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A numerical model for air concentration distribution in self-aerated open channel flows

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Journal of Hydrodynamics 2015年第3期27卷 394-402页

作者：卫望汝邓军张法星田忠 State Key laboratory of hydraulics and Mountain River Engineering Sichuan University

The self-aeration in open channel flows, called white waters, is a phenomenon seen in spillways and steep chutes. The air distribution in the flow is always an important and fundamental issue. The present study develops a numerical model to predict the air concentration distribution in self-aerated open channel flows, by taking the air-water flow as consisting of a low flow region and an upper flow region. On the interface between the two regions, the air concentration is 0.5. In the low flow region where air concentration is lower than 0.5, air bubbles diffuse in the water flow by turbulent transport fluctuations, and in the upper region where air concentration is higher than 0.5, water droplets and free surface roughness diffuse in the air. The air concentration distributions obtained from the diffusion model are in good agreement with measured data both in the uniform equilibrium region and in the self-aerated developing region. It is demonstrated that the numerical model provides a reasonable description of the self-aeration region in open channel flows.

关键词： self-aeration air concentration open channel flows turbulence diffusion numerical model

Development of an aero-thermal coupled through-flow method for cooled turbines

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Science China(Technological Sciences) 2015年第12期58卷 2060-2071页

作者： GU ChunWei LI HaiBo SONG Yin Key laboratory for thermal Science and Power Engineering of Ministry of Education Department of Thermal EngineeringTsinghua University

The influence of complicated interaction between the flow field and heat transfer in cooled turbines becomes more and more significant with the increasing turbine inlet temperature. However, classical through-flow methods did not take into account the influence of the interaction caused by air cooling. The aerodynamic design and cooling design of cooled turbines were carried out separately, and the iterations between the aerodynamic design and cooling design led to a long design period and raised the design cost. To shorten the design period and decrease the design cost, this paper proposes a concise aero-thermal coupled through-flow method for the design of cooled turbines, taking into account the influence of the complicated interaction between the flow field and heat transfer in cooled turbines. The governing equations, such as energy equation and continuity equation in classical through-flow method are re-derived theoretically by considering the historical influence of cooling with the same method that deals with viscous losses in this paper. A cooling model is developed in this method. The cooled blade is split into a number of heat transfer elements, and the heat transfer is studied element by element along both the span and the chord in detail. This paper applies the method in the design of a two-stage axial turbine, of which the first stator is cooled with convective cooling. With the prescribed blade temperature limitation and the knowledge of the flow variables of the mainstream at the turbine inlet, such as the total pressure, total temperature and mass flow rate, the convergence of the calculation is then obtained and the properties of the flow field, velocity triangles and coolant requirement are well predicted. The calculated results prove that the aero-thermal coupled through-flow method is a reliable tool for flow analysis and coolant requirement prediction in the design of cooled turbines.

关键词： aero-thermal coupled through-flow method cooling model cooled turbines

Oxidation characteristics of boron particles

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Science China(Technological Sciences) 2015年第12期58卷 2016-2024页

作者： YU Dan KONG ChengDong ZHUO JianKun LI ShuiQing YAO Qiang Key laboratory for thermal Science and Power Engineering of Ministry of Education Department of Thermal EngineeringTsinghua University

The oxidation characteristics of boron particles, boron-A with the diameter of 2.545 μm and boron-B with the diameter of 10.638 μm, at low temperature（1500 K） have been investigated by thermogravimetry（TG） coupled with simultaneous differential scanning calorimetry（DSC）, infrared and mass spectra. A rapid oxidation stage of boron particles, followed by a slow oxidation stage of sintered particles, is found from the TG and DSC curves. The onset temperatures of the oxidation process of boron-A particles are in the range of 806–889 K, which are at least 105 K lower than those of boron-B at the same condition. As the partial pressure of oxygen increases from 5% to 35%, the onset temperature of boron-A or boron-B particles decreases. However, when the partial pressure of oxygen is above 35%, the onset temperature becomes constant, implying a saturation effect of oxygen on the reaction rate. It indicates that the chemical adsorption of oxygen, i.e. chemical reaction, on the particle surface is the rate-limited step at the beginning of the rapid oxidation stage. Therefore, the first-order chemical reaction model is used to simulate the oxidation of boron particles, even that of the sinter. The average activation energies of the particles are 291.3 kJ/mol for boron-A and 338.4 k J/mol for boron-B. While the average activation energies of the sintered particles are 36.35 k J/mol for boron-A and 31.87 kJ/mol for boron-B. The pre-exponential factor of the particles is -10^4, while that of the sinter is 10^-1. The oxidation rate constant of boron is qualitatively mainly affected by the specific surface of the sample and the thickness of the oxide layer.

关键词： boron particles oxidation activation energy saturation effect

An iterative virtual projection method to improve the reconstruction performance for ill-posed emission tomographic problems

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Chinese Physics B 2015年第10期24卷 200-212页

作者：柳华蔚郑树周怀春 Key laboratory for thermal Science and Power Engineering of Ministry of Education Department of Thermal EngineeringTsinghua University

In order to improve the reconstruction performance for ill-posed emission tomographic problems with limited projections, a generalized interpolation method is proposed in this paper, in which the virtual lines of projection are fabricated from, but not linearly dependent on, the measured projections. The method is called the virtual projection（VP） ***, an iterative correction method for the integral lengths is proposed to reduce the error brought about by the virtual lines of projection. The combination of the two methods is called the iterative virtual projection（IVP） method. Based on a scheme of equilateral triangle plane meshes and a six asymmetrically arranged detection system, numerical simulations and experimental verification are conducted. Simulation results obtained by using a non-negative linear least squares method,without any other constraints or regularization, demonstrate that the VP method can gradually reduce the reconstruction error and converges to the desired one by fabricating additional effective projections. When the mean square deviation of normal error superimposed on the simulated measured projections is smaller than 0.03, i.e., the signal-to-noise ratio（SNR）for the measured projections is higher than 30.4, the IVP method can further reduce the reconstruction error reached by the VP method apparently. In addition, as the regularization matrix in the Tikhonov regularization method is updated by an iterative correction process similar to the IVP method presented in this paper, or the Tikhonov regularization method is used in the IVP method, good improvement is achieved.

关键词： ill-posed problem emission tomography limited projections Tikhonov regularization

Regeneration behavior of tin oxide sorbent for warm syngas desulfurization

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Journal of Energy Chemistry 2018年第4期27卷 1231-1238页

作者： Yi Yang Yixiang Shi Ningsheng Cai Key laboratory for thermal Science and Power Engineering of Ministry of Education Department of Thermal Engineering Tsinghua University

The steam regeneration and SO2 regeneration of tin oxide for warm syngas desulfurization is studied in the temperature range of 400-600 ℃. In the steam regeneration, reversible removal of H2S achieved. Regenerated H2S concentration increased with the increasing regeneration temperature. SnO2 sorbent can achieve a complete regeneration by steam at 500 and 600 ℃. In the 502 regeneration, elemental sulfur was produced by the reaction of SnS and SO2. Raising the regeneration temperature （500-600 ℃） or SO2 concentration （1.5-10 vol%） improved the regeneration rate. Under SO2 regeneration at 500 ℃, SnS2 formed in the sorbent due to the interconversion of tin sulfides. Under steam regeneration or SO2 regeneration, the cyclic breakthrough sulfur capacity of SnO2 sorbent decreased because of the sintering caused by low melting component SnS. A two-stage regeneration process was applied to recover the elemental sulfur which achieved a complete regeneration.

关键词： SnO2 Regeneration Steam SO2 Tin sulfide Sintering

CO_2 Mitigation in Coal Gasification Cogeneration Systems with Integration of the Shift Reaction, CO_2 Absorption and Methanol Production

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Journal of thermal Science 2004年第3期13卷 193-198页

作者： Yuanyuan DUAN Jin ZHANG Key laboratory of thermal Science and Power Engineering, Department of thermal Engineering, Tsinghua University, Beijing 100084, China Key laboratory of thermal Science and Power Engineering Department of Thermal Engineering Tsinghua University Beijing China

Cogeneration of electricity and liquid fuel can achieve higher efficiencies than electricity generation alone in Integrated Gasification Combined Cycle (IGCC), and cogeneration systems are also expected to mitigate CO2 emissions. A proposed methanol-electricity cogeneration system was analyzed in this paper using exergy method to evaluate the specified system. A simple cogeneration scheme and a complicated scheme including the shift reaction and CO2 removal were compared. The results show that the complicated scheme consumes more energy, but has a higher methanol synthesis ratio with partial capture of *** those methanol and electricity cogeneration systems, the CO2 mitigation is not merely an additional process that consumes energy and reduces the overall efficiency, but is integrated into the methanol production.

关键词： cogeneration system methanol synthesis CO2 mitigation exergy analysis

Effect of temperature on the effective thermal conductivity of n-tetradecane-based nanofluids containing copper nanoparticles

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Particuology 2015年第5期13卷 95-99页

作者： Haifeng Jiang Qianghui Xu Chao Huang Lin Shi Key laboratory for thermal Science and Power Engineering of Ministry of Education Department of Thermal Engineering Tsinghua University

Nanofluids were prepared by dispersing Cu nanoparticles （-20nm） in n-tetradecane by a two-step method. The effective thermal conductivity was measured for various nanoparticle volume fractions （0.0001-0.02） and temperatures （306.22-452.66 K）. The experimental data compares well with the Jang and Choi model, The thermal conductivity enhancement was lower above 391.06 K than for that between 306,22 and 360,77 K, The interfacial thermal resistance increased with increasing temperature, The effective thermal conductivity enhancement was greater than that obtained with a more viscous fluid as the base media at 452,66 K because of nanoconvection induced by nanoparticle Brownian motion at high temoerature.

关键词： Nanofluid thermal conductivity High temperature Brownian motion

Flexible molecules dedicate to release strain of inverted inorganic perovskite solar cell

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Journal of Energy Chemistry 2025年第1期100卷 87-93页

作者： Hongrui Sun Sanlong Wang Pengyang Wang Yali Liu Shanshan Qi Biao Shi Ying Zhao Xiaodan Zhang Institute of Photoelectronic Thin Film Devices and Technology Renewable Energy Conversion and Storage Center State Key Laboratory of Photovoltaic Materials and CellsNankai University Key laboratory of Photoelectronic Thin Film Devices and Technology of Tianjin Haihe laboratory of Sustainable Chemical Transformations Engineering Research Center of Thin Film Photoelectronic Technology of Ministry of Education Collaborative Innovation Center of Chemical Science and Engineering (Tianjin)

The tensile strain in inorganic perovskite films induced by thermal annealing is one of the primary factors contributing to the inefficiency and instability of inorganic perovskite solar cells （IPSCs）,which reduces the defect formation ***,a flexible molecule 5-maleimidovaleric acid （5-MVA） was introduced as a strain buffer to release the residual strain of *** anhydride and carboxyl groups in 5-MVA interact strongly with the uncoordinated Pb2+through Lewis acid-base reaction,thus tightly“pull”the perovskite *** in-between soft carbon chain increased the structural flexibility of CsPbI2.85Br0.15perovskite materials,which effectively relieved the intrinsic internal strain of CsPbI2.85Br0.15,resisted the corrosion of external strain,and also reduced the formation of defects such as VIand *** addition,the introduction of 5-MVA improved crystal quality,passivated residual defects,and narrowed energy level ***,power conversion efficiency （PCE） of NiOxbased inverted IPSCs increased from 19.25% to 20.82% with the open-circuit voltage enhanced from 1.164 V to 1.230 *** release of strain also improved the stability of CsPbI2.85Br0.15perovskite films and devices.

关键词： Inverted inorganic perovskite solar cells Flexible molecules Strain release Crystallization Energy barrier High PCE

Erosion pattern of artificial gravel deposits

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International Journal of Sediment Research 2018年第1期33卷 57-67页

作者： Fabian Friedl Volker Weitbrecht Robert M.Boes laboratory of hydraulics Hydrology and Glaciology (VAW)ETH Zurich

Sediment replenishment with artificial gravel deposits is an option to compensate for sediment deficits in rivers and to improve their ecological conditions. Predicting and quantifying the erosion rate of an artificial gravel deposit is important to successfully perform river restoration projects. laboratory experiments have been done to investigate the influence of various parameters on the erosion pattern of artificial gravel deposits. In the present paper the effects of deposit geometry, bulk density, grain size distribution, and hydraulic load on the erosion process are described. The temporal evolution of the deposit geometry and the corresponding mean erosion rates were studied. The mean erosion rate increases with deposit height, deposit width, and decreasing grain size. Furthermore, no significant impact of the bulk density was observed. Equations to predict the mean erosion rate are proposed. This investigation helps to determine the design frequency of gravel dumping and deposit volumes for restoration projects.

关键词： Artificial gravel deposits Bed load transport laboratory experiments Sediment replenishment