Role of heat flow direction, monolayer film thickness, and periodicity in controlling thermal conductivity of a Si–Ge superlattice system

2009 ◽  
Vol 105 (1) ◽  
pp. 013541 ◽  
Author(s):  
Vikas Samvedi ◽  
Vikas Tomar
Keyword(s):  
Thermal Conductivity ◽  
Heat Flow ◽  
Film Thickness ◽  
Flow Direction ◽  
Monolayer Film ◽  
Heat Flow Direction

scholarly journals Composites with Excellent Insulation and High Adaptability for Lightweight Envelopes

Energies ◽  
2018 ◽  
Vol 12 (1) ◽  
pp. 53 ◽  
Author(s):  
Liang Guo ◽  
Wenbin Tong ◽  
Yexin Xu ◽  
Hong Ye
Keyword(s):  
Thermal Conductivity ◽  
Effective Thermal Conductivity ◽  
Flow Direction ◽  
Base Material ◽  
Core Material ◽  
Insulation Materials ◽  
The Core ◽  
Cross Section Area ◽  
Heat Flow Direction ◽  
Section Area

Lightweight insulation materials are widely used in lightweight buildings, cold-chain vehicles and containers. A kind of insulation composite, which can combine the super insulation of state-of-the-art insulation materials or structures and the machinability or adaptability of traditional insulation materials, was proposed. The composite consists of two components, i.e., polyurethane (PU) foam as the base material and vacuum insulation panel (VIP) or silica aerogel as the core material. The core material is in plate shape and covered with the base material on all sides. The thermal conductivity of the core material is nearly one order lower than that of the base material. The effective thermal conductivity of the insulation composite was explored by simulation. Simulation results show that the effective thermal conductivity of the composite increases with the increase of the thermal conductivity of the core material. The effective thermal conductivities of the composites decrease with the increase of the cross-section area of the core material perpendicular to heat flow direction and the thicknesses of the core material parallel with heat flow direction. These rules can be elucidated by a series-parallel mode thermal resistance network method, which was verified by the measured results. For composite with a VIP as the core material, when the cross-section area and thickness of the VIP are respectively larger than 60% and 21% of the composite, the composite’s effective thermal conductivity can be 50% or less than that of the base material. Simulated heat loss of the envelope adopting the insulation composites with VIP as the core material is nearly a half of that of the envelope adopting traditional insulation materials.

scholarly journals Influence of heat flow direction on solder ball interfacial layer

2018 ◽  
Vol 69 (4) ◽  
pp. 305-310 ◽  
Author(s):  
Alexandr Otáhal ◽  
Ivan Szendiuch
Keyword(s):  
Heat Flow ◽  
Flow Direction ◽  
Intermetallic Layer ◽  
Point Of View ◽  
Infrared Heating ◽  
Root Mean Square Roughness ◽  
Sac305 Solder ◽  
Heat Flow Direction ◽  
Solder Balls ◽  
Bga Package

Abstract This paper deals with the research of an intermetallic layer of SAC305 solder balls soldered from three directions of the heat flow in the ball-attach process for BGA package. From the point of view of the heat flow direction, the samples were soldered by infrared heating. The heat sources were placed on the top, bottom and both lateral sides of the BGA package. After the solder balls-attach process, a metallographic cross-section was performed, followed by selective etching to visualize the relief of the intermetallic layer. Images of the interfacial between the solder and solder pad were taken from the created samples, followed by measurement of the average thickness and root mean square roughness of the intermetallic layer. The results showed changes in the intermetallic layer. The largest thickness of the intermetallic layer was observed on samples soldered from the top and both sides. Soldering with the bottom infrared heater resulted to the smallest thickness of the intermetallic layer. The same trend was in the roughness of the IMC layer. The greatest roughness was found for samples soldered by the top and both side heaters. The top soldered samples exhibit the smallest roughness.

scholarly journals Orientation and Microstructure Evolution of Al-Al2Cu Regular Eutectic Lamellar Bifurcating in an Abruptly Changing Velocity under Directional Solidification

Materials ◽  
2020 ◽  
Vol 13 (4) ◽  
pp. 1004
Author(s):  
Ka Gao ◽  
Zan Zhang ◽  
Junliang Zhao ◽  
Dejian Sun ◽  
Fu Wang
Keyword(s):  
Heat Flow ◽  
Directional Solidification ◽  
Flow Direction ◽  
Solidification Rate ◽  
Lateral Diffusion ◽  
Interfacial Instability ◽  
Growth Orientation ◽  
Al2cu Phase ◽  
Heat Flow Direction ◽  
Solidification Microstructures

In an abruptly changing velocity under directional solidification, microstructures and the growth orientation of Al-Al2Cu eutectic lamellar were characterized. The change in solidification rate led to an interfacial instability, which results in a bifurcation of the eutectic lamella into new, refined lamellae. The growth orientation of the eutectic Al2Cu phase was also only in its (001) direction and more strongly oriented to the heat flow direction. The results suggest that the eutectic lamellar Al-Al2Cu bifurcation and the spacing adjustment may be caused by the rate determining lateral diffusion of the solutes after interfacial instability.

Thermal Characterization of High-Density Interconnects in the Form of Equivalent Thermal Conductivity

2009 ◽  
Author(s):  
Wataru Nakayama ◽  
Katsuhiro Koizumi ◽  
Takashi Fukue ◽  
Masaru Ishizuka ◽  
Tatsuya Nakajima ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Heat Conduction ◽  
Heat Flow ◽  
Numerical Solutions ◽  
Flow Direction ◽  
Thermal Characterization ◽  
High Density ◽  
Cooperative Effort ◽  
Equivalent Thermal Conductivity ◽  
Metal Pattern

The issue addressed in the present study is how to model wiring substrates to perform heat conduction analysis on moderate computational resource. Equivalent thermal conductivity is a convenient measure in thermal modeling. However, its notion needs re-examination where higher accuracy of heat conduction analysis is pursued. Proposed is a scheme where the indexed volumetric metal contents are used to estimate the equivalent conductivity of representative volume element (RVE). The index is designed to reflect the effect of metal pattern on heat flow through RVE. In order to illustrate the core concept we report the analysis performed on template models of high-density interconnect (HDI) substrates. The element of HDI contains copper in several forms; through-via, continuous plane, and cross wires. Five heat flow directions are assumed; two are linear and three are right-angled turn. From combinations of the metal pattern and the heat flow direction twenty five templates are created, then, they are subjected to detailed numerical analysis. The values of equivalent thermal conductivity derived from the numerical solutions reveal that the gross volumetric metal content is totally inadequate as a parameter of thermal characterization. The paper also outlines the overall organization of our analysis system which is being developed in an industry-academia cooperative effort under the auspices of JSME.

The importance of heat flow direction for reproducible and homogeneous freezing of bulk protein solutions

2013 ◽  
Vol 29 (5) ◽  
pp. 1212-1221 ◽  
Author(s):  
Miguel A. Rodrigues ◽  
Gustavo Balzan ◽  
Mónica Rosa ◽  
Diana Gomes ◽  
Edmundo G. de Azevedo ◽  
...  
Keyword(s):  
Heat Flow ◽  
Flow Direction ◽  
Protein Solutions ◽  
Heat Flow Direction ◽  
Homogeneous Freezing

scholarly journals Preparation of Anisotropic Aerogels with Pristine Graphene by Heat Flow and Study of Their Effects on Heat Transfer in Paraffin

Nanomaterials ◽  
2019 ◽  
Vol 9 (11) ◽  
pp. 1622 ◽  
Author(s):  
Jinhui Huang ◽  
Buning Zhang ◽  
Ming He ◽  
Xue Huang ◽  
Guoqiang Yin ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Heat Flow ◽  
Flow Direction ◽  
Structural Characteristics ◽  
Low Cost ◽  
Microwave Treatment ◽  
Thermal Conductivity Enhancement ◽  
Graphene Sheets ◽  
Pristine Graphene ◽  
Conductivity Enhancement

In this study, anisotropic graphene/graphene oxide (GO) aerogels (AGAs) were obtained by freeze-drying after direct participation of pristine graphene in the self-assembly of anisotropic gel by the heat flow method. After vacuum microwave treatment, the physical, chemical and structural characteristics of the AGAs were investigated. The results show that AGAs, in which the internal graphene sheets are parallel to the heat flow direction, are successfully prepared. After microwave treatment, the amount of oxygen and nitrogen reduces significantly and the sp2 domain increases. However, at the same time, many fragments and holes are generated in the graphene sheets. The effects of AGAs on the phase transition of paraffin is studied, and the results show that the melting enthalpy, solidification enthalpy and initial melting temperature of AGA/paraffin composites decreases as the GO content in the AGAs increases, whereas the melting range, solidifying range and subcooling degree increases. The highest axial thermal conductivity of the AGA/paraffin composite is 1.45 W/(mK), and the thermal conductivity enhancement efficiency is 884% (AGA content was 0.53 vol %). Compared with previously investigated, similar AGA/paraffin composites, the aerogels fabricated in this study have the obvious advantages of a simple fabrication process, a low cost and a high thermal conductivity enhancement efficiency. These aerogels possess the potential for application in phase-change energy storage (PES), thermal energy management and other fields.

scholarly journals Analysis of Temperature Field, Heat and Fluid Flow of Two-Phase Zone Continuous Casting Cu–Sn Alloy Wire

2016 ◽  
Vol 16 (1) ◽  
pp. 33-40 ◽  
Author(s):  
J. Luo ◽  
X. Liu ◽  
X. Wang
Keyword(s):  
Temperature Field ◽  
Fluid Flow ◽  
Heat Flow ◽  
Continuous Casting ◽  
Flow Direction ◽  
Phase Zone ◽  
Two Phase ◽  
Alloy Wire ◽  
Heat Flow Direction ◽  
Heat And Fluid Flow

Abstract Cu–4.7 wt. % Sn alloy wire with Ø10 mm was prepared by two-phase zone continuous casting technology, and the temperature field, heat and fluid flow were investigated by the numerical simulated method. As the melting temperature, mold temperature, continuous casting speed and cooling water temperature is 1200 °C, 1040 °C, 20 mm/min and 18 °C, respectively, the alloy temperature in the mold is in the range of 720 °C–1081 °C, and the solid/liquid interface is in the mold. In the center of the mold, the heat flow direction is vertically downward. At the upper wall of the mold, the heat flow direction is obliquely downward and deflects toward the mold, and at the lower wall of the mold, the heat flow deflects toward the alloy. There is a complex circular flow in the mold. Liquid alloy flows downward along the wall of the mold and flows upward in the center.

Thermoelectric Power of Gradient Fex(Al2O3)100-x Composite Films

2015 ◽  
Vol 233-234 ◽  
pp. 694-698 ◽  
Author(s):  
Oleg Stognei ◽  
Ahmed Al-Maliki ◽  
Alexander Sitnikov ◽  
Vladimir Makagonov
Keyword(s):  
Heat Flow ◽  
Temperature Gradient ◽  
Thermoelectric Power ◽  
Concentration Gradient ◽  
Flow Direction ◽  
Composite Films ◽  
Sputter Deposition ◽  
Deposition Technique ◽  
Opposite Edge ◽  
Heat Flow Direction

Nanocomposite Fex(Al2O3)100-x films with concentration gradient along the long axis of the samples (40 mm) have been obtained by sputter deposition technique and investigated. Based on the electric and magnetoresistive investigations the gradient Fex(Al2O3)100-x samples in which concentration of one edge of the sample is smaller than concentration of a percolation threshold while concentration of opposite edge of this sample is upper the threshold have been determined. Influence of the heat flow direction on the thermoelectric power of the gradient samples has been investigated. Hysteresis of the thermoelectric power is observed when temperature gradient direction is changed.

scholarly journals Advanced Modeling of Enclosed Airspaces to Determine Thermal Resistance for Building Applications

Energies ◽  
2021 ◽  
Vol 14 (22) ◽  
pp. 7772
Author(s):  
Hamed H. Saber ◽  
David W. Yarbrough
Keyword(s):  
Heat Flow ◽  
Aspect Ratio ◽  
Thermal Resistance ◽  
Flow Direction ◽  
Total Heat Transfer ◽  
Temperature Variations ◽  
One Dimensional ◽  
Heat Flow Direction ◽  
R Value ◽  
The Impact

Enclosed airspaces to reduce heat flow have been recognized for well over 100 years. Airspaces with one or more reflective surfaces define reflective insulation (RI) assemblies, a product type used in walls, roofs, windows with multiple panes, curtain walls and skylights. The thermal resistance (R value) of airspaces depends on the emittance of all surfaces, airspace dimensions and orientation, heat flow direction and surfaces temperatures. The modeling of RI now includes CFD coupled with radiation to quantify the total heat transfer. This study compares a validated model for airspace R values with existing methods such as ISO 6946 and hot-box results that provide the R values in the ASHRAE Handbook of Fundamentals. The existing methods do not include an airspace aspect ratio. This study showed that the aspect ratio can impact the R value by a factor of two. The impact of aspect ratio was calculated for double airspaces variation such as that for single airspaces. The present calculations are two-dimensional and also consider all the bounding airspace surfaces, while previous methods are one-dimensional and do not include surface temperature variations or detailed radiative transport.

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