Totally enclosed water-cooled permanent magnet machines have been widely applied in electric vehicles due to their advantages of high torque density, high power factor, and strong overloading ...capacity. However, this type of machine often suffers from extremely high ambient temperature in a very limited space, which may lead to serious faults during operation, such as demagnetization. In order to study the thermal performance in depth, after investigation on the air convection within end-space, this paper presents a thermal model which takes into account the influence of the air temperature within the end-space on the temperature distribution by convection. Combining electromagnetic finite-element analysis with thermal resistance network, the thermal model is established, which is based on the law of heat flux balance in two continuous iterative calculations. Furthermore, computational fluid dynamic technology and experiments are implemented to further validate the proposed thermal model.
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•A new effort combining numerical simulation and four-resistance model was proposed.•Taguchi method and analysis of variance for optimization were developed.•Most favorable parameters ...set of borehole and internal resistance were obtained.•Relative importance of eight variables were compared.•Energy efficiency of all cases were analyzed.
The borehole thermal resistance and internal thermal resistance are both the significant design factors for the ground heat exchanger (GHE). Careful design procedures are required for these two values to decrease GHE’s length and initial cost. In this study, the effects of eight parameters (flow rate, pipe size, borehole diameter, pipe-pipe distance, layered soil, grout thermal conductivity, pipe thermal conductivity, and borehole depth) on the value of borehole thermal resistance and internal thermal resistance are investigated. In order to implement the analysis, L32 orthogonal array has been established. An improved 3D numerical model with the four-resistance model is applied to calculate corresponding thermal resistances in all cases. Furthermore, the Taguchi method is carried out to obtain the optimal scenarios of parameters combination. Results using the optimal parameters set reveal 67.64% increase in the borehole thermal resistance and 148.29% decrease in the internal thermal resistance. The heat transfer performance can be enhanced by 9.63% at least, up to a maximum of 77.07%. The analysis of variance (ANOVA) technique is carried out lastly to figure out the relative importance of tested parameters. The results indicate that the pipe-pipe distance has the most significant impact on the borehole thermal resistance, whereas the flow rate and layered soil almost play no role in it. The pipe size and flow rate are important driving parameters in determining the internal thermal resistance while the layered soil and borehole diameter’s impact can be nearly neglected.
Miniature power semiconductor devices mounted on printed circuit boards (PCBs) are normally cooled by means of PCB vias, copper pads, and/or heatsinks. Various reference PCB thermal designs have been ...provided by semiconductor manufacturers and researchers. However, the recommendations are not optimal, and there are some discrepancies among them, which may confuse electrical engineers. This paper aims to develop analytical thermal resistance models for PCB vias and pads, and further to obtain the optimal design for thermal resistance minimization. First, the PCB via array is thermally modeled in terms of multiple design parameters. A systematic parametric analysis leads to an optimal trajectory for the via diameter at different PCB specifications. Then, an axisymmetric thermal resistance model is developed for PCB thermal pads where the heat conduction, convection, and radiation all exist; due to the interdependence between the conductive/radiative heat transfer coefficients and the board temperatures, an algorithm is proposed to fast obtain the board-ambient thermal resistance and to predict the semiconductor junction temperature. Finally, the proposed thermal models and design optimization algorithms are verified by computational fluid dynamics simulations and experimental measurements.
Contact Thermal Resistance
In article number 2214071, Kai Wu, Qiang Fu, and co‐workers report a joint‐inspired interfacial engineering strategy by employing liquid metal to the surface of rigid ...alumina, which improves material's thermal conductivity and thixotropy. This method will inspire development of high‐performance polymer‐based thermal interface materials for future advanced electronics.
Despite the rapid progression of silicon carbide (SiC) power devices, the thermal characteristic evaluation during power cycling at high temperature (>200 °C) is an issue. In this article, a fast and ...miniaturized evaluation system with online thermal characteristic measurement function was introduced by an n-doped 4H SiC thermal engineering group (TEG) chip. Online thermal resistance measurement of a power module structure by Ag sinter joining with micron/submicron Ag particles paste in low temperature, low pressure, and cooling system by a thermal interface material bonding was performed. High-temperature reliability was systemically investigated by power cycling tests by switching on / off the power source which is connected to the SiC-TEG chip by Au wires. The total thermal resistance of the power module from the SiC-TEG chip to the cooling system increased from 0.5 to 0.53 K/W with the enhanced power source, and remained almost same after 20 000 power cycling at a swing temperature ΔTj of 150 °C. Furthermore, the SiC-TEG power module structure with the die attached with Pb and Pb-free solders, alongwith the same power source as sinter Ag paste was also measured. The Ag sinter joint possesses the lowest thermal resistance and highest high temperature reliability during power cycling compared with Pb and Pb-free die-attach materials.
A contact resistance (<inline-formula> <tex-math notation="LaTeX">{R}_{c} </tex-math></inline-formula>) becomes a major parasitic resistance in highly scaled modern semiconductor devices. A ...wrap-around contact (WAC) has been suggested as a promising solution to reduce the <inline-formula> <tex-math notation="LaTeX">{R}_{c} </tex-math></inline-formula>, because its contact area is larger than that for the conventional top contact (TC) structure. Therefore, in this article, the electrical and thermal characteristics are widely investigated in vertically stacked gate-all-around (GAA) MOSFET with a WAC by using a 3-D technology computer-aided design (TCAD) simulation. First, compared with the TC, the WAC shows 1.74 times higher ON-state current. It is attributed in part to the low <inline-formula> <tex-math notation="LaTeX">{R}_{c} </tex-math></inline-formula> and in part to the low source-drain resistance (<inline-formula> <tex-math notation="LaTeX">{R}_{\text {SD}} </tex-math></inline-formula>). Furthermore, thermal resistance (<inline-formula> <tex-math notation="LaTeX">{R}_{\text {th}} </tex-math></inline-formula>) is also reduced by 9.73% in WAC, which improves self-heating effects (SHEs). Considering the results, it is expected that the WAC structure could be an attractive candidate to simultaneously improve device performance and reliability.
Polymers are usually considered thermal insulators; however, significant enhancements in thermal conductivity (k) have been observed in oriented fibers and films. Despite being advantageous in ...real‐world applications, extending the linear thermal‐transport advantage of polymers into the 3D space in bulk materials is still limited due to the spatially interfacial phonon‐conduction barriers. Herein, inspired by the structure of tropocollagen, it is discovered that weaving hierarchically arranged poly(p‐phenylene benzobisoxazole) (PBO) fibers with a spiral configuration into an epoxy matrix can yield a 3D continuous thermal pathway. This achieves both a through‐plane k of 10.85 W m−1 K−1 and an in‐plane k of 7.15 W m−1 K−1. Theoretical molecular simulations in combination with classical nonlinear modeling attribute the above spatially thermally conductive achievement to not only the hierarchical molecular, spiral and weaving structure of PBO, but also the noncrystalline chains that carry overlapping phonon density of states, thus thermally bridging adjacent high‐k crystals in the PBO fiber. Consequently, the interfacial thermal resistance among high‐k PBO crystals is suppressed to be on the order of 10−10 m2 K W−1 in both the through‐plane and in‐plane directions. Other advantages include being lightweight, mechanically strong, flexible, and non‐combustible. This material creates opportunities for organic polymers in high‐performance thermal management applications.
A fully organic yet 3D thermoconductive bulk material is fabricated via weaving the hierarchical spiral poly(p‐phenylene benzobisoxazole) fibers into an epoxy matrix. Significantly, not only the hierarchical molecular, spiral, and weaving structure of poly(p‐phenylene benzobisoxazole), but also the bridging noncrystalline chains enable spatially phonon transport. This paves the way for fully organic materials in the fields of advanced thermal management.
Zeolites have been game-changing materials in oil refining and petrochemistry over the last 60 years and have the potential to play the same role in the emerging processes of the energy and ...environmental transition. Although zeolites are crystalline inorganic solids, their structures are not perfect and the presence of defect sites - mainly Brønsted acid sites and silanols - influences their thermal and chemical resistance as well as their performances in key areas such as catalysis, gas and liquid separations and ion-exchange. In this paper, we review the type of defects in zeolites and the characterization techniques used for their identification and quantification with the focus on diffraction, spectroscopic and modeling approaches. More specifically, throughout the review, we will focus on silanol (Si-OH) defects located within the micropore structure and/or on the external surface of zeolites. The main approaches applied to engineer and heal defects and their consequences on the properties and applications of zeolites in catalysis and separation processes are highlighted. Finally, the challenges and opportunities of silanol defect engineering in tuning the properties of zeolites to meet the requirements for specific applications are presented.
The main approaches for engineering and healing of defects in zeolites known for their iconic shape-selective properties widely explored in key areas such as catalysis, waste management, gas separation and biomedicine are revealed.
The finite element method (FEM) is conventionally employed to evaluate the thermal performance of power modules (TPPM), but it demands substantial computational resources and time. This study ...introduces a novel approach for TPPM assessment through a Fourier series-based steady-state thermal resistance model (FSS-TRM), which offers enhanced computational efficiency and accuracy. The FSS-TRM integrates conduction and spreading resistance via a mathematical-physical method, explicitly focusing on redefining conduction resistance to optimize computational efficiency. The accuracy of the FSS-TRM is ensured by solving the heat conduction differential equation to obtain spreading resistance.To assess the reliability of the FSS-TRM, the model is tested across varying direct bonded copper (DBC) configurations and chip sizes. Experimental results reveal that the maximum error of the FSS-TRM compared to the conventional COMSOL approach is below 4%. Additionally, the FSS-TRM's capability to predict TPPM is verified through testing a representative power module in a 34 mm package, demonstrating an error of only 0.9% compared to both COMSOL and experimental results. Notably, the computational efficiency of the FSS-TRM is significantly improved, excelling COMSOL by 5 orders of magnitude. Therefore, the proposed FSS-TRM provides an accurate and efficient alternative to FEM for TPPM estimation.
Cyclotides: From Structure to Function de Veer, Simon J; Kan, Meng-Wei; Craik, David J
Chemical reviews,
12/2019, Letnik:
119, Številka:
24
Journal Article
Recenzirano
This Review explores the class of plant-derived macrocyclic peptides called cyclotides. We include an account of their discovery, characterization, and distribution in the plant kingdom as well as a ...detailed analysis of their sequences and structures, biosynthesis and chemical synthesis, biological functions, and applications. These macrocyclic peptides are around 30 amino acids in size and are characterized by their head-to-tail cyclic backbone and cystine knot motif, which render them to be exceptionally stable, with resistance to thermal or enzymatic degradation. Routes to their chemical synthesis have been developed over the past two decades, and this capability has facilitated a wide range of mutagenesis and structure–activity relationship studies. In turn, these studies have both led to an increased understanding of their mechanisms of action as well as facilitated a range of applications in agriculture and medicine, as ecofriendly crop protection agents, and as drug leads or scaffolds for pharmaceutical design. Our overall objective in this Review is to provide readers with a comprehensive overview of cyclotides that we hope will stimulate further work on this fascinating family of peptides.
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