Heat Dissipation Ability Research Articles

Elastomer Composites with High Damping and Low Thermal Resistance via Hierarchical Interactions and Regulating Filler.

Modern microelectronics and emerging technologies such as wearable electronics and soft robotics require elastomers to integrate high damping with low thermal resistance to avoid damage caused by vibrations and heat accumulation. However, the strong coupling between storage modulus and loss factor makes it generally challenging to simultaneously increase both thermal conductance and damping. Here, a strategy of introducing hierarchical interaction and regulating fillers in polybutadiene/spherical aluminum elastomer composites is reported to simultaneously achieve extraordinary damping ability of tan δ>1.0 and low thermal resistance of 0.15cm2 KW-1 , which surpasses state-of-the-art elastomers and their composites. The enhanced damping is attributed to increased energy dissipation via introducing the hierarchical hydrogen bond interactions in polybutadiene networks and the addition of spherical aluminum, which also functions as a thermally conductive filler to achieve low thermal resistance. As a proof of concept, the polybutadiene/spherical aluminum elastomer composites are used as thermal interface materials, showing effective heat dissipation for electronic devices in vibration scenarios. The combination of outstanding damping performance and extraordinary heat dissipation ability of the elastomer composites may create new opportunities for their applications in electronics.

Quality assurance thermophysical aspects of highly porous implants with cellular structure obtained by selective laser melting

Selective laser melting (SLM) is an additive manufacturing process that involves the layer-by-layer construction of a three-dimensional object by local melting of a powder layer based on a prepared CAD model. This technology makes it possible to manufacture products of complex configuration, including internal channels of complex geometry. Such products include personalized highly porous implants, which are subject to very strict requirements in the field of elastic and strength properties, ensuring their compliance with the properties of the biological objects being replaced. The quality of highly porous cellular products formed by the selective laser melting method based on metal powder compositions is determined by a significant number of factors, the combined influence of which is difficult to control. At the same time, the structure and mechanical properties of highly porous cellular materials (HPCM) obtained by laser synthesis are largely determined by the melt bath shape stability, which depends on the ability of local heat dissipation, which in turn is determined by the fused product geometry. Under these conditions, simulation of thermal processes, including the prediction of the part fusion temperature modes, is of paramount importance. This study focuses on the numerical analysis of the powder layer thermophysical parameters during the laser melting process, which is difficult to analyze by direct measurements, and a computational model based on COMSOL Multiphysics has been created to predict the melt bath temperature field. The numerical model made it possible to quantify the influence of the selective laser melting process parameters (laser power and scanning speed) in combination with the choice of material and topology of the part on the temperature fields formation to determine the process technological parameter and the features of creating geometry for additive manufacturing, which make it possible to obtain products of proper quality. Cellular implants based on Ti6Al4V powder have been grown by selective laser melting.

Force-thermal analysis of large-area microchannel embedded cooling plate in improving thermal management of high-power density data centers

ABSTRACT A thermal management method for data centers from the server level is proposed in this paper. This paper explores the high energy consumption of the server itself, proposing a principle of microchannel shape design for a cooling plate based on the principal stress lines (PSLs). Under the condition of a uniform load, the influence of the cross-sectional shape of the microchannel on the contact thermal resistance was found to be insignificant. From the analysis of cooling plate plane, the uniformity of the stress distribution of the microchannel determined the uniformity of the contact thermal resistance, which determined the heat dissipation ability. Experiments were developed to test and verify the cooling performance of the cooling plate as well as the performance differences with the microchannels along and away from the PSLs under deformation. It was concluded that compared with the conventional serpentine microchannel, the cooling performance of the cooling plate proposed in this paper was 4.5 reduction in average temperature. Furthermore, when the ultra-thin cooling plate was subjected to a uniform load distribution, the microchannel along a single PSL had the best stress distribution, that is, the contact thermal resistance had the least variation.

Novel Color Converters for High Brightness Laser‐Driven Projection Display: Transparent Ceramics–Glass Ceramics Film Composite

AbstractLaser‐driven projection display puts forward urgent demand for color converter materials to simultaneously achieve balanced‐spectrum properties and strong heat dissipation. Herein, this work develops a novel optofunctional composite by coupling Y3Al5O12:Ce3+ transparent ceramics (TC) with CaAlSiN3:Eu2+ phosphor‐in‐glass film (PiGF) for the first time. Remarkably, this new material architecture design enables a balance between the spectrum properties and heat dissipation ability, and can yield high‐quality white light with brightness of over 2500 lm, luminous efficacy (LE) of over 200 lm W−1, correlated color temperature (CCT) of 3700–4100 K, and improved color rendering index (CRI) of 60–70. Furthermore, the PiGF@TC‐converted laser projection system is also successfully designed, showing natural and real color restoration. Additionally, the combined action of thermal quenching and optical excitation intensity quenching is confirmed for the luminescence saturation upon high‐power blue laser driven. The main mechanism of optical quenching is identified to be energy upconversion dominated by second‐order nonlinear processes. The findings described here suggest a step toward developing the admirable laser‐driven color converters for next‐generation lighting sources.

The solution of wetting issues in GaN epitaxy on (111) SCD with magnetron sputtered AlN

Single crystal diamond (SCD) is an ideal heatsink for GaN-based devices. However, wetting issue of buffer on SCD hinders the GaN quality, limiting the full utilization of SCD's heat-dissipation ability. In this paper, the first-principles calculation revealed the high adsorption energy of Al and N adatoms on the surface of (111) SCD. The high energy of adatoms lead to a poor nucleation of AlN on (111) SCD, which caused inferior buffer layer. We propose a solution by pre-depositing AlN on (111) SCD via the ex-magnetron sputtering, which greatly enhances the quality of buffer layer and GaN film. Three different thicknesses of sputtered AlN (25 nm, 50 nm, and 100 nm were studied, and all showed improvement in GaN quality. The enhanced quality had been confirmed by the detailed characterization. GaN on (111) SCD with sputtered AlN presents narrower rocking curves of X-ray Diffraction (XRD). Additionally, GaN on 50 nm sputtered AlN/(111) SCD demonstrated superior quality, achieving a full width at half maximum of XRD for 1878/1945″ at 002/102.

Fabrication of diamond/copper composite thin plate based on a single-layer close packed diamond particles network for heat dissipation

High-efficiency heat dissipation is crucial for the reliability and durability of high-power electronics devices. Diamond/copper composites have drawn much attention as promising candidate materials for thermal management due to their high thermal conductivity and tunable coefficient of thermal expansion. In this work, a novel method was proposed to fabricate a thin plate of diamond/copper composite based on the construction of single-layer close packed diamond particles network. The composite with a sandwich structure was prepared by press-brazing method, which is cost-effective for both preparation and post-processing. The microstructures of the composite plate containing diamond, AgCuTi filler and Cu were examined. The influence of diamond particle size on thermal conductivity, coefficient of thermal expansion, and mechanical properties were also experimentally measured and theoretically simulated. The results show that a single-layer close packed diamond particles network is densely brazed between copper layers to form a composite thin plate. The interface TiC layer is in-situ formed between diamond and AgCuTi matrix. With increase in the diamond particle size to 1200 μm, thermal conductivity of 552.7 W⋅m−1⋅K−1, coefficient of thermal expansion of 10.1 × 10-6 K−1, and flexural strength of 204.3 MPa are achieved, which are in agreement with the theoretical simulated results. As a heat spreader substrate, the heat dissipation ability of diamond/Cu composite is increased by 5.7 °C in comparison with pure Cu plate. Finite element analysis and testing of actual scenarios further confirm the excellent thermal performance of the sandwich structured diamond/Cu composite thin plate, making it a prospective candidate for thermal management.

Fabrication and characterization of graphene‐loaded recycled poly(ethylene terephthalate) electrospun composite nanofibrous mats with improved thermal conductivity

AbstractIn this study, graphene‐loaded electrospun recycled poly(ethylene terephthalate) (rPET) nanofibrous mats were produced and characterized morphologically, spectrally, mechanically and thermally. Particularly, the effects of graphene nanoplatelets (GNP) and multilayer graphene (GML) in improving the thermal conductivity and heat dissipation abilities of rPET‐based composite nanofibers were investigated. The morphological analyzes pointed out that 1% graphene loading led to smooth nanofibers while 5 and 10% of GNP‐loading resulted in coarser nanofibers with rougher surfaces and agglomerations. The differential scanning calorimetry results pointed out that the crystallization temperature increased with increasing graphene content as a result of the pronounced nucleation effect. The thermogravimetric analysis demonstrated an improvement in the thermal stability of the composite nanofibers. The thermal conductivity coefficients increased to 25.422 W/mK‐35.842 W/mK for rPET/GNP nanofibers and up to 62.669 W/mK for rPET/GML nanofibers, compared to that of 12.753 W/mK for neat rPET nanofibers which correspond to an increase between 99 and 391%. Heat dissipation capability of the graphene‐loaded composite nanofibers was illustrated with infrared thermography data, displaying an increase in the average surface temperature of the nanofibrous mats between 2 and 19°C at 30 s of heating. The results suggest the use of the graphene‐loaded rPET composite nanofibers as textile materials for thermoregulating applications.Highlights Recycled poly(ethylene terephthalate)/graphene composite nanofibers are electrospun. Thermal conductivity of graphene‐loaded nanofibers increases by up to 391%. Graphene loading in nanofibers leads to faster and more uniform heat dissipation. Mechanical properties of composite nanofibers improve. Value‐added recycled polyester materials for thermal management are foreseen.

Design and Analysis of Brake Drum using Finite Element Analysis

Because of the need for safety, braking performance has become a very important factor for automotive manufacturers and passengers. Despite all the stresses experienced by the drum brake doesn’t damage the drum due to high tensile strength but the drum may fail under fatigue loading. The critical region of concentrated stress is determined, and appropriate modifications are being made to improve it. The distribution of stress and the heat dissipation obtained from the result of the analysis are employed as input for the failure region. The findings of stress and thermal analysis are crucial for improving the component design at the first stage of development. The objectives of this study are to modify and improve the circumferential strength and heat dissipation and to optimize the design of the drum brake with simulation using Finite Element Analysis. The simulation was run on the initial model and modified on its to make it better. it shows that 27.33% decrease in maximum von Mises stress. Thermal analysis for heat flux on the material will show the ability of heat dissipation. Overall, It has been determined that aluminium alloy is the optimum material for drum brake design in terms of total heat flux.

Thermal Performance and Parametrical Analysis of Topologically-optimized Cross-flow Heat Sinks Integrated with Impact Jet

In this work, two novel cross-flow heat sink structures are firstly designed by means of topological optimization with the objective function which aims to achieve the minimum temperature difference and pressure drop or with the other objective function which aims to get the minimum mean temperature and pressure drop, namely, TOS1 and TOS2. By analyzing the effect of six channel heights Hch of TOS1 and TOS2 with the evaluation criterion j/f, we obtain that TOS2 with the Hch of 5 mm has the best ability of heat dissipation. A impact jet part is then implemented into the TOS2 to form a new integrated heat sink, that is, ITOS. Numerical results show that the ITOS exhibits much better thermal performance than TOS2 and TOS1. The in-depth parametric study on the flow and thermal behaviors of the ITOS shows that the average temperature of the bottom surface of the ITOS increases with the height of the channel of the bottom plate, while the temperature difference peaks at the Hch of 2 mm. The increase of the ratio of cross-flow fluid to total fluid leads to a reduction of the heat dissipation ability, implying that the high thermal performance of the impinging jet plays an important role in the heat transfer process of such ITOS. Finally, the convective heat transfer experiment of the ITOS with the Hch of 5 mm is conducted to testify the optimization and simulation results.

Surface integrity of drilling Ti-6Al-4V micro-holes using the ultrashort pulse laser with different three-dimensional paths planning

The improvement of aero-engine performance posed a challenge to the heat dissipation ability of blades, resulting in a substantial increase in the demand for micron-sized (≤1 mm) film cooling holes. In this paper, an improved three-dimensional path machining method for ultrashort pulse laser drilling of Ti-6Al-4V titanium alloy is studied. The influence of four representative paths that are contour offset path, broken line path, raster path and jagged path on hole quality is described and discussed in detail. By establishing a three-dimensional two-temperature model in cylindrical coordinates, the defocusing control of the machining process is carried out, and the temperature field distribution with different drilling paths is simulated and analyzed. Finally, the experimental study of drilling round holes with a diameter of 800 μm is carried out on the titanium alloy Ti-6Al-4V plate with a thickness of 1 mm, and the wear resistance of the workpieces is tested. The experimental results show that, compared with the other three paths, the temperature field uniformity of laser processing with the contour offset path is the best, the quality of the processed holes is significantly improved, the outlet roundness is increased by 26.54 %–36.59 %, the cone angle is reduced by 12.7° and the wear resistance is increased by >1.3 times. Moreover, there is no obvious recast layer and micro cracks on the pore wall, and dense nano oxide particles are produced on the surface. In summary, the contour offset path controlled by three-dimensional defocusing is an effective hole processing path, which provides the possibility for machining efficient and high-quality film cooling holes.

Embedded Microfluidic Cooling in Aluminum Nitride HTCC Substrate for High-Power Radio Frequency Chip Array

Abstract Radio frequency (RF) electronics are developing toward high power, high integration, and high-power density, resulting in a continuous increase in heat flux. The traditional high-power RF package, which is usually composed of aluminum nitride (AlN) substrate, aluminum silicon housing shell, and aluminum alloy cold plate, exhibits poor heat dissipation ability and high thickness due to excessive interfaces and a long thermal conduction path. In this paper, aimed at improving heat dissipation ability and reducing the thickness of RF electronics, the microchannel was transferred from the cold plate to the AlN high-temperature co-fired ceramic (HTCC) substrate which plays the role of electrical connection, structural support, and liquid cooling cold plate. The embedded AlN microchannel cooler was firstly designed. Then, a prototype of the AlN substrate with 64 simulated chip arrays and microchannels was fabricated and the thermal performance was evaluated using an experimental setup. Finally, the thermal performances of the proposed and traditional cooler were compared using a CFD simulation. The results indicated that the proposed embedded cooling structure could enhance the heat-flux dissipation ability by 61% and reduce the packaging thickness by 40% compared with the traditional cooling structure.

Improvement methods for thermal backflow phenomenon in engine compartment blow-type air cooler module

Regarding the thermal backflow problem in the central area of the engine compartment's blow-type cooler module, a computational model for the entire machine's outflow field is first established and validated using experimental results. Next, the formation of thermal backflow phenomenon is analyzed, and a more accurate calculation method for the cooler that takes into account the thermal backflow phenomenon is proposed. Finally, a new structure that can eliminate the thermal backflow phenomenon is presented, and the heat dissipation effect is analyzed. The conclusion shows that the calculated values of the engine compartment cooler module are consistent with experimental results, verifying the correctness of the computational model. The negative pressure caused by the “pump” suction effect in the central area of the cooler module is the fundamental reason for the generation of the thermal backflow phenomenon. The dual heat exchanger model can significantly improve the calculation accuracy of the cooler when taking into account the thermal backflow phenomenon (by at least 10%), providing a more accurate method for evaluating the cooler's heat dissipation ability. The proposed new structure can eliminate the thermal backflow phenomenon in the cooler module and improve the heat dissipation uniformity. After the elimination of the thermal backflow phenomenon, the heat dissipation ability of the cooler is improved by at least 25%. In addition, the improvement of the heat dissipation uniformity of the cooler can effectively solve the problem that multiple coolers in the engine compartment have inconsistent heat dissipation capabilities. The proposed calculation method for the cooler taking into account the thermal backflow phenomenon and the new structure for eliminating the thermal backflow provide a reference for the development of similar products in the future.

Flexible and lightweight graphene grown by rapid thermal processing chemical vapor deposition for thermal management in consumer electronics

Next-generation consumer electronics require excellent thermal management. Graphene is a good choice because its thermal conductivity is 13 times that of copper. Single-, bi- and few-layer graphene (SLG, BLG, FLG) with large sp2 domains were grown by rapid thermal processing chemical vapor deposition (RTP-CVD) from CH4 and H2 using Ar as the diluting gas. The quality of graphene was investigated by Raman spectroscopy and TEM. To demonstrate the heat dissipation capability of RTP-CVD-grown graphene, a 2 TB solid state drive was used and the temperature was measured by a FLIR thermal camera. Results indicate that high thermal conductivity graphene was prepared by diluting the precursor gas with Ar. SLG was prepared at a growth temperature of 1 000 °C and a time of 25 min. A transition from FLG to high-quality BLG was observed at low H2 concentrations. Using SLG, there was a 5 °C lower temperature rise than using a commercial copper heat dissipator. The heat dissipation ability of SLG was approximately 200 times that of commercial copper heat dissipators.

Performance Analysis and Prospect of Piezoelectric Ultrasonic Transducers Based on Vibration Modes

With the maturity of ultrasonic transducer technology, as a traditional ultrasonic transducer, piezoelectric ultrasonic transducer has leaped into the public view. This article briefly summarizes the development of ultrasonic transducers and the classification of piezoelectric ultrasonic transducers. In practical applications, different piezoelectric ultrasonic transducers are mostly selected based on the different sound source vibrations in the application scenarios. The principle analysis and structure introduction of longitudinal vibration type ultrasonic transducers, longitudinal bending vibration mode conversion type ultrasonic transducers, and torsional vibration piezoelectric ceramic ultrasonic transducers are conducted respectively, and the application fields are pointed out. Besides, heat dissipation is an important link that affects the energy transfer efficiency of piezoelectric ultrasonic transducers. For traditional air-cooled heat dissipation and phase change heat dissipation, the heat dissipation ability is investigated and analyzed separately, and the advantages and disadvantages of the two are compared. It is concluded that phase change heat dissipation can effectively solve the impact caused by excessive temperature difference inside the transducer, while traditional heat dissipation methods cannot solve this problem.

High Out-of-Plane Thermally Conductive Polyimide Film for Electronic Thermal Management by the Incorporation of Core–Shell Ag/Polyimide Microparticles

Polyimide (PI) films with high out-of-plane thermal conductivity are highly desirable for effectively alleviating thermal failure in advanced flexible electronics. However, it is still a great challenge to achieve high out-of-plane thermal conductivity with a low filler content by a simple method. Herein, an Ag-coated PI microsphere (PIM@Ag) as a thermally conductive filler with a considerable heat-transfer path in the out-of-plane direction is prepared to improve the out-of-plane thermal conductivity of the PI film. Because of the introduction of thermal welding between Ag nanoparticles during thermal imidization further eliminating the interface thermal resistance, the resultant PI/PIM@Ag composite film exhibits a high out-of-plane thermal conductivity of 1.2 Wm–1K–1 with an ultralow Ag content of 6.08 wt % and a superior tensile strength of 124.0 MPa compared to 78.9 MPa of a pure PI film. Practical application and comsol simulation results verify that the PI/PIM@Ag composite film has excellent heat dissipation ability for a chip. This work provides an idea for improving the out-of-plane thermal conductivity of polymers with low filler contents.

A novel thermal interface membrane structure based on phase change material for thermal management of electronics

As an important part of the heat dissipation system of electronic devices, thermal interface membranes (TIM) can largely eliminate the interface thermal resistance between electronic devices and heat sinks. However, the minimum thickness of TIM which is constrained by the maximum assembly pressure that the electronic chip can withstand and the marginal cost caused by the continuous improvement of thermal conductivity makes the development of conventional TIM bottlenecked. This paper proposes a novel laminar temperature control structure based on form-stable phase change material with thermal-induced flexibility (TF-FSPCM). When the TF-FSPCM is thin (<500 μm), the structure appears as a TIM. Different from conventional TIMs, the structure provides a unique lateral thermal conductivity channel to increase the maximum heat flux. And the TF-FSPCM simultaneously solves the problem of excessive assembly pressure and leakage of PCM. 6 wt% EG increases the thermal conductivity of PCM by 223 %. When the carbon fiber net (CFN) is functional layer material, the actual thermal resistance of CFN-TIM is not >0.79 cm2K/W and the minimum theoretical thermal resistance is <0.1 cm2K/W at the preparation pressure in 0.04 MPa. In particular, the assembly pressure on TF-FSPCM is reduced to a normal level due to its excellent self-repair. In addition, the membrane structure of CFN greatly improves the tensile strength and puncture resistance so that it has a broader application prospect. Finally, the actual temperature control experiments show that the equilibrium temperatures of CFN-TIM and CFN/CF-TIM are reduced by 12.8 °C and 15.6 °C, respectively. This indicates that the membrane structure has a small actual thermal resistance and a large elastic modulus. And it proves that the unique lateral conduction channel of the laminar composite structure has the actual heat dissipation ability.

Thermal performance of open microchannel heat sink with NACA airfoil shaped pin fins

ABSTRACT The main purpose of this study is to numerically investigate the effect of pin-fin National Advisory Committee for Aeronautics (NACA) airfoil on the heat transfer performance of a single open microchannel heat sink with a fixed surface area and a constant wall heat flux. It was found that the helical flow within the microchannel and the converging–diverging flow near the two sides of the microchannel, caused by the periodically arranged NACA airfoil shaped pin fins with an attack angle, dominate the overall heat dissipation ability of the heat sink. The heat dissipation ability can be further improved by increasing the attack angle and Reynolds number. Of the airfoils considered, the symmetrical airfoil NACA0012 in no attack angle case presents the smallest pressure drop, but also the smallest thermal performance value, which can still achieve a Nusselt number improvement of 35.15% and a thermal performance factor (TPF) improvement of 1.38%, compared to the no-fin case. The NACA airfoil effect can be improved when asymmetric airfoils are considered. In terms of overall thermal performance, the NACA6412 would be the best choice. Its percentage increases in the Nusselt number and TPF can be further enhanced by up to 57.62% and 35.43%, respectively, compared to the no-attack-angle NACA0012 case.

Soft and thermally conductive gels by introducing free-movable polymer chains into network

The rapid development of electronic devices has been putting forward requirements for higher thermal conductivity, softness, and stability of thermal interface materials. However, thermal interface materials simultaneously achieving softness, stability, and thermal conductivity is still challenging. Here, we propose a strategy of introducing free-movable polymer chains to prepare thermally conductive gels possessing high thermal conductivity (6.91 W m−1 K−1), good softness (Young's modulus ∼400 KPa, and stretchability increasing 262.4%). The high thermal conductivity is due to the high addition of microscale spherical Aluminum. The good softness is attributed to the free-movable poly (ethylene propylene diene), which reduces the interaction between polymer networks. When thermally conductive gels simulate practical applications, it shows excellent heat-dissipation ability and thermal stability after 1000 heating-cooling cycles. This work provides a simple strategy for constructing thermally conductive gels with high performance and promotes their potential applications in the thermal management of electronic devices.

AlGaN UV Detector with Largely Enhanced Heat Dissipation on Mo Substrate Enabled by van der Waals Epitaxy

The epitaxy of AlGaN on metallic substrates exhibits numerous advantages including flexibility, vertical carrier injection, and enhanced heat dissipation for optoelectronic devices; however, there are still many challenges for the growth of AlGaN according to the serious interfacial reaction and lattice mismatch by conventional epitaxial techniques. In this work, the c-oriented AlGaN is grown on polycrystalline Mo substrate by van der Waals (vdWs) epitaxy with graphene as the insertion layer. A high-temperature annealed AlN is deposited as the nucleation layer, which optimizes the crystalline quality of following AlGaN. The isolation effect of the graphene insertion layer results in a good epitaxial interface, which suppresses the atoms diffusion and chemical reaction, demonstrating by the theoretical calculation of high energy barriers for Al/Mo atoms penetrating through graphene insertion layer. The ultraviolet (UV) detector is fabricated by further growing a n-AlGaN layer as the photosensitive absorber, whose responsivity (1.7 × 10–3 A W–1) is comparable with that fabricated on conventional sapphire. Even better, the UV detector on the Mo substrate possesses enhanced heat dissipation ability due to its higher thermal conductivity, and the temperature elevation after consistently applying a drive voltage largely decreases by 50%. This work enlightens the growth of AlGaN materials and fabrication of high-power/high-voltage optoelectronic devices on polycrystalline metallic substrates by the mean of vdWs epitaxy.

Simulation Research on Parameters Matching of Vehicle Engine Cooling System Based on AMEsim

The engine cooling system equipped on a 1.5T vehicle is regarded as the research object in this article, and the heat dissipation capacity under different working conditions of this vehicle is simulated based on AMEsim software. The simulation results show that the heat dissipation ability of this cooling system is insufficient under extreme high-temperature climbing conditions. Therefore, the component parameters of the cooling system need to be matched again, and the effectiveness of simulation tests is verified based on AMEsim software. The simulation research in this article has certain engineering application value. It can provide guidance for vehicle engineers of the Original Equipment Manufacturer (OEM) to match the parameters quickly in the early development process of the vehicle engine cooling system.