The classical approach to prepare nanocomposites is often applied to chemical or physical modification of nanofillers to improve interfacial interaction between nanofillers and matrices. However, ...those methods might disturb the original reinforcement of nanoparticles due to the inhibition and even the absence of association among fillers. Here, we inspected a molecular design strategy using rod-like cellulose nanocrystals (CNCs) as fillers to study whether regulating the surface structure of CNC could allow a better reinforcement effect. Toward that, we prepared four modified CNCs by esterification with mono or binary anhydrides of different lengths of carbon chains. The long hydrocarbon chains were supposed to further improve the interfacial compatibility between CNC and poly(lactic acid) (PLA), and the terminal carboxyl groups should retain the association between nanoparticles. Results from transmittance of visible light for the nanocomposite films revealed homogeneous dispersion and good compatibility between modified nanocrystals and PLA matrix, especially for the long carbon-chain grafting CNCs. With an addition of 4 wt% dodecenyl succinic anhydride-modified CNC, the nanocomposite showed an increase in the tensile strength by ca. 170%. This was ascribed to the improved entanglement of grafting long chains and the potential interaction of terminal carboxyl groups on the CNC surface with the segments of PLA matrix, which enhanced association and compatibility between nanoparticles and matrix. This strategy prepared a biomass alloy of green materials reinforced by natural polymers and promoted the sustainable development of materials with high mechanical properties.
•An ultra-thin flattened heat pipe with biporous spiral woven mesh wick is proposed.•The biporous wick is hybrid woven using 0.05 and 0.04 mm diameter copper wires.•The biporous wick has advantages ...of high permeability and large capillary force.•The effects of wick parameters on the performance of heat pipe are investigated.•The biporous wick realizes the demands of low cost and high thermal performance.
In this work, a novel biporous spiral woven mesh wick is developed to enhance the thermal performance of an ultra-thin flattened heat pipe for cooling high heat flux electronic devices. The biporous wick with different sized pores is hybrid woven using 0.05 and 0.04 mm diameter copper wires in every strand. Three different structures are designed to study the effect of the characteristic parameters of the wick on the thermal performance of the ultra-thin flattened heat pipe. The working fluid flow characteristics of the wick are analyzed theoretically. The capillary rate-of-rise experiment with deionized water using the infrared camera method is carried out to characterize the capillary performance of the wick. The thermal performance of the ultra-thin flattened heat pipe is experimentally investigated. The results indicate that the biporous wick combines the advantages of high permeability due to the large pores and large capillary force due to the small pores. The optimal biporous wick has 22% fewer copper wires than the monoporous wick, but the maximum heat transport capacity of the ultra-thin flattened heat pipe is able to approach 24 W, which realizes the demands of both low production cost and high thermal performance using the biporous wick.
•A novel vapour-liquid channel-separated ultra-thin vapour chamber was designed.•A mathematical model of heat transfer limit was established.•The effects of different etching structures on the ...thermal performance were studied.•The cooling modules with and without ultra-thin vapour chamber were compared.
In this work, a novel vapour-liquid channel-separated ultra-thin (0.4-mm-thick) vapour chamber fabricated via etching and diffusion bonding was designed for cooling electronic devices. The heat performance of ultra-thin vapour chamber was tested under five states, and micropillar arrays were etched into the chamber to study their effect on heat transfer. Additionally, infrared thermal imaging was performed to investigate the heat dissipation of cooling modules with and without the ultra-thin vapour chamber. The maximum heat transfer capacity of the ultra-thin vapour chamber in the horizontal state was 4.50 W, and the temperature difference was 4.75 °C. The experimentally measured values were very close to the theoretical capillary limit. Under normal and reverse gravities, the maximum heat transfer capacity changed by less than 11%. The effective thermal conductivity of the ultra-thin vapour chamber was 12000 W/(m·K), which is 30 times higher than that of pure copper. The cooling module with the ultra-thin vapour chamber exhibited better heat dissipation, thermal uniformity and thermal response properties. When the heating input power was 6 W, the heating block temperature, maximum surface temperature difference and equilibrium time of the cooling module with the ultra-thin vapour chamber were 8%, 54% and 32% lower, respectively, than those of the module without the ultra-thin vapour chamber. The proposed cooling solution is promising for heat dissipation problems in high-power portable electronic devices.
•UTHP with a novel spiral woven mesh wick was designed for cooling smartphones.•The wick was woven in a band-shape to realize an ultra-thin and tight structure.•Cross-sectional area ratio of the wick ...to the UTHP affected its thermal performance.•Increasing woven wires did not significantly improve the UTHP thermal performance.•Gravity had little effect on the heat dissipation performance of the UTHP module.
In this work, a novel spiral woven mesh (SWM) wick was developed to enhance the thermal performance of ultra-thin flattened heat pipe (UTHP) for cooling thin portable electronics. The SWM overall structure was woven in a band-shape to realize an ultra-thin and tight structure. Three different SWM structures were designed to study the effect of the wick on the UTHP thermal performance. The maximum heat transport capacity data of UTHPs were compared with the calculated capillary and entrainment limits. The effects of the cross-sectional area ratio of the wick to the UTHP on the heat transfer performance were analyzed. The heat dissipation performance of the UTHP cooling module at different inclination angles was experimentally investigated. The results indicate that the cross-sectional area ratio affected the flow characteristics of the vapor and liquid in the UTHP, thereby affecting its heat transfer performance. A further increase in the number of SWM wires did not significantly improve the UTHP thermal performance. Gravity had little effect on the heat dissipation performance of the UTHP cooling module. Compared with a copper sheet cooling module, the maximum heat dissipation power of the UTHP cooling module increased by 28.57–42.86%, and the weight reduced by 64.51%.
•A composite wick with multi-artery structure is developed for thin vapor chambers.•Different evaporator and condenser wicks are designed to enhance the performance.•The influence of cooling ...condition on the vapor chamber performance is evaluated.•The effects of wick structure and filling ratio on vapor chamber are investigated.
In this work, two types of thin vapor chambers, namely, copper foam vapor chamber (CFVC) and copper mesh vapor chamber (CMVC), are developed to enhance the thermal performance of vapor chambers for cooling high heat flux electronic devices. The evaporator wick is a composite wick of sintered copper powder-mesh with multi-artery structures made of several sintered powder bars on a thin evaporator zone. The condenser wicks for CFVC and CMVC are copper foam wick and 3-layer 200 mesh wick, respectively. A water-cooled testing system is set up to investigate the thermal performance of the vapor chamber. The characteristic parameters, including the temperature distribution, thermal resistance, filling ratio and critical heat flux (CHF) of vapor chambers are studied. The results indicate that the thermal performance of the vapor chamber is significantly affected by the cooling water temperature. At cooling water temperatures of 50 and 30 °C, the CHF of the CFVC can reach 180 W/cm2, which is increased by 100–200% compared to that of the CMVC. The CFVC exhibits a better heat transfer performance and adaptability to the cooling water temperature, given that the copper foam wick has a larger capillary performance parameter and a smaller contact thermal resistance.
•An ultra-thin flattened heat pipe with a composite mesh wick is proposed.•Effect of the passage area ratio of liquid to vapor on the performance is studied.•The passage area ratio of liquid to vapor ...is adjusted by changing the wick width.•The optimum design of passage area ratio for high heat transfer is provided.
The effect of the passage area ratio of liquid to vapor on the heat transfer performance of ultra-thin heat pipe (UTHP) in horizontal state was experimentally investigated in this work. The wick was sintered with a layer of 100- and 180-mesh copper mesh. The passage area ratio of liquid to vapor of UTHP was adjusted by changing the wick width. The capillary limits of UTHPs with various wick widths were analyzed theoretically. The effects of the wick width and filling ratio parameters on the thermal performance of UTHPs were studied experimentally. The maximum heat transport capacity of UTHPs were compared with the calculated capillary limits. The results indicated that the optimum filling ratio of the UTHP gradually decreased with increasing wick width. An appropriate wick width was beneficial to enhance the UTHP's thermal performance by increasing the vapor-liquid circulation efficiency during heat transfer. When the wick width was 4 mm, the maximum heat transport capacity of UTHP could reach 8.5 W, which was 4.25 times that of UTHPs with 2 and 7 mm wide wicks. From the capillary limit calculation and sample testing, the optimum passage area ratio of liquid to vapor of the experimental UTHP was 67.28%.
•An ultra-thin flattened heat pipe with hybrid spiral woven mesh wick is designed.•The wick is hybrid woven from different-diameter copper wires in every strands.•Effect of the number and ...distribution of the wires on the performance is studied.•The optimum design of weaving wick structure for high heat transfer is provided.
In this work, eight different spiral woven mesh (SWM) structures, namely, SA, SB, SC, SD, SE, SF, SG and SH, were designed to investigate the effect of the SWM weaving method on the heat transfer performance of ultra-thin heat pipes (UTHPs). The SA and SH were SWMs, severed as the control group, and they were woven using only 0.05 and 0.04 mm diameter copper wires, respectively. The other six types were hybrid SWM (HSWM) structures that were woven from the two diameters copper wires. The thermal performance of the UTHPs with different SWM/HSWM wick structures was experimentally investigated. The results indicated that the number and distribution of different-diameter copper wires in every strand of HSWM determine the pore size and total pore volume inside the wick. The staggered arrangement of different-diameter copper wires in the HSWM is conducive to the formation of more multisize pores in the wick, thereby improving its comprehensive hydraulic performance. Compared with the SA and SH UTHPs, the maximum heat transport capacity of the SB and SF UTHPs increased by 33.33–53.85% and the total thermal resistance decreased by 27.53–42.92%, significantly improving the heat transfer performance of UTHP by using the appropriate HSWM wicks.
•An ultra-thin vapour chamber with a spiral woven mesh wick is proposed.•The effect of the passage area ratio of wick and test direction on performance is investigated.•The optimum design of the ...passage area ratio for high heat transfer is provided.•The passage area ratio of wick is adjusted by changing the number of spiral woven meshes.
The effect of passage area ratio of wick on the heat transfer performance of the ultra-thin (0.4 mm-thick) vapour chamber (UTVC) which fabricated by brazing bonding was experimentally investigated, the spiral woven mesh (SWM) was utilized as the wick structure and support for the steam chamber of UTVC. The passage area ratio of wick of UTVC was adjusted by changing the number of SWMs. The capillary limits of UTVCs with different passage area ratio of wick were analyzed theoretically. The effect of SWM number and test direction on the thermal performance of UTVCs was experimentally investigated. The results indicated that the maximum heat transport capacity of UTVC increased and then decreased with increasing SWM number. An appropriate SWM number was beneficial to enhance the UTVC’s thermal performance by increasing the vapour-liquid circulation efficiency during heat transfer. The maximum heat transfer capacity of UTVC with 3 SWMs under gravity test direction was 6 W, which was 2 times, 1.4 times, and 1.3 times that of UTVC with SWM number of 1, 2, 4, respectively. The maximum heat transfer capacity of UTVCs changed by less than 10% under different test directions. The optimum passage area ratio of wick of the experimental UTVC was 62.5%.
•A novel ultra-thin vapour chamber manufacturing process was developed.•Vapour chambers that were 0.55-mm thick were fabricated and investigated.•The effects of liquid-filling ratios on the thermal ...performance were studied.•The effects of test states on the thermal performance were investigated.
With the increasing heat flux required in portable electronic devices, ultra-thin vapour chambers (UTVCs) have attracted increasing attention as efficient phase-change heat-transfer components. In this work, a sintered copper powder wick fabricated through a screen-printing process is proposed, providing a novel method for manufacturing large-area and complex-shaped UTVCs. UTVCs with a thickness of 0.55-mm and printed copper powder wicks were fabricated, and the copper powder paste preparation and UTVC manufacturing processes are described in detail. The copper powder paste was made by mixing dipropylene glycol monomethyl ether and copper powder with a particle size of 65–75 μm in a 5:1 ratio. The thickness of the copper layer after sintering was 0.2 mm and its porosity was 59.7%. The heat transfer performance of UTVCs under different liquid-filling ratios and test states was investigated. The results showed that the optimal liquid-filling ratio of the presented UTVCs is 43.2% and that its maximum heat-transfer capability is 6.5 W with a thermal resistance of 0.46 °C/W in the horizontal state. The thermal resistance of the UTVC in the anti-gravity state is more than twice that of the UTVC in the horizontal state. The proposed manufacturing process provides a new solution for the research of the thinner VC and the patterned wick structures.
In this paper, ultrathin vapour chambers (UTVCs) with two kinds of wick, namely, NO.250 copper mesh + 1 spiral woven mesh (SWM) and NO.250 copper mesh, were fabricated by brazing process. Capillary ...rise rate experiment was carried out using infrared (IR) camera method to characterize capillary performance of wicks and verify the SWM liquid pumping action. Effect of filling rate and SWM liquid pumping action on the heat transfer performance of UTVC were studied experimentally, and a model to predict the capillary limit of UTVC was established. The results show that the average rising speed of composite wick increased by 38.89%. The optimal filling rate of composite wick UTVC and copper mesh wick UTVC were 100%, and the maximum heat transfer capacities were 6 W and 5 W, respectively. The heat transfer performance of UTVC was greatly improved by SWM liquid pumping action, the maximum heat transfer capacity of UTVC increased by 20%–60% under different filling rate. The error of growth rate caused by SWM liquid pump action between capillary limit Qcl and maximum heat transfer capacity Qmax is less than 5%.
•The composite wick (copper mesh + 1 spiral woven mesh (SWM)) ultrathin vapour chamber (UTVC) and the copper mesh wick UTVC with thickness of 0.4 mm were fabricated by brazing process.•A model to predict the capillary limit of UTVC was established.•Effect of spiral woven mesh liquid pumping action and filling rate on the heat transfer performance of UTVC was studied.
