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  • 2019 Volume 39 Issue 6
    Published: 15 June 2019
      
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  • Design and Optimization of Variable Radius Fillets Based on the Control of Secondary Flow
    ZHANG Xuyang, CHEN Liu, DAI Ren
    2019, 39(6): 433-440.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    Based on the simulation results of Langston cascade, an analysis was conducted on the flow characteristics in the cascade with uniform fillets of different radius, so as to comprehensively evaluate the effects of fillet radius on the flow characteristics in different positions of cascade, and to design and optimize the structure of the variable radius fillet. Results show that with the rise of corner radius in the leading edge of cascade, the diversion capacity increases, and the intensity of horseshoe vortex reduces in the leading edge. The adoption of large radius fillet in the lower side of cascade would intensify the secondary flow and increase the outlet loss of cascade. The intensity of both the horseshoe vortex and the passage vortex could be suppressed by using variable radius fillet, when the increase of the total pressure loss coefficient is inhibited along the flow direction, the entropy increase rate decreases and the flow effectiveness improves.
  • Effect of Volumetric Radiative Heating on the Temperature Field of TBCs in a TBC-Film Cooling System
    JIANG Lingxin, JIANG Jishen, WANG Weizhe
    2019, 39(6): 441-446.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    The temperature field of thermal barrier coatings (TBCs) was predicted by fluid-structure interaction method, and the volumetric radiative heating process was simulated using discrete ordinate (DO) radiation model. Meanwhile, studies were conducted on the effects of volumetric radiative heat transfer on the temperature field of TBCs in the TBC-film cooling system, as well as on the effects of cooling hole structure and ceramic top coating (TC) thickness over the volumetric radiative heat transfer behavior. Results reveal that the temperature of TBCs is significantly increased by volumetric radiative heating; cooling hole structure intensifies the influence of volumetric radiative heating on the temperature field of TBCs at cooling hole edges; the increase of TC thickness could not effectively reduce the effects of volumetric radiative heating on the temperature field of TBCs.
  • Modelling and Calculations for the Reaction and Heat-transfer Processes in a High-temperature Aluminium Water Reactor
    SHI Wei, HU Yi, CHEN Zhisha, CHEN Chao, YANG Weijuan, LIU Jianzhong
    2019, 39(6): 447-453.
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    To analyze the thermal characteristics of a typical high-temperature molten aluminum water reactor, physical and mathematic models were established, while program algorithm and coupling algorithm were designed for the water evaporation, reaction and heat-transfer processes, with simulation software compiled using Visual Basic language. The software was then used to simulate the key operating parameters of the reactor. Results show that the reaction water flow is positively correlated with the wall maximum temperature of the system, while the cooling water flow is negatively correlated with the wall maximum temperature. The calculated results are proved to be in good agreement with the experimental data.
  • Numerical Analysis on Flow Characteristics Around the Tube in a Spiral Channel with Rectangular Cross Section
    CHEN Guidong, WANG Qiuwang
    2019, 39(6): 454-460.
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    Using Fluent software and numerical calculation method, a hybrid calculation model was established to study the heat-transfer characteristics of fluid flow around the heat-exchange tube in a spiral channel and a straight channel, and to compare the thermal characteristics of fluid flow around a heat-exchange tube in above two channels. Results show that the inner detachment angle of spiral channel is smaller than outer detachment angle, and the detachment points are distributed in the turbulent region. The Num of spiral channel is higher than that of straight channel; in the case of β=15° and 20°, compared with straight channel heat-exchange tube, the Num of spiral channel heat-exchange tube is respectively 4.0% and 4.5% higher on the windward side, and 14% and 18% higher on the leeward side. Around β=40°, the heat-transfer performance is maximally enhanced for the tube in spiral channel, when the tube wall Num is increased by 19%, compared with the straight channel.
  • Experimental Research on Simultaneous Removal of SO2 and NOx by a Spray-and-Bubbling Scattered Reactor Based on Ozone Pre-oxidation
    YAN Xuenan, WANG Chunbo, SI Tong, CHEN Shilei, REN Yujie, HU Jian
    2019, 39(6): 461-467.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    Experimental tests were conducted on the simultaneous removal of SO2 and NOx by a spray-and-bubbling scattered reactor based on ozone pre-oxidation, while the effects of following factors on the removal efficiency were investigated, such as the molar ratio of O3 to NO, the initial volume fraction of SO2, the liquid-gas volume ratio and the immersion depth, etc. Results show that the removal efficiency of both SO2 and NOx by a spray-and-bubbling scattered reactor is higher than that by single spray or single bubbling method. With the rise of O3-NO molar ratio and initial SO2 volume fraction, the denitrification efficiency increases continuously, while the desulfurization efficiency basically keeps unchanged. The removal efficiency increases with the rise of liquid-gas volume ratio and bubbling pipe immersion depth. Compared with the conditions of single spray at larger liquid-gas volume ratios, higher removal efficiency could be obtained by the spray-and-bubbling scattered reactor at smaller liquid-gas volume ratios. Compared with the conditions of single bubbling at larger immersion depths, higher removal efficiency could be achieved by the spray-and-bubbling scattered reactor at smaller immersion depths.
  • A Novel Cascade Mechanism Simulation Model for SCR Systems of Thermal Power Plants
    XIAO Yunqi, HE Tong
    2019, 39(6): 468-473.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    Aiming at the difficulties in modeling the simulation model for selective catalytic reduction (SCR) systems of thermal power plants, a novel cascaded modeling method was proposed. Furthermore, a model parameter identification method was designed based on the particle swarm optimization to identify the parameters of related kinetic equations, such as the gas adsorption and desorption, NO consumption rate and NH3 oxidation rate, etc., taking account of the following two key objectives:the NOx concentration at SCR outlet and the ammonia escape rate. The method proposed was then verified by modeling the SCR system of a 600 MW power plant. Results show that the proposed method is able to solve the matching problem between the simulation model and the simulation step size, which therefore may serve as a reference for overall design and optimization of the controller for ammonia injection systems.
  • Emission and Conversion Characteristics of NO and SO2 from Co-firing of Algae Biomass and Coal
    HE Xiaoming, ZHAO Bingtao
    2019, 39(6): 474-477.
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    To explore the emission and conversion characteristics of NO and SO2 from co-firing of algae biomass and coal, a series of co-firing tests were conducted by blending the Huating coal with algae biomass in different ratios. Results show that the co-firing of coal and algae biomass could effectively reduce the emission of typical pollutants. Compared with burning pure coal, the NO conversion rate in burning the coal mixture containing 25% and 50% algae biomass could be accordingly reduced by 4.37% and 44.49%, while the SO2 conversion rate reduced by 32.16% and 53.81%, respectively.
  • Numerical Simulation on Aerodynamic Characteristics of the Split Airfoil for Horizontal Axis Wind Turbines
    ZHOU Wei, YE Zhou, WANG Zhihong, LI Chun
    2019, 39(6): 478-485.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    To improve the wind energy utilization of a horizontal axis wind turbine, taking the NREL S809 airfoil as a reference, the effects of relative position and relative width of split airfoil slot on following characteristics of the airfoil were studied, such as the flow field structure, aerodynamic performance, and lift and drag characteristics, etc. Results show that the split airfoil slot would affect the development and variation of vortices around the airfoil, which can not only improve the stall characteristics of the airfoil, but also enhance its aerodynamic performance. When the relative position and relative width of slot are relatively 40/90 and 1.0%, the lift coefficient of split airfoil would reach the maximum, which would be increased by 10.797%, compared with the original airfoil, with better splitting effect obtained in improving the aerodynamic performance of the airfoil.
  • Numerical Analysis on the Aerodynamic Characteristics of a Wind Turbine with Different Winglets
    HU Danmei, WU Zhixiang, ZHANG Kaihua, ZHANG Zhiwei
    2019, 39(6): 486-491.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    A study was conducted on the aerodynamic characteristics and flow field distribution of a wind turbine with plane or fusion winglets, so as to analyze the effects of different winglets on the power of the wind turbine under rated conditions, the surface pressure of the blade and the flow field distribution in the tip region, etc. Numerical simulation results show that the power of a wind turbine could be increased by adding tip winglets. The wind turbine with fusion winglets has better aerodynamic characteristics, and its power could be increased by 10.61%, compared with that without winglets. The presence of tip winglet reduces the pressure on suction surface of blade in tip region and increases the pressure differential on blade surface. Fusion winglet produces larger pressure difference on blade surface, compared with plane winglet. In addition, the tip winglet could weaken the flow intensity of tip vortex, reduce the local induction velocity, improve the aerodynamic angle of attack, and makes the core position of tip vortex move to the place far away from the blade, which therefore reduces the adverse effect of the tip vortex.
  • Factors Influencing the Energy Consumption and Operation Economy of a Multi-stage Air Compressor in a Cryogenic Air Separation System for Oxy-fuel Combustion
    GAO Daming, CHEN Hongwei, YANG Jianmeng, GU Junjie
    2019, 39(6): 492-497.
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    Based on R-K state equation, the theoretical air compression work and outlet air temperature in the adiabatic steady-flow compression process of a compressor were calculated by deviation function method, so as to establish calculation models for the energy consumption in air compression process and the exhaust heat release in inter-stage cooling process of the multi-stage air compressor. Based on exergy analysis method, calculation models were also set up to quantitatively analyze the physical exergy loss in air compression process, the heat exergy loss in exhaust cooling process and the exergy efficiency of the multi-stage air compressor. On above basis, an analysis was conducted on the energy consumption and operation economy of the multi-stage air compressor influenced by the volume fraction of the oxygen produced and the variation of the air temperature at outlet of the inter-coolers in oxygen production process. Results show that the energy consumption and operation economy of the cryogenic air separation system could be reduced by properly reducing the volume fraction of the oxygen produced and by choosing relatively low air temperature at outlet of the inter-coolers.
  • Study on Microstructure Aging Behavior of T91 Reheater Tubes After Long-term Services
    ZHANG Zuogui, WAN Haibo, WANG Yanfeng
    2019, 39(6): 498-503.
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    The microstructure aging behavior of T91 reheater tubes in a domestic 350 MW subcritical power unit after long-term services for 120 000 h was investigated by optical microscopy (OM), scanning electron microscope (SEM), electron backscattered diffraction (EBSD) and transmission electron microscope (TEM), while a comparison was made on the microstructure and properties of the original and the long-term serviced T91 steel. Results show that after long-term services for 120 000 h, the M23C6 carbide particles gather and grow at the grain boundary, with the particle size growing from original 107.8 nm to123.8 nm. Meanwhile, new Laves phase precipitates and gets coarsened at the grain boundary, with the Mo element precipitated from the matrix, making the content of Cr and Mo elements reduce in ferrite matrix, thus weakening the solid solution strengthening effect of T91 steel.
  • Study on Steam Oxidation Resistance of Al-based and Ni-Cr-based Coatings
    MA Yunhai
    2019, 39(6): 504-511.
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    The steam oxidation resistance of Al-based and Ni-Cr-based coatings over T91 base metal was investigated at 600℃/27 MPa for 1 300 h using scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) to analyze the surface morphology, cross-section morphology, microstructure and chemical composition of the oxide films. Results show that the oxidation resistance of above coatings is significantly higher than T91 base metal, and that of Al-based coating is better than Ni-Cr-based one. In the process of steam oxidation, a continuous dense layer of aluminum rich oxides with a certain amount of chromium oxide and silicon oxide form on the surface of Al-based coating, while a (Ni,Cr)-rich oxide layer forms on the Ni-Cr-based coating.
  • Oil Whirl Vibration Analysis for Thrust Bearings of Large Nuclear Steam Turbines
    SHI Qingfeng
    2019, 39(6): 512-516.
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    Aiming at the coupling phenomenon of axial vibration with radial vibration existing in some nuclear steam turbines, a mechanism analysis was conducted on the self-excited vibration caused by oil whirl based on the model of thrust bearing tilting pad for large nuclear power turbo-generator sets. By establishing a dynamic equation for rotor axial shifting, and through the measurement of thrust bearing load in start-up process of a 650 MW nuclear power unit, the stiffness and damping of the oil film were calculated under different conditions of axial load and thrust bearing clearance ratio. Meanwhile, the characteristic frequency of rotor axial vibration caused by the oil film instability was analyzed. Results show that the axial load, rotary speed and oil film damping are the main factors leading to the self-excited vibration of the thrust bearing tilting pad. The axial low-frequency vibration of the turbine rotor could be inhibited by reducing the thrust bearing clearance and increasing the lubricating oil pressure.