γ射线法测量高压管束间气液两相流的截面含气率分布

在立式蒸汽发生器垂直管束间的气液两相流中，截面含气率是其中一个重要参数。使用γ射线法对高温高压下垂直管束间气液两相流截面含气率的分布规律进行了实验研究。实验压力分别为5、7、9 MPa，质量流速为300 kg/(m²?s)，热力学干度的范围为0.003 ~ 0.4。实验得到了垂直管束间截面含气率随热力学干度、体积含气率和压力的变化关系；并与经典公式的计算结果对比发现，在低干度区域，实验结果与Miropolskii模型、Smith模型和Armand模型偏差较大，均大于30%，在高干度区域偏差较小；基于Armand理论，通过多元线性回归法拟合出本文工况下平均截面含气率的计算关联式，与日本核动力工程公司(NUPEC)的实验数据偏差小于15%。本研究对蒸汽发生器的结构设计和流动特性研究具有重要意义。     

5×5棒束通道内流动转捩特性研究

棒束通道的特殊结构导致其内部流动转捩情况较为复杂，探究其内部流动转捩规律具有重要意义。本文针对棒束通道内的流动转捩特性开展实验与CFD模拟研究，通过实验获得了棒束通道内沿程阻力系数的变化规律；采用不同湍流模型进行了数值模拟。结果表明，SST k-ω模型能较好地反映实验结果。进一步对比了不同雷诺数工况下通道内不同位置的沿程阻力系数与湍流强度，发现对于不同子通道，中心子通道湍流强度与沿程阻力系数高于边角子通道；对于同一子通道，子通道中心处湍流强度与壁面切应力高于子通道边缘处。这一结果说明，受壁面影响，棒束内湍流强度、壁面切应力、阻力特性具有不均匀性，这些空间上的不均匀性相互作用会引起总体上棒束转捩点不明显。     

Evaluation of a large dish‐type concentrator solar lighting system for underground car park

To utilize solar energy more efficiently and reduce lighting power consumption in underground public spaces such as car park, a large dish‐type concentrator solar lighting system is put forward along with its evaluation, which is a unique design to apply a laminated layer of beam split thin‐film coating and thin‐film solar cells onto the dish reflector. The collected sunlight is split into 2 parts, one being reflected into a fiber optical bundle and transmitted for daylighting, while the rest being absorbed by solar cells for electricity generation as the other way to replenish daylighting. A set of 4 solar lighting systems using 3.28‐m diameter dish are designed to meet the lighting requirement in a 1771‐m² underground car park. A mathematical model is adopted to calculate the output power and conversion efficiency of solar cells distributed on the parabolic dish surface. The indoor illuminance distribution is given by lighting simulation. The results indicate that the average daylight illuminance in the car park can vary between 62.7 and 284 lx on February 25, 2016 and between 62.7 and 353 lx on August 17, 2016 for 2 chosen days, respectively. For the presented design, the electricity produced by solar cells is just enough to power light‐emitting diodes for lighting meeting a criterion at night. Considering about 19% conversion efficiency of solar cells and the efficacy of 129.5 lm/W of light‐emitting diodes, the hybrid solar lighting system can have about 40% utilization ratio of solar energy, so it can be concluded that a sufficient lighting provision can be provided by the proposed large dish‐type concentrator solar lighting system for applications in underground car park.     

Probing Protein Folding with Sequence-Reversed α-Helical Bundles

Recurrent protein folding motifs include various types of helical bundles formed by α-helices that supercoil around each other. While specific patterns of amino acid residues (heptad repeats) characterize the highly versatile folding motif of four-α-helical bundles, the significance of the polypeptide chain directionality is not sufficiently understood, although it determines sequence patterns, helical dipoles, and other parameters for the folding and oligomerization processes of bundles. To investigate directionality aspects in sequence-structure relationships, we reversed the amino acid sequences of two well-characterized, highly regular four-α-helical bundle proteins and studied the folding, oligomerization, and structural properties of the retro-proteins, using Circular Dichroism Spectroscopy (CD), Size Exclusion Chromatography combined with Multi-Angle Laser Light Scattering (SEC-MALS), and Small Angle X-ray Scattering (SAXS). The comparison of the parent proteins with their retro-counterparts reveals that while the α-helical character of the parents is affected to varying degrees by sequence reversal, the folding states, oligomerization propensities, structural stabilities, and shapes of the new molecules strongly depend on the characteristics of the heptad repeat patterns. The highest similarities between parent and retro-proteins are associated with the presence of uninterrupted heptad patterns in helical bundles sequences.     

Numerical study of thermal-hydraulic and dust-deposition of tube bundles in an intermediate heat exchanger

Very-high-temperature gas-cooled reactors (VHTRs) are promising for efficient, zero-carbon hydrogen production. The intermediate heat exchanger (IHX) is a key piece of equipment for VHTR-coupled hydrogen production. Constrained by the limited space within the VHTR, the IHX must be efficient and compact. Besides, radioactive graphite dust deposition will reduce the performance and reliability of IHXs. Therefore, understanding the thermal-hydraulic and dust-deposition characteristics of IHX tube bundles is crucial for the design and safe operation of IHXs. This study uses the unsteady k-kl-ω model to simulate flow and heat transfer in IHX tube bundles. The discrete particle model combined with a deposition model is used to predict the movement and deposition behavior of graphite dust. The deposition model is achieved using user-defined functions. The model and code are first validated by empirical correlations and experimental results. The transient flow fields show that, in the in-line arrangement, unsteady and asymmetric periodic flow occurs with a period of about 0.047 s. The flow is steadier and more symmetric in the staggered arrangement due to the restriction of the main flow to the separation vortices. The maximum circumferential heat-transfer coefficient for inner tubes occurs at the impact point, where the central angle θ is about 60° and 0° for the in-line and staggered arrangement, respectively. The graphite-dust deposition rate decreases with increasing Reynolds number and particle size and the deposition mechanism is also analyzed in detail. With the current design conditions, the Nusselt number of the staggered arrangement increases by 27.90%–29.17% compared with the in-line arrangement, and the deposition rate decreases by 1.52%–3.15%. Furthermore, new correlations for Nusselt number and friction factor are developed for the thermal-hydraulic design of IHX tube bundles.     

GPS用于单航线航空摄影测量加密的可行性研究

精度是表征平差系统各未知数求解质量的绝对数字指标之一，本文采用一组带ＧＰＳ导航数据的实际航摄资料，通过平差计算出精度矩阵Ｑｘｘ的数值，然后分析了单航线ＧＰＳ辅助光束法平差的质量。在此基础上，经与区域网ＧＰＳ辅助光束法平差的精度相比较，对ＧＰＳ用于单航线航空摄影测量加密的可行性进行了探讨并提出了相应的作业方法。     

煤矿岩巷束状孔掏槽爆破掘进试验研究

国内煤矿井下岩巷掘进以传统钻爆法施工为主,其效率低,难以适应煤矿强化开采的需要,研究提高钻爆法的掘进效率对于煤矿生产具有重要意义。影响掘进效率的关键因素是炮眼深度和掏槽爆破效果,本文从增加炮眼深度和改善掏槽效果的角度出发,设计采用束状中深孔掏槽方式,在发挥中深孔掏槽优势的同时,利用束状孔最优埋深条件下的当量球形漏斗,实现炮孔的充分利用,改善掏槽效果,从而提高掘进循环进尺和效率。试验表明,与传统浅孔楔形掏槽相比,束状中深孔掏槽爆破掘进每炮循环进尺提高了45%,效果显著。     

尼龙束捻度对水泥砂浆界面粘结的影响

通过织物拔出试验、抗折强度试验和扫描电镜对水泥基体微观破坏形貌的分析，研究了织物中尼龙束捻度对其增韧水泥砂浆界面粘结的影响。研究结果表明：存在着1个尼龙束捻度范围，在该范围内，捻度的增加有助于复合材料的界面粘结，且界面粘结强度随之提高；超出这一范围，捻度的增加反而不利于复合材料的界面粘结，界面粘结强度随之下降。     

水平管束冷凝换热设计计算问题讨论

针对大型水平管束冷凝换热设计计算,对水平管束膜状冷凝换热系数典型公式进行了对比分析;结合管束结构及冷凝液膜流动行为,阐明了相关公式的适用条件、计算结果差异及原因。然后通过工程实例计算对比和壳程蒸汽流动模拟进一步表明,现有相关公式因未能充分考虑冷凝加热器中蒸汽流动的多方向性及其对冷凝液膜的扰动,其换热系数计算值明显低于实际;并针对大型水平管束冷凝换热工程计算模型的完善,对进一步的研究工作提出了建议。     

超高分辨率石英光纤传像束

石英光纤传像束在医疗诊断、工业设备探伤、电力设施监测、大视场成像等领域具有重要应用。本文利用溶胶-凝胶法在像元单丝间隙中引入吸收剂,解决了传像束光串扰难题。采用一次复丝工艺,制备出外径为600 μm、像元为15 000的石英光纤传像束,像元单丝直径约4.4 μm,分辨率约为113 lp/mm。结果表明,传像束无暗丝、断丝,成像清晰,无畸变,达到了商品化使用需求。