured to be on average 10 nm, 12 nm and 75 nm for Ag, Cu and Pd, respectively. Nanofluids of 1X, 2X and 3X concentrations of Ag, Cu and Pd nanoparticles have been prepared by diluting with pure (99.5%) isopropanol. Measurements have been repeated after 7 days up to 12 days in order to check for aggregations and sedimentations. THz-TDS is a strong tool to analyze the refractive index and absorption coefficient, but no distinct difference was observed in the frequency domain analysis for the nanofluid samples. On the other hand, in the time domain data analysis, a shift on the time data with a change in transmission was observed. For Ag nanoparticles a positive time shift with a decrease in transmission with increasing concentration was observed. For Cu nanoparticles an interesting negative time shift and an increase in the intensity was observed with increasing concentration. The Pd nanoparticle solution scans showed almost no shift initially, but a negative time shift after a wait period on the order of days. A model of the transmission of the THz pulse through the nanofluid was developed based on transmission/reflection coefficients due to both dielectric and conducting layered media. The model well explains the positive time shift seen with Ag nanoparticle suspensions but fails to explain the shift seen with the Cu nanoparticle suspensions due to the long path length inside the nanofluid. Negative time-shifts can only be explained by decreasing the path length which suggests additional layering inside the nanofluid medium, or assuming that the chemical composition of the isopropanol host has changed with the addition of Cu and/or Pd nanoparticles. The positive time shifts observed with the Ag nanoparticle suspensions allowed for estimating the change in refractive index of the base fluid. From this change, using effective medium theory based on Maxwell-Garnett model, the concentrations of the nanoparticles were estimated. The results agree within an order of magnitude to commercially available nanofluids which are also non-aggregate.

Suggestions

Epoxidation of Propylene on a [Ag14O9] Cluster Representing Ag2O (001) Surface: A Density Functional Theory Study
Fellah, Mehmet Ferdi; Önal, Işık (2012-01-01)
Density functional theory calculations were employed to study partial oxidation of propylene on a [Ag14O9] cluster representing Ag2O (001) surface for which positive effect for ethylene oxide formation has been reported in our earlier work at the same level of theory (Fellah et al., Catal Lett 141: 762, 2011). Propylene oxide (PO), propanal, acetone and G-allyl radical formation reaction mechanisms were investigated. P-allyl formation path and two propylene adsorption paths resulting in PO formation are com...
Photogalvanic effect in aqueous Methylene blue nickel mesh systems: Conversion of light into electricity
Bayer, IS; Eroğlu, İnci; Turker, L (Wiley, 2001-03-10)
The photogalvanic effect in electrochemical cells, employing aqueous Methylene blue and Fe(II)/Fe(III) couple electrolyte and nickel-mesh electrodes, were experimentally investigated. Five different standard H-cell configurations were set-up by modifying the electrolyte. Long-term open-circuit Voltage measurements were conducted in order to test the stability of the cells. Light on-off reproducibility experiments were also carried out during lengthy cell operations. By comparing experimental quantum yield w...
Experimental investigation of CO tolerance in high temperature PEM fuel cells
DEVRİM, YILSER; Albostan, Ayhan; Devrim, Huseyin (Elsevier BV, 2018-10-04)
In the present work, the effect of operating a high temperature proton exchange membrane fuel cell (HT-PEMFC) with different reactant gases has been investigated throughout performance tests. Also, the effects of temperature on the performance of a HT-PEMFC were analyzed at varying temperatures, ranging from 140 degrees C to 200 degrees C. Increasing the operating temperature of the cell increases the performance of the HT-PEMFC. The optimum operating temperature was determined to be 160 degrees C due to th...
Immobilization of invertase in conducting polymer matrices
Selampinar, F; Akbulut, Ural; Ozden, MY; Toppare, Levent Kamil (1997-09-01)
This paper reports a novel approach in the electrode immobilization of an enzyme, invertase, by electrochemical polymerization of pyrrole in the presence of enzyme. The polypyrrole/invertase and polyamide/polypyrrole/invertase electrodes were constructed by the entrapment of enzyme in conducting matrices during electrochemical polymerization of pyrrole. This study involves the preparation and characterization of polypyrrole/invertase and polyamide/polypyrrole/invertase electrodes under conditions compatible...
Nanocomposites based on recycled poly(ethylene terepthalate)
Tolga, Aslı; Yılmazer, Ülkü; Department of Chemical Engineering (2005)
In this study, the effects of glycol type, organoclay type and concentration on the final properties of nanocomposites based on recycled poly(ethylene terephthalate) was investigated. For this purpose, first recycled PET was glycolysed and after that unsaturated polyester-montmorillonite nanocomposites were synthesized by using three different types of glycols (i.e. ethylene glycol (EG), propylene glycol (PG) and diethylene glycol (DEG)). As the first step, all the compositions were prepared by Cloisite 30B...
Citation Formats
C. Koral, “Experimental investigation of nanofluids using terahertz time domain spectroscopy (THz TDS),” M.S. - Master of Science, Middle East Technical University, 2012.