Thermal Dissipation Performance Research Articles

Large-area, highly thermally conductive, but electrically insulative industrial aramid papers with hierarchical multiscale compositing structures

The rapid development of emerging 5G electrical fields has put forward high requirements to the thermal dissipation performance of industrial aramid papers (IAPs), which are commonly used as the insulation layers of electrical equipment. Herein, we reported a facile method for preparing large-area (> 7000 cm2), thermally conductive, but electrically insulative IAPs by compounding multiscale boron nitride nanosheets (BNNSs), industrial diamond microparticles (DMPs), and industrial aramid micropulps and microfibers (AMPs & AMFs) towards hierarchical compositing structures. Specifically, BNNSs can adhere to the surface of DMPs through electrostatic interaction and reduce the thermal resistance between neighboring DMPs, which ultimately ensures high in-plane thermal conductivity (11.66 W/(mK)) of IAPs, which is about 7 times that of pure aramid papers. Meanwhile, IAPs also exhibit high volume resistivity of 4.95×1015 Ω·cm. At last, the IAPs were successfully applied in a transformer for insulation and thermal conducting, demonstrating their high potential in industrial electrical equipment.

3-D-Lumped Thermal Network Models for the Reliability Analysis of Fan-Cooled Plate-Fin Heatsink

Conventional lumped thermal networks are most commonly used to model the thermal dissipation in the heatsink. However, they lack accuracy in addressing the temperature information when the thermal dissipation performance of the heatsink declines due to the impurities (dust) blocking the air channels. Especially in the reliability field, they cannot provide accurate temperatures to realize the reliability analysis of the cooling system. This paper proposes two novel 3-D RC-lumped thermal network models for the reliability analysis of the fan-cooled plate-fin heatsink. In the established thermal circuits, the effects of impurities on the heatsink’s thermal dissipation performance are modeled as a few adjustable thermal resistances whose value can be adjusted in accordance with the distribution of the impurities. Moreover, the proposed thermal network models are performed in SIMSCAPE and computational fluid dynamic (CFD)–based simulations and experimental results are carried out to verify the proposed 3-D thermal networks. It is demonstrated that the proposed 3-D thermal networks enable accurate and fast temperature estimation of the heatsink under different reliability conditions (different impurities profiles on the heatsink). Therefore, it can be used for the reliability analysis of the heatsink under long-term load profiles when the thermal dissipation performance decreases.

An Online Identification Method of Thermal Dissipation State for Forced Air-Cooled System of Power Converters

Thermal stress is the primary cause of malfunction and failure in power modules. As the main heat dissipation component, the heatsink plays a significant role in improving the reliability of power converters. However, due to the continuous accumulation of dust and impurities on the heatsink’s air inlet side, the thermal dissipation performance of the cooling system constantly declines, which influences the reliable operation of power modules. In this article, a computational fluid dynamics (CFD)-based simulation analyzes the declining mechanism of the heatsinks’ thermal transfer performance. Moreover, a novel online method is proposed for the cooling system’s thermal dissipation state identification. This method regards the steady-state thermal resistance as the feature parameter of the thermal dissipation state evaluation. And a parameter identification method is employed to identify the steady-state thermal resistance due to the difficulty of obtaining it in the transient thermal process. In addition, an ac/dc/ac pulsewidth modulation (PWM) converter is built for verification. The experimental results demonstrate that the proposed method enables accurate and fast identification of the cooling systems’ thermal dissipation state. It can be one of a solution for replacing the existing off-line manual periodic detection method, which helps improve detection efficiency and decrease maintenance costs.

Partially-covered fractal induced turbulence on fins thermal dissipation

The impacts of partially-covered fractal grids induced turbulence on the forced convective heat transfer across plate-fin heat sink at Reynolds number ReDh = 22.0 × 103 were numerically and experimentally investigated. Results showed that partially covered grids rendered a higher thermal dissipation performance, with partially-covered square fractal grid (PCSFG) registering an outstanding increase of 43% in Nusselt number relative to the no grid configuration. The analyzation via an in-house developed single particle tracking velocimetry (SPTV) system displayed the findings of unique “Turbulence Annulus” formation, which provided a small degree of predictivity in the periodic annulus oscillations. Further assessments on PCSFG revealed the preferred inter-fin flow dynamics of (i) high flow velocity, (ii) strong turbulence intensity, (iii) vigorous flow fluctuations, (iv) small turbulence length scale, and (v) heightened decelerated flow events. These features stemmed from the coupling effects of multilength-scale fractal bar thicknesses in generating a veracity of eddy sizes, and a vertical segmentation producing heightened mass flow rate while inducing favourable wake-flow structures to penetrate inter-fin regions. Teeming effects of such energetic eddies within plate-fin array unveiled a powerful vortex shedding effect, with PCSFG achieving fluctuation frequency f = 18.5 Hz close to an optimal magnitude. The coaction of such traits limits the growth of fin boundary layers, providing superior thermal transfer capabilities which benefits the community in developing for higher efficiency heat transfer systems.

A novel modified expanded graphite/epoxy 3D composite with ultrahigh thermal conductivity

Polymer-based composites with efficient thermal energy dissipation performance can be prospectively applied in electronics and military industry. However, significantly improving the thermal conductivity (TC) of polymer-based composites is still challenging. Herein, 3D sulfanilamide-modified expanded graphite/epoxy (EG-SA/EP) composites with interconnected filler network were successfully prepared by a pre-filling and hot-pressing method. Benefiting from the interconnected network, the composite with 70 wt% EG-SA demonstrated ultrahigh bulk TC of 98 W/m·K (which exceeds some commercially-used metals) and up to 44,445% TC enhancement efficiency. Meanwhile, the EG-SA/EP composites exhibited excellent electromagnetic interference shielding performance of 85 dB (which is sufficient to block 99.9999997% of incident radiation), high electric conductivity of 7153 S/m and excellent thermal infrared response capability (the time to raise surface temperature from 19 to 82 °C is only 3 s). As for the mechanism of heat transfer, the 3D structure of EG-SA maintained through epoxy pre-filling in EG-SA is the main reason for the significantly improved TC. This is because the new method enables EG-SA to build a unique dense interconnected network in composites in the subsequent hot-pressing process, but the traditional direct mixing method easily destroys the inherent micro-3D structure of EG. The above excellent performances endow the EG-SA/EP composites with huge potential application value.

A modified spin-casting approach for scalable preparation of ultra-thick reduced graphene oxide films with high thermal conductivity

With the fast development of high-power electronic devices in recent years, the demand for high-performance thermal dissipation films with high thermal conductivity and large thickness has dramatically increased. Graphene has shown great potential in thermal management due to its extremely high thermal conductivity. However, it remains a significant challenge to achieve high thermal conductivity in thick graphene films (≥100 μm). Herein, a scalable strategy combining a modified layer-by-layer ‘spin-casting’ solution deposition method and multi-step annealing post treatment was adopted for preparing ultra-thick, highly thermal conductive graphene films. The properties of the graphene films were characterized by SEM, XRD, Raman, and XPS, exhibiting excellent graphitic crystallinity, well aligned and dense packing assembly structure. These nearly ideal structural features endow the graphene films with high in-plane thermal conductivity of 1265 ± 46 W m−1 K−1 at a large thickness of 100 μm. The ultra-thick graphene films show superior thermal dissipation performance as compared with traditional Cu/Al foil, demonstrating their great potential in the field of highly-efficient heat spreader films for the next generation of high-power devices.

The Thermal Dissipation Characteristics Analysis of the Rotatable Circular Pantograph–Catenary System

As the unique power entrance of high-speed trains, the pantograph–catenary system (PCS) plays the critical role of power transmission for high-speed trains. The pantograph achieves the electrical power based on the sliding electrical contact between the pantograph strip and the high-voltage contact line. However, when the environmental temperature is relatively low especially during the winter, the contact line is covered by ice or snow easily. The ice or snow adhering on the surface of contact line may lead to poor electrical contact between the pantograph strip and the contact line, which may trigger the pantograph–catenary arc appearing. Accompanying with mechanic shock and friction heat, the off-line arc may deteriorate the quality of power transmission and meanwhile erode the contacting surface of the pantograph strip and the contact line to some extent. In order to solve this technique bottleneck, a novel rotatable circular-shape pantograph strip is proposed to improve the overall performance of the traditional pantograph strip. Compared with the traditional strip, the circular pantograph strip owns many advantages, such as less friction, better thermal dissipation, and better shock resistance. The thermal dissipation performance of both the traditional and circular pantograph strip is evaluated in this article, with the consideration of suffering off-line arc under the icing conditions.

Enhanced Optical and Thermal Performance of QD White LEDs Using a Centrifugation Packaging Structure

In this study, we propose a centrifugation packaging (CP) structure to enhance the optical and thermal dissipation performance of LEDs, using SBA-15 particles to facilitate the sedimentation and dispersion of QDs. The results indicate that the EL spectra of the LEDs remains almost unchanged after the centrifugation time of 60 min and a CP structure can be obtained. The radiation power and luminous flux of LEDs with a CP structure improve by 9.1% and 10.4%, respectively, compared with the uniform distribution (UD) structure. The surface temperature of LED devices with the CP structure is reduced to 34.4 °C from 41.8 °C at a current of 100 mA. Furthermore, the simulation results show that the maximum temperature in the CP structure is 22.4% lower than that in the UD structure at a current of 500 mA. Thus, this study can provide a new perspective for designing settlement structures of QD-LEDs to enhance their optical and thermal performance.

A reduced-order model based on finite element method for fast prediction of thermal performance of lattice structures

Lattice structures, emerging with additive manufacturing technology, have broad application prospects in industry, and desirable thermal and mechanical properties of which can be obtained by changing the internal cells and their array mode. However, the computational cost for the design and analysis of a lattice structure is usually extremely high due to the structural complexity. For fast prediction of thermal performance of lattice structures, a reduced-order model was developed, in which the complex lattice structure is simplified into a three-dimensional rod system and the heat conduction, convection, and radiation are modeled in a reduced second-order way based on the finite element principle. The convergence and accuracy was examined, and the model validation was done by comparing with the corresponding full model. The results showed that the calculation error of the reduced-order model decreases as the rod aspect ratio increases and the computational efficiency is improved by more than 1000 times. The reduced-order model was then applied to evaluate the thermal insulation and thermal dissipation performance of seven kinds of lattice cells, and their characteristics of the thermal performance were found and compared. We finally gave a better designed cell, which shows the best thermal insulation and dissipation performance simultaneously.

Bispyrene Functionalization Drives Self-Assembly of Graphite Nanoplates into Highly Efficient Heat Spreader Foils.

Thermally conductive nanopapers fabricated from graphene and related materials are currently showing great potential in thermal management applications. However, thermal contacts between conductive plates represent the bottleneck for thermal conductivity of nanopapers prepared in the absence of a high temperature step for graphitization. In this work, the problem of ineffective thermal contacts is addressed by the use of bifunctional polyaromatic molecules designed to drive self-assembly of graphite nanoplates (GnP) and establish thermal bridges between them. To preserve the high conductivity associated to a defect-free sp2 structure, non-covalent functionalization with bispyrene compounds, synthesized on purpose with variable tethering chain length, was exploited. Pyrene terminal groups granted for a strong π–π interaction with graphene surface, as demonstrated by UV–Vis, fluorescence, and Raman spectroscopies. Bispyrene molecular junctions between GnP were found to control GnP organization and orientation within the nanopaper, delivering significant enhancement in both in-plane and cross-plane thermal diffusivities. Finally, nanopapers were validated as heat spreader devices for electronic components, evidencing comparable or better thermal dissipation performance than conventional Cu foil, while delivering over 90% weight reduction.

Avoiding heating interference and guided thermal conduction in stretchable devices using thermal conductive composite islands

The miniaturization and high integration of devices demand significant thermal management materials. Current technologies for the thermal management of electronics show some limitations in the case of multiple chip arrays. A device in multiple chip array is affected by heat from adjacent devices, along with thermal conductive composite. To address this problem, we present a nano composite of aligned boron nitride (BN) nanosheet islands with porous polydimethylsiloxane (PDMS) foam to have mechanical stability and non-thermal interference. The islands of tetrahedrally-structured BN in the composite have a high thermal conductivity of 1.219 W·m−1·K−1 in the through-plane direction (11.234 W·m−1·K−1 in the in-plane direction) with 16 wt.% loading of BN. On the other hand, porous PDMS foam has a low thermal conductivity of 0.0328 W·m−1·K−1 in the through-plane direction at 70% porosity. Heat pathways are then formed only in the structured BN islands of the composite. The porous PDMS foam can be applied as a thermal barrier between structured BN islands to inhibit thermal interference in multiple device arrays. Furthermore, this composite can maintain selective thermal dissipation performance with 70% tensile strain. Another beauty of the work is that it could have guided heat dissipation by assembling of multiple layers which have high vertical thermal conductive islands, while inhibiting thermal interference. The selective heat dissipating composite can be applied as a heatsink for multiple chip arrays electronics.

Study on the thermal dissipation performance of GPU cooling system with nanofluid as coolant

The graphic processing unit is the active component that is an important heat source in electronic devices. The GPU cooling system's thermal dissipation performance with de-ionized water and nanofluid as coolants are presented. In the experiment, the GPU cooling system was embedded with the personal computer's GPU board, which in the overclock operating condition. The Ag nanofluid with 0.015% by volume concentration and de-ionized water is used as coolants flowing in the cooling system, considering the effects of coolant types and heat sink configurations on the thermal resistance. It found that the nanoparticles suspending in the base fluid significantly impact the nanofluid's physical properties and flow features, which results in higher removal capacity and, consequently, lower thermal resistance. The heat sink with a lower flow channel gives lower thermal resistance than those from higher ones. The results from this work have been used to develop a knowledge base that can be used to a design-related thermal cooling system for GPU or other components of electronic devices.

Cooling Mechanisms in a Rotating Brake Disc With a Wire-Woven-Bulk Diamond Cellular Core

Abstract Thermofluidic behaviors governing the enhanced cooling performance of the wire-woven-bulk diamond (WBD) cored brake disc in comparison with the conventional pin-finned brake disc used on heavy vehicles were characterized experimentally. For each type of brake disc, detailed internal thermofluidic data of the two rotating brake discs were obtained using transient thermochromic liquid crystal (TLC) for end-wall heat transfer and particle image velocimetry (PIV) for the inflow field. The results demonstrate that the pin-finned brake disc exhibits a circumferentially periodic curved inline-like passage flow and large dead flow regions, with strong recirculation that reduces its thermal dissipation performance. The cooling advantage of the WBD core is primarily attributed to the combination of enlarged heat transfer surface area (both end-wall and core) and greater utilization of the larger surface due to favorable fluidic behavior developed from the WBD topology. The internal WBD core has approximately three times the surface density of the pin-finned disc which, in combination with the smaller and weaker recirculation zones, leads to more effective usage of the available core surface area for thermal dissipation. The aerodynamic anisotropy of the WBD core induced by its topological anisotropy causes a globally irregular thermofluidic distribution in the brake disc.

Thermal and dielectric properties of epoxy-based composites filled with flake and whisker type hexagonal boron nitride materials

In this work, the epoxy-based composites filled with 3-Aminopropyltriethoxysilane (KH-550) modified binary filler of hexagonal boron nitride (h-BN) flakes and h-BN whiskers were fabricated, and the thermal and dielectric properties of composites were systematically investigated. Adding h-BN whiskers to the filler could effectively form heat conduction paths and improve the phonon transmission efficiency, thereby improving the thermal conductivity of the composites. According to our results, the thermal conductivity of composite with 27 wt% h-BN flakes and 3 wt% h-BN whiskers reached up to 0.819 W·m−1·K−1, which was 3.9 times that of pure epoxy resin. At the same time, the dielectric loss value and dielectric constant of this composite at 1 MHz were 0.02678 and 4.55, respectively, while pure epoxy resin were 0.03602 and 4.33. In addition, introducing h-BN whiskers into the matrix could effectively improve the thermal stability and heat dissipation performance of composites.

Thermal transport characteristics of supported carbon nanotube: Molecular dynamics simulation and theoretical analysis

With the rapid development of carbon nanotube (CNT)-based devices, thermal transport characteristics of CNT supported on substrate is to be urgently explored. Herein, we systematically study the thermal transport properties of supported single-wall CNT including length, temperature and substrate coupling strength dependence of thermal conductivity using molecular dynamics (MD) simulation. Interestingly, a theoretical model is proposed to describe the length dependent thermal conductivity of supported SWCNT, which matches well with our MD results. Moreover, the phenomenon of non-monotonic change of thermal conductivity with the variation of coupling coefficient is first discovered in supported CNT. The underlying mechanism is revealed by spectral energy density (SED), phonon transport and stress distribution analysis. Our study provides valuable insights towards the thermal dissipation performance of CNT-based electronic and photonic devices.

Simultaneously improving the thermal conductive and flame retardant performance for epoxy resins thermosets by constructing core‐shell‐brush structure and distributing of MWCNTs in brush intervals

Fire safety and thermal dissipation performance of epoxy resins thermosets were critical for its application in key fields such as electronic devices. The simultaneous improvement of flame retardant and thermal conductivity properties were still a challenge. Herein, ammonium polyphosphate (APP) was firstly encapsulated with 5‐wt% epoxy resins based on APP and then surface grafted with polyurethane polymer chain, and the resulting APP with core‐shell‐brush structure was constructed. Finally, the multiwalled carbon nanotube (MWCNT) was assembled in the intervals of polymer brush on APP surface, and the prepared filler was defined as MF‐APP. Its chemical structure and morphologies were characterized and confirmed. The wettability of MF‐APP was evaluated by water contact angles tests (WCA) and MF‐APP exhibited hydrophobic property with the WCA of 138°. When 9‐wt% MF‐APP was incorporated into EP thermosets, the thermal conductive value of EP/MF‐APP achieved 1.02 Wm−1 K−1, and the MWCNTs concentration was only 1.8 wt% in thermosets. Compared with the previous work, the prepared EP/MF‐APP thermosets exhibited outstanding thermal conductive efficiency because of the homogeneously distribution of MWCNTs. Moreover, the samples fulfilled UL‐94 V‐0 grade during vertical burning tests with the limiting oxygen index of 30.8%. As a result, the thermal conductivity and flame retardancy of EP thermosets were simultaneously enhanced with a relatively low addition amount of MF‐APP, which would bring more chance for wider application of EP thermosets in key fields.

Characteristics of Organic-Based Thermal Interface Materials Suitable for High Temperature Operation

Abstract Historically, for semiconductors subject to standard operating temperatures--which tend not to exceed 125°C--the Tg (glass transition temperatures) of the organic packaging materials protecting the chips is usually around 175°C. Given that, when it comes to electronics operating at high temperatures—typically an environment where the ambient temperature exceeds 200°C—the use of organic materials is generally prohibited due to rapid degradation. At those elevated temperatures, the packaging materials selected are generally composed of metals and ceramics but these materials come with their own shortfalls as well as higher material and manufacturing costs. Therefore, it would be desirable if there were ‘ruggedized’ versions of the organic compounds so commonly used in semiconductor packaging but available for more extreme temperatures, both to reduce cost and package footprint. Meanwhile, the demands from recent developments in high performance computing (HPC) and high-speed data networks means a greater need for increased power and thermal dissipation coupled with very large package body sizes to accommodate the high I/O count. The latest in server microprocessor (MPU) products can easily generate up to 300W during operation, and the heat generated must be quickly transported away from chip to prevent the threat of thermal shutdown. The thermal dissipation issue is controlled by the use of heat spreaders and heat sinks, both of which are intended to make contact with the back-side of a flipped MPU via a thermal interface material (TIM), as part of a large die, large body-size flip-chip ball grid array (FCBGA) package. The thermal interface materials discussed here are examples of organic engineered materials that are capable of withstanding higher operating temperatures than typically seen by semiconductors encased in organic-based packaging. This paper will look at the key material and mechanical attributes for a good thermal interface material, examines the pros-and-cons of various thermal interface material formulations, and discusses the factors for reliable thermal dissipation performance.

Enhanced Thermal Conductivity of Epoxy Composites Filled with 2D Transition Metal Carbides (MXenes) with Ultralow Loading

With the development of electronic devices such as integrated circuits toward the continual increase in power density and consumption, the efficient heat dissipation and low thermal expansion of materials become one of the most important issue. However, conventional polymers have the problem of poor thermal dissipation performance, which hinder application for electronic devices. In this work, the two-dimensional material, MXene (Ti3C2), is used as the reinforcement additive to optimize the thermal properties of polymers. We reported the preparation of multilayer Ti3C2 MXene by HF etching method and obtained few-layer Ti3C2 MXene by simple ultrasonication. Meanwhile, Ti3C2/epoxy composites were prepared by a solution blending method. The results show that the thermal properties of the composites are improved in comparison with the neat epoxy. Thermal conductivity value (0.587 W/mK) of epoxy composite with only 1.0 wt% Ti3C2 MXene fillers, is increased by 141.3% compared with that of neat epoxy. In addition, the composite presents an increased glass transition temperature, high thermal stability and lower coefficient of thermal expansion. This work is of great significance for the research of high-performance composite materials.

Silicon-Doped Diamond-Like Composite Film to Improve the Thermal Dissipated Performance of Light-Emitting Diode

With the progress of light-emitting diodes (LEDs) research deepening, LEDs are gaining more and more widespread. During the use of LED, the excessive temperature of the P-N junction has a bad influence on the life of the LED. In order to reduce the junction temperature of the LED, efficient thermal management has become the key to the popularity of LEDs. The graphite materials are promising thermal conductivity material due to their superior thermal conductivity. In this experiment, Al/AlCX/Diamond-like carbon (DLC) composite film was coated on the surface of the LED substrate by direct current (DC) sputtering and radio frequency (RF) magnetron sputtering. On studying the effect of this composite film on the thermal dissipation performance of LED, the results show that the Al/AlCX/DLC composite film can effectively improve the thermal conductivity of the LED and reduce the thermal resistance. When the LED was driven using a 350-mA drive current, the thermal resistance of the uncoated device was 36.69 K/W and the thermal resistance of the coated device was 30.06 K/W. Compared with the uncoated device, the thermal resistance of the coated device is reduced by 18.1% and the junction temperature is reduced by 4.27 °C.

Numerical Simulation of the Thermal Performance of a Dry Storage Cask for Spent Nuclear Fuel

In this study, the heat flow characteristics and thermal performance of a dry storage cask were investigated via thermal flow experiments and a computational fluid dynamics (CFD) simulation. The results indicate that there are many inner circulations in the flow channel of the cask (the channel width is 10 cm). These circulations affect the channel airflow efficiency, which in turn affects the heat dissipation of the dry storage cask. The daily operating temperatures at the top concrete lid and the upper locations of the concrete cask are higher than those permitted by the design specification. The installation of the salt particle collection device has a limited negative effect on the thermal dissipation performance of the dry storage cask.