基于机器学习的螺旋流动过冷沸腾CHF预测研究

过冷沸腾广泛应用于以国际热核聚变实验堆（ITER）为代表的高热流冷却场合。本文聚焦高热流、螺旋流动条件下水的过冷沸腾临界热流密度（CHF）的预测方法,建立了该类工况下的过冷沸腾CHF实验数据库。选用了4种典型机器学习模型：反向传播（BP）神经网络、遗传算法( GA )-BP神经网络、 径向基函数（RBF）神经网络和极限学习机（ELM）;利用传统的经验关联式和新兴的机器学习方法对螺旋流动过冷沸腾CHF进行预测研究。经与实验数据库对比,结果表明,相关机器学习模型能够有效预测螺旋流动过冷沸腾CHF,其预测性能相较于传统的经验关联式有大幅提升,其中ELM模型预测效果最优,平均绝对误差和均方根误差分别为2.79%和4.22%。研究成果为高热流螺旋流动过冷沸腾CHF的准确预测提供了新途径。     

Critical heat flux in a two-phase thermosyphon: Relationship between maximum falling liquid rate and instability on interface of falling liquid

Critical heat flux in a two-phase thermosyphon is usually dealt with in one of two different ways: one uses the maximum falling liquid rate obtained from the envelope method, the other uses the instability. We first clarify the difference between the maximum and the instability criteria. The CHF in the thermosyphon is shown to be well predicted by the maximum liquid rate obtained using the maximum criterion and this prediction is better than that using the instability criterion. This comparison implies that CHF phenomenon in a thermosyphon is caused by the falling liquid reaching a maximum value rather than by instability of the falling liquid on the interface. © 1998 Scripta Technica. Heat Trans Jpn Res, 26(6): 372–384, 1997     

Wettability of heated surfaces under pool boiling using surfactant solutions and nano-fluids

The wettability of the heated surface under pool boiling of surfactant solutions and nano-fluids has been investigated. Tri-sodium phosphate (TSP, Na₃PO₄) solutions (0.01, 0.05, 0.1, 0.3, 0.5, 0.8 wt.%) and Aluminum oxide (Al₂O₃) nano-fluids (NF) (0.5, 1, 2, 4 vol.%) were prepared for experiments. Stainless steel (SUS 304) strips (30 × 30 × 3 mm) were heated by an alcohol lamp and quenched in the prepared solutions. Before complete quenching, when the surface temperature was 150 ± 10 °C (nucleate boiling region), the strip was taken out and excessive liquid on the surface was removed. Contact angles of pure water and the solutions on the quenched surface and fresh surface were measured. Contact angles of pure water on the quenched surfaces (5°–25°) were much smaller than those on the fresh surface (65°–70°). The solutions (TSP, NF) on the quenched surface shows the smallest contact angle (5°–15°). Surfaces deposited TSP and nano-particle could affect surface energy of the strips and enhance hydrophilicity of the surfaces. Several implications of the experimental results on the pool boiling CHF model and CHF enhancement using TSP and NF were discussed.     

Clad-to-Coolant Heat Transfer in NSRR Experiments

The evolution of the clad temperature during a Reactivity Initiated Accident plays a key role in the accidental sequence because it strongly influences the rod mechanical resistance against failure. The present study aimed at quantifying the heat transfer in NSRR experiments. Transient boiling curves were determined by inverse conduction calculations of NSRR experiments in which the clad outer surface temperature had been measured by spot-welded thermocouples. Critical Heat Fluxes (CHFs) as high as 13 MW/m² have been obtained, highlighting a considerable increase compared to stationary pool boiling conditions. The elevated CHFs are due to the intense transient fluid vaporization at the surface induced by a fast clad heating rate. A transient boiling model has been implemented in the SCANAIR code on the basis of the physical interpretation of the boiling curves. A good agreement between computed and experimental clad temperatures is obtained for high burnup fuel tests as for fresh fuel tests.     

The effect of fouling on nucleate pool boiling of small wires

Pool boiling experiments with small diameter wires were conducted in earth gravity and microgravity conditions. Bare wire and fouled wire with a scale deposition of calcium carbonate was used. The wettability on the scale wire was higher than that on the bare wire. Though more vigorous bubbling was observed on the scale wire when compared to that on the bare wire at the same heat flux, the boiling curve for the scale wire was approximately the same as that on the bare wire. However, the critical heat flux (CHF) on the scale wire was higher than that of the bare wire. On the scale wire, the departure diameter of bubbles was relatively smaller than that on the bare wire. The smaller diameter of bubbles detaching from the scale wire is considered to be due to the high wettability and high nucleation site density. As the result, the coalescence of bubbles near the wire was prevented, and the CHF was delayed and increased on the scale wire when compared to that on the bare wire. © 2004 Wiley Periodicals, Inc. Heat Trans Asian Res, 33(5): 316–329, 2004; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20016     

高低热导率相间表面强化饱和池沸腾的格子玻尔兹曼模拟

采用格子玻尔兹曼方法模拟高低热导率相间表面的饱和池沸腾过程,研究不同表面高低热导率区域热导率比值、低热导率区域宽度和深度对沸腾换热性能的影响。对比均匀热导率表面与高低热导率相间表面的沸腾曲线发现：高低热导率相间表面的沸腾过程可被分为5个阶段,并且其临界热流密度最高可达均匀表面的12倍;高低热导率相间可促使表面维持一定的温度差异,从而保持明显的气液流动;随着低热导率区域宽度增大,气液分离更加明显,低热导率区域宽度存在一个最优值,其与毛细长度的量级接近;随着低热导率区域的深度增大,表面过热度的差异更加明显。     

平板滞止区过冷水喷流沸腾临界热流密度实验研究

对高温平板滞止区内过冷水圆形喷流冲击沸腾的临界热流密度进行了系统的稳态实验研究。考察了水过冷度、流速、喷流直径等流动条件对喷流沸腾临界热流密度的影响。建立了一个预示临界热流密度的经验型方程。研究结果证明,过冷水喷流冲击沸腾的临界热流密度取决于过冷度、滞止冲击速度及喷流直径、过冷度的影响尤为强烈。经验式能较好的预示本实验和他人结果。     

Poly(lactide‐co‐glycolide) solution behavior in supercritical CO2, CHF3, and CHClF2

Cloud point and solution density data between 20 and 100°C and pressures to 3000 bar are presented for poly(lactide) (PLA) and poly(lactide‐co‐glycolide) (PLGA_x, where the molar concentration of glycolide in the backbone x ranges from 0 to 50 mol %) in supercritical CO₂, CHClF₂, and CHF₃. PLA dissolves in CO₂ at pressures near 1400 bar, in CHF₃ at pressures of 500 to 750 bar, and in CHClF₂ at pressures of 20–100 bar. As glycolide (GA) is added to the backbone of PLGA, the cloud point pressure increases by 50 bar/(mol GA) in CO₂, 25 bar/(mol GA) in CHF₃, and by only 2.5 bar/(mol GA) in CHClF₂. PLGA₅₀ does not dissolve in CO₂ to pressures of 3000 bar whereas it is readily soluble in CHClF₂ at pressures as low as 100 bar at 50°C. In comparison, the increases in cloud point pressure with increasing weight average molecular weight (M_w) are only approximately 2.3 bar/(1000 M_w) for PLGA copolymers in CO₂. The solution densities with all three SCF solvents range from 1.1 to 1.5 g/cm³ and they vary only by a small amount over the 80°C range used to obtain cloud point data. More than likely, the ability of the acidic hydrogen in CHF₃ and CHClF₂ to complex with the ester linkage in PLGA makes these better solvents than CO₂ especially since any change in favorable energetic interactions is magnified due to the liquid‐like densities exhibited by these SCF solvents. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 1155–1161, 2001     

CF3I气相催化合成机理研究

CHF3分别进行了空管裂解及活性炭催化裂解,并对反应后的活性炭进行XPS分析。实验结果表明：CHF3在催化剂作用下热解生成CF2卡宾,并在活性炭表面形成稳定结合,为CF3I气相催化合成的CF2卡宾机理提供了有力证据。     

Sensitivity analysis of the MASLWR helical coil steam generator using TRACE

Accurate simulation of transient system behavior of a nuclear power plant is the goal of systems code calculations, and the evaluation of a code's calculation accuracy is accomplished by assessment and validation against appropriate system data. These system data may be developed either from a running system prototype or from a scaled model test facility, and characterize the thermal hydraulic phenomena during both steady state and transient conditions. The identification and characterization of the relevant thermal hydraulic phenomena, and the assessment and validation of thermal hydraulic systems codes, has been the objective of multiple international research programs. The validation and assessment of the best estimate thermal hydraulic system code TRACE against the Multi-Application Small Light-Water Reactor (MASLWR) Natural Circulation (NC), helical coil Steam Generator (SG), Nuclear Steam Supply System (NSSS) design is a novel effort, and is the topic of the present paper. Specifically, the current work relates to the assessment and validation process of TRACE code against the NC database developed in the OSU-MASLWR test facility. This facility was constructed at Oregon State University under a U.S. Department of Energy grant in order to examine the NC phenomena of importance to the MASLWR reactor design, which includes an integrated helical coil SG. Test series have been conducted at this facility in order to assess the behavior of the MASLWR concept in both normal and transient operation and to assess the passive safety systems under transient conditions. In particular the test OSU-MASLWR-002 investigated the primary system flow rates and secondary side steam superheat, used to control the facility, for a variety of core power levels and Feed Water (FW) flow rates. This paper illustrates a preliminary analysis, performed by TRACE code, aiming at the evaluation of the code capability in predicting NC phenomena and heat exchange from primary to secondary side by helical SG in superheated condition and to evaluate the fidelity of various methods to model the OSU-MASLWR SG in TRACE. The analyses of the calculated data show that the phenomena of interest of the OSU-MASLWR-002 test are predicted by the code and that one of the reasons of the instability of the superheat condition of the fluid at the outlet of the SG is the equivalent SG model used to simulate the different group of helical coils. The SNAP animation model capability is used to show a direct visualization of selected calculated data.