Thermal Conductivity of Metal Cloth Heat Pipe Wicks

1987 ◽  
Vol 109 (3) ◽  
pp. 775-781 ◽  
Author(s):  
J. R. Phillips ◽  
L. C. Chow ◽  
W. L. Grosshandler
Keyword(s):  
Thermal Conductivity ◽  
Heat Conduction ◽  
Heat Pipe ◽  
Effective Conductivity ◽  
Correction Term ◽  
Three Dimensional ◽  
Experimental Procedure ◽  
Conductivity Enhancement ◽  
Layer Contact ◽  
The Mean

Heat conduction through a metal cloth wick saturated with a fluid has been investigated. An apparatus used to measure thermal conductivity, in which the condition of wick packing geometry is carefully controlled, and the basic experimental procedure are described. Experimental results are presented and compared to a new mean-gap-conductance model based upon the wick geometry, and to the simple series model. The mean-gap-conductance model evaluates the effects of the mesh geometry, and with the addition of a correction term to account for three-dimensional effects and layer-to-layer contact, the effective conductivity can be accurately predicted. In addition, a correlation of the mean gap which directly includes three-dimensional and contact conductance effects is presented. The correlation predicts the data within 10 percent whereas the series model may be more than 40 percent in error. From a parametric study using the new model, theoretical limits on the maximum and minimum conductivity enhancement have been determined as a function of geometric parameters. The implications of the research on heat pipe wick design are discussed.

Heat Transport by Countercurrent Blood Vessels in the Presence of an Arbitrary Temperature Gradient

1990 ◽  
Vol 112 (2) ◽  
pp. 207-211 ◽  
Author(s):  
J. W. Baish
Keyword(s):  
Thermal Conductivity ◽  
Temperature Gradient ◽  
Vascular Tissue ◽  
Asymptotic Methods ◽  
Three Dimensional ◽  
Conductive Materials ◽  
Arbitrary Temperature ◽  
The Mean ◽  
Conductive Fibers ◽  
Arteries And Veins

This paper presents a three-dimensional analysis of the temperature field around a pair of countercurrent arteries and veins embedded in an infinite tissue that has an arbitrary temperature gradient along the axes of the vessels. Asymptotic methods are used to show that such vessels are thermally similar to a highly conductive fiber in the same tissue. Expressions are developed for the effective radius and thermal conductivity of the fiber so that it conducts heat at the same rate that the artery and vein together convect heat and so that its local temperature equals the mean temperature of the vessels. This result allows vascular tissue to be viewed as a composite of conductive materials with highly conductive fibers replacing the convective effects of the vasculature. By characterizing the size and thermal conductivity of these fibers, well-established methods from the study of composites may be applied to determine when an effective conductive model is appropriate for the tissue and vasculature as a whole.

Numerical Simulation of Thermal Conductivity of Nanofluids

2010 ◽  
Author(s):  
Jing Fan ◽  
Liqiu Wang
Keyword(s):  
Thermal Conductivity ◽  
Heat Conduction ◽  
Volume Fraction ◽  
Particle Volume Fraction ◽  
Interfacial Thermal Resistance ◽  
Thermal Conductivity Ratio ◽  
Radius Of Gyration ◽  
Particle Volume ◽  
Geometrical Structures ◽  
Conductivity Enhancement

The recent first-principle model shows a dual-phase-lagging heat conduction in nanofluids at the macroscale. The macroscopic heat-conduction behavior and the thermal conductivity of nanofluids are determined by their molecular physics and microscale physics. We examine numerically effects of particle-fluid thermal conductivity ratio, particle volume fraction, shape, aggregation, and size distribution on macroscale thermal properties for nine types of nanofluids, without considering the interfacial thermal resistance and dynamic processes on particle-fluid interfaces and particle-particle contacting surfaces. The particle radius of gyration and non-dimensional particle-fluid interfacial area in the unit cell are two very important parameters in characterizing the effect of particles’ geometrical structures on thermal conductivity of nanofluids. Nanofluids containing cross-particle networks have conductivity which practically reaches the Hashin-Shtrikman bounds. Moreover, particle aggregation influences the effective thermal conductivity only when the distance between particles is less than the particle dimension. Uniformly-sized particles are desirable for the conductivity enhancement, although to a limited extent.

Evaporation, Condensation, and Flow in an Idealized Micro Heat Pipe

2002 ◽  
Author(s):  
Jin Zhang ◽  
Harris Wong
Keyword(s):  
Thermal Conductivity ◽  
Heat Pipe ◽  
Effective Thermal Conductivity ◽  
Three Dimensional ◽  
Heat Pipes ◽  
Rigorous Analysis ◽  
Evaporation And Condensation ◽  
Micro Heat Pipe ◽  
Complicated Geometry ◽  
Micro Heat Pipes

Micro heat pipes have been used in cooling micro electronic components. However their effective thermal conductivity is low compared with that of conventional heat pipes. Due to the complexity of the coupled heat and mass transport, and to the complicated three-dimensional bubble geometry inside micro heat pipes, there is a lack of rigorous analysis. As a result, the relatively low effective thermal conductivity remains unexplained. We have conceptualized an idealized micro heat pipe that eliminates the complicated geometry, but retains the essential physics. Given the simplified geometry, many effects can be studied, such as thermocapillary flow, and evaporation and condensation physics. In this talk, we will present the flow field induced by evaporation.

Computational Evaluation of Effective Conductivity of Particulate Composites with Imperfect Interfaces

2009 ◽  
Vol 631-632 ◽  
pp. 35-40
Author(s):  
M. Zhang ◽  
Peng Cheng Zhai ◽  
Qing Jie Zhang
Keyword(s):  
Thermal Conductivity ◽  
Effective Thermal Conductivity ◽  
Effective Properties ◽  
Effective Conductivity ◽  
Three Dimensional ◽  
Particulate Composite ◽  
Imperfect Interface ◽  
Particulate Composites ◽  
Imperfect Interfaces ◽  
Volume Fractions

This paper is aimed to numerically evaluate the effective thermal conductivity of randomly distributed spherical particle composite with imperfect interface between the constituents. A numerical homogenization technique based on the finite element method (FEM) with representative volume element (RVE) was used to evaluate the effective properties with periodic boundary conditions. Modified random sequential adsorption algorithm (RSA) is applied to generate the three dimensional RVE models of randomly distributed spheres of identical size with the volume fractions up to 50%. Several investigations have been conducted to estimate the influence of the imperfect interfaces on the effective conductivity of particulate composite. Numerical results reveal that for the given composite, due to the existence of an interfacial thermal barrier resistance, the effective thermal conductivity depends not only on the volume fractions of the particle but on the particle size.

Review of Heat Conduction in Nanofluids

2011 ◽  
Vol 133 (4) ◽  
Author(s):  
Jing Fan ◽  
Liqiu Wang
Keyword(s):  
Thermal Conductivity ◽  
Brownian Motion ◽  
Heat Conduction ◽  
Empirical Parameter ◽  
Conductivity Enhancement ◽  
Potential Applications ◽  
Exciting Potential ◽  
Heat Conduction Process ◽  
Liquid Layering

Nanofluids—fluid suspensions of nanometer-sized particles—are a very important area of emerging technology and are playing an increasingly important role in the continuing advances of nanotechnology and biotechnology worldwide. They have enormously exciting potential applications and may revolutionize the field of heat transfer. This review is on the advances in our understanding of heat-conduction process in nanofluids. The emphasis centers on the thermal conductivity of nanofluids: its experimental data, proposed mechanisms responsible for its enhancement, and its predicting models. A relatively intensified effort has been made on determining thermal conductivity of nanofluids from experiments. While the detailed microstructure-conductivity relationship is still unknown, the data from these experiments have enabled some trends to be identified. Suggested microscopic reasons for the experimental finding of significant conductivity enhancement include the nanoparticle Brownian motion, the Brownian-motion-induced convection, the liquid layering at the liquid-particle interface, and the nanoparticle cluster/aggregate. Although there is a lack of agreement regarding the role of the first three effects, the last effect is generally accepted to be responsible for the reported conductivity enhancement. The available models of predicting conductivity of nanofluids all involve some empirical parameters that negate their predicting ability and application. The recently developed first-principles theory of thermal waves offers not only a macroscopic reason for experimental observations but also a model governing the microstructure-conductivity relationship without involving any empirical parameter.

Numerical Analysis of a Metal Hydride Reactor With Embedded Heat Pipes to Enhance Heat Transfer Characteristics

2009 ◽  
Author(s):  
Joon Hong Boo ◽  
Young Hark Park ◽  
Masafumi Katsuta ◽  
Sang Chul Bae
Keyword(s):  
Thermal Conductivity ◽  
Numerical Analysis ◽  
Heat Pipe ◽  
Metal Hydride ◽  
Three Dimensional ◽  
Heat Pipes ◽  
Thermal Control ◽  
Hydrogen Gas ◽  
Outer Diameter ◽  
Reactor Model

Numerical analysis was conducted for a heat pipe application in a metal hydride (MH) reactor for hydrogen gas storage. The hydriding and dehydriding characteristics of MH strongly depend on temperature and pressure. Due to its extremely low thermal conductivity however, it is very difficult to control the temperature of MH, especially when it is of vast bulk as in an MH reactor. This study deals with heat pipes embedded into the MH to increase the effective thermal conductivity of the system and thus to enhance the thermal control characteristics. The existing model was a brine-tube type MH reactor having cylindrical container with outer diameter of 76 mm and length of 1 m, which was partially filled with 8 to 10 kg of MH material. The hydriding and dehydriding processes occur at 10°C and 80°C, respectively. The heat-pipe type reactor model replaced the brine tubes and channels with copper-water heat pipes of the same dimensions. Three-dimensional numerical analysis predicted that the heat-pipe type MH reactor model enhanced thermal performance with faster response to the change of boundary conditions and higher degree of isothermal characteristics. Discussion is presented based on the numerical results of the two models compared with experimental results.

scholarly journals Experimental Methodology to Determine Thermal Conductivity of Nanofluids by Using a Commercial Transient Hot-Wire Device

2021 ◽  
Vol 12 (1) ◽  
pp. 329
Author(s):  
Jose I. Prado ◽  
Uxía Calviño ◽  
Luis Lugo
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Theoretical Model ◽  
Ethylene Glycol ◽  
Experimental Methodology ◽  
Transient Hot Wire ◽  
Hot Wire ◽  
Experimental Procedure ◽  
Transfer Processes ◽  
The Mean

The lack of a standard experimental procedure to determine thermal conductivity of fluids is noticeable in heat transfer processes from practical and fundamental perspectives. Since a wide variety of techniques have been used, reported literature data have huge discrepancies. A common practice is using manufactured thermal conductivity meters for nanofluids, which can standardize the measurements but are also somewhat inaccurate. In this study, a new methodology to perform reliable measurements with a recent commercial transient hot-wire device is introduced. Accordingly, some extensively studied fluids in the literature (water, ethylene glycol, ethylene glycol:water mixture 50:50 vol%, propylene glycol, and n-tetradecane) covering the range 0.100 to 0.700 W m−1 K−1 were used to check the device in the temperature range 283.15 to 333.15 K. Deviations between the collected data and the theoretical model, and repeatabilities and deviations between reported and literature values, were analyzed. Systematic deviations in raw data were found, and a correction factor depending on the mean thermal conductivity was proposed to operate with nanofluids. Considering all tested effects, the expanded (k = 2) uncertainty of the device was set as 5%. This proposed methodology was also checked with n-hexadecane and magnesium-oxide-based n-tetradecane nanofluids.

Lattice Boltzmann Modeling of Phonon Heat Conduction in Superlattice Structures

2010 ◽  
Author(s):  
Cristian J. San Marti´n ◽  
Amador M. Guzma´n ◽  
Rodrigo A. Escobar
Keyword(s):  
Thermal Conductivity ◽  
Free Path ◽  
Lattice Boltzmann ◽  
Phonon Dispersion ◽  
Effective Conductivity ◽  
Mean Free Path ◽  
One Dimension ◽  
The Mean ◽  
Superlattice Structures ◽  
Boltzmann Method

The results of temperature prediction and determination of effective thermal conductivity in periodic Si-Ge superlattice in one dimension, at length scale comparable to the mean free path are presented. Classical heat transfer models such as Fourier’s law do not represent what actually happens within electronic devices at these length scales. Phonon-border and phonon-interface scattering effects provide discontinuous jumps in temperature distribution when the mean free path is comparable with the device’s characteristic length, a relation given by the Knudsen number (Kn). For predicting the temperature within the periodic Si-Ge superlattice use is made of the lattice Boltzmann method in one dimension, using Debye’s model in the phonon dispersion relation. The predictions show that as Kn increases, so do the jumps at the borders, the same as at the interfaces. The prediction also shows that the effective conductivity of the Si-Ge superlattice decreases as Kn and the number of layers of material increase, and that keff decreases as the magnitude of p increases, a factor that allows heat flow between one layer and another. Use of gray LBM leads to good approximations of the actual temperature field and thermal conductivity values for the superlattice materials model when the physics of phonons established by Debye’s model is used.

Sign in / Sign up

Export Citation Format

Share Document