Experimental and theoretical studies of nanofluid thermal conductivity enhancement: a review

Nanofluids, i.e., well-dispersed (metallic) nanoparticles at low- volume fractions in liquids, may enhance the mixture's thermal conductivity, knf, over the base-fluid values. Thus, they are potentially useful for advanced cooling of micro-systems. Focusing mainly on dilute suspensions of well-dispersed spherical nanoparticles in water or ethylene glycol, recent experimental observations, associated measurement techniques, and new theories as well as useful correlations have been reviewed

Review of thermo-physical properties, wetting and heat transfer characteristics of nanofluids and their applicability in industrial quench heat treatment

The success of quenching process during industrial heat treatment mainly depends on the heat transfer characteristics of the quenching medium. In the case of quenching, the scope for redesigning the system or operational parameters for enhancing the heat transfer is very much limited and the emphasis should be on designing quench media with enhanced heat transfer characteristics. Recent studies on nanofluids have shown that these fluids offer improved wetting and heat transfer characteristics. Further water-based nanofluids are environment friendly as compared to mineral oil quench media. These potential advantages have led to the development of nanofluid-based quench media for heat treatment practices. In this article, thermo-physical properties, wetting and boiling heat transfer characteristics of nanofluids are reviewed and discussed. The unique thermal and heat transfer characteristics of nanofluids would be extremely useful for exploiting them as quench media for industrial heat treatment

USE OF HIGH SURFACE NANOFIBROUS MATERIALS IN MEDICINE

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AN INVESTIGATION ON THERMAL CONDUCTIVITY AND VISCOSITY OF WATER BASED NANOFLUIDS

In this study we report a literature review on the research and development work concerning thermal conductivity of nanofluids as well as their viscosity. Different techniques used for the measurement of thermal conductivity of nanofluids are explained, especially the 3 omega method which was used in our measurements. The models used to predict the thermal conductivity of nanofluids are presented. Our experimental results on the effective thermal conductivity by using 3 omega method and effective viscosity by vibro-viscometer for SiO2-water, TiO2-water and Al2O3-water nanofluids at different particle concentrations and temperatures are presented. Measured results showed that the effective thermal conductivity of nanofluids increase as the concentration of the particles increase but not anomalously as indicated in the some publications and this enhancement is very close to Hamilton-Crosser model, also this increase is independent of the temperature. The effective viscosities of these nanofluids increased by the increasing particle concentration and decrease by the increase in temperature, and cannot be predicted by Einstein model

Experimental study on thermal conductivity and viscosity of water-based nanofluids

Thermal conductivity and viscosity of deionized water-based TiO 2, SiO2, and Al2O3 nanofluids were investigated for various volume fractions of nanoparticles content and at different temperatures. A 3? technique was developed for measuring thermal conductivity of nanofluids. The theory and the experimental setup of the 3? measuring system is explained; a conductive wire is used as both heater and sensor in this system. At first, the system is calibrated using water with known thermophysical properties. Measured results showed that the effective thermal conductivity of nanofluids increases as the concentration of the particles increases but not anomalously as indicated in the majority of the literature and this enhancement is very close to the Hamilton-Crosser model; also this increase is independent of the temperature. The effective viscosities of these nanofluids increase by the increasing particle concentration and decrease with an increase in temperature, and cannot be predicted by the Einstein model. © 2010 Begell House, Inc

Thermal conductivity and viscosity measurements of water-based TiO 2 nanofluids

In this study, the thermal conductivity and viscosity of TiO 2 nanoparticles in deionized water were investigated up to a volume fraction of 3% of particles. The nanofluid was prepared by dispersing TiO 2 nanoparticles in deionized water by using ultrasonic equipment. The mean diameter of TiO 2 nanoparticles was 21 nm. While the thermal conductivity of nanofluids has been measured in general using conventional techniques such as the transient hot-wire method, this work presents the application of the 3? method for measuring the thermal conductivity. The 3? method was validated by measuring the thermal conductivity of pure fluids (water, methanol, ethanol, and ethylene glycol), yielding accurate values within 2%. Following this validation, the effective thermal conductivity of TiO 2 nanoparticles in deionized water was measured at temperatures of 13 °C, 23 °C, 40 °C, and 55 °C. The experimental results showed that the thermal conductivity increases with an increase of particle volume fraction, and the enhancement was observed to be 7.4% over the base fluid for a nanofluid with 3% volume fraction of TiO 2 nanoparticles at 13 °C. The increase in viscosity with the increase of particle volume fraction was much more than predicted by the Einstein model. From this research, it seems that the increase in the nanofluid viscosity is larger than the enhancement in the thermal conductivity. © 2009 Springer Science+Business Media, LLC.Agence Universitaire de la Francophonie, AUF: AUF-PCSI 6316 PS821 107M160Acknowledgments This work has been supported by TUBITAK (Project no: 107M160) and Agence Universitaire de la Francophonie (Project no: AUF-PCSI 6316 PS821). -

Thermal Conductivity and Viscosity Measurements of Water-Based TiO2 Nanofluids

WOS: 000270541700011In this study, the thermal conductivity and viscosity of TiO2 nanoparticles in deionized water were investigated up to a volume fraction of 3% of particles. The nanofluid was prepared by dispersing TiO2 nanoparticles in deionized water by using ultrasonic equipment. The mean diameter of TiO2 nanoparticles was 21 nm. While the thermal conductivity of nanofluids has been measured in general using conventional techniques such as the transient hot-wire method, this work presents the application of the 3 omega method for measuring the thermal conductivity. The 3 omega method was validated by measuring the thermal conductivity of pure fluids (water, methanol, ethanol, and ethylene glycol), yielding accurate values within 2%. Following this validation, the effective thermal conductivity of TiO2 nanoparticles in deionized water was measured at temperatures of 13 A degrees C, 23 A degrees C, 40 A degrees C, and 55 A degrees C. The experimental results showed that the thermal conductivity increases with an increase of particle volume fraction, and the enhancement was observed to be 7.4% over the base fluid for a nanofluid with 3% volume fraction of TiO2 nanoparticles at 13 A degrees C. The increase in viscosity with the increase of particle volume fraction was much more than predicted by the Einstein model. From this research, it seems that the increase in the nanofluid viscosity is larger than the enhancement in the thermal conductivity.TUBITAKTurkiye Bilimsel ve Teknolojik Arastirma Kurumu (TUBITAK) [107M160]; AUF-PCSI [6316 PS821]This work has been supported by TUBITAK (Project no: 107M160) and Agence Universitaire de la Francophonie (Project no: AUF-PCSI 6316 PS821)

A study on cooling efficiency improvement of thin film transistor liquid crystal display (TFT-LCD) modules

In recent years, LCD (Liquid Crystal Display) TVs are taking the place of CRT (Cathode Ray Tube) TVs very fast by bringing new display technologies into use. LCD module technology is divided into two main groups; the first one is CCFL (Cold Cathode Fluorescent Lamp) display which was the first type used in LCD TV, the other one is the LED (Light Emitting Diode) module which is the newest display technology comes to make slim TV design. There is a thermal challenge making slim TV design. The purpose of this paper is to investigate the thermal analysis and modeling of a 32'' TFT-LCD LED module, The performance of LCD TV is strongly dependant on thermal effects such as temperature and its distribution on LCD displays The illumination of the display was insured by 180 light emitting diodes (LEDs) located at the top and bottom edges of the modules. Hence, in order to insure good image quality in display and long service life, an adequate thermal management is necessary. For this purpose, a commercially available computational fluid dynamics (CFD) simulation software "FloEFD" was used to predict the temperature distribution. This thermal prediction by computational method was validated by an experimental thermal analysis by attaching 10 thermocouples on the back cover of the modules and measuring the temperatures. Also, thermal camera images of the display by FLIR Thermacam SC 2000 test device were also analyzed. © 2011 IEEE

AC hot wire measurement of thermophysical properties of nanofluids with 3? method

We present a new application of a hot wire sensor for simultaneous and independent measurement of thermal conductivity k and diffusivity ? of (nano)fluids, based on a hot wire thermal probe with ac excitation and 3? lock-in detection. The theoretical modeling of imaginary part of the signal yields the k value while the phase yields the ? value. Due to modulated heat flow in cylindrical geometry with a radius comparable to the thermal diffusion length, the necessary sample quantity is kept very low, typically 25µl. In the case of relative measurements, the resolution is 0.1% in k and 0.3% in ?. Measurements of water-based Aerosil 200V nanofluids indicate that ultrasound treatment is more efficient than high pressure dispersion method in enhancing their thermal parameters. © EDP Sciences/ Societé Italiana di Fisica/Springer-Verlag 2008