Heat Conduction Rectification in Nanostructure With Step Change in Cross-Section

2010 ◽  
Author(s):  
Xingang Liang ◽  
Bao Yue
Keyword(s):  
Heat Flux ◽  
Heat Conduction ◽  
Thermal Resistance ◽  
Cross Section ◽  
Temperature Difference ◽  
Flow Direction ◽  
Step Change ◽  
Dynamics Simulation ◽  
Rectification Effect ◽  
Thick Part

Heat conduction rectifier is attracting more attention due to its potential application to process thermal currents independently and convert them into electronic signals. This work reports an investigation by molecular dynamics simulation on the heat conduction rectification effect in the nanostructure whose cross-section have step change along the heat flux. It is found that thermal resistance is different with reversed heat flux direction, which is called the heat conduction rectification. The heat conduction rectification depends on the temperature difference. By reducing temperature difference across the nanostructure, the rectification could be reversed. When the temperature difference is small enough, the thermal resistance is larger when the heat flux flows from the thick part to the thin part when the length of the structure is about 10 nm. The larger variation in the cross-section leads the larger difference in the thermal resistance with opposite heat flux. The mechanism of the rectification is discussed. If we take phonons as liquid particles and consider the case of a liquid flowing through a channel with step expansion in cross-section, the flow resistance is less with liquid flowing from the narrow part to the wide part than that in the case with contrary flow direction. In fact, the scattering of phonons at the step face reduces the mean free path of phonon when heat flux conducts from the narrow end to the wide end.

scholarly journals Optimization of Geometric Parameters of Thermal Insulation of Pre-Insulated Double Pipes

Energies ◽  
2019 ◽  
Vol 12 (6) ◽  
pp. 1012 ◽  
Author(s):  
Dorota Krawczyk ◽  
Tomasz Teleszewski
Keyword(s):  
Heat Flux ◽  
Heat Conduction ◽  
Cross Section ◽  
Thermal Insulation ◽  
Major Axis ◽  
Heat Losses ◽  
Sectional Area ◽  
Cross Sectional ◽  
Elliptical Shape ◽  
Half Axis

This paper presents the analysis of the heat conduction of pre-insulated double ducts and the optimization of the shape of thermal insulation by applying an elliptical shape. The shape of the cross-section of the thermal insulation is significantly affected by the thermal efficiency of double pre-insulated networks. The thickness of the insulation from the external side of the supply and return pipes affects the heat losses of the double pre-insulated pipes, while the distance between the supply and return pipes influences the heat flux exchanged between these ducts. An assumed elliptical shape with a ratio of the major axis to the minor half axis of an ellipse equaling 1.93 was compared to thermal circular insulation with the same cross-sectional area. All calculations were made using the boundary element method (BEM) using a proprietary computer program written in Fortran as part of the VIPSKILLS project.

Molecular Dynamics Simulation of Heat Conduction in Si Thin Films Induced by Ultrafast Laser Heating

2012 ◽  
Author(s):  
Yu Zou ◽  
Xiulan Huai ◽  
Fang Xin ◽  
Zhixiong Guo
Keyword(s):  
Molecular Dynamics ◽  
Heat Flux ◽  
Heat Conduction ◽  
Temperature Distribution ◽  
Laser Heating ◽  
Ultrafast Laser ◽  
Average Stress ◽  
Dynamics Simulation ◽  
Net Heat Flux ◽  
Si Films

Molecular dynamics simulations are carried out to study the thermal and mechanical phenomena of ultra-high heat flux conduction induced by ultrafast laser heating in thin Si films. Nanoscale Si films with various depths in heat flux direction are treated as a semi-infinite model for the study of ultrafast heat conduction. A distribution of internal heat source is applied to simulate the absorption of the laser energy in films and the induced temperature distribution. Stress distribution and the evolution of the displacement are calculated. Thermal waves are observed from the development of temperature distribution in the heat flux direction, though the average temperature of the simulated Si films increases monotonically. The average stress shows periodic oscillations. The time development of strain has the same trend as the average stress, and the net heat flux shows the same trend as the stress at different depths of the Si films in the direction of heat flux. This reveals a close relationship between stress and net heat flux in the Si films in the process of ultrafast laser heating.

scholarly journals Nonlinear Heat Transport in Superlattices with Mobile Defects

Entropy ◽  
2019 ◽  
Vol 21 (12) ◽  
pp. 1200 ◽  
Author(s):  
David Jou ◽  
Liliana Restuccia
Keyword(s):  
Thermal Conductivity ◽  
Heat Flux ◽  
Heat Conduction ◽  
Thermal Resistance ◽  
Heat Transport ◽  
Concentration Dependence ◽  
Transport Coefficients ◽  
Nonlinear Behavior ◽  
Strongly Nonlinear

We consider heat conduction in a superlattice with mobile defects, which reduce the thermal conductivity of the material. If the defects may be dragged by the heat flux, and if they are stopped at the interfaces of the superlattice, it is seen that the effective thermal resistance of the layers will depend on the heat flux. Thus, the concentration dependence of the transport coefficients plus the mobility of the defects lead to a strongly nonlinear behavior of heat transport, which may be used in some cases as a basis for thermal transistors.

Transient Response of Straight Fins

1975 ◽  
Vol 97 (3) ◽  
pp. 417-423 ◽  
Author(s):  
N. V. Suryanarayana
Keyword(s):  
Heat Flux ◽  
Cross Section ◽  
Transient Response ◽  
Laplace Transforms ◽  
Step Change ◽  
Graphical Form ◽  
Constant Area ◽  
Sinusoidal Temperature

The transient response of a fin of constant area of cross section and perimeter, with its end insulated, is analyzed using Laplace transforms. Solutions are developed for small and large values of times when the base is subjected to a step change in temperature or heat flux. Fins with base subjected to sinusoidal temperature or heat flux are also analyzed. Typical results are represented in graphical form.

Molecular Dynamics Study on Effect of Interface Between Silicon and Silicon Carbide Crystals on Phonon Heat Conduction on Nanoscale

2019 ◽  
Author(s):  
Xianhua Nie ◽  
Li Zhao ◽  
Shuai Deng ◽  
Yue Zhang ◽  
Zhenyu Du
Keyword(s):  
Molecular Dynamics ◽  
Silicon Carbide ◽  
Heat Conduction ◽  
Temperature Difference ◽  
Reference Group ◽  
Phonon Transport ◽  
Dynamics Simulation ◽  
Average Temperature ◽  
Different Temperatures ◽  
Materials Used

Abstract Both silicon (Si) and silicon carbide (SiC) are promising materials used in nano-electro-mechanical system (NEMS), however, the understanding on its phonon heat conduction is rare, which restrict the performance improvement of NEMS. Moreover, the effects of the interface between crystals, which could significantly impact the phonon transport, on heat conduction are not sufficient in the existing publication pool. In this paper, two systems, Si/Si and Si/SiC, are simulated at different temperatures and temperature differences using molecular dynamics simulation and the results were analyzed. The temperature of Si inside Si/SiC system was set at 280K, and the temperatures of SiC were set as a certain absolute value based on temperature difference setting. Meanwhile, 6 groups of temperature difference are applied as simulated conditions. In addition, simulated results from Si/Si system are also applied in comparative analysis as a reference group. The results suggested that the existence of the interface of Si/SiC system would reduce the capability of heat conduction compared to the heat conduction of Si/Si and reverse temperature differences are discovered. When the average temperature is higher than 280K, the heat conduction rate of Si/SiC system is higher than that of Si/Si system initially and as the temperature differences between crystals increases to 60.90K, the heat conduction rate of Si/Si system is higher than that of Si/SiC system. Similar conclusion can also be obtained when the average temperature is lower than 280K. This work provides an open opportunity to study the effect of interface on phonon heat conduction between crystals at typical temperature differences and average temperatures.

Heat Conduction and Thermo-Elastic Stress Field Disturbed by a Thermal-Medium Crack Propagating in Orthotropic Materials Characterized by Real or Complex Eigenvalues

2017 ◽  
Vol 139 (12) ◽  
Author(s):  
Yue-Ting Zhou ◽  
Tae-Won Kim
Keyword(s):  
Heat Flux ◽  
Heat Conduction ◽  
Temperature Difference ◽  
Crack Velocity ◽  
Crack Opening ◽  
Elastic Field ◽  
Orthotropic Materials ◽  
Crack Model ◽  
Complex Eigenvalue ◽  
Thermal Medium

A dynamic, partially permeable crack model for orthotropic materials is established with the crack full of thermal medium. Besides external thermal and elastic loadings, the heat flux generated by the crack interior full of a medium also contributes to the crack boundary conditions, which is dependent on the crack opening displacement. Thus, the heat conduction is dependent on elastic field. First, the heat conduction equation is solved exactly in terms of unknown heat flux of the crack interior. Then, the elastic field is presented for real or complex eigenvalue cases on the basis of the operator theory. Finally, the thermal and elastic fields are presented analytically, and the heat flux of the crack interior is determined explicitly. Numerical results are offered to show the influences of the thermal conductivity coefficient, normal and shear loadings and crack velocity on the distributions of the heat flux, temperature difference across the crack surfaces, and thermal stress intensity factor. Figures illustrate that increasing the crack velocity leads to a more thermally impermeable crack and produces a bigger temperature difference across the crack surfaces.

Comparative Study of Thermal Performance of Longitudinal and Transversal-Wavy Microchannel Heat Sinks for Electronic Cooling

2013 ◽  
Vol 135 (2) ◽  
Author(s):  
Gongnan Xie ◽  
Jian Liu ◽  
Yanquan Liu ◽  
Bengt Sunden ◽  
Weihong Zhang
Keyword(s):  
Reynolds Number ◽  
Pressure Drop ◽  
Thermal Resistance ◽  
Cross Section ◽  
Thermal Performance ◽  
Heat Load ◽  
Rectangular Cross Section ◽  
Flow Direction ◽  
Heat Sinks ◽  
Liquid Cooling

Liquid cooling incorporating microchannels are used to cool electronic chips in order to remove more heat load. However, such microchannels are often designed to be straight with rectangular cross section. In this paper, on the basis of straight microchannels having rectangular cross section (SRC), longitudinal-wavy microchannel (LWC), and transversal microchannel (TWC) were designed, respectively, and then the corresponding laminar flow and heat transfer were investigated numerically. Among them, the channel wall of LWC undulates along the flow direction according to a sinusoidal function while the TWC undulates along the transversal direction. The numerical results show that for removing an identical heat load, the overall thermal resistance of the LWC is decreased with increasing inlet Reynolds number while the pressure drop is increased greatly, so that the overall thermal performance of LWC is inferior to that of SRC under the considered geometries. On the contrary, TWC has a great potential to reduce the pressure drop compared to SRC, especially for higher wave amplitudes at the same Reynolds number. Thus the overall thermal performance of TWC is superior to that of SRC. It is suggested that the TWC can be used to cool chips effectively with much smaller pressure drop penalty. In addition to the overall thermal resistance, other criteria of evaluation of the overall thermal performance, e.g., (Nu/Nu0)/(f/f0) and (Nu/Nu0)/(f/f0)1/3, are applied and some controversial results are obtained.

Numerical Simulation of Heat Conduction for Error Analysis on Heat Flux Sensor Embedded in Flat Steel Plate

2014 ◽  
Vol 563 ◽  
pp. 133-136
Author(s):  
Chun Lai Tian ◽  
Shan Zhou ◽  
Li Yong Han
Keyword(s):  
Numerical Simulation ◽  
Heat Flux ◽  
Heat Conduction ◽  
Temperature Difference ◽  
Heat Conduction Problem ◽  
Maximum Temperature ◽  
Heat Flux Sensor ◽  
Maximum Temperature Difference ◽  
Maximum Heat ◽  
Errors Analysis

A numerical simulation model of heat flux sensors embedded in a flat plate is established. Each sensor has four thermal couples and is inserted into the specified hole. The problem is defined as a steady heat conduction problem with specified boundary conditions and solved by the finite element method. The results of the simulation case demonstrate that the maximum heat flux appears near the sensor shell. The average heat flux of the plate is much smaller than the maximum. Due to exiting of the contact heat resistance, the temperature of the sensor is much lower than that of the plate at horizontal surface. The maximum temperature difference appears on the bottom shell of the sensor. The maximum temperature difference between the simulation results and the experimental data at test points is 1.5 K. The model is verified and could be accepted for the further errors analysis.

Optimized Expanding Microchannel Geometry for Flow Boiling

2011 ◽  
Author(s):  
Mark J. Miner ◽  
Patrick E. Phelan ◽  
Brent A. Odom ◽  
Carlos A. Ortiz ◽  
Jonathan A. Sherbeck ◽  
...  
Keyword(s):  
Heat Flux ◽  
Critical Heat Flux ◽  
Cross Section ◽  
Flow Boiling ◽  
Flow Direction ◽  
Experimental Studies ◽  
Separated Flow ◽  
Channel Geometry ◽  
Heated Channel ◽  
Expanding Channel

This study discusses the simulation of flow boiling in a microchannel and the predicted effects of channel geometry variation along the flow direction. Recent experimental studies have generated interest in expanding the cross-section of a microchannel to improve boiling heat transfer. The motivation for this geometry change is discussed, constraints and model selection are reviewed, and Revellin and Thome’s critical heat flux criterion is used to bound the simulation of separated flow in a heated channel, via MATLAB. Expanding channel geometry permits higher heat rates before reaching critical heat flux.

Effect of Process Parameters on the Temperature of 4Cr9Si2 Martensite Refractory Steel during CWR

2012 ◽  
Vol 572 ◽  
pp. 148-153
Author(s):  
Jiang Hua Huang ◽  
Jin Ping Liu ◽  
Bao Yu Wang ◽  
Zheng Huan Hu
Keyword(s):  
Heat Conduction ◽  
Cross Section ◽  
Process Parameters ◽  
Temperature Difference ◽  
Rolling Speed ◽  
Plastic Work ◽  
Constitutive Relationship ◽  
Preheat Temperature ◽  
Cross Wedge Rolling ◽  
Refractory Steel

Based on the constitutive relationship of 4Cr9Si2 martensite refractory steel obtained by Gleeble-1500 hot simulation isothermal compression, a finite element model of Cross Wedge Rolling was build up for 4Cr9Si2 Martensite and the heat conduction, convection, plastic work and friction work were taken in account in the model. The forming process of 4Cr9Si2 martensite refractory steel by cross wedge rolling was simulated by means of DEFORM-3D software. The influence regularities of temperature of rolling process parameters were obtained: temperature rise rapidly result from plastic work and friction work in the cross-section at the process of rolling, with the completion of rolled piece cross-section, temperature descending due to heat conduction and radiation with atmosphere. The rolled piece temperature difference decrease with rolling speed and die preheat temperature increasing, the billet heating temperature is little for rolled piece temperature difference compared with rolling speed and die preheat temperature.

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