Chaohong Guo

Analysis of Micro Vapor Bubble Growing Process in Open Capillary Microgrooves

The growing process of the individual microbubble in an open rectangular capillary microgroove was theoretically analyzed in this study. Several correlations of bubble growth rate for pool boiling were proved not available for microgroove boiling. A theoretical model based on thermal equilibrium and force balance was developed in this article. The growing process of the individual microbubble was divided into three stages: initial growing stage, normal and axial confined ellipsoidal growing stage, and axial subcylindrical growing stage. Growth period and volume increment of the micro vapor bubble were analyzed. The calculation results indicate that the growth of the micro vapor bubble is confined by the geometric structure of the microgroove. Comparison of the results between calculation and experiment shows that the correlation is available to predict the bubble growth rate for boiling in microgrooves.

Analysis of Axial Meniscus Jump-Like Transition in Rectangular Microgrooves

The meniscus receding process was studied for the axial steady flow in open rectangular microgrooves based on experimental results. Experimental results show that the liquid film recedes remarkably as a cubic trendline from the accommodation stage to the bottom corner-flow stage, but the dead zone and the step change don’t exist. The receding process of the liquid film between the accommodation stage and the bottom corner-flow stage is named jump-like transition in the paper. Characteristics of the axial flow in rectangular microgrooves were theoretically analyzed considering the meniscus receding performance in the jump-like transition, calculation results show that radius of the meniscus curvature decreases along the groove axis, which provides drive for the axial flow; the liquid cross sectional area and the liquid height decrease evidently at the stage of the jump-like transition; the liquid velocity increases along the axis, and increases promptly at the transition stage and the corner flow stage.© 2010 ASME

Online measurements of surface tensions and viscosities based on the hydrodynamics of Taylor flow in a microchannel

This paper demonstrates an online measurement technique which can measure both surface tension and viscosity for confined fluids in microfluidic systems. The surface tension and viscosity are determined by monitoring the liquid film thickness deposited in a microchannel based on the hydrodynamics of Taylor flow. Measurements were carried out for pure liquids and binary aqueous liquid mixtures. The results agreed well with reference data and theoretical models. This novel method has considerable potential for measuring dynamic interfacial tension of complex mixtures. Furthermore, it offers opportunity for integrating property measurement with two-phase flow in microchannel, opening new lines of applications.

Experimental investigation of flow-boiling characteristics in a single micro-channel with inlet cavitation structure

This research article investigates the effect that hydrodynamic cavitation has on flow-boiling characteristics in a single micro-channel. Flow and heat transfer characteristics have been investigated over a range of effective heat fluxes (71–330 W/cm2) and vapor quality (0.25–0.92) over a broad range of mass flow rates. The images of flow condition have been photographed. A fully developed cavitation flow, including inception, growth, and collapse of bubble, can be presented in the micro-channel. The intensity of bubble and length of the two-phase region increase with increase in the mass flow rates, and bubble flow pattern dominates the fully developed cavitation flow. Heat transfer coefficient has also been calculated at experimental conditions, and the coefficients decrease with increase in the vapor quality, but increase with increase in the heat fluxes.

Surface with recoverable mini structures made of shape-memory alloys for adaptive-control of boiling heat transfer

A number of technologies have been developed to enhance boiling heat transfer (BHT). The enhancements of BHT depend on the size and geometry of the micro/mini structures and it seems difficult to design a structure that is optimum for all heat transfer conditions. This letter reports a study on adaptive control and enhancement of BHT by shape-memory alloy (SMA) structures. The experimental results of BHT on structured porous surfaces show that the SMA surface with recoverable structures has advantages for heat transfer both in the improvement of heat transfer coefficient and in the extending of operating range. The potential applications of such enhancement structures in diverse heat transfer devices are perhaps the most exciting.

Study on the Characteristics of Contact Line and Liquid Film in Rectangular Microgrooves Under Vibration Conditions

With the help of a high-speed camera (30000 Frames/second) and a wide-field stereo-microscope, the effects of mechanical vibration on the meniscus film and triple-phase contact line in rectangular microgrooves were experimentally investigated. Distilled water was used as working liquid. The images of the oscillated meniscus film in an oscillation period were captured through the high speed camera and they were analyzed using a MATLAB program. The results show that as the vibration table moves upward, the length of contact line increases; as the vibration table moves downward, the length of contact-line decreases. During the oscillation, the axial liquid film spreads upward further along the microgrooves and the deformation of the contact line becomes more obvious. The increase of the triple-phase contact line length caused by the external mechanical vibration is helpful for contact line heat transfer enhancement. Besides, deformation curve of the contact line with and without heat input under different vibration conditions is similar, while the contact line with heat input is shorter.Copyright

Effect of Microgroove Dimensions on Deformation of the Liquid Film Under Vibration Conditions

Deformation of the triple-phase contact line in various sizes of rectangular microgrooves under vertical vibration conditions was studied in this paper. Width of the rectangular microgroove ranges from 0.2 mm to 0.4mm and depth of the microgrooves is 0.2∼0.6mm. The frequency of vibration is 10Hz, and the amplitude of vibration is approximately 3.5mm. The research results show that oscillation of the liquid film in microgrooves becomes more obvious, and the triple-phase contact line is deformed more greatly when the groove width or the groove depth increases. The main reason is that the flow resistance of the liquid film in microgrooves decreases when the groove width or the groove depth increases.Copyright

Thermodynamic coupling characteristics in hybrid (dry/wet) cooling system

ABSTRACT A hybrid cooling system consisting of both a dry section and wet section is proposed in this paper as a means to conserving energy and water by combining the benefits of both dry and wet cooling modes. A new thermodynamic coupling characteristics computing model was established to identify the best combination of dry and wet cooling subsystems in the hybrid tower throughout year-round operation based on its air thermodynamic state under the “no plume” principle. A hybrid cooling tower in Inner Mongolia, China, consisting of an elliptical tube heat exchanger with rectangular fins and counter-flow wet packing, was designed as an example under the no plume principle. The minimum number of heat exchanger units in service and the corresponding thermodynamic operating parameters were obtained under a year-round operation. The tower exhibited notable advantages in regards to water conservation compared to the traditional evaporative cooling tower at an estimated yearly savings of 3.74 × 107 kg water.

Smart materials for energy harvesting and thermal management: Adaptive control and self-driven devices for heat transfer

O to excellent heat resistance and physical properties (especially, impact strength), as well as transparency, Polycarbonates (PC) have been used widely in various applications such as electronics, construction materials and automotive components. Certain applications such as product exterior casings for electronics and headlamp reflectors require additional heat resistance due to their constant exposure to heat. We, at Samyang Corp., developed new oligomer structures consisting of polyester compounds along with its synthesizing technique. We synthesized the oligomers with varying molecular weights by altering the experimental conditions and investigated the mathematical relationships between the experimental conditions and the molecular weight of the oligomer. These novel oligomers exhibit high heat resistance due to its rigid structure; moreover, a block copolymer containing the polyester oligomer along with polycarbonate features a higher heat resistance capability compared to the regular PC.T metallic nanostructure has the physical properties as remarkable increase in surface-to-volume ratio and the development of nanostructure fabrication has revolutionized many applications ranging from electronics to photonics, information strage and sensing, as well as energy conversion and storage. Electrochemical Migration (ECM) is known as a cause of invoking insulation deterioration on the printed circuit board in high-humid and high temperature environment. Although a considerable number of studies have been reported on suppressing ECM, utilization using ECM has not really been studied so far. The previous studies of suppressing reveal that eluting metal grows as dendrites. Recent years, the concern with utilization using ECM has been growing because ECM is the low cost and green fabrication technique and the reaction is caused by DC voltage and water. The attempt has been made at fabricating the metallic nanostructure using ECM. However, it has reported that ECM stops during growth of dendrites between electrodes because dendrites form short circuit. Thus, the sustainable and large-scale fabrication for the metallic nanostructure has not been established. The purpose of this study is to demonstrate sustainable and large-scale fabrication for the metallic nanostructure using ECM. In this study, we changed experimental conditions and evaluated these results.D graphene growth on functional substrates via chemical vapor deposition is an attractive approach to manufacturing flexible electronic devices, as it avoids the drawbacks of transferred graphene. To fabricate flexible devices on plastic substrates, the growth temperature must be below ~200 °C to prevent substrate deformation. Here, we report the direct growth of wrinkle and defect-free graphene on flexible substrates at low temperatures and without transfer processes. We show that defect-free graphene can be directly grown on a variety of substrates via the introduction of an ultra-thin titanium buffer layer, due to perfect lattice matching between titanium and carbon atoms. We further show that ex situ Ti layers (TixOy) with a thickness of ~10 nm does not influence the transmittance or electrical conductivity of functional substrates. We report theoretical and experimental evidence for large-scale (4×4 cm2) high-quality graphene grown on in situ deposited titaniumbuffered substrates at 150 °C in a CH4/H2 atmosphere via plasma-assisted thermal CVD. We applied the proposed methodology to fabricate flexible and transparent thin-film capacitors with direct grown topand bottom-graphene electrodes. These findings could pave the way to the practical exploitation of flexible electronic devices via large-scale high-quality monolayer graphene grown directly with no transfer processes.G Oxide (GO) is a novel low-cost material, presenting intriguing proprieties. Obtained by oxidation of graphite, graphene oxide is a hydrophilic and so water-soluble biocompatible compound, making it the perfect candidate in the design of nanocarriers. The presence of hydroxyl, epoxy and carboxyl groups on its surface enables its easy functionalization and high loading capacity (circa 200% in some cases). In addition, it presents photo-thermal activity, which means it is able to convert light absorbed into heat. Photo-Thermal Therapy (PTT) is an emerging discipline envisaged for Cancer and Antibiotic treatments. The photo production of cytotoxic species, known as Photodynamic Therapy (PDT), presents several advantages, such as good spatiotemporal release control, fast reaction rates and the absence of residues after the reaction. Nitric Oxide (NO) is an example of those species, which can have beneficial or deleterious effect, depending on the concentration. This short half live radical presenting reduced distance diffusion in cellular environment does not suffer Multidrug Resistance (MDR). Here resides the interest of combining light-controlled NO release with suitable nanocarriers. Covalent link of a nitro-aniline derivative nitric oxide photo donor to nanoGO results in a bimodal nanoplatform that combine light-controlled NO release with photo-thermal proprieties.T polyoxazolines is an attractive polymers family characterized by a pseudo-peptidic structure, own bio and hemocompatibility, low toxicity and furtivity towards immune systems-basic properties for biomedical applications. They offer an additional attraction with the ability to self-assembly under various morphologies including spherical nanoparticles, nanowires using hydrogen bonds, dipolar interactions, etc. In this study, we focused on poly (2-methyl-2-oxazoline) decorated by coumarin units, able to photo-activity and able to pi-stacking and further original self-assemblies as already shown with peptides. In a previous work, we demonstrated the UV-activity and the self-organization of amphiphilic di-block and triblock co-polyoxazolines in water. Herein, well-defined single strand helicoidal fibers were elaborated using amphiphilic graft copolymers. These polymeric filo micelles grow according to Crystallization-Driven Self-Assembly (CDSA) between polyoxazoline repetitive units and the coumarin ones. In other experimental conditions, the UV-activity of spherical nanoparticles of the same copolymers were also examined particularly the photo-cross-linking of the nanoparticle core.I recent years, frequent occurrence of cyanobacteria bloom has disrupted the balance of lakes and reservoirs around the world. Copper-Core Carbon-Shell Nanoparticles (CCCSNPs), as a novel material, have showed a good antibacterial and anti-mildew performance in previous study. In this study, we tried to demonstrate the potential effect of CCCSNPs on cyanobacterium Microcystis aeruginosa growth and clarify the mechanism to know the application prospects of the material in controlling cyanobacteria bloom. Compared with the widely used algaecides CuSO4, CCCSNPs significantly reduced chlorophyll a content of M aeruginosa when the concentration of Cu2+ in the medium was the same as the CuSO4, so the inhibitory effect of CCCSNPs on algae was better and lasted longer than that of CuSO4. We further explored the mechanism of inhibitory effect, finding that intracellular excess Reactive Oxygen Species (ROS) were produced after exposure to CCCSNPs, which were 2.4 and 1.5-fold higher than the control and the CuSO4 treatment, respectively. Excess ROS formation caused oxidative damage to algae and reduced the photosynthetic efficiency, which further inhibited algal growth. Therefore, it is reasonable to propose that CCCSNPs could induce excess ROS production and further interfere with algal photosynthesis to achieve a satisfactory effect with a longer action time.T ability of lanthanide ions to generate fascinating Near-Infrared (NIR) emissions has played important roles in optical fiber communication, semiconductor optoelectronic devices, biomedical imaging and bioanalyses. Two aspects of my group’s recent works on the lanthanide activated advanced materials and nanotechnology will be introduced. Firstly, we have developed various lanthanide doped nanocrystals for photonic and biological applications. For instance, biosensors with both high sensitivity and rapid response are greatly desired for enabling rapid and sensitive detection of various virus gene in a cost-effective way. We have developed lanthanide doped up-conversion nanoprobe/nanoporous membrane to form a heterogeneous assay. Compared to the homogeneous assay, the limit of detection in the heterogeneous assay is significantly improved. Secondly, the ultimate goal of making nanoscale electronic and optoelectronic devices greatly stimulates atomically thin material and heterostructure research. We have introduced lanthanide dopants into two-dimensional (2D) layered semiconductor nanosheet hosts and realize NIR-to-NIR down and up-conversion photoluminescence. Importantly, the luminescence of 2D materials simply pumped by a single NIR laser diode can be extended to a wide range of NIR spectrum, including telecommunication range at 1.55 μm. By considering the abundant energy levels arisen from lanthanide ions, our works open a door to greatly extend and modulate the luminescence wavelengths of 2D semiconductors, which will benefit for not only investigating many appealing fundamental issues, but also developing novel nanophotonic devices.T electronics market had a strong driving force and tendency for developing portable and wearable electronic devices has stimulated the research interests in flexible, renewable and sustainable energy sources. Poly(vinylidene difluoride) (PVDF) is a pyroelectric and piezoelectric polymer and widely investigated for flexible electronics because of its high flexibility, biocompatibility and simplicity of production. A pyroelectric material such as PVDF can effectively convert thermal energy into a temporary voltage when they are heated or cooled. If the temperature stays constant at its new value, the pyroelectric voltage gradually disappears due to leakage current. Thus, a new heating technique such as light irradiation is important to replace the traditional conductive heating method and leads to the poor thermal conductive PVDF polymer with repeatedly fast heating and cooling behavior. A highly effective photo-thermal conversion material reduced tungsten oxide (WO2.72), having the temperature change of 60 °C within 30 seconds under infrared light radiation (IR) was developed in our research group. Therefore, it is highly interesting to study the pyroelectric response of the electrospun PVDF nanofibrous membranes incorporated with efficient photo-thermal conversion material (WO2.72) under IR radiation. In this study, a novel flexible pyroelectric power generator was developed by electrospun PVDF nanofibrous membranes incorporated with various weight fractions of WO2.72 powders. The effects of WO2.72 and electro-spinning (ES) parameters on the crystal structure and pyroelectric properties of PVDF/WO2.72 nanofibrous membranes were examined. Results show that ES effectively induced the β-phase of PVDF and the fraction of β-phase was further increased from 79% to 84% after adding with 7 wt% WO2.72. Besides, the temperature of electrospun PVDF/WO2.72 nanofibrous membrane increased rapidly and reached 98.7 °C from room temperature while pure PVDF nanofibrous membranes only reach to 60.5 °C after 300 seconds under IR radiation. It demonstrated that WO2.72 presents excellent photo-thermal conversion characteristics due to the presence of free electrons or oxygen-deficiency-induced small polarons. As for the pyroelectricity measurement, the PVDF/WO2.72 nanofibrous membranes were sandwiched between two electrodes and the output voltage was measured by repeated heating and cooling process. Controlling by IR radiation, the temperature of the as received PVDF pyroelectric unit with WO2.72 was increased from room temperature to 51.6 °C during heating process and then rapidly cooled down to 29.9 °C within 3 minutes. When the temperature change is 21.7 °C, the maximum output voltage of the pyroelectric unit with WO2.72 reached to 80 mV which is largely enhancement compare to 30 mV of the unit without WO2.72 with 10.1 °C temperature change. Hence, the PVDF/WO2.72 with higher temperature change induces stronger pyroelectric response than pure PVDF sample. In addition, the PVDF/ WO2.72 also shows good stability and durability of pyroelectric power output.P Fluoride (PVDF) is a popular piezoelectric polymer because of its high flexibility, biocompatibility and simplicity of production. These features make PVDF attractive in energy conversion applications between mechanical force and electrical power, such as strain sensors, mechanical actuators and energy harvesters. The aforementioned applications rely on the piezoelectric property of PVDF and it is well-known that appropriate mechanical stretching and electrical polarization are essential factors to achieve good piezoelectricity. Electro-spinning processes can provide PVDF fibers mechanical stretching and electrical poling simultaneously and produce ultrafine and well-distributed nanofibers. Furthermore, previous studies discovered that the nanoparticles addition such as carbon nanomaterials or metallic nanoparticles could help improving the β content of the electrospun PVDF nanofibers. In this study, a rotation drum was used to collect aligned PVDF nanofibers during the electro-spinning process. The aligned fiber membranes were collected by changing the electro-spinning parameters of the rotating speed and the applied voltage. The PVDF nanofiber membranes collected by rotating drum showed higher β content and better mechanical property than the membranes collected on a fixed copper grid collector. The results showed that the orientation and contents of β phase of the aligned nanofiber membranes were both increased with the rotating speed and the applied voltage during the electro-spinning process. The β content of the PVDF fiber membrane reached to 87% at rotating speed of 3000 rpm and applied electric field of 1500 V/cm. Moreover, the aligned PVDF nanofibers with Carbon Nanotubes (CNTs) addition exhibited enhanced β phase content. The received PVDF nanofiber membranes were loaded and evaluated by three types of dynamic mechanical forces: Compression, tensile and bending. According to the different types of the mechanical loading, corresponding piezoelectric units were circumspectly designed. The piezoelectric response (electrical output voltage) of the PVDF nanofiber membranes increased linearly with the applied forces and showed good stability during the cyclic loading.T understand and modify the nonlinear optical properties of transition metal dichalcogenides, TMDs, two-dimensional layered materials are very important research topics nowadays as they can serve as building block for developing next generation high performance micro optics and photonic devices. These materials are very compact with atomic thick layer and have natural band-gap so they can provides strong interaction with light and other favorable features e.g. broadband absorption, transparent and high carrier mobility etc. WS2, which is a typical TMDs material, has layer number depending band gap energy. The WS2 band gap energy and optical properties can be modified by varying their size, layer number and structures. The WS2 nanomaterials and film in various size, layer number or film thickness are fabricated by two methodsultrasounds and sputtering. The nonlinear optical properties of different samples are then studied by using z-scan technique. We have successfully demonstrated some viable methods to tune the nonlinear absorption properties of WS2. We also use the fabricated WS2 film within the diode pumped solid state Nd:YVO4 crystal laser to generate pulsed laser output. A stable pulsed laser operation is achieved by using the fabricated WS2 saturable absorber. The average output power obtained is 19.6 mW (135 kHz). These research findings indicate strong nonlinear optical properties of WS2 and high potential for nonlinear optical devices.S materials, that can change structures and/or physical-chemical properties by active or passive control, has potential applications in energy engineering. They can be used to design cute and efficient energy converting systems, e.g., waste heat generation systems made of Shape-Memory-Alloys (SMA). The advances of electronic and aerospace engineering calls for more robust thermal management technologies that can help the devices to discharge intensive heat release and mitigate the temperature fluctuation. To this end, smart materials can take their inherent advantages in heat transfer enhancing and in providing extra measures for driving coolant flow. In our latest studies, a novel deformable structured surface was fabricated by SMA for the enhancement of boiling heat transfer. Pool boiling heat transfer on deformable structures were performed in three fluids (ethanol, FC-72, water) with different thermal properties was explored. Comparing heat flux versus wall superheat and HTC at different fluxes with fixed geometry, it is found that deformable structure combines the merits of closed-tunnel and open-tunnel. At low heat fluxes, it can increase the numbers of nucleation sites inside the closed tunnels with bent fins and after recovering with open tunnels, the nucleation sites are activated and the bubble growth and departure is accelerated to enhance the HTC significantly. On the other hand, by choosing the appropriate time and opportunity for different fluid to open the tunnels, the deformable structures can be used to achieve adaptive-control of boiling heat transfer. In another study, researchers from POSTECH proposed a smart TiO2-Coated Surface (TCS) for boiling heat transfer. The surface changes its wettability with temperature. Measurement of the contact angle of a water droplet on the tested surfaces after heat treatment showed a wettability increase of TCS, a contact angle reduction from 83.1o to 32.7o when the heat treatment temperature changed from 100oC to 200oC, in other words, TCS is hydrophobic at a low wall temperature and becomes hydrophilic as the wall temperature increases. Hydrophobicity of TCS at low wall temperatures. The TCS improved both the heat transfer coefficient near the boiling inception point at low heat flux regime and critical heat flux at high wall temperatures. People are also developing heat transfer devices that have SMA self-driven unit for flow circulations that working with temperature differences. The study on energy harvesting and thermal management by use of smart materials is a quite young interdiscipline research field, which is still in the initial stage. This presentation gives a critical review to the latest pioneering work. By summarizing the advancements, we propose some comments on the principles and prospect for the future development.D attachment is one of the most important processes in the packaging of power semiconductor devices. Sintered silver has demonstrated superior properties in microelectronic packaging as compared to the traditional solders and conductive epoxies. The sintering joints formed by atomic diffusion of silver nanoparticle can be processed at a temperature significantly lower than the melting temperature of the bulk and can be used for high temperature applications. The potential advantages such as high temperature stability, high electrical and thermal conductivity, good mechanical properties etc. makes silver nanoparticle a promising candidate for die-attach applications. In the present invention, we have synthesized capped silver nanoparticle and nanosilver paste which can be used for pressure-less die attach applications. The percentage of capping according to thermo-gravimetric analysis is around 1%. TEM reveals the size of the silver nanoparticle to be around 3 nm to 80 nm. The heterogeneous particle sizes help in sintering of the nanoparticle at a faster rate because of their large point of contact between each other which also leads to good packing fraction. The die attach paste made from these heterogeneous size silver nanoparticles is used for pressure-less die attach applications on different metallized substrate (Au, Ag and Cu) to achieve a joint strength of 25-30 MPa when sintered at 180oC for 60 minutes. The thermal conductivity of the sintered material was around 200 W/m.K. The above results clearly show that the nanosilver paste sintered at lower temperature has a slight edge over the traditional solder and conductive epoxies.T tribology community presently relies on phenomenological models to describe the various seemingly disjointed steadystate regimes of metal wear. Pure metals such as gold-frequently used in electrical contacts, exhibit high friction and wear. In contrast, nanocrystalline metals, such as hard gold, often show much lower friction and correspondingly low wear. The engineering community has generally used a phenomenological connection between hardness and friction/wear to explain this macro-scale response and thus to guide designs. We present the results of recent simulations and experiments that demonstrate a general framework for connecting materials properties (i.e., microstructural evolution) to tribological response. We present evidence that the competition between grain refinement (from cold working), grain coarsening (from stress-induced grain growth) and wear (delamination and plowing) can be used to describe transient and steady state tribological behavior of metals, alloys and composites. We will explore the seemingly disjointed steady-state friction regimes of metals and alloys, with a goal of elucidating the structure-property relationships, allowing for the engineering of tribological materials and contacts based on the kinetics of grain boundary motion.W can learn how nature produces hierarchical micro-nanostructures for realization of specific functions. Superb mechanical properties as well as unique optical properties can be distinguished examples. These examples have inspired researchers to develop and design new artificial materials. Structural organization with parallel stacking of nanosheets was found in internal structure of nacre of abalone shell and it presents strong and tough mechanical properties. On the other hand, the vertically orientation of nanostructures are also ubiquitous in biocomposites such as teeth and seashells. In this presentation, two types of nanocomposites will be presented, planar shaped nanocomposites with silica layer and vertically oriented nanocomposites with ZnO nanopillars. We demonstrated that 2D and 3D structural organization of nanomaterials can show enhancements of mechanical properties which can exceed limit of conventional nanocomposites.C Nanotubes (CNTs) have received great attentions with their extraordinarily fascinating behaviors such as structural, mechanical, optical and electrical properties. They can be added into various polymers as fillers to prepare advanced functional polymeric composites. However, due to their intrinsically poor dispersibility, achieving a uniform dispersion is generally difficult. As one of the effective methods, milling processes are introduced to reduce the original size of the nanotubes to improve dispersion, especially in the case of CNT suspension rheology for potential battery applications. With interesting functionalities under external fields implying typical flow fields of laminar flow with most cases of rheological aspects and electrical and magnetic fields, electro-responsive Electro-Rheological (ER) characteristics of polymer/CNT composite systems from material rheological viewpoint are examined for various CNT composite particles with polystyrene and PMMA. Interesting characteristics of their ER suspensions include yield stress, flow curve behavior and dielectric analysis. As for Magneto-Responsive Magneto-Rheological (MR) materials, we coated the surface of soft-magnetic carbonyl iron particles with CNT along with polymers to produce their favorable core-shell structure with apparently decreased particle density for better dispersion and then characterized their MR characteristics under magnetic fields applied.F and foldable electronic components require materials that can retain their electrical conductivity even after hard mechanical manipulations and multiple folding events. Such a material was realized with two different methods exploiting the combination of all-biodegradable components (substrate and the polymer matrix) and graphene nanoplatelets (GnPs). A fibrous cellulose substrate was sized with a biopolymer-GnPs conductive ink rendering it electrically conductive (sheet resistance ≈10 Ω/sq). The obtained nanocomposites can be used as electrodes for surface electromyography and for terahertz electromagnetic interference shielding. With a similar approach, a flexible cotton-GnPs conductive nanocomposite was realized. This material addresses several drawbacks related to durability and washability of wearable electronics material. Micro-cracks formed after repeated folding-unfolding events can be healed through a hot-pressing process. Such cotton based conductive composites could find several applications in smart textile industry.P of inks with proper viscoelasticity is the key pre-requirement for extrusion based 3D printing. Here, extrusion based 3D printing Graphene Oxide (GO)/Geopolymer (GOGP) nanocomposite was reported for the first time. We found that, the addition of GO in geopolymeric aqueous mixture (alumio-silicate and alkaline-source particles) dramatically changes its rheology properties and enable the 3D printing that cannot be realized solely by geopolymer, indicating a strong GO/ alumio-silicate interaction. We proposed a model, in which a water layer is laminated between GO and alumio-silicate, based on the facts that both of GO and alumio-silicate are hydrophilic and negatively charged, to account for such phenomenon. The chemical and microstructure analysis showed that the GO nanosheets anchor themselves around and encapsulate individual geo-polymer grains to resist being pullout and at the same time, form a continuous 3D network throughout the whole nanocomposites, which was proved by selective etching of geo-polymer and left behind free-standing porous GO aerogel. Therefore, not only the mechanical properties of geo-polymer were significantly increased by GO, but also very high electrical conductivity was obtained after sintering and endow our 3D printing nanocomposite among the highest conductive ceramic nanocomposites. In addition, we found that, enhancing mechanical properties at material level by employing large GO nanosheets, will inevitably switch failure model from stretching/compression to buckling instability, thus limit the fully exploitation of material properties and thus in turn, structural performance. This finding suggests the local modification of 3D printed structures, especially weakening the rotational stiffness of nodes, is critical for the realization of 3D printing superstrong cellular solid.F more than two decades, many researchers have focused on Carbon Nanotubes (CNTs) which have the superior electrical, thermal and mechanical properties, motivating their use in composites as a fibrous reinforcing agent. Although mechanical properties of CNT reinforced composites have been widely studied, only a few groups have reported strengthening effects for the composites. Before the utilization of CNTs becomes mainstream, it is necessary to develop protocols for tailoring the material properties, so that composites and devices can be engineered to given specifications. In this presentation, we review our recent studies, in which we investigate the nominal tensile strength and strength distribution of Multi-Walled CNTs (MWCNTs) synthesized by the CVD method, followed by a series of high-temperature annealing steps. The structuralmechanical relationships of such MWCNTs are investigated through tensile-loading experiments with individual MWCNTs, Weibull-Poisson statistics, Transmission Electron Microscope (TEM) observation and Raman spectroscopy analysis. The comparatively low value of the shape parameter for MWCNTs resulted from the irregular nanotube structure, which reflects a larger tube defect density relative to conventional fiber materials. Nonetheless, the MWCNTs with an intermediate level of crystallinity produced complete fracture of nanotube walls and exhibited higher nominal tensile strength, suggesting that improvements to the nominal tensile strength of MWCNTs might be achieved by inducing appropriate interactions between adjacent nanotube walls to enable sufficient load transfer to the MWCNT inner layers. This effect should be balanced to permit an adequate load transfer between the inner and outer walls to give clean break fractures.Eng Sanit Ambient | v.24 n.4 | jul/ago 2019 | 833-842 ABSTRACT A set of experiments were carried out in order to establish and evaluate the potential of activated carbon, produced from coffee waste in adsorption process, in the depuration of landfill leachate. Different reagents were studied in the activation of carbon: HCl, HCl + H 2 O 2 , H 3 PO 4 , H 3 PO 4 + H 2 O 2 , all with an impregnation rate of 1:1. The activated carbon that showed the best global results was activated with H 3 PO 4 , obtaining a 51.0, 32.8, 66.0, 81.0 and 97.1% elimination of chemical oxygen demand, ammonia, total chlorine, bromine and copper, respectively. This activated carbon has a total pore area of 4.85 m/g and a median pore diameter of 65.32 micrometers. When different loads of this carbon were placed in a stirrer system in contact with landfill leachate, with the aim of evaluating the effect of the adsorption load and contact time, the concentration of ammonia decreased from the beginning of the adsorption process to the end of it, and the removal of ammonia increased with the increase in the adsorbent load. However, the trend of the amount adsorbed per unit mass decreased with increased dosage. The model Freundlich equilibrium isotherm fits experimental data adequately, giving R values of 0.95, 1/n of 0.5183, and a K value of 7.08*10 L/g, being favourable for adsorption process.

Effect of Mechanical Vibration on Heat Transfer Characteristics of Liquid Film in Rectangular Microgrooves

The effects of vertical mechanical vibration on the heat characteristics of liquid film in vertical rectangular microgrooves are observed. The vibration frequencies are 6Hz, 10Hz and 30Hz, respectively; the vibration amplitudes are in the range of 1.95∼3.23mm. Three sizes of rectangular microgrooved plate are used in experiments. The microgrooved plate is vertically mounted on a vibration plane; DC heat load is added on the back wall of the microgrooved plate. Vibration of the liquid film in the microgroove is observed by a high-speed digital camera, and temperature on the back of the plate is recorded by a data acquisition. The experimental results show that temperature on the plate back decreases obviously with the increase of the vibration frequency or amplitude, heat transfer of the microgrooved plate is intensively enhanced. The main reason is that the forced convections on the groove surface and in the liquid film, caused by the mechanical vibration, enhance the heat transfer. The investigation provides more information for the application of the micro-configuration heat sink under fierce vibration conditions.Copyright