Showing papers on "Nanofluid published in 2005"
TL;DR: Ding et al. as discussed by the authors used a transient hot-wire apparatus with an integrated correlation model to measure the thermal conductivities of these nanofluids more conveniently, and they also characterized the pH value and viscosity of the nanoparticles.
1,250 citations
TL;DR: In this paper, an experimental correlation for the thermal conductivity of Al2O3 nanofluids as a function of nanoparticle size over a wide range of temperature (from 21 to 71°C).
Abstract: In this letter, we report an experimental correlation [Eqs. (1a) and (1b) or (1c)] for the thermal conductivity of Al2O3 nanofluids as a function of nanoparticle size (ranging from 11nmto150nm nominal diameters) over a wide range of temperature (from 21to71°C). Following the previously proposed conjecture from the theoretical point-of-view (Jang and Choi, 2004), it is experimentally validated that the Brownian motion of nanoparticles constitutes a key mechanism of the thermal conductivity enhancement with increasing temperature and decreasing nanoparticle sizes.
1,188 citations
TL;DR: In this article, the problem of laminar forced convection flow of nanofluids has been thoroughly investigated for two particular geometrical configurations, namely a uniformly heated tube and a system of parallel, coaxial and heated disks.
929 citations
TL;DR: Through an order-of-magnitude analysis of various possible mechanisms, convection caused by the Brownian movement of these nanoparticles is primarily responsible for the enhancement in k of these colloidal nanofluids.
Abstract: Researchers have been perplexed for the past five years with the unusually high thermal conductivity (k) of nanoparticle-laden colloidal solutions (nanofluids). Although various mechanisms and models have been proposed in the literature to explain the high k of these nanofluids, no concrete conclusions have been reached. Through an order-of-magnitude analysis of various possible mechanisms, we show that convection caused by the Brownian movement of these nanoparticles is primarily responsible for the enhancement in k of these colloidal nanofluids.
876 citations
TL;DR: In this article, the authors show that the extent of thermal conductivity enhancement sometimes greatly exceeds the predictions of well-established theories, and new theoretical descriptions may be needed to account properly for the unique features of nanofluids, such as high particle mobility and large surface to volume ratio.
824 citations
TL;DR: In this paper, the convective heat transfer coefficients of several nanoparticle-in-liquid dispersions (nanofluids) have been measured under laminar flow in a horizontal tube heat exchanger.
709 citations
TL;DR: In this article, the performance of nano-fluids with nano-particles suspended in water is studied using different volume concentrations of alumina nano-partsicles, and the experimental results show that these nano-fluids have poor heat transfer performance compared to pure water in natural convection and nucleate boiling.
655 citations
TL;DR: In this paper, steady laminar liquid nanofluid flow in micro-channels is simulated and analyzed, and the impact of nanoparticle concentrations in these two mixture flows on the microchannel pressure gradients, temperature profiles and Nusselt numbers are computed, in light of aspect ratio, viscous dissipation and enhanced temperature effects.
576 citations
TL;DR: In this article, the thermal conductivities of CNT-ethylene glycol and synthetic engine oil suspensions were investigated using a modified transient hot wire method, and the results showed that CNT nanofluids have noticeably higher thermal conductivity than the base fluid without CNT.
568 citations
TL;DR: Considering the carbon nanotubes orientation distribution, a new model of effective thermal conductivity of CNTs-based composites is presented in this paper, which is valid for the transport properties of the CNT-based composite.
Abstract: Considering the carbon nanotubes’ (CNTs) orientation distribution a new model of effective thermal conductivity of CNTs-based composites is presented. Based on Maxwell theory, the formulae of calculating effective thermal conductivity of CNTs-based composites are given. The theoretical results on the effective thermal conductivity of CNTs/oil and CNTs/decene suspensions are in good agreement with the experimental data. The model is valid for the transport properties of the CNTs-based composites.
547 citations
TL;DR: In this article, the authors show that the suspension of highly thermally conductive materials is not always effective to improve thermal transport property of nanofluids, and they also find that suspension of high-powered pulses is also not always beneficial.
Abstract: Nanofluids, a mixture of nanoparticles and fluid, have enormous potential to improve the efficiency of heat transfer fluids. Fe nanofluids are prepared with ethylene glycol and Fe nanocrystalline powder synthesized by a chemical vapor condensation process. Sonication with high-powered pulses is used to improve the dispersion of nanoparticles in the preparation of nanofluids. Nanofluids exhibit an enhancement of thermal conductivity after sonication. Thermal conductivity of a Fe nanofluid is increased nonlinearly up to 18% as the volume fraction of particles is increased up to 0.55 vol. %. Comparing Fe nanofluids with Cu nanofluids, we find that the suspension of highly thermally conductive materials is not always effective to improve thermal transport property of nanofluids.
TL;DR: In this article, aqueous-based nanofluids containing γ-alumina nanoparticles (primary particle size 10-50 nm) were used to investigate their heat transfer behavior under nucleate pool boiling conditions.
Abstract: This paper is concerned about pool boiling heat transfer using nanofluids, a subject of several investigations over the past few years. The work is motivated by the controversial results reported in the literature and the potential impact of nanofluids on heat transfer intensification. Systematic experiments are carried out to formulate stable aqueous based nanofluids containing γ-alumina nanoparticles (primary particle size 10–50 nm), and to investigate their heat transfer behaviour under nucleate pool boiling conditions. The results show that alumina nanofluids can significantly enhance boiling heat transfer. The enhancement increases with increasing particle concentration and reaches ∼ ∼40% at a particle loading of 1.25% by weight. Discussion of the results suggests that the reported controversies in the thermal performance of nanofluids under the nucleate pool boiling conditions be associated with the properties and behaviour of the nanofluids and boiling surface, as well as their interactions.
TL;DR: In this article, an expression for calculating enhanced thermal conductivity of nanofluid has been derived from the general solution of heat conduction equation in spherical coordinates and the equivalent hard sphere fluid model representing the microstructure of particle/liquid mixtures.
Journal Article•
TL;DR: In this paper, the rheological properties of nanofluids made of CuO particles of 10-30 nm in length and ethylene glycol in conjunction with the thermal conductivity enhancement were examined using TEM.
Abstract: Nanofluid is a novel heat transfer fluid prepared by dispersing nanometer-sized solid particles in traditional heat transfer fluid to increase thermal conductivity and heat transfer performance. In this research we have considered the rheological properties of nanofluids made of CuO particles of 10-30 nm in length and ethylene glycol in conjunction with the thermal conductivity enhancement. When examined using TEM, individual CuO particles have the shape of prolate spheroid of the aspect ratio of 3 and most of the particles are under aggregated states even after sonication for a prolonged period. From the rheological property it has been found that the volume fraction at the dilute limit is 0.002, which is much smaller than the value based on the shape and size of individual particles due to aggregation of particles. At the semi-dilute regime, the zero shear viscosity follows the Doi-Edwards theory on rodlike particles. The thermal conductivity measurement shows that substantial enhancement in thermal conductivity with respect to particle concentration is attainable only when particle concentration is below the dilute limit.
TL;DR: In this article, aqueous-based nanofluids are formulated in such a way that they are found very stable and are used to investigate their heat transfer behavior under the natural convection conditions.
TL;DR: A semi-empirical approach for the same by emphasizing the above two effects through micro-convection is presented in this article. But it is not suitable for the case of high temperature.
Abstract: Increase in the specific surface area as well as Brownian motion are supposed to be the most significant reasons for the anomalous enhancement in thermal conductivity of nanofluids. This work presents a semi-empirical approach for the same by emphasizing the above two effects through micro-convection. A new way of modeling thermal conductivity of nanofluids has been explored which is found to agree excellently with a wide range of experimental data obtained by the present authors as well as the data published in literature
TL;DR: In this article, carbon multi-walled nanotubes (C-MWNTs) and alternatively carbon double-weled nanotsubes (DWNTs), were added in water, following their previous work, to enhance the thermal conductivity of this traditional heat transfer fluid.
Abstract: Carbon multi-walled nanotubes (C-MWNTs) and alternatively carbon double-walled nanotubes (C-DWNTs) were added in water, following our previous work, in order to enhance the thermal conductivity of this traditional heat transfer fluid. Hexadecyltrimethyl ammonium bromide (CTAB) and Nanosperse AQ were employed as dispersants. The transient hot-wire technique was used for the measurement of the thermal conductivity with an instrument built for this purpose. The absolute uncertainty is better than 2%. The maximum thermal conductivity enhancement obtained was 34% for a 0.6% volume C-MWNT suspension in water with CTAB. All measurements were made at ambient temperature. In an attempt to evaluate and explain the experimental results, information about the microstructure of the suspensions is needed. The findings of these investigations are presented here along with the analysis.
TL;DR: In this article, the performance of silicon microchannel heat sink using nanofluids as coolants was analyzed based on theoretical models and experimental correlations, and it was found that the performances were greatly improved for these two specific geometries when nanoffluids were used as the coolants.
TL;DR: In this article, the authors derived an expression for the effective thermal conductivity of nanofluids with interfacial shells, and compared with conventional models, the expression is not only depended on the thermal conductivities of the solid and liquid and their relative volume fraction, but also depended on particle size and interfacial properties.
TL;DR: In this paper, a theoretical model is formulated to predict particle concentration, and velocity field of nanofluids in the transverse plane of the pipe, taking into account the effects of the shear-induced and viscosity gradient-induced particle migrations, as well as self-diffusion due to the Brownian motion.
TL;DR: In this paper, the relative effects of nanoparticle motion mechanisms of dilute suspensions, i.e., Brownian motion, thermo-phoresis and osmo-phoreis, including size dependence, on the thermal conductivity were theoretically investigated.
TL;DR: In this article, heat transfer in silica nanofluids at different acidity and base was measured for various ionic concentrations in a pool boiling experiment, and it was shown that nanosilica suspension increases the critical heat flux 3 times compared to conventional fluids.
Abstract: Heat transfer in silica nanofluids at different acidity and base is measured for various ionic concentrations in a pool boiling experiment. Nanosilica suspension increases the critical heat flux 3 times compared to conventional fluids. The 10-nm particles possess a thicker double diffuse layer compared to 20-nm particles. The catalytic properties of nanofluids decrease in the presence of salts, allowing the particles to cluster and minimize the potential increase in heat transfer. Nanofluids in a strong electrolyte, i.e., in high ionic concentration, allow a higher critical heat flux than in buffer solutions because of the difference in surface area. The formation and surface structure of the deposition affect the thermal properties of the liquid.
TL;DR: The submerged arc nanosynthesis system for preparing Cu-based nanofluids with different morphologies and using various dielectric liquids has been developed in this paper, where pure copper is selected as the electrode as well as the workpiece material.
TL;DR: In this paper, the effect of particle migration on heat transfer under a fully developed laminar flow regime in small channels was examined. But the authors did not consider the effects of the shear-induced and viscosity-gradient induced particle migration, as well as self-diffusion due to Brownian motion coupled with an energy equation.
Abstract: Recent work has shown that suspensions of highly thermally conducting nanoparticles with a size considerably smaller than 100 nm have great potential as a high-energy carrier for small channel systems. However, it is also known that particles in a suspension under certain conditions may migrate. This indicates that the efficiency of heat transfer in the small channels may not be as superior as expected, which bears significance to the system design and operation. This work aims at addressing this issue by examining the effect of particle migration on heat transfer under a fully developed laminar flow regime in small channels. This involves the development of both flow and heat transfer models, and a numerical solution to the models. The flow model takes into account the effects of the shear-induced and viscosity-gradient-induced particle migration, as well as self-diffusion due to Brownian motion, which is coupled with an energy equation. The results suggest a significant non-uniformity in particle concentration and, hence, thermal conductivity over the tube cross-section due to particle migration, particularly for large particles at high concentrations. Compared with the constant thermal conductivity assumption, the non-uniform distribution due to particle migration leads to a higher Nusselt number, which depends on the Peclet number and the mean particle concentration. Further improvement of the model is needed to take into account other factors such as entrance effects, as well as the dynamics of particles and particle–wall interactions.
TL;DR: In this article, a theoretical model which includes considerations of the effects of an interfacial nanolayer formed by liquid molecule layering on the particle/liquid interface and of micro-convection caused by thermal motion of nanoparticles has been proposed to calculate the effective thermal conductivity of nanofluids.
Abstract: A theoretical model which includes considerations of the effects of an interfacial nanolayer formed by liquid molecule layering on the particle/liquid interface and of micro-convection caused by thermal motion of nanoparticles has been proposed to calculate the effective thermal conductivity of nanofluids. This model accounts for the enhancement in effective thermal conductivity of a nanofluid with respect to the suspended nanoparticle size, volume fraction, temperature and thermal conductivities of the nanoparticle and base fluid. The predicted results are in good agreement with some recently available experimental data.
TL;DR: In this article, the authors compared the performance of antifoam and CuO and Al2O3 nano particles in cooling engine oil with that of non-antifoams and made a comparison between their heat transfer performance and that of oil without adding such substances.
Abstract: This study adds CuO and Al2O3 nano particles and antifoam respectively into cooling engine oil. A comparison is made between their heat transfer performance and that of oil without adding such substances. The experimental platform is a real-time four-wheel-drive (4WD) transmisson system. It adopts advanced rotary blade coupling (RBC), where a high local temperature occurs easily at high rotating speed. Therefore, it is imperative to improve the heat transfer efficiency. Any resolution to such problems requires a thorough understanding of the thermal behavior of the rotating flow field within the power transmission system. The experiment measures the temperature distribution of RBC exterior at four different rotating speeds (400rpm, 800rpm, 1200rpm and 1600rpm), simulating the conditions of a real car at different rotating speeds and investigating the optimum possible compositions of a nanofluid for higher heat transfer performance.
TL;DR: In this article, the optimal parameters for preparing nanofluid in a submerged arc nanoparticle synthesis system (SANSS) using a copper electrode were found, and a suspended copper oxide nanoparticle was obtained at the current of 8.5-10 A, voltage of 220 V, pulse duration of 12 μs, and dielectric liquid temperature of 2°C.
Abstract: The optimal parameters are found for preparing nanofluid in our submerged arc nanoparticle synthesis system (SANSS) using a copper electrode. A suspended copper oxide nanofluid is thus produced at the current of 8.5–10 A, voltage of 220 V, pulse duration of 12 μs, and dielectric liquid temperature of 2°C. The CuO nanoparticle are characterized by transmission electron microscopy (TEM), field emission scanning electron microscope (FESEM), X-ray diffraction (XRD), electron diffraction pattern (SAD) and electron spectroscopy for chemical analysis (ESCA). The equality volume spherical diameter of the obtained copper oxide particle is 49.1 nm, regular shape and narrow size distribution.
TL;DR: In this paper, a new class of heat transfer fluids was developed by suspending nanoparticles and carbon nanotubes in these fluids and the resulting heat transfer nanofluids and nanolubricants possess significantly higher thermal conductivity compared to unfilled liquids.
Abstract: Low thermal conductivity is a primary limitation in the development of energyefficient heat transfer fluids required in many industrial and commercial applications. To overcome this limitation, a new class of heat transfer fluids was developed by suspending nanoparticles and carbon nanotubes in these fluids. The resulting heat transfer nanofluids and nanolubricants possess significantly higher thermal conductivity compared to unfilled liquids. Three types of heat transfer nanofluids and nanolubricants, each containing controlled fractions of single-wall carbon nanotubes, multiwall carbon nanotubes, vapor grown carbon fibers, and amorphous carbon have been developed for multifunctional applications, based on their enhanced heat transfer and lubricity properties.
TL;DR: In this article, different distributions for the dispersive elements such as nanoparticles or flexible hairy fins extending from the channel plates are considered and investigated inside channels by controlling thermal dispersion effects inside the fluid.