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Theoretical and Experimental Analysis of Heat Transfer and Condensation in Micro-Ribbed Tubes

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Fluid Dynamics & Materials Processing 2023年第6期19卷 1411-1424页

作者： Daoming Shen Jinhong Xia Chao Gui songtao xue Xinxiang University Xinxiang453000China Department of Architecture Tohoku Institute of TechnologySendai982-8577Japan

The thermal transmission coefficient for a micro-ribbed tube has been determined using theoretical relationships and the outcomes of such calculations have been compared with experiments conducted using a R1234yf refrigerant undergoing condensation.In particular four theoretical single-phase flow and three multi-phase flow models have been used in this regard.The experimental results show that:the Oliver et al.criterion equation overestimates the experimental results as its accuracy is significantly affected by the specific conditions realized inside micro-fin tubes;the Miyara et al.criterion equation prediction error is less than 15%;the Cavallini et al.approach gives the highest prediction accuracy;the Goto et al.model overestimates the test data.Such results are critically discussed and some indications for the improvement of such models are provided.

关键词： Micro-ribbed tube flow condensation thermal transmission coefficient dimensionless criterion equation

Peridynamics versus XFEM:a comparative study for quasistatic crack problems

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Frontiers of Structural and Civil Engineering 2018年第4期12卷 548-557页

作者： Jinhai ZHAO Hesheng TANG songtao xue Research Institute of Structural Engineering and Disaster Reduction Tongji UniversityShanghai 200092China State Key Laboratory of Disaster Prevention in Civil Engineering Tongji UniversityShanghai 200092China

Peridynamics (PD) is a nonlocal continuum theory based on integro-differential equations without spatial derivatives. The fracture criterion is implicitly incorporated in the PD theory and fracture is a natural outcome of the simulation. However, capturing of complex mixed-mode crack patterns has been proven to be difficult with PD. On the other hand, the extended finite element method (XFEM) is one of the most popular methods for fracture which allows crack propagation with minimal remeshing. It requires a fracture criterion which is independent of the underlying discretization though a certain refinement is needed in order to obtain suitable results. This article presents a comparative study between XFEM and PD. Therefore, two examples are studied. The first example is crack propagation in a double notched specimen under uniaxial tension with different crack spacings in loading direction. The second example is the specimens with two center cracks. The results show that PD as well as XFEM are well suited to capture this type of behaviour.

关键词： XFEM peridynamic bilateral crack parallel double cracks nonlocal theory

A new fracture criterion for peridynamic and dual-horizon peridynamics

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Frontiers of Structural and Civil Engineering 2018年第4期12卷 629-641页

A new fracture criterion based on the crack opening displacement for peridynamic (PD) and dual-horizon peridynamics (DH-PD) is proposed. When the relative deformation of the PD bond between the particles reaches the critical crack tip opening displacement of the fracture mechanics, we assume that the bond force vanishes. A new damage rule similar to the local damage rule in conventional PD is introduced to simulate fracture. The new formulation is developed for a linear elastic solid though the extension to nonlinear materials is straightforward. The performance of the new fracture criterion is demonstrated by four examples, i.e. a bilateral crack problem, double parallel crack, monoclinic crack and the double inclined crack. The results are compared to experimental data and the results obtained by other computational methods.

关键词： Castigliano’s theorem breaking energy critical extension XFEM COD PD-COD

Experimental Analysis of the Performances of Unit Refrigeration Systems Based on Parallel Compressors with Consideration of the Volumetric and Isentropic Efficiency

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Fluid Dynamics & Materials Processing 2020年第3期16卷 489-500页

作者： Daoming Shen Chao Gui Jinhong Xia songtao xue College of Civil Engineering and Architecture Xinxiang UniversityXinxiang453000China Research Institute of Structural Engineering and Disaster Reduction Tongji UniversityShanghai20092China Department of Architecture Tohoku Institute of TechnologySendai982-8577Japan

The performances of a refrigeration unit relying on compressors working in parallel have been investigated considering the influence of the compressor volumetric efficiency and isentropic efficiency on the compression ratio.Moreover,the following influential factors have been taken into account:evaporation temperature,condensation temperature and compressor suction-exhaust pressure ratio for different opening conditions of the compressor.The following quantities have been selected as the unit performance measurement indicators:refrigeration capacity,energy efficiency ratio(COP),compressor power consumption,and refrigerant flow rate.The experimental results indicate that the system refrigeration capacity and COP decrease with a decrease in evaporation temperature,increase of condensation temperature,and increase in pressure ratio.The refrigerant flow rate increases with the increase in evaporation temperature,decrease in condensing temperature and increase in pressure ratio.The compressor power consumption increases with the increase in condensing temperature and increase in pressure ratio,but is not significantly affected by the evaporation temperature.

关键词： Parallel compressor unit evaporation temperature condensation temperature pressure ratio refrigeration capacity energy efficiency ratio(COP)

Heat Transfer Enhancement Using R1234yf Refrigerants in Micro-Ribbed Tubes in a Two-Phase Flow Regime

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Fluid Dynamics & Materials Processing 2020年第6期16卷 192-205页

作者： Daoming Shen Xia Zhang Wei He Jinhong Xia songtao xue School of Civil Engineering&Architecture Xinxiang UniversityXinxiangChina Department of Architecture Tohoku Institute of TechnologySendai982-8577Japan

Experiments about heat transfer in the presence of a two-phase flow due to the condensation of a R1234yf refrigerant have been performed considering a smooth tube and two micro-fin tubes.The following experimental conditions have been considered:Condensation temperatures of 40℃,43℃ and 45℃,mass fluxes of 500–900 kg/(m^(2)·s),vapor qualities at the inlet and outlet of the heat transfer tube in the ranges 0.8–0.9 and 0.2–0.3,respectively.These tests have shown that:(1)The heat transfer coefficient increases with decreasing the condensation temperature and on increasing the mass flux;(2)The heat transfer coefficient inside the micro-fin tube is larger than that for the smooth tube;(3)The heat transfer enhancement factors for the micro-fin tube with a fin helical angle of 8°and 15°are 2.51–2.89 and 3.11–3.57,respectively;both are higher than the area increase ratio.These experimental results have been compared with correlations available in the literature:the Cavallini et al.correlation has the highest accuracy in predicting the heat transfer coefficient inside the smooth tube,the related percentage error and the average prediction error are±8%and 0.56%,respectively;for the micro-fin tube these become±25%and 6%,respectively.

关键词： R1234yf micro-ribbed tube heat transfer coefficient heat transfer enhancement factor

X形软钢阻尼器延性断裂的试验研究与数值模拟

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建筑结构 2024年第7期54卷 59-63,71页

作者：谢丽宇仝运佳薛松涛李林王兵同济大学结构防灾减灾工程系上海200092 日本东北工业大学工学部仙台982-8577

为了研究X形软钢阻尼器在大变形状态下的耗能性能和损伤演化规律,设计了6组试件进行单向和循环荷载作用下延性断裂的试验研究,分析了软钢阻尼器的破坏过程和滞回曲线。采用Lemaitre-Chaboche混合强化模型,分别对各工况下包含与不包含基... 详细信息

为了研究X形软钢阻尼器在大变形状态下的耗能性能和损伤演化规律,设计了6组试件进行单向和循环荷载作用下延性断裂的试验研究,分析了软钢阻尼器的破坏过程和滞回曲线。采用Lemaitre-Chaboche混合强化模型,分别对各工况下包含与不包含基于应力三轴度的钢材微观损伤模型的软钢阻尼器进行了精细的有限元模拟。对比有限元模拟结果和试验结果,分析结果表明,颈部为X形耗能软钢阻尼器的薄弱位置,最容易发生集中损伤甚至破坏。考虑钢材损伤准则的有限元模拟的荷载-位移曲线与试验结果更加吻合,能够表征软钢阻尼器的承载力与刚度退化现象,并能较为准确地预测软钢阻尼器的损伤演化过程和断裂破坏位置。

关键词： X形软钢阻尼器应力三轴度损伤模型延性断裂承载力退化

Numerical investigation of the seismic response of a UHV composite bypass switch retrofitted with wire rope isolators

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Earthquake Engineering and Engineering Vibration 2021年第1期20卷 275-290页

作者： Yang Zhenyu Xie Qiang He Chang xue songtao Department of Civil Engineering Tongji UniversityShanghai 200092China

An ultra-high voltage(UHV)composite bypass switch(BPS)faces increasing seismic challenges when UHV projects extend to high seismic intensity areas.The UHV composite BPS still generates excessive stress at the bottom section although hollow composite insulators with high flexural strength are adopted.Since the standard retrofitting strategy by using stiffer supports cannot reduce stress responses,wire rope isolation is introduced.The optimal design of isolation considers both stress and displacement responses since the slenderness and composite material of insulators contribute to significant displacement.The results show that properly designed isolation can significantly reduce stress without excessive displacement responses.A larger radius configuration helps to improve the applicability of small stiffness isolators under high winds.When the isolation still cannot satisfy the requirement,smaller stiffness isolators with a larger radius,or isolators with increased loops and smaller radius,can be introduced to gain better energy dissipation capacity and effectiveness in response mitigation.Accordingly,a three-step design procedure is proposed to increase the damping force but fix the rotational stiffness of isolation.Hence,the application of wire rope isolation can be extended to UHV composite BPS with a low natural frequency,but conductors with enough redundancy should be used.

关键词： UHV composite bypass switch seismic analysis seismic performance upgrading wire rope isolator

Evidence Theory for Uncertainty Quantification of Portal Frames with Semi-rigid Connections

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Evidence Theory for Uncertainty Quantification of Portal Fra...

双向地震作用下拉索支撑惯容系统及其在钢结构中的应用

2012 International Conference of Health,Structure,Material and Environment(HSME 2012)

作者： Hesheng Tang Jiao Wang Yu Su songtao xue Research Institute of Structural Engineering and Disaster Reduction Tongji University State Key Laboratory of Disaster Prevention in Civil Engineering Tongji University Department of Architecture Tohoku Institute of Technology

The buckling load or the equivalent buckling length factor of the portal frame structures is greatly influenced by stiffness of bracing elements and semi-rigid connections.In engineering the problem p

关键词： Portal frame Semi-rigid connection Evidence theory Differential evolution Uncertainty semirigid connection Evidence Theory Gabled frames buckling load Uncertainty

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建筑结构学报 2023年第3期44卷 11-19页

作者：康建飞薛松涛谢丽宇同济大学结构防灾减灾工程系上海200092 日本东北工业大学建筑系仙台982-8577

近年来,惯容系统作为一种高效被动减震系统被广泛关注,其中拉索支撑惯容系统得益于跨层便利,经济优势显著。为研究双向地震动作用下拉索支撑惯容系统的减震性能,提出了一种拉索支撑惯容系统的双向减震设计方法并给出了实用设计流程。采... 详细信息

近年来,惯容系统作为一种高效被动减震系统被广泛关注,其中拉索支撑惯容系统得益于跨层便利,经济优势显著。为研究双向地震动作用下拉索支撑惯容系统的减震性能,提出了一种拉索支撑惯容系统的双向减震设计方法并给出了实用设计流程。采用杠杆机制模拟拉索支撑的转向特性,基于各元件的拓扑组合模拟惯容系统,在OpenSees中实现了拉索支撑惯容系统的有限元模型的建立。利用场地实测地震动数据对安装有跨层型拉索支撑惯容系统的一栋实际钢结构的双向减震性能进行了评估。有限元计算结果表明,所建立的拉索支撑惯容系统有限元模型可以很好地表达其位移传递效率及惯容元件特性;依据等效参数进行设计的拉索支撑惯容系统具有良好的双向减震性能及显著的阻尼增效性能,可用于实际拉索支撑惯容系统的钢结构设计。

关键词：拉索支撑惯容系统钢结构双向地震动 OpenSees 减震性能