Reduction In Thermal Resistance Research Articles

Self-draining microchannel surface structure for droplet condensation with controlled droplet radius distribution

Surface dewetting is technically important in industrial applications, particularly where phase change processes are involved. We present an intrinsically driven water-permeable microchannel surface system. It has two important advantages: its self-draining capability to remove surface droplets and its ability to limit both the maximum size of droplets condensing on the surface and the thickness of the water film in the microchannel system. This results in a reduction in the overall thermal resistance of the condensate on the cooled surface. We have successfully applied this surface drainage concept to water condensation. An improved condensation efficiency of 5%–9% has been achieved operating the device in an environmental chamber (60% relative humidity, 30 °C chamber temperature, 6 °C cooling temperature) without any optimization of the stable surface structure involved.

Enhancing heat pipe performance through hybrid wick structures: Balancing pore size and permeability

This study investigates the impact of wick structures on heat pipe performance by optimizing the balance between effective pore radius and permeability for efficient heat dissipation. It addresses the challenge of enhancing capillary pumping forces while maintaining optimal liquid replenishment to the evaporator. A novel hybrid wick structure is proposed, strategically integrating sintered and screened elements within the heat pipe to improve thermal performance. Experimental tests include varying inclination angles (antigravity up to 60°) to assess thermal resistance and liquid return capabilities. Results show a 13.31 % reduction in thermal resistance compared to conventional sintered heat pipes, particularly at higher power levels (40 W– 60 W). At a 40° inclination angle, optimal evaporation and liquid flow improve thermal performance, with thermal resistance for sintered and hybrid heat pipes decreasing by 14.05 % and 27.72 %, respectively. However, at 60° inclination, the hybrid’s thermal resistance increases significantly due to local dry-out. The study identifies limitations beyond 45° inclination, which is attributed to increased receding contact angles, and the influence of gravity becomes more pronounced, affecting capillary limits. This research underscores the importance of innovative wick designs in advancing heat pipe technology for diverse applications.

Development of polysaccharide bioplastic: Analysis of thermo-mechanical properties and different environmental implications

Despite the distinct benefits of plastics, the environmental impacts stemming from their production and accumulation in the environment have become a global concern. Therefore, the development of new technologies that mitigate these impacts is of notable importance. The present study aimed to evaluate the physicochemical properties of starch-xylan-based bioplastic, and to discuss the viability of this material in terms of applications and ecological impacts. Holocellulose, xylan, and α-cellulose were extracted from waste biomass and combined with starch for bioplastic production. Solubility in food simulants (3% acetic acid, and 90% ethanol) was performed for xylan and starch-based bioplastics. Bioplastic was evaluated to grow Aspergillus versicollor for xylanase production. The bioplastic was evaluated as a photoprotector with yeast exposed to UVC light-covered by the bioplastic for 2 h. Bioplastic disintegration was evaluated in different soil moistures and the disintegration on the surface of the compost. Liquid washes from soils exposed to bioplastic biodegradation were tested for Lactuca sativa seed germination/inhibition. Water from a local lake was exposed to bioplastic and microbial cell density modification was verified. Images of the surface of the bioplastics were obtained by scanning electron microscopy, and characterized by thermogravimetric and dynamic-mechanical analysis. The xylan addition in bioplastic led to a material with a 40–50% decreased ultraviolet light transmittance. An increase in xylan concentration reduced solubility in lipid food simulant solutions, with no fatty solubilization with 25% of xylan. It suggests potential applications in photoprotective and packaging contexts. The thermal degradation temperature of the pure starch bioplastic was 324 °C, and the addition of 10% (287 °C), 15% (286 °C), and 25% (296 °C) xylan (w/w) indicated a reduction in thermal resistance, possibly due to suboptimal interaction between polymer chains. The decrease in crystallinity in the compositions 10/90% (Xc = 20%), 15/85% xylan/starch (Xc = 21%) compared to 25/75% xylan/starch (Xc = 11%) also underscored the complexity of polymer interactions within the bioplastic matrix. Tensile strength of pure starch was 1.21 MPa, while the composition of 15/85% xylan/starch exhibited improved strength 2.99 MPa. Further investigation into the interaction between starch and xylan is warranted. Concerning the disintegration of the 25/75% xylan/starch formulation in the soil, the humidity of the soil matrix played a significant role. The disintegration occurred over 5 days and 16 days in compost (55% humidity) and soil (32.6% humidity), respectively. The results of phytotoxicity (Lactuca sativa seeds) and changes in the physicochemical and biological profile of water (smell, turbidity, phosphorus and nitrogen levels, pH, and bacterial and phytoplankton density/richness), in response to exposure to bioplastics, highlight the necessity of developing this biologically-based and biodegradable technology in concerns about potential environmental impacts. Furthermore, the present study introduces the approach of bioplastic waste recycling using enzyme production biotechnology. In line with the legitimacy of bioplastics as important materials for addressing the challenges posed by their non-biodegradable synthetic counterparts, the presented results broaden the discourse on the feasibility of this biologically based material, contributing to the development of a sustainable society.

An optimizing study of silicon-based microchannels for enhanced thermal transfer

The thermal transport efficiency of microchannel heat sinks is critically influenced by the solid-liquid interface thermal resistance, an aspect that has historically been underappreciated in the design of these systems. We introduce a hybrid model that combines molecular dynamics simulations with computational fluid dynamics to rigorously investigate the interfacial heat transfer characteristics of microchannels. Our methodology involves constructing a nanochannel composed of silicon atoms and water molecules to accurately measure the thermal resistance at the Si–H2O interface. We then extend our analysis by developing two-dimensional rectangular microchannel models. These models are utilized to examine the effects of thermal resistance, channel dimensions, and inlet velocity on the overall interfacial heat transfer rate. Our findings indicate a pronounced size dependency in the variation of the total heat transfer rate, highlighting the critical role of scale in these systems. Significantly, enhancements in heat transfer efficiency are observed with an increase in inlet velocity and a reduction in thermal resistance. These results underscore the importance of optimizing both physical and operational parameters to enhance the efficiency of microchannel heat sinks. The findings are expected to inform future designs and promote more efficient thermal management solutions in various applications.

Effect of ultrasonic on thermo-hydraulic characteristics of shell and tube heat exchangers with twisted tape

Ultrasonic technology was combined with twisted tape insert technology to improve the performance of shell and tube heat exchangers. The effects of sound intensity, sound frequency, and ultrasonic transducer position on thermal transfer, resistance reduction, and overall performance of shell and tube heat exchangers with twisted tape (STHXTT) at different Reynolds numbers were investigated compared to the non-ultrasonic conditions. The experimental results show that applying ultrasonic can significantly enhance thermal transfer, reduce flow resistance, and improve the overall performance. The maximum increase of Nu is 36.53 %, the maximum decrease of f is 12.50 %, and the maximum value of PEC is 1.41. With the increase in Reynolds number, the performance is enhanced but the resistance reduction and overall performance are weak. When the ultrasonic intensity increases, the thermal transfer and resistance reduction performance is enhanced, but a critical ultrasonic intensity exists. When the ultrasonic intensity is large enough, the ability to reduce resistance is enhanced with the decrease of ultrasonic frequency. When the ultrasonic transducer is installed vertically, the thermal transfer performance is the best, however, the resistance reduction effect is the worst. When installed horizontally, the STHXTT has the best resistance reduction performance but the worst thermal transfer effect.

Ultrahigh Thermal Conductivity of Epoxy/Ag Flakes/MXene@Ag Composites Achieved by In Situ Sintering of Silver Nanoparticles.

The growing use of high-power and integrated electronic devices has created a need for thermal conductive adhesives (TCAs) with high thermal conductivity (TC) to manage heat dissipation at the interface. However, TCAs are often limited by contact thermal resistance at the interface between materials. In this study, we synthesized MXene@Ag composites through a direct in situ reduction process. The Ag nanoparticles (Ag NPs) generated by the reduction of the MXene interlayer and surface formed effective thermally conductive pathways with Ag flakes within an epoxy resin matrix. Various characterization analyses revealed that adding MXene@Ag composites at a concentration of 3 wt % resulted in a remarkable TC of 40.80 W/(m·K). This value is 8.77 times higher than that achieved with Ag flakes and 7.9 times higher than with MXene filler alone. The improved TC is attributed to the sintering of the in situ reduced Ag NPs during the curing process, which formed a connection between MXene (a highly conductive material) and the Ag flakes, thereby reducing contact thermal resistance. This reduction in contact thermal resistance significantly enhanced the TC of the thermal interface materials (TIMs). This study presents a novel approach for developing materials with exceptionally high TC, opening new possibilities for the design and fabrication of advanced thermal management systems.

Evaluation of thermo-fluidic performance of micro pulsating heat pipe with and without evaporator side surface structures

Interfacial behaviour and thermal performance of a 4-loop micro pulsating heat pipe are examined through experiments performed at different filling ratio (30–60 %), working fluid (acetone, ethanol, and methanol), and heat input (0–40 W). During the heat pipe operation, nucleation, growth and merging of bubbles, elongation, and movement of vapor plug, and dry out conditions are noticed upon ramp heating (0–40 W) inside smooth surface evaporator pulsating heat pipe. Experiments show that preparation and boiling inception lead to steady operation of heat pipe. Pulsating heat pipe showed minimum thermal resistance when operated with 40 % filling ratio and acetone as working fluid, which has low viscosity, surface tension and boiling point. Additionally, effect of surface structures (rectangular pillar protrusion and hemispherical dimple cavity) on the evaporator section is tested against base smooth surface micro pulsating heat pipe to understand augmentation of heat transfer. Hemispherical dimple cavities show better nucleation, bubble growth, and vapor plug elongation and thereby reduction in thermal resistance. On the other hand, rectangular pillar protrusions showed clogged bubble, least bubble detachment and vapor plug length in the adiabatic zone which results in higher thermal resistance than even smooth surface.

Preparations and Thermal Properties of PDMS-AlN-Al2O3 Composites through the Incorporation of Poly(Catechol-Amine)-Modified Boron Nitride Nanotubes

As one of the emerging nanomaterials, boron nitride nanotubes (BNNTs) provide promising opportunities for diverse applications due to their unique properties, such as high thermal conductivity, immense inertness, and high-temperature durability, while the instability of BNNTs due to their high surface induces agglomerates susceptible to the loss of their advantages. Therefore, the proper functionalization of BNNTs is crucial to highlight their fundamental characteristics. Herein, a simplistic low-cost approach of BNNT surface modification through catechol-polyamine (CAPA) interfacial polymerization is postulated to improve its dispersibility on the polymeric matrix. The modified BNNT was assimilated as a filler additive with AlN/Al2O3 filling materials in a PDMS polymeric matrix to prepare a thermal interface material (TIM). The resulting composite exhibits a heightened isotropic thermal conductivity of 8.10 W/mK, which is a ~47.27% increase compared to pristine composite 5.50 W/mK, and this can be ascribed to the improved BNNT dispersion forming interconnected phonon pathways and the thermal interface resistance reduction due to its augmented compatibility with the polymeric matrix. Moreover, the fabricated composite manifests a fire resistance improvement of ~10% in LOI relative to the neat composite sample, which can be correlated to the thermal stability shift in the TGA and DTA data. An enhancement in thermal permanence is stipulated due to a melting point (Tm) shift of ∼38.5 °C upon the integration of BNNT-CAPA. This improvement can be associated with the good distribution and adhesion of BNNT-CAPA in the polymeric matrix, integrated with its inherent thermal stability, good charring capability, and free radical scavenging effect due to the presence of CAPA on its surface. This study offers new insights into BNNT utilization and its corresponding incorporation into the polymeric matrix, which provides a prospective direction in the preparation of multifunctional materials for electric devices.

Heat transfer performance study of fluid rotating microchannel heat sink

The study presents a novel fluid rotating microchannel heat sink (FR-MC) and reports its heat transfer performance. The FR-MC features two cross ribs positioned in the channel. These cross ribs are inclined in the direction of fluid flow, with each rib inclining in opposite directions. This design enables the fluid to ascend or descend along the ribs, creating rotation after passing through the center to alter the flow direction. Experimental validation confirms the accuracy of the model and numerical simulations. The study investigates the heat transfer capability of FR-MC through comparative analysis, and explores the reasons for the improved performance. The results indicate a 45 % reduction in thermal resistance compared to a rectangular microchannel (R-MC). This improvement is attributed to the rotation of fluid promoting the exchange between the upper and lower parts and the mixing of hot and cold portions, effectively disrupting the thermal boundary layer near the wall. Further exploration into the impact of microchannel dimensions on heat transfer performance indicates that the FR-MC outperforms the R-MC across various heights and widths, achieving thermal resistance reductions ranging from 16 % to 50 %, illustrating the superior heat transfer performance of FR-MC.

Simultaneous Reduction of Bulk and Contact Thermal Resistance in High‐Loading Thermal Interface Materials Using Self‐Assembled Monolayers

AbstractThermal interface materials (TIMs) play a pivotal role in the transfer of heat from high‐temperature sources, such as CPUs, to heat sinks in power electronics. The effectiveness of grease‐type TIMs is determined by their effective thermal impedance (REFF), which hinges on optimizing both the specific bulk (RB) and contact (RC) thermal resistances. Achieving concurrent optimization of these resistances poses a significant challenge, especially in high filler loading TIMs, typically above 76 vol%. This research leverages interface engineering through Self‐Assembled Monolayers (SAMs) to address this challenge. A substantial decrease in REFF is realized to 0.169 K cm2 W−1, a tenfold enhancement compared to non‐SAM treated TIMs, which exhibit REFF values of 2.265 K cm2 W−1. This leap in performance is primarily ascribed to the reduced surface energy of SAM treated Al2O3, leading to lower particle‐to‐particle Van der Waals forces, thereby improving particle dispersion and strengthening interfacial bonds. Furthermore, longer carbon chains in SAMs result in increased RB, yet a decrease in RC, due to the chains' capacity for enhanced energy absorption and molecular entanglement. The investigation underscores the significance of shorter‐chain SAMs in fine‐tuning thermal resistance, highlighting the crucial role of molecular architecture in the design of advanced TIMs.

Experimental Research on an Embedded Heat Source Vapor Chamber for Aerospace Electronic Cooling

Abstract In this work, an embedded heat source vapor chamber (EHS-VC) is proposed for efficient and cost-effective heat dissipation in a limited space of aerospace electronics. The effect of the filling liquid mass and the layers of copper mesh under different working conditions on the heat transfer performance is systematically investigated. EHS-VCs are filled by deionized water with different filling liquid mass of 0.5 g, 0.75 g, 1.0 g, 1.25 g, and 1.5 g. The layer numbers of 250 in−1 copper mesh in EHS-VC are 3, 5, and 7. The results indicate that the optimized EHS-VC with a filling liquid mass of 1.0 g and 5 layers of copper mesh shows superior thermal performance among all tested working conditions. The surface temperature distribution of the optimized EHS-VC remains relatively stable and the surface temperature of the optimized EHS-VC increases linearly with heat load. The optimized EHS-VC can achieve a minimum thermal resistance of 0.19 ℃/W and a maximum critical power of 140 W. Compared with diamond/copper composite plate (D/C CP), EHS-VC shows great potential for efficient and cost-effective heat dissipation in a limited space of aerospace electronics, resulting in a 25% reduction in thermal resistance at the same heat load of 140 W.

Molecular dynamics investigation of the effect of nanostructured surfaces on flow boiling

As a prominent limiting factor in the performance of microelectronic devices, the improvement of heat dissipation is of utmost importance. The enhancement of heat and mass transfer during boiling by nanostructured surfaces has been demonstrated in many studies. In this study, a nanoscale flow-boiling model is developed by molecular dynamics method in order to deeply investigate the microscopic mechanism of nanostructure-enhanced heat transfer. Simple liquid argon is heated by grooved substrate to explore the effect of the depth of the cavities on the boiling heat transfer. The results indicate that the grooved surface improves heat transfer performance through two key mechanisms. Firstly, it induces bubble nucleation, and secondly, it delays the onset of film boiling. The presence of cavities allows the argon atoms within to absorb additional energy from the surrounding walls and be in closer proximity to the heating layer. This reduction in solid thermal resistance results in increased heat transfer efficiency, leading to earlier bubble nucleation and a greater propensity for nucleation within the cavities. The low horizontal velocity of argon atoms within the cavities suggests their ability to retain a significant number of atoms, thereby effectively mitigating the deterioration of heat transfer caused by the formation of a vapor film on the solid wall. The comprehensive performance is observed to improve with increasing depth of the cavities within the range investigated in this study.

Self-healing thermally conductive polymer composites based on polyvinyl alcohol with dynamic borate ester and hydrogen bonds

Traditional thermally conductive polymer materials exhibit a propensity for damage when applied in dynamic environments, which leads to shortened service life and suboptimal utilization of resources. Herein, polyvinyl alcohol (PVA)-based thermally conductive composites with a self-healing capability are prepared based on dynamic borate ester bonds and hydrogen bonds. Poly(dopamine) functionalized graphene oxide (denoted as PGO) is used as a thermally conductive filler to achieve a high thermal conductivity (TC) of 0.79 W/(m·K) for the PGO/PVA composites, which is 527% of pure PVA (0.15 W/(m·K)). The improved TC of PGO/PVA composites is mainly attributed to the reduction in interface thermal resistance and the construction of heat conduction channels. Additionally, the PGO/PVA composites display a self-healing efficiency higher than 60% at room temperature without external simulation. Furthermore, the as-prepared PGO/PVA composites exhibit excellent mechanical properties, with a tensile strength of 409 kPa and an elongation at break of 479%, respectively. This work provides a promising strategy for fabricating thermally conductive polymer composites, which can be deployed as thermal interface materials for long-term applications.

High efficient personal thermoregulatory device: Metallized interface layer between flexible polyimide substrate and foam copper heat sink enables thermal resistance reduction

Customizable flexible thermoelectric devices (f-TED) designed for personal thermal management (PTM) have the potential to substantially diminish energy consumption while enhancing comfort. Currently, studies focus on optimizing thermoelectric device performance and reducing radiator thermal resistance, neglecting the crucial interface between them. In this innovative work, the interface layer between the flexible polyimide substrate of f-TED and the foam copper heat sink was metallized, thereby significantly mitigating the thermal resistance at the interface. In contrast to the conventional thermal conductive adhesive, the metallized welding thermoelectric system (4 × 4 cm² in the plane) demonstrates a 37.0 % augmentation in cooling temperature difference (5.4 ℃ → 7.4 ℃) at 0.3 A. When bending 1000 times (r: ∞ → 20 mm → ∞ → …), the change rate of internal resistance is less than 1.5 %. At a temperature difference of 20 K, it reaches a maximum output power as high as 4.45 mW. Furthermore, an intelligent personal thermal management system was developed. Users can monitor and adjust the working status of the f-TED in real-time via a mobile terminal, achieving personalized thermoregulation. In actual human wear tests, the highest cooling temperature difference reached 13.7 °C, which is one of the highest reported values. This work holds significant implications for advancing f-TED technology innovation, personalized thermoregulation, energy conservation, and environmental protection.

Experimental investigation on thermal-hydraulic performance of manifold microchannel with pin-fins for ultra-high heat flux cooling

The manifold microchannel (MMC) with pin-fins is fabricated and its thermal-hydraulic performance is experimentally investigated. The MMC with pin-fins is an embedded cooling device made of a manifold wafer and a microchannel wafer, anodically bonded to form a total thickness of 1 mm. A microchannel wafer has the etched micro pin-fins with a porosity of 0.75, fin diameter of ▪, and fin height of ▪. For comparison, MMC with plate-fins is also fabricated, in which the plate-fins have the same porosity, fin thickness, and fin height as the pin-fins. Experiments are performed using single-phase deionized water as the working fluid with flow rates ranging from 50 to 300 ml/min, corresponding to pumping powers ranging from 0.28 to 33 mW, which enables the dissipation of an effective heat flux up to 1.2 kW/cm2. The experimental results demonstrate that employing pin-fins improves the thermal-hydraulic performance of the MMC heat sinks compared to using the plate-fins: an average 40% reduction in the effective thermal resistance (the total thermal resistance subtracting the conduction resistance) at a fixed pumping power condition. This is attributed to the fact that the MMC with pin-fins exhibits 20% higher heat transfer coefficient and 40% greater effective heat transfer area, even with 25% lower pressure drop on average compared to the MMC with plate-fins. At the highest tested flow rate of 300 ml/min, the MMC with pin-fins successfully dissipates the heat flux of about 1.2 kW/cm2 without phase-change heat transfer while maintaining the heater temperature below ▪. This is achieved with only 7 mW of pumping power, corresponding to the COP of 41,300 – a 5.3-fold increase in the COP compared to the MMC with plate-fins under the identical heater temperature and the flow rate conditions. Therefore, this study suggests that the MMC with pin-fins is an energy-efficient cooling device for the thermal management of ultra-high heat flux electronics.

Remarkable reduction in thermal contact resistance between target and heat exchanger using TIMs in isotope neutron source accelerator

The high thermal contact resistance (TCR) between the target and the heat exchanger in the Isotope Neutron Source Accelerator will cause the high-energy charged particle beam to stay in the target, resulting in a remarkable increase of temperature which affects the production of stable isotopes. At present, the usage of thermal interface materials (TIMs) can fill the gap at the contact surface and thus reduces the TCR. In this paper, aiming at the actual working condition of neutron source, the steady-state TCR measurement experiment is designed under vacuum and high temperature environment. The TCR at the contact surface was reduced after adding graphite films, thermal greases, liquid metals and preloads. The improvement of TCR of the contact surface between palladium (Pd), copper (Cu) and graphite (Gr) were measured respectively. The results show that the TCR between palladium and graphite is reduced by 95 % by adding liquid metal (Gallium alloy). The TCR between copper and graphite was reduced by 91 % by brazing method. Compared with other TIMs, graphite film has the advantages of high thermal conductivity, high temperature resistance and no fluidity. Adding 0.08 mm thick graphite film between Pd/Gr and Cu/Gr contact surface can reduce the TCR by 50 % and 70 %, respectively. The improvement effect between the two contact surfaces was not obvious when 15.9–318.3 kPa preload was applied.

Numerical Investigation on Thermal Performance of Nanofluid-Assisted Wickless Heat Pipes for Electronic Thermal Management

Abstract Heat pipes are passive heat transfer systems and serve as an effective thermal management solution for electronic devices. The adaptability of heat pipes makes these suited for a wide application range, especially in the field of electronic thermal management. The current study highlights the transient numerical analysis of wickless heat pipes (thermosyphons) for the thermal management of electronic devices. The thermal performance of the thermosyphon is analyzed using both copper oxide (CuO) and aluminum oxide (Al2O3) nanofluids with their concentrations at 1% and 5%. Deionized (DI) water is employed as a reference case for comparison. The study is carried out for variable heat inputs to the thermosyphon ranging 10–50 W for a time interval of 30 s. The idea is to analyze the effect of the evaporator heat input and the nanoparticles concentration on the temperature, heat transfer coefficient, thermal resistance, and effective thermal conductivity of the heat pipe. The results indicate that CuO nanoparticles at a 5% concentration lead to a maximum thermal resistance reduction of 4.31% at 50 W, while alumina nanoparticles at the same concentration lead to a more substantial reduction of 6.66% at the same heat load. The evaporator temperature varies between 377.52 K to 374.99 K using deionized water, and 376.95 K to 374.29 K using CuO nanofluid (at 1% concentration). The heat pipe's evaporator attains its highest convective heat transfer coefficient (437.91 W/m2K) by using alumina nanofluid with 1% nanoparticle concentration at 50 W. Moreover, the effective thermal conductivity of the heat pipe is enhanced by 5% and 7% for copper oxide and aluminum oxide nanofluids (with 5% concentration), respectively, at 50 W. Thus, the nanofluids play a significant role in improving the efficiency and reliability of electronic components. These findings demonstrate the potential of using the nanofluids in thermosyphons to enhance their thermal performance in electronic cooling applications.

A Comparative Numerical Analysis of Cold Plates for Thermal Management of Chips With Hotspots

Abstract Thermal and hydraulic performances of seven water-cooled minichannel cold plates with different internal structures are compared using numerical analysis. Recent increasing demands for high-performance computing have led to serious challenges in the thermal management of electronic devices. In addition to dangerous on-chip temperatures, heterogeneous integration and local regions of elevated temperatures (hotspots) lead to nonuniform chip-level temperature distributions. As a result, the lifespan and reliability of electronic devices are adversely impacted. Due to the limitation of the air-cooled heat sinks, several new methods, such as liquid-cooled microchannel cold plates are developed to remedy these challenges. The objective of this work is to provide a comparative numerical study of the effectiveness of different minichannel cold plate internal structures in the thermal management of a chip with a nonuniform power map and a hotspot. Cold plate thermal resistance, on-chip temperature uniformity, and pump power were the metrics used for this comparison. For four coolant inlet flow rates within the laminar regime, it is seen that increasing the inlet flowrate enhances the thermal resistance of all cold plate designs while creating less uniformity in chip-level temperature distribution relative to the conventional straight microchannels. Concentrating pin fins on the hotspot showed a 7.2% reduction in thermal resistance, despite increasing temperature nonuniformity by about 7.6%. However, it is observed that hotspot-focused pin fins are more effective in lowering the chip's maximum temperature. Obtaining lower chip-level nonuniformity may be possible by modifying the inlet and outlet conditions of the cold plates.

Performance of Pulsating Heat Pipe with a stimulus of auxiliary heat load for Battery Thermal Management System

Stimulus strategy is proposed to enhance the heat dissipation performance of Pulsating Heat Pipe (PHP) at low heat load for local hot spot regression in Battery Thermal Management (BTM). An auxiliary heat load is applied to stimulate the start-up of PHP. The performances of PHP with and without stimulus are compared and the properties of PHP after stimulus are discussed. It is concluded that the application of auxiliary heat load is able to stimulate the start-up of PHP in experiments. The strategy is mainly based on the phase-change mechanism as well as the hysteresis of working medium. Thermal resistance and the evaporator temperature are significantly reduced, if PHP starts operation after stimulus. Long period of stimulus and strong auxiliary heat load are favored for the reduction of thermal resistance and the shortening of period for start-up. The thermal resistance may be reduced by 29.1 ∼ 69.6 % and the temperature may be regressed by around 8 °C. However, PHP may suffer from temperature uplift and overshot to the maximum evaporator temperature. Therefore, high interference temperature coupled with weak auxiliary heat load and long period of stimulus are suggested as the optimal strategy. The verified strategy offers a new method for local hot spot regression and a possible way to mitigate the risk of thermal runaway, since the heat dissipation is enhanced at the initial stage of damage or destruction.

Preparation of GNP/SBR thermal conductivity composites with high strength and toughness by synergistic construction of interfacial multiple non‐covalent and covalent bonds

Abstract[AMIm]Cl@GNP/SBR composites were prepared by blending ionic liquid 1‐allyl‐3‐methylimidazolium chloride salt([AMIm]Cl) modified graphene nanoplatelets (GNP) and styrene‐butadiene rubber (SBR). The mechanical and thermal properties as well as the structure–activity relationship of the obtained composites based on the modified filler were investigated under the synergistic effect of non‐covalent and covalent bonding. The experimental results indicated that the modification of GNP by [AMIm]Cl occurred under mild conditions. The dispersibility of [AMIm]Cl@GNP in SBR was enhanced by its participation in vulcanization and the synergistic effect of non‐covalent and covalent cross‐linking networks such as cation‐π, π‐π, and hydrogen bonds. This improvement led to an increase in the interfacial bond strength of the composites and a reduction in the interfacial thermal resistance. These effects resulted in both reinforcement and thermal conductivity properties. The tensile strength and elongation at break of [AMIm]Cl@GNP/SBR composites increased from 18.2 to 22.9 MPa and from 737.9% to 923.5%, respectively, when the modification ratio of [AMIm]Cl was 1% and the loading of [AMIm]Cl@GNP was only 4 phr (mass ratio). At the same time, the thermal conductivity in the vertical direction of the composites increased from 0.25 to 0.44 W/(m·K), and the thermal conductivity in the horizontal direction increased from 0.27 to 0.81 W/(m·K).Highlights Modified powder [AMIm]Cl@graphene nanoplatelets were prepared; [AMIm]Cl@graphene nanoplatelet/styrene‐butadiene rubber blend was prepared; Mechanical properties of blends significantly improved over blank; The horizontal thermal conductivity of the blends increases obviously; The vertical thermal conductivity of the blends was improved.