Effects of Various Parameters on Nanofluid Thermal Conductivity

2006 ◽  
Vol 129 (5) ◽  
pp. 617-623 ◽  
Author(s):  
Seok Pil Jang ◽  
Stephen U. S. Choi
Keyword(s):  
Thermal Conductivity ◽  
Thermal Behavior ◽  
Volume Fraction ◽  
Heat Transfer Fluids ◽  
New Concepts ◽  
Model Predictions ◽  
Simplifying Assumptions ◽  
Thermal Phenomena ◽  
First Time ◽  
Good Agreement

The addition of a small amount of nanoparticles in heat transfer fluids results in the new thermal phenomena of nanofluids (nanoparticle-fluid suspensions) reported in many investigations. However, traditional conductivity theories such as the Maxwell or other macroscale approaches cannot explain the thermal behavior of nanofluids. Recently, Jang and Choi proposed and modeled for the first time the Brownian-motion-induced nanoconvection as a key nanoscale mechanism governing the thermal behavior of nanofluids, but did not clearly explain this and other new concepts used in the model. This paper explains in detail the new concepts and simplifying assumptions and reports the effects of various parameters such as the ratio of the thermal conductivity of nanoparticles to that of a base fluid, volume fraction, nanoparticle size, and temperature on the effective thermal conductivity of nanofluids. Comparison of model predictions with published experimental data shows good agreement for nanofluids containing oxide, metallic, and carbon nanotubes.

The Estimation of Thermal Conductivity for Alumina-Epoxy Composite Material with High Filling Volume Fraction

2014 ◽  
Vol 918 ◽  
pp. 21-26
Author(s):  
Chen Kang Huang ◽  
Yun Ching Leong
Keyword(s):  
Thermal Conductivity ◽  
Composite Material ◽  
Composite Materials ◽  
Physical Model ◽  
Electron Scattering ◽  
Volume Fraction ◽  
Epoxy Composite ◽  
The Matrix ◽  
Transport Theorem ◽  
Good Agreement

In this study, the transport theorem of phonons and electrons is utilized to create a model to predict the thermal conductivity of composite materials. By observing or assuming the dopant displacement in the matrix, a physical model between dopant and matrix can be built, and the composite material can be divided into several regions. In each region, the phonon or electron scattering caused by boundaries, impurities, or U-processes was taken into account to calculate the thermal conductivity. The model is then used to predict the composite thermal conductivity for several composite materials. It shows a pretty good agreement with previous studies in literatures. Based on the model, some discussions about dopant size and volume fraction are also made.

Gas Phase and Surface Reactions in Mocvd of GaAs from Triethylgallium, Trimethylgallium, and Organometallic Arsenic Precursors

1988 ◽  
Vol 131 ◽  
Author(s):  
Thomas R. Omstead ◽  
Penny M. Van Sickle ◽  
Klavs F. Jensen
Keyword(s):  
Gas Phase ◽  
Low Temperatures ◽  
Surface Reactions ◽  
Rate Data ◽  
Gas Phase Reactions ◽  
Heated Zone ◽  
Model Predictions ◽  
First Time ◽  
Good Agreement

ABSTRACTThe growth of GaAs from triethylgallium (TEG) and trimethylgallium (TMG) with tertiarybutylarsine (tBAs), triethylarsenic (TEAs), and trimethylarsenic (TMAs), has been investigated by using a reactor equipped with a recording microbalance for in situ rate measurements. Rate data show that the growth with these precursors is dominated by the formation of adduct compounds in the gas lines, by adduct related parasitic gas phase reactions in the heated zone, and by the surface reactions. A model is proposed for the competition between deposition reactions and the parasitic gas phase reactions. Model predictions are in very good agreement with experimental data for all combinations of precursors except for TEG/TMAs where extensive gallium droplet formation is observed at low temperatures. Growth of reasonable quality GaAs with Hall mobilities of 7600 cm2/Vs at 77 K using TEG and tBAs is reported for the first time.

Nanofluid Extinction Coefficients for Photothermal Energy Conversion

2011 ◽  
Author(s):  
Robert A. Taylor ◽  
Patrick E. Phelan ◽  
Ronald Adrian ◽  
Ravi Prasher ◽  
Todd P. Otanicar
Keyword(s):  
Bulk Properties ◽  
Extinction Coefficients ◽  
Energy Harvesters ◽  
Nanoparticle Suspensions ◽  
Model Predictions ◽  
Testing Data ◽  
Simplifying Assumptions ◽  
Solar Thermal Collectors ◽  
Base Liquid ◽  
Good Agreement

Suspensions of nanoparticles in liquids (i.e. nanofluids) have been shown to dramatically affect thermal and optical properties of the base liquid at low particle loadings [1–3]. Recent studies by the co-authors have indicated that selected nanofluids are promising as solar energy harvesters [4,5]. In order to determine the effectiveness of nanofluids in solar applications, their ability to convert light energy to thermal energy must be known. That is, the extinction coefficient of real nanofluids must be established. Although it is relatively straight-forward to model these properties from knowledge of bulk properties, with the help of some simplifying assumptions, real spectroscopy tests do not always match these calculations. This study compares model predictions of extinction coefficients to spectroscopic measurements. Unfortunately, the models and the optical testing data do not show very good agreement. Some possible reasons for this are discussed. Also, some simple experiments are presented to investigate the extent of scattering in nanoparticle suspensions. As alluded to above, all of these tests are conducted on nanofluid compositions which are considered to be suitable for solar thermal collectors.

Thermal and Viscoelastic Properties of Underfill Using hexagonal Boron Nitride (hBN) Nanofiller

2017 ◽  
Vol 2017 (1) ◽  
pp. 000542-000546 ◽  
Author(s):  
S. A. Razgaleh ◽  
Shyam Aravamudhan
Keyword(s):  
Thermal Conductivity ◽  
Thermal Analysis ◽  
Boron Nitride ◽  
Thermal Behavior ◽  
Viscoelastic Properties ◽  
Volume Fraction ◽  
Hexagonal Boron Nitride ◽  
Filler Loading ◽  
Curing Agent ◽  
Underfill Material

Abstract Epon 826 epoxy resin in conjunction with Epikure 3140 curing agent was used in this study to fabricate underfill composites. Nanofiller of 500nm hexagonal boron nitride (hBN) was incorporated in the underfill epoxy using ultrasonication technique to alter their thermal and viscoelastic properties. Filler contents ranging from 1% to 5% volume fraction (vol.%) were used to investigate changes in thermal behavior and viscoelasticity of underfill with an increase in filler loading. Thermal analysis has shown an increase in thermal conductivity of the underfill by increasing the filler loading. Using 5% vol.% of 500nm hBN nanofiller a thermal conductivity of 0.32 W/m.K was obtained as compared to neat epoxy with thermal conductivity of about 0.2 W/m.K, showing an enhancement in thermal conductivity of the underfill material. Furthermore, studying viscoelastic properties of fabricated underfills suggested the influence of filler and filler loading on viscoelasticity of underfill.

Studies on few Water Based Nanofluids Behavior at Heating

2015 ◽  
Vol 1128 ◽  
pp. 384-389
Author(s):  
Madalina Georgiana Moldoveanu ◽  
Alina Adriana Minea
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Unsolved Problem ◽  
Volume Fraction ◽  
Transfer Enhancement ◽  
Two Phase ◽  
Heat Transfer Fluids ◽  
Surface Areas ◽  
Water Based ◽  
Semi Empirical

Application of nanoparticles provides an effective way of improving heat transfer characteristics of fluids. Particles less than 100 nm in diameter exhibit different properties from those of conventional solids. Compared with micron-sized particles, nanophase powders have much larger relative surface areas and a great potential for heat transfer enhancement. Some researchers tried to suspend nanoparticles into fluids to form high effective heat transfer fluids. Some preliminary experimental results showed that increase in thermal conductivity of approximately 60% can be obtained for some nanofluids consisting of water and 5 vol% CuO nanoparticles. So, the thermal conductivity of nanofluid was found to be strongly dependent on the nanoparticle volume fraction. So far it has been an unsolved problem to develop a sophisticated theory to predict thermal conductivity of nanofluids, although there are some semi empirical correlations to calculate the apparent conductivity of two-phase mixture. In this article, several correlations for predicting the nanofluid thermal conductivity will be compared and results will be discussed for three water based nanofluids.

Parametric Experimental Study of Viscosity of Nanofluids

2006 ◽  
Author(s):  
Ravi Prasher ◽  
David Song ◽  
Jinlin Wang ◽  
Patrick Phelan
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Experimental Study ◽  
Pressure Drop ◽  
Volume Fraction ◽  
Systematic Investigation ◽  
Research Community ◽  
Transfer Enhancement ◽  
Heat Transfer Fluids ◽  
Potential Applications

There is a lot of interest in the research community about nanofluids due to their high thermal conductivity and potential applications as heat transfer fluids, however a systematic investigation on the viscosity of the nanofluids is still lacking from the literature. Any heat transfer enhancement due to force convention, also leads to increase in the pressure drop. Knowledge of the pressure drop is very important to understand the pumping requirements. Pressure drop is directly proportional to the viscosity of the liquid. Addition of nanoparticles will enhance the viscosity of the nanofluids. In this paper experimental results on the viscosity of propylene glycol based nanofluids are reported for various parameters such as nanoparticle size, temperature and volume fraction. Effect of Brownian motion on the viscosity of nanofluids is also explored.

scholarly journals Characterization of Local Nano-Heat Transfer Fluids for Solar Thermal Collection

2020 ◽  
Vol 2020 ◽  
pp. 1-8
Author(s):  
Kawira Millien
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Heat Exchanger ◽  
Copper Nanoparticles ◽  
Energy Demand ◽  
Volume Fraction ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Solar Thermal ◽  
Heat Transfer Fluids

Performance of organic oils in solar thermal collection is limited due to their low thermal conductivity when they are compared to molten salt solutions. Extraction of organic oils from plants can be locally achieved. The purpose of this study was to investigate the effect of use of copper nanoparticles in some base local heat transfer fluids (HTFs). Addition of volume fraction of 1.2% of the copper nanoparticles to oil-based heat transfer fluids improved their thermal conductivity as deduced from the thermal heat they conducted from solar radiation. The oil-based copper nanofluids were obtained by preparation of a colloidal solution of the nanoparticles. Impurities were added to increase the boiling point of the nano-heat transfer fluids. Stabilizers were used to keep the particles suspended in the oil-based fluids. The power output of the oil-based copper nano-heat transfer fluids was in the range of 475.4 W to 1130 W. The heat capacity of the steam in the heat exchanger was 93.7% dry and had a thermal capacity of 5.71 × 103 kJ. The heat rate of flow of the oil-based copper nano-heat transfer fluids was an average of 72.7 Js−1·kg−1 to 89.1 Js−1·kg−1. The thermal efficiency for the oil-based copper nano-heat transfer fluids ranged from 0.85 to 0.91. The average solar thermal solar intensity was in the range 700 Wm−2 to 1180 Wm−2. The heat exchanger used in this study was operating at 4.15 × 103 kJ and a temperature of 500.0°C. The heat transfer fluids entered the exchanger at an average temperature of 381°C and exited at 96.3°C and their heat coefficient ranged between 290.1 Wm−2°C and 254.1 Wm−2°C. The average temperatures of operation ranged between 394.1°C and 219.7°C with respective temperature efficiencies ranging between 93.4% and 64.4%. It was established that utilization of copper nanoparticles to enhance heat transfer in oil-based local heat transfer fluids can mitigate energy demand for meeting the world’s increasing energy uses, especially for areas inaccessible due to poor land terrain.

Thermal transport properties of carbon-carbon fibre composites III. Mathematical modelling

1990 ◽  
Vol 430 (1878) ◽  
pp. 199-211 ◽  
Keyword(s):  
Thermal Conductivity ◽  
Thermal Transport ◽  
Volume Fraction ◽  
Fibre Volume Fraction ◽  
Microstructural Characterization ◽  
Fibre Volume ◽  
Porosity Level ◽  
Using Data ◽  
Carbon Fibre Composites ◽  
Good Agreement

Measured thermal transport data are interpreted using data obtained by careful microstructural characterization concerning the porosity distribution and graphite grain sizes. The separate thermal conductivity components for one-dimensional composites are deduced using a simple series addition to determine ג f1 and ג m1 and using an adaptation of the Bruggeman analysis for calculating ג f┴ and ג m┴ . Parallel to the fibre axis the calculated thermal conductivities are shown to be in good agreement with existing theories of the thermal conductivity of graphite using experimentally determined values of grain size. The derived data are recombined in a simple series model to predict the thermal conductivity of two-dimensional composites containing a different fibre volume fraction and porosity level. Good agreement with measured data is obtained.

scholarly journals Effect of Phonon Dispersion on Thermal Conduction Across Si/Ge Interfaces

2009 ◽  
Author(s):  
Dhruv Singh ◽  
Jayathi Y. Murthy ◽  
Timothy S. Fisher
Keyword(s):  
Thermal Conductivity ◽  
Volume Fraction ◽  
Phonon Dispersion ◽  
Boltzmann Transport ◽  
Host Materials ◽  
Wide Range ◽  
Heterogeneous Interfaces ◽  
Silicon And Germanium ◽  
First Time ◽  
Superlattice Period

We report finite volume simulations of the phonon Boltzmann transport equation (BTE) for heat conduction across the heterogeneous interfaces in SiGe superlattices. We employ the diffuse mismatch model with full details of phonon dispersion and polarization. Simulations are performed over a wide range of Knudsen numbers. Similar to previous studies we establish that thermal conductivity of a superlattice is much lower than the host materials for superlattice period in the submicron regime. Details of the non-equilibrium between optical and acoustic phonons that emerge due to the mismatch of phonon spectrum in silicon and germanium are delineated for the first time. Conditions are identified for which this can lead to a significant additional thermal resistance than that attributed primarily to boundary scattering of phonons. We report results for thermal conductivity for various volume fraction and superlattice periods.

Study of Iron Nanopowders into Fluids of Industrial Lubrication

2012 ◽  
Vol 727-728 ◽  
pp. 1654-1659 ◽  
Author(s):  
Mabelle Biancarde Oliveira ◽  
Maryana Antonia Braga Batalha Souza ◽  
José Adilson de Castro ◽  
Alexandre José da Silva
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Effective Viscosity ◽  
Heat Transfer Performance ◽  
Volume Fraction ◽  
Cell Model ◽  
Heat Extraction ◽  
Unit Cell Model ◽  
Metal Parts ◽  
Heat Transfer Fluids

The machines and equipment has required increasing performance of lubricating fluids and coolants which plays important role on reducing friction with the metal parts and heat extraction. Viscosity and thermal conductivity are the most important properties of lubricants, in relation to the friction between the fluid molecules. This paper presents two useful models to predict this properties and their relation with the particles volume fraction and temperature in the nanofluid formed by adition of iron or particles produced by friction. Nanofluids are innovative heat transfer fluids with superior potential for enhancing the heat transfer performance of conventional fluids. In this paper the Unit Cell Model (UCM) which considers the Brownian movement experienced by the nanoparticles are adapt to predict the increment of thermal conductivity of iron nanopowders and standard lubrication oil. The viscosity of the nanofluids was adapt from a model usually suitable for predict the effective viscosity of emulsions. Model results indicated a strong effect of the particle size and volume fractions on the increment of thermal conductivity.

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