Free surface vortex, especially in a pattern of full air core vortex, causes serious security problems in the residual heat removal system. Vortex in a T-junction pipe system was numerically investigated under the pre...
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Free surface vortex, especially in a pattern of full air core vortex, causes serious security problems in the residual heat removal system. Vortex in a T-junction pipe system was numerically investigated under the premise that the simulation results are in agreement with the experimental results. First, four typical states were obtained in the formation and evolution process of vortex, namely, surface dimple, critical submergence state, air entrainment vortex state, and large air entrainment state. With increasing Froude (Fr) number, the time from an initiate flow field to the critical submergence state decreased, and the time interval between critical submergence state and large air entrainment state increased. Finally, the variation law of vortex intensity was analyzed during the evolution process. The vortex intensity initially increased with time and reached its maximum value and then decreased until it reached a minimum value before the large air entrainment state. With the increase of Fr, the maximum values of vortex intensity gradually increased.
In this paper, the water droplet erosion (WDE) performance of a typical martensitic blade material 17-4 PH (0Cr17Ni4Cu4Nb), surface strengthened laser cladding stellite and brazed stellite alloy is studied based on hi...
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In this paper, the water droplet erosion (WDE) performance of a typical martensitic blade material 17-4 PH (0Cr17Ni4Cu4Nb), surface strengthened laser cladding stellite and brazed stellite alloy is studied based on high-speed water jet test system. The WDE resistances from high to low are the brazed stellite alloy, laser cladding stellite alloy and 17-4 PH. For the same material, the greater the initial roughness of the target surface, the more severe is the WDE damage. Improving the surface finish of the target is conducive to the diversion and expansion of the liquid flow, prolonging the incubation period, and thus enhancing the WDE resistance.
The condensation induced water hammer (CIWH) phenomenon may cause serious damage to the pipes and related system, which often occurs during the steam-water direct contact condensation process. In this paper, an experi...
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The condensation induced water hammer (CIWH) phenomenon may cause serious damage to the pipes and related system, which often occurs during the steam-water direct contact condensation process. In this paper, an experimental investigation was performed to study CIWH phenomenon caused by steam-water direct contact condensation in a horizontal pipe. The entire CIWH process was captured by a high speed video camera and its pressure fluctuation was synchronously measured. Four typical flow patterns were observed during CIWH process: stratification flow, wave flow, slug flow and bubble collapse. Bubble collapse would generate a high pressure peak. Based on different variations of steam-water phase interface and pressure fluctuation signals, three types of CIWH were defined: non-periodic CIWH, periodic CIWH and no CIWH. A CIWH region map was given considering the effect of steam mass flux and water temperature. In periodic CIWH region, the generation frequency of CIWH was found to range from 0.19 Hz to 0.39 Hz, which decreased with the rise of steam mass flux and water temperature. A dimensionless correlation was obtained to predict Strouhal number of CIWH generation frequency. Predicted values corresponded well to the experimental data with the deviation in the range of -16% to +23%.
This paper focuses on the dynamic modeling of the cold end system of a thermal power plant and its operation optimization during cycling load processes. A revised logarithm mean temperature difference is recommended t...
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This paper focuses on the dynamic modeling of the cold end system of a thermal power plant and its operation optimization during cycling load processes. A revised logarithm mean temperature difference is recommended to calculate the heat transfer quantity between exhaust steam and condenser tubes. With this method, a condenser model is developed with a maximum relative error limited within 3%. Coupled with a turbo-generator, a condenser, water pumps, and a cooling tower, a closed cooling system model is established. The total power supply (TPS) during cycling load is calculated and analyzed to optimize the operation during transient processes. A method for obtaining the maximum value of TPS is provided and used to calculate the optimal operating load rate points for switching pumps (OPSP). OPSP increases with the cycling load rate (V-e) during loading up processes decreases with V-e during loading down processes. When V-e is identical, OPSP declines with the ambient temperature for the loading up and down processes. TPS during transient processes is relevant with the switching pump load rate. The maximum value of difference in TPS with different switching pump periods is 691.4 (kW h) for switching pump numbers from 3 to 2 during loading down processes. (C) 2017 Elsevier Ltd. All rights reserved.
Integrated porous/dense/porous tri-layer BaZr0.8Y0.2O3-delta (BZY) electrolyte asymmetrical matrices were designed for protonic ceramic membrane fuel cells (PCMFCs) and fabricated by multilayer tape-casting and solid-...
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Integrated porous/dense/porous tri-layer BaZr0.8Y0.2O3-delta (BZY) electrolyte asymmetrical matrices were designed for protonic ceramic membrane fuel cells (PCMFCs) and fabricated by multilayer tape-casting and solid-state reactive sintering. The effects of pore-former, sintering aid and sintering program on the microstructure of integrated electrolyte matrices (IEMs) were studied. Graphite and NiO were appropriate pore-former and sintering aid, respectively, and an accelerated heating program was more desirable. The conductivities of the IEM with designed microstructure in different atmospheres were measured by AC impedance spectroscopy at 400-600 degrees C. The highest conductivity of 6.9 x 10(-3) S cm(-1) at 600 degrees C was obtained in wet air atmosphere, and the corresponding activation energy was 0.602 eV. Gas-tightness of the IEM was confirmed by a stable open circuit voltage (OCV) of 0.97 V at 600 degrees C from a button fuel cell with impregnated NiO anode and BaCo0.4Fe0.4Zr0.1Y0.1O3-delta (BCFZY) cathode. These indicate that the fabricated BZY-based IEM has great potential for PCMFC application. (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
The thermal hydraulic and neutronics coupling analysis is an important part of the high-fidelity simulation for nuclear reactor core. In this paper, a thermal hydraulic and neutronics coupling method was proposed for ...
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The thermal hydraulic and neutronics coupling analysis is an important part of the high-fidelity simulation for nuclear reactor core. In this paper, a thermal hydraulic and neutronics coupling method was proposed for the plate type fuel reactor core based on the Fluent and Monte Carlo code. The coupling interface module was developed using the User Defined Function (UDF) in Fluent. The three-dimensional thermal hydraulic model and reactor core physics model were established using Fluent and Monte Carlo code for a typical plate type fuel assembly, respectively. Then, the thermal hydraulic and neutronics coupling analysis was performed using the developed coupling code. The simulation results with coupling and noncoupling analysis methods were compared to demonstrate the feasibility of coupling code, and it shows that the accuracy of the proposed coupling method is higher than that of the traditional method. Finally, the fuel assembly blockage accident was studied based on the coupling code. Under the inlet 30% blocked conditions, the maximum coolant temperature would increase around 20 degrees C, while the maximum fuel temperature rises about 30 degrees C. The developed coupling method provides an effective way for the plate type fuel reactor core high-fidelity analysis.
Signals of pressure fluctuation and local solids holdup were measured from different axial locations in a 70 mm x 70 mm, 4.424 m-high circulating fluidised bed with sand particles and white carbon black particles. The...
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Signals of pressure fluctuation and local solids holdup were measured from different axial locations in a 70 mm x 70 mm, 4.424 m-high circulating fluidised bed with sand particles and white carbon black particles. The original signals were decomposed into multiscale signals based on multi-resolution analysis of wavelet transformation. A new fractal method was used to classify the different scales into three categories through the similarity of the trend on the energy ratio in different scales and the veracity of this method have been discussed. Through this method, the microscales, mesoscales and macroscales were identified and the frequencies of different categories were obtained, which was 15.6-500 hz, 0.5 (or 1) -15.6 hz, below 0.5 (or 1) hz respectively, the characteristics of different categories were further discussed and signals of pressure fluctuation and local solids holdup were analysed to comprehensively understand fluidised bed dynamics. Meanwhile, we research the relationship between statistical analysis and multiscale analysis in a circulating fluidised bed. As for pressure fluctuation signals, the average value is mainly affected by individual particles and clusters, the standard deviation is mainly affected by clusters or the background fluctuation of the entire system, which is dependent on the characteristic of fluidised particles. As for local solids holdup signals, the average value is mainly affected by clusters, the standard deviation is greatly affected by clusters at a relatively low gas velocity and influenced significantly by the individual particles when the gas velocity is relatively high. (C) 2018 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.
flow and heat transfer of supercritical water in the vertical helically-coiled tube were investigated numerically using RNG k-epsilon model. The inner side of the coil was heated by constant heat flux and the outer si...
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flow and heat transfer of supercritical water in the vertical helically-coiled tube were investigated numerically using RNG k-epsilon model. The inner side of the coil was heated by constant heat flux and the outer side was adiabatic. Heat transfer performance under half-side heating is obtained and compared with that under uniform heating at the same heat transfer rate. Effect of specific heat, secondary flow velocity and buoyancy are discussed. The decrease of specific heat in the near-wall region, and the attenuated turbulence caused by the strong buoyancy force lead to a decrease in heat transfer for half-side heating. The deviations of heat transfer correlations on predicting half-side heating condition are evaluated, and a new heat transfer correlation for supercritical water in the vertical helically-coiled tube under inner half-side heating is proposed. The investigation into different statistical parameters shows that it is superior to the existing correlations.
Diminishing fossil fuel resources have intensified the need for energy saving. Heat transfer is a basic method of energy delivery and convention, and heat transfer during the transient processes may be affected by the...
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Diminishing fossil fuel resources have intensified the need for energy saving. Heat transfer is a basic method of energy delivery and convention, and heat transfer during the transient processes may be affected by the dynamic performances of heaters. Analysis of the heater performances during the transient process based on the second law of thermodynamics may show the room for the improvement in energy saving. Variations of boundaries, such as the flow rates and temperatures of the work fluids, may affect the dynamic behaviors of heaters. The variation rates, formats and ranges of the inlet work fluids flow rates and temperatures on the irreversibility and exergy delivery characteristics are discussed in this paper. The average exergy efficiency (eta(E,avg)) of the heater during the transient process with different operational parameters are presented and compared. The results show that, in the identical variation range, the maximum difference in eta(E,avg) with different flow rates and temperature variation rates of the cold work fluid are 0.3% and 0.4%, respectively. With step variation format, the maximum difference in eta(E,avg) for the different variation ranges of the cold work fluid is 0.85%. (C) 2018 Elsevier Ltd. All rights reserved.
Waste heat recovery from boiler exhaust flue-gas is an effective way to save energy in coal-fired power plants. The integration of a low-pressure economizer (LPE) is a conventional choice for waste heat recovery. In t...
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Waste heat recovery from boiler exhaust flue-gas is an effective way to save energy in coal-fired power plants. The integration of a low-pressure economizer (LPE) is a conventional choice for waste heat recovery. In this study, thermodynamic analyses of a coal-fired power plant (CFPP) integrated with an LPE is conducted on a 600 MW CFPP as reference case. Standard coal consumption rate (SCCR) of the power plant could be decreased by 1.76 g.(kW h)(-1) by the LPE. Exergetic analysis reveals that significant irreversibility is exhibited by the air pre-heater (APH) of the waste heat recovery system with an LPE. Guided by the exergetic analysis of the conventional waste heat recovery system, a new conceptual system for waste heat recovery integrated with an S-CO2 cycle for CFPPs is designed in this study. In this novel system, the boiler flue-gas is split into two flows: one to heat air in APH, and another to drive an S-CO2 power cycle as the heat source. Parameters of the S-CO2 power cycle are thermodynamically optimized with the help of Genetic Algorithm. Optimal initial pressure and pressure ratio are 9.136 MPa and 5.84, respectively. Maximum cycle efficiency of the S-CO2 power cycle is 17.39%. With the optimal parameters, SCCR of the CFPP integrated with the S-CO2 power cycle decreases by 3.80 g.(kW h)(-1). If the LPE is further integrated, the reduction of SCCR can reach 5.19 g.(kW h)-1. The essential reason for the significant energy saving is revealed through exergetic analysis. Exergy losses and destructions also decrease significantly in the novel waste heat recovery system. Finally, the economic performance of the proposed system is evaluated. Results show that the novel waste heat recovery system is economically suitable, and that capital investment could be recycled in 3.067 years.
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