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The temperature rise of key internal components and ambient temperature changes during machining processes are the main causes of thermal displacement in machine tool spindle. This wastes materials and reduces working efficiency. A highly accurate and robust thermal spindle displacement estimation scheme is proposed in this paper which is based on the convolutional neural network (CNN) technique. Several key signals of specific dimensions related to spindle thermal displacement were first collected as two-dimensional (2D) signal maps. A multi-level feature expression for these 2D signal maps was extracted using convolution and pooling. A relationship between the extracted features and spindle thermal displacement was then learned using the neural architecture of the full connection layer. Optimized hyperparameter settings were determined by design of experiments (DoE) applied to the proposed CNN model. Experimental results showed that the proposed method had better performance than the multiple regression analysis (MLR) or back propagation neural network (BPNN) methods in terms of estimation accuracy and robustness at different spindle speeds. [ABSTRACT FROM AUTHOR]

In this study, a thermal balance control method by local heating on the spindle head structure of a vertical milling machine was proposed to improve the squareness error of the Y-Z plane. Thermal deformation and temperature distribution of the spindle head structure was analyzed to determine the key positions on the structure for prediction and control of the spindle pose. A long short-term memory (LSTM) neural network with time series characteristics was used to build the in-situ spindle tilt error prediction model. The particle swarm optimization algorithm was integrated with a neural network model to dynamically determine and find temperature control targets in local positions on the spindle head. Finally, the temperatures at selected local locations of spindle head was adjusted by elective heating to suppress thermal bending and improve the spindle tilt on the Y-Z plane. The proposed method was verified using a five-axis vertical milling machine. The experimental results showed that the proposed method could effectively maintain the spindle tilt in the Y direction at [10, −10] μrad after long-time operation of the spindle at both 7200 and 12,000 rpm. • The radian of spindle tilt can be controlled by local heating of the spindle head structure. • The main cause of spindle tilt is thermal bending of the spindle head structure. • Spindle tilt can be suppressed online using thermal balance control. No modification of the existing machine structure is necessary. • The neural network integrated with the optimization algorithm provides accurate implementation parameters for active thermal balance control. [ABSTRACT FROM AUTHOR]

A novel method of triple line focused on solar-powered receiver/reactor with a thermal storage medium for methanol steam reforming (MSR) hydrogen production is proposed in this paper. The photo-thermal-chemical energy conversion and coupling equations of the receiver/reactor are established, and the dynamic regularity between solar radiation and the hydrogen production characteristics is obtained by numerical simulation. The results show that a high solar radiation intensity helps to stabilize the duration of the reaction. For every 100 W m−2 increase in the solar radiation intensity, the duration of the reaction maintained at the phase change point temperature of the phase change material (PCM) increases by approximately 11%. The daily hydrogen production performance of the system in Kunming (102°43′E and 25°02′N) during typical solar days is studied. The average annual total hydrogen production per unit of the lighting area is approximately 1300 m3. This research can guide similar issues related to solar thermochemical technology. • A novel method of triple line focused on solar reactor/receiver is proposed. • A comprehensive model of solar-driven adapted to different powers is established. • Dynamic regularity of hydrogen production rate with solar radiation is revealed. • System goes well when solar radiation is 400 W m−2 or above on partly cloudy skies. [ABSTRACT FROM AUTHOR]

Synchronous scattering and diffraction were demonstrated using reflectance from gold nanotextured surfaces at oblique (θ i  = 15° and 60°) incidence of wavelength λ = 405 nm. Two samples of unique auto-correlation functions were cost-effectively fabricated. Multiple structure factors of their profiles were confirmed with Fourier expansions. Bi-directional reflectance function (BRDF) from these samples provided experimental proofs. On the other hand, standard deviation of height and unique auto-correlation function of each sample were used to generate surfaces numerically. Comparing their BRDF with those of totally random rough surfaces further suggested that structure factors in profile could reduce specular reflection more than totally random roughness. [ABSTRACT FROM AUTHOR]

Abstract: Microreactors have important advantages due to the increased heat and mass transfer resulting from the small dimensions of the system. This results in enhanced performance and efficiency. Microreformers with wall-coated or suspended catalytic layer configurations have been studied due to their lower transport resistances compared to packed-bed microreformers. In the present work, a theoretical study of the reacting flow in a wall-coated microreformer is carried out. The theoretical results for the conversions and carbon monoxide concentration of wall-coated reformers are compared with the reported experimental data. The effects of important parameters for wall-coated reformers such as the catalyst layer thickness, wall temperature, and the flow velocity of the reactants are studied. Recommendations for the design of micro wall-coated reformers are provided. [Copyright &y& Elsevier]

Abstract: In the present study a small steam–methanol reformer with a colloid nanocatalyst is utilized to produce hydrogen. Radiation from a focused continuous green light laser (514nm wavelength) is used to provide the energy for steam–methanol reforming. Nanocatalyst particles, fabricated by using pulsed laser ablation technology, result in a highly active catalyst with high surface to volume ratio. A small novel reformer fabricated with a borosilicate capillary is employed to increase the local temperature of the reformer and thereby increase hydrogen production. The hydrogen production output efficiency is determined and a value of 5% is achieved. Experiments using concentrated solar simulator light as the radiation source are also carried out. The results show that hydrogen production by solar steam–methanol colloid nanocatalyst reforming is both feasible and promising. [Copyright &y& Elsevier]

Abstract: An experimental and analytical study of nanocatalyst fabrication and the production of hydrogen utilizing photon energy was carried out. The porous structure of the nanocatalyst provides a high surface to volume ratio of the catalytic layer thereby increasing the activity of the catalyst. An experiment was carried out to obtain an effective nanocatalyst by using pulsed laser ablation (PLA) technology. The properties of the nanocatalyst are directly related to the performance of the catalytic reaction and are analyzed. Experiments and analyses were carried out to evaluate the activity enhancement of the nanocatalyst. Photonic energy provides the heat for the endothermic steam–methanol reforming reaction producing hydrogen. It is shown that photonic induced steam–methanol reforming in a nanocatalyst reformer is feasible and promising. [Copyright &y& Elsevier]

Abstract: An experimental and theoretical study of steam reforming of methanol is carried out in a packed-bed microreactor with internal heating. Experimental results of the methanol conversion and carbon monoxide concentration in an internally heated reformer are compared with those of an externally heated reformer. Higher methanol conversion and carbon monoxide concentration are obtained for internal heating at the same conditions. The results show the conversion efficiency of methanol and CO concentration increase with increasing internal heating rate over the range of operating conditions. A correlation for the conversion efficiency of methanol has been obtained as a function of the internal heating rate and a dimensionless time parameter which represents the ratio of the characteristic time of the methanol flow to the time for chemical reaction. [Copyright &y& Elsevier]

Abstract: Steam reforming of methanol is investigated numerically considering both heat and mass transfer of the species in a packed bed microreactor. The numerical results are shown to be in good agreement with experimental data [M.T. Lee, R. Greif, C.P. Grigoropoulos, H.G. Park, F.K. Hsu, J. Power Sources Transport in, 166 (2007) 194–201] with a BASF F3-01(CuO/ZnO/Al2O3) catalyst. A correlation for the conversion efficiency of methanol has been obtained as a function of the operating temperature and a dimensionless time parameter which represents the ratio of the characteristic time of the methanol flow to the time for chemical reaction. The results show that for the constant wall temperature condition the steam reforming process of methanol results in a nearly uniform temperature throughout the microreactor over the range of operating conditions. [Copyright &y& Elsevier]

Abstract: Methanol-steam reforming can be utilized as a fuel processing system for hydrogen fuel cells. A study of the reacting flow in packed-bed and wall-coated catalytic reactors is presented. The wall-coated reformer has a smaller power requirement for delivering fuel than the packed catalytic bed reformer. Also, the coated catalytic layer has a smaller thermal resistance compared to the packed catalytic bed. This yields enhanced thermal field management for the wall-coated reformer that is essential for reformer performance. Understanding the transport in reformers is essential for improving both the efficiency of the reforming process and the quality of the processed fuel. [Copyright &y& Elsevier]

Abstract: In the present study, a hydrogen polymer electrolyte fuel cell (PEFC) micropowerplant in combination with a steam reformer fed by methanol and a direct methanol fuel cell (DMFC) micropowerplant are analyzed numerically regarding their exergetic efficiency. The effects of concentration and activation overpotentials, and ohmic resistance on the efficiency are considered in quasi-two-dimensional fuel cell models. The influence of significant operational parameters on the exergetic efficiency is examined numerically. Experimental results are conducted for the steam reformer. This work shows the importance of an exergy analysis of the fuel cell as part of an entire thermodynamic system generating electric power and compares PEFC and DMFC micropowerplants exergetically. [Copyright &y& Elsevier]

Quick progress in the field of smart wearable devices requires self‐sustainable power systems to help the devices execute the desired functions within a sufficient time scale. Because these devices have started to become small, light, compliant, complex, and multifunctional, it is challenging to provide them with the large amounts of energy necessary for their operation. Thus, future multifunctional wearable devices should not only incorporate mechanical flexibility for conformal contacts but also include sustainable energy units for stable operation. Hence, strategies for designing the assembly of nanoscale materials in macroscale‐structured devices have attracted intense interest, with an aim to achieve mechanically deformable and sustainable wearable devices while exploiting the recent advances in nanomaterials and device fabrication. This review highlights the recent progress in nanomaterial‐enabled and structured energy harvesting, energy storage, and hybrid devices for powering sustainable wearables. In particular, one summarizes describe biomechanical energy harvesters (piezoelectric nanogenerators and triboelectric nanogenerators), solar energy harvesters (solar cells), biothermal energy harvesters (thermoelectric nanogenerators), energy storage devices (batteries and supercapacitors), and hybrid devices and focus on the use of nanomaterials and device configurations in 1D, 2D, and 3D structures, with an aim to shape the future demand for self‐sustainable wearables. [ABSTRACT FROM AUTHOR]

• Investigated bubble dynamics in laser induced reaction process of liquid precursor. • Analyzed liquid-vapor phase change to determine the reaction rate from bubble growth. • Obtained the transient triple contact point temperature by experiment and simulation. • Developed a semi-empirical model for reaction rate vs triple contact point temperature. • Validated the transport and reaction model experimentally with an excellent accuracy. Laser assisted low-temperature nano/microfabrication of functional materials on a flexible or rigid substrate using water-based liquid precursor have gained significant attention owing to its high process efficiency and low environment impact. Both of which are essential for the green and low-carbon manufacturing technologies needed for the next generation of electronic devices. Laser induced photo-hydrothermal synthesis (LIPHS) utilizes thermally induced reductive reaction in a liquid precursor to synthesize and deposit nano/micro-patterns on temperature sensitive substrates. During LIPHS, microbubble generation is inevitable as a result of byproduct gas formation and liquid-vapor phase change of the precursor. Transport phenomena of the laser-induced reduction reaction coupled with microbubble dynamics on the liquid-vapor-solid triple contact interface significantly affects the quality of fabricated nano/microstructures. Herein, we investigated microbubble formation and growth on the substrate surface during a LIPHS process for silver on a polyimide substrate surface. Framewise growth of microbubble was captured for different laser powers and solute concentrations to reveal the time dependent bubble diameter variation. It was found that the bubble size and growth rate decreased with increasing solute concentration owing to increased boiling point of the precursor. Bubble temperature and reduction reaction rate were obtained by theoretical analyses on the microbubble growth rate. Transient solid-liquid-vapor triple contact point temperature of the microbubble during the LIPHS process was obtained from a numerical simulation to develop a comprehensive model the first time for predicting the chemical reaction rate. The proposed model was validated experimentally with a relative error of 6.2% at the highest reaction rate. [Display omitted] [ABSTRACT FROM AUTHOR]

Manufacturing strategies to create three‐dimensional (3D) structures with multifunctional nanomaterials are of intense interest for fabricating building blocks in many electromechanical applications. A coil spring composed of graphene provides an important step toward the realization of all‐carbon devices, as it is one of the essential elements for a wide range of systems. In this connection, here an unprecedented fabrication strategy to create a new type of 3D coil spring composed of laser‐induced graphene springs (LIG‐S) which is spontaneously produced via the pyrolytic jetting technique, is presented. Similar to wood or metal shavings observed in traditional machining processes, a pair of LIG‐S with two opposite chiralities and controllable macroscopic dimensions is produced by a single scanning of a focused continuous‐wave (CW) laser on a polyimide (PI) substrate. The resulting LIG‐S, plastic shavings by laser, exhibits sufficient mechanical and electrical properties to enable many applications including strain‐tolerant spring electrodes, antennas, supercapacitors, gas sensors, and luminescent filaments under extreme conditions. Without using any conventional fabrication techniques or other labor‐intensive, time‐consuming, and expensive processes, this novel approach enables a high‐throughput mass production of macro‐, micro‐, and nanoscale featured LIG‐S that can be manufactured within seconds to realize many open opportunities in all‐carbon electromechanical systems. [ABSTRACT FROM AUTHOR]

A microscopic finite element model validated by the quasi-static mechanical test on lithium ion battery cell is presented in this study. The investigated condition involves three-point bending and cell discharge test, which include the mechanical response and thermal response of lithium ion battery cell. The cell is investigated through computational simulation. Results show great correlation between the experiment and finite element simulation. A microscopic model requires a greater effort during simulation. Investigating the fracture on steel casing and cell core is possible by considering the fracture mechanism in steel shell and jelly roll. The classic von-Mises criterion is applied to predict the failure of carbon steel shell, and the maximum von-Mises strain criterion is used to investigate the jelly roll region. On the basis of the verified battery cell model, battery package with microscopic model, including cell core (cathode, anode, and separator) is constructed to analyze the mechanical response of battery pack. The von-Mises criterion is used to predict the fracture point location of the battery pack with various packing modes and packing densities. [ABSTRACT FROM AUTHOR]

We have fabricated CuO/ZnO nanowire (NW) catalyst for hydrogen production by solar thermal steam-methanol reforming (SMR). Such NW catalyst is expected to be more durable than the conventional nanoparticle catalysts by avoiding agglomeration. ZnO NWs are synthesized by hydrothermal growth on quartz and glass substrates. The ZnO NWs are then coated with CuO by thermal decomposition of copper nitrate using UV pulsed laser as a heat source for prototyping. A solar simulator is used as a heat source for the demonstration of the SMR in water/methanol mixture solution. Gas chromatograph (GC) exhibits increasing mole fraction of produced hydrogen with irradiated time. We then fabricate the catalyst on a large area glass plate substrate by the CuO deposition using an electric heater to confirm the SMR and demonstrate scaling-up. The SMR is briefly demonstrated by feeding water vapor/methanol mixture gas to the catalyst heated by an electric heater, giving thermally produced hydrogen (CO/H 2 = 0.019) in the product gas detected by GC. [ABSTRACT FROM AUTHOR]

Emphasis on nanomaterials, device fabrication techniques, and device architectures emerging from recent studies is provided. Recent Advances in Sustainable Wearable Energy Devices with Nanoscale Materials and Macroscale Structures (Adv. Funct. Keywords: energy harvesting; energy storage; functional nanomaterials; wearables EN energy harvesting energy storage functional nanomaterials wearables 1 1 1 04/21/22 20220419 NES 220419 B Sustainable Wearable Energy Devices b In article number 2110535, Ming-Tsang Lee, Ha Beom Lee, Seung Hwan Ko, and co-workers discuss energy harvesting and storage devices to provide large amounts of energy needed to power wearable devices. [Extracted from the article]

Abstract: In this study, thermal performance of the cooling modules applicable for Par 38 light bulb is investigated. A total of six heat sink modules, including the basic reference design, metal foam, and carbon foam are tested and compared. Tests are performed and analyzed using the transient test method based on JESD51-1 standard. It is found that the thermal resistance from junction to die attach is quite small. By contrast, the thermal resistance of the heat sink dominates the total resistance, and it comprises 55% of the total resistance for the standard heat sink module. With some slight opening on the base plate, the thermal resistance can be improved by approximately 12%. The thermal resistance for the carbon foam having an embedded metal plate shows the least thermal resistance of 1.14K/W, followed by the carbon foam, and then the metal foam. The lower thermal resistance of carbon foam in association with copper metal foam is due to its higher emissivity. In addition to better heat transfer performance as compared to the standard plate heat sink, the utilization of carbon foam and metal foam can also significantly reduce the weight of the heat sink. In this study, the weight of the heat sink can be reduced as much as 33%. [Copyright &y& Elsevier]

Copper oxide particles of various sizes and constituent phases were used to form conductive circuits by means of photonic sintering. With the assistance of extremely low-energy-density xenon flash pulses (1.34 J/cm2), a mixture of nano/submicron copper oxide particles can be reduced in several seconds to form electrical conductive copper films or circuits exhibiting an average thickness of 6 μm without damaging the underlying polymeric substrate, which is quite unique compared to commercial nano-CuO inks whose sintered structure is usually 1 μm or less. A mixture of submicron/nano copper oxide particles with a weight ratio of 3:1 and increasing the fraction of Cu2O in the copper oxide both decrease the electrical resistivity of the reduced copper. Adding copper formate further improved the continuity of interconnects and, thereby, the electrical conductance. Exposure to three-pulse low-energy-density flashes yields an electrical resistivity of 64.6 μΩ·cm. This study not only shed the possibility to use heat-vulnerate polymers as substrate materials benefiting from extremely low-energy light sources, but also achieved photonic-sintered thick copper films through the adoption of submicron copper oxide particles. [ABSTRACT FROM AUTHOR]

This work developed a type of energy-saving glass for regions undergoing sun glare and high temperature. Its functions cost zero energy and negligible weight increment (1.81 g/m2). The key to its success was two-dimensionally periodic nanostructures composed of single material. These nanostructures were arranged in a hexagonal way and added on a commonly-seen glass substrate. The area of these structures was scalable, and their fabrication was cost-effective using nanoimprint lithography technology. The glass was able to exhibit broadband wavelength-selective transmittance. Measured spectra confirmed transparency in the visible and approximate opaqueness in the near-infrared regions. The power for indoor illumination and air conditioner could thus be simultaneously saved. This work also utilized numerical modeling to obtain electromagnetic field patterns in the near-field. The patterns explained the broadband wavelength-selectivity and influences from an adhesive layer existing in real samples. • An energy-saving glass was elaborately designed and experimentally verified. • Area was scalable and mass fabrication was feasible using nanoimprint lithography. • Functions of the glass took zero energy and only 1.81 g/m2 weight increment. • Transmittance in UV and near-IR was suppressed, while transparency in VIS was kept. • Wavelength-selectivity was explained via near-field electromagnetic analysis. [ABSTRACT FROM AUTHOR]

Oblique angle deposition (OAD) has become a cost-effective method for depositing nanostructured films. Films with various degrees of porosity, anisotropy, and crystallographic texture have been successfully demonstrated. However, most studies were based on the more established processes, such as evaporation and sputtering; oblique angle deposition using atmospheric pressure plasma jet (APPJ) has not been reported. Here we deposit Ga-doped zinc oxides (GZO) on tilted substrate using APPJ, and study how the film properties are affected by the oblique angle and nozzle scanning trajectory. We found that the trajectory plays a key role in determining the optoelectronic properties of the obliquely deposited films. If the nozzle scans from the upstream side of the substrate to the downstream side, the resistivity, carrier concentration and mobility deteriorate considerably near the downstream region. The film becomes more porous with the haze factor rising significantly from <5% to ∼80%, while the total transmittance remains high (>80% at 550 nm). This degradation can be attributed to the "pre-deposition" of the GZO adsorbed particles on the downstream side of the bare glass where the nozzle has not scanned. Such undesirable pre-deposition occurs due to the combined effect of asymmetric plasma jet and gas flow, both pointing toward downstream, compared to axial symmetric pattern observed in the normal case. More importantly, this undesirable phenomenon can be removed by merely reversing the scanning trajectory, i.e. from downstream to upstream. In this case, a dense film has been formed in the downstream region so the subsequent exposure of the biased plasma jet and gas flow do not result in ad-particles deposition. Therefore, highly transparent and conductive OAD films as good as the normally deposited films can be achieved, a unique phenomenon not reported before. Our findings may shed light on the development of curved display technology, and may also be applied to other deposition methods with moving nozzle or moving stage such as spray pyrolysis. Image 1 • Oblique angle deposition of GZO films by atmospheric pressure plasma jet (APPJ). • Porosity and haziness can be tuned by the oblique angle and deposition trajectory. • Highly transparent and conductive films can be deposited on tilted substrates. • Formation of nuclei under asymmetric plasma jet and gas flow causes high haziness. [ABSTRACT FROM AUTHOR]

Selective laser melting (SLM) is a popular additive manufacturing (AM) technique for the fabrication of precise components. The success of SLM relies on accurate control of the melt pool, where the metal powder melts and solidifies. Fluid flow inside the melt pool is driven by forces like Marangoni force and recoil pressure. SLM process begins with the fabrication of support, which involves the process of joining dissimilar metals. A strong support-base substrate connection ensures the success of subsequent additive manufacturing. In this study a comprehensive model was developed to predict the dimensions and characteristics of the melt pool with a focus on the first layer of the SLM process. An initial numerical simulation was done to obtain transient melt pool temperature and velocity distribution during the SLM process. The results were then coupled with a theoretical analysis development of the proposed model. The effectiveness of the model was validated by experimental results and melt pool characteristics from previous publications. The model shows Root Mean Square Error (RMSE) of 0.53 and 0.49 for height-to-width ratio and normalized area, respectively. The Mean Absolute Percentage Error (MAPE) of normalized area is 15.7 % for the majority of the data, which demonstrates a good accuracy of the model. In addition, the transition from conduction mode to keyhole mode can be identified with the model. This model can be used to rapidly and effectively predict the melt pool characteristics for SLM and other similar AM processes with a wide range of processing parameters. [ABSTRACT FROM AUTHOR]

Without using any labor-intensive, time-consuming, and expensive processes, the presented strategy enables high-throughput mass production of LIG springs for a wide range of all-carbon electromechanical applications. Plastic Shavings by Laser: Peeling Porous Graphene Springs for Multifunctional All-Carbon Applications (Adv. Sci. 21/2023) B Laser-Induced Graphene b One of the keys to utility of laser-induced graphene (LIG) is the ability to manufacture designed macroscopic geometries in a high-throughput manner. [Extracted from the article]

Transparent conductive oxides (TCOs) are indispensable as transparent electrodes in optoelectronic applications due to their unique features of high optical transmittance, high electrical conductivity, and cost-effective industrial-scale manufacturability. However, patterning TCO films for functional devices requires lengthy and expensive photolithography and etching processes. Although the laser patterning technique—based on nanoparticle ink and particle-free ink—has been used to fabricate patterned metal electrodes without photolithography, it is still unknown if it works for TCO, such as doped zinc oxide (ZnO). Here, we introduce a novel single-step maskless, particle-free, and ink-free process to deposit transparent, conductive Ga-doped ZnO (GZO) patterns on glass substrates via a laser-assisted atmospheric pressure plasma jet (APPJ) technique. With the exposure of a plasma jet, GZO patterns can be deposited by scanning a continuous-wave CO 2 laser using a galvanometer and computer-aided design (CAD) images. The GZO patterns (∼100 nm thick) are visually transparent and exhibit remarkably low resistivity of 7.89 × 10–4 Ω cm, comparable with that of uniform (unpatterned) GZO films prepared by APPJ only. Our present work fundamentally differs from prior works since neither particles nor ink is applied to the substrate before processing. The entire process is conducted in ambient conditions without substrate preheating and pre-/post-processing. Also, it does not require expensive vacuum apparatus and pulsed laser sources and has a high potential for cost-effective and sustainable fabrication of TCO patterns and circuits. [Display omitted] • Transparent GZO patterns by single-step maskless, particle- and ink-free process. • Highly transparent and low electrical resistivity (7.89 × 10–4 Ω cm). • Convenient integration of APPJ and continuous CO 2 laser under ambient conditions. • A facile and cost-effective method suitable for commercial mass production. • New functionality that conventional techniques such as sputtering cannot achieve. [ABSTRACT FROM AUTHOR]

The selective laser melting (SLM) process involves irradiation from a high-power laser to melt and sinter powdered material. The high temperature gradient near the laser spot generates high residual stress that can lead to failure of fabricated parts. Estimation of the residual stress for real transient SLM processes by simulation involves considerable computation effort which makes its application in real industrial SLM processes rather difficult. To tackle this challenge, a two-stage coupled transient thermomechanical model with a quasi-transient heat source was developed. In the first stage, a transient thermal analysis was performed to acquire temperature distribution of the full SLM process. The temperature distribution serves as thermal loading input for subsequent transient thermal stress analysis. This quasi-transient thermomechanical model can provide residual stress data consistent with that of a conventional full transient model in 68% less computation time. The data provided by the new model also includes the dynamic stress release due to re-heating and re-melting in overlapped laser scanned regions which was in close confirmation with experimental results. This efficient quasi-transient model is useful for rapid analysis and optimization of SLM processing parameters. [ABSTRACT FROM AUTHOR]

In this study a numerical simulation was carried out to analyze the transport phenomena in a vertical type metal organic chemical vapor deposition (MOCVD) reactor for Gallium Nitride (GaN) growth. The simulated results were compared and validated by experiment. The effects of showerhead design and chamber height are investigated and discussed. It was found that, by properly adjusting the height of the chamber, both the growth rate and film uniformity could be significantly improved. This is attributed to the suppression of the thermal and mass transfer boundary layers by the injection flow of reacting gas mixtures, as well as the confined vertical vortices caused by the geometry of the reduced space. However, inappropriate design of the distance between the showerhead and the susceptor can result in uneven distribution of the organic source in the vicinity of the substrate surface resulting in an uneven growth rate of the GaN film. Consequently, there exists an optimal chamber height that will give the best growth rate and uniformity to the GaN film as discussed in this study. This study provides comprehensive insight into the transport phenomena of GaN growth that includes coupled heat and mass transfer as well as chemical reactions. The results provide important information in a succinct format and enable decisions to be made about the showerhead and the geometrical design and size of a vertical MOCVD reactor. [ABSTRACT FROM AUTHOR]

In this study experiments were conducted to study the porous thin plate drying process. An analysis was also carried out to determine the moisture transfer coefficients that vary with the moisture content of the plate during drying. The study is useful for analyzing the transient drying process of porous thin plates. Furthermore, energy and exergetic analyses based on the measured results were carried out to determine the dryer performance. It is found that, although the drying rate increases, the energy utilization ratio of the drying process decreases with either an increase in the rate of air flow or an increase in the size of the drying air inlet. The results indicate that a significant amount of the energy provided to the system was lost and not utilized for drying, especially for high drying rate dryers. An exergetic analysis showed that by adjusting the configuration of the air inlet and flow rate, the exergetic efficiency of the dryer can be significantly increased (from 0.5% to 10%). An overall transport phenomena analysis and performance evaluation including the transient moisture transfer coefficients, drying rate, energy utilization ratio, and exergetic efficiency in the current study provide comprehensive and important insights to the thermal physics of porous thin plate drying processes and the design of efficient dryer systems. [ABSTRACT FROM AUTHOR]

The efficiency and heat transfer characteristics of a newly designed flat polymer heat pipe that uses copper micro thermal via was investigated using a fabricated laboratory model to measure the amount of heat that could be removed from a given heat source (a heater or a light emitting diode (LED) module) under a range of different operating conditions. The heat pipe consists of a copper frame 1 mm thick which is sandwiched between top and bottom sheets of FR4 polymer to form a vapor chamber. Copper meshes were used for the wick structure in the vapor chamber. The design also includes an array of thermal via, formed by 0.5 mm holes drilled through the polymer, which are copper plated and filled with resin similar to the FR4 polymer. This novel design enhances heat conduction through the wall of the polymer heat pipe. A transient dual interface method (TDIM) was used to measure the thermal resistance of the LED module mounted on the flat heat pipe. Experimental results showed that use of the thermal via design reduced the lateral thermal resistance by 20–25%. The thermal resistance of the flat heat pipe was also affected by the filling ratio of working fluid and the tilt angle. When the flat heat pipe with thermal via was used as a mounting substrate with the LED module located in the center of the top surface, experimental results showed the thermal resistance of the substrate was reduced by 57%. [ABSTRACT FROM AUTHOR]

Abstract: Based on our previous study, experiments were conducted to explore frictional pressure drop and heat transfer performance of de-ionized water flowing through rectangular microchannels having longitudinal vortex generators (LVGs). The experimental investigation was conducted under three-sided constant wall temperature boundary condition for the Reynolds numbers ranging from 350 to 1500 for LVGs with different number of pairs and dimensions. The aspect ratios of rectangular microchannels were 0.25 and 0.0667, and the corresponding hydraulic diameters were 160μm and 187.5μm, respectively. The heights of associated LVGs were 1/4H, 3/4H and H, respectively, where H was the height of microchannel. It was found that heat transfer performance was enhanced by 12.3–73.8% and 3.4–45.4% for microchannels with aspect ratios of 0.0667 and 0.25, respectively, while the pressure losses were increased by 40.3–158.6% and 6.5–47.7%, respectively; and the overall heat transfer performances of some specific microchannels were more than 1 in our study. With the help of LVGs, the critical Reynolds numbers were lower than 1000, which were smaller than the generally accepted value of 2300 for regular channel flow. [Copyright &y& Elsevier]

Abstract: The present study proposes a combination of solar-powered components (two heaters, an evaporator, and a steam reformer) with a proton exchange membrane fuel cell to form a powerplant that converts methanol to electricity. The solar radiation heats up the mass flows of methanol–water mixture and air and sustains the endothermic methanol steam reformer at a sufficient reaction temperature (typically between 220 and 300°C). In order to compare the different types of energy (thermal, chemical, and electrical), an exergetic analysis is applied to the entire system, considering only the useful part of energy that can be converted to work. The effect of the solar radiation intensity and of different operational and geometrical parameters like the total inlet flow rate of methanol–water mixture, the size of the fuel cell, and the cell voltage on the performance of the entire system is investigated. The total exergetic efficiency comparing the electrical power output with the exergy input in form of chemical and solar exergy reaches values of up to 35%, while the exergetic efficiency only accounting for the conversion of chemical fuel to electricity (and neglecting the ‘cost-free’ solar input) is increased up to 59%. At the same time, an electrical power density per irradiated area of more than 920Wm−2 is obtained for a solar heat flux of 1000Wm−2. [Copyright &y& Elsevier]

The selective laser melting (SLM) process is an additive manufacturing technique that can fabricate three-dimensional workpiece by laser scanning and sintering of designated material in powder form on a preset scanning route along a bed of powders. This process involves a moving laser heating source which causes local transient mass and heat transfer with phase change, i.e., melting and solidifying, in a pool of melted powders. To fully investigate such a complicated transport process with reasonable computation cost, a novel quasi-transient numerical model (hopping model) was proposed and validated experimentally in this study. This approach includes a volumetric heat source defined as an elliptical Gaussian laser spot which hops along the scan path. Inconel 718 (IN718) superalloy powder is selected as the material for demonstration. Thermal analysis was carried out using a number of laser power and scan speeds in the range from 80 W to 120 W and from 80 mm/s to 140 mm/s, respectively. The comparison of molding appearance of the work pieces from the developed hopping model, full transient model, effective-transient model, and experiments illustrates the accuracy and the efficiency of the proposed hopping model. Molding appearance obtained from the quasi-transient model was consistent with experimental results with a relative error of less than 1.71% on the width of the IN718 stripes fabricated by SLM. For the cases analyzed in the current study, the quasi-transient model showed a 99% and a 60% reduction in both the computation time and the amount of computer memory needed compared to the full transient model and the effective-transient model, respectively. This novel quasi-transient simulation technique can be used to rapidly and effectively optimize process parameters for intelligent additive manufacturing. [ABSTRACT FROM AUTHOR]

• Laser direct synthesis and patterning (LDSP) is applicable for flexible electronics. • Thermocapillary yields concave surface profile of microline fabricated from LDSP. • A model is derived and validated to analyze the marangoni effect in LDSP. Laser direct synthesis and patterning technology (LDSP) is a promising way to realize flexible electronic circuitry. In LDSP, functional materials microstructure can be fabricated in-situ on flexible substrates using laser induced photo thermal reduction of ions from precursor that is free of nanoparticles. However, previous studies showed that concave curvature was found on the surface of developed LDSP micro-lines. This occurrence of concave curvature is contradictory to the convex structure expected from the temperature distribution of the precursor and on the substrate. Controlled surface morphology is crucially important for the fabrication of electronic circuitry with ultra-fine structure. Therefore, an analysis of the transport phenomena prevailing near the laser processing spot by both numerical simulation and experiment was carried out. The underlying physics behind the surface reconstruction of silver micro-lines fabricated by LDSP was investigated. The analysis included the opto-thermo-fluidic transport phenomena as well as thermo-capillary flow, i.e. the Marangoni effect. Results showed that the Marangoni effect dominated the movement kinetics on the interfacial surface between the ultra-thin silver nanocluster film and the surrounding fluid during the LDSP process. The surface morphology of the synthesized and deposited silver micro-line is therefore affected by the Marangoni effect. An empirical model was developed to determine the values of characteristic parameters for the Marangoni effect in the present case. The model was applied successfully to determine the micro-line surface morphology evolved during multiple laser scans in LDSP process with three different scanning speeds. Theoretical solution on the silver line thickness was compared with that obtained from the experiments, and the discrepancy was less than 12%. The results and analysis techniques developed provide insights to the coupled heat and mass transport phenomena with thermo-capillary effects, and can be used to improve the quality of microstructures fabricated by LDSP and similar technologies. [ABSTRACT FROM AUTHOR]

Laser-assisted, one-step direct nanoimprinting of metal and semiconductor nanoparticles (NPs) was investigated to fabricate submicron structures including mesh, line, nanopillar and nanowire arrays. Master molds were fabricated with high-speed (200 mm s−1) laser direct writing (LDW) of negative or positive photoresists on Si wafers. The fabrication was completely free of lift-off or reactive ion etching processes. Polydimethylsiloxane (PDMS) stamps fabricated from master molds replicated nanoscale structures (down to 200 nm) with no or negligible residual layers on various substrates. The low temperature and pressure used for nanoimprinting enabled direct nanofabrication on flexible substrates. With the aid of high-speed LDW, wafer scale 4 inch direct nanoimprinting was demonstrated. [ABSTRACT FROM AUTHOR]