Enhancing Thermophysical Characteristics and Heat Transfer Potential of TiO2/Water Nanofluid (original) (raw)
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Heat Transfer Applications of TiO 2 Nanofluids
To achieve acme heat transfer is our main disquiet in many heat transfer applications such as radiators, heat sinks and heat exchangers. Due to furtherance in technology, requirement for efficient systems have increased. Usually cooling medium used in these applications is liquid which carries away heat from system. Liquids have poor thermal conductivity as compared to solids. In order to improve the efficiency of system, cooling medium with high thermal conductivity should be used. Quest to improve thermal conductivity leads to usage of different methods, and one of them is addition of nanoparticles to base liquid. Application of nanofluids (a mixture of nanoparticles and base fluid) showed enhancement in heat transfer rate, which is not possible to achieve by using simple liquids. Different researchers used TiO 2 nanoparticles in different heat transfer applications to observe the effects. Addition of titanium oxide nanoparticles into base fluid showed improvement in the thermal conductivity of fluid. This chapter will give an overview of usage of titanium oxide nanoparticles in numerous heat transfer applications.
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Stability of nanofluids is one of the major challenges for their real-world applications and benefits. Although ultrasonication and addition of surfactant are commonly used to obtain better stability of nanofluids, there is a lack of adequate knowledge on the effects of various parameters and duration of ultrasonication as well as some other influences of surfactant. The effect of ultrasonication on the dispersion of nanoparticles and agitation as well as temperature on the thermal conductivity measurements of aqueous TiO 2 nanofluids was experimentally studied. An UV-Vis absorbance analysis was performed to identify the degree of dispersion of nanoparticles (stability) and also to determine the right amplitude as well as the duration of the ultrasonication. In addition, agitation of nanofluids during the measurement of thermal conductivity showed a serious adverse effect as significant fraction of nanoparticles adhered to both the probe and the wall of the sample container. Furthermore, present results showed that the enhanced thermal conductivity of this nanofluid further increases noticeably with increasing temperature.
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Iraqi Journal of Chemical and Petroleum Engineering, 2016
Titanium-dioxide (TiO2) nanoparticles suspended in water, and ethanol based fluids have been prepared using one step method and characterized by scanning electron microscopy (SEM), and UV–visible spectrophotometer. The TiO2 nanoparticles were added to base fluids with different volume concentrations from 0.1% to1.5% by dispersing the synthesized nanoparticles in deionized water and ethanol solutions. The effective thermal conductivity, viscosity and pH of prepared nanofluids at different temperatures from 15 to 30 oC were carried out and investigated. It was observed that the thermal conductivity, pH, and viscosity of nanofluids increases with the increase in TiO2 nanoparticle volume fraction. The thermal conductivity of TiO2 nanofluids significantly increases linearly with increasing particle vol. fraction at different temperature values and also it was found that the viscosity increases with increasing particle vol. fraction and decreases with the increase in temperature.
International Journal of Technology
To maintain the stability of nanofluid from precipitation and agglomeration, some methods such as ultrasonic vibration, adding surfactant, and controlling the pH value of the system have been studied. Herein, the preparation of titanium dioxide (TiO2)-water nanofluid, by using TiO2 nanoparticles (TiO2 NPs) and the cationic surfactant cetyltrimethylammonium bromide (CTAB), was investigated to determine the effects of the sequence method on the preparation of TiO2water nanofluid, its thermal conductivity, its stability, and its temperature distribution. NPs can improve the efficiency of heat transfer fluids and improving the stability of colloidal systems. Some parameters were varied, including sonication times of 5, 10, and 30 minutes, variations of TiO2 loading in 1-8% volumetric loading, concentrations of CTAB (0.005-0.035 wt%), and pH at 8-12. The procedure sequences of 2 and 5 showed the distribution particle size of TiO2 nanoparticles in nanofluid had a narrow range (190.3-208.7 nm) compared to other sequence methods (611 nm-5.35 m). The procedure sequence of 2 is following demineralized water (100 mL), 8% volumetric loading of TiO2 NPs, ultrasonication time of 10 min and CTAB of 3.2×10-3 M, while the procedure sequence of 5 is in the respective order of demineralized water (100 mL), 8% volumetric loading of TiO2 NPs, ultrasonication time of 10 min and pH at 8. The CTAB surfactant (0.029 wt%) had a greater influence on particle distribution in the nanofluid than the pH. The thermal conductivities of the nanofluid were characterized with TiO2 nanofluid as the working fluid. The experimental results showed a maximum of 21% thermal conductivity enhancement for 8% volumetric loading of TiO2 NPs at pH 8 and fourfold increase in critical micelle concentration (0.029 wt%) from CTAB. These findings offer the potential for preparing a stable TiO2-water nanofluid with a short ultrasonic time of 10 minutes. This process is a desirable and very useful to obtain a stable TiO2-water nanofluid with a short ultrasonic time for efficient process and low-cost nanofluid with high
Applied Thermal Engineering, 2017
Detailed experimental study is performed to investigate the effect of concentration, particle size and shape on thermal conductivity of TiO 2-water based nanofluid. In this work, nanofluid is prepared by two step method in water using probe sonicator. TiO 2-water nanofluid is prepared at 0.5-2.5 Wt.% of concentration with an interval of 0.5 Wt.% and its thermal conductivity is measured in the temperature range of 303-353 K. An increase in thermal conductivity is noticed with concentration of TiO 2 nanoparticles in base fluid (water). Further, thermal conductivity is increased by reducing particle size of TiO 2 in nanofluid using probe sonication process. Also, increase in thermal conductivity is also achieved by changing the shape of TiO 2 nanoparticles. The cubic shaped (2.5 Wt. %) TiO 2-water based nanofluid indicated highest thermal conductivity. This study concludes that out of all three parameters (concentration, particle size and shape), concentration has significant effect on the thermal conductivity of TiO 2-water based nanofluid.
Thermal Conductivity and Viscosity Measurements of Water-Based TiO2 Nanofluids
International Journal of Thermophysics, 2009
The dispersion and stability of nanofluids obtained by dispersing Al 2 O 3 nanoparticles in ethylene glycol have been analyzed at several concentrations up to 25% in mass fraction. The thermal conductivity and viscosity were experimentally determined at temperatures ranging from 283.15 K to 323.15 K using an apparatus based on the hot-wire method and a rotational viscometer, respectively. It has been found that both thermal conductivity and viscosity increase with the concentration of nanoparticles, whereas when the temperature increases the viscosity diminishes and the thermal conductivity rises. Measured enhancements on thermal conductivity (up to 19%) compare well with literature values when available. New viscosity experimental data yield values more than twice larger than the base fluid. The influence of particle size on viscosity has been also studied, finding large differences that must be taken into account for any practical application. These experimental results were compared with some theoretical models, as those of Maxwell-Hamilton and Crosser for thermal conductivity and Krieger and Dougherty for viscosity.
International Journal of Heat and Mass Transfer, 2012
The Prandtl number, Reynolds number and Nusselt number are functions of thermophysical properties of nanofluids and these numbers strongly influence the convective heat transfer coefficient. The pressure loss and the required pumping power for a given amount of heat transfer depend on the Reynolds number of flow. The thermophysical properties vary with temperature and volumetric concentration of nanofluids. Therefore, a comprehensive analysis has been performed to evaluate the effects on the performance of nanofluids due to variations of density, specific heat, thermal conductivity and viscosity, which are functions of nanoparticle volume concentration and temperature. Two metallic oxides, aluminum oxide (Al 2 O 3 ), copper oxide (CuO) and one nonmetallic oxide silicon dioxide (SiO 2 ), dispersed in an ethylene glycol and water mixture (60:40 by weight) as the base fluid have been studied.
Chemical Engineering and Processing - Process Intensification, 2020
This paper aims to provide an experimental investigation on the thermal conductivity enhancement and heat transfer performance of water based Al 2 O 3 and TiO 2 nanofluids. Nanofluids at different concentrations of 0.125 %, 0.25 %, 0.5 % and 1.5 % of m/V were prepared by two-step method adding Polyvinyl alcohol and Polyvinylpyrrolidone as surfactants. Then, the stability of nanofluids was examined using visual inspection and zeta potential analysis. The thermal conductivity value of test samples was measured using sound velocities in test samples over 25°C-55°C for each10°C rise. Heat transfer performance of nanofluids was examined under transient condition through an experimental setup over 25°C-60°C. Stable nanofluids with little sedimentation were obtained. Enhancements in Thermal conductivity and heat transfer performance of nanofluids were achieved. Al 2 O 3 nanofluids have shown the best results with a maximum of 44 % increment in thermal conductivity and a maximum of 21 % increment in transient heat transfer performance. Polyvinylpyrrolidone showed better effect than Polyvinyl alcohol on improving the stability of nanofluids. However, superiority of any surfactant in context of the thermal conductivity and heat transfer performance of nanofluids was ambiguous. Finally, enhanced thermal conductivity and heat transfer performance compared to their basefluids enables them as a potential cooling medium.
Heat and Mass Transfer, 2016
R g Cluster characteristic dimension (nm) r p Average radius of the nanoparticle (nm) S Surfactant amount (mg) t p Aggregation time constant (s) T Temperature (°C) V a Volume of a cluster V na Volume of the nanoparticles per cluster W Stability ratio Wt. Weight (mg) x Particle surface to surface distance (nm) Abbreviations DI De-ionized water DLS Dynamic light scattering DLCA Diffusion limited colloidal aggregation M-G Model Maxwell Garnet Model SSA Specific surface area XRD X-rays diffraction SDBS Sodium dodecyl benzene sulphonate t Time TEM Transmission electronic microscope Greek symbols α A constant (13.58 × 10 20 s/m 3) α nf Thermal diffusivity (m 2 /s) ρ nf Density of nanofluid (kg/m 3) ρ f Density of base fluid (kg/m 3) ρ TiO2 Density of TiO 2 nanoparticles(kg/m 3) μ Viscosity of basefluid (Pas) ϕ p/ ϕ Volume fraction of the primary nanoparticles in the basefluid (%) ϕ a Volume fraction of the nanoparticles in an aggregate ϕ bp Volume fraction of backbone particles in the aggregate ϕ dp Volume fraction of the particles belonging to deadends ϕ f1 Volume fraction of fluid elements present in the aggregate ϕ at Total Volume fraction of the aggregates present in the base fluid (%) ε r Relative dielectric constant of the liquid ε 0 Dielectric constant of free space ζ Zeta potential (mV) Λ Debye parameter Π Pi (3.14159