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• 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]

• 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]

• 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 enhanced pool boiling by nano-structure is firstly investigated at low pressure in this study. • The enhanced nanoporous copper surface (NCS) is fabricated by the hot-dip galvanizing & dealloying and the galvanization time is optimized. • The low pressure significantly affects the boiling behaviors and bubble dynamics, such as increasing bubble departure diameter and decreasing departure frequency. • The heat transfer coefficient enhancement of the NCS ranges from 71.6% (at 65 kPa) to 139% (at 25 kPa) compared to the plain wall. The nano-structure enhanced pooling boiling at standard atmosphere has been fully studied in literature but it is rarely investigated under low pressure. However, the boiling behaviors and bubble dynamics of nano-structures highly depend on the working pressure. This study investigated the enhanced pool boiling (under low pressure) of a nanoporous copper surface (NCS) fabricated by the hot-dip galvanizing & dealloying. The boiling curves and bubble characteristics of the NCS under low-pressure boiling conditions (25 kPa and 65 kPa) were evaluated by a test set up with high-speed visualization. To validate the present experimental plain-wall HTC under low pressure, three predicted models (Labuntsov, modified Rohsenow, and Stephan-Abdelsalam) were applied to obtain the theoretical HTC s for comparison. Besides, the optimization of the galvanization time has been conducted. Experimental results showed that the NCS significantly improved the pool boiling heat transfer and mitigated the negative influence of sub-atmospheric conditions. The enhanced mechanisms are the augmented nucleate site density, decreased bubble departure diameter, and increased bubbles generation frequency induced by the promoted hydrophilicity and rough morphology of the NCS. Among the three analyzed samples, the NCS-500 °C-3 min surface yielded the lowest wall superheat at the onset of boiling (ONB) and the highest heat transfer coefficient (HTC). In addition, the nanoporous surface leads to higher HTC enhancement upon the plain surface at a lower pressure. Specifically, the HTC enhancement percentage was increased from 71.6% (at 65 kPa) to 139% (at 25 kPa) as the pressure decreased. [Display omitted]. [ABSTRACT FROM AUTHOR]