During hypothetical accidents of sodium-cooled fast reactors, such as unprotected loss of flow, transient power surge accidents, unprotected thermal trap accidents, etc., sodium boiling may occur. A series of boiling ...
详细信息
During hypothetical accidents of sodium-cooled fast reactors, such as unprotected loss of flow, transient power surge accidents, unprotected thermal trap accidents, etc., sodium boiling may occur. A series of boiling incipient phenomena for liquid sodium flow in an annular channel were investigated experimentally. The boiling incipience signal in different experimental conditions were analyzed through the Discrete Wavelet Transform (DWT). The various differential pressure signals in the process of boiling incipience were collected by a differential pressure transducer installed on the effective heating section. The experiment was performed in the heat flux range of 128-846 kW/m(2), mass flow rate range of 7.2-122.0 kg/h, system pressure range of 0.85-28.79 kPa and inlet subcooling range of 63.1-287 degrees C. Since these correlations of predicting the boiling incipience for water in different channels are not suitable for the boiling incipience of liquid sodium, a semi-empirical correlation for the prediction of boiling incipience is obtained in the present study. The prediction error of the new semi-empirical correlation for experimental data is basically within +/- 30% in this paper. This work provides a meaningful liquid sodium boiling incipience prediction method.
Distinguishing the contributions from localized surface plasmon resonance (LSPR)induced photothermal effect is a significant challenge in the study of solar hydrogen production. Herein, a well-defined one-dimensional ...
详细信息
Distinguishing the contributions from localized surface plasmon resonance (LSPR)induced photothermal effect is a significant challenge in the study of solar hydrogen production. Herein, a well-defined one-dimensional Cu/TiO(2)heterostructure with Cu size of 3-6 nm is designed to address such issue. Cu nanoparticles present notable LSPR absorption from visible to near-infrared light, while no hydrogen is produced in the presence of simulated light with lambda >= 700 nm. Interestingly, a remarkable improvement of hydrogen evolution under full-spectrum light was observed which is almost twice of that under only ultraviolet-visible light irradiation, implying the critical yet auxiliary role of LSPR-induced photothermal effect in promoting photocatalytic performance. Significantly, a notable reduction of the apparent activation energy and strengthened charge separation efficiency are observed due to the increased local temperature of catalyst surface caused by the plasmon-induced photothermal effect. The kinetic and thermodynamic changes should be responsible for the enhanced hydrogen production.
An analytical model for the prediction of the onset of dryout quality in annular flow regime in helically coiled tubes is present in this paper. According to the liquid film dryout mechanism, film dryout is primarily ...
详细信息
An analytical model for the prediction of the onset of dryout quality in annular flow regime in helically coiled tubes is present in this paper. According to the liquid film dryout mechanism, film dryout is primarily dependent on the competition between droplet entrainment and deposition with a certain heat flux. To this effect, it is necessary to define the net entrainment rate in the helical tube. The factors significantly affecting the droplet entrainment and deposition characteristics in the helical tube are analyzed theoretically. Three dimensionless numbers are used to modify the net entrainment rate in straight tube. A total of 252 experimental points from 6 different datasets are used to test the performance of the model. Comparisons between the calculated and experimental results in literatures indicate that the present model has good predictive capability in predicting onset of dryout in helically coiled tubes. (C) 2017 Elsevier Ltd. All rights reserved.
Poor rate performance limits the application of high-areal-loading electrodes in energy storage, and optimizing the microstructure of the cathode is considered as a way to improve this limitation. In this study, we in...
Poor rate performance limits the application of high-areal-loading electrodes in energy storage, and optimizing the microstructure of the cathode is considered as a way to improve this limitation. In this study, we integrated X-ray computed tomography (XCT) with digital technology (virtual electrodes and microstructure-based numerical simulations) to quantify the correlation between electrode structure and internal kinetic performance of lithium-ion electrodes. Results show that electrode structure alters the internal kinetic properties, thereby affecting rate capacity and nominal potential. Based on the parametric relationship between electrode structure and electrochemical-thermal properties, we explored the effects of structural regulation on electrode performance. Vertical channels significantly enhanced the rate capability and ohmic heating rate of small-particle electrodes, while solid-phase diffusion (SPD) dominated the discharge performance of large-particle electrodes, exhibiting low sensitivity to tortuous strategies. Furthermore, electrodes with abundant SPD barriers exhibit unidirectional propagation of reaction fronts, resulting in a deeper SPD-limited region. This observation inspired the integration of two structural strategies that favor both mass transport and reaction penetration. Optimized electrode structures enhanced energy density at high rates and accommodated diverse particle sizes and thicknesses. Additionally, the coupling effect of the heat transfer environment on electrode performance was investigated. This study presents a novel paradigm for bottom-up electrode design using microstructure-resolved model, providing both microscopic mechanisms and quantitative insights for advanced battery development.
Accurate design of air-cooled condensers using inclined flat tubes requires a reliable method for determining heat transfer and pressure drop in the downflow and upflow sections. This paper presents experimental study...
详细信息
Accurate design of air-cooled condensers using inclined flat tubes requires a reliable method for determining heat transfer and pressure drop in the downflow and upflow sections. This paper presents experimental study of downflow and upflow condensation in an inclined flat tube under vacuum. Experimental results and analysis confirm that the heat transfer mechanism underlying the condensation in an inclined flat tube with a large flatter cross section is the same as for downflow condensation on a vertical plate under gravity influence. The characteristics of two-phase pressure drop in an inclined flat tube are also similar for downflow condensation inside a circular tube. Upflow reflux condensation has a better heat transfer performance compared to downflow condensation due to the opposite vapor and condensate flow, thus enhancing heat transfer on the vapor-liquid interface. Using experimental data, the empirical constants in the Nusselt model and the Chisholm two-phase frictional multiplier in the Lockhart-Martinelli pressure drop model were modified. Comparisons show that the modified Nusselt correlation predicts heat transfer data within +/- 15% and pressure drop predictions can be achieved within +/- 30% for the majority of experimental data. This study provides an alternate approach for design and optimization of air-cooled condensers with inclined flat tubes.
Flue gas recirculation (FGR), which is widely adopted to control the steam temperature of ultra-supercritical (USC) double-reheat boiler, significantly affects the temperature distribution, NOx generation, and flue ga...
详细信息
Flue gas recirculation (FGR), which is widely adopted to control the steam temperature of ultra-supercritical (USC) double-reheat boiler, significantly affects the temperature distribution, NOx generation, and flue gas temperature deviation in furnace. This study presents a numerical study on the combustion process in a 1000MW tower-type double-reheat boiler with deep-air-staging. The effect of FGR injection position on the temperature distribution, NOx emission, and gas temperature deviation was studied and discussed under 100% boiler maximum continuous rating (BMCR), 75% turbine heat acceptance (THA), and 50% THA loads. The numerical model was validated by the in-house thermal calculation code and design parameters provided by the boiler manufacturer. The results show that, under the same load, when recirculating flue gas (RFG) is injected into the furnace from the nozzle blow the burner, the burner zone temperature is lower but the NO generation is higher than the case in which RFG is injected from the nozzle above the burner. Compared to the former, NOx emission of the latter reduced by 12.3%, 31.2%, and 33.8% under 100% BMCR, 75% THA, and 50% THA load, respectively. Both the inlet flue gas temperature and the heat flux of the primary superheater decrease when RFG was introduced from the nozzle above the burner. The case in which RFG is injected from the nozzle above the burner was found to be an applicable and effective method to control the NO generation and regulate the steam temperature of the double-reheat boiler.
The erosion-corrosion behavior poses a significant threat to marine equipment, driven by complex multi-physics processes such as sand movement, surface erosion, electrochemical reactions, and corrosive ion transport. ...
详细信息
The erosion-corrosion behavior poses a significant threat to marine equipment, driven by complex multi-physics processes such as sand movement, surface erosion, electrochemical reactions, and corrosive ion transport. Aiming at the widely used rotating liquid-solid two-phase flow system in a marine environment, this study investigates the role of flow velocity in the erosion-corrosion behavior of Ni2FeCrMo0.2 alloy. The coupling analysis of multi-component weight loss, electrochemical kinetics, and microstructure characterization clarifies the interactions between fluid flow, sand migration, ion transfer, and damage morphology, revealing the synergistic erosion-corrosion mechanism. The results show that the erosion-corrosion mechanism transfers with flow velocity. At low velocities, the erosion effect on the harder metal matrix is weak due to insufficient kinetic energy of the sand particles. However, the sand-surface impingement on the softer corrosion products and the mass transfer of corrosive ions lead to erosion-enhanced corrosion, which dominates the material damage process. In contrast, at higher velocities, the impact kinetic energy and frequency of sand particles rise, causing the erosion rate to increase exponentially, which surpasses corrosion, making erosion as the dominant damage mechanism at high velocities. These results highlight the critical role of flow velocity in controlling the erosion-corrosion synergy behavior.
This article presents a 3D numerical investigation on ferrofluid droplet motion in magnetic field using VOSET. A nonuniform magnetic field mimicking the one produced by an electric wire loop was generated in a finite ...
详细信息
This article presents a 3D numerical investigation on ferrofluid droplet motion in magnetic field using VOSET. A nonuniform magnetic field mimicking the one produced by an electric wire loop was generated in a finite computational domain. A validation problem on droplet deformation in uniform magnetic field was first studied, and it gives consistent aspect ratios with reported experiments. The simulation revealed an entire process of the ferrofluid droplet movement, and the influences by the intensity of the magnetic field was investigated and analyzed. Finally, a set of simulations were conducted for net magnetic force on spherical droplet, and the achieved data led to a correlation, which gives accurate prediction in the magnitude of the magnetic force and can be applied to droplet with a certain degree of deformation.
The coupling modes of dyes with corresponding supports play key roles in the performance of dye-sensitized heterogeneous photocatalytic systems. Herein, a solvothermal method was developed to synthesize a typical kind...
详细信息
The coupling modes of dyes with corresponding supports play key roles in the performance of dye-sensitized heterogeneous photocatalytic systems. Herein, a solvothermal method was developed to synthesize a typical kind of dye-sensitized metal-organic frameworks (MOFs), Eosin Y (EY)-sensitized UiO-66-NH2, in which EY was anchored on UiO-66-NH2 via the bidentately bridging configuration of Zn <- O-C=O -> Zr. Such a coupling mode of chemical bonding strengthened the linking between EY and UiO-66-NH2, increased the content of EY on UiO-66-NH2, and facilitated the transfer of photogenerated electrons from EY to UiO-66-NH2. Correspondingly, the H-2 evolution rate of EY-sensitized UiO-66-NH2 via solvothermal treatment (2760 mu mol g(-1) h(-1)) was 8 times as that via room-temperature sensitization, with apparent quantum efficiency (AQE) -17.6 % at 500 nm. The as-obtained AQE and excellent stability performance exceeds most dye-sensitized photocatalytic systems for H-2 production. This work provides valuable information about developing dye-based or MOFs-based materials for efficient photocatalytic application.
暂无评论