Time identification of design knowledge push based on cognitive load measurement

The reuse of multidisciplinary design knowledge is pivotal in product development because of the increasingly fierce market competition. It can assist designers, particularly those who lack sufficient experience, in making correct decisions and achieving rapid design. Traditionally, designers primarily acquire design knowledge through information retrieval, which is typically time-consuming and inefficient. A solution that is widely considered to overcome the deficiencies of traditional knowledge retrieval approaches and actively provide designers with necessary knowledge is knowledge push. However, achieving the timely push of required knowledge to designers during the design process remains a challenging task. Accordingly, this paper presents a time identification method based on cognitive load measurement to identify the suitable time for design knowledge push. First, behavioral indicators related to the changes in cognitive load are identified by investigating the influence of the load on three types of behaviors: mouse dynamics, keystroke dynamics, and emotional states. Second, the possibility and efficacy of inferring the cognitive load by simultaneously and unobtrusively tracking the three aforementioned behaviors are considered through behavioral observations. Finally, predicting the knowledge push time based on the cognitive load using classification algorithms is investigated. The experimental results indicate that the accuracy of the proposed method in inferring the cognitive load is 55%, and that of push time is 83%.     

3D non-isothermal dynamic simulation of high temperature proton exchange membrane fuel cell in the start-up process

High temperature proton exchange membrane fuel cell (HT-PEMFC) with phosphoric acid doped polybenzimidazole (PBI) electrolyte shows multiple advantages over conventional PEMFC working at below 373 K, such as faster electrochemical kinetics, simpler water management, higher carbon monoxide tolerance. However, starting HT-PEMFC from room temperature to the optimal operating temperature range (433.15 K–453.15 K) is still a serious challenge. In present work, the start-up strategy is proposed and evaluated and a three-dimensional non-isothermal dynamic model is developed to investigate start-up time and temperature distribution during the start-up process. The HT-PEMFC is preheated by gas to 393.15 K, followed by discharging a current from the cell for electrochemical heat generation. Firstly, different current loads are applied when the average temperature of membrane reaches 393.15 K. Then, the start-up time and temperature distribution of co-flow and counter-flow are compared at different current loads. Finally, the effect of inlet velocity and temperature on the start-up process are explored in the case of counter-flow. Numerical results clearly show that applied current load is necessary to reduce start-up time and just 0.1 A/cm² current load can reduce startup time by 45%. It is also found that co-flow takes 18.8% less time than counter-flow to heat membrane temperature to 393.15 K, but the maximum temperature difference of membrane is 39% higher than the counter-flow. Increasing the inlet gas flow velocity and temperature can shorten the start-up time but increases the temperature difference of the membrane.     

Experimental investigation of the effect of hydrogen recirculation on the performance of a proton exchange membrane fuel cell

The hydrogen recirculation in proton exchange membrane fuel cell (PEMFC) is recommended for the hydrogen supply of PEMFC, and hydrogen ejectors are gradually being used in fuel cell vehicles due to low noise and low energy consumption. However, there is a lack of discussion about the influence of recirculation rate on the stack. Due to passive regulating mechanism of the ejectors, a miniature speed-adjustable peristaltic pump is used to simulate the hydrogen ejector in this study to investigate the effect of hydrogen recirculation on the performance of PEMFC stack. Experiments are conducted under different pump flow rates. The stack with hydrogen recirculation is proven to have better performance, but over high pump flow rate can lead to hydrogen shortage. It is interesting to find that the flow rate fluctuation of hydrogen inlet affects the stability of stack performance, and pressure drop and recovery time during purge process are proposed as effective indicators for performance analysis. Finally, pump flow rates between 60 ml/min and 105 ml/min are defined as “effective area”. Based on the analysis of effective indicators, keeping at “effective area” is further proved to improve the performance of the stack, which is also useful to design hydrogen recirculation.     

Experimental studies on the explosion indices in turbulent stoichiometric H2/CH4/air mixtures

Explosion characteristics of the stoichiometric hydrogen/methane/air mixtures with different hydrogen fractions (λ) and different turbulent intensities (u'_rms) in a fan-jet-stirred spherical explosion vessel. From the experimental results, it could be clearly found that both the maximum explosion overpressure (p_max) and the maximum rise rate of overpressure rose with the increase of u'_rms, but the major reasons to such rising were not totally the same. In turbulence, with the increase of λ, p_max declined but (dp/dt)_max rose, and such behaviours were mainly attributed to the completion on the variations between propagation speed and adiabatic explosion pressure. The explosion duration (t_c) was also measured, it rose with the increase of u'_rms and/or λ for the enhancement on propagation albeit such enhancement was attributed to different mechanism for different influence factors. The variations of deflagration index (K_G) indicated that the hazardous level of stoichiometric hydrogen/methane mixtures would become more hazardous in the presence of turbulence. Furthermore, the heat loss during the explosion also was calculated and analysed. The results reported in this article could provide more basic but important information to practical utilizations of hydrogen/methane blended fuels, especially on the safety protection strategies.     

Interlaminar reinforcement of glass fiber/epoxy composites with graphene nanoplatelets

This work investigated the ability of graphene nanoplatelets (GnPs) to improve the interlaminar mechanical properties of glass-reinforced multilayer composites. A novel method was developed for the inclusion of GnPs into the interlaminar regions of plain-weave, glass fabric fiber-reinforced/epoxy polymer composites processed with vacuum assisted resin transfer molding. Flexural tests showed a 29% improvement in flexural strength with the addition of only 0.25 wt% GnP. At the same concentration, mode-I fracture toughness testing revealed a 25% improvement. Additionally, low-velocity drop weight impact testing showed improved energy absorption capability with increasing concentration of GnPs. Ultrasonic C-scans and dye penetration inspection of the impact- and back-sides of the specimens qualitatively support these results. Finally, the impact damage area was quantified from the C-scan data. These results showed that the impact-side damage area decreased with increasing concentration of GnP, while the back-side damage area increased.     

Thermal design and model analysis of the Swiss-roll recuperator for an innovative micro gas turbine

For the advanced power systems based on the use of microturbines, the major considerations are higher power density as well as higher efficiency for energy-saving. In order to achieve higher efficiency, recuperated systems which recover the exhaust heat then become mandatory and the paramount requirements for the recuperator are high effectiveness and low pressure loss. Here, the thermal design and model analysis of a proposed Swiss-roll recuperator for future higher efficiency microturbines were made with both theoretical approach and numerical simulation. The proposed Swiss-roll recuperator is basically the primary surface type. It is composed of two flat plates that are wrapped around each other, creating two concentric channels of rectangular cross-section. The characteristics of Swiss-roll recuperator resemble the counter-flow spiral plate heat exchanger and have the excellent performance in effectiveness and pressure-loss. From a theoretical analysis, the thermal characteristics of the Swiss-roll recuperator were investigated and its preliminary designs at a given effectiveness for an innovative micro gas turbine were also demonstrated, including the determination of the number of turns, the corresponding channel widths and the required number of transfer unit (NTU). The consequent pressure loss through the recuperator was also predicted. For a given design of the recuperator, the model simulation was then made to provide the insights and needs for further improving the performance of the Swiss-roll recuperator.     

Fabrication and properties of CNTs/carbon fabric hybrid multiscale composites processed via resin transfer molding technique

Carbon nanotubes (CNTs) are effective fillers/reinforcements regarding improving the properties of polymer. In the present paper, carboxylic acid functionalized CNTs were used to modify epoxy with intent to develop a nanocomposite matrix for hybrid multiscale composites combining benefits of nanoscale reinforcement with well-established fibrous composites. CNTs were dispersed in epoxy by using high energy sonication. At low contents of CNTs, hybrid multiscale composites specimens were manufactured via resin transfer molding (RTM) process. The processibility of CNTs/epoxy systems was explored with respect to their viscosity. The dispersion quality and re-agglomeration behavior of CNTs in epoxy were characterized using optical microscope. A CNTs loading of 0.025 wt% significantly improved the glass transition temperatures (Tg) of the hybrid multiscale composites. Scanning electron microscopy (SEM) was used to examine the fracture surface of the failed specimens. It is demonstrated that the addition of small amount of CNTs (0.025 wt%) to epoxy for the fabrication of multiscale carbon fabric composites via RTM route effectively improves the matrix-dominated properties of polymer based composites. Hybridization efficiency in carbon fiber reinforced composites using CNTs is found to be highly dependent on the changes in the dispersion state of CNTs in epoxy.