Good Guidance For Design Research Articles

Numerical study on the effect of complex structural barrier walls on high-pressure hydrogen horizontal jet flames

Hydrogen has the potential to produce energy with no emissions, and therefore offers a strategic opportunity for rapid development of renewable energy storage. However, jet flames caused by the leakage of high-pressure hydrogen may cause casualties and damage equipment, so the safety issues associated with hydrogen incidents are a key issue restricting its development. Barrier walls can be an important mitigative action to reduce the hazard of hydrogen jet flames. Previous studies have evaluated the protective effect of different vertical or inclined arrangements of a single barrier wall in the vertical direction. However, in the vertical direction, a single barrier wall is not sufficient to reduce the hazards associated with high-pressure hydrogen jet flames. In this paper, a two-dimensional CFD model of high-pressure hydrogen jet flames are established. A simplified form of the hydrogen real gas equation of state is used to describe the complex behavior of high-pressure hydrogen. This CFD study employs the standard k-ε turbulence model, the eddy dissipation concept (EDC) model, and the discrete ordinate (DO) radiation model. The results display good agreement with the experimentally obtained flame shape and thermal radiation values, which confirms the applicability of the model. Based on this model, the characteristics of high-pressure jet flames are systematically studied under different forms of barrier walls and different pressures of hydrogen storage. Compared with the vertical barrier wall, barrier walls with complex structures can block the flames in front of the wall more effectively. This is proven through a remarkable decline in the vertical flame length and a reduction in the high temperature area. Comparing the five barrier wall patterns for their combined flame shape and flame temperature, it is more preferred to choose 60° Plate. The results of this study will help to better analyze the consequences of hydrogen jet flames and provide guidance for better design of barrier walls for mitigation.

Design and analysis of a d15 mode piezoelectric energy generator using friction-induced vibration

Research works have been conducted on transverse and longitudinal mode piezoelectric energy generation to collect energy from ambient vibrations. However, the inconsistency with the frequency of the energy source and low output power density remain problems for high energy output. In this work, we propose a shear mode piezoelectric energy generator, which utilizes the friction-induced vibration (FIV) and high shear mode piezoelectric coefficient to improve the energy output. A piezoelectric coupled FIV mathematical model is developed to accurately calculate the dynamic vibration response and voltage output. The dynamic voltage response is validated by experiment, and it proves the possibility of continuous friction-induced high-frequency vibration. The energy generation process is evaluated by transient charging simulation of a storage capacitor through an iteration process, which was experimentally validated in the literature. Parameter studies have been conducted to investigate the influences of the piezoelectric patch dimensional parameters, vibration system parameters, friction model parameters, methods of electrical connections, and different piezoelectric materials on the energy generation performance to provide guidance for better design. Under ideal experiment conditions with proper parameters, a volume of m3 PZT4 piezoelectric material indicates root mean square (RMS) charging power density of Wm−3 and Wm−3 with electrically in parallel and electrically in series, respectively. While using the same amount of material and structural setup, the single crystal PMN-PT piezoelectric material shows RMS charging power density of Wm−3 and Wm−3 with electrically in parallel and electrically in series, correspondingly. These promising results demonstrate that close to W-level RMS charging power output may be realized by structure optimization of energy generator design and incorporating multiple generators together for operation. Possible incorporation into vehicle braking systems can be considered to utilize the wasted friction energy, and it may offer an energy supply for low-power wireless devices.

Influences of longitudinal gradients on methane-driven membrane biofilm reactor for complete nitrogen removal: A model-based investigation

Integrating anammox with denitrifying anaerobic methane oxidation (DAMO) in the membrane biofilm reactor (MBfR) is a promising technology capable of achieving complete nitrogen removal from wastewater. However, it remains unknown whether reactor configurations featuring longitudinal gradients parallel to the membrane surface would affect the performance of the CH4-driven MBfR. To this end, this work aims to study the impacts of longitudinal heterogeneity potentially present in the gas and liquid phases on a representative CH4-driven MBfR performing anammox/DAMO by applying the reported modified compartmental modeling approach. Through comparing the modeling results of different reactor configurations, this work not only offered important guidance for better design, operation and monitoring of the CH4-driven MBfR, but also revealed important implications for prospective related modeling research. The total nitrogen removal efficiency of the MBfR at non-excessive CH4 supply (e.g., surface loading of ≤0.064 g-COD m−2 d−1 in this work) was found to be insensitive to both longitudinal gradients in the liquid and gas phases. Comparatively, the longitudinal gradient in the liquid phase led to distinct longitudinal biomass stratification and therefore played an influential role in the effective CH4 utilization efficiency, which was also related to the extent of reactor compartmentation considered in modeling. When supplied with non-excessive CH4, the MBfR is recommended to be designed/operated with both the biofilm reactor and the membrane lumen as plug flow reactors (PFRs) with co-current flow of wastewater and CH4, which could mitigate dissolved CH4 discharge in the effluent. For the reactor configurations with the biofilm reactor designed/operated as a PFR, multi-spot sampling in the longitudinal direction is needed to obtain a correct representation of the microbial composition of the MBfR.

Influence of alloying elements on mechanical and electronic properties of NbMoTaWX (X = Cr, Zr, V, Hf and Re) refractory high entropy alloys

NbMoTaW refractory high entropy alloy (RHEA) has shown great potential applications for high temperature components due to its high temperature mechanical strength. However, the brittleness at room temperature hinders its engineering application and further development. To overcome this deficiency, refractory alloying elements with melting temperatures over 1850 °C, i.e., Cr, Zr, V, Hf, and Re, were chosen to enhance the mechanical performance of NbMoTaW RHEA in the present work. The effects of refractory alloying elements on the strength and ductility of NbMoTaW RHEA were investigated via a combination of theory and experiment. To be specific, the first-principle calculations based on density functional theory were employed to predict the mechanical properties of the alloyed NbMoTaWX (X = Cr, Zr, V, Hf and Re) RHEAs and explain the alloying effect from the atomic and electronic level. Moreover, the phase structures of the alloyed RHEAs were determined based on the formation enthalpy and cohesive energy, as well as some empirical parameters, such as the average valence electron concentration VEC and atomic size difference δ. In combination with the experimental results, the calculated elastic constants and modulus indicated that most of these alloying elements enhanced the strength of NbMoTaW RHEA, while only Zr-alloying significantly improved the ductility. The strengthening mechanism of different elements was well analyzed based on the total and partial density of states, overlapping Mulliken population, charge density contour, and atomic distance. The improvement of the ductility for Zr-alloying was attributed to the formation of Zr–Zr metallic bonds in the alloyed NbMoTaWX RHEAs. The theoretic predictions were confirmed by the experimental investigations. The present work provides a good guidance for design and construction of NbMoTaW RHEA.

Comparative study of two loop heat pipes using R134a as the working fluid

In order to promote future commercial applications of loop heat pipe (LHP) especially in the civil fields, environmentally friendly R134a is considered a good candidate working fluid to replace the commonly used anhydrous ammonia. In this work, two sets of LHPs with R134a as the working fluid were designed and fabricated, one with a nickel wick, and the other with a stainless steel wick. Their thermal performance, mainly including the startup, the power increment test, the thermal resistance and the heat transport capability, were experimentally studied, evaluated and compared. Based on the experimental results, it is found that both of the R134a LHPs present excellent startup performance, achieve a maximum heat transfer capacity greater than 100 W, and exhibit good response characteristics to stepwise change of heat load. The R134a LHP with a nickel wick shows good anti-gravity capability; however, the one with a stainless steel wick is quite sensitive to the adverse elevation. The physical mechanisms responsible for the experimental results mentioned above have been analyzed and discussed. This work contributes to a better understanding on the operating performance and characteristics of the R134a LHPs, providing good design guidance and reference for its future applications.

Experimental study on an acetone-charged loop heat pipe with a nickel wick

In order to push forward the commercial applications of loop heat pipe (LHP) especially in an environment where people are present, it is of great importance to explore alternative working fluids to substitute the commonly used anhydrous ammonia. In this work, an acetone-charged LHP with a nickel wick is developed and experimentally studied, mainly focusing on its startup and heat transport capability. Based on the experimental results and theoretical analysis, some important conclusions have been drawn, as summarized below: 1) The acetone-charged LHP with 2 mm inner diameter pipeline can successfully realize the startup, and reach a heat transport capability of 60 W × 0.5 m; 2) When the inner diameter of the pipeline is increased from 2 to 4 mm, the LHP can start up with a much smaller heat load, i.e., 5 W, achieving a much lower steady-state operating temperature; 3) When the inner diameter of the pipeline is increased from 2 to 4 mm, the heat transport capability of the acetone-charged LHP can be increased from 60 to 100 W. 4) Adverse elevation affects greatly the heat transport capability of the acetone-charged LHP. With the adverse elevation increasing from 0 to 0.2 m, the heat transport capability is decreased from 100 to 60 W. The physical mechanisms responsible for the experimental results mentioned above have been analyzed and discussed. This work contributes to a better understanding on the operating performance and characteristics of the acetone-charged LHP, providing good design guidance and reference for its future applications.

Quiet power-free cooling system enabled by loop heat pipe

Taking full advantage of LHP’s efficient long distance heat transport capability, a LHP-based power-free cooling system has been developed in this work. The heat source was simulated by a film heater, which was connected to the cylindrical evaporator of the LHP via an aluminum saddle. The condenser line was embedded into the bottom surface of a fin radiator where heat dissipation to the ambient was completely by air natural convection. Extensive experiments on this cooling system were conducted, mainly focusing on its startup and system thermal resistance. Experimental results show that this cooling system can successfully start up with a very small heat load. With the film heater temperature not exceeding 80 °C, this cooling system can manage a heat load as large as 150 W over a distance of 1.05 m, corresponding to a system thermal resistance about 0.30 °C/W. Moreover, this cooling system exhibited very strong anti-gravity capability. With an adverse elevation of 0.5 m, it can still maintain normal operation, and no obvious performance decay was observed except an increased operating temperature at small heat loads. This work provides good design guidance and reference for future applications of this advanced cooling system.

Theoretical modelling and experimental analysis of the vertical stiffness of a convoluted air spring including the effect of the stiffness of the bellows

A new refined model including a model of the bellows to describe the vertical stiffness of a convoluted air spring is developed. The new model of a convoluted air spring incorporates the structural parameters including the effective area, the rate of change in the effective area, the effective volume, the rate of change in the effective volume and the stiffness of the bellows. Analytical models of the structural parameters of a convoluted air spring are established using a geometrical analysis approach. Two convoluted air springs (type 1B5002 and type 2B5281) are designed and manufactured for testing purposes. An experimental set-up is designed in order to carry out identification of the structural parameters and to test the vertical static stiffness and the vertical dynamic stiffness. The analytical models of the structural parameters are validated by experiments, which provide good design guidance and improvement in the convoluted air spring at the design stage. Tests on the vertical static stiffness and the dynamic stiffness indicate that the stiffness of the bellows should be considered; furthermore, the stiffness of the bellows exhibits amplitude-dependent chacteristics and frequency-dependent characteristics. In a different approach from the previous studies, a model of the bellows is developed in this paper and is composed of a smooth friction model and a fractional derivative Zener model in parallel to represent the viscoelastic properties of the bellows. It is concluded that the simulation results of the proposed new model are in good agreement with the experimental data. The new refined model may be an effective tool for predicting the mechanical behaviours of a convoluted air spring before a prototype is constructed. The proposed refined model can also be practically utilized as a guide for designing the parameters and for matching the air suspension of the vehicle.

On the machinability and surface finish of cutting nanoparticle and elastomer modified epoxy

In the present paper, we investigate the material removal behaviour of epoxy-based composites in an orthogonal cutting process, and its dependence on two different fillers: a rigid nanosilica (SiO2) and a soft carboxyl-terminated butadiene-acrylonitrile (CTBN) elastomer. The results obtained show that fracture plays a key role in the formation of the newly cut surface as the chip is separated from the workpiece by the cutting tool. The surface finish after cutting is dependent on the cutting depth, h, and the ratio between fracture toughness and yield strength, Gc/σy. The latter can be determined by a cutting theory. In general, a smaller value of h and/or a higher value of Gc/σy favour the controllability of the surface finish, i.e., a stable material removal process with enhanced surface integrity. This work highlights the important role of the fillers in determining not only the mechanical properties of epoxy composites but also their machinability. It provides useful guidance for better design and processing of epoxy-based materials for different engineering applications.

Statistical Rare-Event Analysis and Parameter Guidance by Elite Learning Sample Selection

Accurately estimating the failure region of rare events for memory-cell and analog circuit blocks under process variations is a challenging task. In this article, we propose a new statistical method, called EliteScope , to estimate the circuit failure rates in rare-event regions and to provide conditions of parameters to achieve targeted performance. The new method is based on the iterative blockade framework to reduce the number of samples, but consists of two new techniques to improve existing methods. First, the new approach employs an elite-learning sample-selection scheme, which can consider the effectiveness of samples and well coverage for the parameter space. As a result, it can reduce additional simulation costs by pruning less effective samples while keeping the accuracy of failure estimation. Second, the EliteScope identifies the failure regions in terms of parameter spaces to provide a good design guidance to accomplish the performance target. It applies variance-based feature selection to find the dominant parameters and then determine the in-spec boundaries of those parameters. We demonstrate the advantage of our proposed method using several memory and analog circuits with different numbers of process parameters. Experiments on four circuit examples show that EliteScope achieves a significant improvement on failure-region estimation in terms of accuracy and simulation cost over traditional approaches. The 16b 6T-SRAM column example also demonstrates that the new method is scalable for handling large problems with large numbers of process variables.

Quantum efficiency of transmission-mode AlxGa1−xAs/GaAs photocathodes with graded-composition and exponential-doping structure

A transmission-mode AlxGa1−xAs/GaAs photocathode with the combination of composition-graded AlxGa1−xAs window layer and exponential-doping GaAs emission layer is developed to maximize the cathode performance. The theoretical quantum efficiency model with this complex structure containing twofold built-in electric fields is deduced by solving the one dimensional continuity equations combined with the three-step model. By comparison of spectral characteristics of photocathodes with different composition and doping structures, and through analysis of cathode structure parameters, it is found that the twofold built-in electric fields can effectively improve photoemission performance of AlxGa1−xAs/GaAs photocathode, which is related to Al proportion variation range and thicknesses of window layer and emission layer. The quantum efficiency model would provide theoretical guidance for better design of transmission-mode graded bandgap photocathodes.

Research on Spatial Distribution and Mutual Inductance of Superconducting Pancake Coils

This paper studies the numerical calculation method of mutual inductance between two superconducting pancake coils. And the calculation results are proved through experiment. Use this calculation method, the isoline map of two superconducting pancake coils’ coupling coefficient with the different spatial distributions is calculated. Then the designer can rapidly design the spatial distribution of superconducting pancake coils according to the coupling coefficient they needs. Specially, there is a curve of coupling coefficient equals 0 in the isoline ma. For the occasions which want to eliminate the mutual inductance between two superconducting pancake coils, this curve can provide a good guidance for design a compact layout and reduce the volume. Finally, the 0 value curve is tested under the guidance of calculation result. Through this experiment, the correctness and engineering guidance of isoline map is verified.

Characterization of the 5′ to 3′ nuclease activity of Thermus aquaticus DNA polymerase on fluorogenic double-stranded probes

Taq DNA polymerase contains a polymerase domain for synthesizing new DNA strands and a 5′-nuclease domain for cleaving damaged DNA strands or RNA primers. Both of these domains play key roles in nucleic acid amplification and detection, especially in fluorogenic probe-based, real-time PCR. However, the 5′-nuclease activity is substrate dependent and its consequences remain largely unexplored, except for its role in 5′-nuclease-based TaqMan assays. Using both kinetic studies and matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS), we comprehensively examined the 5′-nuclease activity of Taq DNA polymerase on fluorogenic double-stranded probes of varied structures. We observed that double-stranded probes with destabilized 5′-terminal could be hydrolyzed, and the major cleavage was the removal of the 5′-terminal fluorophore-labeled nucleotide. These observations can serve as guidance for better design of double-stranded probes with reduced or no interfering background for real-time PCR detection.