Nanofluids Suspensions: Possible Explanations for the Apparent Enhanced Effective Thermal Conductivity

2005 ◽  
Author(s):  
Peter Vadasz
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Heat Conduction ◽  
Effective Thermal Conductivity ◽  
Heterogeneous Medium ◽  
Alternative Possibilities ◽  
Dual Phase ◽  
Transfer Enhancement ◽  
Scale Level ◽  
Macro Scale

The spectacular heat transfer enhancement revealed experimentally in naofluids suspensions is being investigated theoretically at the macro-scale level aiming at explaining the possible mechanisms that lead to such impressive experimental results. In particular, the possibility that Dual-Phase-Lagging heat conduction in the heterogeneous medium (nanofluid suspension) could have been the source of the excessively improved effective thermal conductivity of the suspension is shown to provide a viable explanation. The investigation of alternative possibilities is needed however prior to reaching an ultimate conclusion.

The Effect of Thermal Waves on Heat Transfer Enhancement in Nanofluid Suspensions

2008 ◽  
Author(s):  
Johnathan J. Vadasz
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Heat Conduction ◽  
Heat Transfer Enhancement ◽  
Hyperbolic Heat Conduction ◽  
Thermal Waves ◽  
Transfer Enhancement ◽  
Scale Level ◽  
Macro Scale ◽  
Wave Effects

The spectacular heat transfer enhancement revealed experimentally in nanofluids suspensions is being investigated theoretically at the macro-scale level aiming at explaining the possible mechanisms that lead to such impressive experimental results. In particular, the anticipation that thermal wave effects via hyperbolic heat conduction could have been the source of the excessively improved effective thermal conductivity of the suspension is shown to be impossible.

Enhancement of Thermal Conductivity by Using Polymer-Zeolite in Solid Adsorption Heat Pumps

1997 ◽  
Vol 119 (3) ◽  
pp. 627-629 ◽  
Author(s):  
E. J. Hu ◽  
D.-S. Zhu ◽  
X.-Y. Sang ◽  
L. Wang ◽  
Y.-K. Tan
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Heat Transfer Enhancement ◽  
Effective Thermal Conductivity ◽  
Heat Pumps ◽  
Synthesis Process ◽  
Transfer Enhancement ◽  
New Synthesis ◽  
Zeolite Particle ◽  
Enhancement Method

A thermal conductivity augmentation technology for zeolite beds has been studied in this paper. To enhance the effective thermal conductivity of zeolite, the zeolite particle was coated with a thermal polymer material in a new synthesis process. It was found that the effective thermal conductivity of the polymerzeolite was increased two to three times, while its adsorptive ability remains the same. The results of the experiment show that the polymer synthesis technique could be used as a heat transfer enhancement method to improve thermal conductivity among zeolite particles.

Influence of Inserting the Heat Pipe Into the MH Particle Bed on Refrigeration Performance

2011 ◽  
Author(s):  
Sangchul Bae ◽  
Eiji Morita ◽  
Keisuke Ishikawa ◽  
Yusuke Haruna ◽  
Masafumi Katsuta
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Carbon Fiber ◽  
Heat Pipe ◽  
Effective Thermal Conductivity ◽  
Refrigeration System ◽  
Transfer Enhancement ◽  
Heat Transfer Characteristics ◽  
Particle Bed ◽  
Cooling Part

In the refrigeration and air conditioning fields, the needs of energy conservation and renewable energy spread have become stronger recently. In this study, we aim at the development of the heat driven type metal hydride (abbr, MH) that can be driven by the low temperature exhausted heat or solar heat under 100°C. In order to commercialize this system, the heat transfer characteristics and the activation characteristics of MH particle bed must be more improved, and production cost must be more reduced. In this study, we use the two heat transfer enhancement methods for improving the low effective thermal conductivity of MH particle bed. One is by heat pipe (abbr., HP) and another is by brush type carbon fiber. HP is inserted into heat source part MH (abbr., MH1). By this method, we aim not only to enhance the heat transfer of MH1 particle bed but also to achieve the temperature uniformity of MH1 particle one. The effective thermal conductivity of cooling part MH (abbr., MH2) particle bed is enhanced by inserting the brush type carbon fiber. The influence of these heat transfer methods on our MH refrigeration system is estimated by measurement and calculation.

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.

PDMS nanocomposites for heat transfer enhancement in microfluidic platforms

Lab on a Chip ◽  
2014 ◽  
Vol 14 (17) ◽  
pp. 3419-3426 ◽  
Author(s):  
Pyshar Yi ◽  
Robiatun A. Awang ◽  
Wayne S. T. Rowe ◽  
Kourosh Kalantar-zadeh ◽  
Khashayar Khoshmanesh
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Heat Transfer Enhancement ◽  
Transfer Enhancement ◽  
Microfluidic Platforms

This work introduces a method to enhance the thermal conductivity of PDMS microfluidic platforms through the use of PDMS/Al2O3 nanocomposites.

Figure of Merit-Based Optimization Approach of Phase Change Material-based Composites for Portable Electronics Using Simplified Model

2021 ◽  
Author(s):  
Ayushman Singh ◽  
Srikanth Rangarajan ◽  
Leila Choobineh ◽  
Bahgat Sammakia
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Phase Change ◽  
Effective Thermal Conductivity ◽  
Phase Change Material ◽  
Figure Of Merit ◽  
Volume Fraction ◽  
Simplified Model ◽  
Transient Temperature ◽  
Change Material

Abstract This work presents an approach to optimally designing a composite with thermal conductivity enhancers (TCEs) infiltrated with phase change material (PCM) based on figure of merit (FOM) for thermal management of portable electronic devices. The FOM defines the balance between effective thermal conductivity and energy storage capacity. In present study, TCEs are in the form of a honeycomb structure. TCEs are often used in conjunction with PCM to enhance the conductivity of the composite medium. Under constrained composite volume, the higher volume fraction of TCEs improves the effective thermal conductivity of the composite, while it reduces the amount of latent heat storage simultaneously. The present work arrives at the optimal design of composite for electronic cooling by maximizing the FOM to resolve the stated trade-off. In this study, the total volume of the composite and the interfacial heat transfer area between the PCM and TCE are constrained for all design points. A benchmarked two-dimensional direct CFD model was employed to investigate the thermal performance of the PCM and TCE composite. Furthermore, assuming conduction-dominated heat transfer in the composite, a simplified effective numerical model that solves the single energy equation with the effective properties of the PCM and TCE has been developed. The effective thermal conductivity of the composite is obtained by minimizing the error between the transient temperature gradient of direct and simplified model by iteratively varying the effective thermal conductivity. The FOM is maximized to find the optimal volume fraction for the present design.

scholarly journals Effective thermal conductivity of the hair coat of Holstein cows in a tropical environment

2009 ◽  
Vol 38 (11) ◽  
pp. 2218-2223 ◽  
Author(s):  
Alex Sandro Campos Maia ◽  
Roberto Gomes da Silva ◽  
João Batista Freire de Souza Junior ◽  
Rosiane Batista da Silva ◽  
Hérica Girlane Tertulino Domingos
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Free Convection ◽  
Effective Thermal Conductivity ◽  
Tropical Environment ◽  
Holstein Cows ◽  
Hair Coat ◽  
Black And White ◽  
Low K

The objective of the present study was to assess the effective thermal conductivity of the hair coat (k ef, mW.m-1.K-1) of Holstein cows in a tropical environment, as related to conduction and radiation in the absence of free convection. The average k ef was 49.72 mW.m-1.K-1, about twice the conductivity of the air (26 mW.m-1.K-1) and much less than that of the hair fibres (260 mW.m-1.K-1). The low k ef values were attributed mainly to the small cross area of individual hairs, ρef/ρf (17.2% and 21.3% for black and white hairs, respectively). White coats were denser, with longer hairs and significantly higher k ef (53.15 mW.m-1.K-1) than that of the black hairs (49.25 mW.m-1.K-1). The heritability coefficient of the effective thermal conductivity was calculated as h²=0.18 the possibility was discussed of selecting cattle for increased heat transfer through the hair coat.

scholarly journals Design and Implementation of a Laboratory Equipment for Studying Heat Transfer by Conduction

2019 ◽  
Vol 11 (1) ◽  
pp. 153-156
Author(s):  
István Padrah ◽  
Judit Pásztor ◽  
Rudolf Farmos
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Heat Conduction ◽  
Thermal Conduction ◽  
Transfer Mechanism ◽  
Measuring Instrument ◽  
Heat Transfer Mechanism ◽  
Laboratory Equipment ◽  
Insulating Materials ◽  
Design And Implementation

Abstract Thermal conduction is a heat transfer mechanism. It is present in our everyday lives. Studying thermal conductivity helps us better understand the phenomenon of heat conduction. The goal of this paper is to measure the thermal conductivity of various materials and compare results with the values provided by the manufacturers. To achieve this we assembled a measuring instrument and performed measurements on heat insulating materials.

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