•Thermal management system (TMS) based on PCM-fin structure is proposed.•The electro-thermal model considers thermal contact resistance during heat transfer.•PCM-fin structure achieves superior ...thermal control compared with pure PCM.•Optimization design is discussed on the cooling performance of PCM-fin structure.•The suitable thermal performance is exhibited in continuous charge-discharge cycles.
The safety, performance and durability of the Li-ion battery module are limited by the operating temperature especially in the hot temperature regions, hence the thermal management system is essential for battery module. In this paper a novel phase change material (PCM) and fin structure was proposed for the thermal management system of LiFePO4 battery module to reduce the maximum temperature and improve the temperature uniformity in high-temperature environment (40 °C). Carefully designed experiments were performed for model validation. The effects of PCM species, fin thickness, fin spacing and PCM thickness on the cooling performance of battery module were investigated numerically. The results showed that PCM-fin structure thermal management system with optimized design exhibited good thermal performance, keeping the maximum temperature of the battery surface under 51 °C at relatively high discharge rate of 3C. Moreover, by investigating the thermal behavior of PCM during discharge process and cycle test, it has been found that PCM-fin structure has the advantage of improving natural convection and heat conduction within the PCM structure, and as a result enhances heat dissipation efficiency and reduces failure risk in passive thermal management systems using PCMs.
Due to the wide applications of solar photovoltaic (PV) technology, safe operation and maintenance of the installed solar panels become more critical as there are potential menaces such as hot spot ...effects and DC arcs, which may cause fire accidents to the solar panels. In order to minimize the risks of fire accidents in large scale applications of solar panels, this review focuses on the latest techniques for reducing hot spot effects and DC arcs. The risk mitigation solutions mainly focus on two aspects: structure reconfiguration and faulty diagnosis algorithm. The first is to reduce the hot spot effect by adjusting the space between two PV modules in a PV array or relocate some PV modules. The second is to detect the DC arc fault before it causes fire. There are three types of arc detection techniques, including physical analysis, neural network analysis, and wavelet detection analysis. Through these detection methods, the faulty PV cells can be found in a timely manner thereby reducing the risk of PV fire. Based on the review, some precautions to prevent solar panel related fire accidents in large-scale solar PV plants that are located adjacent to residential and commercial areas.
•The inhibition of N2 and CO2 on methane/hydrogen/air premixed flame was investigated.•CO2 has better inhibiting performance than N2 at corresponding conditions.•The inhibiting mechanisms were ...revealed from thermal and kinetic aspects.
Hydrogen enriched natural gas (HNG) is a promising alternative fuel. But the blended fuel will inevitably have different ignition and combustion characteristics as compared to natural gas. The extent of the resulting difference depends on the percentage of hydrogen addition. It may affect the compatibility of combustion systems and have safety implications. The present study was aimed at enhancing the safety of HNG through inhibition by inert gases. Laboratory tests were conducted for methane/hydrogen/air premixed flame propagating in a closed channel with either nitrogen (N2) or carbon dioxide (CO2) as the inhibitor. Mixtures with different hydrogen volumetric fractions in fuel, including 0%, 20%, 50% or 80% were investigated. The flame shape evolution and the overpressure in the channel were recorded by high-speed Schlieren photography and pressure sensor, respectively. The flame shape was found to change in various ways depending on the inhibitor and hydrogen content. The pressure wave had remarkable impacts on flame and pressure dynamics. The effect of buoyancy on the flame deformation was observed and discussed. Both N2 and CO2 were found to have considerable inhibiting effect on the flame speed and overpressure build-up in the channel while the inhibiting effect of CO2 was stronger. The inhibition mechanisms of either N2 or CO2 were revealed from thermal and kinetic aspects.
The present study aims to gain insight of the mechanisms and characteristics for pulsating and uniform flame spread over liquid fuel at subflash temperatures. A specific goal is to use the validated ...three-dimensional (3-D) numerical model to reveal fine details of the gas and liquid phase flows as well as the resulting flame characteristics, which are challenging to obtain experimentally. To facilitate the study, 3-D formulations have been developed to explicitly solve the transport equations in both phases. A compressible solver was formulated for flame propagation in the gas phase using a one-step chemical reaction expression and mixture-averaged diffusion coefficients for the gaseous species. An incompressible solver with temperature dependent thermo-physical properties was employed to describe the convective motions and heat transfer in the liquid fuel region. Validation has been conducted for both uniform and pulsating spreads over a narrow 1-propanol tray with varying fuel depths through comparing the predicted flame front evolution with published measurements. Further qualitative comparison has also been conducted for some predicted fine features of the gas and liquid phase flows and flame spreading characteristics with published experimental observations. For both the uniform and pulsating spread, the detailed flame structure including the main diffusion flame and a small stratified premixed flame at the front have been captured. Wherever relevant, the detailed predictions were also used to shed light on some discrepancies in previously reported features in different laboratory studies and numerical simulations. Finally, the detailed 3-D predictions were used to illustrate fine features of the subsurface convective flow and its relative position to the flame front, the relative magnitudes of the subsurface flow velocity and that of the spread rate as well as the role of the thermocapillary-driven subsurface flow in the flame spread mechanism.
Hydrogen process equipment are often housed in 20-foot or 40-foot container either be at refueling stations or at the portable standalone power generation units. Shipping Container provide an easy to ...install, cost effective, all weather protective containment. Hydrogen has unique physical properties, it can quickly form an ignitable cloud for any accidental release or leakages in air, due to its wide flammability limits. Identifying the hazards associated with these kind of container applications are very crucial for design and safe operation of the container hydrogen installations. Recently both numerical studies and experiment have been performed to ascertain the level of hazards and its possible mitigation methods for hydrogen applications. This paper presents the numerical modelling and the simulations performed using the HyFOAM CFD solver for vented deflagrations processes. HyFOAM solver is developed in-house using the opensource CFD toolkit OpenFOAM libraries. The turbulent flame deflagrations are modelled using the flame wrinkling combustion model. This combustion model is further improved to account for flame instabilities dominant role in vented lean hydrogen-air mixtures deflagrations. The 20-foot ISO containers of dimensions 20′ × 8′ × 8′.6″ filled with homogeneous mixture of hydrogen-air at different concentration, with and without model obstacles are considered for numerical simulations. The numerical predictions are first validated against the recent experiments carried out by Gexcon as part of the HySEA project supported by the Fuel Cells and Hydrogen 2 Joint Undertaking (FCH 2 JU) under the Horizon 2020 Framework Programme for Research and Innovation. The effects of congestion within the containers on the generated overpressures are investigated. The preliminary CFD predictions indicated that the container walls deflections are having considerable effect on the trends of generated overpressures, especially the peak negative pressure generated within the container is overestimated. Hence to account for the container wall deflections, the fluid structure interactions (FSI) are also included in the numerical modelling. The final numerical predictions are presented with and without the FSI. The FSI modelling considerably improved the numerical prediction and resulted in better match of overpressure trends with the experimental results.
•HyFOAM has been modified and extended for simulating vented deflagrations.•HyFOAM considers flame instabilities which play an important role in vented deflagration.•Lean hydrogen laminar and turbulent flame speeds correlations with Lewis number effects are used.•Pseudo two-way coupling is used to incorporate the effect of fluid structure interaction.
The manuscript firstly describes the data collection and validation process for the European Hydrogen Incidents and Accidents Database (HIAD 2.0), a public repository tool collecting systematic data ...on hydrogen-related incidents and near-misses. This is followed by an overview of HIAD 2.0, which currently contains 706 events. Subsequently, the approaches and procedures followed by the authors to derive lessons learned and formulate recommendations from the events are described. The lessons learned have been divided into four categories including system design; system manufacturing, installation and modification; human factors and emergency response. An overarching lesson learned is that minor events which occurred simultaneously could still result in serious consequences, echoing James Reason's Swiss Cheese theory. Recommendations were formulated in relation to the established safety principles adapted for hydrogen by the European Hydrogen Safety Panel, considering operational modes, industrial sectors, and human factors. This workprovide an important contribution to the safety of systems involving hydrogen, benefitting technical safety engineers, emergency responders and emergency services. The lesson learned and the discussion derived from the statistics can also be used in training and risk assessment studies, being of equal importance to promote and assist the development of sound safety culture in organisations.
•Overview of the 706 hydrogen incidents and accidents currently in HIAD 2.0 database.•Lessons learned for system design; system manufacturing; human factors and emergency response.•Minor events which occurred simultaneously could still result in serious consequences.•Recommendations formulated referring to the established safety principles adapted for hydrogen.•Specific consideration for operational modes, industrial sectors, and human factors.
•Two-step method is applied to radiation calculation of developing flames.•Focusing of evaporating water droplets in local areas of the flame is studied.•A strong infrared scattering by small water ...droplets is analyzed.•The use of the infrared scattering in flame observations is discussed.
A procedure based on two-step method is suggested to simplify time-consuming spectral radiative transfer calculations in open flames containing scattering particles. At the first step of the problem solution, the P1 approximation is used to calculate the divergence of radiative flux, and it is sufficient to determine the flame parameters. The second step of solution is necessary to obtain the radiation field outside the flame, and this can be made independently using the ray-tracing procedure and the transport source function determined at the first step. Such a splitting of the complete problem results in much simpler algorithm than those used traditionally. It has been proved in previous papers that the combined two-step method is sufficiently accurate in diverse engineering applications. At the same time, the computational time decreases in about two orders of magnitude as compared with direct methods. An axisymmetric pool fire at the initial stage of fire suppression by a water spray is considered as the case problem. It is shown that evaporating small water droplets characterised by a strong scattering of infrared radiation are mainly located in regions near the upper front of the flame and one can observe the scattered radiation. This effect can be used in probe experiments for partial validation of transient Computational Fluid Dynamics (CFD) simulations.
For small-scale pool fires, Vali et al. 1 showed a pair of vortices in the liquid pool. The first vortex appeared just close to the sidewall of the container, and the second one emerged slightly away ...from the first vortex. Large-eddy simulations of small methanol pool fires coupled with liquid fuel convective flow were conducted using an in-house version of FireFOAM to investigate the above phenomenon. In this study, a three-dimensional liquid phase model is newly developed. The model incorporates the effects of thermocapillary Marangoni convection, buoyancy, shear stress, and evaporation. For the gas phase, the combustion model is the extended eddy dissipation concept model coupled with the laminar combustion model. This combustion model uses the viscous diffusion rate to consider laminar-turbulent transition. The predictions were in reasonably good agreement with the measured local mass burning rate, flame height and distributions of liquid temperature. The error of the mass burning rate was within 4%. The present predictions captured a pair of vortices in line with Vali et al.'s experiment 1. Their sizes increased with increasing the liquid temperature. The Reynolds analogy could explain the sensible reason behind this trend. Shear stress and thermocapillary force caused convection in the liquid pool, and this convection formed a pair of vortices. Thermocapillary force was due to the different distributions of convective and radiative heat transfer. Sensitivity test for sub-models for the liquid phase demonstrated that their effects on the mass burning rate were all less than 5.1%. Conversely, the simulation assuming zero gravity only in the liquid phase resulted in almost 64% reduction in the mass burning rate.
Polybrominated diphenyl ethers (PBDEs) were commonly used flame retardants in the world, while some of PBDEs have been listed as persistent organic pollutants (POPs). Decabrominated diphenyl ether ...(BDE-209) was the most commercially used PBDEs. A farm near the factory located in Northern Taiwan was highly contaminated with BDE-209. Since PBDEs in the contaminated soils can be uptake by crops shown in our previous studies and could be potentially consumed by humans, it is very important to establish a feasible treatment method for PBDE remediation in this contaminated farm. Thermal treatment of PBDEs in soil was studied. The initial concentration of BDE-209 in contaminated soil was 1.472 mg/kg. A series of thermal experiments under different operating conditions including various temperature (105, 150, 200, 250, 300, 350, 400 and 450 °C), holding time (10, 20 and 30 min), heating rate (5, 10, 20 and 40 °C/min), and soil amount (10, 100, 1000 and 2000 g) were investigated. The optimal heating conditions for thermal treatment of contaminated soil were heating at 450 °C for 30 min with a heating rate of 10 °C/min. Under this condition, the removal of BDE-209 in the different weights of contaminated soil was tested. The soils in the contaminated farm were tested to further evaluate the feasibility of remediating the on-site PBDE contaminated soil through thermal treatment, suggesting that the holding time was extended to 2 h for the field-scale contaminated soil. The results showed that BDE-209 had been removed to below the detection limit in on-site soil. This investigation is the first study using thermal treatment to remediate soils really contaminated with PBDEs.
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•PBDEs can be completely degraded by thermal treatment at 450 °C in on-site soil.•Thermal treatment mechanism of BDE-209 in field contaminated soil is debromination.•Optimal thermal treatment on PBDE-contaminated soil is 450 °C (10 °C/min) for 30 min.•For field trial, extending above parameter to 2 h can completely degrade PBDEs.
High-resolution direct numerical simulations are conducted for under-expanded cryogenic hydrogen gas jets to characterize the nearfield flow physics. The basic flow features and jet dynamics are ...analyzed in detail, revealing the existence of four stages during early jet development, namely, (a) initial penetration, (b) establishment of near-nozzle expansion, (c) formation of downstream compression, and (d) wave propagation. Complex acoustic waves are formed around the under-expanded jets. The jet expansion can also lead to conditions for local liquefaction from the pressurized cryogenic hydrogen gas release. A series of simulations are conducted with systematically varied nozzle pressure ratios and systematically changed exit diameters. The acoustic waves around the jets are found to waken with the decrease in the nozzle pressure ratio. The increase in the nozzle pressure ratio is found to accelerate hydrogen dispersion and widen the regions with hydrogen liquefaction potential. The increase in the nozzle exit diameter also widens the region with hydrogen liquefaction potential but slows down the evolution of the flow structures.
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