Physical limitations of fountain effect pumps

Turbulent He II flow behaviour in superfilters of non-cylindrical shape at large temperature gradients was investigated. It was found that the mass flow rates were always lower than those that would follow from a straightforward extrapolation of results obtained at small temperature gradients; under certain conditions they even went through maxima with respect to the temperature gradient. This is analogous to turbulent classical flow in comparable geometries. Such effects limit the performance of fountain effect pumps and must be taken into account in efficiency calculations.     

纳米多孔碳对MgO/Mg(OH)2化学蓄热性能影响的实验研究

为提高Mg O/Mg(OH)₂的热化学蓄/放热性能,采用焙烧法将氧化镁(Mg O)负载在纳米多孔碳(NCP)材料上制备纳米碳基氧化镁(NCP-Mg O)复合材料。研究结果表明,NCP载体使MgO在其表面形成粒径为10～30 nm大小的颗粒,复合材料NCP-MgO具有较高的导热系数,负载80%MgO后导热系数是纯MgO的2.6倍。在反应温度110℃、水蒸气压力57.8 kPa的实验工况下,发现水合速率的大幅提升是强化Mg O/Mg(OH)₂蓄热性能的主要原因,在水合反应60 min和120 min时,NCP-MgO复合材料的水合转化率分别是纯MgO的2.25倍和1.6倍。在水合反应120 min后,MgO负载率为80%的NCP-MgO复合材料的蓄热密度可达1 053 kJ/kg,是纯MgO的1.4倍。该研究可为MgO/Mg(OH)₂在化学蓄热系统的应用提供一定的参考。     

变化环境下流域水-碳平衡演化研究综述

流域水量平衡与碳平衡通过植物光合作用与蒸散发过程紧密相联。在全球环境变化的背景下,研究流域水-碳平衡的耦合关系与对变化环境的响应规律对于发展生态水文科学具有重要科学意义,也可为区域水安全保障、生态系统服务功能评价、气候变化适应性对策制定等提供科学支撑。本文从水循环与碳循环要素的监测、水-碳耦合关系的量化和模拟、变化环境对水-碳平衡的干扰、流域尺度上水-碳平衡演化规律识别与归因等方面对相关研究进展进行综述,探讨当前的研究热点、面临的问题与挑战、以及未来的发展趋势。     

深水气井天然气水合物生成、沉积特性与防治方法

井筒中天然气水合物生成和沉积形成的流动障碍是影响深水气井安全高效开发的重要因素。在深水气井不同工况下多相流动特性研究的基础上,考虑不同工况下的水合物生成和沉积特点及影响因素,建立了不同工况下的水合物流动障碍预测模型,揭示了不同工况下的水合物流动障碍形成机制,探讨了不同工况下的水合物流动障碍风险及防治方法。研究结果表明:初开井、测试、关井和冷启动工况下井筒中均存在水合物生成区域,但初开井和短时间关井工况下井筒中发生水合物流动障碍的风险较小,而测试和冷启动工况下井筒中可能会发生水合物流动障碍。上述工况下井筒中的水合物沉积层生长均是非均匀分布的,水合物沉积层厚度最大的位置是发生水合物流动障碍最危险的部位。针对深水气井不同工况的具体特点,提出了不同工况下的水合物流动障碍防治措施,并探讨了一些其他可能适用于深水气井的水合物防治方法。     

智能自愈合凝胶研究进展及在钻井液领域的应用前景

自愈合凝胶是一类受损后能自行愈合形成接近整体凝胶强度的智能材料。通过系统介绍基于疏水、氢键和静电作用的物理自愈合凝胶和基于亚胺键、酰腙键和Diels-Alder反应的动态化学键作用的化学自愈合凝胶的研究进展,结合钻井液应用实践以及不同类型自愈合凝胶材料自身特性,总结了自愈合凝胶材料在钻井液防漏、堵漏、固壁和降滤失领域的应用前景。自愈合凝胶材料可作为随钻防漏和堵漏剂,进入井下高渗基质和裂缝后聚集堆积,自行愈合形成整体高强度凝胶封堵漏失通道;作为固壁材料可通过氢键、静电和黏滞作用吸附聚集在井筒壁面,愈合后形成高强度凝胶固壁层,封堵孔隙和微裂缝,强化井壁稳定性;作为降滤失材料可与黏土、聚合物协同作用,愈合后在井壁形成一层致密的高强度滤饼,降低钻井液滤失量。自愈合凝胶材料在钻井液领域的研究和应用将促进钻井液技术的智能化。     

Effect of random field element size on reliability and risk assessment of soil slopes

Bulletin of Engineering Geology and the Environment - Slope reliability analyses considering spatially variable soil properties generally necessitate a discretization of a slope region into...     

Pyrolysis waste char supported metallic catalyst for syngas production during catalytic reforming of benzene

Waste rice husk char supported Fe and Ni were synthesized to prepare the monometallic and bimetallic catalysts for removing the tar model compound benzene in a laboratory dual-stage reactor. The prepared catalysts were examined by microstructure and textural characterization to analyse catalytic performance and stability. The molar proportions of CO, H₂, CO₂ and CH₄ in the generated gas and the influence of residence time (τ) and the steam-to-carbon ratio (S/C) on the catalytic reaction were investigated. The results show that the rice husk char-based catalysts showed excellent catalytic activity for syngas production and benzene conversion. Under optimized conditions, the benzene conversion can reach 95.2%, and the mol% of syngas in the generated gas is greater than 93.0%, of which 91.0% is H₂. The experimental results show that the influence of residence time on catalytic performance is greater than that of the steam-to-carbon ratio, and that excessive τ or S/C values will have no more positive effect on the performance of the catalyst. The stable active sites on the catalyst surface can guarantee the catalytic activity in the reaction. Ultimately, rice husk char-based catalysts can be used to remove tar and produce syngas.     

Parametric optimization and control for a smart Proton Exchange Membrane Water Electrolysis (PEMWE) system

Hydrogen production from Proton Exchange Membrane Water Electrolysis (PEMWE) system is attracting attention due to its ability to circumvent the effect of the intermittent nature of variable renewal energy. However, the relatively high operating temperatures of the PEMWE system exacerbates the degradation of polymer membranes in PEMWE system. This paper describes the development of an optimal thermal management strategy for a PEMWE system that can attenuate the long-term effects of high operating temperatures or rapid temperature changes on the polymer membranes. The thermal management strategy is tested on a laboratory scale smart PEMWE system. First, a high fidelity mathematical model of the smart PEMWE is developed and validated based on which the application of the PARameteric Optimization and Control (PAROC) framework results in the design of an explicit model predictive controller which is deployed into the laboratory PEMWE system. It is shown that the smart PEMWE prototype system empowered with the embedded control policy achieves effective temperature control across the electrolyzer maintaining the integrity of the membrane electrode assembly.     

海水温度对金鲳鱼保活过程中应激和代谢的影响

目的 低温休眠是鱼类保活运输中的关键技术之一，以金鲳鱼为对象，探讨海水温度对其保活过程中应激和代谢的影响，确定保活运输的重要温度参数。方法 对鱼体进行梯度降温使之休眠，在不同温度下进行保活，得出最佳保活温度，对保活过程中的各项指标进行测定。结果 在金鲳鱼保活过程中，鱼体代谢会使水体中氨氮总含量和pH值上升；金鲳鱼受低温胁迫会产生应激反应，血清的皮质醇含量上升，血糖含量下降，尿素氮和总胆固醇含量上升，乳酸脱氢酶活性稍有升高，谷草转氨酶活性显著升高，肌肉中糖原含量下降，乳酸含量上升；将金鲳鱼在(25±2)℃下暂养6 h后，梯度降温至13～14℃时金鲳鱼逐渐进入休眠状态，然后再移入15～17℃海水中进行保活；在15℃和17℃保活36 h存活率均为100%，保活48h存活率分别为83%和75%。结论 海水温度对金鲳鱼保活过程中应激和代谢具有重要影响，且为金鲳鱼的有水保活运输提供了理论指导和关键温度参数。