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71.
基于核磁共振技术的岩石孔隙结构冻融损伤试验研究 总被引:6,自引:1,他引:6
为研究岩石在冻融循环作用下的孔隙结构损伤特性,选取寒区花岗岩为岩样,在冻结温度为-40 ℃,融解温度为20 ℃条件下,分别进行3轮冻融循环试验,并对每轮冻融循环后的岩样进行核磁共振(NMR)测量,得到同一块岩样不同冻融循环次数后的孔隙度、横向弛豫时间T2分布及核磁共振图像(NMRI)。结果表明:花岗岩的T2分布主要为3个峰,随着冻融循环次数的增多,岩石的孔隙度、核磁共振T2谱分布和T2谱面积均会增大,但每个岩样的增大幅度均不同,反映出冻融循环作用下岩石中孔隙的发育和扩展特性;核磁共振图像显示同一块岩样在不同冻融循环次数后的内部微观结构分布,动态地显示岩石的冻融损伤过程。冻融循环条件下岩石核磁共振特征为岩石冻融损伤机制研究提供可靠的试验数据。 相似文献
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总结了钠基膨润土防水毯(GCL)的防渗机理,从膨润土质量特性、渗透液水质、干湿循环、冻融循环等方面对GCL防渗性能及服务期稳定性的影响因素进行了论述,希望对改善防水毯性能研究提供参考。 相似文献
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本科研训练是一种很好的实践教育手段,越来越多的高校利用科研训练提高本科生的综合素质.本文通过具体的例子介绍了我校本科生科研训练的实施情况,包括选题、训练内容和训练效果等方面.每个科研训练项目均经历了查阅资料、方案设计、方案评审和方案实施等过程,结果表明本科科研训练可以很好地培养学生的创新能力,提高学生分析问题和解决问题的能力,为学生研究生阶段的学习和工作打下了良好的基础. 相似文献
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The primary mode of deactivation of automotive emission control catalysts is thermal aging, and it is well-known that high-temperature lean aging conditions are particularly detrimental. Since evaluating the long-term durability of automotive catalysts is costly and time-consuming, rapid catalyst aging cycles have been developed to mimic (in a reduced time) the catalyst deactivation under real-world driving conditions. One of the commonly used rapid catalyst aging tests is an exothermal aging cycle, which involves a combination of fuel-rich engine operation and supplemental air injection to generate high-temperature lean conditions within the catalyst bed. In this work, we use the previously developed transient three-way catalyst model to investigate the time evolution of the axial temperature profiles and exhaust air–fuel ratio (A/F) along the catalyst bed during the course of the exothermal rapid aging cycles. We find that the thermal front propagates downstream through the catalyst bed relatively slowly (compared to the concentration front) and this can limit the location within the catalyst bed and duration for high-temperature lean exposure. We also investigate how variations of some of the key system design and operating parameters can affect the extent and duration of high-temperature lean exposure. Finally, a simple analytical expression is developed which allows one to estimate the time it takes for the thermal front to travel through the catalyst bed. This time can be compared with the period of the lean A/F operation during the aging cycle to determine the location and duration of high-temperature lean exposure. 相似文献
79.
In this paper, the problem of optimal sizing of a series PHEV is studied by formulating a convex program that minimizes the sum of operational and component costs. The solution gives the optimal sizes of the main powertrain components, simultaneously with the vehicle's optimal energy management. Investigations are performed on driving cycles generated stochastically from real data using Markov chains, with different driving distance distributions and charging patterns. The results show that the optimal component sizing is affected more from the driving distances between charging opportunities, than the speed profile of the driving. With anticipated future battery and petroleum prices, larger battery sizes are obtained. 相似文献
80.
A study about the performance of Pt(0.3 wt%)Sn(0.3 wt%) catalysts supported on different materials in n-butane dehydrogenation is reported in this paper. The materials used as supports were γ-Al2O3, ZnAl2O4 spinel, MgAl2O4 spinel and spheres of α-Al2O3 with a washcoating of γ-Al2O3. The syntheses of both spinels leaded to very pure ZnAl2O4 and MgAl2O4 supports. The material prepared by washcoating showed the presence of an uniform and homogeneous layer of γ-Al2O3 (with a thickness between 12 and 18 μm) deposited on the spheres of α-Al2O3.The best behavior in activity, selectivity and stability through five severe cycles was achieved by bimetallic PtSn catalysts supported on MgAl2O4 spinel and on the material prepared by washcoating. The very good performance of these catalysts through the different cycles of reaction-regeneration can be due to the presence of metallic phases which preserve the strong intermetallic interaction along the different treatments, thus avoiding segregation processes. 相似文献