The Z-type manifold microchannel (MMC) heat sink could efficiently dissipate the heat for electronic devices. However, this structure has a drawback of non-uniform flow distribution. To enhance the flow uniformity, three optimization schemes are proposed in this study. The first one is to add a rectangular restrictor in each microchannel and the rectangular restrictor width is set to an uneven size. The second one is to add a rectangular restrictor on the top of each fin and the gap of adjacent rectangular restrictors is set into uneven dimensions. The third one is to set the width of each microchannel into uneven dimensions. The influences of the rectangular restrictor height and the microchannel widths on the flow and heat transfer characteristics have been numerically investigated. The results show that the MMC with uneven microchannel width exhibits the best flow uniformity and minimum thermal resistance. The flow uniformity factors of the three optimization schemes are all below 13.35% and the MMC with uneven microchannel widths has the lowest flow uniformity factor of 7.87%. The flow uniformity of the MMC with uneven microchannel widths is improved by 84.88%, and the thermal resistance of the case is reduced by an average of 21.67%. On the other hand, the flow uniformity of the MMCs with restrictors in each microchannel and on the top of each fin is improved by 74.34% and 80.53%, respectively. The thermal resistance of the two cases is reduced by 9.74% and 11.22%, respectively. Moreover, the pressure drops of the three optimized MMCs are relatively similar in magnitude.

Condensation is a crucial factor affecting the thermal performance of various types of heat pipes, with the porous wick structure playing a significant role in condensation. In this study, an experimental platform was set up in a saturated atmosphere to investigate the condensation process of steam on a vertical plane surface with sintered copper screen. The effects of subcooling, mesh number, layer, and screen structure on condensation mode, droplet departure diameter, and heat transfer coefficient (HTC) were explored. The results indicate that the condensation mode of the screen is different from that of the smooth copper surface, with the screen exhibiting a rivulet mode, whereas the smooth copper surface shows a dropwise mode. Sintering pressure affects the condensation mode of a single layer of 300-mesh screen but has minimal effect on the HTC. As subcooling increases, the droplet departure diameter on the screen surface also increases. The HTC of the screen is lower than that of the smooth copper surface, with reduction varying depending on the mesh number. The effect of the layer number of screen on the HTC varies with the mesh number. The thermal resistance of condensation in the vertical orientation is not linearly related to the layer number of screen, which contrasts with the conventional thermal resistance theory. Gradient screens appear to have a minimal impact on the HTC. This study proposes an empirical formula to predict the HTC suitable for vertical mesh-covered surfaces, with an average absolute error of 13.07%, significantly improving the thermal design accuracy of heat pipes compared to conventional heat resistance theories.

This study investigated the potential of integrating separate heat pipe and adsorption refrigeration systems as a data center efficient cooling system. Compared to water-cooled data centers, this approach demonstrates improved heat transfer efficiency and reduced energy consumption. The effectiveness of heat transfer in this approach is illustrated by applying exergy and entranspy theories. By conducting numerical simulations across five representative Chinese cities with different climates, both Power Usage Effectiveness (PUE) and key cooling system performance indicators are assessed. The analysis reveals that all cities can achieve a PUE below 1.095, realized a 65.87 % and 13.60 % reduction in cooling system energy consumption and entransy dissipation, respectively. Data centers using mechanical chiller cooling cause a high energy consumption. This paper indicates the benefits of integrating heat pipe and adsorption refrigeration systems in reducing energy consumption and optimizing overall data center performance.

The microencapsulated phase change material suspension (MPCMS) is a novel functional thermal fluid. The application of MPCMS to loop thermosyphon is an innovative attempt, which can effectively improve the heat transfer efficiency of loop thermosyphon. In this paper, a three-phase loop thermosyphon using water-based MPCMS as the medium is developed. A comprehensive experimental investigation was conducted to study the heat transfer performance by varying the filling ratio (50 %, 60 %, and 70 %), heat flux (25 - 125 W/cm 2 ), and mass concentration (0 %, 0.1 wt%, and 1 wt%). The findings of this study indicate that the loop thermosyphon incorporating MPCMS exhibits improved heat transfer performance compared to a two-phase loop thermosyphon utilizing pure water. The addition of MPCMS has been observed to reduce the wall temperature by up to 6.6 degrees C and decrease the loop thermal resistance by 13.5 %. Furthermore, the loop thermosyphon with MPCMS demonstrates superior start -up characteristics and thermal homogeneity when compared to water-based systems.

Abstract Microencapsulated phase change material suspension (MPCMS) represents an innovative category of functional thermal fluids. This novel working fluid not only preserves the substantial energy density and high latent heat of phase change materials (PCM), but also mitigates the issues related to PCM, including susceptibility to aggregation and low thermal conductivity. This article selects phase change microcapsules with a phase change temperature of 70 °C, and uses pure water as the base liquid to prepare MPCMS as the working fluid for the loop thermosyphon. A series of heat transfer experiments are conducted, and the results are compared with those of pure water experiments. A 135mm*650mm copper loop thermosyphon, is designed and constructed to investigate the effect of various input power on the heat transfer performance. The results show that the addition of MPCMS can reduce the wall temperature by up to 2.9°C and the loop thermal resistance by 6.3%. Compared with water, the loop thermosyphon with MPCMS has better start-up characteristics. The performance of the MPCMS is affected by various parameters, which are interconnected. Particles in close proximity to the wall display erratic movement, fluctuating across different temperature zones, thereby undergoing a continuous cycle of melting and solidification. This study establishes a basis for further investigation into the practical implementation of MPCMS in industries.

Energy efficiency issues are being focused on the growing concern of global warming and environmental pollution. The high-temperature heat pipe (HTHP) is an effective and environmental-friendly heat transfer device employed in many industries, including solar power generation, high-temperature flue gas waste heat recovery, industrial furnaces, nuclear industries, and aviation. As a critical factor in HTHPs, thermal performance is mainly introduced in the entire paper. To date, most reviews have been published concerning one or several application scenarios. However, to the best of authors’ knowledge, it is hard to find a review discussing how to improve the thermal performance of HTHPs comprehensively. First, the impact on the performance of three main components of HTHPs over the past 30 years is introduced: the working fluid, the HTHP structure, and the wick structure. Herein, it is a considerable review of the optimal operating conditions for each direction, and we expect this paper contribute to improving the thermal performance of HTHPs. Then, current numerical simulations and theoretical research on the heat transfer limit of HTHPs are recommended. The significant hypotheses used in numerical simulations and the present theoretical studies are compiled here. Finally, some potential future directions and tentative suggestions for HTHP research are put forward.

In this study, pool boiling from micro -pillar modified surface has been simulated numerically by a 3-D lattice Boltzmann method. Effects of geometries and wettability of micro -pillar on boiling heat transfer performance were also systematically evaluated. Result showed that compared within micro -pillar surface, heat flux of cubic micro -pillar surface was the highest with the lowest wall temperature. In addition, compared to hydrophilic condition, Heat flux of cubic micro -pillar surface with hydrophobic wettability increased by 98.3%. This is because hydrophobic wettability influenced nucleation site density, vapor -liquid -flow field and heat transfer performance much more than cubic shaped geometry. Finally, heat flux of cubic micro -pillar surface with hybrid wettability increased by 430.7% compared to pure hydrophilic wettability. That is due to optimal hybrid wettability surface could control nucleate site location, restrict bubble growth, and increase obviously heat transfer performance.

The miniaturization and ever-increasing performance of electronic devices has made the thermal management to be a key bottleneck in their rapid development. In this paper, a novel 2-mm-thick ultra-thin vapor chamber (UTVC) with radial-gradient hierarchical wick was firstly designed and fabricated for high-power electronics cooling. The wick had a sunflower-like shape, in which a radial-gradient hierarchical structure was employed to facilitate the circulation of the working fluid. Systematical studies were conducted under forced water cooling condition in order to fully examine the effects of the cooling water inlet temperature and flow rate on the thermal performance of the UTVC. Moreover, aiming at establishing a benchmark for the evaluation of the heat transfer performance of the UTVC, a comparison study between the UTVC and a pure copper plate with the same dimension was conducted. Results showed that the UTVC could effectively transport a heat load of 420 W (about 186.7 W/cm(2)), attaining a minimum thermal resistance of 0.0531 degrees C/VV. Additionally, at a given heat load of 120 W, both decreasing the cooling water inlet temperature and increasing the cooling water flow rate could distinctly improve the UTVC performance. Finally, compared to copper plate, the proposed UTVC exhibited a relatively higher heat transfer performance, and reduced the thermal resistance by up to 59.2%.

In order to control the temperature of CPU in laptop,a flexible heat pipe was used to transfer CPU heat to the back of the display panel,and the heat was taken away by natural convection.The related physical models of laptop using heat pipe for heat dissipation were established with the software Fluent,heat dissipation by changing the bending angle of the flexible heat pipe under natural convection was studied,and temperature change curves of model monitoring part were analyzed.The back plate of the display screen was designed as the main heat dissipation structure of the model.The results showed that heat dissipation capacity of model increased with bending angle decreases under the same or angle-dependent thermal conductivity of flexible heat pipe.Meaningwhile,the influence of radiation on the heat dissipation capacity of the model was studied.After considering radiation,there was no significant change in the overall heat dissipation trend.

The boom of the advanced technologies, such as microprocessors, 5G, and big data, has led the thermal man-agement to be a crucial factor in determining the operating speed, reliability, and efficiency as well as lifetime of electronic devices. As passive heat transfer devices utilizing the liquid-vapor phase change, vapor chambers are greatly attractive due to the high thermal conductivity and passive operation. Here, we present a novel vapor chamber with leaf-vein-inspired wick structure, which could effectively facilitate the condensate to flow back to the evaporation region. Besides, the capillary wick functioned as the supporting structure instead of traditional solid supporting columns to withdraw the deformation of the vapor chamber. The heat transfer performance of the proposed vapor chamber was experimentally investigated under forced water cooling condition, and the effects of the cooling water temperature and mass flow rate were analyzed systematically. The results showed that the vapor chamber could effectively tolerate a wide heat load range from 20 W to 500 W with no noticeable performance degradation, and a minimum thermal resistance of 0.029 degrees C/W was attained at 200 W. Addition-ally, increasing the cooling water temperature and decreasing the cooling water mass flow rate could lead to the increase of the total thermal resistance at all heat loads. Finally, compared to other reported works, the vapor chamber featured a lowest thickness and vapor chamber thermal resistance, demonstrating a promising solution for cooling high-power and miniaturized electronics.

Phase change materials (PCMs) have become some of the most promising materials in thermal management systems. However, in practice, they are inevitably restricted by the issues of low thermal conductivity, liquid leakage, and strong rigidity. Herein, a flexible and form-stable phase change composite (PEA) with a pinecone-like structure is fabricated by a facile and scalable approach. In the PEA composite, paraffin wax (PW) is employed as PCM, styrene-b-(ethylene-co-butylene)-b-styrene triblock co-polymer (SEBS) is used as the supporting skeleton, Vaseline is used to reduce hardness, and expanded graphite (EG) and aluminum (Al) powders are used to enhance thermal conductivity. The pinecone-like EG-Al powder architecture exhibits more efficient heat transfer performance. The thermal conductivity of PEA-5 composite can reach 5.09 W m(-1) K-1, which is 28 times that of the matrix. In addition, the PEA-5 composite has good shape stability and thermal stability as well as excellent heat dissipation capability in LED modules. Interestingly, the PEA-5 composite also shows superior Joule heating performance with a saturated temperature up to 112.1 degrees C at an applied voltage of 3.5 V. This work provides insight for the rational design of highly thermally conductive and form-stable phase change composites, showing great potential for application in thermal management.

Pool boiling heat transfer from structured surface is simulated numerically with a 3D OTRT (optimal two relaxation time) Lattice Boltzmann method. This work shows in detail that multiple bubbles grow and coalesce over hydrophilic (θ = 50°) surfaces in 3D view, heat flux transfers from heater surface to fluid, and temperature of heater surface varies with time. Specifically, four types of geometry in microstructure surfaces are examined and compared. It is found that heat flux of S5 is the highest and its wall temperature is the lowest. When compared with S0, the heat flux of S5~S7 increased a lot due to the easier formation of vapor blanket, and cubic shaped cavity alleviates largely this deterioration. Next, the large quantity of heat from the three phase contact line in the vicinity of side wall accounts for bubble nucleation and energy from the evaporation of thin liquid between bubbles and superheated wall helps bubbles to grow further. Besides, it is found that S5 increases nucleate site density, reduces boiling incipience superheat, and enhances remarkably heat transfer performance.

As high-power electronics continue to advance rapidly, the pursuit of efficient thermal management has emerged a critical challenge for their further high-performance and large-scale applications. Capillary-driven thin film boiling phase-change cooling, harnessing the high latent heat of vaporization, presents an effective strategy to efficiently dissipate waste heat and meet the escalating cooling requirements of high-heat-flux applications. In this study, a cost-effective gradient wicking structure was proposed to enhance the thermal performance of the wick by promoting bubble dynamics and optimizing the balance between capillary pressure and permeability in homogeneous wicks. The comprehensive capillary properties of the homogeneous wicks were analyzed through theoretical calculations, and the capillary-driven thin film boiling heat transfer performance of four wick samples was systematically studied experimentally. Additionally, the effects of reduced pressures on the thermal performance of the gradient wick were investigated. Notably, the gradient porous wicking structure demonstrated exceptional thermal performance, with a critical heat flux reaching as high as 202.8 W/cm(2) and a maximum heat transfer coefficient of 121.9 kW/m(2)center dot K achieved at 88.5 W/cm(2). The findings of this study offer valuable design guidelines for the wick structures utilized in phase change equipment, with potential wide-ranging applications in advanced thermal management.

Generally, the function of thermal interface material (TIM) is filling rough surfaces, eradicating air pockets, decreasing thermal resistance, and improving heat dissipating effects. On this basis, we provide the TIM with another identity, "adhesion", rendering it not only play a role of heat dissipation, but also serve as an adhesive to bond contacting surfaces. In this work, nano- to microscopic liquid metal (LM) droplets are embedded into the epoxy matrix to fabricate a LM-epoxy in-situ cured composite. By adding the curing agent, the LM-epoxy composite is cured into an entity structure, transforming from an amorphous grease state to a self-adaptive pad state. When the average droplet size is in a reasonable range of approximately 5-25 mu m, the composite's thermal resistance (R-total) decreases to 2.19 mm(2)K/W at 70% volume fraction with its adhesive strength of 0.497 MPa, and the thermal conductivity (k(TIM)) could increase to 10.05 W/(m.K) at 85%. Both R-total and k(TIM) change rapidly for droplet size approximately ranging from 10(2) nm to 10(1) mu m and then tend to level off when it further increases to 10(2) mu m. A conception of equivalent contact thickness, delta, is presented to elucidate the contacting thermal resistance R-c, and set up predictive models of R-total for different volume fractions by considering the microscopic interfacial thermal resistance R-b between filler and matrix or not. This composite simultaneously possesses characteristics of the low thermal resistance like thermal grease, the whole entity like thermal pad, and the anti-leak characteristics by in-situ cured process. Actual cooling tests show it has a considerable temperature difference of 4.75 degrees C lower than the commercial thermal grease at 650 W heating power. This in-situ cured strategy, via decreasing the thermal resistance and solving the problem of LM leakage, remarkably promotes the LM-TIMs achieving a broader application prospect in the future.

Enhancing the performance of cooling modules is crucial for mitigating the heat dissipation problem of high -power-density electronic devices and simultaneously improving the energy efficiency of cooling systems. In this study, three 2-mm-thick vapor-liquid channel separation vapor chambers with different wick structures were fabricated. A novel radial-gradient sintered copper powder wick was firstly developed to improve the vapor-liquid conversion efficiency of working fluid, while the other two had homogeneous porosity wick structures with varying pore sizes. Experiments were systematically conducted with forced air cooling to comprehensively examine the effects of internal wick structures on heat transfer performance. The results indicated that the thermal performance of the vapor chamber can be improved by implementing the radial -gradient porosity wick. Specifically, the vapor chamber with a radial-gradient wick exhibited an improved thermal resistance of merely 0.052 degrees C/W, representing a 55.8% reduction in thermal resistance compared to a copper plate. Furthermore, when the improved vapor chamber was coupled with a heat sink to serve as the cooling module for a 100 W LED in practical applications, the operating temperature was kept below 49.4 degrees C. The proposed vapor chambers provide a highly efficient and reliable solution for thermal management in a wide range of applications.

The novel airfoil fins (AFFs) printed circuit heat exchanger (PCHE) has excellent thermal-hydraulic performance, while experimental investigations about this PCHE are few. The overall thermal-hydraulic performance of the novel AFFs PCHE is tested in this study and compared with that of the straight channels PCHE and the zigzag channels PCHE under identical experimental conditions. The mechanisms of the performance difference among the three PCHEs are numerically analysed. The new Nusselt number (Nu) and Fanning friction factor (f) correlations of supercritical CO2 in the novel AFFs PCHE are proposed. The results indicate that the overall heat transfer coefficient of the novel AFFs PCHE is higher than that of the straight channels PCHE, while the pressure drop of the novel AFFs PCHE is lower than that of the zigzag channels PCHE. The performance evaluation criteria (PEC) of the novel AFFs PCHE is 6.6-15.5% higher than that of the straight channels PCHE and is 12.8-27.8% higher than that of the zigzag channels PCHE, which indicates that the comprehensive performance of the novel AFFs PCHE is the best. The relative errors between the Nu and f predicted by the new thermal-hydraulic correlations and the Nu and f calculated from the experimental and numerical data are within & PLUSMN;20%. The correlations obtained in this work are useful to design and optimize the novel AFFs PCHE.

Portable electronic products are continuously evolving towards compactness, integration, and high performance, resulting in electronic chips generating significant heat in a confined space. This has led to severe heat dissipation challenges that impede further development. Ultra-thin vapor chambers have garnered considerable attention due to their exceptional thermal performance and potential applications in various fields. Enhancing the heat transfer capabilities of ultra-thin vapor chambers is crucial for overcoming the heat dissipation bottleneck in electronic products. This review provides a comprehensive overview of recent advancements in ultra-thin vapor chambers, with a focus on the vapor-liquid transport mechanism, working fluid selection, packaging processes, wick structure design and optimization, and surface modification of the capillary wick. Additionally, the challenges and potential solutions in ultra-thin vapor chambers fabrication are discussed, including the selection of suitable working fluids and capillary structure design. Furthermore, the review concludes by highlighting the future research directions and prospects of ultra-thin vapor chambers, such as improving theoretical guidance, exploring new working fluids, designing micro-nano composite multi-gradient coupled wicks, and developing advanced manufacturing processes. The objective of this review is to serve as a valuable reference for the design and development of future ultra-thin vapor chambers.& COPY; 2023 Elsevier Ltd. All rights reserved.

The moving granular bed filter is a promising technology for handling the challenges of hot gas clean-up and waste heat recovery in various fields. The purpose of this study was to investigate the heat transfer characteristics and waste heat recovery of a moving granular bed filter during hot gas clean-up. The novelty of this study lies in its investigation of the heat transfer performance of coagulative particles. Experiments were carried out to study the influence of the flue gas inlet temperature, granular velocity, and filtration superficial velocity. The results revealed that increasing the superficial velocity and inlet temperature and reducing the granular velocity are beneficial for improving the heat storage capacity of granules in terms of single factor. However, moderate granular velocity and superficial velocity are recommended to achieve a high waste heat recovery efficiency considering multiple factors. In the present study, a granular velocity of 2 cm.min(-1) and a superficial velocity of 0.3 m.s(-1 )are optimal. The superficial velocity is the main factor affecting the comprehensive heat transfer coefficient. The results reveal that the melting and solidification processes of the coagulative particles affect the heat transfer. They also reveal that improving the heat transfer performance is necessary for enhancement of waste heat recovery. The focus of the present study is essentially the development of a moving granular bed filter that contains coagulative particles for use in the metallurgy industry. The results are significant for the design and evaluation of a moving granular bed filter in practical applications that can improve energy efficiency.

Incorporating liquid metal droplets into polymer matrix has become one of the most promising strategies to enhance the thermally conductive performance of thermal interface materials (TIMs) for the escalating heat dissipation demands from highly integrated electronic devices. However, most of the TIMs typically choose silicone polymer as the matrix material, which would exhibit silicone oil precipitation and siloxane evaporation after long time utilization. Here, we present a non-silicone TIM with efficient heat dissipation capability by incorporating multi-shaped and proper-sized liquid metal droplets into an epoxy matrix via a combined fabrication approach. This liquid metal epoxy composite (LMEC) exhibits a high thermal conductivity enhanced up to 14 W $$\hbox {m}^{-1}$$ $$\hbox {K}^{-1}$$ (nearly 78 $$\times$$ increase over the matrix) at 85% volume fraction and an ultra-low thermal resistance of 0.0043 K $$\hbox {W}^{-1}$$ at 65% volume fraction. Its Kapitza radius and thermal interfacial resistance are estimated from the experimental results, respectively, about 75 nm and $$4.17 \times 10^{-7}$$ $$\hbox {m}^{2}$$ K $$\hbox {W}^{-1}$$ , which helps explaining the reduced thermal conductivity of composites with small droplet inclusions. Moreover, actual cooling tests on a high power heating device demonstrate that 65% LMEC shows superior cooling effects than the non-silicone TIMs of indium foil, pure liquid metal, 85% LMEC, and the silicone oil-based liquid metal composites of 65 and 85% volume fraction, which indicate that not the TIMs with higher intrinsic thermal conductivity would exhibit superior heat dissipation effects, but those possessing low thermal resistance between the heat source and heat sink show better heat transfer properties.

Driven by the continuously increasing cooling demands of electronic devices, ultra-thin vapor chambers (UTVCs) possessing the characteristics of easy-fabrication, low-cost and high-performance are urgently required. In this research, an integrated composite wick with multi-artery channels structure was proposed, which imitates the Laval nozzle in porosity. The designed wick was not only better for liquid reflow and vapor diffusion, but also for supporting the upper and lower covers instead of supporting columns. Under the heat load of 50 W, the UTVC introduced a reduction in maximum temperature difference for 67.7% compared with copper plate with the identical dimensions under natural convection. Under the heat load of 180 W and cooling air flow rate of 72.8 CFM, the UTVC's minimum spreading resistance reaches about 0.063 °C/W. The experimental results and LED's practical applications both indicate that the UTVC enhanced cooling capacity remarkably and yield a notable favorable performance for the heat dissipation of high-power electronic devices.