Due to its merit of rapid start-up, lower pollution and high energy conversion efficiency, polymer electrolyte membrane fuel cell (PEMFC) system has been considered as one of the most promising ...propulsion system for electric vehicles. Although the development of PEMFC system has been experienced rapid growth for several decades, many challenges still need to be overcome for promoting commercialize fuel cell technology. In order to understand the design concept of PEMFC system and update the development status of fuel cell system for electric vehicle, as well as help fuel cell system developers or electric vehicle manufacturers to improve the performance and durability of fuel cell electric vehicles, the up-to-date technical targets such as power density, operation temperature, dynamic response and lifetime for PEMFC systems in different countries have been summarized and compared in this review. Furthermore, from the aspects of hydrogen management and air management and major degradation mechanisms under various operation conditions, the design status of the system configuration in fuel cell has also been analyzed in detail. Finally, according to the design and intended operation the mitigation strategies have also been proposed to promote the development of PEMFC system for electric vehicle applications.
•Up-to-date technical targets for PEMFC systems are stated from different countries.•The design status of fuel cell system configurations has been analyzed in detail.•Difficulties encountered during PEMFC system design and development are emphasized.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Display omitted
•Large scale 3D multiphysics model for tubular SOFC stack with anode support feature is developed.•There is complex turbulent flow process within external air flow path of anode ...support T-SOFC stack.•For 1in1out line external flow path most air flow are concentrated through the central zones of each tubes.•For 2in2out U type external air flow path most air will flow along the margin zone of T-SOFC stack.•An optimized external air flow path design for anode support T-SOFC stack is proposed and checked.
Although solid oxide fuel cell (SOFC) stacks are generally considered promising devices due to their many unique advantages, there are very few experiments and reports on anode support-type SOFC stacks with tubular (T-) designs, since it is quite difficult to determine a proper external air flow path design to support proper air and heat distribution qualities compared with cathode support T-SOFC stacks. In this paper, a large-scale 3D multiphysics model for the external air flow path of a convenient anode support T-SOFC stack is developed for the first time to investigate the general flow distribution characteristics of the external air flow paths. A novel external air flow path for an anode support T-stack is achieved by modifying the main and sub inlet/outlet manifolds, feed/exhaust headers structures and cross-section parameters. This new design is proven to greatly increase the air supply qualities among the tubes and over each tube surface and decrease the temperature gradients in the entire stack. The design could be the proper basic form used for anode support for T-SOFC stacks to achieve good stack performance and duration time in the near future.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPUK, ZRSKP
The transition‐metal nitrogen‐carbon (M‐N‐C) catalysts, as one of the optimal bifunctional oxygen catalysts, are vital for cathodic oxygen electrode of Zn‐based air flow batteries (ZAFBs). However, ...chemical complexity of M‐N‐C catalysts prepared via the traditional pyrolytic process increases the difficulties of precise control toward configuration and repeatability, especially in large‐scale synthesis. Herein, a bifunctional oxygen catalyst via a pyrolysis‐free approach based on closed π‐conjugated covalent organic polymers (COPs, microwave synthesis) is developed, which inherits the advantage of the well‐defined configuration in an atomic manner. Profited from distinct catalytic centers and strong electronic coupling at the interface between COP and layered double hydroxides, the as‐synthesized catalyst not only more easily permits large quantity production (>1 kg per batch), but also maintains an ultrahigh bifunctional activity and a long cycle stability even after scale synthesis (ΔE Ej10 – E1/2 = 591 mV; energy efficiency drops by only 2.02% after 1200 cycles), which overwhelmingly exceeds the benchmark Pt/C+IrO2 and the state‐of‐the‐art pyrolytic bifunctional M‐N‐C oxygen catalysts.
A structurally well‐defined bifunctional oxygen catalyst is prepared via a pyrolysis‐free approach. The as‐synthesized catalyst more easily permits large quantity production while maintaining ultrahigh bi‐functional catalyst activity, overwhelmingly exceeding the benchmark Pt/C+IrO2 and the state‐of‐the‐art pyrolytic M‐N‐C catalysts.
Full text
Available for:
BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
In this paper we proposed a Y-shaped bi-stable energy harvester (YBEH) to scavenge the low-speed wind energy. The system is composed of a cantilever beam with a tip magnet and two curved wings, a ...piezoelectric laminate and two fixed magnets. To demonstrate the harvesting performance, corresponding validation experiments were performed over a range of velocities. The experimental results prove that this new wind harvester could execute snap-through and reach coherence resonance in a wide range of air flow speeds. Our findings may open a new opportunity to utilize coherence resonance to enhance the energy harvesting performance for low-speed wind flows.
•A new Y-shaped bi-stable energy harvester (YBEH) configuration is presented.•The YBEH uses the flow as a disturbance to trigger the snap-through motion.•The YBEH can execute snap-through for a wide range of air velocities.•The YBEH can be designed to reach coherence resonance to give large outputs.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
•Inlet air flow maldistribution in heat exchangers is investigated.•3D CFD simulations are performed for plain-fin-and-tube heat exchangers.•Effects of nonuniformity on system design and performance ...is analysed.•CFD simulation is an efficient tool for optimum designs of heat exchanger designs.
Plate fin-and-tube heat exchangers are used extensively in heating, ventilating, and air conditioning as well as in refrigeration systems. Non-uniform inlet air flow distribution has a substantial effect on heat exchanger performance. Building upon and extending the work of Yaïci et al. (2014), the present study utilises three-dimensional (3D) Computational Fluid Dynamics (CFD) simulations in order to predict the effect of inlet air flow maldistribution on the design and thermal–hydraulic performance of heat exchangers used in air handling units. Computational assessments of the air-side heat transfer and pressure drop characteristics for a variety of inlet air flow distributions and geometrical parameters of staggered plate fin-and-tube heat exchangers were undertaken on heat exchangers with different longitudinal tube pitches, transversal tube pitches, and fin pitches. Characteristics of predicted thermal–hydraulic performance were reported in terms of Colburn j-factor, Fanning friction f-factor, and efficiency index j/f as a function of Reynolds (Re) numbers. The 3D CFD simulations reveal that air flow maldistribution and the effects of geometrical parameters significantly impact the design and performance of heat exchangers. When compared to baseline (i.e., a uniform inlet air velocity profile), substantial fluctuations in the j- and f-factors—deviations as pronounced as 50–70%, 60–66%, and 63–67% for cases with longitudinal tube pitch, transversal tube pitch, and fin pitch variations with non-uniform air flows, respectively—were observed. The 3D CFD method employed by this study has great potential for use in, first, assessments of correlations centred on air flow maldistribution and, second, efforts to optimally design the headers of heat exchangers in order to minimise inlet flow maldistribution and maximise overall system performance.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
•The partitions are transversely arranged in the battery box to improve the heat dissipation.•The cooling flow field is divided into a multi-layered flow channel by the partitions.•The cooling fluid ...in the adjacent channels flows in the opposite direction.•The reverse layered sir flow improves the temperature uniformity of the battery pack.
This study proposes a novel reverse layered air flow for Li-ion battery thermal management to improve the temperature consistency of the battery pack. In this new thermal management structure, the partitions are transversely arranged in the battery box, and divide the cooling flow field into polylaminate flow channels. The cooling air in the adjacent channels flows in the opposite direction, and exchanges heat through the transverse partitions. The partitions are made of diathermanous material to strengthen the air counter current heating exchanging in the adjacent channels, enhance heat dissipation and decrease temperature difference of the battery pack. This paper compares the reverse layered air flow with the unidirectional air flow by three-dimensional computational fluid dynamics. The results of the CFD model are validated with the experimental results. The results show that the reverse layered air flow can lower the highest temperature and the maximum average temperature difference of the battery pack than that of the unidirectional air flow. Additionally, adding rectifier grids at the entrance the highest temperature reduces by 0.5 °C, and the maximum average temperature difference reduces by 0.6 °C (54.5% reduction). Finally, the parameters such as the distance between the cells and the air inlet velocity are optimized, and the optimal parameters are obtained, which can guide the design of novel thermal management.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Measurement of the swirling air flow rate and average speed of air at air distribution units of ventilation systems is a rather difficult task due to the fact that the air flow enters the measuring ...device at different angles. As a result, significant measurement errors can occur when using point thermoanemometers or other flow meters. The use of integral anemometers facilitates the measurement process. However, it is necessary to eliminate the errors associated with changes in the angle of the air flow to the sensing element of the measuring device. To do this, it is necessary to ensure a rectilinear structure of the air flow using a transitional air collector and rectifier. The aim of this paper is to develop a design of an air collector device that will allow to measure the flow rate of a swirling air flow. The objectives of the paper are to optimize the geometrical parameters of the air collector to ensure a rectilinear flow, minimize its dimensions and aerodynamic drag. The correctness of the air collector design was evaluated by matching the calibration characteristic of the probe of an integral thermoanemometer in the presence of a vortex diffuser in front of the air collector and in its absence. The proposed device has a rectangular shape and consists of a receiver, a rectifying grid, a chamber, an accelerating and stabilizing section, at the outlet of which a thermoanemometer probe is installed. The receiver and the accelerating section are tapered along their length, while the chamber and the stabilizing section have a constant cross-section. The rectifying grid is installed inside the chamber and has a square-shaped honeycomb structure. Several options of the air collector design with different geometrical parameters were studied using computer modelling. The dependence of aerodynamic drag on air flow was plotted. The optimal design of the air collector was chosen, for which a life-size physical model was created. The calibration characteristics of the measuring probe with an air collector were experimentally obtained when a swirling air flow was applied. The developed universal air collector allows the air flow rate measurement at the outlets of almost any air distribution devices of ventilation systems of buildings.
We report a hybridized nanogenerator with dimensions of 6.7 cm × 4.5 cm × 2 cm and a weight of 42.3 g that consists of two triboelectric nanogenerators (TENGs) and two electromagnetic generators ...(EMGs) for scavenging air-flow energy. Under an air-flow speed of about 18 m/s, the hybridized nanogenerator can deliver largest output powers of 3.5 mW for one TENG (in correspondence of power per unit mass/volume: 8.8 mW/g and 14.6 kW/m3) at a loading resistance of 3 MΩ and 1.8 mW for one EMG (in correspondence of power per unit mass/volume: 0.3 mW/g and 0.4 kW/m3) at a loading resistance of 2 kΩ, respectively. The hybridized nanogenerator can be utilized to charge a capacitor of 3300 μF to sustainably power four temperature sensors for realizing self-powered temperature sensor networks. Moreover, a wireless temperature sensor driven by a hybridized nanogenerator charged Li-ion battery can work well to send the temperature data to a receiver/computer at a distance of 1.5 m. This work takes a significant step toward air-flow energy harvesting and its potential applications in self-powered wireless sensor networks.
Full text
Available for:
IJS, KILJ, NUK, PNG, UL, UM
•Effect of tunnel longitudinal slope on the smoke propagation were investigated.•Ceiling smoke behavior was characterized by considering the natural ventilation in tunnel.•Correlation for estimating ...the ceiling temperature in the sloping tunnel was developed.•Research findings were compared with the existing experimental works worldwide.•Advancement for fire protection and detection in tunnelling technology was achieved.
In order to reduce risk and increase resilience of transportation tunnels, the early-phase detection and protection of fire are of great significance for the safety assessment of tunnel. In this work, numerical simulations are conducted to characterize the thermal plume propagation and ceiling temperature profile in a tunnel with longitudinal slope increasing from 0% to 15%. For the sloping tunnel, as there exists elevation difference between the tunnel ends, the longitudinal air flow will be induced from the lower end. Under such circumstances, the stack effect occurs and it becomes the primary driving force for the smoke movement in tunnel. Results show that the thermal plume behaviors in the sloping tunnel, including the thermal flow field and the temperature profile, show apparently different from those in the horizontal one. The induced air flow rate that directly related to the strength of stack effect is quantified, and on this basis, the predictive correlation of the temperature profile under the ceiling is proposed by considering the influence of the stack effect for different tunnel slopes. Besides, the accuracy and applicability of the obtained correlation are further verified by comparing to a total of four series of previous experimental data with a wider range of tunnel slopes, dimensions, and heat release rates.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
PDF
