scholarly journals Heat Transfer at the Interface of Graphene Nanoribbons with Different Relative Orientations and Gaps

Energies ◽  
2019 ◽  
Vol 12 (5) ◽  
pp. 796 ◽  
Author(s):  
Shahin Mohammad Nejad ◽  
Masoud Bozorg Bigdeli ◽  
Rajat Srivastava ◽  
Matteo Fasano
Keyword(s):  
Composite Materials ◽  
Thermal Resistance ◽  
Interplanar Spacing ◽  
Graphene Nanoribbons ◽  
Angular Displacement ◽  
Filler Loading ◽  
Interfacial Thermal Resistance ◽  
Geometrical Parameters ◽  
Thermal Transfer ◽  
The Impact

Because of their high thermal conductivity, graphene nanoribbons (GNRs) can be employed as fillers to enhance the thermal transfer properties of composite materials, such as polymer-based ones. However, when the filler loading is higher than the geometric percolation threshold, the interfacial thermal resistance between adjacent GNRs may significantly limit the overall thermal transfer through a network of fillers. In this article, reverse non-equilibrium molecular dynamics is used to investigate the impact of the relative orientation (i.e., horizontal and vertical overlap, interplanar spacing and angular displacement) of couples of GNRs on their interfacial thermal resistance. Based on the simulation results, we propose an empirical correlation between the thermal resistance at the interface of adjacent GNRs and their main geometrical parameters, namely the normalized projected overlap and average interplanar spacing. The reported correlation can be beneficial for speeding up bottom-up approaches to the multiscale analysis of the thermal properties of composite materials, particularly when thermally conductive fillers create percolating pathways.

Enhanced Thermal Conductivity of Composite Materials by Filling Sheet and Fiber Under Effect of Filler Contact

2021 ◽  
Author(s):  
Xiao-jian Wang ◽  
Liang-Bi Wang
Keyword(s):  
Thermal Conductivity ◽  
Heat Flux ◽  
Composite Materials ◽  
Thermal Resistance ◽  
Percolation Threshold ◽  
Filler Content ◽  
Interfacial Thermal Resistance ◽  
Combined Effects ◽  
Enhanced Thermal Conductivity ◽  
The Ideal

Abstract The most common non-granular fillers are sheet and fiber. When they are distributed along the heat flux direction, the thermal conductivity of composite increases greatly. Meanwhile, the filler contact also has large effect on the thermal conductivity. However, the effect of filler contact on the thermal conductivity of composite with directional fillers has not been investigated. In this paper, the combined effects of filler contact, content and orientation are investigated. The results show that the effect of filler orientation on the thermal conductivity is greater than filler contact in low filler content, and exact opposite in high filler content. The effect of filler contact on fibrous and sheet fillers is far greater than cube and sphere fillers. This rule is affected by the filler contact. The filler content of 8% is the ideal percolation threshold of composite with fibrous and sheet filler. It is lower than cube filler and previous reports. The space for thermal conductivity growth of composite with directional filler is still very large. The effect of interfacial thermal resistance should be considered in predicting the thermal conductivity of composite under high Rc (>10-4).

scholarly journals Effects of the Circuit Arrangement on the Thermal Performance of Double U-Tube Ground Heat Exchangers

Energies ◽  
2020 ◽  
Vol 13 (12) ◽  
pp. 3275
Author(s):  
Aminhossein Jahanbin ◽  
Giovanni Semprini ◽  
Andrea Natale Impiombato ◽  
Cesare Biserni ◽  
Eugenia Rossi di Schio
Keyword(s):  
Thermal Resistance ◽  
Thermal Performance ◽  
Numerical Code ◽  
Geometrical Parameters ◽  
Fluid Temperature ◽  
The Finite Element Method ◽  
Ground Heat Exchangers ◽  
Borehole Thermal Resistance ◽  
The Impact ◽  
Circuit Configuration

Given that the issue of variations in geometrical parameters of the borehole heat exchanger (BHE) revolves around the phenomenon of thermal resistance, a thorough understanding of these parameters is beneficial in enhancing thermal performance of BHEs. The present study seeks to identify relative changes in the thermal performance of double U-tube BHEs triggered by alterations in circuit arrangements, as well as the shank spacing and the borehole length. The thermal performance of double U-tube BHEs with different configurations is comprehensively analyzed through a 3D transient numerical code developed by means of the finite element method. The sensitivity of each circuit configuration in terms of the thermal performance to variations of the borehole length and shank spacing is investigated. The impact of the thermal interference between flowing legs, namely thermal short-circuiting, on parameters affecting the borehole thermal resistance is addressed. Furthermore, the energy exchange characteristics for different circuit configurations are quantified by introducing the thermal effectiveness coefficient. The results indicate that the borehole length is more influential than shank spacing in increasing the discrepancy between thermal performances of different circuit configurations. It is shown that deviation of the averaged-over-the-depth mean fluid temperature from the arithmetic mean of the inlet and outlet temperatures is more critical for lower shank spacings and higher borehole lengths.

scholarly journals Photoacoustics of core–shell nanospheres using comprehensive modeling and analytical solution approach

2019 ◽  
Vol 2 (1) ◽  
Author(s):  
Khosro Shahbazi ◽  
Wolfgang Frey ◽  
Yun-Sheng Chen ◽  
Salavat Aglyamov ◽  
Stanislav Emelianov
Keyword(s):  
Analytical Solution ◽  
Thermal Resistance ◽  
Imaging Techniques ◽  
Silica Coating ◽  
Photoacoustic Signal ◽  
Interfacial Thermal Resistance ◽  
Core Shell ◽  
Contrast Imaging ◽  
Solution Approach ◽  
The Impact

Abstract Photoacoustic visualization of nanoparticles is capable of high contrast imaging at depth greater than that of traditional optical imaging techniques. Identifying the impact of various parameters on the photoacoustic signal is crucial in the design of effective medical imaging and diagnostics. Here, we develop a complete model of Fourier heat conduction incorporating the interfacial thermal resistance and photoacoustic equation for core-shell nanospheres in a fluid under nanosecond pulsed laser illumination. An analytical solution is obtained, elucidating the contribution of each region (core, shell, or the fluid) in the generation of the photoacoustic signal. The model reveals that the sharper the laser pulse temporal waveform is, the higher the sensitivity of the generated photoacoustic signal will be to the interfacial thermal resistance, and, thus, the higher the possibility of photoacoustic signal amplification will be using silica-coating. The comprehensive model and adopted analytical solution reveal the underlying physics of the photoacoustic signal generation  form core-shell nanosphere systems.

Investigation on the interfacial thermal resistance of partially overlapped bilayer graphene

2021 ◽  
Author(s):  
Bingcheng Wang ◽  
Qun Cao ◽  
Wei Shao ◽  
Zheng Cui
Keyword(s):  
Thermal Conductivity ◽  
Composite Materials ◽  
Thermal Resistance ◽  
Bilayer Graphene ◽  
High Thermal Conductivity ◽  
Interfacial Thermal Resistance ◽  
Filler Network

The graphene has been extensively applied in composite materials due to its high thermal conductivity, and the multi-layered graphene has great potentials in the construction of the continuous filler network...

A Micromechanics Model for the Thermal Conductivity of Nanotube-Polymer Nanocomposites

2008 ◽  
Vol 75 (4) ◽  
Author(s):  
Gary D. Seidel ◽  
Dimitris C. Lagoudas
Keyword(s):  
Thermal Conductivity ◽  
Carbon Nanotube ◽  
Thermal Resistance ◽  
Effective Thermal Conductivity ◽  
Polymer Nanocomposites ◽  
Interphase Layer ◽  
Interfacial Thermal Resistance ◽  
Kapitza Resistance ◽  
End Effects ◽  
The Impact

A micromechanics approach for assessing the impact of an interfacial thermal resistance, also known as the Kapitza resistance, on the effective thermal conductivity of carbon nanotube-polymer nanocomposites is applied, which includes both the effects of the presence of the hollow region of the carbon nanotube (CNT) and the effects of the interactions amongst the various orientations of CNTs in a random distribution. The interfacial thermal resistance is a nanoscale effect introduced in the form of an interphase layer between the CNT and the polymer matrix in a nanoscale composite cylinder representative volume element to account for the thermal resistance in the radial direction along the length of the nanotube. The end effects of the interfacial thermal resistance are accounted for in a similar manner through the use of an interphase layer between the polymer and the CNT ends. Resulting micromechanics predictions for the effective thermal conductivity of polymer nanocomposites with randomly oriented CNTs, which incorporate input from molecular dynamics for the interfacial thermal resistance, demonstrate the importance of including the hollow region in addition to the interfacial thermal resistance, and compare well with experimental data.

THEORETICAL STUDY OF THE EFFECT OF GEOMETRICAL PARAMETERS AND LOCATION OF ROTOR IMPACT ELEMENTS OF AN IMPACT-CENTRIFUGAL GRINDER ON SPEED AND ANGLES OF CRUSHED PARTICLES FLIGHT

2020 ◽  
Keyword(s):  
Granulometric Composition ◽  
Theoretical Study ◽  
Process Efficiency ◽  
Geometrical Parameters ◽  
Grinding Process ◽  
Main Work ◽  
Impact Element ◽  
The Impact ◽  
Positive Effect ◽  
Efficiency Indicators

One of efficiency indicators of grain grinders is grain granulometric composition. The basis of mixed fodder is crushed grain, the particles of which must have a leveled granulometric composition for subsequent mixing and obtaining a high-quality feed mixture. In agricultural production, hammer crushers are widely used, in which the destruction of grain occurs due to the impact of a hinged hammer. The main disadvantage of these crushers is that not the entire surface of the hammers is involved in grinding, thus reduces grinding process efficiency. A slightly different principle of material destruction is laid down in the basis of the proposed design of the shock-centrifugal grinder. Main work is performed by flat impact elements located on the rotor, which serve to accelerate crushed particles with subsequent impact of them on the bump elements. An important step in the design of new constructions of shock-centrifugal grinders is to determine size and location of the impact elements on the rotor, without which the grinding process is not possible. In the calculation method presented, the dependencies for determining the velocities and angles of a single particle flight from the surface of a flat impact element for its specified dimensions are proposed. Two variants of an impact element location on the rotor are considered and analyzed: radial and at an angle in the direction of rotor rotation. As a result of research carried out, it is noted that in the case of inclined position of an impact element on the rotor an increase in flight speed and flight angles change in crushed particles, which gives the opportunity to have a positive effect on grinding process.

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