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As flexible heat dissipation devices are urgently needed for flexible electronics, polymers with the advantages of good flexibility, insulation, and low density have attracted wide attention. It would be interesting to fabricate thermal functional structures on polymers to overcome their low thermal conductivity. This study aims to design and fabricate a micro-embossing mold to process polymer three-dimensional microgroove wicks (3D-MWs), which are applied in flexible heat pipes and achieve high thermal conductivity. Three kinds of tungsten steel molds were processed by using two wire electrical discharge machining processes (WEDM), two electrical discharge shaping machining processes (EDSM), and a combination of WEDM and EDSM. The 3D-MWs of the tungsten steel mold were reprinted onto the polymer films by a two-step embossing process. To investigate the effects of microstructures on boiling heat transfer performances, tungsten steel molds fabricated by different methods were tested to reflect the heat dissipation potential of the polymer 3D-MWs. The results showed that the 3D-MWs fabricated by the combination of WEDM and EDSM exhibit good boiling heat transfer performance and high processing efficiency, with a critical heat flux of 1040.1 kW/m2 and a maximum heat transfer coefficient of 38.4 kW/m2·°C. These values are 46% and 611% higher than those of the smooth tungsten steel surface, respectively, making it a superior choice for micro-embossing molds. [ABSTRACT FROM AUTHOR]

Aluminum vapor chambers have become an important component used to solve heat dissipation problems in lightweight applications due to their low density and good heat transfer characteristics. In this paper, a new sintered aluminum powder wick is provided for an aluminum vapor chamber. An aluminum porous wick was sintered using liquid phase sintering technology. Using acetone as the working medium, the influence of the structural parameters of the aluminum wick on its boiling heat transfer performance was studied. The influence of thickness on the boiling heat transfer performance of a sintered porous wick is particularly significant. Thinner, porous wicks have better critical heat flux (CHF). The porosity and particle diameter mainly affect the heat transfer coefficient (HTC). At a low heat flux, the sintered wick with low porosity and a small particle diameter has a higher HTC. The HTC of porous wicks, with a larger particle diameter and porosity, decreases slower. The optimal porosity ranges from 46.4 ± 2.5% to 51.8 ± 2.5%. Compared with the polished aluminum plate, the CHF is increased by 1.7 times, and the HTC is increased by about 4.6 times under the same heat flux. [ABSTRACT FROM AUTHOR]

Featured Application: This work proposed a novel necking heat pipe with double-end heating, which could be utilized in the heat pipe systems to obtain different thermal performances for complicated working situations, especially for the overload operation situation. For example, the waste heat of a low-power chip can be utilized to drive a high-power chip working under the overload situation on the same circuit board, which can be considered waste heat recovery and utilization. This work proposed a novel necking heat pipe with double-end heating for thermal management of the overload operation. The addition of another heat load was adopted to obtain a higher threshold critical power for the heat pipe system. The thermal performance of thermal switch heat pipe (TSHP) and traditional grooved heat pipe (TGHP) was investigated experimentally, including the threshold critical power, starting characteristic, recovery characteristic, surface temperature distribution, thermal resistance, etc. The optimized TSHP exhibited a larger threshold critical power range with low additional heat load input (from 55 W to 65 W, almost 20% increase), low starting additional heat load input (2 W), good recovery characteristic (less than 150 s from 75 °C to normal after overload), and low thermal resistance with additional heat load input (less than 0.13 °C/W). These results indicate that the optimized TSHP can offer great potential for the overload operation situation with the additional heat load. Such a novel necking heat pipe with double-end heating can be utilized in heat pipe systems to obtain different thermal performances for complicated working situations, especially for the overload operation situation. [ABSTRACT FROM AUTHOR]

Due to the demands of thermal performance enhancement of heat pipe solar collector, the fabrication of large-area flat heat pipes with the advantages of low cost and outstanding thermal performance has become more urgent. In this paper, a large-area ultra-thin flat heat pipe (LUFHP) with multiple parallel microchannels was fabricated by the aluminum extrusion process. Its total thickness is only 1.5 mm while the effective width is 170 mm. The effect of different filling ratios on the thermal performance was investigated under natural air convection and forced water cooling, respectively, including heat transport capability and thermal resistance. The experimental results indicate that the maximum heat transport capabilities for natural air convection and forced water cooling are 40 W with an optimal filling ratio of 25% and 25 W with an optimal filling ratio of 30%, respectively. The minimum total thermal resistances of the LUFHP are about 0.22 °C/W (natural air convection) and 0.73 °C/W (forced water cooling), which decrease by 74% and 57% compared with these of aluminum plate, respectively. That is, the proposed LUFHP shows better thermal performance under NAC for the replacement of aluminum plate in a wider range of heat load. • A large-area ultra-thin flat heat pipe is fabricated by aluminum extrusion. • Its effective width and thickness are 170 mm and 1.5 mm, respectively. • The effects of filling ratio under two cooling conditions were evaluated. • This flat heat pipe shows better thermal performance under natural air convection. [ABSTRACT FROM AUTHOR]

A novel permanent magnet synchronous motor with heat pipe for electric vehicle is designed with the aim to reduce the end winding temperature. Software FLUENT is used to simulate the temperature fields. The temperature distribution profile of the winding of the permanent magnet synchronous motor with heat pipe is similar to that of the traditional permanent magnet synchronous motor. But the temperature values of the winding of the permanent magnet synchronous motor with heat pipe are lower than those of the traditional permanent magnet synchronous motor. The area of the region with relative low temperature at permanent magnet synchronous motor with heat pipe is also larger than at traditional permanent magnet synchronous motor. The highest temperature of the winding of the permanent magnet synchronous motor with heat pipe is 16.4°C lower than that of the traditional permanent magnet synchronous motor. The highest temperature and the lowest temperature of the lamination of the permanent magnet synchronous motor with heat pipe are all lower than those of the traditional permanent magnet synchronous motor. The temperatures of the two end caps of the permanent magnet synchronous motor with heat pipe are apparently higher than those of the traditional permanent magnet synchronous motor since some heat generated at the end winding is transferred to the end cap by the heat pipe. The low temperature area at the middle housing of the permanent magnet synchronous motor with heat pipe is larger than that of the traditional permanent magnet synchronous motor. The temperature discrepancy between the evaporator of the heat pipe and the end winding is about 60°C. [ABSTRACT FROM AUTHOR]

Micro-grooved aluminum flat plate heat pipes (MFPHPs), fabricated by hot extrusion and subsequent inner surface treatment via chemical corrosion, were developed to improve the thermal efficiency and reduce the costs of solar collectors. Thermal performances of MFPHPs, including temperature distribution, maximum heat transfer capability, and thermal resistance, were experimentally conducted. The effects of treatment time and solution concentration on the thermal performance enhancement of MFPHPs were also investigated. The experimental results show that inner surface treatment can substantially enhance the thermal performance of MFPHPs, and different treatment morphologies of inner surfaces result in differences in thermal performance enhancement. The optimal treatment parameters were determined to be a treatment time of 10 min with a solution concentration of 1.5 moL/l. This resulted in the optimal thermal performance enhancement: an increase of approximately 80% in heat transfer capability and a decrease of more than 44% in thermal resistance, compared to the untreated MFPHP. This study provides a convenient, effective, and low-cost method to enhance the thermal performance of MFPHPs applied in solar collectors. • MFPHPs with inner surface treatment were developed to improve the thermal efficiency of solar collectors. • Thermal performances of MFPHPs are subsequently enhanced by inner surface treatment. • Optimum inner surface treatment parameters for MFPHP were determined. [ABSTRACT FROM AUTHOR]

This paper presents a novel method combining the preforming and multi-tooth plowing processes to fabricate aluminum-based ultrathin flat heat pipes (UTFHPs). The use of a preforming process makes it more effective to machine arrayed microgrooves on the inner wall of UTFHPs. The multi-tooth plowing process helps greatly increase the capillary pressure and hydrophilicity of the heat pipe wick. The morphologies of the wick structures are characterized and a self-designed experimental platform is constructed to investigate the thermal performances of UTFHP samples under incremental heat loads. The results indicate that the multi-tooth plowing process is able to significantly reduce the minimum thermal resistance of the heat pipe by 83%. The thermal resistance of the UTFHP with a unilateral porous wick is smaller than that based on a central porous wick at the same liquid filling rate. The UTFHP has excellent radial temperature uniformity with the minimum radial temperature difference of 1.2 °C, because the structures made by multi-tooth plowing can effectively reduce the temperature difference. [ABSTRACT FROM AUTHOR]

Quantum dots (QDs) attract great attention due to their narrow emission spectra, providing excellent light quality for light-emitting diodes (LEDs) in illumination and display applications. However, their low thermal reliability suppresses the commercial applications of QD-based LEDs. In this report, it is the first time that we realize high thermal performance and reliability QD-based LEDs with watt-level injection power. The QD-on-reflector (QOR) structure is proposed to separate QDs from the heat source of chips, and targeted cooling for QD/polymer composites is achieved with an Al-based reflector. Compared with the reference [conventional QD-on-chip (QOC) structures], the QOR-LEDs exhibit higher total radiant power/luminous flux and color consistency. Most important, the QOR-LED has a steady temperature of only approximately 50 °C in QD/polymer composites, which is 90 °C lower than the reference and is the reported lowest temperature for QD-based LEDs. The working-aging test shows that the luminous flux maintenance (LFM) factor of the QOR-LED is 92.2%, whereas that of the reference is only 21.2% after aging for 20 min. This corresponds to a lifetime of 88.5 times longer than that of the QOC-LED at the same LFM of 20%. Consequently, the QOR structure can provide better optical performance, superior thermal performance, and longer lifetime for QD-based LEDs. [ABSTRACT FROM AUTHOR]

The development of miniaturization and high-density packaging of electronic components demands heat dissipation components that are compact and exhibit high performance. An ultra-thin micro heat pipe (UTHP), as a novel heat pipe with a flat shape that is highly suitable for application with high power and limited heat dissipation space, has been extensively investigated and widely used in mobile electronics. Understanding the influence of the manufacturing processes, capillary wick structures and flattened thickness on the thermal performance of UTHPs has been the aim of numerous studies. This paper presents a comprehensive review of the recent developments and applications of UTHPs for thermal management of electronics. The different types and applications of UTHPs are introduced, and the packaging technologies of UTHPs are summarized and compared. Furthermore, the fabrication methodology and heat transfer characteristics of various wick structures used for UTHPs are reviewed and analysed in detail. Finally, the challenges affecting the development and application of UTHPs are outlined, and recommendations for future research are presented. [ABSTRACT FROM AUTHOR]

Featured Application: solar collector; solar thermal system; thermal energy storage system; heat exchanger. A micro heat pipe array is desirable owing to its high heat transfer capacity, compact size, and high surface–volume ratio compared with conventional heat pipes. In this study, micro flat aluminium heat pipe arrays (MF-AHPA) were developed and systematically characterised by varying working fluid and inclination angle. Three MF-AHPAs with different working fluids, i.e., acetone, cyclopentane, and n-hexane, were fabricated. The acetone MF-AHPA achieved the best thermal performance. The underlying mechanism is the small flow viscous friction and small shearing force of liquid vapour. Additionally, the experimental results show a strong dependence of MF-AHPAs’ thermal resistance on the orientation due to the gravitational effect on axial liquid distribution. Finally, a criterion is proposed to determine the optimal inclination angle of the MF-AHPA. In the present study, a volumetric fraction (αa,c) of 74 ± 7% has been shown to well predict an optimal inclination angle of the MF-AHPAs with various working fluids and heat loads. [ABSTRACT FROM AUTHOR]

This study proposes a novel cooling approach called double-ended heating and middle-cooling (DHMC), which is suitable for overcoming the problems encountered in the cooling of multiple heat source systems with horizontal orientation as well as of those with inclined orientation. Two heat sources were placed at the two ends of an ordinary heat pipe, and a heat sink was installed at the middle section of the pipe. An experimental apparatus was used to study the thermal performance of the heat pipe with DHMC. The effects of various heat inputs, cooling locations, and negative inclination angles on the thermal performance of the heat pipe were analysed, and the experimental results were compared with those obtained by a traditional cooling approach. The experimental results demonstrate that the heat transport capability of a heat pipe can be significantly enhanced using this method in both horizontal and inclined orientations. The external wall temperature of the heat pipe can be controlled by installing the cooling block closer to the upper evaporator when employing this novel approach for large inclination angles (8° < θ ≤ 16°). The results indicate that this novel cooling method is highly suitable for cooling multiple heat source systems in both horizontal and inclined orientations because of its stable operation at high heat flux and its space efficiency. [ABSTRACT FROM AUTHOR]

Anti-gravity loop shaped heat pipe (AGLSHP) with continuous step-graded sintered wick is useful for enhancing the effective heat transfer in the anti-gravity direction. In this work, a complete steady state model has been presented to investigate in the thermal performance and hydraulic behavior of the AGLSHP. The governing equations for the heat and mass transfer are developed for the loop operation, with specific attention given to the evaporator region. By comparing the numerical simulation with the experimental data, the heat transfer mechanism is revealed. The liquid/vapor velocity and pressure distribution in the evaporator are discussed, and the temperature distribution along the transport line is also analyzed. The numerical results indicate that with the increase of the heat load, the maximum velocity and pressure value of the liquid and vapor increase as expected. The highest temperature position occurs at the outlet of evaporator surface. Providing the capillary pressure for the circulation of working fluid, the wick in the liquid line is paid more attention. Moreover, the longer condensation length is more effective in decreasing the temperature at the outlet of condenser and improving the heat transfer capacity of the AGSLHP. [ABSTRACT FROM AUTHOR]

• Silica coatings were enveloped on nylon mesh by the sol-gel method and endowed it with superhydrophilicity. • Superhydrophilic nylon mesh wicks (SNMWs) yielded good capillary performances. • SNMWs with the maximum volumetric flow rate of 1.19 mm3/s were promising wicks for flexible heat pipes. • SNMWs maintained good capillary performances even after 10,000 bending cycles. The rapid development of flexible electronic devices brings the demand for flexible thermal management systems. Nylon mesh with excellent flexibility is ideal for flexible thermal management systems, especially acting as wicks in flexible heat pipes (FHPs). In this study, novel superhydrophilic nylon mesh wicks (SNMWs) with enhanced capillary performance are fabricated by the sol-gel method. Silica coating is formed on the surface of nylon mesh and endowed the mesh with superhydrophilicity. Capillary rise tests and cyclic bending reliability tests are conducted to evaluate the capillary performance and bending fatigue resistance of the SNMWs. The results show that the SNMWs yield excellent capillary performance, the maximum equilibrated wicking height of the SNMWs reaches 87.38 mm and the largest wicking coefficient is 5.91 mm/s0.5. The average volumetric flow rate proportional to wicking velocity and wetted volume is taken as a comprehensive index to evaluate the feasibility of applying SNMWs in FHPs and the maximum average volumetric flow rate reaches 1.19 mm3/s. Simultaneously, the SNMWs maintain good capillary performance even after 10,000 bending cycles, which means strong bending fatigue resistance. This study provides a high-performance, high-reliability, and cost-effective flexible wick for enhancing the thermal performance of FHPs. [ABSTRACT FROM AUTHOR]

Thermal management of a Li-ion battery is a critical issue affecting its performance, endurance, and operation security. This paper focuses on the effects of a self-designed thermal management module (TMM) on the temperature characteristics of the Li-ion battery. This TMM uses heat pipes as the main elements for heat transfer with the aid of a heat collecting plate and cooling fins. The thermal issues and necessity of using this TMM are evaluated. The influences of heat collecting plate, heat pipe layout, and air-blowing operation are all discussed. The influential factors and related mechanisms are accordingly analyzed. Results indicate that the use of a heat collecting plate, the setup of a dual heat pipe, and forced air convection are all helpful to reduce the battery temperature. The simulation results based on Icepak also suggest that this heat-pipe-based TMM is able to depress the temperature rise of the battery pack at an appropriate level. [ABSTRACT FROM AUTHOR]

• An ultrasonic modification method for the aluminum grooves was proposed. • The porous microstructures were fabricated on the surface of aluminum grooves. • The capillary performance of the modified groove was enhanced significantly. The grooved wick has a promising potential in the field of ultra-thin flat heat pipes, and the porous structure can improve the capillary performance of grooved wicks significantly. In this paper, an environmentally friendly method, named as ultrasonic modification, was developed to fabricate porous microstructures on grooved aluminum wick. The effects of ultrasonic modification times on the morphology, wettability and capillary performance of the porous grooved wick were investigated. The results indicate that appropriate ultrasonic modification times can realize an excellent distribution of porous microstructures throughout the groove surface. After ultrasonic modification, the modified surface became hydrophobic since the porous microstructures were covered with a low-surface-energy coating. However, in case of aluminum heat pipes with acetone as working liquid, the wettability and capillary performance of the modified grooved wick can still be enhanced significantly. The maximum capillary rise height and the capillary performance parameter of the modified grooved wicks were increased for a factor of 3 and an order of magnitude, respectively. This study provides a new idea for the fabrication of porous aluminum wicks, which is beneficial to promote the development of ultra-flat aluminum heat pipes. [ABSTRACT FROM AUTHOR]

A miniature loop heat pipe (mLHP) is a promising device for heat dissipation of electronic products. Experimental study of heat transfer performance of an mLHP employing Cu-water nanofluid as working fluid was conducted. It is found that, when input power is above 25 W, the temperature differences between the evaporator wall and vapor of nanofluid, Te − Tv, and the total heat resistance of mLHP using nanofluid are always lower than those of mLHP using de-ionized water. The values of Te − Tv and total heat resistance of mLHP using nanofluid with concentration 1.5 wt. % are the lowest, while when the input power is 25 W, the values of Te − Tv and total heat resistance of mLHP using de-ionized water are even lower than those of mLHP using nanofluid with concentration 2.0 wt. %. At larger input power, the dominant interaction is collision between small bubbles and nanoparticles which can facilitate heat transfer. While at lower input power, nanoparticles adhere to the surface of large bubble. This does not benefit boiling heat transfer. For mLHP using nanofluid with larger concentration, for example 2.0%, the heat transfer may even be worse compared with using de-ionized water at lower input power. The special structure of the mLHP in this study, two separated chambers in the evaporator, produces an extra pressure difference and contributes to the heat transfer performance of the mLHP. [ABSTRACT FROM AUTHOR]

Abstract A novel composite heat pipe (CHP) that consists of a conventional heat pipe (HP) with a phase change material (PCM) storage chamber wrapped on the adiabatic section was proposed in this work. The CHP combines the advantages of the high thermal conductivity of HP and the high thermal storage capacity of the PCM. A measurement system was established to analyze the thermal performance with different effect factors of the CHP, including the filling rate of the PCM, heating power and wind speed. Multi-cycle transient thermal controlling performance was also investigated. Results show that the CHP can enhance the absorption-dissipation thermal performance, improve the isothermality, decrease the start-up temperature and greatly reduce the thermal shock in cyclic thermal scenarios. We believe that the CHP can be developed as high-potential heat-transfer medium for reliable thermal management. [ABSTRACT FROM AUTHOR]

The thermal performance in various orientations of gravity was investigated for operating multi-branch heat pipes (MBHPs) with different sintered wicks in the case of cooling a heat source with dual condenser. The effect of sintered particle size in different orientations on heat transfer performance were investigated systematically. The particle size effect was examined with three copper powders of particle size of 50–75 μm, 75–100 μm and 100–125 μm in four orientations of gravity-assisted orientation, anti-gravity orientation, horizontal orientation, and compound orientation of gravity, respectively. All MBHPs were filled by deionized water to the filling ratio of 100%. Experiment results indicate that all MBHPs can operate with similar performance in all the tested orientations before dry-out occurring. Further, the MBHP with 75–100 μm copper powder performs best in all the tested orientations, considering both the thermal resistance and the heat transport capability. In addition, it can start up successfully within 10 min without temperature overshoot and oscillation. That is, a MBHP can perform well in all the tested orientations and the copper powder of 75–100 μm is a good candidate for better thermal performance. [ABSTRACT FROM AUTHOR]

The ultra-thin heat pipe (UTHP) has been established as a highly effective thermal control component for cooling electronics with large heat generation rate and limited space for cooling. However, UTHP has been severely limited in application because of buckling or breaking on the shell of UTHP during the flattening process. In this study, a series of high-accuracy UTHPs with a thickness of 0.38–0.47 mm were fabricated by the phase-change flattening process. An internal vapor pressure model of the heat pipe during flattening was constructed and the heat transfer performances of UTHPs under different working conditions were experimentally investigated. According to the internal vapor pressure model, the pipe wall stress after flattening was the first to reach the yield strength of the material, and the upper limit heating temperature of UTHPs decreased with the decrease of flattened thickness. The maximum heat transfer capacity decreased with the decreased flattened thickness. UTHP with a thickness of 0.47 mm has a maximum heat transfer capacity of 4.5 W and a minimum thermal resistance of 0.64 °C/W. Moreover, gravity appeared to impose minimal effects on the heat transfer performance of UTHPs and the heat transfer capabilities of the UTHPs fluctuated within ±0.5 W for different gravity orientations. • The phase-change flattening process was used to fabricate UTHPs with no buckling or breaking. • An internal vapor pressure model of UTHP was established to optimize the phase-change flattening process. • The limited heating temperature of flattening process decreased with the decreased flattening thickness. • Gravity was found to have a minimal effect on the heat transfer performances of UTHPs. [ABSTRACT FROM AUTHOR]

In this study, a multi-scale copper mesh wick structure fabricated by oxidation treatment and sintering is proposed for increasing the heat transport capabilities of ultrathin heat pipes (UTHPs). Experimental apparatus and a thermal resistance network model were established to analyse the heat transfer characteristics of UTHPs. The effects of various heating loads and negative inclination angles on the thermal performance of a UTHP with an oxidised mesh wick (OMHP) were experimentally investigated. The results were compared with those of an untreated mesh wick ultrathin heat pipe (NMHP) and a sintered powder wick ultrathin heat pipe (CPHP). The experimental results demonstrate that the heat transport capabilities of UTHPs with a mesh wick in the horizontal and inclined orientations were enhanced significantly owing to oxidation. The oxidised mesh wick exhibited the same or better capillary performance as the sintered powder wick in inclined orientations. Moreover, when the inclination angle increased to 90°, the temperature difference of OMHP was 36.4% and 26% lower than that of OMHP and CPHP, respectively, under the input power of 14 W. The thermal resistances of OMHP were lower than those of NMHP (by approximately 57%) and CPHP under identical test conditions. [ABSTRACT FROM AUTHOR]

Abstract This study proposes a novel ultra-thin aluminum flat heat pipe with thickness of 1.5 mm for the first time in order to satisfy the ever increasing requirements for cost-effective, physically compact and highly efficient thermal management solutions. The extruded aluminum tube contains multiple separate micro cavities that work as independent micro heat pipes and a two-level compressing process is applied to flatten the tube to the ideal thickness. Sintered aluminum fibers and aluminum fiber meshes with surface treatment are inserted into each cavity of the ultra-thin heat pipe as the extra wicks for comparison. The thermal response characteristics of the fabricated aluminum heat pipes, including the temperature uniformity, thermal resistance, and effects of wick structure and inclination angles, are fully investigated. Under large inclination angle (90°), the smooth heat pipe without any extra wick performs lower temperature difference, lower thermal resistance, and higher heat transport capacity compared to that with aluminum fiber wick whereas the heat pipes with wicks present superiority under smaller inclination angles (60° and 30°) due to the liquid backflow enhancement. Besides, comparative study also shows that wick structure optimization holds the potential to improve the thermal performance of this ultra-thin two-phase device. Highlights • Ultra-thin aluminum heat pipe with only 1.5 mm thickness is developed. • It contains multiple separate micro cavities working as independent heat pipes. • The thermal response characteristics are fully investigated. • Wick structure optimization holds potential to improve the thermal performance. [ABSTRACT FROM AUTHOR]

• Microsorum fortunei structural-like wicks for high-performance flexible heat pipes (FHPs) were produced. • FHPs achieved the smallest fluctuation in thermal conductivity of 5.3% under 0–180° bending angles. • FHPs achieved the maximum thermal conductivity of 1943.5 W/m∙K with a heating power of 17.1 W. • FHPs with Microsorum fortunei structural-like wicks have the feasibility of application in flexible electronics. Ultrathin flexible heat pipes (FHP) with Microsorum fortunei structural-like wicks were fabricated to meet the cooling demands of flexible electronics. The biomimetic wick was fabricated by high-temperature sintering and composed of multi-layer copper mesh and porous micropillars, which corresponded to the veins and spores of Microsorum fortunei leaves, respectively. The aluminum-plastic film was adopted as the casing and endowed the FHPs with insulating capability. FHPs with the thickness of 0.8 mm and 0.67 mm were fabricated by regulating the height of the porous micropillars to form vapor channels with different thicknesses, which reached the maximum thermal conductivity of 1943.5 W/m·K and 1449.5 W/m·K under heating power of 17.1 W and 8.1 W, respectively. The optimum filling ratio was found to be 100% due to its higher thermal conductivity under lower heating powers. FHPs with Microsorum fortunei structural-like wicks achieved good bending heat transfer performances while incurring thermal conductivity fluctuation to within 5.3% under 0–180° bending angles. The infrared tests highlighted that the FHPs maintained good heat transfer performance under natural convection conditions. The advantages of simple manufacture coupled with good bending heat transfer performance and insulating made the FHPs with Microsorum fortunei structural-like wick highly suitable for thermal management of flexible electronics. [ABSTRACT FROM AUTHOR]

This paper proposes a novel multi-branch heat pipe (MBHP) that can be utilized for heat dissipation in multi-heat source electronics. The proposed heat pipe consists of three branches—two with an evaporator and one with a condenser—connected by vapor lines and liquid lines. A test system was implemented to study the filling ratio, the start-up characteristics, the power distribution characteristics, the dynamic characteristics and the thermal resistance of the heat pipe. The experimental results obtained indicate the following: 1) the optimal working fluid filling ratio of MBHP is between 75% and 100%; 2) the MBHP can start up steadily under tested heating load; 3) the ideal heat load of the MBHP (filling ratio 75%) was within a range of 30–160 W, in which the minimum total thermal resistance was 0.04 °C/W and the maximum temperatures of both evaporators were less than 110 °C under the limiting heating load of 160 W. [ABSTRACT FROM AUTHOR]

The Anti-Gravity Loop-Shaped Heat Pipe (AGLSHP), designed with a special sintered wick structure, is a novel device used in electronic heat dissipation under the anti-gravity condition. Two kinds of wick structures, single-powder (SP) and continuous step-graded (CSG) structures were evaluated for design optimization. The copper powder utilized in the experiment were divided into six particle sizes (<25, 25–50, 50–75, 75–100, 100–125, and >125 μm) to investigate their influence. The results show that the heat transfer performance of the sintered wick samples changes significantly with the variation of the copper powder size. SP75–100 is the optimal particle size for single-powder sintered wick heat transfer, while CSG25–50 is the optimal particle size for the continuous step-graded sintered wick. Furthermore, the CSG sintered wick possesses better overall performance than the SP sintered wick, obtaining higher maximum operating power and lower start-up temperature. [ABSTRACT FROM AUTHOR]

Stainless steel heat pipes have attracted increasing attentions for applications in extreme environments. The stainless steel wick structure as the key component is of high importance for the thermal performance of stainless steel heat pipe. Here, sintered porous wicks using stainless steel powders are developed to evaluate the capillary performance that directly governs the liquid circulation in heat pipes. Systematical experiments of permeability tests and capillary rise tests are conducted for porous wicks with spherical and irregular morphologies in different powder sizes. Water droplets spread entirely on both kinds of porous samples in tens of milliseconds, implying the sintered powder wicks present excellent wetting property. The irregular powder samples show a permeability improvement with a factor of 1.5–4.8 compared to the spherical powder ones with the same powder size, whereas they provide smaller capillary pressures. This is attributed to the more complicated morphologies of the irregular powders that are easier to form larger interconnected inner pores. The wicks with medium powder size of 90–120 um, maintaining a good balance between permeability and capillary pressure, exhibit the optimal capillary performance, which is indicated by the highest capillary factor that can comprehensively reflects the combined effects. [ABSTRACT FROM AUTHOR]