Thermal Conductivity of Nanofluids

2013 ◽  
Vol 757 ◽  
pp. 111-137 ◽  
Author(s):  
Amit Sobti ◽  
R.K. Wanchoo
Keyword(s):  
Thermal Conductivity ◽  
Critical Analysis ◽  
Base Fluid ◽  
Size Range ◽  
Volume Fraction ◽  
Nano Particles ◽  
Research Groups ◽  
Single Model ◽  
Nano Fluid ◽  
Enhanced Thermal Conductivity

Enhanced thermal conductivity of nanofluids compared to that of the base fluid has received attention of many researchers in the last one decade. Experimental data on thermal conductivity of nanofluids using varied nanoparticles in the size range 10-100 nm have been reported. However, there is lot of variance in the data and needs critical analysis. Many models have been proposed by various research groups for predicting the thermal conductivity of nanofluids. Due to complexity of various parameters involved (size, % volume fraction, specific surface area and the type of nano particles, pH of nano fluid, thermal conductivity and viscosity of base fluid) no single model can be used for predicting the thermal conductivity of nanofluids. Inconsistent and conflicting results are reported on the enhanced thermal conductivity of nanofluids. Further, insufficient understanding and inconclusive mechanism behind enhanced thermal conductivity requires further attempt to work in this field. This article critically reviews the available literature on thermal conductivity of nanofluids.

Study of the boundary layer heat transfer of nanofluids over a stretching sheet: Passive control of nanoparticles at the surface

2015 ◽  
Vol 93 (7) ◽  
pp. 725-733 ◽  
Author(s):  
M. Ghalambaz ◽  
E. Izadpanahi ◽  
A. Noghrehabadi ◽  
A. Chamkha
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Boundary Layer ◽  
Nusselt Number ◽  
Heat Transfer Enhancement ◽  
Base Fluid ◽  
Stretching Sheet ◽  
Volume Fraction ◽  
Enhancement Ratio ◽  
Transfer Enhancement

The boundary layer heat and mass transfer of nanofluids over an isothermal stretching sheet is analyzed using a drift-flux model. The relative slip velocity between the nanoparticles and the base fluid is taken into account. The nanoparticles’ volume fractions at the surface of the sheet are considered to be adjusted passively. The thermal conductivity and the dynamic viscosity of the nanofluid are considered as functions of the local volume fraction of the nanoparticles. A non-dimensional parameter, heat transfer enhancement ratio, is introduced, which shows the alteration of the thermal convective coefficient of the nanofluid compared to the base fluid. The governing partial differential equations are reduced into a set of nonlinear ordinary differential equations using appropriate similarity transformations and then solved numerically using the fourth-order Runge–Kutta and Newton–Raphson methods along with the shooting technique. The effects of six non-dimensional parameters, namely, the Prandtl number of the base fluid Prbf, Lewis number Le, Brownian motion parameter Nb, thermophoresis parameter Nt, variable thermal conductivity parameter Nc and the variable viscosity parameter Nv, on the velocity, temperature, and concentration profiles as well as the reduced Nusselt number and the enhancement ratio are investigated. Finally, case studies for Al2O3 and Cu nanoparticles dispersed in water are performed. It is found that increases in the ambient values of the nanoparticles volume fraction cause decreases in both the dimensionless shear stress f″(0) and the reduced Nusselt number Nur. Furthermore, an augmentation of the ambient value of the volume fraction of nanoparticles results in an increase the heat transfer enhancement ratio hnf/hbf. Therefore, using nanoparticles produces heat transfer enhancement from the sheet.

scholarly journals Synthesis of hybrid nanofluid with two-step method

2018 ◽  
Vol 67 ◽  
pp. 03057 ◽  
Author(s):  
Wayan Nata Septiadi ◽  
Ida Ayu Nyoman Titin Trisnadewi ◽  
Nandy Putra ◽  
Iwan Setyawan
Keyword(s):  
Thermal Conductivity ◽  
Base Fluid ◽  
Volume Fraction ◽  
Heat Transfer Fluid ◽  
Hybrid Nanofluid ◽  
Test Results ◽  
Step Method ◽  
Fluid Mixture ◽  
High Level ◽  
Better Than

Nanofluid is a liquid fluid mixture with a nanometer-sized solid particle potentially applied as a heat transfer fluid because it is capable of producing a thermal conductivity better than a base fluid. However, nanofluids have a weakness that is a high level of agglomeration as the resulting conductivity increases. Therefore, in this study, the synthesis of two nanoparticles into the base fluid called hybrid nanofluids. This study aims to determine the effect of nanoparticle composition on the highest thermal conductivity value with the lowest agglomeration value. This research was conducted by dispersing Al2O3-TiO2 nanoparticles in water with volume fraction of 0.1%, 0.3%, 0.5%, 0.7% in the composition of Al2O3-TiO2 ratio of 75%:25%, 50%:50%, 25%:75%. The synthesis was performed with a magnetic stirrer for 30 minutes. The tests were carried out in three types: thermal conductivity testing with KD2, visual agglomeration observation and absorbance measurements using UV-Vis, wettability testing with HSVC tools and Image applications. The test results showed that the ratio composition ratio of 75% Al2O3-25% TiO2 with a volume fraction of 0.7% resulted in an increase in optimum thermal conductivity with the best wettability and the longest agglomeration level.

Thermal Transport Properties of Nanofluids Containing Carbon Nanotubes

2008 ◽  
Author(s):  
Huaqing Xie ◽  
Lifei Chen ◽  
Yang Li ◽  
Wei Yu
Keyword(s):  
Thermal Conductivity ◽  
Carbon Nanotubes ◽  
Base Fluid ◽  
Volume Fraction ◽  
Thermal Conductivity Enhancement ◽  
Mechanochemical Reaction ◽  
Multiwalled Carbon ◽  
Conductivity Enhancement ◽  
Lower Viscosity ◽  
Potential Applications

Multiwalled carbon nanotubes (CNTs) have been treated by using a mechanochemical reaction method to enhance their dispersibility for producing CNT nanofluids. The thermal conductivity was measured by a short hot wire technique and the viscosity was measured by a rotary viscometer. The thermal conductivity enhancement reaches up to 17.5% at a volume fraction of 0.01 for an ethylene glycol based nanofluid. Temperature variation was shown to have no obvious effects on the thermal conductivity enhancement for the as prepared nanofluids. With an increase in the thermal conductivity of the base fluid, the thermal conductivity enhancement of a nanofluid decreases. At low volume fractions (<0.4 Vol%), nanofluids have lower viscosity than the corresponding base fluid due to lubricative effect of nanoparticles. When the volume fraction is higher than 0.4 Vol%, the viscosity increases with nanoparticle loadings. The prepared nanofluids, with no contamination to medium, good fluidity, stability, and high thermal conductivity, would have potential applications as coolants in advanced thermal systems.

Liquid Layering and the Enhanced Thermal Conductivity of Ar-Cu Nanofluids: A Molecular Dynamics Study

2016 ◽  
Author(s):  
Jithu Paul ◽  
A. K. Madhu ◽  
U. B. Jayadeep ◽  
C. B. Sobhan
Keyword(s):  
Thermal Conductivity ◽  
Molecular Dynamics ◽  
Particle Size ◽  
Molecular Dynamics Simulations ◽  
Volume Fraction ◽  
Strong Dependence ◽  
Particle Sizes ◽  
Dynamics Simulations ◽  
Enhanced Thermal Conductivity ◽  
Liquid Layering

Nanofluids — colloidal suspensions of nanoparticles in base fluids — are known to possess superior thermal properties compared to the base fluids. Various theoretical models have been suggested to explain the often anomalous enhancement of these properties. Liquid layering around the nanoparticle is one of such reasons. The effect of the particle size on the extent of liquid layering around the nanoparticle has been investigated in the present study. Classical molecular dynamics simulations have been performed in the investigation, considering the case of a copper nanoparticle suspended in liquid argon. The results show a strong dependence of thickness of the liquid layer on the particle size, below a particle diameter of 4nm. To establish the role of liquid layering in the enhancement of thermal conductivity, simulations have been performed at constant volume fraction for different particle sizes using Green Kubo formalism. The thermal conductivity results show 100% enhancement at 3.34% volume fraction for particle size of 2nm. The results establish the dominant role played by liquid layering in the enhanced thermal conductivity of nanofluids at the low particle sizes used. Contrary to the previous findings, the molecular dynamics simulations also predict a strong dependence of the liquid layer thickness on the particle size in the case of small particles.

scholarly journals Numerical study of heat transfer in 90° bend tube by AI2O3 nano fluids using fluid injection

2020 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Hadi Mahdizadeh ◽  
Nor Mariah Adam
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Reynolds Number ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Volume Fraction ◽  
Fluid Injection ◽  
Content Type ◽  
Nano Fluid ◽  
The Impact

Purpose This paper aims to investigate increasing heat transfer in bend tube 90° by fluid injection using nano fluid flow that was performed by expending varying Reynolds number. This paper studies the increased heat transfer in the bent tube that used some parameters to examine the effects of volume fraction, nanoparticle diameter, fluid injection, Reynolds number on heat transfer and flow in a bend pipe. Design/methodology/approach Designing curved tubes increases the thermal conductivity amount between fluid and wall. It is used the finite volume method and simple algorithms to solve the conservation equations of mass, momentum and energy. The results showed that the nanoparticles used in bent tube transfusion increase the heat transfer performance by increasing the volume fraction; it has a direct impact on enhancing the heat transfer coefficient. Findings Heat transfer coefficient enhanced 1.5% when volume fraction increased from 2 % to 6%, the. It is due to the impact of nanoparticles on the thermal conductivity of the fluid. The fluid is injected into the boundary layer flow due to jamming that enhances heat transfer. Curved lines used create a centrifugal force due to the bending and lack of development that increase the heat transfer. Originality/value This study has investigated the effect of injection of water into a 90° bend before and after the bend. Specific objectives are to analyze effect of injection on heat transfer of bend tube and pressure drop, evaluate best performance of mixing injection and bend in different positions and analyze effect of nano fluid volume fraction on injection.

Experimental Measurement of Thermophysical Properties of Alumina- MWCNTs/Salt–Water Hybrid Nanofluids

2020 ◽  
Vol 16 (5) ◽  
pp. 734-747 ◽  
Author(s):  
Amir Hossein Sharifi ◽  
Iman Zahmatkesh ◽  
Fatemeh F. Bamoharram ◽  
Amir Hossein Shokouhi Tabrizi ◽  
Safieh Fazel Razavi ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Electrical Conductivity ◽  
Salt Concentration ◽  
Thermophysical Properties ◽  
Base Fluid ◽  
Volume Fraction ◽  
Ph Value ◽  
Nanoparticle Volume Fraction ◽  
Optimal Conditions ◽  
Hybrid Nanofluids

Background: Hybrid nanofluids are considered as an extension of conventional nanofluids which are prepared through suspending two or more nanoparticles in the base fluids. Previous studies on hybrid nanofluids have measured their thermal conductivity overlooking other thermophysical properties such as viscosity and electrical conductivity. Objective: An experimental investigation is undertaken to measure thermal conductivity, viscosity, and electrical conductivity of a hybrid nanofluid prepared through dispersing alumina nanoparticles and multiwall carbon nanotubes in saltwater. These properties are the main important factors that must be assessed before performance analysis for industrial applications. Methods: The experimental data were collected for different values of the nanoparticle volume fraction, temperature, salt concentration, and pH value. Attention was paid to explore the consequences of these parameters on the nanofluid’s properties and to find optimal conditions to achieve the highest value of the thermal conductivity and the lowest values of the electrical conductivity and the viscosity. Results: The results demonstrate that although the impacts of the pH value and the nanoparticle volume fraction on the nanofluid’s thermophysical properties are not monotonic, optimal conditions for each of the properties are reachable. It is found that the inclusion of the salt in the base fluid may not change the thermal conductivity noticeably. However, a considerable reduction in the viscosity and substantial elevation in the electrical conductivity occur with an increase in the salt concentration. Conclusion: With the addition of salt to a base fluid, the thermophysical properties of a nanofluid can be controlled.

The Thermal Conductivity and Viscosity of Non-Polar Hybrid CuO Nanofluid (CuO+ DEA + Cyclohexane) (CuO + DEA + 1-4 Dioxane)

2019 ◽  
Vol 17 (12) ◽  
pp. 965-967
Author(s):  
B. Rohini ◽  
A. Kingson Solomon Jeevaraj
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Copper Oxide ◽  
Viscosity Measurement ◽  
Nano Particles ◽  
Conductivity Measurements ◽  
Transfer Enhancement ◽  
Binary Fluid ◽  
New Class ◽  
Nano Fluid

Nano fluid is the new class of engineering fluid for the heat transfer applications. Copper Oxide (CuO) nano particles were dispersed in the binary fluid (Cyclohexane + DEA) and (1-4 dioxane + DEA) then prepared non-polar hybrid CuO nano fluid. Thermal conductivity (K ) and viscosity (η) of non-polar hybrid CuO nanofluid measured for very low concentration from 0.01 M to 0.06 M and various temperatures ranging from 298 K to 318 K. The transient hotwire method is used for the thermal conductivity measurements and viscometer is used for the viscosity measurement. As the concentration increases K decreases but it increases with the increase of temperature. η increases with the increase of concentration as well as with temperature. From the results the spectacular heat transfer enhancement occurred in the hybrid CuO nanofluid compared to the binary mixtures. The percentage increment of thermal conductivity of non-polar hybrid CuO nano fluid is of 15% to 20% and the viscosity increment is of from 18% to 25%.

Experimental Research on Thermal Conductivity of Metal-Oxide Nanofluids

2011 ◽  
Vol 148-149 ◽  
pp. 587-590
Author(s):  
Qing Yun Shou ◽  
Ru Dong Chen ◽  
Sheng Su
Keyword(s):  
Thermal Conductivity ◽  
Metal Oxide ◽  
Experimental Research ◽  
Base Fluid ◽  
Volume Fraction ◽  
Suspension Stability ◽  
Transient Hot Wire ◽  
Hot Wire ◽  
Engineering Material ◽  
Wire Method

Nanofluid is a kind of new engineering material consisting of nanometer-sized particles dispersed in base fluid. In this study, the thermal conductivity of four kinds of nanofluids is measured by the transient hot-wire method. The thermal conductivity of nanofluids is not only influenced by volume fraction of nanoparticles, but also by other factors such as diameter and suspension stability of nanoparticles and the temperature. The experimental results show that nanofluids have substantially higher thermal conductivity than the same liquids without nanoparticles.

Temperature and Viscosity Effects on the Thermal Conductivity of Ferro-Nanofluid

2009 ◽  
Author(s):  
Chin-Ting Yang ◽  
Shao-Hua Cheng
Keyword(s):  
Thermal Conductivity ◽  
Brownian Motion ◽  
Diesel Fuel ◽  
Base Fluid ◽  
Volume Fraction ◽  
Volume Ratio ◽  
Polydimethyl Siloxane ◽  
Viscosity Effects ◽  
Lower Viscosity ◽  
Lower Temperature

The aim of this study is to understand the temperature and viscosity effects on the thermal conductivity of ferro-nanofluid. The base-fluid of ferro-nanofluid is made of polydimethyl-siloxane (PDMS) and diesel fuel which have similar thermal property but different viscosity. The viscosity of base-fluid is controlled by changing the volume ratio of both fluids. The measured results show that the thermal conductivity is smaller when the base fluid is highly viscous, and the thermal conductivity approaches to the value predicted by the Maxwell equation. It should be that the Brownian motion effect on highly viscous fluid is not as important as on lower viscosity fluid. Usually rising temperature will decrease viscosity of base fluid. In our study, rising temperature to 58°C can reduce the viscosity of 90%diesel fuel+10%PDMS to pure diesel fuel base fluid at 23 °C. At the same viscosity condition, rising temperature will decrease the thermal conductivity of ferro-nanofluid. The reason is that the thermal conductivity of base-fluid decrease dramatically. Comparing thermal conductivity of 2% volume fraction ferro-nanofluid to base-fluid at 23°C and 58°C respectively, the value increases 8.3% at 23 °C but increases 18.8% when the temperature is 58°C. This means the Brownian motion is more active at higher temperature than lower temperature.

scholarly journals Thermo-Acoustical and FTIR Spectroscopic Research of Nanofluids at Different Temperatures

2020 ◽  
Vol 8 (5) ◽  
pp. 5306-5309
Keyword(s):  
Thermal Conductivity ◽  
Bond Formation ◽  
Nano Particles ◽  
Wide Spread ◽  
Nano Fluid ◽  
Cohesive Properties ◽  
Physical Chemical ◽  
Different Temperatures ◽  
Chemical Studies ◽  
Nano Fluids

In recent years the greater interest of increase in thermal conductivity have attracted because there is comparison to that of the base fluids by Nano fluids. The wide spread of nano particles of the formation nano fluid of a base fluid, takes place. These nano fluids are very much useful in thermo dynamical applications and in the study of so many physical-chemical studies. The properties of molecular of sound in nano fluids like transmission undergo changes of associated systems in highly dependent and the cohesive properties of liquids. Generally nano fluid is having high thermal conductivity values. Four different temperatures have been studied in this thermo-acoustical work and FTIR Spectrum of Coo Nano fluid at T (303.15, 308.15, 313.15 and 318.15) K. The observed results are explained in the nature of interactions and bond formation.

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