COMPUTATION OF THE EFFECTIVE CONDUCTIVITY OF THREE-DIMENSIONAL ORDERED COMPOSITES WITH A THERMALLY-CONDUCTING DISPERSED PHASE

1998 ◽  
Author(s):  
Manuel Ernani C. Cruz
Keyword(s):  
Effective Conductivity ◽  
Three Dimensional ◽  
Dispersed Phase ◽  
Thermally Conducting

scholarly journals Nonlinear effects of locally heterogeneous hydraulic conductivity fields on regional stream–aquifer exchanges

2015 ◽  
Vol 19 (11) ◽  
pp. 4531-4545 ◽  
Author(s):  
J. Zhu ◽  
C. L. Winter ◽  
Z. Wang
Keyword(s):  
Groundwater Flow ◽  
Effective Conductivity ◽  
Model Simulation ◽  
Three Dimensional ◽  
Small Scale ◽  
Heihe River ◽  
Effective Parameters ◽  
Aquifer Systems ◽  
Basin Scale ◽  
Local Grid

Abstract. Computational experiments are performed to evaluate the effects of locally heterogeneous conductivity fields on regional exchanges of water between stream and aquifer systems in the Middle Heihe River basin (MHRB) of northwestern China. The effects are found to be nonlinear in the sense that simulated discharges from aquifers to streams are systematically lower than discharges produced by a base model parameterized with relatively coarse effective conductivity. A similar, but weaker, effect is observed for stream leakage. The study is organized around three hypotheses: (H1) small-scale spatial variations of conductivity significantly affect regional exchanges of water between streams and aquifers in river basins, (H2) aggregating small-scale heterogeneities into regional effective parameters systematically biases estimates of stream–aquifer exchanges, and (H3) the biases result from slow paths in groundwater flow that emerge due to small-scale heterogeneities. The hypotheses are evaluated by comparing stream–aquifer fluxes produced by the base model to fluxes simulated using realizations of the MHRB characterized by local (grid-scale) heterogeneity. Levels of local heterogeneity are manipulated as control variables by adjusting coefficients of variation. All models are implemented using the MODFLOW (Modular Three-dimensional Finite-difference Groundwater Flow Model) simulation environment, and the PEST (parameter estimation) tool is used to calibrate effective conductivities defined over 16 zones within the MHRB. The effective parameters are also used as expected values to develop lognormally distributed conductivity (K) fields on local grid scales. Stream–aquifer exchanges are simulated with K fields at both scales and then compared. Results show that the effects of small-scale heterogeneities significantly influence exchanges with simulations based on local-scale heterogeneities always producing discharges that are less than those produced by the base model. Although aquifer heterogeneities are uncorrelated at local scales, they appear to induce coherent slow paths in groundwater fluxes that in turn reduce aquifer–stream exchanges. Since surface water–groundwater exchanges are critical hydrologic processes in basin-scale water budgets, these results also have implications for water resources management.

scholarly journals Oxidization resistance and sorption properties of oleogels as new-generation fatty systems

2021 ◽  
pp. 89-95
Author(s):  
P.О. Nekrasov ◽  
◽  
N.A. Tkachenko ◽  
О.P. Nekrasov ◽  
О.M. Gudz ◽  
...  
Keyword(s):  
Sunflower Seed ◽  
Three Dimensional ◽  
Scientific Basis ◽  
Tocopherol Content ◽  
Sorption Properties ◽  
Dimensional Structure ◽  
Dispersed Phase ◽  
Technological Parameters ◽  
High Oleic Sunflower Oil ◽  
New Generation

Fats as complex mixtures of acylglycerols with lipid and non-lipid substances are an integral part of human nutrition. The presence of acylglycerols of trans-isomers of fatty acids causes many cardiovascular diseases and metabolic disorders. A promising approach to solving the problem of minimizing the content of these undesirable compounds in food recipes is to create a new generation of fat systems, oleogels, which are the subject of this study. High-oleic sunflower oil was used as a dispersion medium of oleogels, which allows obtaining systems with increased resistance to oxidation, as opposed to the oils of traditional kinds. Sunflower seed wax and tocopherols are chosen as a dispersed phase of these fatty systems. The choice of these components was based on their properties to create a three-dimensional structure in oleogels with specified thermomechanical characteristics. Currently, there is a lack of information on the influence of the content of the dispersed phase on the technological parameters of oleogels, namely oxidative resistance and sorption properties. The purpose of the presented work was to study these features of oleogels and establish their dependences on their composition. To solve this problem, the yield surface method is used in the work. The unknown values of the parameter vector were determined by using regression analysis algorithms. Deviation functionality was minimized by finding the appropriate combinations of the experimental series of predictors. A mathematical model was developed which allows predicting oxidative stability and sorption properties of oleogels based on the data on their composition. The suitable mass fractions of the components of the dispersed phase of oleogels have been determined as follows: tocopherol content is 0.10–0.14 wt.% and the sunflower seed wax content is 1.8–4.0 wt.%. The results obtained can serve as a scientific basis for the development of technology for the industrial production of oleogels as new generation fatty systems.

Transferred-Substrate InGaAsP-Based Thermionic Emission Coolers

2000 ◽  
Author(s):  
Christopher J. LaBounty ◽  
Gerry Robinson ◽  
Patrick Abraham ◽  
Ali Shakouri ◽  
John E. Bowers
Keyword(s):  
Thermal Resistance ◽  
Three Dimensional ◽  
Thermionic Emission ◽  
Copper Film ◽  
Cooling Power ◽  
Material System ◽  
Inp Substrate ◽  
Order Of Magnitude ◽  
Thin Copper Film ◽  
Thermally Conducting

Abstract Most optoelectronic devices are based on III-V semiconductors such as the InP/InGaAsP material system. Solid state refrigerators based on the same material system can be monolithically integrated with optoelectronics. Thermionic emission cooling in InGaAsP-based heterostructures has been shown experimentally to provide cooling power densities of several 100 W/cm2. Cooling by several degrees across thin films on the order of a micron thick has been demonstrated. Thermionic emission of hot electrons over heterobarriers allows for enhanced cooling power beyond what is possible from the bulk thermoelectric properties. The thermal resistance of the InP substrate between the hot side of the thin film cooler and the heat sink is found to be a limitation in cooler performance. Several possibilities are examined for replacing the InP substrate with a higher thermally conducting one such as silicon, copper, or even diamond, and a process for substrate transfer to a thin copper film has been developed. Three-dimensional simulations predict an order of magnitude improvement in the thermal resistance of the substrate. Experimental results of packaged InGaAsP coolers with copper substrates will be discussed.

scholarly journals Numerical Simulation of Mixed Convective Flow Over a Three-Dimensional Horizontal Backward Facing Step

2005 ◽  
Vol 127 (9) ◽  
pp. 1027-1036 ◽  
Author(s):  
J. G. Barbosa Saldana ◽  
N. K. Anand ◽  
V. Sarin
Keyword(s):  
Convective Flow ◽  
Three Dimensional ◽  
Step Length ◽  
Expansion Ratio ◽  
Step Height ◽  
Streamwise Direction ◽  
Backward Facing Step ◽  
Thermal Features ◽  
Mixed Convective Flow ◽  
Thermally Conducting

Laminar mixed convective flow over a three-dimensional horizontal backward-facing step heated from below at a constant temperature was numerically simulated using a finite volume technique and the most relevant hydrodynamic and thermal features for air flowing through the channel are presented in this work. The channel considered in this work has an aspect ratio AR=4, and an expansion ratio ER=2, while the total length in the streamwise direction is 52 times the step height (L=52s) and the step length is equal to 2 times the step height (l=2s). The flow at the duct entrance was considered to be hydrodynamically fully developed and isothermal. The bottom wall of the channel was subjected to a constant high temperature while the other walls were treated to be adiabatic. The step was considered to be a thermally conducting block.

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.

Propagation of three-dimensional Alfvén waves in a stratified, thermally conducting solar wind

1996 ◽  
Vol 101 (A11) ◽  
pp. 24443-24456 ◽  
Author(s):  
S. Orlando ◽  
Y.-Q. Lou ◽  
R. Rosner ◽  
G. Peres
Keyword(s):  
Solar Wind ◽  
Three Dimensional ◽  
Alfven Waves ◽  
Alfvén Waves ◽  
Thermally Conducting

Numerical Analysis of Junction Point Pressure during Droplet Formation in Y-Junction Microchannel

2013 ◽  
Vol 481 ◽  
pp. 241-246
Author(s):  
Zhao Miao Liu ◽  
Li Kun Liu
Keyword(s):  
Numerical Simulation ◽  
Three Dimensional ◽  
Droplet Formation ◽  
Continuous Phase ◽  
Contact Angles ◽  
Junction Point ◽  
Dispersed Phase ◽  
Wetting Property ◽  
Point Pressure ◽  
Pressure Changes

Junction point pressure changes during droplet formation in Y-junction microchannels with differed Y-angles, wetting property and capillary number of the liquid by using a three dimensional numerical simulation. The pressure of the junction point fluctuates throughout the droplet formation process, and it can be used to depict exactly and directly different stages of droplet in microchannels. And the pressure of junctions with different Y-angles of microchannel, different contact angles of dispersed phase with the surface, and different capillary numbers of continuous phase could thus be investigated via the droplet formation mechanism.

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.

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