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Extreme-wettability-patterned surfaces have attracted great attention due to their excellent application prospects for liquid manipulation. However, developing a simple and universal method to fabricate wettability patterns on a variety of metals remains a great challenge. In this work, three specific preparation approaches were developed to fabricate wettability patterns on copper substrates using chemical processing combined with mask technology. Surface wettability can be suitably controlled by changing the solution concentration and immersion time. The surface has good stability and low pollution under external action. The three preparation methods have differences in preparation process, wettability and mask function. On the basis of these approaches, various complex wettability patterns could be prepared on different metal substrates using designed masks. Furthermore, various wettability-patterned surfaces were successfully fabricated for liquid manipulation applications, such as controlling the fluid shape and water transport. The methods proposed are expected to have promising application potential in patternable printing, water collection and heat-dissipation devices.

The ability of predicting a grinding force is important to control, monitor, and optimize grinding process. Few theoretical models were developed to predict grinding forces when a structured wheel was used in a grinding process. This paper aimed to establish a single grit grinding force model to predict the ploughing, friction and cutting forces in a grinding process. It took into the consideration of actual topography of the grinding wheel, a theoretical grinding force model of the grinding wheel with orderly-micro-grooves was proposed. The model was innovative in sense that it represented the random thickness of undeformed chips by a probabilistic expression, and it reflected the microstructure characteristics of the structured wheel explicitly. Note that the microstructure depended on the randomness of the protruding heights and distribution density of the grits over wheel. The proposed force prediction model was validated by surface grinding experiments, and the results showed (1) a good agreement of the predicted and measured forces and (2) a good agreement of the changes of the grinding forces along with the changes of grinding parameters in the prediction model and experiments. The proposed model was proven its accuracy, reliability and effectiveness in predicting grinding forces by an orderly-micro-grooved grinding wheel.

Microstructures of wicks have been widely investigated on their performances of heat and mass transfer and various structures have been attempted. As have been optimized by the nature, the microstr...

Electroplated grinding wheel has significant advantages, such as longer service life, higher removal rate, reduction of preparation work, reapplication of the wheel bub. Then it is an efficient, green and eco-friendly abrasive tool. In order to reveal the mechanism that the service life of the electroplated grinding wheel is increased by pre-quenched substrate, the tensile behavior and interfacial stresses of the laser-discrete-quenched substrate/nickel coating were studied through tensile experiment and simulation. The results show that random initial cracks appear in the nickel coating over the unquenched zone before the tensile experiment. There is an inter-diffusion region at the interface of steel substrate and nickel coating; in comparison with the unquenched zone, the size of the inter-diffusion region in the laser-quenched zone was decreased significantly (e.g., 1.2 μm in comparison with 2.6 μm). In tensile testing, the coating over the pre-quenched specimen remains bonded with the substrate firmly even the fracture occurs. In contrast, the damages in the forms of blistering, stripping and exfoliating occurred in the coating over the unquenched specimen. When a fracture occurs, there is a significant difference of the ultimate strains of quenched and unquenched zones; the ultimate strain of quenched zone is 0.0714, while that of the unquenched zone is 0.1667. At the bonding interface, the pre-quenched specimen ensured the overall shear stress and the maximum normal stress, which are lower than those of unquenched specimen. The initial cracks in pre-quenched specimen propagate during stretching, the effect of the absorbed strain energy reduces strain mismatch between the substrate and coating at the interface, and this improves the bonding strength at the interface of the laser-discrete-quenched specimen significantly.

Separator is an essential component of lithium-ion battery, affecting the electrochemical performance and safety of battery. The material-structure-tensile property relationship is significant, her...

It is of great essence to unveil relationship between structure, mechanical properties, and application of bionic design. Targeting at alleviating the debonding failure issue in the internal struct...

Thin-walled structures play an important role as an energy absorber in all kinds of crash accidents due to their excellent energy absorption characteristics and lightweight. This paper aims to inve...

With the rapid development of photoelectric products, their miniaturization and high integration have intensified the problem of heat dissipation. Vapor chamber is a special type of heat pipe that is a particularly effective heat spreader for electronics. In this paper, a novel Leaf-vein-inspired Gradient Porous (LGP) wick structure is designed macroscopically and the LGP design is verified using a general model. After that, the gradient porous design Model 1G is selected for the subsequent mesoscopic modeling. Then a connected 2D random LGP wick model presenting porosity gradient is generated by the expanded quartet structure generation set method. Using the mesoscopic Lattice Boltzmann Method (LBM), the flow and heat transfer in the LGP wick model is analyzed. For verification, FLUENT based on the macroscopic finite volume method is used as a benchmark. Finally, the microscopic flow behaviors in the 2D random LGP wick model are analyzed using the LBM developed. Observing the entire flowing process from the inlet to outlet, it is possible to explain the mesoscopic and macroscopic phenomena well based on the microscopic flow behaviors.

Combining the fan aerodynamic efficiency with the wind tunnel pressure loss coefficient, a new equation which points out the inherent relationship of the fan blade setting angle, fan rotating speed and gas flow rate in wind tunnel circuit is derived according to the two-dimensional flow theory of the axial fan rotor blades and the aerodynamic characteristics of the low speed wind tunnel. So a new method for setting angle adjustment of fan rotor blade to satisfy the fan performance at off-design point by getting the test results of fan operation parameters but without the fan total pressure rise in the low speed wind tunnel is developed. Flowing the new method, the setting angle adjusting value of fan rotor blade was provided only with the fan rotating speed and flow velocity in the test section of a low speed wind tunnel directly before the fan setting angle altered, the adjusting target was achieved by the new blade setting angle successfully and the time and cost of the wind tunnel commissioning test were saved. The test results show that, after increasing the fan rotor blade setting angle by 4.5 degrees, when the flow velocity in the wind tunnel test section reaches 60 m/s, the fan rotating speed is 570 r/min, the deviation from the predicted fan rotating speed value of 575 r/min is 0.9%. For the same test section flow velocity, the predicted value of the fan rotating speed is in a good agreement with the real value, it proves that this method is reliable and accurate in practical application.

Heat generation during insertion of Kirschner wires (K-wires) may lead to thermal osteonecrosis and can affect the construct fixation. Unidirectional and oscillatory drilling modes are options for K-wire insertion, but understanding of the difference in heat generation between the two modes is lacking. The goal of this study was to compare the temperature rise during K-wire insertion under these two modes and provide technical guidelines for K-wire placement to minimize thermal injury. Ten orthopedic surgeons were instructed to drill holes on hydrated ex vivo bovine bones under two modes. The drilling trials were evaluated in terms of temperature, thrust force, torque, drilling time, and tool wear. The analysis of variance showed that the oscillatory mode generated significantly lowered peak bone temperature rise (13% lower mean value, p = 0.036) over significantly longer drilling time (46% higher mean time, p

To design an ideal tree-like branching networks with good performance on both heat transfer and flow of working fluid, the thermal conductivity and permeability of the tree-like branching networks are calculated. In addition, the thermal conductivity created by heat convection is analyzed and compared with that created by heat conduction. It’s found that when the temperature difference between wall and fluid in each branching level is treated as different, heat convection accounts for larger proportion than heat conduction in heat transfer. Furthermore, the difference of each branching level’s temperature difference between wall and fluid plays a key role in heat transfer. There exists large error in calculation of heat transfer, if the difference of each branching level’s temperature difference between wall is not considered.

Cortical bones are semi-brittle and anisotropic, this brings the challenge to suppress vibration and avoid undesired fracture in precise cutting processes in surgeries. In this paper, we proposed a novel analytical model to represent cutting processes of cortical bones, and we used to evaluate cutting forces and fracture toughness, and investigate the formations of chips and cracks under varying bone osteon cutting angles and depths. To validate the proposed model, the experiments are conducted on orthogonal cuttings over cortical bones to investigate the impact of bone osteon cutting angle and depth on cutting force, crack initialization and growth, and fracture toughness of cortical bone microstructure. The experimental results highly agreed with the prediction by the proposed model in sense that (1) curly, serrated, grainy and powdery chips were formed when the cutting angle was set as 0°, 60°, 90°, and 120°, respectively. (2) Bone materials were removed dominantly by shearing at a small depth of cut from 10 to 50 µm, and by a mixture of pealing, shearing, and bending at a large depth of cut over 100 µm at different cutting orientations. Moreover, it was found that a cutting path along the direction of crack initialization and propagation benefited to suppress the fluctuation of cutting force thus reduce the vibration. The presented model has theoretical and practical significance in optimizing cutting tools and operational parameters in surgeries.

Droplet control technology has broad application prospects and the wettability-patterned surface is a popular way to realize it. However, the existing preparation methods are either not suitable for copper or not suitable for its batch fabrication. In this paper, three specific preparation schemes with different effects are proposed for the wettability-patterned copper surfaces. Then the influences of preparation conditions on the contact angle are investigated. Using the selected preparation conditions, the effects among different preparation schemes are compared and the wettability-patterned copper surface prepared following preparation scheme 3 shows the best effect. Subsequently, according to different design purposes, the motions and spreading of water droplets on wettability-patterned copper surfaces with four new patterns are observed. It indicates that the hydrophilicity/hydrophobicity and directional liquid transport functions basically reach the pre-designed effects, which verifies the applicability of preparation scheme 3 on the wettability-patterned copper surfaces with different patterns for droplet control. Finally, compared with the existing preparation schemes, only the new preparation scheme proposed in this paper is conducted under room temperature and it does not require any special equipment. What’s more, its preparation time is the shortest (18 min). Hence, it is suitable for batch fabrication, which can extend the applications of wettability-patterned copper surfaces.

According to the two-dimensional flow theory of the axial fan rotor blades and the aerodynamic characteristics of the low speed wind tunnel, combined with the fan aerodynamic efficiency and wind tunnel pressure loss coefficient, a new equation which points out the inherent relationship of the fan blade setting angle, fan rotating speed and flow rate in wind tunnel circuit is derived. So a new method for fan rotor blade setting angle adjustment to satisfy the fan performance at off-design point by getting the test results of fan operating parameters but without the fan total pressure rise in the low speed wind tunnel is developed. Following the new method, the fan rotor blade setting angle adjusting value was provided directly only with the fan rotating speed and flow velocity in the wind tunnel test section, the adjusting target was achieved successfully by the new blade setting angle, the cost of the wind tunnel commissioning test were saved. The test results show that, after increasing the fan rotor blade setting angle by 4.5 degrees, when the flow velocity in the wind tunnel test section reaches 60m/s, the fan rotating speed is 570rpm, the deviation from the predicted fan rotating speed value of 575rpm is 0.9%. For the same test section flow velocity, the predicted value and the real value of the fan rotating speed are in good agreement, it proves that this method is reliable and accurate in practical application.

In this work, a new vapor chamber (VC) was fabricated and tested, on which a novel compound columns was proposed by considering the mechanical property and the thermal performance comprehensively. The columns consisted of the solid copper bars and the porous functional structures sintered on the cylinder surface of the pillars. Copper foam was selected to manufacture the wick structures and the cladding layers due to its distinct porous structures. To verify the superiority of the compound columns, a testing system was used to evaluate the thermal behaviors of the VCs under different inclination tilts. In this parametric investigation, the filling ratios included 70% and 100%, the sintering layer porosities were configured as 0%, 50% and 95%, and the heat loads varied from 6 W to 96 W. The experimental results indicated that the cladding layers of the columns enhanced the capillary limit and contributed to recycling the working fluid in the anti-gravity position, which finally broaden the adaptability of the VC.

The ever-increasing performance of thin portable electronic products has made their heat dissipation issues more and more severe, or even become failure. A novel 0.5 mm thick ultra-thin vapor chamber (UTVC) with six spiral woven meshes and single-layer mesh acting as the wick is developed for cooling portable electronic products. The heat load capacity of the UTVC could be improved through the mixed effect of the spaced structure and composite wick by both decreasing the pressure drop of vapor flow and the fluid flow. The UTVC is tested in five typical positions, and the results show that it can withstand heating power of 10.5 W, 10 W, 10 W, 10 W, and 9.5 W in gravity, horizontal, side, inverted and antigravity positions, respectively, implying that the influence of position on the heat transfer performance of the proposed UTVC is not significant. The effective thermal conductivity of the vapor chamber in the gravity position reaches about 18,000 W/m·K. Compared to the thermal module without UTVC, the one with UTVC has effectively improved the cooling effect of thin electronics and eliminated the hot spots.

Kirschner wire (K-wire) is a common tool in clinical orthopedic surgery for bone fracture fixation. A significant amount of heat is generated in bone drilling using K-wires, causing bone thermal necrosis and osteonecrosis. To minimize the temperature rise, a hollow notched K-wire in a modified surgical hand drill with through-tool cooling was developed to study the bone temperature, debris evacuation, and material removal rate. The hollow notched K-wire was fabricated by grinding and micro-milling on a stainless steel tube. Bone drilling tests were conducted to evaluate its performance against the solid K-wires. Results showed that compared with solid K-wires, hollow notched K-wire drilling without cooling reduced the peak bone temperature rise, thrust force, and torque by 42%, 59%, and 62% correspondingly. The through-tool compressed air reduced the peak bone temperature rise by 48% with the forced air convection and better debris evacuation. The through-tool water cooling decreased the bone temperature by only 26% due to accumulation and blockage of bone debris in the groove and channel. This study demonstrated the benefit of using the hollow notched K-wire with through-tool compressed air to prevent the bone thermal necrosis. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:2297-2306, 2019.

Hydrogels have attractive characteristics such as notable biocompatibility, outstanding hydrophilia and efficient mass transport (MT), which makes hydrogel suitable for tissue engineering scaffold materials. Stereolithography is a prevalent method to prepare hydrogel scaffold with complex structure. However, it is difficult to ensure dimension accuracy in printing complex hydrogel scaffold since solvents can migrate in gel and render MT behavior, which consequently induce deformation and dimensional inaccuracy of printed hydrogel. Little investigation of MT of gel in mixture like solution is conducted. Aiming to depict multiple solvents MT in gel, a model is established by mainly modifying the representation of free energy of mixing to the multi-component one. This model is feasible to describe concurrent multiple solvents migration and mechanical deformation for hydrogel in liquid mixtures, which fulfills understanding of multi-component MT. In this work, the transient MT behaviors of poly(ethylene glycol) diacrylate gel in its photocurable solution are investigated by the model. The numerical model is validated by experimental results and then applied to simulate free and confined MT process of the system. It is found that the deformation trend is not monotonous and total gel deformation can be regulated by adjusting printing time. The correspondence between numerical and experimental results proved that this model can promisingly illustrate multi-component MT induced deformation and provide instructions on improving dimensional accuracy for printing hydrogels.

In order to accelerate the development of large transport aircraft, it is important to build a continuous transonic wind tunnel. The re-import section, acted as a key part of the wind tunnel, plays an important role in maintaining the stability and balance of the wind tunnel. On this account, the structure design and strength check of the re-import section is investigated. Firstly, the 3-D model of re-import section is established based on NX software. Secondly, the layout of stiffeners is optimized to solve the bearing problem of components. Finally, the strength check of the re-import section is carried out based on ABAQUS software to validate the effectiveness of the designed structure.

Leaf veins are the channels for water and nutrient transportation within plant leaves. In recent years, the excellent heat and mass transfer characteristics of natural reticulate leaf veins structure has inspired many researchers in the structural design of various microchannels. In this paper, three different models of leaf-vein-inspired microchannels with wall thickening patterns are established base on the real microstructures of the xylem vascular bundles in the midribs of the leaves of three ordinary species of plants with heat-resistance. Their heat and mass transfer characteristics are investigated through numerical simulation and compared by using three assessment criteria, the Poiseuille number, the average Nusselt number and the thermal performance index. Numerical analyses about the influences of the dimensions of the reticulate/pitted wall thickening patterns are also performed. Additionally, an application of the leaf-vein-inspired microchannels on microchannel heat sink is demonstrated and the heat and mass transfer characteristics among six different models are compared. The results indicate that the natural selected structure of the xylem vascular bundles in the leaf veins can provide excellent heat transfer characteristic with a smaller volume while sacrificing a little bit ability in mass transfer, which might be used as a promising design method for some heat dissipation devices.

The performance of a novel vapor chamber based on the leaf vein system is tested in this study. In this vapor chamber, the conceptual structure, being composed of leaf-vein-like fractal network and micro fin-pins and used to simulate the transportation principle of plant leaf, is made on the inner surface of the top copper plate to form the wick of the condenser. To the inner surface of the bottom, a copper plate sintered with a layer of porous wick is used as the evaporator. Because the conceptual structure is not restricted by the shape, the vapor chamber is made into circular and rectangular shape respectively. In the circular vapor chamber, the supporting columns sintered with copper powder are used to strength the vapor chamber. However, in the rectangular vapor chamber, the wick of the condenser contacts directly with the wick of the evaporator so as to strength the vapor chamber and shorten the back flow length of the liquid condensed on the groove surface. In the circular vapor chamber, the fractal angle of the leaf-vein-like fractal network is 30–70°, and the vapor chamber is packaged with eight bolts for convenience. In the measurement, the vapor chamber has small thermal resistance when the fractal angle is 40° and 50°, and in the rectangular vapor chamber, the thermal resistance of the vapor chamber is about 0.06 °C/W.

Lithium-ion batteries have been developing intensively and earn an unprecedented reputation, yet advanced performance and safety issue still require considerable investigation. Separator is vital to comprehensive properties of batteries, where the mechanical properties are key to breaking through of new-type separator. Unfortunately, electrolyte submersion has caused damage to strength of cellulose separator. Whereupon, in this work, cellulose separator is optimized by introducing lignin particles to promote electrolyte-immersed mechanical strength. Experiments are conducted concerning surface morphology, contact angle, porosity, electrolyte uptake, mechanical properties and electrochemical performance. Molecular simulation is implemented to explore the mechanism of tensile behavior of cellulose and lignin subjected to electrolyte solvents. Experimental results confirm positive effect of lignin addition in improving mechanical properties and simultaneously maintaining impressive electrochemical performance of the cellulose/lignin composites separators. Besides, lignin addition amount of 2.5% and 5% is recommended to achieve promising overall properties. Molecular simulation has successfully unveiled that weakening of cellulose separator submerged in electrolyte is resulted by the deformed cellulose amorphous region and the promoting effect of adding lignin is contributed from the new hydrogen bonds generated between cellulose and lignin molecules. Hopefully, this work provides novel insight on preparing remarkable separator and mechanism of materials behavior.

Separator is an essential component for lithium-ion batteries, subtly providing transporting micro-channels for lithium ions and electric insulation between electrodes. In this paper, bleached eucalyptus cellulose pulp is implanted with TEMPO-mediated oxidization and high-pressure homogenization to attain cellulose pulps with both micro- and nano-sized fibers, where the blending ratio is regulated by homogenization times. Then the cellulose pulp is formed into separators through vacuum filtration after uniformly dispersed. Macro-properties, micro-structures, physical properties and electrochemical performance of the cellulosic separators are characterized and analyzed. And t commercial Celgard 2500 polypropylene separator is also investigated as comparison. The influence of homogenizing degree on comprehensive properties of the separators is investigated. Besides, the relationship between micro-structure and electrochemical performance is detailedly discussed. Results show that higher homogenization degree contributes to more nano-sized fibers and less micro-fibers, resulting in smaller porosity, poorer electrolyte uptake and larger contact angle. The nano-sized fibers are effective in promoting mechanical strength of separators, but are negative to the impedance performance. This study has unveiled the impact of high-pressure homogenization on the performance of separators, providing meaningful instruction for further development of qualified cellulose separators.

With the rapid development of photoelectric products, their miniaturization and high integration have intensified the problem of heat dissipation. In this paper, a new type of bionic vapor chamber is designed and manufactured. The wick structure for the condenser combines the fractal network microchannels and copper foam, which are used to imitate the macroscopic leaf vein network and microscopic mesophyll tissue, respectively. Furthermore, the permeability gradient distribution between the leaf veins and mesophyll tissue is added, presented as the porosity gradient distribution of the copper foams around the fractal network microchannels. Then the fractal network microchannels on the wick are processed by laser engraving and mould coining, respectively. The wick structure for the evaporator is homogeneous copper foam. The minimum value of the maximum temperature difference on the upper surface of the condenser of the bionic vapor chamber is only 1.21 K and that of the overall thermal resistance of the bionic vapor chamber is only 0.094 K/W. Compared with the existing novel vapor chambers, when using deionized water as the working fluid, the maximum through-plane effective thermal conductivity and minimum in-plane effective thermal conductivity are 9.52 W/m·K and 10500 W/m·K, respectively, which are higher than most existing vapor chambers.

Ultra-thin vapor chamber (UTVC) is an efficient heat transfer element that meets the heat dissipation requirement of miniaturized electronics. In this study, a novel UTVC (0.5 mm thick) with four spiral woven meshes and one bottom mesh composite wick was designed for cooling portable electronic devices. The UTVCs were manufactured using a cost-effective process suitable for mass production. The heat transfer performance of the UTVCs with different filling ratios were tested and the maximum heat transfer capacity of the UTVCs with filling ratios of 90%, 100%, 110% and 120% were 5.10 W, 7.58 W, 6.58 W and 6.33 W, respectively. Furthermore, the maximum heat transfer capacity of the optimal filling ratio UTVC (100%) in five representative placement states: horizontal state, gravity state, anti-gravity state, side state and inverted state were 7.58 W, 9.06 W, 6.33 W, 7.33 W and 7.58 W, respectively. The maximum effective thermal conductivity of the UTVC was found to be about 20900 W/(m·K) in horizontal state and 25200 W/(m·K) in gravity state, which were about 52 times and 63 times higher than that of pure copper, respectively. The proposed novel UTVC is promising for solving the heat dissipation problem of high performance ultra-thin portable electronic devices.

With the miniaturization and integration of portable devices, ultra-thin vapor chamber (UTVC) is required to have thinner thickness and better heat transfer performance. However, the reduction in thickness usually causes a decrease in heat transfer capability. Thus, it is necessary to optimize the internal structure to improve the heat transfer performance. In this study, the relationship between the thickness and width of the steam chamber and the channel coefficient (Sv) was studied. When the thickness of the steam chamber is less than 0.3 mm, Sv increases rapidly as the thickness decreases. At the same time, Sv also rises rapidly with the decrease of steam channel width (Wv ≤ 2 mm). For the layered structure, the influence of different support column types on the vapor pressure drop was analyzed. It indicates that reducing the diameter and spacing of the support columns simultaneously is a good way to balance the support effect and vapor pressure drop. The calculation method for solving the optimal values of the spaced structure is derived. For ultra-thin limited space, the sum of Fv and Fl of the optimal spaced structure is smaller than the layered structure, which is more suitable for UTVC.

A force model is presented to theoretically predict single-tooth sawing force based on mechanics. The model is used to study the effect of the saw tooth profile parameters, such as rake and setting angles, on the sawing process so as to optimize the sawing process. Then, the force model is experimentally verified by a series of sawing force measurements. This study shows that the resultant force decreases with an increase in the rake/setting angle. Theoretically, there exists maximum rake/setting angle which, however, can never been reached in practice due to the process restrictions. Therefore, the optimal rake/setting angle is the maximum that can be obtained in the process. The study provides a theoretical foundation for design and optimization of the saw tooth profiles.

The perfect performance of a heat pipe or a vapor chamber is not only decided by the excellent structure design, but also closely related to the proper working conditions. In the present work, a novel evaporator wick structure was fabricated through chemical etching. A mathematical model of the thermal resistance was developed. To better understand the influence of the filling quantity of working fluid and the heat source power on the thermal resistance, an experiment was set up to simulate the working conditions of an evaporator. From the comparison between the experimental results and theoretical analysis, it revealed that the heat source power and filling quantity had different impacts on the wick's thermal resistance. As the thermal conduction resistance was relatively low, the total thermal resistance of the evaporator was mainly influenced by the thermal evaporation resistance. The total thermal resistance of the novel evaporator wick structure ranged from 0.13 to 0.19 K/W.

Lumped compliant parallel-guiding mechanism (CPGM) is a particular type of compliant mechanisms. This paper establishes a new mathematical model of the lumped-CPGM based on the elastic beam (EB) theory with an increasing precision discussed from four different situations. In situation D, both the parasitic rotation and deflection of the guiding plate and rigid beams are taken into account, which might be tiny but do exist in reality. As for a comparison, a pseudo-rigid-body (PRB) model is also established. Then the guiding displacement, parasitic displacement and parasitic angle in the four situations are analyzed at different distances between two supporting arms, which have not been involved by any former researchers. Furthermore, the relations between the displacements and some other structural parameters are analyzed respectively comparing with the finite element method. The results indicate that the EB model in situation D is very effective with a much higher precision than other models, although the computation is more complicated. Our work could be a reference and supplement to the design and manufacture of the current lumped-CPGM.

Fractal networks are widely applied in the field of heat and mass transfer. As one of the important parts of the fractal network, Y-shaped structure definitely has a significant impact on the performance of the whole network. In this paper, the analytical relationship between Y-shaped microchannel geometry and its capillary flow time is established through theoretical analysis with mass continuity equation and Navier-Stokes (N-S) equations. The result reveals that the capillary flow time increases with the increase of the topology length and bifurcation angle of the Y-shaped microchannel, but decreases with the increase of the channel width.

Ultra-thin vapor chamber (UTVC) is an efficient heat transfer element that meets the heat dissipation requirement of miniaturized electronics. In this study, cost-effective mesh-type UTVCs (total thickness: 1.26–1.77 mm) were fabricated and investigated. One single layer of coarse copper mesh was used as mechanical support and to provide vapor path, and two layers of fine copper mesh were sintered together as wick. The copper meshes and the bottom copper sheet were treated by plasma to obtain hydrophilicity, and the upper and bottom copper sheets were bonded by a new welding process. The effects of coarse mesh count and wire diameter, fine mesh count, tilt angle and cooling water temperature on the UTVC heat transfer performance were studied experimentally. Results showed that SP3 (1.53 mm) could dissipate 50 W in the horizontal orientation with a thermal resistance of 0.197 °C/W, about 4.4 times lower than that of 1.5 mm copper sheet. With the good thermal performance and low fabricating cost of the UTVCs, we hope that our work could promote the application of UTVC in the field of high performance miniaturized electronics.

In electric vehicles, the performance of the power battery is closely related to its operating temperature, which makes it necessary to develop an effective and compact thermal management system. In this paper, a novel battery thermal management system for cylindrical Li-ion battery pack based on vapor chamber combined with fin structure is developed. A set of experiments concerning temperature control performance of the system under different discharge rates (2C, 3C, 5C) at ambient temperature of 25 °C is conducted. Subsequently, the effects of heat dissipation area, flow rate and way of condensation (air-forced cooling and water cooling) on cooling performance of the system are investigated and analyzed. The results show that the vapor chamber can notably alleviate the average temperature rise and improve the uniformity of temperature distribution within the battery pack. Furthermore, with the rising of dissipation area, the temperature control effect of the system becomes more effective. In addition, comparing to air-forced cooling, the system hybridized with water cooling exhibits lower maximum temperature and more uniform temperature distribution. However, flow rate has little effect on cooling performance. The above results indicate that applying vapor chamber combined with fin structure is a viable solution to thermal management of Li-ion battery pack.

The Li-ion battery (LIB) with the innovative internal cooling methods is designed to substitute for the NCCB used in electric vehicles (EVs). In this paper, the NiCoMn battery with a hollow mandrel is fabricated. The pure phase change materials (PCM) and heat pipe (HP) assisted PCM are filled in the mandrel, respectively, to constitute the PCM internal cooling battery (PICB) and the HP-PCM internal cooling battery (HPPICB). Experimental investigations are conducted to assess the thermal performance of the as-constructed battery. A complete cycle with low charge and discharge currents is used to measure the capacity of the manufactured battery. Then the proper mandrel diameter of PICB is obtained by calculation and experiment methods. The thermal behaviors of natural convection cooling method (NCCB), PICB and HPPICB are estimated by comparing their maximum temperatures as well as the temperature uniformity. The feasibility and efficiency of the batteries in practical applications are further taken into consideration by a cycling test. The experimental results demonstrate that NCCB shows the worst performance at all conditions due to its low efficient cooling system. While relying on the heat storage ability of the PCM, PICB with 6 mm mandrel diameter exhibits a moderate performance. Further, the HPPICB possesses the best thermal performance by means of integrating the PCM with the heat pipe.