scholarly journals Limits for thermal conductivity of nanofluids

2010 ◽  
Vol 14 (1) ◽  
pp. 65-71 ◽  
Author(s):  
Chandrasekar Murugesan ◽  
Suresh Sivan
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Thermal Conductivity ◽  
Brownian Motion ◽  
Particle Shape ◽  
Large Degree ◽  
The Past ◽  
Upper Limit ◽  
Upper Limits ◽  
Transfer Mechanisms

Nanofluids have offered challenges to thermal engineers and attracted many researchers over the past decade to determine the reasons for anomalous enhancement of thermal conductivity in them. Experiments on measurement of nanofluid thermal conductivity have ended in a large degree of randomness and scatter in their values. Hence in this paper, lower and upper limits for thermal conductivity of nanofluids are developed. The upper limit is estimated by coupling heat transfer mechanisms like particle shape, Brownian motion and nanolayer while the lower limit is based on Maxwell's equation. Experimental data from a range of independent published sources is used for validation of the developed limits.

Possible Mechanisms for Thermal Conductivity Enhancement in Nanofluids

2006 ◽  
Author(s):  
Amit Gupta ◽  
Xuan Wu ◽  
Ranganathan Kumar
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Brownian Motion ◽  
Brownian Dynamics ◽  
Lattice Vibration ◽  
Experimental Studies ◽  
High Heat ◽  
Conductivity Enhancement ◽  
High Heat Transfer ◽  
Dynamics Simulations

This study discusses the merits of various physical mechanisms that are responsible for enhancing the heat transfer in nanofluids. Experimental studies have cemented the claim that ‘seeding’ liquids with nanoparticles can increase the thermal conductivity of the nanofluid by up to 40% for metallic and oxide nanoparticles dispersed in a base liquid. Experiments have also shown that the rise in conductivity of the nanofluid is highly dependent on the size and concentration of the nanoparticles. On the theoretical side, traditional models like Maxwell or Hamilton-Crosser models cannot explain this unusually high heat transfer. Several mechanisms have been postulated in the literature such as Brownian motion, thermal diffusion in nanoparticles and thermal interaction of nanoparticles with the surrounding fluid, the formation of an ordered liquid layer on the surface of the nanoparticle and microconvection. This study concentrates on 3 possible mechanisms: Brownian dynamics, microconvection and lattice vibration of nanoparticles in the fluid. By considering two nanofluids, copper particles dispersed in ethylene glycol, and silica in water, it is determined that translational Brownian motion of the nanoparticles, presence of an interparticle potential and the microconvection heat transfer are mechanisms that play only a smaller role in the enhancement of thermal conductivity. On the other hand, the lattice vibrations, determined by molecular dynamics simulations show a great deal of promise in increasing the thermal conductivity by as much as 23%. In a simplistic sense, the lattice vibration can be regarded as a means to simulate the phononic transport from solid to liquid at the interface.

Experimental and theoretical investigation of heat transfer characteristics of cylindrical heat pipe using Al2O3–SiO2/W-EG hybrid nanofluids by RSM modeling approach

2021 ◽  
Vol 68 (1) ◽  
Author(s):  
R. Vidhya ◽  
T. Balakrishnan ◽  
B. Suresh Kumar
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Heat Transfer Coefficient ◽  
Thermal Resistance ◽  
Transfer Coefficient ◽  
Heat Pipe ◽  
Diffraction Spectrum ◽  
Step Method ◽  
Ceramic Nanoparticles ◽  
Transfer Mechanisms

AbstractNanofluids are emerging two-phase thermal fluids that play a vital part in heat exchangers owing to its heat transfer features. Ceramic nanoparticles aluminium oxide (Al2O3) and silicon dioxide (SiO2) were produced by the sol-gel technique. Characterizations have been done through powder X-ray diffraction spectrum and scanning electron microscopy analysis. Subsequently, few volume concentrations (0.0125–0.1%) of hybrid Al2O3–SiO2 nanofluids were formulated via dispersing both ceramic nanoparticles considered at 50:50 ratio into base fluid combination of 60% distilled water (W) with 40% ethylene glycol (EG) using an ultrasonic-assisted two-step method. Thermal resistance besides heat transfer coefficient have been examined with cylindrical mesh heat pipe reveals that the rise of power input decreases the thermal resistance and inversely increases heat transfer coefficient about 5.54% and 43.16% respectively. Response surface methodology (RSM) has been employed for the investigation of heat pipe experimental data. The significant factors on the various convective heat transfer mechanisms have been identified using the analysis of variance (ANOVA) tool. Finally, the empirical models were developed to forecast the heat transfer mechanisms by regression analysis and validated with experimental data which exposed the models have the best agreement with experimental results.

Forced Convection Heat Transfer of Nanofluids: A Review

2017 ◽  
Author(s):  
Aditya Kuchibhotla ◽  
Debjyoti Banerjee
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Thermal Conductivity ◽  
Heat Capacity ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Specific Heat ◽  
Forced Convection ◽  
Convection Heat Transfer ◽  
Convection Heat

Stable homogeneous colloidal suspensions of nanoparticles in a liquid solvents are termed as nanofluids. In this review the results for the forced convection heat transfer of nanofluids are gleaned from the literature reports. This study attempts to evaluate the experimental data in the literature for the efficacy of employing nanofluids as heat transfer fluids (HTF) and for Thermal Energy Storage (TES). The efficacy of nanofluids for improving the performance of compact heat exchangers were also explored. In addition to thermal conductivity and specific heat capacity the rheological behavior of nanofluids also play a significant role for various applications. The material properties of nanofluids are highly sensitive to small variations in synthesis protocols. Hence the scope of this review encompassed various sub-topics including: synthesis protocols for nanofluids, materials characterization, thermo-physical properties (thermal conductivity, viscosity, specific heat capacity), pressure drop and heat transfer coefficients under forced convection conditions. The measured values of heat transfer coefficient of the nanofluids varies with testing configuration i.e. flow regime, boundary condition and geometry. Furthermore, a review of the reported results on the effects of particle concentration, size, temperature is presented in this study. A brief discussion on the pros and cons of various models in the literature is also performed — especially pertaining to the reports on the anomalous enhancement in heat transfer coefficient of nanofluids. Furthermore, the experimental data in the literature indicate that the enhancement observed in heat transfer coefficient is incongruous compared to the level of thermal conductivity enhancement obtained in these studies. Plausible explanations for this incongruous behavior is explored in this review. A brief discussion on the applicability of conventional single phase convection correlations based on Newtonian rheological models for predicting the heat transfer characteristics of the nanofluids is also explored in this review (especially considering that nanofluids often display non-Newtonian rheology). Validity of various correlations reported in the literature that were developed from experiments, is also explored in this review. These comparisons were performed as a function of various parameters, such as, for the same mass flow rate, Reynolds number, mass averaged velocity and pumping power.

Numerical Computation of the Effects of Brownian Motion on the Effective Thermal Conductivity of Suspensions

2007 ◽  
Author(s):  
P. E. Phelan ◽  
J. R. Pacheco
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Brownian Motion ◽  
Dimensional Space ◽  
Numerical Technique ◽  
Heat Transfer Process ◽  
Immersed Boundary ◽  
Brownian Dynamic ◽  
Dynamic Simulations ◽  
Bulk Fluid

In this paper, a numerical scheme based on the immersed boundary method is used to study the motion of nano-sized particles subjected to Brownian motion and heat transfer. Our objective is to use this numerical technique as a tool to better understand the effect that Brownian forces have on the overall heat transfer process. The conventional approach to perform Brownian dynamic simulations is based on the use of a random force in the particle motion such that the fluctuation-dissipation theorem is satisfied. Our preliminary computational results suggest an increase in the thermal conductivity of the bulk fluid. Results are presented for several particles in a two-dimensional space.

scholarly journals Composite Materials Based on Henequen Fiber as a Thermal Barrier in the Automotive Sector

2019 ◽  
Vol 2019 ◽  
pp. 1-9
Author(s):  
J. M. Olivares-Ramírez ◽  
A. Dector ◽  
A. Duarte-Moller ◽  
D. Ortega Díaz ◽  
Diana Dector ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Carbon Fiber ◽  
Solar Radiation ◽  
High Performance ◽  
Natural Fiber ◽  
Reference Sample ◽  
Thermal Barrier ◽  
Transfer Mechanisms ◽  
Reference Samples

Currently, the automotive industry has made great advances in the incorporation of materials such as carbon fiber in high-performance cars. One of the main problems of these vehicles is warming, which is generated inside due to the heat transfer produced by solar radiation falling on the car, mainly on the roof. This research proposes the preparation of a composite material containing henequen natural fiber as a thermal barrier to be used as the roof of the car. In this research, 35 different laminates of 5 layers were prepared, combining carbon fiber, henequen natural fiber, fiberglass, and additives such as resin + Al2O3 or resin + Al. Reference samples were taken from stainless steel and one reference sample was extracted from the roof of the car. Considering the solar radiation and the heat transfer mechanisms, the temperature of the surface exposed to solar radiation was determined. The thermal conductivity of the 37 samples was determined, and the experimental results showed that the thermal conductivity of the steel with which the roof of the car is manufactured was 13.43 W·m−1·K−1 and that of the proposed laminate was 5.22 W·m−1·K−1, achieving a decrease in the thermal conductivity by 61.13%. Using the temperature and thermal conductivity data, the simulation (ANSYS) of the thermal system was performed. The results showed that the temperature inside the car with the carbon steel, which is currently used to manufacture high-performance cars, would be 62.34°C, whereas that inside the car with the proposed laminate would be 44.96°C, achieving a thermal barrier that allows a temperature difference of 17.38°C.

scholarly journals Modeling heat transfer process in soils

2018 ◽  
Vol 251 ◽  
pp. 02048 ◽  
Author(s):  
Ian Ofrikhter ◽  
Alexander Zaharov ◽  
Andrey Ponomaryov ◽  
Natalia Likhacheva
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Thermal Conductivity ◽  
Analytical Calculation ◽  
Accurate Method ◽  
Heat Transfer Process ◽  
Preliminary Evaluation ◽  
Soil Base ◽  
Undisturbed Sample ◽  
Analytical Formulas

In this paper, a new model is presented for calculating the thermal conductivity of soils, and the main provisions for the derivation of analytical formulas are given. The presented model allows taking into account the density, moisture content and temperature of the soil base. The technique presented in the paper makes it possible to dispense with laborious experiments to estimate the thermal conductivity of the soil. The method of analytical calculation is step by step presented in the paper. Two variants of using the method are proposed: 1) Less accurate method, for preliminary evaluation, without the need to take probe and conduct experiments. 2) More accurate method, with at least one experiment with a disturbed or undisturbed sample. The results of comparison of calculated values of thermal conductivity and experimental data are presented.

Convective Heat Transfer Enhancement With Nanofluids: The Effect of Temperature-Variable Thermal Conductivity

2010 ◽  
Author(s):  
Sezer O¨zerinc¸ ◽  
Almıla G. Yazıcıog˘lu ◽  
Sadık Kakac¸
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Thermal Conductivity ◽  
Heat Transfer Enhancement ◽  
Forced Convection ◽  
Convection Heat Transfer ◽  
Thermal Dispersion ◽  
Convection Heat ◽  
Transfer Enhancement ◽  
Experimental Values

A nanofluid is defined as the suspension of nanoparticles in a base liquid. Studies in the last decade have shown that significant amount of thermal conductivity and heat transfer enhancement can be obtained by using nanofluids. In the first part of this study, classical forced convection heat transfer correlations developed for pure fluids are used to predict the experimental values of heat transfer enhancement of nanofluids. It is seen that the experimental values of heat transfer enhancement exceed the enhancement predictions of the classical correlations. On the other hand, a recent correlation based on the thermal dispersion phenomenon created by the random motion of nanoparticles predicts the experimental data well. In the second part of the study, in order to further examine the validity of the thermal dispersion approach, a numerical analysis of forced convection heat transfer of Al2O3/water nanofluid inside a circular tube in the laminar flow regime is performed by utilizing single phase assumption. A thermal dispersion model is applied to the problem and variation of thermal conductivity with temperature and variation of thermal dispersion with local axial velocity are taken into account. The agreement of the numerical results with experimental data might be considered as an indication of the validity of the approach.

Dual Role of Nanoparticles in the Thermal Conductivity Enhancement of Nanoparticle Suspensions

2005 ◽  
Author(s):  
Calvin H. Li ◽  
G. P. Peterson
Keyword(s):  
Experimental Data ◽  
Thermal Conductivity ◽  
Brownian Motion ◽  
Theoretical Models ◽  
Conductivity Enhancement ◽  
Nanoparticle Suspensions ◽  
The Difference ◽  
Physical Phenomena ◽  
Good Agreement

Experimental evidence exists that the addition of a small quantity of nanoparticles to a base fluid, can have a significant impact on the effective thermal conductivity of the resulting suspension. The causes for this are currently thought to be due to a combination of two distinct mechanisms. The first is due to the change in the thermophysical properties of the suspension, resulting from the difference in the thermal conductivity of the fluid and the particles, and the second is thought to be due to the transport of thermal energy by the particles, due to the Brownian motion of the particles. In order to better understand these phenomena, a theoretical model has been developed that examines the effect of the Brownian motion. In this model, the well-known approach first presented by Maxwell, is combined with a new expression that incorporates the effect of the Brownian motion and describes the physical phenomena that occurs because of it. The results indicate that the enhanced thermal conductivity may not in fact be due to the transport of energy by the particles, but rather, due to the stirring motion caused by the movement of the nanoparticles which enhances the heat transfer within the fluid. The resulting model shows good agreement when compared with the existing experimental data and perhaps more importantly helps to explain the trends observed from a fundamental physical perspective. In addition, it provides a possible explanation for the differences that have been observed between the previously obtained experimental data, the predictions obtained from Maxwell’s equation and the theoretical models developed by other investigators.

Temperature-dependent effect of percolation and Brownian motion on the thermal conductivity of TiO2–ethanol nanofluids

2016 ◽  
Vol 18 (22) ◽  
pp. 15363-15368 ◽  
Author(s):  
Chien-Cheng Li ◽  
Nga Yu Hau ◽  
Yuechen Wang ◽  
Ai Kah Soh ◽  
Shien-Ping Feng
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Brownian Motion ◽  
Thermal Storage ◽  
Temperature Dependent ◽  
Dependent Effect ◽  
And Brownian Motion ◽  
Potential Applications

Ethanol-based nanofluids have attracted much attention due to the enhancement in heat transfer and their potential applications in nanofluid-type fuels and thermal storage.

Thermal Conductivity Equations Based on Brownian Motion in Suspensions of Nanoparticles (Nanofluids)

2008 ◽  
Vol 130 (4) ◽  
Author(s):  
Bao Yang
Keyword(s):  
Experimental Data ◽  
Thermal Conductivity ◽  
Brownian Motion ◽  
Relaxation Time ◽  
Kinetic Theory ◽  
Significant Role ◽  
Particle Velocity ◽  
Long Time ◽  
Theoretical Results ◽  
Enhanced Thermal Conductivity

Thermal conductivity equations for the suspension of nanoparticles (nanofluids) have been derived from the kinetic theory of particles under relaxation time approximations. These equations, which take into account the microconvection caused by the particle Brownian motion, can be used to evaluate the contribution of particle Brownian motion to thermal transport in nanofluids. The relaxation time of the particle Brownian motion is found to be significantly affected by the long-time tail in Brownian motion, which indicates a surprising persistence of particle velocity. The long-time tail in Brownian motion could play a significant role in the enhanced thermal conductivity in nanofluids, as suggested by the comparison between the theoretical results and the experimental data for the Al2O3-in-water nanofluids.

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