Measuring Thermal Conductivity of Unsaturated Sand under Different Temperatures and Stress Levels Using a Suction-Controlled Thermo-Mechanical Method

The objective of this work is the enhancement of metal-to-metal bonding to provide high thermal conductivity together with electrical insulation, to be used as heat sinks at room and cryogenic temperatures. High thermal conductive metal (copper) and epoxy resin (Stycast 2850FT) were used in this study, with the latter also providing the required electrical insulation. The copper surface was irradiated with laser to induce micro- and nano-patterned structures that result in an improvement of the adhesion between the epoxy and the copper. Thus, copper-to-copper bonding strength was characterized by means of mechanical tensile shear tests. The effect of the laser processing on the thermal conductivity properties of the Cu/epoxy/Cu joint at different temperatures, from 10 to 300 K, is also reported. Using adequate laser parameters, it is possible to obtain high bonding strength values limited by cohesive epoxy fracture, together with good thermal conductivity at ambient and cryogenic temperatures.

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Influence of Temperature and Moisture Content on Thermal Performance of Green Roof Media

Energies ◽

10.3390/en14092421 ◽

2021 ◽

Vol 14 (9) ◽

pp. 2421

Author(s):

Bohan Shao ◽

Caterina Valeo ◽

Phalguni Mukhopadhyaya ◽

Jianxun He

Keyword(s):

Thermal Conductivity ◽

Moisture Content ◽

Green Roof ◽

Green Roofs ◽

Power Functions ◽

Thick Substrate ◽

Different Temperatures ◽

Test Cells ◽

Substrate Moisture ◽

Phase Transition Zone

The influence of moisture content on substrate thermal conductivity at different temperatures was investigated for four different commercially available substrates for green roofs. In the unfrozen state, as moisture content increased, thermal conductivity increased linearly. In the phase transition zone between +5 and −10 °C, as temperature decreased, thermal conductivity increased sharply during the transition from water to ice. When the substrate was frozen, thermal conductivity varied exponentially with substrate moisture content prior to freezing. Power functions were found between thermal conductivity and temperature. Two equally sized, green roof test cells were constructed and tested to compare various roof configurations including a bare roof, varying media thickness for a green roof, and vegetation. The results show that compared with the bare roof, there is a 75% reduction in the interior temperature’s amplitude for the green roof with 150 mm thick substrate. When a sedum mat was added, there was a 20% reduction in the amplitude of the inner temperature as compared with the cell without a sedum mat.

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Thermal conductivity investigations of granular and powdered silica aerogels at different temperatures and pressures

Energy and Buildings ◽

10.1016/j.enbuild.2016.03.008 ◽

2016 ◽

Vol 118 ◽

pp. 226-231 ◽

Cited By ~ 17

Author(s):

Gaosheng Wei ◽

Lixin Wang ◽

Chao Xu ◽

Xiaoze Du ◽

Yongping Yang

Keyword(s):

Thermal Conductivity ◽

Silica Aerogels ◽

Different Temperatures

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Dislocation Generation and Crack Propagation in Metals Examined in Molecular Dynamics Simulations

MRS Proceedings ◽

10.1557/proc-278-173 ◽

1992 ◽

Vol 278 ◽

Cited By ~ 6

Author(s):

J. A. Rifkin ◽

C. S. Becquart ◽

D. Kim ◽

P. C. Clapp

Keyword(s):

Crack Propagation ◽

Atomistic Simulations ◽

Many Body ◽

Dislocation Generation ◽

Embedded Atom ◽

Stress Levels ◽

Different Temperatures ◽

The Many ◽

Dynamics Simulations ◽

Many Body Interactions

AbstractWe have carried out a series of atomistic simulations on arrays of about 10,000 atoms containing an atomically sharp crack and subjected to increasing stress levels. The ordered stoichiometric alloys B2 NiAl, B2 RuAl and A15 Nb3AI have been studied at different temperatures and stress levels, as well as the elements Al, Ni, Nb and Ru. The many body interactions used in the simulations were derived semi-empirically, using techniques related to the Embedded Atom Method. Trends in dislocation generation rates and crack propagation modes will be discussed and compared to experimental indications where possible, and some of the simulations will be demonstrated in the form of computer movies.

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Interfacial instabilities in plane Poiseuille flow of two stratified viscoelastic fluids with heat transfer. Part 1. Evolution equation and stability analysis

Journal of Fluid Mechanics ◽

10.1017/s0022112095003491 ◽

1995 ◽

Vol 299 ◽

pp. 241-265 ◽

Cited By ~ 3

Author(s):

Sang W. Joo

Keyword(s):

Heat Transfer ◽

Thermal Conductivity ◽

Stability Analysis ◽

Evolution Equation ◽

Vertical Channel ◽

Viscoelastic Fluids ◽

Lubrication Approximation ◽

Plane Poiseuille Flow ◽

Interfacial Instabilities ◽

Different Temperatures

An evolution equation is derived that describes the nonlinear development of the interface between two viscoelastic fluids flowing, under the action of imposed pressure gradient and gravity, in a vertical channel. The channel walls are kept at different temperatures, resulting in heat transfer across the layers. The equation, based on the lubrication approximation, models the effects of stratifications in density, viscosity, elasticity, shear thinning, and thermal conductivity. It also describes the capillary and thermocapillary effects, as well as the sensitivity of viscosities to temperature. Linear-stability analysis is performed based on the evolution equation to understand the competing effects of viscous, elastic, and Marangoni instabilities. Particular attention is paid to the active control of the interfacial instabilities through the thermocapillarity.

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Effects of sonication duration and nanoparticles concentration on thermal conductivity of silica-ethylene glycol nanofluid under different temperatures: An experimental study

Powder Technology ◽

10.1016/j.powtec.2020.03.058 ◽

2020 ◽

Vol 367 ◽

pp. 464-473 ◽

Cited By ~ 14

Author(s):

Yicheng Li ◽

Rasool Kalbasi ◽

Quyen Nguyen ◽

Masoud Afrand

Keyword(s):

Thermal Conductivity ◽

Experimental Study ◽

Ethylene Glycol ◽

Different Temperatures ◽

Nanoparticles Concentration

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Stress Relaxation Aging Behavior and Constitutive Modelling of AA7150-T7751 under Different Temperatures, Initial Stress Levels and Pre-Strains

Metals ◽

10.3390/met9111215 ◽

2019 ◽

Vol 9 (11) ◽

pp. 1215 ◽

Cited By ~ 1

Author(s):

Yixian Cai ◽

Lihua Zhan ◽

Yongqian Xu ◽

Chunhui Liu ◽

Jianguang Wang ◽

...

Keyword(s):

Activation Energy ◽

Stress Relaxation ◽

Initial Stress ◽

Stress Level ◽

Relaxation Behavior ◽

Average Error ◽

Aging Behavior ◽

Stress Relaxation Behavior ◽

Stress Levels ◽

Different Temperatures

Age forming is an advanced manufacture technology for forming large aluminum panels. Temperature, initial stress level and pre-strains have a great effect on the formability and performance. The stress relaxation aging behavior of AA7150-T7751 under different temperatures, initial stress levels and pre-strains was studied through stress relaxation tests, tensile tests and TEM observations. The results show that the formability can be improved with the increase of temperature, initial stress levels and pre-strains. Deformation mechanisms during stress relaxation of the material were analyzed on the basis of creep stress exponent and apparent activation energy. The aging precipitates of the studied alloy were not sensitive to the age forming conditions, but drastically coarsened at over aging temperature, which decreased the mechanical properties. In addition, the relationship between stress relaxation behavior and aging strengthening is discussed. Based on the dislocation theory and the modified Arrhenius equation, a stress relaxation constitutive equation considering the initial mobile dislocation density and temperature dependent activation energy was established. This model can predict very well the stress relaxation behavior under various temperature, stress level and pre-strain conditions, with an average error of 2%.

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Temperature Dependence of Thermal Conductivity of Amorphous and Crystal Thin Film by Molecular Dynamics Simulation

ASME 5th International Conference on Nanochannels, Microchannels, and Minichannels ◽

10.1115/icnmm2007-30085 ◽

2007 ◽

Cited By ~ 1

Author(s):

Zhengxing Huang ◽

Zhenan Tang ◽

Suyuan Bai ◽

Jun Yu

Keyword(s):

Thin Film ◽

Thin Films ◽

Thermal Conductivity ◽

Integrated Circuits ◽

Temperature Dependence ◽

Amorphous Materials ◽

Dynamics Simulation ◽

Amorphous Sio2 ◽

Film Boundary ◽

Different Temperatures

For crystal materials, thermal conductivity (TC) is proportional to T3 at low temperatures and to T−1 at high temperatures. TCs of most amorphous materials decrease with the decreasing temperatures. If a material is thin film, boundary will influence the TC and then influence the temperature dependence. In this paper, we calculate the TC of crystal and amorphous SiO2 thin films, which is a commonly used material in micro devices and Integrated Circuits, by NEMD simulations. The calculation temperatures are from 100K to 700K and the thicknesses are from 2nm to 8nm. TCs of crystal thin films reach their peak values at different temperatures for different thicknesses. The smaller thickness the larger peak values obtained. But for amorphous thin films, the results show that the temperature dependence of thin films is the same as bulk materials and not relative to their thicknesses. The obtained temperature dependence of the thin films is consistent with some previous measurements and the theory predictions.

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Measurement of the Thermophysical Properties of Anisotropic Insulation Materials with Consideration of the Effect of Thermal Contact Resistance

Materials ◽

10.3390/ma13061353 ◽

2020 ◽

Vol 13 (6) ◽

pp. 1353 ◽

Cited By ~ 2

Author(s):

Dongxu Han ◽

Kai Yue ◽

Liang Cheng ◽

Xuri Yang ◽

Xinxin Zhang

Keyword(s):

Thermal Conductivity ◽

Thermal Resistance ◽

Contact Resistance ◽

Thermal Contact Resistance ◽

Thermal Contact ◽

Thermal Contact Conductance ◽

Maximum Deviation ◽

Insulation Materials ◽

Steady State Method ◽

Different Temperatures

A novel method involving the effect of thermal contact resistance (TCR) was proposed using a plane heat source smaller than the measured samples for improving measurement accuracy of the simultaneous determination of in-plane and cross-plane thermal conductivities and the volumetric heat capacity of anisotropic materials. The heat transfer during the measurement process was mathematically modeled in a 3D Cartesian coordinate system. The temperature distribution inside the sample was analytically derived by applying Laplace transform and the variables separation method. A multiparameter estimation algorithm was developed on the basis of the sensitivity analysis of the parameters to simultaneously estimate the measured parameters. The correctness of the algorithm was verified by performing simulation experiments. The thermophysical parameters of insulating materials were experimentally measured using the proposed method at different temperatures and pressures. Fiber glass and ceramic insulation materials were tested at room temperature. The measured results showed that the relative error was 1.6% less than the standard value and proved the accuracy of the proposed method. The TCRs measured at different pressures were compared with those obtained using the steady-state method, and the maximum deviation was 8.5%. The thermal conductivity obtained with the contact thermal resistance was smaller than that without the thermal resistance. The measurement results for the anisotropic silica aerogels at different temperatures and pressures revealed that the thermal conductivity and thermal contact conductance increased as temperature and pressure increased.

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Experimental Study of Heat Conduction in Aqueous Suspensions of Aluminum Oxide Nanoparticles

Journal of Heat Transfer ◽

10.1115/1.2945886 ◽

2008 ◽

Vol 130 (9) ◽

Cited By ~ 32

Author(s):

Y. Sungtaek Ju ◽

Jichul Kim ◽

Ming-Tsung Hung

Keyword(s):

Thermal Conductivity ◽

Aluminum Oxide ◽

Average Particle Size ◽

Oxide Nanoparticles ◽

Average Particle ◽

Aluminum Oxide Nanoparticles ◽

Aqueous Suspensions ◽

Effective Medium Model ◽

Transient Hot Wire Technique ◽

Different Temperatures

We report measurements of the thermal conductivity of aqueous suspensions of aluminum oxide nanoparticles with nominal diameters of 20nm, 30nm, and 45nm and at volume concentrations up to 10%. Potential complications in the pulsed transient hot-wire technique for characterizing nanofluids are examined, which motivate the development of a microhot strip setup with a small thermal time constant. The average particle size is monitored for samples subjected to different durations of sonication and the thermal conductivity is determined at two different temperatures for each of the samples. The present data do not reveal any anomalous enhancement in the thermal conductivity previously reported for comparable nanofluids. The concentration dependence of the thermal conductivity can be explained using the conventional effective medium model with a physically reasonable set of parameters.

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