Search

Improving the quality of fuel represents an effective solution to address the long-standing issue of engine emissions. This study adopts CeO2 and carbon nanotubes as additives, which are blended with neat diesel using a physicochemical method to produce nanofuel. The research investigated the combustion and emission performance of a high-pressure common rail four-cylinder engine under various operating conditions, utilizing different types of nanomaterials, nanoparticle sizes, and biofuel substitutes as variables. The outcomes of the study indicate superior performance of the nanofuel compared with neat diesel across all evaluated aspects. Notably, the size of the added particles directly influenced the beneficial enhancements achieved in diesel fuel. Additionally, the nanofuel containing carbon nanotubes demonstrated a greater improvement effect than the one incorporating CeO2. Furthermore, when compared with neat diesel, the combustion of carbon nanotubes (CNT) nanofuel at 100% load resulted in a notable 4.0% increase in brake thermal efficiency, coupled with reductions of 3.0% in brake specific fuel consumption and 8.8%, 4.4%, 4.9%, and 9.6% reductions, respectively, for carbon monoxide (CO), hydrocarbons (HC), nitrogen oxides (NOx), and smoke emissions. It is noteworthy that the incorporation of biofuel alternatives, such as biodiesel and ethanol, into nanofuels exhibited even further enhanced effects in terms of promoting combustion and reducing emissions. The findings of this study serve as an important reference for selecting suitable nanofuels tailored to meet diverse operational demands of engines. [ABSTRACT FROM AUTHOR]

[Display omitted] • Acoustic tweezers with bisymmetric coherent IDT design for reconfigurable colloidal particle manipulation. • The technique enables contactless morphology modulation of individual colloidal multimers. • The reconfigurable switching of colloidal multimer patterning arrays can be achieved. • Controllable rotation can be achieved by regulating coherent wave configurations. The accurate and dynamic manipulation of multiple micro-sized objects has always been a technical challenge in areas of colloid assembly, tissue engineering, and organ regeneration. The hypothesis of this paper is the precise modulation and parallel manipulation of morphology of individual and multiple colloidal multimers can be achieved by customizing acoustic field. Herein, we present a colloidal multimer manipulation method by using acoustic tweezers with bisymmetric coherent surface acoustic waves (SAWs), which enables contactless morphology modulation of individual colloidal multimers and patterning arrays by regulating the shape of acoustic field to specific desired distributions with high accuracy. Rapid switching of multimer patterning arrays, morphology modulation of individual multimers, and controllable rotation can be achieved by regulating coherent wave vector configurations and phase relations in real time. To demonstrate the capabilities of this technology, we have firstly achieved eleven patterns of deterministic morphology switching for single hexamer and precise switching between three array modes. In addition, the assembly of multimers with three kinds of specific widths and controllable rotation of single multimers and arrays were demonstrated from 0 to 22.4 rpm (tetramers). Therefore, this technique enables reversible assembly and dynamic manipulation of particles and/or cells in colloid synthesis applications. [ABSTRACT FROM AUTHOR]

The chopped carbon fiber reinforced SiC (C f /SiC) composite has been regarded as one of the excellent high-temperature structural materials for applications in aerospace and military fields. This paper presented a novel printing strategy using direct ink writing (DIW) of chopped fibers reinforced polymer-derived ceramics (PDCs) with polymer infiltration and pyrolysis (PIP) process for the fabrication of C f /SiC composites with high strength and low shrinkage. Five types of PDCs printing inks with different C f contents were prepared, their rheological properties and alignment of carbon fiber in the printing filament were studied. The 3D scaffold structures and bending test samples of C f /SiC composites were fabricated with different C f contents. The results found that the C f /SiC composite with 30 wt% C f content has high bending strength (∼ 7.09 MPa) and negligible linear shrinkage (∼ 0.48%). After the PIP process, the defects on the C f /SiC composite structures were sufficiently filled, and the bending strength of C f /SiC composite can reach up to about 100 MPa, which was about 30 times greater than that of the pure SiC matrix without C f. This work demonstrated that the printed C f /SiC composites by using this method is beneficial to the development of the precision and complex high-temperature structural members. • The chopped fibers reinforced direct ink writing with PIP processing was proposed. • The carbon fibers reinforced polymer-derived SiC composites were prepared. • The C f /SiC composite with 30 wt% fiber has excellent linear shrinkage (< 0.5%). • The reinforced C f /SiC composite has satisfactory bending strength (∼ 103.14 MPa). [ABSTRACT FROM AUTHOR]

The accurate and efficient manipulation of particles and droplets is crucial for the fields of disease diagnosis, target drug delivery, and sample purification, specific microstructure-based particle and droplet manipulation have been widely utilized in bioassays. However, current techniques are mainly based on the fixed microstructures, which is extremely difficult to achieve dynamic modulation by adjusting microstructure morphology and excitation conditions. Herein, we present a novel particle capture and droplet manipulation methodology by using morphologically reconfigurable magnetic micropillar arrays incorporate with acoustic streaming effects, which enables reconfigurable particle capturing, cargo transportation, and droplet manipulation. The mechanism is to assemble NdFeB magnetic powders by magnetic gradient fields to form morphologically variable magnetic micropillar arrays with porous surfaces, and the localized acoustic streaming effects generated by surface acoustic waves (SAWs) enable micropillar arrays to capture nearby particles onto the surfaces or to drive perturbations in droplets in the vicinity. To demonstrate the capabilities of this technology, we have achieved the high-volume acoustofluidic particle capture and loading (0.214 MCF), targeted complex maze navigation, efficient droplets manipulation (≤ 3.96 mm/s), and acoustofluidic mixing acceleration (≤ 2.5 s). Therefore, this technique enables reconfigurable and versatile manipulation of particles and droplets in biomedical applications. [Display omitted] • A manipulation method using magnetic micropillars with acoustic streaming effects. • The technique enables reconfigurable capturing, transportation, and manipulation. • Magnetic micropillars are morphologically reconfigurable by modulating magnetic fields. [ABSTRACT FROM AUTHOR]

With the continuous development of human society, the shortages of fossil resource and environmental pollution are increasingly prominent. Hydrogen is a clean and efficient alternative energy, among various hydrogen production technologies, methanol reforming has been regarded as a promising candidate to produce hydrogen for daily energy supply due to its low cost and safe transportation. In this review, we discuss the sources of methanol and the methods of methanol reforming for hydrogen production. Then, we focus on the catalysts for methanol reforming and their preparation methods. Particular attention is paid to the structural design and manufacturing process to make methanol reforming microreactors. We also summarize recent studies on the practical applications of methanol reforming technologies, as well as the capture and utilization of the generated carbon to reduce its emission. Finally, the prospect challenges of methanol reforming for highly efficient hydrogen production technologies and contribution to the "double carbon" goals and the challenges are discussed. In summary, this review will be conducive to the development of hydrogen-methanol economy for practical and industry applications. • MR is promising to produce hydrogen for energy supply due to its low cost and safe transportation. • The status and prospect of MR technologies for hydrogen production were summarized. • MR technology can have a significant contribution prospect to "double-carbon" goals. [ABSTRACT FROM AUTHOR]

The addition of nanoparticles to base fuel may bring about remarkable changes in a thermodynamic process such as evaporation, due to the intensified interaction between particles and liquid molecules. In this study, the nano-fuels containing the 20 nm and 50 nm cerium oxide (CeO2) particles with the dosing levels of 50 mg·L−1 and 100 mg·L−1 were prepared using N-tetradecane (C14) as base fuel and cetyltrimethyl ammonium bromide as dispersant. The evaporation characteristics of nano-fuels were investigated via a constant temperature thermogravimetric method. The thermodynamic parameters of nano-fuel evaporation process, such as activation energy, vapor pressure and evaporation enthalpy, were calculated based on Arrhenius equation, Antoine and Langmuir equations and Clausius–Clapeyron equation, respectively. It was revealed that the particle size and mass fraction of CeO2 nanoparticles had a consistent effect on the activation energy, vapor pressure and evaporation enthalpy of nano-fuels. The activation energy required for vaporization increased with the decrease of nanoparticle size or the increase of nanoparticle mass fraction, because of the low-specific heat capacity of nanoparticles. Moreover, the vapor pressure decreased with the decrease of nanoparticle size or the increase of the mass fraction for particle. This is because the addition of nanoparticles could augment the surface tension of fuel, retarding the diffusion of liquid phase molecules into gas phase. The evaporation enthalpy of nano-fuels increased due to the Van der Waals forces between fuel molecules and nanoparticles. [ABSTRACT FROM AUTHOR]

Nano-fuel, as an appealing alternative, provides a new opportunity to promote engine performances. The surface tension is a vital factor affecting spray and evaporation of fuel. In this study, fuel blends containing 20 and 50 nm particles of CNT, CeO 2 and Co 3 O 4 with different mass concentrations (i.e. 50, 100 and 150 mg/L) were prepared by the two-step method, in which diesel worked as the base fuel and CTAB served as the surfactant. The surface tension of nano-fuel was determined experimentally at 10–140 °C based on the pendant drop method, and the effects of mass concentration, particle size, nanoparticle types and temperature on the surface tension of nano-fuel were analyzed. It is revealed that the nano-fuel had higher surface tension than diesel and it increased with the increase in mass concentration or particle size, while decreased linearly with the rise of temperature. Among three types of nano-fuels, CNT nano-fuels had the maximum surface tension, which is followed by CeO 2 nano-fuels and then Co 3 O 4 nano-fuels. [Display omitted] • Surface tension was determined by the pendent droplet method. • Surface tension was higher for nano-fuel due to particle-fuel interactions. • Surface tensions of disparate types of nano-fuels were compared. • Nano-fuels' surface tension increased with higher concentration and larger size. • Nano-fuels' surface tension reduced with the rise of temperature. [ABSTRACT FROM AUTHOR]

Appropriate amount of methyl myristate (C14), methyl palmitate (C16), methyl stearate (C18), methyl oleate (C18:1), methyl linoleate (C18:2), and methyl ricinoleate (C18:1OH) were blended into low-sulfur diesel to conduct the lubrication experiment on four-ball friction tester. Then, based on Materials Studio software, adsorption models of n-tetradecane with various esters on the iron surface were built up. The lubrication performance of diesel blends with 1.0%, 2.0%, 3.0%, and 5.0% (volume fraction) of different esters was improved with the increase of the esters’ fraction. Meanwhile, it is revealed by molecular simulation that the adsorption energy in the film was augmented greatly with the increase in the volume fraction of C14 ester; however, the cohesive energy varied slightly. Therefore, the ester fraction puts more influence on the adsorption energy. Moreover, lubrication experiment of low-sulfur diesel with a given fraction of different esters indicated that the diameter of worn scars decreased with the increase in the length of carbon chain and the number of unsaturated C = C double bond, and at the presence of polar group as well. While via the molecular simulation, the adsorption energy in the films of n-tetradecane with 5% various esters was roughly comparable, but the cohesive energy changed with the carbon chain length, the degree of unsaturation, and the polar group. Namely, the variation of ester composition causes a significant difference in the cohesive energy. Consequently, both the increase of ester fraction and the change of ester composition are effective measures to improve the lubricity of low-sulfur diesel fuel. [ABSTRACT FROM AUTHOR]

Multi particle finite element method (MPFEM) has been extensively used to numerically model the compaction process of powder materials. However, MPFEM is not able to simulate the fracture phenomenon for brittle powder materials. In this study, cohesive zone method (CZM) based MPFEM is developed to simulate the compaction densification process of Al and NaCl laminar composite powders. Cohesive zone layer and initial crack are used in modeling the NaCl particle to reproduce its fracture process. A simulation of gravity effect is first conducted to arrange the powders randomly, and then top punch moves downwards to compact the laminar composite powders. Different initial random packing structures, size ratios of NaCl/Al powders and contents of NaCl powders are constructed for compaction with different pressures. Macro and micro analysis of the numerical modeling results is carried out to identify the densification process. Physical experiments and data fitting are used to validate the accuracy and robustness of the numerical simulation. Results demonstrate that the developed CZM-based MPFEM has successfully simulated the fracture phenomenon of NaCl powders and the compaction process of Al and NaCl laminar powders. Image 1 • Cold compaction behavior of laminar composite powders is studied. • The CZM-based MPFEM is developed to simulate the process. • The densification mechanism of the cold compaction process is obtained. • Effects of process parameters on final properties of the compact are analyzed. [ABSTRACT FROM AUTHOR]

The catalyst support structure has a significant influence on the performance of the methanol steam reforming (MSR) microreactor for in-situ hydrogen production. Triply period minimal surface (TPMS) structures are emerging as an attractive option as porous MSR catalyst supports owing to their excellent specific surface area, smooth surface and highly interconnected pores. This paper develops a numerical model of the sheet TPMS unit structures with catalyst coating to investigate the flow and reaction characteristics for hydrogen production of MSR reaction. The P, G, and D curved surface structural models were constructed with different porosities. The numerical results indicated that the P curved surface structure with the porosity of 90% had the lowest pressure drop of 0.15 Pa and the highest permeability of 6.31 × 10−9 m2, while the G curved surface structure always demonstrated excellent flow performance within the porosity range of 50–90%. The D curved surface structure exhibited the best reaction performance with hydrogen production exceeding P and G curved surface structures by about 23% and 78% respectively. Furthermore, the performance differences between the two flow phases of the sheet TPMS structures were investigated for the bicontinuous characteristic. The flow phases of the G curved surface structure demonstrated the best consistency in flow and reaction performances. Finally, the optimal design of the sheet, network, and multi-unit heterogeneous TPMS structural catalyst supports was discussed. • A numerical model of the TPMS structures with catalyst coating was developed. • The flow and reaction characteristics of the TPMS structures were studied. • The performance of two flow phases in the TPMS structures were compared. [ABSTRACT FROM AUTHOR]

Methanol steam reforming (MSR) has been used for in-situ hydrogen production, while hydrogen purification remains a technical challenge to limit the applications of using hydrogen for fuel cells. This study presents a pure hydrogen generation system (PHGS) by integrating MSR and hydrogen purification modules, this system enables low-temperature reforming and high-temperature purification to achieve high yield and recovery of hydrogen. To investigate the combined effects of feedstock flow rates and pressure on MSR and purification, the performance of each module and overall PHGS system were tested. The results showed that PHGS can stably produce high purity hydrogen (>99.99%) under different conditions, the synergistic effects of two modules lead to hydrogen yield exceeding the numerical sum of individual modules. At methanol feed rate of 1.00 g/min and system pressure of 5.0 bar, the pure hydrogen flow rate, CO content, pure hydrogen yield, hydrogen recovery and thermal power output were tested about 1.70 ± 0.01 L/min, 2.4 ± 0.1 ppm, 81.1 ± 0.5%, 87.6 ± 0.5% and 350 W. The PHGS can deliver up to 500 W of thermal power and is suitable for small range-extended electric vehicles. Our work on the developed PHGS can provide a significant reference for future practical applications of systems combining MSR and membrane purification. [Display omitted] • A separated system based on MSR and Pd membrane is proposed for hydrogen generation. • The effects of feed rate and pressure on system and its modules are investigated. • The system can generate 350 W of high-purity H 2 with an H 2 recovery of 87.6%. [ABSTRACT FROM AUTHOR]

• Unsaturated fatty acid causes poor oxidation stability of biodiesel. • Trans-isomers have a negative effect on biodiesel fuel. • Catalytic transfer hydrogenation method produces fewer trans-isomers. • Partial hydrogenation improves biodiesel oxidation stability and cold flow property. Biodiesel has gained much attention as it is a promising renewable substitute fuel to conventional diesel in the future. Although biodiesel has numerous advantages such as lower toxicity, higher flash point and its biodegradability over conventional diesel, the challenges of its poor cold flow properties and oxidation stability limit its application. This is attributed to the high level of polyunsaturated fatty acid methyl esters in the biodiesel feedstock. Oxidation stability is determined by the fatty acid compositions and natural antioxidants of the biodiesel. A higher amount of unsaturated fatty acid methyl esters are susceptible to oxidative degradation and this in turns shortens the induction period and improves the cold flow properties of the biodiesel. Conversely, a full saturated fatty acid also results in higher cetane number and increases the oxidation stability of the biodiesel but tends to worsen the cold flow properties and this may result in low heating value and high viscosity which may affect the engine in a negative way during lower temperature climate especially winter. Partial hydrogenation of biodiesel is one of the techniques to improve the challenges of cold flow properties and oxidation stability. This review paper seeks to summarize the developments in terms of the production, cold flow properties, oxidation stability, catalytic material for the hydrogenation process, and feedstock for the production and ways to reduce trans-isomers in hydrogenated biodiesel. [ABSTRACT FROM AUTHOR]

Ni layer is widely utilized in Bi 2 Te 3 -based thermoelectric generators (TEGs) as a diffusion barrier layer. However, its influences on the contact resistance of the solder joints and the power generation properties of the TEGs are still unclear, which are of great importance in practical applications. In this study, Bi 2 Te 3 -based thermoelectric (TE) modules with Ni (NiTM) and without Ni (TM) layer were fabricated by using Sn 96.5 Ag 3 Cu 0.5 (SAC305) solder. Experimental results showed that Ni layer could effectively reduce 32% of contact resistances in P-type and N-type solder joints. P-type solder joint with Ni avoided voids forming on the border of the Bi 0.5 Sb 1.5 Te 3 and SAC305 by suppressing severe Te and Sb elements diffusion. In N-type solder joint, since Ni inhibited the formation of Bi-Te self-diffusion barrier layer, no cracks generated at the interface between Bi 2 Te 2.5 Se 0.5 and SAC305. In terms of power generation abilities, the inherently superior performance of TE legs was maintained due to effective suppression of element diffusion. When the temperature difference was 161 °C, the open circuit voltage of NiTM exhibited an enhancement of 13% compared with that of TM. The lower contact resistance and higher open circuit voltage resulted in a much higher maximum output power (an enhancement of 90%) in NiTM. • The effects of Ni layer on contact resistance of Bi 2 Te 3 -based module were studied. • Cracks generated at the interface of Bi 2 Te 2.5 Se 0.5 and SAC305 were avoided by Ni layer. • Voids formed on the border of Bi 0.5 Sb 1.5 Te 3 and SAC305 were suppressed by Ni layer. • The changes of intermetallic compounds brought by Ni layer were investigated. [ABSTRACT FROM AUTHOR]

The nano-fuel are prepared by dispersing CNT, CeO2, and Co3O4 nanoparticles in n-tetradecane (C14). This experimental study investigates the effect of nanoparticles mass fraction as well as the variation of nanoparticles sizes on the viscosity and evaporation characteristics. It is revealed that the viscosity increases with the increase in mass fraction and the decrease in particle size. In addition, the presence of nanoparticles leads to a reduction of the evaporation rate during constant contact line phase. However, the droplet evaporation rate is augmented remarkably in constant contact angle and hybrid phase. As a result, the whole evaporation time of nano-fuel droplets is shorter than base fuel. [ABSTRACT FROM AUTHOR]

Abstract In this study, n -type Bi 2 Te 3 -based bulk materials were prepared using the ultrasonic-assisted hot pressing. The effects of ultrasonic vibration on the mechanical and thermoelectric properties of the prepared samples were investigated. Field-emission scanning electron microscope (FESEM) tests revealed that the ultrasonic vibration refined the grain size to the submicron level. The grain size became smaller as the ultrasonic vibration duration is extended. The results showed that the sample with an ultrasonic vibration duration of 20 min (namely, Ultra 20) has a hardness of 64 HV0.3 and a flexural strength of 22.4 MPa, which represents an 82.9% and 50.2% improvement, respectively, over the untreated hot-pressed sample (namely, Ultra 0). As the ultrasonic vibration duration increased, the absolute value of the Seebeck coefficient was found to increase, whereas the electrical conductivity and the thermal conductivity decreased. The maximum dimensionless figure of merit (ZT max) was 0.78 at 480 K for the Ultra 20 sample, which was 10.9% and 16.4% higher than the Ultra 10 and Ultra 0 samples, respectively. The results proved that both the mechanical properties and the thermoelectric properties of the Bi 2 Te 2.7 Se 0.3 bulk materials are improved by ultrasonic vibration. [ABSTRACT FROM AUTHOR]

• A multilevel amplified MSR microreactor with high hydrogen production rate was developed. • A simulation model of five layer reactor was established and the velocity distribution was studied. • The reactor has the maximum reformate flowrate of 20 L/min and power density of 1.7 kW/L. Methanol steam reforming using microreactors has been regarded as a promising approach for in-situ hydrogen production, while the generally low hydrogen production rate limits its real application. This study proposed a multilevel series scaled-up methanol steam reforming microreactor with the aim to improve the hydrogen production rate, five methanol combustion chambers are parallel arranged and interspersed into the steam reforming chambers to improve the temperature heating rate and temperature distribution uniformity. A numerical model of methanol steam reforming chamber was established to investigate the flow velocity distribution inside the chamber. The flow velocity in the copper foam region are uniformly distributed, the variations of average flow velocity in cross sections of the copper foams are below 20 %. Experimental results showed that the temperature differences between different layers was lower than 6.7 °C and the variation is smaller than 7.3 °C. A stepwise methanol solution feeding rate test was performed and found the developed microreactor has a quite rapid response speed, the maximum reformate flowrate of 20683 ml/min can be achieved with methanol conversion of 88.3 %. The developed microreactor can significantly improve the hydrogen production rate and temperature distribution uniformity, indicating a potential application in high hydrogen consumption equipment. [ABSTRACT FROM AUTHOR]

Due to the tunable porosity at multiple scales, hierarchical porous ceramics feature large specific surface area and excellent heat and mass transfer performance, which can effectively improve the catalytic reaction performance. This paper presents a method to fabricate SiC scaffolds with regular and hierarchical pore structures by direct ink writing (DIW) combined with sacrificial template technology, which can be used as methanol steam reforming (MSR) microreactor catalyst supports. Through printing along a defined path, primary pores with a regular pore structure were created. After sintering, the sacrificial template was removed and secondary pores appeared. Four different types of hierarchical porous SiC scaffolds were successfully prepared and the pore structure, total porosity, linear shrinkage and compressive strength of these scaffolds were investigated. The catalyst coating was then loaded onto the scaffold, and the microstructure characterization showed that the pore structure would not be damaged and blocked. Finally, the hydrogen production experiments were carried out on the MSR microreactor, and the results showed that the support with larger and denser secondary pores had the best fluid flow and hydrogen production characteristics. At the temperature of 280 °C and the gas hourly space velocity (GHSV) of 30000 ml g−1 h−1, the methanol conversion and hydrogen production of the best support can reach 90.95 % and 44.96 ml/min, respectively. [ABSTRACT FROM AUTHOR]

Human‐machine interaction(HMI) is extensively employed in various applications such as robotic control and augmented reality/virtual reality. However, HMIs are mainly based on single‐interaction mode, requiring bulky equipment to be worn or sustaining physical contact with the interfaces, resulting in limited interaction efficiency and intelligence. Here, it proposes a novel flexible dual‐mode capacitive sensor using 12 sensing units for touchless and tactile sensing during HMIs, the sensor has a labyrinth‐patterned electrode to improve the performance of proximity sensing and a truncated pyramid‐shaped porous hierarchical dielectric structure to improve the pressure sensing performance. The fabricated dual‐mode sensor is characterized by a high proximity detection range of up to 110 mm, the pressure detection range is from 0 to 200 kPa with a sensitivity of 0.464% kPa−1. Further, the dual‐mode sensor exhibits excellent discrimination between proximity and pressure signals, along with remarkable stability and repeatability. Then, a touchless‐tactile HMI platform is developed for real‐time control of robotics through accurate perception of touchless hand gestures and contact‐pressing interactions. This platform demonstrates the superior dual‐mode sensing performance of the sensor and validates its potential in future intelligent HMI scenarios. [ABSTRACT FROM AUTHOR]

Underwater perception of a broad range of force holds great importance in aquatic explorative activities, while flexible tactile sensors face technical challenges to realize. This paper presents a novel flexible aquatic tactile sensor based on waterproof graphene (GR)/carbon nanotube (CNT)/Polydimethylsiloxane (PDMS) composites. The prepared GR/CNT/PDMS composites possess excellent hydrophobic and electromechanical properties with a water contact angle over 134° and an ultrahigh gauge factor of 2296, making them an ideal piezoresistive sensing material for underwater broad‐range force sensing. The proposed tactile sensor has 3 × 3 sensing units and uses dual interlocked water‐ripple structures to improve its sensitivity and force detection range. The fabricated tactile sensor is characterized by two distinct sensitivities: a high sensitivity of 0.0338 kPa−1 at 0.062–150 kPa and a low sensitivity of 0.00357 kPa−1 at 150–450 kPa. Further, the sensor exhibited excellent resistance response, fast dynamic recovery, and both mechanical and electrical stability in aquatic environments. Then, the aquatic tactile sensor is worn on the palm of the human hand to detect the distribution and variation of contact forces when grasping objects with different shapes and hardness, demonstrating the potential underwater applications of the developed aquatic tactile sensor for broad‐range force sensing. [ABSTRACT FROM AUTHOR]

The partially hydrogenated soybean methyl ester (PHSME) is produced from soybean methyl ester (SME) via catalytic transfer hydrogenation. It is revealed that after the catalytic transfer hydrogenation of SME, the high unsaturated components are selectively converted to low unsaturated or saturated components by Gas Chromatography-Mass Spectrometer (GC-MS) analysis. Although the kinematic viscosity of PHSME is increased slightly, its oxidation stability is improved significantly, and the cetane number of PHSME rises to a desirable level as well. Based on the analysis of thermogravimetry-differential scanning calorimeter (TG-DSC), it is found that PHSME has a greater average oxidation rate. In summary, the hydrogenated biodiesel has excellent ignition characteristic. [ABSTRACT FROM PUBLISHER]

To improve the flow and heat transfer performance of micro-reactors with micro-pin-fin arrays (MPFAR), a micro-reactor with non-uniform micro-pin-fin arrays (NMPFAR) was proposed. To investigate its flow and heat transfer characteristic at low Reynolds number, the Navier–Stokes and energy equations in the NMPFAR were established. Simulated results indicated that the NMPFAR has the better heat transfer performance than micro-reactors with staggered and aligned micro-pin-fin arrays. Also, the heat transfer performance of three different NMPFARs with two, four and eight kinds of pin diameter was investigated by numerical simulation. Results showed the Nusselt number is larger when the change of pin diameter in NMPFAR is less, which means the NMPFAR with two kinds of pin diameter has the better heat transfer performance. Meanwhile, the experiments were carried out for validating the simulation model, and the experimental results agreed well with the simulated ones. The research result shows that the NMPFAR does have the merit for enhancing flow and heat transfer performance of the micro-reactor with micro-pin-fin arrays. [ABSTRACT FROM AUTHOR]

[Display omitted] Effective enrichment and separation of particles and mixing of multiphase microflows can be technically challenging in microfluidic sample processing and analysis. Acoustofluidic techniques have advantages such as high biocompatibility, versatility, and simple device design to meet these demands. Here, we present a novel tri-symmetrical acoustofluidic centrifuge based on traveling surface acoustic waves (TSAWs), achieving particle enrichment and bidirectional size-based separation, pushing away the larger particles while enriching the smaller ones, in a rapid time (<6 s). A microfluidic chamber was designed for further extraction of treated particles and cells. Experimental results show that our device can achieve enrichment of particles in a range of sizes and high purity separation (e.g. >90 % in 5 µm and 40 µm sample), demonstrating its sample processing capabilities. The acoustic treatment did not affect cells (consistent with the control group above 80 %). TSAW-induced acoustic streaming enabled efficient mixing (mixing efficiency χ >85 %) of fluorescent multi-phase microflows within a short time (<0.5 s). The underlying physical mechanisms have been verified by numerical simulations. [ABSTRACT FROM AUTHOR]

[Display omitted] • Nano-fuel evaporation was suppressed at 400 °C but promoted at 700 °C. • Nano-fuel evaporation deviated the D 2-law at 700 °C owing to micro-explosion. • Nano-fuel evaporation was greatly affected by nanoparticles' concentration and size. • Micro-explosion was strengthened by nanoparticles in fuel. • On a whole, CNT nano-fuel evaporated faster than CeO 2 nano-fuel. To investigate the effect of nanoparticles on the evaporation evolution of nano-fuels and reveal the mechanism of heterogeneous heat and mass transfer induced by the dispersion of nanoparticles, carbon nanotubes and CeO 2 nano-fuels with different mass concentrations and particle sizes were prepared based on the two-step method and inspected using a laser particle size analyzer. An evaporation visualization apparatus for a single suspended droplet and an image processing technology were utilized to study the evaporation of diesel and nano-fuels at 400 and 700 °C. At 400 °C, the evaporation of diesel and nano-fuel droplets accorded with the D 2-law and can be categorized as constant-volume and quasi-steady evaporation stages. The addition of nanoparticles suppressed the evaporation of fuel droplet and increasing the mass concentration or particle size can intensify the extent of suppression. At 700 °C, however, the micro-explosion of droplets occurred, and the variation in the droplet diameter did not conform with the D 2-law. Evaporation can be categorized into the constant-volume and fluctuating evaporation stages. Nanoparticles, as heterogeneous nucleation sites, enhanced the expansion and micro-explosion intensities, thereby promoting the fuel droplet evaporation. An increase in the mass concentration or a decrease in the particle size can promote evaporation significantly. [ABSTRACT FROM AUTHOR]

• Spray characteristics were studied by combining experiment and CFD simulation. • Nano-fuel spray appeared longer penetration distance, smaller cone angle and larger SMD. • Increasing nanoparticles' concentration widened the gap in spray between nano-fuel and diesel. • Spray of nano-fuel with higher mass concentration developed more quickly. • Injection pressure affected fuel spray the most by grey relationship analysis. Combining experiment and simulation, spray characteristics of CeO 2 nano-fuels and diesel including penetration distance, cone angle, and Sauter mean diameter (SMD) were investigated at various working conditions to reveal the effect of nanoparticles on the fuel spray. The correlation degree between spray characteristics and injection pressure, ambient pressure, and mass concentration of nanoparticles was assessed using the grey relationship analysis. Due to stronger axial diffusion and relatively weaker radial diffusion, nano-fuels showed a longer spray penetration, a smaller cone angle, and a larger SMD than diesel. The difference in spray characteristics between nano-fuel and diesel widened along with an increase in mass concentration. Additionally, the kinetic energy of spray, air resistance, and entrainment were susceptible to injection and ambient pressures. In general, higher injection pressure increased spray penetration and cone angle while reduced SMD. Oppositely, higher ambient pressure decreased the spray penetration while increased the cone angle and SMD. Among the three factors, the injection pressure had the greatest effect on spray characteristics, followed by ambient pressure and then mass concentration. [ABSTRACT FROM AUTHOR]

Flexible pressure sensors have attracted considerable interests in the fields of intelligent robotics, human-machine interfaces and health monitoring for their portability, flexibility and real-time sensing performance. The microstructures of dielectric layer significantly affect the sensing performance of capacitive pressure sensors, but the common methods to fabricate microstructures always need physical and/or chemical molds, thus may not suit for low-cost fabrication of sensors. The wavy-shaped microstructures on the surface of fluid can be generated with the excitation of standing surface acoustic waves (SSAWs), which is suitable to be used as dielectric layers. Here, we developed a 6 × 6 flexible capacitive pressure sensor array with fingerprint-like surface cover layer and latticed dielectric layer. Both two layers were fabricated through the novel and rapid acoustic-assisted process. The fabricated capacitive sensor array exhibits high sensitivity of 28.8%/N for normal force loading, with spatial resolution of 1.5 mm. It has been successfully used to monitor the vibration of the Adam's apple during swallowing and detecting the wrist activities in cycles. These studies demonstrate the great potential of the pressure sensor array with acoustically fabricated microstructures in wearable electronics for health monitoring. [Display omitted] • A novel flexible pressure sensor array with spatial resolution of 1.5 mm for distributed force sensing is developed. • An acoustic-assisted method based on SSAWs is used to fabricate the microstructured surface layer and dielectric layer. • The tactile sensor array features high flexibility and can be easily worn on neck or wrist for health monitoring. • Both Adam's apple vibration sensing and wrist activity detection can be achieved by the developed tactile sensor array. [ABSTRACT FROM AUTHOR]

Biodiesel is mainly composed of methyl palmitate (MeC16), methyl stearate (MeC18), and methyl oleate (MeC18:1). In order to explore the crystallization behavior of biodiesel, the thermal parameters of the three fatty acid methyl esters, their binary mixtures, and biodiesel have been analyzed based on the differential scanning calorimeter. Supposing that biodiesel is a complex solution of various fatty acid methyl esters, the saturated fatty acid methyl esters MeC16 and MeC18 are treated as solutes and the unsaturated fatty acid methyl ester MeC18:1 is served as the solvent; thus a thermodynamic model according to the solid–liquid equilibria for predicting the crystallization onset temperature has been established. As a result, the model is effectively verified when the estimated crystallization onset temperatures for four types of actual biodiesel are compared with the experimental results. [ABSTRACT FROM AUTHOR]

High-frequency vibration is capable of modifying metallic surface topography significantly, while the underlying mechanisms are still unclear. In this study, the acoustic softening effect is considered to explain and model the effects of high-frequency normal vibration on surface topography. The surface asperities can be softened by the high-frequency vibration due to acoustic softening, leading to the enhancement of surface topography modification. A theoretical model for metallic surface topography modification by high-frequency vibration is proposed based on the acoustic plasticity. Numerical predictions of surface roughness evolution were conducted under various working conditions based on the model developed. It was found that the reduction of surface roughness (RSR) after vibration-assisted forming was affected by static stress, vibration amplitude, material properties and initial specimen surface roughness. The predictions using the developed model were compared with experimental data. Results showed that the predicted RSR agreed well with the experimental results, indicating that the analytical model is able to accurately capture surface topography evolution during vibration-assisted metal forming. This study provides a basis for understanding the underlying mechanisms of surface topography modification in vibration-assisted manufacturing. [ABSTRACT FROM AUTHOR]

To improve the energy conversion of a micro-channel reactor, an innovative micro-channel catalyst support with a micro-porous surface is proposed and fabricated by a layered powder sintering and dissolution method (LPSDM). The catalyst adhesion strength is analyzed by an ultrasonic vibration test and results show the catalyst has a 7 wt. % loss on the catalyst support with micro-porous surface and a 16 wt. % loss on the non-porous surface. Subsequently, the coated catalyst support is applied to methanol steam reforming for hydrogen production. Results show that the micro-channel catalyst supports with micro-porous and non-porous surfaces respectively have a hydrogen production rate of 18.07 ml/min and 9.65 ml/min at 573 K under the inlet flow rate of 30 μl/min. Compared with the catalyst support with a non-porous surface, the catalyst support with a micro-porous surface shows better catalyst adhesion and obvious advantages in hydrogen production rate and methanol conversion. [ABSTRACT FROM AUTHOR]

The investigation of the geometric structure of TEG (thermoelectric generator) pins is essential, as their geometry determines the performance of devices. In this study, nominal power density (NPD) is used to find a better geometric structure of thermoelectric pins of TEGs, since a comparison of maximum dimensionless efficiencies for different geometric pins cannot be used to identify the optimum geometry. The influence of shape parameter on NPD for TEG pins in linear, quadratic and exponential cross-sectional functions is studied. The NPD decreases when the shape parameter increases for different geometric pins, while the maximum values of NPD are the same. Then, the effects of dimensionless efficiency and the temperature ratio on the NPD are analyzed. The NPD decreases with the increase in dimensionless efficiency and temperature ratio. Pins with linear variation in cross section have the highest NPD among the three geometries of pins evaluated. [ABSTRACT FROM AUTHOR]

Achieving grains of less than 100 nm in bulk PbTe-based alloys is challenging, and yet can improve the thermoelectric performance of the alloys by reducing lattice thermal conductivity κ lat . In this study, nanostructured Na 0.02 Pb 0.98 Te samples with grain sizes of 20–100 nm were fabricated by high energy ball milling and semisolid powder processing. Microstructures were investigated by scanning and transmission electron microscopies. The κ lat values of the samples showed significant reductions compared with those of reference samples with grains larger than 100 nm, mainly due to stronger phonon scattering at grain boundaries. The κ lat reached a minimum value of 0.74 W m −1 K −1 at 623 K. [ABSTRACT FROM AUTHOR]

The diesel particulate filter (DPF) with the trapping has become an effective and broadly used measure. However, the trapped particulates adhering to the carrier channel easily block the exhaust channel, and then consequently affect the power performance and fuel economy of the diesel engine. Catalytic technology can effectively reduce the temperature for soot combustion by coating the active catalytic material on the channel wall of DPF. The molybdenum catalyst shows excellent catalytic performance in many research fields. The high catalytic activity of molybdenum catalysts is mainly related to the mobility of the active species in the reaction condition, or by the surface migration or by the melting of molybdenum catalyst, so this mobility could improve the contact between reactants and catalyst. Thus, according to that idea, in a loose contact situation between soot and catalyst, the migration of the active component across the soot surface could play an important role in the oxidation reaction during trap regeneration. In order to thoroughly study the surface activity structure phase of the supported molybdenum catalyst and its' function mechanism on soot oxidation, nano-scale MoO3/TiO2 catalysts for soot oxidation were prepared by loading different amounts (5%, 10%, 20% and 40%) of MoO3 on the TiO2 particles through an impregnation method. The structures and physico-chemical properties for those catalysts were characterized using BET, Fourier transform infrared spectra (FT-IR), X-Ray diffraction (XRD) and a Scanning electron microscope (SEM). Printex-U carbon black has been often used in the research field of catalytic oxidation of diesel soot. The practical engine soot and Printex-U carbon black have more characteristics in common such as components and structures. Besides, the reproducibility of the test seemed satisfactory, too. Printex-U carbon black was chosen to replace the practical engine soot. The catalytic activity of molybdenum catalysts for soot oxidation was evaluated using a TG/DTA analyzer. Based on the Starink method, the catalytic oxidation process of soot was quantitatively analyzed. The results showed that, for the limitation of dispersion threshold value, the structure of active MoO3 was amorphous or micro crystalline at the low molybdenum loading. When the MoO3 loading rate was more than 10%, the significant MoO3 orthorhombic crystals appeared on the catalyst surface. The light sheet and octahedral crystal structure with close texture appeared in the MoO3 catalyst surface. The functional groups Mo=O were stable in all samples, and its content increased with the increase in molybdenum loading rate. Under a loose contact state, MoO3 characterized with low melting point, still showed good catalytic effect. With the increase in MoO3 loading rate, TG and DTG curve moved to the low temperature area, the characteristic temperatures of soot oxidation were decreased, and the catalytic activity of catalyst was increased. Conversely, the specific surface area and pore volume of the molybdenum catalyst were decreased. However, the catalytic activity was not limited by the specific surface area and threshold effect, and it was closely bound up with the content of the active component MoO3. Among all samples, the catalyst loaded by 40% MoO3 exhibited the highest catalytic activity for soot oxidation. The ignition temperature, the temperature of weight loss peak and the burnout temperature of soot oxidation were reduced about 84.4, 122.6 and 122.7? respectively, as compared with the non-catalyzed particulates. The order of the activation energy for soot oxidation worked out by the Starink method was soot < Mo:Ti (mass ratio 5:95) < Mo:Ti (mass ratio 10:90) < Mo:Ti (mass ratio 20:80) < Mo:Ti (mass ratio 40:60). Thereby, with the increase in the MoO3 loading rate, the catalytic activity of MoO3/TiO2 catalyst was increased. [ABSTRACT FROM AUTHOR]

The methanol steam reforming (MSR) performance in a microchannel reactor is directly related to the flow pattern design of the microchannel reactor. Hydrogen production improvements can be achieved by optimal design of the flow pattern. In this study, an A-type microchannel reactor with a flow pattern design of one inlet and two outlets was applied to conduct the MSR for hydrogen production. The MSR performance of the A-type microchannel reactor was investigated through numerical analysis by establishing a three-dimensional simulation model and compared with that of the conventional Z-type microchannel reactor. Experiments were also conducted to test the MSR performance and validate the accuracy of the simulation model. The results showed that compared with the conventional Z-type microchannel reactor, the species distributions in the A-type microchannel reactor were more homogeneous. In addition, compared with the Z-type microchannel reactor, the A-type microchannel reactor was shown to effectively increase the methanol conversion rate by up to 8% and decrease the pressure drop by about 20%, regardless of a slightly higher CO mole fraction. It was also noted that with various quantities of microchannels and microchannel cross sections, the A-type microchannel reactor was still more competitive in terms of a higher methanol conversion rate and a lower pressure drop. [ABSTRACT FROM AUTHOR]

Abstract: The introduction of mesoscale (∼0.1–1.0μm) structures is one of effective approaches to reduce the thermal conductivity of thermoelectric materials. In this study, n-type PbTe bulk samples were fabricated by semisolid powder processing (SPP) using powders synthesized by melting. The field emission scanning electron microscope (FESEM) results showed that there were circular mesoscale pores in the grains of the samples fabricated by SPP. The mesoscale pores effectively reduced the lattice thermal conductivity by enhancing the scattering of phonons with long mean free paths. The samples fabricated by SPP had a figure of merit (ZT) value of 1.33 at 773K, which showed an enhancement of 77% compared with that of their hot-pressed counterparts. This enhancement mainly resulted from the lower lattice thermal conductivity and higher power factor of the SPP samples. [Copyright &y& Elsevier]

Micro/meso forming is an economically competitive process for the fabrication of miniature metallic parts. Scaling conventional metal forming down to micro/meso scale leads to the so-called size effects. In this study, the size effects in micro/meso semisolid extrusion-forging (MSEF) of A356 aluminum alloy were numerically and experimentally investigated. An experimental setup for MSEF was developed, and the mechanical performance of A356 aluminum alloy in the semisolid state was tested. Then, the MSEF with various die-hole diameters and various friction coefficients were numerically investigated to examine the size effects in the processes. With certain punch displacements, it was found that the aspect ratio of the extruded pin decreased and the forging load increased during the miniaturization of the die-hole. In addition, the contact condition and the lubrication became increasing critical when the die-hole got smaller. Furthermore, various experiments were performed using A356 aluminum alloy. When the die-hole shrunk in the experiments, the changes of the pin aspect ratio and the forging load followed similar trends with the numerically simulated results. The size effects in the MSEF experiments mainly belong to the first-order size effect. In addition, no significant defect was found in the formed specimens with a die-hole diameter down to 0.55 mm, indicating great formability of the MSEF. The size effects identified in the MSEF process in this study assist in understanding the material flow and the cavity filling in the micro/meso semisolid forming with complicated geometrical shapes. [ABSTRACT FROM AUTHOR]

Velocity uniformity in reaction channels has a significant effect on the performance of laminated microreactors with micro-pin-fin arrays (MPFAR) for hydrogen production. The hydrogen production efficiency can be improved by optimizing the structure of flow manifolds. The relationship between the flow manifold structure and the velocity distribution in the reaction channel with MPFAR is established by an equivalent electrical resistance network model validated via simulation. The effects of the flow manifold structure on the velocity distribution are investigated. The results show that the velocity distribution can be improved by increasing the y-direction coordinate Ypi of the flow manifold inlet tube. The flow manifold structure is optimized for better velocity distribution in reaction channels with different MPFAR widths. [ABSTRACT FROM AUTHOR]

Highlights: [•] Calculation model of acoustic radiation force in half space is built. [•] The delivery target is detached from the rigid surface during transportation. [•] The three procedures of delivery process can be realized in the same device. [ABSTRACT FROM AUTHOR]

In order to achieve the target of emission purification within the aspect of combustion optimizing in a cylinder, as well as the partial replacement of fossil fuels, a study on the combustion process of dimethyl carbonate (DMC)-diesel fuel blend was carried off. A fuel blend D10 (10% DMC and 90% diesel by volume) was chosen as the test fuel. The experiments were conducted on a single-cylinder research engine originated from a Daimler Benz OM646 2.2 litre common rail direct injection four-cylinder in-line diesel engine. As for the research engine, the indicated mean effective pressure pmi was adopted as the baseline for assessment of engine performance. A given load at 1900 r/min was chosen as the engine operating mode. According to the first law of thermodynamics, the heat release rate can be presented in real-time by the IndiCom software. The exact position in the crank angle of the center of heat release (COHR, 50% of the total heat release) can be figured out by interpolation. It was a key parameter to describe the combustion process of the engine. Through a fuel injection strategy characterized by an adjustable first pre-injection phase but constant phase intervals between the three injections and adjustable main injection duration but fixed durations of first pre-injection and second pre-injection, the accurate COHR target at a steady working mode can be implemented. Therefore five modes with an even interval of COHR, under the same engine speed and pmi, were inspected. As for D10 fuel, to compensate for its energy density falling, the rail pressure of D10 was 3 MPa higher than that of a diesel. While using D10 fuel, two schemes were considered. One was to keep the injection parameters of fuel system unchanged. The other was to slightly adjust the injection parameters, thus the COHR can be precisely accorded with the original diesel engine. When multiple injection strategy was adjusted to achieve the exact COHR which was delayed in constant step, the features of the combustion process of a diesel engine were analyzed. The ignition for each operating mode occurred between the second pilot injection and the main injection. For every two adjacent modes varying with COHR, the crank angle intervals of the fuel injection timings as well as center of heat release and the location of heat release peak were almost identical. With the increase of COHR, the duration in crank angle taken from injection timing to ignition became shorter, while the duration in the crank angle taken from ignition to the center of the heat release became longer. As compared with the location of a peak pressure in-cylinder, the COHR would be moved backward far away. As for D10 fuel, because the easy vaporization of dimethyl carbonate promoting the mixing of fuel and air and combustion, both crank angle intervals, from the ignition to 10% of heat release and from ignition to 90% of heat release, were shorter, which indicated that the added dimethyl carbonate could help to promote the combustion process. These analyses of combustion features based on COHR will provide a fundamental guidance for the application of dimethyl carbonate/diesel blends, multiple injections regulating the combustion process, and emission control theory. [ABSTRACT FROM AUTHOR]

Biodiesel, as a renewable alternative fuel, is easily crystallized at low temperature, which limits the application of engines fueled with biodiesel. Biodiesel is mainly composed of methyl palmitate (C16:0), methyl stearate (C18:0) and methyl oleate (C18:1). The properties of fuel are closely related to the properties of its compositions, and the fuel properties will change with different mole fraction ratios of some composition. So, it is very important to research the thermal parameters of different compositions. Differential scanning calorimetry (DSC) is a thermo analytical technique by which the difference in the amount of heat required to increase the temperature of a sample and reference is measured as a function of temperature. The result of a DSC experiment is a curve of heat flux related to temperature or time. Through this curve, it is easy to determine transition temperatures and enthalpies, which makes DSC a valuable tool in producing phase diagrams for various chemical systems. Based on the differential scanning calorimeter, thermal parameters of the three methyl esters have been analyzed. The melting point and fusion enthalpy of saturated fatty acid esters (C16:0 and C18:0) are much higher than the ones of unsaturated fatty acid ester (C18:1), the melting points of C16:0, C18:0 and C18:1 are 301.57, 310.92 and 255.01 K, respectively. The binary solution of fatty acid methyl esters has also been scanned, where each curve exhibits two distinct exothermic peaks. These phenomena can be explained in that the high melting point saturated ester precipitated first and the low melting point unsaturated ester precipitated later. Moreover, the crystallization temperature of these solutions is lower than the melting point temperature of the pure saturated fatty acid esters, which precipitated earliest in the solution. It is also clear that the solution crystallization temperature rises accordingly, because the increase of the mass fraction of saturated fatty acid esters. Supposing that biodiesel is a solution combined with different fatty acid methyl esters, the saturated fatty acid esters C16:0 and C18:0 are treated as solutes and the unsaturated fatty acid ester C18:1 is played as solvent, thus the thermodynamic model for calculating the crystallization temperature of the solution has been established. While predicting the crystallization temperature, the solution of fatty acid esters has been dealt with further as an ideal solution; because it just looks at liquid composition as the ideal solution and solid phase composition as not mutually soluble, the model has been simplified. The crystallization temperature of the four different kinds of biodiesel has been calculated by this simplified model, and also has acquired effective verification as compared with the experimental data. [ABSTRACT FROM AUTHOR]

Abstract: To optimize and improve the thermal and hydrodynamic performance of micro-reactors with micro-pin–fin arrays (MPFAR), the effect of tip clearance on the performance of the heat transfer and pressure drop at low Reynolds number was investigated by computational fluid dynamics (CFD). Unlike with high Reynolds number flow, it was found that the heat transfer and pressure drop performance in the case of low Reynolds number is quite sensitive to the tip clearance, and the introduced tip clearance can enhance the heat transfer and reduce the pressure drop effectively. Previous correlations were examined and found to overpredict the average Nusselt number and friction factor. New heat transfer and friction factor correlations accounting for the effect of tip clearance were developed, providing a valuable approach to the design and optimization of the tip clearance of the MPFAR. Finally, a series of experiments was carried out to validate the numerical simulation approach, and the experimental results agreed well with those from simulation. [Copyright &y& Elsevier]

Abstract: Flow distribution among microchannels is a fatal factor affecting the performance of laminated microchannel reactors for hydrogen production. Homogeneous flow strongly depends on the structural design of the microchannel reactor. The present work concentrates on improving the flow distribution in microchannel reactors for hydrogen production by optimization of the structural design. An innovative A-type microchannel reactor for hydrogen production with one inlet/two outlets was developed and analyzed. The equivalent electrical resistance network model was used to calculate the flow distribution in the microchannel reactor which was validated by computational fluid dynamics (CFD). The influences of structural parameters on flow distribution in the A-type were investigated quantitatively. The calculated results showed that longer microchannels with a higher aspect ratio and a small side length in the manifolds were beneficial for attaining uniform flow distribution in the A-type microchannel reactor. Furthermore, it was found that flow distributions among the microchannels in the A-type were much more uniform than those in the conventional Z-type microchannel reactor with one inlet/one outlet. Finally, an optimization strategy was proposed to optimize the manifold geometries to obtain a comparatively even flow distribution among microchannels. [Copyright &y& Elsevier]

To further understand the tribological performance in metal forming, it is critical to accurately evaluate the friction between tool and workpiece. However, the unclear contact conditions at the interfaces and the complex mechanisms of the tribology lead to challenges to assess friction in metal forming processes. In this study, a friction evaluation method by the barrel compression test and its principle model were proposed based on the theoretical analysis and the numerical simulations. Besides the friction factor at the die-specimen interfaces and the initial aspect ratio of the specimen, the strain hardening exponent of the specimen was found to affect the barreling profiles based on the theoretical analysis. Furthermore, the effects of the three influencing factors, including the friction factor at the interfaces, the initial aspect ratio and the strain hardening exponent of the specimen, on the defined barreling factor were numerically analyzed by the finite element method. A predictive model of the barreling factor accounting for these three factors was developed. A friction evaluation method, proposed based on this model, was implemented by various cylinder compression experiments of CuZn40 brass. The method proposed in this study provided a convenient means to identify the contact friction in metal forming processes. [ABSTRACT FROM AUTHOR]

Abstract: To enhance the energy conversion efficiency of the micro-reactor with micro-pin-fin arrays (MPFAR) for hydrogen production, the effect of structural parameters (the height of the micro-pin-fin, the transverse and longitudinal center distance between two adjacent micro-pin-fins) on the performance of the MPFAR for hydrogen production is investigated. Based on the geometrical parameters, a theoretical model of material balance for hydrogen production in the MPFAR is established. The calculated results show that with the increase of the micro-pin-fin height or the decrease of the distance between two adjacent micro-pin-fins, the methanol conversion rate and the CO molar fraction increase. The methanol conversion rate increases by about 10% when the height of micro-pin-fin increases from 0.2 to 1mm or the center distance between the two adjacent micro-pin-fins increases from 1.2 to 2.6mm. The comparisons between the experimental and calculated results validate the theoretical model of material balance utilized in this study. Finally, a better geometrical structure of micro-pin-fin arrays is obtained, in which the height of the micro-pin-fin, the transverse and longitudinal center distances between two adjacent micro-pin-fins are 1.0mm, 1.2mm and 1.2mm, respectively. The hydrogen yield in the MPFAR can reach about 8.3ml/min under the condition that the methanol conversion rate is above 90%. [Copyright &y& Elsevier]

Abstract: To enhance the compactness of the micro-reactors for hydrogen production via methanol steam reforming (SMR) for fuel cell, a novel micro-reactor with micro-pin-fin arrays (MPFAR) is designed and fabricated based on the micro thixo-forming technology. A three-dimensional model is adopted in the numerical analysis to investigate the heat and mass transfer in the micro-reactor. The results show that the methanol conversion in the MPFAR is higher than that in a micro-channel reactor, the velocity and temperature distribution is uniform in the catalyst support. Higher reaction temperature and contact time result in higher methanol conversion and CO molar fraction at the outlet, while a higher steam to methanol (SC−1) molar ratio results in a lower CO molar fraction. Finally, experiments are conducted to test the performance of the MPFAR for hydrogen production. The experimental results agree well with the simulated ones, which validate the accuracy of the simulation model. When the SC−1 molar ratio and the contact time are 1.2 and 0.12s, respectively, the methanol conversion of the MPFAR reaches to 87.5% with the hydrogen molar fraction of about 75% at the outlet, which is suitable for the application in the fuel cell system. [Copyright &y& Elsevier]

A high pressure EGR system was adopted to a turbocharged inter-cooled diesel engine, to analyze its combustion and emission characteristics under the condition of different loads and constant speed. Under the same steady operating mode, with the increase of EGR rate, the temperature of compressed gas ascended, the ignition delay was shortened, the pressure and temperature of the burned gas descended, and the combustion process was prolonged. According to the experimental data, it was found that, at the same EGR rate, lower the load of engine was, lower the temperature in cylinder, and higher the increase rate of CO was. However, the increase rate of HC present a falling trend. The decrease rate of the specific emission of NOx linearly varied with EGR rate with a slope of 1.651. The increase rate of smoke opacity behaved a second-order polynomial uprising trend, and the higher the load was, the sharpener the smoke opacity deteriorated, with the increase of EGR rate. Fromthe point of emission view, the engine with EGR system can achieve the lesser exhaust emissions in some operations by adjusting the engine parameters. [ABSTRACT FROM AUTHOR]

Abstract: Chatter vibration leads to challenges in precise machining due to its harmful effect on productivity and surface quality. In this study, a chatter suppression method based on parametric excitation was developed. The effect of parametric excitation on self-excited vibration was investigated based on a model of a van der Pol–Mathieu–Duffing oscillator with a time delay. It reveals that there can be a zero solution for the oscillator under the effect of parametric excitation, while it is impossible to have a stable zero equation without parametric excitation. The stability of a parametrically excited vibration system regarding the regenerative effect in the cutting processes was studied by the averaging method. The stability analysis shows that parametric excitation with an appropriate frequency and large amplitude has a chatter suppression effect no matter whether the waveform is a sinusoidal wave, square wave or triangular wave. To validate the effect of parametric excitation for chatter suppression, experiments were conducted based on a magnetorheological (MR) fluid-controlled boring bar, which can generate high-frequency parametric excitation based on the quick response of the MR fluid. Cutting experiments with an excitation current of different waveforms and diverse frequencies show that chatter can be significantly suppressed by the effect of parametric excitation. [Copyright &y& Elsevier]

Abstract: Chatter is very harmful to precision machining process. To avoid cutting chatter effectively, a method based on wavelet and support vector machine is presented for chatter identification before it has fully developed. Wavelet transform, which can image the information in both the time and frequency domain, is applied as an amplification for the chatter premonition. Each wavelet packet''s energy regularly changes during the development of the chatter, which has a time advantage for the identification. Therefore, a two-dimensional feature vector is constructed for chatter detection based on the standard deviation of wavelet transform and the wavelet packet energy ratio in the chatter-emerging frequency band. A support vector machine (SVM) is designed for pattern classification based on the feature vector. The intelligent recognition system, composed of the feature extraction and the SVM, has an accuracy rate of 95% for the identification of stable, transition and chatter state after being trained by the experiment data. The method can be applied in different machining processes. [Copyright &y& Elsevier]

Abstract: An innovative chatter suppression method based on a magnetorheological (MR) fluid-controlled boring bar for chatter suppression is developed. The MR fluid, which changes stiffness and undergoes a phase transformation when subjected to an external magnetic field, is applied to adjust the stiffness of the boring bar and suppress chatter. The stiffness and energy dissipation properties of the MR fluid-controlled boring bar can be adjusted by varying the strength of the applied magnetic field. A dynamic model of a MR fluid-controlled boring bar is established based on an Euler–Bernoulli beam model. The stability of the MR fluid-controlled boring system is analyzed, and the simulation results show that regenerative chatter can be suppressed effectively by adjusting the natural frequency of the system. Experiments in different spindle speeds utilizing a MR fluid-controlled boring bar are conducted. Under a 1Hz square wave current, chatter can be suppressed, as evidenced by the elimination of chatter marks on the machined surfaces and the reduction in the vibration acceleration at the tip of the boring bar. [Copyright &y& Elsevier]

To eliminate the limitation of the conventional acoustic radiation torque theory, which is only applicable to a disklike scatterer in a plane sound field, a new theory is established to calculate the radiation torque on any irregularly shaped scatterer in any arbitrary sound field. First, with the aid of the conservation law of angular momentum, the acoustic radiation torque is expressed as the angular momentum flux through a spherical surface with the center at the scatterer’s centroid. Second, the velocity potential of the scattered field is derived, taking into account the influences of the translational and rotational movements of the scatterer induced by the first order stress of the incident sound field. Finally, a general calculating formula of the acoustic radiation torque is achieved. For a disklike scatterer in a plane sound filed, results from the above formula are well identical with those conventional formulas. By studying the case of a semicircular cylinder scatterer in a standing-wave sound field, it is found that for an irregularly shaped scatterer its rotation velocity is normally nonzero and the radiation torque changes with the spatial attitude. [ABSTRACT FROM AUTHOR]

Electric field has the potential to influence the combustion characteristics of hydrocarbon fuel. In this paper, the atomization and combustion characteristics of the droplets of biodiesel and biodiesel–ethanol blend in a uniform direct-current electric field were investigated using photography. It was revealed that a certain electric field strength could induce droplet deformations and cone jets. For the droplet blended with 10 vol. % ethanol, the sizes of the secondary droplets from bubble breakups decreased with the increase in electric field strength, possibly due to the Coulomb repulsion in the ligament. The high breakup intensity of the droplet blended with 30 vol. % and 50 vol. % ethanol covered up the effect of electric field on the sizes of secondary droplets from bubble breakups. During the entire range of electric field strength, cone jets generated smaller secondary droplets in comparison with bubble breakups. Moreover, the electric field distorted the flame morphology, especially the flame width increased at the electric field strength of 50 kV/m. The maximum droplet temperature decreased with the electric field strength, in addition to the biodiesel droplet. Overall, the electric field ameliorates fuel droplets' atomization and combustion characteristics. [ABSTRACT FROM AUTHOR]

The springback behavior of thin metal sheets will significantly affect the forming accuracy of microchannels during microstamping process, especially as the forming scale reduced to micro-/meso levels due to the size effects and grain structures. This paper aims to study the size effects on springback behavior and microchannel's formability in microstamping process. The thin sheet of SUS304 specimens with different grain sizes was prepared and employed in uniaxial tensile tests to examine the stress–strain relationship and used to study the effects of grain sizes on the material's plastic deformation behavior. A constitutive model incorporate surface layer and grain structures is developed to characterize the deformation behavior of thin-metal sheet with different grain sizes. Then, the constitutive model is utilized in finite element simulation of microstamping process to fabricate microchannel structures, and the results are verified by experimental testing. Both numerical simulation and experimental results showed that the size effect is critical in microstamping process, and the developed constitutive model is able to accurately characterize the global springback behavior of thin metal sheets during microstamping process. [ABSTRACT FROM AUTHOR]