Short shaped copper fibers in an epoxy matrix: Their role in a multifunctional composite

Previous research indicates that short shaped copper fibers improve the fracture and impact toughness of brittle thermoset polymer matrix composites. This paper investigates the potential multifunctional ability of these same shaped copper fibers by determining their electromagnetic interference (EMI) shielding effectiveness (SE). Fiber shapes were selected based on previous single fiber pullout experiments where they displayed high toughness. The two fiber diameters tested were: 0.325 and 0.162 mm. Fiber shapes used in the experiments were: straight, flat end-impacted, rippled, and acid roughened. A SE of greater than 45 dB at 1.0 GHz was attained in epoxy that contained 15 vol% of 0.162 mm diameter shaped fibers. Composites with 15 vol% of the 0.325 mm diameter shaped fibers showed poor SE, less than 20 dB. Experimental results indicate that besides improving the fracture and impact toughness of a thermoset polymer matrix, short shaped copper fibers can also significantly improve the SE and electrical conductivity of the composite, resulting in a multifunctional material. This increase in SE and electrical conductivity can be attributed to: shape effects that increase the skin volume, surface discontinuities which increase the amount of electromagnetic (EM) wave scattering, and the fiber count which determines the number of conducting paths.     

Optimizing thermal performances and NOx emission in a premixed ammonia-hydrogen blended meso-scale combustor for thermophotovoltaic applications

As a carbon-free energy carrier, ammonia has attracted significant interest in the combustion field as a potential substitute for fossil fuels. However, the focus has been given to the application at meso-scale conditions, particularly with regard to thermal performance and NO_x emissions. Therefore, the present study numerically investigates a 3-dimensional time-domain premixed ammonia/oxygen meso-scale combustor to optimize its' thermal performance and NO_x emission for power generation applications. The numerical model is firstly validated by using experimental data available in the literature. Then, the effects of 1) the inlet pressure (P_in), 2) the equivalence ratio, and 3) the hydrogen blended ratio on the temperature uniformity, the combustor outer wall mean temperature (OWMT), NO emission, and exergy efficiency are examined. The results indicate that increasing P_in intensifies the mixing process of the mixture gases, thus reducing the residence time for the high-temperature flame in the combustion chamber. The optimized OWMT and NO emissions are up to 26% and 40.3% respectively, with only 9% compensation of the standard deviation achieved, when the inlet velocity is set to 0.5 m/s and P_in is 3.0 bar. Furthermore, varying the equivalence ratio in the range of 0.95–1.1 has a minor influence on improving thermal performances, but a significant impact on mitigating the NO_x emission performance. Additionally, blending less than 15% hydrogen has a significant reduction in the maximum NO_x emission (up to 53%); however, the influence on the OWMT can be neglected. Further exergy analysis reveals that elevating P_in results in a decrease in the exergy efficiency due to the increased inlet exergy. In general, this work provides a preliminary method for improving the thermal performance and NO_x emission of an ammonia/hydrogen-oxygen-fueled meso-scale combustor for power generation purpose.     

Impact of urban development on residents’ public transportation travel energy consumption in China: An analysis of hydrogen fuel cell vehicles alternatives

Urban development has an important influence on the energy consumption of transportation. To develop public transportation is one of the important ways to decrease the energy consumption of urban transportation. It is very urgent to upgrade technology to reduce the energy consumption and emissions of the vehicles constantly. The popularization of hydrogen fuel cell vehicles is the trend of the future automobile industry, which can effectively reduce traffic energy consumption and alleviate urban pollution. This article analyzes the impact of urban development on public transport and private transportation energy consumption from 2013 to 2015; and uses hydrogen fuel cell vehicles alternatives in urban public transport as a scenario. It shows that urban economic development can effectively reduce public transport. Population growth will increase greatly energy consumption of public transport, while larger cities with reasonable spatial density can reduce traffic energy consumption. Moreover, hydrogen fuel cell vehicles can effectively reduce the energy consumption and pollution emissions of urban transportation during operating. Based on the above conclusions, this article will eventually provide targeted recommendations for the development of Chinese cities, public transport, and hydrogen fuel cell vehicles.     

Preparation and Properties of Nano-cellulose/Sodium Alginate Composite Hydrogel

Cellulose nanofiber (CNF) was isolated from Okara using deep eutectic solvent (DES) with high-speed stirring. The composite hydrogels obtained by using different proportions of CNF and sodium alginate (SA) had different properties. The CNF/SA composite hydrogels were analyzed using Fourier transform infrared spectroscopy and scanning electron microscopy and tested for compression properties, rheological properties, water content, and swelling degree. Physical crosslinking between SA and Ca²⁺, and different degrees of hydrogen bond formation between SA and CNF were observed. The CNF/SA composite hydrogel have great potential as reinforcements in eco-friendly composite hydrogels for diverse applications.     

PET和关中麦秆共热解特性及其动力学研究

利用TG-FFIR技术研究陕西关中地区小麦秸秆(麦秆)、聚对苯二甲酸乙二醇酯(PET)及其两者混合物麦秆-PET(质量比1∶1)在20 K/min的升温速率下的热解行为、主要热解产物、协同效应和动力学.研究结果表明:PET热解初始温度为375℃,最大热失重速率处的温度为454.9℃,失重率为62.87％,其热解残余质量...     

Synthesis of Reprocessable Lignin-based Non-isocyanate Poly(imine-hydroxyurethane)s Networks

In this study,an environmentally friendly and non-toxic route to synthesize lignin-based non-isocyanate poly(imine-hydroxyurethane)s networks was explored.Specifically,the NH₂-terminated polyhydroxyurethanes(NPHUs)prepolymer was first synthesized from bis(6-membered cyclic carbonate)(BCC)and diamine via the ring-opening reaction.Subsequently,the corresponding ligninbased non-isocyanate polyurethanes(NIPUs)with tunable properties were synthesized from NPHUs and levulinate lignin derivatives containing ketone groups via the Schiff base reaction.The structural,mechanical,and thermal properties of NIPUs with different stoichiometric feed ratios of BCC and levulinate lignin were characterized by Fourier transform infrared spectroscopy(FT-IR),nuclear magnetic resonance(NMR),differential scanning calorimetry(DSC),dynamic mechanical analysis(DMA),and thermogravimetric analysis(TGA).The results indicated that the tensile strength,Young's modulus,toughness,storage modulus,glass transition temperature,and thermal stability of lignin-based NIPUs gradually increased with increasing lignin content,and the highest Young's modulus of 41.1 MPa was obtained when lignin content reached 45.53%.With good reprocessing properties,this synthetic framework of ligninbased NIPUs also provides sustainable non-isocyanate-based substitutions to traditional polyurethane networks.     

Numerical study on unsteady heat transfer and fluid flow in a closed cylinder of reciprocating liquid hydrogen pumps

Modeling and optimization of liquid hydrogen (LH₂) pumps require accurate in-cylinder heat transfer correlations. However, the applicability of existing correlations based on gas mediums to LH₂ remains to be verified. In this paper, the unsteady heat transfer and fluid flow in a closed LH₂ pump cylinder are numerically studied by adopting the gas spring model. The phase shifts and temperature distribution in the closed pump cylinder are investigated. LH₂ is less affected by in-cylinder heat transfer and has a more uniform temperature distribution compared to nitrogen gas, while a low-temperature zone appears near the piston face at 120 rpm. Finally, the validity of Lekic's correlation in predicting the heat flux of the LH₂ compression process in the closed pump cylinder is verified, and the efficiency decrement versus rotational speed is analyzed based on the correlation. This work would be useful for selecting a proper in-cylinder heat transfer model for predicting the thermodynamic process in reciprocating LH₂ pumps.     

Rational design of moldable calcium chloride ceramic-like material with supramolecular structure

Calcium chloride is widely used in various fields of society because of its good chemical stability and non-toxic properties. As an inorganic salt with low ductility at low temperature, it is never used to prepare bulk materials but is usually used to prepare energy storage materials. The work in this paper presents the first synthesis of a moldable calcium chloride ceramic-like material (flexural strength up to 32 MPa) using calcium chloride. The process results in occurring ion-dipole interactions between calcium chloride and glycerol by means of direct heating and forms supramolecular structure. Due to the presence of dynamic and reversible non-covalent bonds, the bonds break upon heating bringing good flowability; the re-established bonds upon cooling allow the formation of rigid materials. The preparation is also a green and recyclable process, as the molded material can be reshaped by heating. Such a brilliant moldable property reveals the potential of this new approach for the design and production of calcium chloride materials with adjustable shapes.     

Synthesis of FeCo2O4@Co3O4 nanocomposites and their electrochemical catalytical performaces for energy-saving H2 prodcution

In this study, FeCo₂O₄@Co₃O₄ bifunctional catalysts with a unique structure combining nanosheets and nanowires were prepared on nickel foam by a simple hydrothermal + annealing method. The catalysts exhibited excellent catalytic activity for hydrogen production during urea electrooxidation reaction (UOR) and ethanol oxidation reaction (EOR). For UOR, the potential at 10 mA/cm² current density is 1.387 V and the tafel slope is 67 mV/dec. In the configured two-electrode electrolytic cell, the FeCo₂O₄@Co₃O₄ catalysts in the UOR and EOR processes required only 1.425 and 1.471 V, respectively, to produce a current density of 10 mA/cm², which is much less than that of the (oxygen evolution reaction) OER (1.640 V). In addition, the current density remained stable at a fixed potential during a long time (20 h) i-t test in the urea solution.