PolyHIPE composite based-form stable phase change material for thermal energy storage

A novel shape-stabilized n-hexadecane/polyHIPE composite phase change material (PCM) was designed and thermal energy storage properties were determined. Porous carbon-based frameworks were produced by polymerization of styrene-based high internal phase emulsions (HIPEs) in existence of the surface modified montmorillonite nanoclay. The morphological and mechanical properties of the obtained polyHIPEs were investigated by scanning electron microscopy analysis and the compression test, respectively. The polyHIPE composite with the best pore morphology and the highest compression modulus was determined as a framework to prepare the form stable n-hexadecane/polyHIPE composite phase change material using the one-step impregnation method. The chemical structure and morphologic property of composite PCM was investigated by FT-IR and polarized optical microscopy analysis. Thermal stability of the form-stable PCM (FSPCM) was examined by TG analysis. The n-hexadecane fraction engaged into the carbon foam skeleton was found of as 55 wt% from TG curve. differential scanning calorimetry analysis was used for determining melting temperature and latent heat storage capacity of FSPCM and these values were determined as (26.36°C) and (143.41 J/g), respectively. The results indicated that the obtained composite material (FSPCM) has a considerable potential for low temperature (18°C-30°C) thermal energy storage applications with its thermal energy storage capacity, appropriate phase change temperatures and high thermal stability.     

Immobilized phosphotungstic acid for the construction of proton exchange nanocomposite membranes with excellent stability and fuel cell performance

Phosphotungstic acid (HPW) has a good potential as nanofillers in nanocomposite proton exchange membrane with the prerequisite of solving the leakage issue. It is immobilized onto mesoporous graphitic carbon nitride (mg-C₃N₄) nanosheets surface, and then incorporated into sulfonated poly (aryl ether sulfone) (SPAES) membrane. Structures of the HPW/mg-C₃N₄ nanocomposites and corresponding SPAES/HPW/mg-C₃N₄ membranes are characterized by spectroscopic techniques. Fundamental properties and fuel cell performance of the fabricated nanocomposite membranes, and the leakage of HPW are investigated. Along with the highly suppressed HPW leakage, the SPAES/HPW/mg-C₃N₄ membranes show improved dimensional stability, water affinity and physicochemical stability, as well as better proton conductivity and fuel cell performance. At 80 °C and 60–100% RH, the SPAES/HPW/mg–C₃N₄–1.5 membrane exhibits 2–3.6 times peak power densities (354.9–584.2 mW/cm²) of the pristine SPAES membrane, and proton conductivity of 203 mS/cm, dimensional change less than 7.5% and weight loss of 1.4% in Fenton oxidation test at 80 °C.     

Thermal performance of a packed bed reactor for a high‐temperature chemical heat pump

The thermal performance of a chemical heat pump that uses the reaction system of calcium oxide/lead oxide/carbon dioxide, which is developed for utilization of high‐temperature heat above 800°C, is studied experimentally. The thermal performance of a packed‐bed reactor of a calcium oxide/carbon dioxide reaction system, which stores and transforms a high‐temperature heat source in the heat pump operation, is examined under various heat pump operation conditions. The energy analysis based on the experiment shows that it is possible to utilize high‐temperature heat with this heat pump. This heat pump can store heat above 850°C and then transform it into a heat above 900°C under an approximate atmospheric pressure. An applied system that combines the heat pump and a high‐temperature process is proposed for high‐efficiency heat utilization. The scale of the heat pump in the combined system is estimated from the experimental results. Copyright © 2001 John Wiley & Sons, Ltd.     

1000t/h锅炉一次风系统和燃烧器的试验研究

分析了姚孟电厂１０００ｔ／ｈ锅炉排烟温度、飞灰含碳量偏高的原因,提出了相应的改造方案并用数值计算的方法模拟了改造前后的炉内流场,认为变化不大。改造后排烟温度降低了１５．１℃,飞灰含碳量从原来的８．６％降低到３．４％左右,机械不完全燃烧损失降低３％以上。图５表４     

循环流化床锅炉的飞灰含碳量问题

循环流化床锅炉的飞灰含碳量问题近年来受到关注。对实际运行的多台燃烧各种燃料的220t／h锅炉的飞灰样品测定表明：飞灰的含碳量具有明显的不均匀性。分析了煤质、分离器及运行条件对飞灰含碳量的影响。结果表明：循环流化床锅炉燃烧过程中焦炭反应性逐渐下降;焦炭燃烧过程中发生的爆裂、磨损、失活等行为与煤种有关,对循环流化床锅炉飞灰碳燃尽有很大影响。气固混和不均匀是导致较高的飞灰含碳量的原因之一。图7表2参13     

Computational study on heat transfer and MHD-electrified flow of fractional Maxwell nanofluids suspended with SWCNT and MWCNT

Recent developments in fluid dynamics have been focusing on nanofluids, which preserve significant thermal conductivity properties and magnify heat transport in fluids. Classical nanofluid studies are generally confined to models described by partial differential equations of an integer order, where the memory effect and hereditary properties of materials are neglected. To overcome these downsides, the present work focuses on studying nanofluids with fractional derivatives formed by differential equations with Caputo time derivatives that provide memory effect on nanofluid characteristics. Further, heat transfer enhancement and boundary layer flow of fractional Maxwell nanofluid with single-wall and multiple walls carbon nanotubes are investigated. The Maxwell nanofluid saturates the porous medium. Also, buoyancy, magnetic, electric, and heating effects are considered. Governing continuity, momentum, and energy equations involving Caputo time-fractional derivatives reduced nondimensional forms using suitable dimensionless quantities. Numerical solutions for arising nonlinear problems are developed using finite difference approximation combined with L1 algorithm. The influence of involved physical parameters on flow and heat transfer characteristics is analyzed and depicted graphically. Our simulations found out that surface drag of Maxwell nanofluid with single-walled carbon nanotubes dominates nanofluids with multiple walls carbon nanotubes, but the reverse trend is noticed for larger Grashof number values.     

H2 production from methane pyrolysis over commercial carbon catalysts: Kinetic and deactivation study

Hydrogen production from catalytic methane decomposition (DeCH₄) is a simple process to produce high purity hydrogen with no formation of carbon oxides (CO or CO₂). However, to completely avoid those emissions, the catalyst must not be regenerated. Therefore, it is necessary to use inexpensive catalysts, which show low deactivation during the process. Use of carbon materials as catalysts fulfils these requirements.     

One-step synthesis in deep eutectic solvents of PtV alloy nanonetworks on carbon nanotubes with enhanced methanol electrooxidation performance

We report a simple one-step chemical reduction strategy in deep eutectic solvents (DESs) for the fabrication of a PtV alloy nanonetwork (ANN)/multiwalled carbon nanotube (MWCNT) nanohybrid, which exhibits excellent electrocatalytic performance in both activity and stability for the methanol oxidation reaction (MOR). The as-synthesized nanohybrid was characterized by X-ray diffraction, transmission electron microscopy and X-ray photoelectron spectroscopy, confirming the formation of a porous nanonetwork structure composed of smaller PtV alloy nanoparticles (~3.8 nm) and the presence of strong electronic transfer interactions between Pt and alloyed V. The electrochemical properties of catalysts for the MOR were evaluated by using cyclic voltammetry and chronoamperometry techniques. The electrocatalytic activity, durability and CO tolerance ability of PtV ANNs/MWCNTs toward the MOR are found to be considerably higher than those of the Pt/MWCNT and commercial Pt/C catalysts. This investigation of the effect of several reaction parameters (e.g., scan rate and methanol concentration) indicates that the electrocatalytic oxidation of methanol on PtV ANNs/MWCNTs is a diffusion-controlled electrochemical process. The performance enhancement mechanism of MOR on the PtV ANN/MWCNT catalyst is analyzed based on the structure and electrochemical studies.     

西沙海槽晚更新世冰期以来原地微生物成因水合物储库的变化

利用基于热力学理论的CSMHYD程序,计算现今及晚更新世冰期琼东南盆地西沙海槽天然气水合物的稳定带厚度及资源量,讨论晚更新世冰期以来海平面、底水温度和沉积速率变化对西沙海槽天然气水合物储库变化的影响。结果表明：①研究区水深超过600 m的海域具备天然气水合物赋存的温压条件。天然气水合物稳定带最大厚度约300 m,位于研究区的中东部和东南部。②晚更新世冰期以来,底水温度的升高抵消了海平面上升对天然气水合物稳定性的影响。研究区冰期和间冰期旋回中沉积速率发生显著变化,沉积速率大的区域,原地微生物成因天然气水合物的浓度也相应较大;导致冰期-间冰期旋回过程中原地微生物成因水合物储库变化的关键因素是甲烷供给及沉积速率,而不是温压条件的变化。③西沙海槽天然气水合物现今的储库比晚更新世冰期的减少了0.78 × 10¹² m³的甲烷气。     

Amorphous carbon anode with controllable pores for rechargeable lithium-ion battery

为满足储能市场对高功率电池的需求,开发兼具高容量和高功率性能的锂离子电池负极材料成为必然趋势。本文通过改变煤基沥青在碳化过程中的空速,考察其对无定形碳材料结构的影响,提高煤基沥青无定形碳材料的电化学性能。应用X射线粉末衍射（XRD）、拉曼（Raman）、N₂吸附-脱附和扫描电镜对所制备的无定形碳材料进行结构表征。通过比容量、库仑效率、倍率、循环性能评判材料的电化学性能。结果表明：可以通过改变气体空速来调控无定形碳材料的孔道和碳层无定形度,实现同步提升容量和倍率性能的效果。当气体空速≥0.5 m/min时,充电容量可达近260 mA·h/g,2C充电容量可达约137 mA·h/g。