With the current development of modern electronics toward miniaturization, high-degree integration and multifunctionalization, considerable heat is accumulated, which results in the thermal failure ...or even explosion of modern electronics. The thermal conductivity of materials has thus attracted much attention in modern electronics. Although polymer composites with enhanced thermal conductivity are expected to address this issue, achieving higher thermal conductivity (above 10 W m–1 K–1) at filler loadings below 50.0 wt % remains challenging. Here, we report a nanocomposite consisting of boron nitride nanotubes and cellulose nanofibers that exhibits high thermal conductivity (21.39 W m–1 K–1) at 25.0 wt % boron nitride nanotubes. Such high thermal conductivity is attributed to the high intrinsic thermal conductivity of boron nitride nanotubes and cellulose nanofibers, the one-dimensional structure of boron nitride nanotubes, and the reduced interfacial thermal resistance due to the strong interaction between the boron nitride nanotubes and cellulose nanofibers. Using the as-prepared nanocomposite as a flexible printed circuit board, we demonstrate its potential usefulness in electronic device-cooling applications. This thermally conductive nanocomposite has promising applications in thermal interface materials, printed circuit boards or organic substrates in electronics and could supplement conventional polymer-based materials.
This paper deals about the response of envelope to various climatic conditions and it is the main reason to know the amount of energy needed to maintain thermal comfort of the inner environment. The ...building envelope reduces external stress especially in hot climates and it was determined by subjecting its individual orientations and composition. The study is to reconstruct the envelope parts by changing wall material, thermal insulation materials in wall pattern and minimize its U-value to reduce the heat the heat transfer and determine it by using AUTOCAD and FOURLY ANALYSIS PROGRAM of ASHRAE 2013 standard.
•PCM and insulation component are used to improve thermal performance of Trombe wall.•Effects of design parameters of insulation component are studied using the validated model.•Design approach of ...heat preservation at night of a TW-PCM is proposed.•Thermal comfort is analyzed based on operative temperature and radiant temperature asymmetry.
A classical Trombe wall cannot satisfy the thermal comfort for the whole day due to the limited heat storage capacity and large heat loss at night. In present work, phase change materials and an external insulation component are used to improve thermal performance of a Trombe wall. The design approach of heat preservation at night is first obtained. An unsteady heat transfer model of a Trombe wall with phase change materials under heat preservation condition in the nighttime is established by MATLAB. The reliability of the mathematical model is validated by an experiment in Yuzhong (Gansu, China). With this model, the effects of the design parameters of the external insulation component on the thermal performance are analyzed. Finally, the indoor thermal comfort of a passive solar room is analyzed based on the experimental data. The results indicate that, it has a significant impact of the thermal conduction resistance of the insulation component and the thermal resistance of the closed air cavity. For closed air cavity, the internal surface emissivity of the insulation component plays an important role. The optimized additional thermal resistance for the external insulation component is 2 m2⋅°C⋅W−1, and the corresponding maximum thermal resistance of the closed air cavity is determined as about 0.5 m2⋅°C⋅W−1. Compared with no heat preservation at night, the operative temperature improves significantly, and the radiant temperature asymmetries of two massive walls are similar. The investigation can provide a design approach of heat preservation at night for a Trombe wall.
This study reports the synthesis and characterization of geopolymer foam concrete (GFC). A Class F fly ash with partial slag substitution was used for GFC synthesis by mechanical mixing of preformed ...foam. The GFCs exhibited 28d compressive strengths ranging from 3 to 48MPa with demolded densities from 720 to 1600kg/m3 (105°C oven-dried densities from 585 to 1370kg/m3), with the different densities achieved through alteration of the foam content. The thermal conductivity of GFCs was in the range 0.15–0.48W/mK, showing better thermal insulation properties than normal Portland cement foam concrete at the same density and/or at the same strength. The GFC derived from alkali activation of fly ash as a sole precursor showed excellent strength retention after heating to temperatures from 100 to 800°C, and the post-cooling compressive strength increased by as much as 100% after exposure at 800°C due to densification and phase transformations. Partial substitution of slag for fly ash increased the strength of GFC at room temperature, but led to notable shrinkage and strength loss at high temperature. Thin GFC panels (20–25mm) exhibited acoustic absorption coefficients of 0.7–1.0 at 40–150Hz, and 0.1–0.3 at 800–1600Hz.
A three-dimensional (3D) integrated packaging method is proposed in this letter. Re-distributed layers (RDLs) are realized by integrating flexible printed circuit (FPC) boards onto gallium nitride ...(GaN) high electron mobility transistor (HEMT) dies to enlarge the electrodes area and the clearance between them. GaN HEMTs with RDLs are sandwiched between a multi-layer printed circuit board (PCB) and an active metal brazing (AMB) board. Additionally, components like decoupling capacitors, gate driver, digital isolator and isolated power supply are integrated into this package. Silver sintering processes are employed to maintain consistent processing temperature for multiple interconnections, addressing reliability concerns associated with conventional multi-temperature gradient soldering methods. Furthermore, sintered silver significantly improves both electrical and thermal performances. Power and thermal managements are decoupled by using a PCB and AMB substrate, resulting in low parasitic inductances, minimal thermal resistance and electric field shielding. The experiment-measured power loop inductance is as low as 0.54 nH, and the simulated thermal resistance from GaN die to AMB board bottom is only 0.05 ℃/W. A detailed description of manufacturing processes, thermal performance test, dynamic switching performance with circuit-level simulated verification are provided in this letter.
In this paper, self-heating effects (SHEs) in three-stacked nanoplate FETs were investigated through the TCAD simulation. In order to obtain high reliability, the evaluation of SHEs was performed ...after <inline-formula> <tex-math notation="LaTeX">{I}_{D} </tex-math></inline-formula>-<inline-formula> <tex-math notation="LaTeX">{V}_{G} </tex-math></inline-formula> curve fitting based on the experimental data. First, general analysis on SHEs was conducted to confirm the influence of SHEs to electrical characteristics. The optimized nanoplate width for great electrical properties was proposed by using the figure-of-merit factor under the consideration of SHEs. In addition, difference of heat flux between FinFET and stacked nanoplate FET was analyzed. Based on the analysis, the two-step thermal resistance (<inline-formula> <tex-math notation="LaTeX">{R}_{\text {th}} </tex-math></inline-formula>) model depending on drain voltage was proposed. The two-step <inline-formula> <tex-math notation="LaTeX">{R}_{\text {th}} </tex-math></inline-formula> model in the stacked nanoplate FET matched well with the Berkeley short-channel IGFET model-common multigate model compared the other <inline-formula> <tex-math notation="LaTeX">{R}_{\text {th}} </tex-math></inline-formula> models. A seven-stage ring oscillator with the proposed <inline-formula> <tex-math notation="LaTeX">{R}_{\text {th}} </tex-math></inline-formula> model was demonstrated, and SHEs in the circuit level were confirmed.
•Flow boiling heat transfer of MgO/therminol 66 was investigated.•Fouling thermal resistance of nanoparticles was modeled.•A new model for flow boiling heat transfer of nanofluid was developed.•The ...boiling surface was a copper made disc.
An experimental investigation was performed on the flow boiling heat transfer characteristics of MgO/therminol 66 nanofluid as a potential coolant on a copper-made disc. Nanofluids were prepared using two step method at wt.% = 0.1, and wt.% = 0.3. Results showed that the presence of MgO/therminol 66 increases the flow boiling heat transfer coefficient in comparison with the base fluid. However, with an increase in the mass concentration of nanoparticles, the heat transfer coefficient decreased. Results also revealed that bubble formation induces a pressure drop within the test section. Heat flux had no influence on the pressure drop, while an increase in the fluid flow rate caused an increase in the pressure drop. It was also found that the heat transfer coefficient decreased with operating time due to the presence of nanoparticles on the boiling surface resulting in the creation of thermal resistance on the surface. Also, an asymptotic behavior for the fouling thermal resistance over the time was registered. Two correlations were re-developed to accurately predict the heat transfer coefficient and fouling thermal resistance of the system. Experiments proved that MgO nanoparticles offer a potential to be used in thermal engineering systems with boiling heat transfer mechanism. The maximum enhancement for the heat transfer coefficient was 23.7% at wt.% = 0.1. For wt.% = 0.2 and wt.% = 0.3, the maximum enhancement of 16.2% and 13.3%, were achieved, respectively.
Materials with ultralong phosphorescence have wide-ranging application prospects in biological imaging, light-emitting devices, and anti-counterfeiting. Usually, molecular phosphorescence is ...significantly quenched with increasing temperature, rendering it difficult to achieve high-efficiency and ultralong room temperature phosphorescence. Herein, we spearhead this challenging effort to design thermal-quenching resistant phosphorescent materials based on an effective intermediate energy buffer and energy transfer route. Co-crystallized assembly of zero-dimensional metal halide organic-inorganic hybrids enables ultralong room temperature phosphorescence of (Ph
P)
Cd
Br
that maintains luminescent stability across a wide temperature range from 100 to 320 K (ΔT = 220 °C) with the room temperature phosphorescence quantum yield of 62.79% and lifetime of 37.85 ms, which exceeds those of other state-of-the-art systems. Therefore, this work not only describes a design for thermal-quenching-resistant luminescent materials with high efficiency, but also demonstrates an effective way to obtain intelligent systems with long-lasting room temperature phosphorescence for optical storage and logic compilation applications.
•The interfacial thermal resistance between epoxy and graphene edges is 7.13 ± 1.58 × 10–9 m2KW-1, which is essential to the overall thermal transport of epoxy/ graphene composites.•The active amino ...groups can reduce the interfacial thermal resistance between epoxy and graphene edges to 42% due to strong covalent bonds.•The amino groups have a great influence on the density distribution near the interface.•The effect of inactive amino groups on the interfacial thermal resistance depends on its coverage rate.
Epoxy/graphene nanocomposites have attracted significant attention in microelectronic devices due to the ultra-high thermal conductivity of graphene. However, the high interfacial thermal resistance between graphene and polymer hinders its application. In this paper, the effect of amino groups on the interfacial thermal resistance between epoxy and graphene edges is investigated by using molecular dynamic simulations. The density distribution and the phonon density of states near the interface are calculated to study the mechanism of interfacial heat transfer. The results show that the active amino group reduces the interfacial thermal resistance to 42%, while the effect of the inactive amino group on the interfacial thermal resistance depends on its coverage rate. The presence of the inactive amino group increases the interfacial gap width and leads to poor heat transfer. In a lower coverage rate, the epoxy fills the spacing between amino groups and half-wraps them. The phonon mismatch is reduced due to the increase of contact areas between graphene and epoxy. Therefore, the interfacial thermal resistance decreases with the decrease of the coverage rate. This work is of practical importance for the design of amino groups distribution on graphene edges in nanocomposites materials.
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