Rafat Mohammadi

We investigate the lattice thermal conductivity of plumbene using molecular dynamics simulations, overcoming existing limitations by optimizing the parameters of Tersoff and Stillinger–Weber potentials via artificial neural networks. Our findings indicate that at room temperature, the thermal conductivity of a 1050 Å × 300 Å plumbene sheet is approximately 8 W m⁻¹ K⁻¹, significantly lower (23%) than that of bulk lead. Our analysis elucidates that thermal conductivity is enhanced by increased sample length, while it is reduced by temperature. Moreover, plumbene samples with zigzag edges display superior thermal conductivity compared to those with armchair edges. In addition, the thermal conductivity of plumbene exhibits an increase at low tensile strains, whereas it decreases as the strains become larger. This investigation provides crucial insights into the thermal conductivity behavior of plumbene under varying conditions.

منظور از فرایند تعلیق خنثی کردن نیروی جاذبه وارد به نمونه به کمک یک نیروی غیرتماسی و تعلیق نمونه در هوا بدون تماس با سطوح ثانویه می‌باشد. فواید حذف تماس یک ماده با سطوح خارجی باعث مورد توجه قرار گرفتن فرایند تعلیق شده‌است. با توجه به این موضوع که در میان روش‌های تعلیق، تعلیق فراصوت تنها روشی است که برای مواد با خواص فیزیکی و هندسه‌های متفاوت قابل اعمال است، تعلیق ماده در فاز مایع نیز به کمک این روش قابل انجام است. پتانسیل تعلیق فراصوت مایعات برای استفاده در مواردی مانند داروسازی، زیست‌شناسی، کنترل ساختار ماده و غیره باعث انجام تحقیقات متعددی در زمینه بهبود شرایط این فرایند شده‌است. در این مقاله سعی شده‌است در بخش اول مروری بر تئوری و روابط تحلیلی فرایند تعلیق فراصوت انجام شود و سپس در بخش دوم مطالعات انجام شده در زمینه بهبود شرایط فرایند تعلیق و عوامل موثر بر آن مورد بررسی قرار گرفته است . در نهایت نگاهی به آینده تحقیقات در این زمینه شده‌است

Efficient thermal management of modern electronics requires the use of thin films with highly anisotropic thermal conductivity. Such films enable the effective dissipation of excess heat along one direction while simultaneously providing thermal insulation along the perpendicular direction. This study employs non-equilibrium molecular dynamics to investigate the thermal conductivity of bilayer graphene (BLG) sheets, examining both in-plane and cross-plane thermal conductivities. The in-plane thermal conductivity of 10 nm × 10 nm BLG with zigzag and armchair edges at room temperature is found to be around 204 W/m·K and 124 W/m·K, respectively. The in-plane thermal conductivity of BLG increases with sheet length. BLG with zigzag edges consistently exhibits 30–40% higher thermal conductivity than BLG with armchair edges. In addition, increasing temperature from 300 K to 600 K decreases the in-plane thermal conductivity of a 10 nm × 10 nm zigzag BLG by about 34%. Similarly, the application of a 12.5% tensile strain induces a 51% reduction in its thermal conductivity compared to the strain-free values. Armchair configurations exhibit similar responses to variations in temperature and strain, but with less sensitivity. Furthermore, the cross-plane thermal conductivity of BLG at 300 K is estimated to be 0.05 W/m·K, significantly lower than the in-plane results. The cross-plane thermal conductance of BLG decreases with increasing temperatures, specifically, at 600 K, its value is almost 16% of that observed at 300 K.

Efficient thermal management of modern electronics requires the use of thin films with highly anisotropic thermal conductivity. Such films enable the effective dissipation of excess heat along one direction while simultaneously providing thermal insulation along the perpendicular direction. In this study, we investigate the thermal conductivity of bilayer graphene (BLG) sheets using non-equilibrium molecular dynamics, examining both in-plane and cross-plane thermal conductivities. The in-plane thermal conductivity of 10 nm × 10 nm BLG with zigzag and armchair edges at room temperature is found to be around 204 W/m.K and 124 W/m.K, respectively. The in-plane thermal conductivity of BLG increases with sheet length. For all sizes, BLG with a zigzag edge exhibits higher thermal conductivity than that of the armchair edge, with this difference becoming more pronounced as the lengths of the sheets increase. In addition, increasing temperature from 300 K to 600 K decreases the in-plane thermal conductivity of a 10 nm× 10 nm zigzag BLG by about 34%. Similarly, the application of a 12.5% tensile strain induces a 51% reduction in its thermal conductivity compared to the strain-free values. Armchair configurations exhibit similar responses to variations in temperature and strain, but with less sensitivity. Furthermore, the cross-plane thermal conductivity of BLG at 300 K is estimated to be 0.05 W/m·K, significantly lower than the in-plane results by approximately four orders of magnitude. The cross-plane thermal conductance of BLG decreases with increasing temperatures, specifically, at 600 K, its value is almost 16% of that observed at 300 K.

Metal/polymer laminate has versatile applications in industry due to the essential roles of its constituents in controlling its mechanical behavior. Therefore, efforts to enhance a laminate’s performance should target its mechanical behavior. One of the most influencing features of the mechanical behavior of this type of thin laminate is the interface layer properties. This study concentrates on the mechanical response of thin aluminum (Al) foil deposited on a polymer substrate by calibrating its interfacial layer properties based on available uniaxial tensile tests performed on thin Al/polymer laminate. Then, taking into account the calibrated parameters for the interface layer, which leads to mimicking the real conditions of the laminate, one type of imperfection is introduced as a wavy roughness on the surface of each layer with different amplitudes to investigate its influence on the overall mechanical behavior of the laminate and its failure mode. The results highlighted that the existence of the roughness on the surface of the polymer layer reduces the maximum engineering stress of the laminate more severely compared to other conditions. As the roughness amplitude increases, the maximum stress reduces a lot. The distribution of equivalent plastic strains represents the appearance of the shear bands in the Al layer and an almost uniform distribution for the polymer layer. In the case of existing roughness on each layer, a higher amount of plastic strain accumulation occurs in the middle of the polymer layer and top corners of the thin Al layer. Due to the significant effect of interfacial layer properties to improve the maximum strength of the laminate and its final elongation, a parametric study is performed, taking into account different interfacial properties. The results indicate that laminate behavior with weaker separation properties in the interface layer is mostly unaffected by adopting higher tractions, and no change happens in the case of high separation considering weak tractions.

In this article, the effect of two different methods of cooling enhancement, including the use of nanofluid as the coolant and sinusoidal wavy walls, on the performance of rectangular microchannel heat sinks (MCHSs) has been numerically investigated. Three-dimensional simulations based on the finite-volume approach are carried out using three different wave amplitudes (50, 100, and 200 µm) and wavelengths (1.3, 2, and 4 mm). Water-based nanofluid containing Al₂O₃ nanoparticles with volume fraction of 1% is employed as the coolant, and its influence on the hydraulic and thermal performance of the MCHS is compared with the water. The simulation of nanofluid flow is performed by both the single-phase method and the two-phase mixture method. Comparison between predicted results and experimental data from literature is carried out, which indicates the two-phase method is more precise than the single-phase method. Results showed that the enhanced microchannels with higher wave amplitudes and lower wavelengths performed better in terms of heat transfer, and among the investigated geometries, the wavelength of 1.3 mm and the amplitude of the 200 µm show the highest cooling performance. Using these optimal geometrical values in the wavy-walled microchannel heat sink (WMCHS), the amount of heat absorbed by the water-Al₂O₃ with volume fraction of 1% increases by 43% compared with the water flow in the straight-walled microchannel heat sink (SMCHS) at Reynolds number of 500. In addition, in a given geometry with fixed length and cross section area, employing wavy walls has a greater effect on heat transfer enhancement than using nanofluid instead of water. Employing optimal wavy walls in the MCHS, the amount of absorbed heat increases by 30% when the coolant is pure water and by 21% when the coolant is nanofluid. Whereas if nanofluid is used instead of water, the heat absorbed increases by 18% in SMCHS and 10% in WMCHS. Although both methods of cooling enhancement increase the pressure drop as well, the negative effect of the increase in pressure drop is less than the positive effect of increasing heat transfer in both methods.

A simulation package for the impedance response of SOFC anodes is presented here. The model couples the gas transport in gas channels and within a porous electrode with the electrochemical kinetics. The gas phase mass transport is modeled using mass conservation equations. A transmission line model (TLM), which is suitably modified to account for the electrode microstructural details, is used for modeling the impedance arising from the electrochemical reactions. In order to solve the system of nonlinear equations, an in‐house code based on the finite difference method was developed. Some of the model constants have been calibrated against experimental data. It is demonstrated that the simulation tool is capable of predicting the impedance response of an experimental data set obtained on symmetrical cells with Ni/ScYSZ SOFC anodes. A parametric study is also carried out using the developed simulation tool and the results are further discussed.