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Effect of Flow Directions on Multiphase Flow Boiling Heat Transfer Enhanced by Suspending Particles in a Circulating Evaporation System 预览
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作者 Feng Jiang Teng Jiang +1 位作者 Guopeng Qi Xiulun Li 《天津大学学报:英文版》 EI CAS 2019年第3期201-213,共13页
A circulating fluidized bed evaporator(including down-flow,horizontal,and up-flow beds) was constructed to study the effect of flow directions on multiphase flow boiling heat transfer.A range of experimental investiga... A circulating fluidized bed evaporator(including down-flow,horizontal,and up-flow beds) was constructed to study the effect of flow directions on multiphase flow boiling heat transfer.A range of experimental investigations were carried out by varying amount of added particles(0-2%),circulation flow rate(2.15-5.16 m^3/h) and heat flux(8-16 kW/m^2).The comparison of heat transfer performance in different vertical heights of the horizontal bed was also discussed.Results reveal that the glass bead particle can enhance heat transfer compared with vapor-liquid two-phase flow for all beds.At a low heat flux(q = 8 kW/m),the heat-transfer-enhancing factor of the horizontal bed is obviously greater than those of the up-flow and down-flow beds.With the increase in the amount of added particles,the heat-transfer-enhancing factors of the up-flow and down-flow beds increase,whereas that of the horizontal bed initially increases and then decreases.However,at a high heat flux(q=16 kW/m),the heat-transfer-enhancing factors of the three beds show an increasing tendency with the increase in the amount of added particles and become closer than those at a low heat flux.For all beds,the heat-transfer-enhancing factor generally increases with the circulation flow rate but decreases with the increase in heat flux. 展开更多
关键词 Heat transfer enhancement CIRCULATING fluidized BED EVAPORATOR FLOW direction DOWN-FLOW BED UP-FLOW BED Horizontal BED
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Surface-to-bed heat transfer for high-density particles in conical spouted and spout–fluid beds
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作者 Onur Yaman Gorkem Kulaha Murat Koksalb 《中国颗粒学报:英文版》 SCIE EI CAS CSCD 2019年第1期35-47,共13页
Bed-to-surface heat transfer experiments from a vertically submerged cylindrical surface were conducted in laboratory-scale (Dc = 25 cm) conical spouted and spout–fluid beds at two different conical angles (31° ... Bed-to-surface heat transfer experiments from a vertically submerged cylindrical surface were conducted in laboratory-scale (Dc = 25 cm) conical spouted and spout–fluid beds at two different conical angles (31° and 66°) in the high particle density range (2500 kg/m3 ≤ρp ≤ 6000 kg/m3). The effects of the bed design parameters (conical angle and inlet diameter of spouting gas entrance) and operating conditions (static bed height, particle size, density, and spouting and fluidization gas flow rates) on the heat transfer characteristics were investigated in detail. The heat transfer coefficients were shown to be dependent on the density and size of the particles. The minimum stable spouting velocities of the denser and larger particles were higher, which led to higher operational spouting velocities and thereby resulted in higher heat transfer coefficients. The positive effect of increasing the particle diameter on heat transfer was more pronounced in the spout and at the spout–annulus interface, whereas this effect was diminished in the annulus region. The heat transfer coefficient increased with increasing spouting gas velocity up to 1.0Ums–1.1Ums, beyond which no significant change was observed regardless of the particle type. The heat transfer coefficient in the annulus decreased with increasing conical angle because of reduced particle circulation. The spout–fluid operation increased the heat transfer coefficient by a maximum of 10% at the expense of a significant increase of the total gas flow rate. This result was attributed to the inability of the fluidizing gas to penetrate the annulus. An empirical correlation for the average heat transfer coefficient in the annulus was also proposed based on the data obtained in this work. 展开更多
关键词 Conical spouted BED Spout–fluid BED Bed-to-surface HEAT TRANSFER Submerged HEAT TRANSFER SURFACE
Critical movement of large rocks in currents and waves 预览
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作者 L.C.van Rijn 《国际泥沙研究:英文版》 SCIE 2019年第4期387-398,共12页
Cobbles, boulders, and rocks often are used in a bed protection layer near a structure to protect the underlying sand bed against erosion by combined current and waves. The design of a bed protection layer consisting ... Cobbles, boulders, and rocks often are used in a bed protection layer near a structure to protect the underlying sand bed against erosion by combined current and waves. The design of a bed protection layer consisting of loose rocks (rubble mound) requires knowledge of the stability and movement (as bed load) of very coarse materials. If some movement (or damage) is acceptable, the rock diameter can be designed to be smaller. This paper addresses the stability and movement of very coarse materials (cobbles, boulders, and rocks) based on the concept of the critical Shields mobility number. It is shown that the bed load transport of large cobbles, boulders, and rocks can be described by the equations of Meyer-Peter and Mueller (MPM) and Cheng. Both are valid for relatively small Shields mobility numbers. New and general equations for the design of a bed protection layer (including some permissible damage) in conditions with a current with or without waves are proposed based on the Shields mobility parameter and the bed load transport equation of Cheng. Laboratory and field data of critical velocities for pebbles, cobbles, boulders, and rocks have been analyzed and compared to the computed results of the proposed equations. Practical applications are given to demonstrate the general applicability of the proposed equations. 展开更多
关键词 Rock stability BED protection CRITICAL MOVEMENT BED load transport ROCKS
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Erodibility study of sediment in a fast-flowing river 预览
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作者 Cheng He David Nguyen 《国际泥沙研究:英文版》 SCIE 2019年第2期144-154,共11页
Determination of sediment stability in the field is challenging because bed shear stress (BSS), a determining factor of sediment erosion, can’t easily be directly measured. To tackle this challenge and reliably asses... Determination of sediment stability in the field is challenging because bed shear stress (BSS), a determining factor of sediment erosion, can’t easily be directly measured. To tackle this challenge and reliably assess sediment erodibility in a fast flowing river, a standalone underwater camera system and a new insitu flume (ISF) were developed and applied in this study. The camera system was used to record sediment movement and the new ISF was used for measuring critical bottom shear stress (CBSS). The camera can be deployed alone in water to record videos or take pictures with light emitting diode (LED) lighting and flexible schedule settings. The ISF is based on the concept that the amount of force needed to erode the same particle under different flow conditions should be similar. Two high resolution Acoustic Doppler Current Profilers (ADCP) also were deployed in the field to collect velocity-depth profiles which are used by conventional methods to calculate BSS with the law of the wall. The sediment erodibility was then assessed based on the comparison between the obtained CBSS and BSS and then further verified with the recorded observations from the deployed camera. The results reveal that the widely used conventional method can produce large uncertainties and is not adequate to provide meaningful conclusion under these conditions. 展开更多
关键词 SEDIMENT ERODIBILITY BED SHEAR stress CRITICAL BED SHEAR stre
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浅谈室内固结法计算地基基床系数 预览
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作者 刘盖 沈亚兰 汤娜娜 《价值工程》 2019年第23期171-172,共2页
基床系数是地质勘查的重要参数。本文引用已有的基床系数的研究成果的取值现状的计算值与规范给出的经验值做对比,经过试验分析研究,对室内固结试验方法基床系数的取值相关问题进行对比,以供同仁参考。
关键词 室内固结法 地基 基床 计算 系数
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Continuous flow removal of acid fuchsine by dielectric barrier discharge plasma water bed enhanced by activated carbon adsorption
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作者 Rusen Zhou Renwu Zhou +2 位作者 Xianhui Zhang Kateryna Bazaka Kostya (Ken) Ostrikov 《化学科学与工程前沿:英文版》 EI CAS CSCD 2019年第2期340-349,共10页
Continuous processes which allow for large amount of wastewater to be treated to meet drainage standards while reducing treatment time and energy consumption are urgently needed. In this study, a dielectric barrier di... Continuous processes which allow for large amount of wastewater to be treated to meet drainage standards while reducing treatment time and energy consumption are urgently needed. In this study, a dielectric barrier discharge plasma water bed system was designed and then coupled with granular activated carbon (GAC) adsorption to rapidly remove acid fuchsine (AF) with high efficiency. Effects of feeding gases, treatment time and initial concentration of AF on removal efficiency were investigated. Results showed that compared to the N2 and air plasmas treatments, O2 plasma processing was most effective for AF degradation due to the strong oxidation ability of generated activated species, especially the OH radicals. The addition of GAC significantly enhanced the removal efficiency of AF in aqueous solution and shorten the required time by 50%. The effect was attributed to the ability of porous carbon to trap and concentrate the dye, increasing the time dye molecules were exposed to the plasma discharge zone, and to enhance the production of OH radicals on/in GAC to boost the degradation of dyes by plasma as well as in situ regenerate the exhausted GAC. The study offers a new opportunity for continuous effective remediation of wastewater contaminated with organic dyes using plasma technologies. 展开更多
关键词 continuous REMOVAL dye-containing WASTEWATER dielectric barrier discharge plasma WATER BED activated carbon adsorption
Advances in reduction of NOx and N2O emission formation in an oxy-fired fluidized bed boiler
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作者 Khalid El Sheikh Mohammad Jakir Hossain Khan +7 位作者 Mahar Diana Hamid Siddhartha Shrestha Brahim Si Ali G.A. Ryabov Lya A. Dolgushin Mohd Azlan Hussain Tatiana V. Bukharkina Elena A. Gorelova 《中国化学工程学报:英文版》 SCIE EI CAS CSCD 2019年第2期426-443,共18页
Fossil fuel combustion is one of the major means to meet the mounting global energy demand. However, the increasing NOx and N2 O emissions arising from fossil fuel combustion process have hazardous effects. Thus, miti... Fossil fuel combustion is one of the major means to meet the mounting global energy demand. However, the increasing NOx and N2 O emissions arising from fossil fuel combustion process have hazardous effects. Thus, mitigating these gases is vital to attain a sustainable environment. Interestingly, oxy-fuel combustion in fluidized bed for carbon capture and minimized NOx emissions is strongly sustainable compare to the other approaches. It was assessed that NOx formation and fuel-N conversion have significant limitation under oxy-fluidized bed compared to air mode and the mechanism of NOx formation is still deficient and requires further development. In addition, this review paper discussed the potential of primary measure as low emission process with others supplementary techniques for feasible NOx reduction. The influences of combustion mode, operating parameters, and reduction techniques such as flue gas recirculation, oxygen staging, biomass co-firing, catalyst, influence of fluidized bed design and structure, decoupling combustion and their merges are respectively evaluated. Findings show that significant minimization of NOx emission can be achieved through combination of primary and secondary reduction techniques. 展开更多
关键词 OXY-FUEL combustion Fluidized BED technology Biomass BLEND Primary/secondary measures NOx emission
Microstructure and mechanical properties of Ti-6Al-4V-5% hydroxyapatite composite fabricated using electron beam powder bed fusion
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作者 Cesar A. Terrazas Lawrenee E. Murr +3 位作者 Diego Bermudez Edel Arrieta David A. Roberson Ryan B. Wicker 《材料科学技术学报:英文版》 SCIE EI CAS CSCD 2019年第2期309-321,共13页
A novel, Ti-6A1-4V (Ti64)/Hydroxyapatite (HA at 5% by weight concentration) metal/ceramic composite has been fabricated using electron beam powder bed fusion (EPBF) additive manufacturing (AM): specifically, the comme... A novel, Ti-6A1-4V (Ti64)/Hydroxyapatite (HA at 5% by weight concentration) metal/ceramic composite has been fabricated using electron beam powder bed fusion (EPBF) additive manufacturing (AM): specifically, the commercial electron beam melting (EBMR) process. In addition to solid Ti64 and Ti64/5% HA samples, four different unit cell (model) open-cellular mesh structures for the Ti64/5% HA composite were fabricated having densities ranging from 0.68 to 1.12g/cm^3, and corresponding Young's moduli ranging from 2.9 to 8.0 GPa, and compressive strengths ranging from -3 to 11 MPa. The solid Ti64/5%HA composite exhibited an optimal tensile strength of 123 MPa, and elongation of 5.5% in contrast to a maximum compressive strength of 875 MPa. Both the solid composite and mesh samples deformed primarily by brittle deformation, with the mesh samples exhibiting erratic, brittle crushing. Solid, EPBF-fabricated Ti64 samples had a Vickers microindentation hardness of 4.1 GPa while the Ti64/5%HA solid composite exhibited a Vickers microindentation hardness of 6.8 GPa. The lowest density Ti64/5%HA composite mesh strut sections had a Vickers microindentation hardness of 7.1 GPa. Optical metallography (OM) and seanning electron microscopy (SEM) analysis showed the HA dispersoids to be highly segregated along domain or grain boundaries, but homogeneously distributed along alpha (hcp) platelet boundaries within these domains in the Ti64 matrix for both the solid and mesh composites. The alpha platelet width varied from -5μm in the EPBF-fabricated Ti64 to -1.1μm for the Ti64/5%HA mesh strut. The precursor HA powder diameter averaged 5μm, in contrast to the dispersed HA particle diameters in the Ti64/5%HA composite which averaged 0.5μm. This work highlights the use of EPBF AM as a novel process for fabrication of a true composite structure, consisting of a Ti64 matrix and interspersed and exposed HA domains, which to the authors knowledge has not been reported before. The results also illustrate the prospects not only for fabrica 展开更多
关键词 HYDROXYAPATITE (HA) Metal-matrix ceramic composites Open-cellular (mesh) structures ELECTRON-BEAM powder bed FUSION (EPBF) Additive manufacturing (AM) Mechanical properties Microstructure characterization
固定结合面不同位置刚度参数对机床动态特性的影响
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作者 张大卫 张军傲 +1 位作者 石一光 高卫国 《机械设计》 CSCD 北大核心 2019年第1期100-105,共6页
框中框式结构机床中以固定结合面联接的床身、立柱为研究对象,通过拉格朗日方程的方法建立床身、立柱的动力学理论模型,不同位置采用不同的结合面刚度参数来研究结合面法向刚度和切向刚度对系统各阶模态频率的影响;然后基于多学科优化... 框中框式结构机床中以固定结合面联接的床身、立柱为研究对象,通过拉格朗日方程的方法建立床身、立柱的动力学理论模型,不同位置采用不同的结合面刚度参数来研究结合面法向刚度和切向刚度对系统各阶模态频率的影响;然后基于多学科优化设计软件iSIGHT,搭建整机动态特性分析优化系统框架来验证计算结果的正确性。结果表明,结合面切向刚度相比较于法向刚度对系统模态频率的影响较小;刚度参数增加,系统各阶模态频率趋于稳定;不同位置结合面刚度值大小影响不同阶次的模态频率值。 展开更多
关键词 床身 立柱 结合面刚度 模态频率
Grain boundary and microstructure engineering of Inconel 690 cladding on stainless-steel 316L using electron-beam powder bed fusion additive manufacturing
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作者 I.A. Segura L.E. Murr +7 位作者 C.A. Terrazas D. Bermudez J. Mireles V.S.V. Injeti K. Li B. Yu R.D.K.Misra R.B. Wicker 《材料科学技术学报:英文版》 SCIE EI CAS CSCD 2019年第2期351-367,共17页
This research explores the prospect of fabricating a face-centered cubic(fcc) Ni-base alloy cladding(Inconel 690) on an fcc Fe-base alloy(316 L stainless-steel) having improved mechanical properties and reduced sensit... This research explores the prospect of fabricating a face-centered cubic(fcc) Ni-base alloy cladding(Inconel 690) on an fcc Fe-base alloy(316 L stainless-steel) having improved mechanical properties and reduced sensitivity to corrosion through grain boundary and microstructure engineering concepts enabled by additive manufacturing(AM) utilizing electron-beam powder bed fusion(EPBF). The unique solidification and associated constitutional supercooling phenomena characteristic of EPBF promotes[100] textured and extended columnar grains having lower energy grain boundaries as opposed to random, high-angle grain boundaries, but no coherent {111} twin boundaries characteristic of conventional thermo-mechanically processed fcc metals and alloys, including Inconel 690 and 316 L stainless-steel.In addition to [100] textured grains, columnar grains were produced by EPBF fabrication of Inconel 690 claddings on 316 L stainless-steel substrates. Also, irregular 2–3 μm diameter, low energy subgrains were formed along with dislocation densities varying from 108 to 109 cm2, and a homogeneous distribution of Cr23C6 precipitates. Precipitates were formed within the grains(with 3 μm interparticle spacing),but not in the subgrain or columnar grain boundaries. These inclusive, hierarchical microstructures produced a tensile yield strength of 0.527 GPa, elongation of 21%, and Vickers microindentation hardness of 2.33 GPa for the Inconel 690 cladding in contrast to a tensile yield strength of 0.327 GPa, elongation of 53%, and Vickers microindentation hardness of 1.78 GPa, respectively for the wrought 316 L stainlesssteel substrate. Aging of both the Inconel 690 cladding and the 316 L stainless-steel substrate at 685?C for50 h precipitated Cr23C6 carbides in the Inconel 690 columnar grain boundaries, but not in the low-angle(and low energy) subgrain boundaries. In contrast, Cr23C6 carbides precipitated in the 316 L stainless-steel grain boundaries, but not in the low energy coherent {111} twin boundaries. Consequently, the Inconel6 展开更多
关键词 Additive manufacturing ELECTRON-BEAM powder bed FUSION (EPBF) INCONEL 690 CLADDING 316L stainless steel Grain boundary engineering Materials characterization Mechanical properties
Laser additive manufacturing of Zn porous scaffolds;Shielding gas flow, surface quality and densification
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作者 Peng Wen Yu Qin +4 位作者 Yanzhe Chen Maximilian Voshage Lucas Jauer Reinhart Poprawe Johannes Henrich Schleifenbaum 《材料科学技术学报:英文版》 SCIE EI CAS CSCD 2019年第2期368-376,共9页
Zn based metals have exhibited promising prospects as a structural material for biodegradable applications. Pure Zn porous scaffolds were produced by laser powder bed fusion(LPBF) based on data files of designing and ... Zn based metals have exhibited promising prospects as a structural material for biodegradable applications. Pure Zn porous scaffolds were produced by laser powder bed fusion(LPBF) based on data files of designing and CT scanning. Massive Zn evaporation during laser melting largely influenced the formation quality during LPBF of Zn metal. The metal vapor in processing chamber was blown off and suctioned out efficiently by an optimized gas circulation system. Numerical analysis was used to design and testify the performance of gas flow. The surface of scaffolds was covered with numerous particles in different sizes. Processing pores occurred near the outline contour of struts. The average grain size in width was8.5m, and the hardness was 43.8 HV. Chemical plus electrochemical polishing obtained uniform and smooth surface without processing pores, but the diameter of struts reduced to 250 αm from the design value 300 m. The poor surface quality and processing pores were resulted by the splashing particles included spatters and powders due to the recoil force of evaporation, and the horizontal movement of liquid metal due to overheating and wetting. The insufficient melting at the outline contour combined with good wetting of Zn liquid metal further increased the surface roughness and processing pores. 展开更多
关键词 ADDITIVE manufacturing Powder bed fusion LASER Porous SCAFFOLD ZN
Maximum Force of Inclined Pullout of A Torpedo Anchor in Cohesive Beds 预览
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作者 WANG Cheng CHEN Xiao-hui YU Guo-liang 《中国海洋工程:英文版》 SCIE EI CSCD 2019年第3期333-343,共11页
Torpedo anchors have been used in mooring systems for deep-water oil and gas projects owing to their prominent advantages, such as low cost and easy installation. The maximum force of torpedo anchors is crucial not on... Torpedo anchors have been used in mooring systems for deep-water oil and gas projects owing to their prominent advantages, such as low cost and easy installation. The maximum force of torpedo anchors is crucial not only to the safety and stability of vessels and other marine facilities, but also for an economical design. It is necessary to develop reliable formula for fast predicting their maximum inclined force of a torpedo anchor in cohesive beds. In this study, the maximum inclined force of a torpedo anchor vertically embedded in cohesive beds was extensively investigated. 316 sets of inclined pullout laboratory tests were carried out for 9 differently shaped torpedo anchors which were vertically embedded in different cohesive beds. The loading curves were automatically acquisitioned and their characteristics were analyzed. The load angle relative to the horizontal varied from 20° to 90°. A new formula for fast calculating the maximum inclined force of the torpedo anchor vertically embedded in cohesive beds was obtained based on force analysis and a nonlinear regression on the data from the present and other studies. Effect aspects on the tests are discussed and further studies are highlighted. 展开更多
关键词 TORPEDO ANCHOR MAXIMUM inclined FORCE COHESIVE bed load angle EMBEDMENT depth
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Ni-Cu作用对于1,4-丁炔二醇一步法低压加氢的影响 预览
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作者 方洁 李娜 +1 位作者 成浪 陆江银 《燃料化学学报》 EI CAS CSCD 北大核心 2019年第6期725-736,共12页
采用沉积沉淀法将金属助剂引入Ni/Al2O3催化剂,考察不同金属助剂对于BYD加氢体系的影响,进一步优选助剂的最佳含量,并结合BET、XRD、H2-TPR、EDX-MAPPING、TEM、XPS、NH3-TPD等表征手段对催化剂物化性质进行研究。结果表明,金属助剂的... 采用沉积沉淀法将金属助剂引入Ni/Al2O3催化剂,考察不同金属助剂对于BYD加氢体系的影响,进一步优选助剂的最佳含量,并结合BET、XRD、H2-TPR、EDX-MAPPING、TEM、XPS、NH3-TPD等表征手段对催化剂物化性质进行研究。结果表明,金属助剂的添加主要影响了活性组分与载体间相互作用,成为影响催化活性的主要原因。Cu与Fe的引入使催化剂中Ni^2+与载体之间相互作用明显减弱,提高了还原性能,BYD转化率提高至95%。通过考察优选金属助剂Cu含量对于催化剂物化性质的影响,发现使Ni^2+与载体间相互作用力减弱的主要原因在于Cu表面氢溢流现象,然而,较多还原后的Ni颗粒由于与载体间的弱相互作用,易发生团聚,对加氢过程造成不利影响,通过Ni-Cu金属作用可有效地将金属固定于在载体表面,避免粒子迁移、团聚,Cu添加量5%时,催化剂凭借较多分散度良好的活性组分和适宜酸性,最终表现出最优加氢性能。 展开更多
关键词 NI/AL2O3催化剂 Ni-Cu作用 改性 1 4-丁炔二醇 1 4-丁烯二醇
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Study of heat transfer by using DEM-CFD method in a randomly packed pebble-bed reactor 预览
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作者 Qiang Niu Na-Xiu Wang 《核技术:英文版》 SCIE CAS CSCD 2019年第2期123-134,共12页
The pebble-bed reactor is one of the most promising designs for the nuclear energy industry. In this paper, a discrete element method-computational fluid dynamics (DEM-CFD) approach that includes thermal conduction, r... The pebble-bed reactor is one of the most promising designs for the nuclear energy industry. In this paper, a discrete element method-computational fluid dynamics (DEM-CFD) approach that includes thermal conduction, radiation, and natural convection mechanisms was proposed to simulate the thermal-fluid phenomena after the failure of forced circulation cooling system in a pebble-bed core. The whole large-scale packed bed was created using the DEM technique, and the calculated radial porosity of the bed was validated with empirical correlations reported by researchers. To reduce computational costs, a segment of the bed was extracted, which served as a good representative of the large-scale packed bed for CFD calculation. The temperature distributions simulated with two different fluids in this DEM-CFD approach were in good agreement with SANA experimental data. The influence of the natural convection mechanism on heat transfer must be taken into account for coolants with strong convective capacity. The proposed DEM-CFD methodology offers a computationally efficient and widely applied method for understanding the heat transfer process in a pebble-bed core. The method can also be easily extended to assess the passive safety features of newly designed fluoride- salt-cooled pebble-bed reactors. 展开更多
关键词 Discrete element METHOD COMPUTATIONAL fluid dynamics PEBBLE BED Heat transfer Natural CONVECTION
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Hydrodynamics and solids mixing in fluidized beds with inclined-hole distributors
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作者 Alhussain Bakhurji Xiaotao Bi John R. Grace 《中国颗粒学报:英文版》 SCIE EI CAS CSCD 2019年第2期19-28,共10页
Experimental fluidization results were compared for three gas distributors with the same opening ratio but different orifice in clinations (30,45 , and 90 ). Hydrodynamic studies were con ducted with glass beads (diam... Experimental fluidization results were compared for three gas distributors with the same opening ratio but different orifice in clinations (30,45 , and 90 ). Hydrodynamic studies were con ducted with glass beads (diameter 154p.m) to evaluate the impacts of orifice inclination and static bed depth on pressure drop, pressure drop fluctuations, bed expansion, and minimum fluidization velocity. Solids residence time distributions were determined using phosphoresce nt tracer particles (mea n diameter 76 pm), activated by ultraviolet light. The bed pressure drop was higher with the inclined-hole distributors and increased with static bed height. In a shallow bed, the inclined-hole distributors gave less expansion;however, in deep beds, the orifice angle had negligible influence on bed expansion. The minimum fluidization velocity varied with static bed height for the inclined-hole distributors and was higher for steeper angles. The turnover time estimated using bubbling-bed equations matched the experimental results well for vertical mixing. Probes and ports at the walls of the fluidization column reduced the dense-phase downward velocity by up to 40%. The tangential particle velocity was highest for the 30 -hole distributor and decreased with increasing orifice angle. Tangential mixing was described by a dispersion model;the dispersion coefficient for the inclined-hole distributors was approximately twice that for the 90 -hole distributor in a shallow bed. 展开更多
关键词 Swirling fluidized bed FLUIDIZATION SOLIDS MIXING Inclined-hole DISTRIBUTOR
A comprehensive CFD combustion model for supercritical CFB boilers
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作者 Linjie Xu Leming Cheng +2 位作者 JieqiangJi Qinhui Wang Mengxiang Fang 《中国颗粒学报:英文版》 SCIE EI CAS CSCD 2019年第2期29-37,共9页
A combustion model of a large-scale supercritical circulati ng fluidized bed (CFB) boiler was developed for comprehensive computational-fluid-dynamics analysis. The model incorporates gas-solid hydrodynamics, coal com... A combustion model of a large-scale supercritical circulati ng fluidized bed (CFB) boiler was developed for comprehensive computational-fluid-dynamics analysis. The model incorporates gas-solid hydrodynamics, coal combustion, heat transfer on heat exchange surfaces in the furnace, and heat transfer between fumace and working medium in the heat transfer tubes. In simulating the dense and dilute phases in the fumace, the gas-solid hydrodynamics is based on the Euler-Euler model and energy-minimization multiscale drag model. Coal combustion entails evaporation, devolatilization, char combustion, gas homoge neous reaction, and pollutant emission. The coefficient ofheat transfer between gas-solid and the waterwall is estimated using the cluster renewal model, and for radiation, the discrete ordinate model is used. Moreover, thermohydraulic processes in the membrane wall are also in eluded in the heat transfer process. The model was successfully applied in simulations of a 350-MW supercritical CFB boiler. Detailed distributions of solids concentration, oxygen, heat flux, and working medium temperature in the boiler furnace are presented. 展开更多
关键词 COMPREHENSIVE combustion model COMPUTATIONAL fluid dynamic THERMAL-HYDRAULICS SUPERCRITICAL CIRCULATING fluidized bed Large-scale FURNACE
Dynamic characterization of the migration of a mining pit in an alluvial channel 预览
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作者 Bandita Barman Bimlesh Kumar Arup Kumar Sarma 《国际泥沙研究:英文版》 SCIE 2019年第2期155-165,共11页
Research on in-channel sand mining is imperative as it may have a significant impact on channel morphology. Following this quest to quantitatively comprehend the phenomenon, experimental studies were done to investiga... Research on in-channel sand mining is imperative as it may have a significant impact on channel morphology. Following this quest to quantitatively comprehend the phenomenon, experimental studies were done to investigate the dynamic characteristics of the migration of a mining pit. The evaluation of the migration rate of a mining pit in a physical scale model has found a rise in the migration rate of the pit's upstream edge with increasing discharge. A wavelet analysis applied for analyzing scale-dependent migration of the bed profile of a mining pit also revealed similar findings. Additionally, the wavelet analysis examined the length-scale dependent migration of a mining pit and a decrease in the migration rate has been observed with an increase in the length scale. The plan form of a pit (length-to-width ratio) governs the erosion and deposition processes around the pit. Both physical and statistical approaches show an increase in the migration rate with an increase in the length-to-width ratio of the pit. An empirical formulation has been developed for calculating the migration rate of the upstream edge of a mining pit based on pit geometry (length-to-width ratio), average flow velocity, and critical shear stress of the bed material. The results also show a higher bed load transport rate in the channel subjected to mining as compared to a plain bed channel. 展开更多
关键词 SAND MINING MIGRATION Wavelet analysis BED load transport
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Borescopic particle image velocimetry in bubbling gas-solid fluidized beds
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作者 M. Banaei R. Dellaert +2 位作者 N.G. Deen J.A.M. Kuipers M. van Sint Annaland 《中国颗粒学报:英文版》 SCIE EI CAS CSCD 2019年第2期66-75,共10页
In this work, the borescopic particle image velocimetry (BPIV) technique was applied to a bubbling gas-solid fluidized bed, and the results were compared with published positron emission particle tracking (PEPT) measu... In this work, the borescopic particle image velocimetry (BPIV) technique was applied to a bubbling gas-solid fluidized bed, and the results were compared with published positron emission particle tracking (PEPT) measurement data. Before performing the experiments, the sensitivity of the BPIV results to the illumination power, light reflectivity of the particles, and location of the borescope was also investigated. The BPIV and PEPT results were in fair agreement;however, some discrepancies were observed.The difference between the two sets of results were mainly caused by the intrusiveness of BPIV, the fact that the local solids volume fraction was not accounted for in the BPIV analysis, and the intrinsic differences of these two methods. Therefore, measurement of the local solids volume fraction with the borescope is highly recommended for further development of the BPIV method, which will also enable measureme nt of the local solids mass fluxes in side dense gas-solid fluidized beds. 展开更多
关键词 Borescopic particle image VELOCIMETRY GAS-SOLID BUBBLING fluidized BED Solid VELOCITY profile Experimental investigation HYDRODYNAMICS
Simultaneous effects of mesh refinement, grid configuration and wall boundary condition on prediction of pressure gradients and velocity profiles of microparticles in a conical fluidized bed
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作者 Alireza Bahramian 《中国颗粒学报:英文版》 SCIE EI CAS CSCD 2019年第2期123-136,共14页
The reliability and accuracy of numerical results of microparticle fluidization in a conical bed, affected simultaneously by mesh refinement, the grid configuration and the wall boundary condition (BC), are analyzed. ... The reliability and accuracy of numerical results of microparticle fluidization in a conical bed, affected simultaneously by mesh refinement, the grid configuration and the wall boundary condition (BC), are analyzed. Specifically, pressure gradients and velocity profiles of titania powder are studied for a conical bed. The Gidaspow drag correlation and different wall BCs are considered using a Eulerian-Eulerian two-fluid model. Predictions of the pressure fluctuation, power spectra of the corresponding pressure fluctuations, bed pressure drop, minimum fluidizati on veloc ity, axial solid velocity, bed expansi on ratio, and particle size distribution are compared with experimental data. Mesh sensitivity analysis using hexahedral and tetrahedral cells with a un iform mesh and n ear-wall mesh refineme nr is con ducted to inv estigate the effects of mesh configurations in estimating particle flow patterns. Simulations show that significant savings in terms of computational time are realized by choosing a uniform mesh while the hexahedral structure, the near-wall mesh refinement, and the free-slip BC give the closest fit to the experimental data. 展开更多
关键词 Conical fluidized bed Mesh CONFIGURATION GRID REFINEMENT Velocity field Pressure gradie nt
A new solution to enhance cuttings transport in mining drilling by using pulse jet mill technique
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作者 LIU YongSheng GAO DeLi +3 位作者 WEI Zheng BALACHANDRAN Balakumar WANG ZhenQuan TAN LeiChuan 《中国科学:技术科学英文版》 SCIE EI CAS CSCD 2019年第5期875-884,共10页
In horizontal drilling, the cuttings bed is frequently formed to result in severe problems such as backing pressure, binding of bottom hole assembly(BHA) and even sticking of tool. Practice and research show that the ... In horizontal drilling, the cuttings bed is frequently formed to result in severe problems such as backing pressure, binding of bottom hole assembly(BHA) and even sticking of tool. Practice and research show that the smaller particle size is, the more favorable to carry out from bottom of hole in extended reach well or horizontal well. This paper presented a new solution to enhance cuttings transport in mining drilling through a new type of bit called pulsed mill bit(PMB) by using pulse jet mill technique. It provides a promising solution to enhance the efficiencies of rock breaking and cuttings carrying for pulsed jet,sucking cuttings to decrease the chip hold down effect, and reducing cuttings’ diameter to eliminate cuttings bed. The design was supported by the calculation models of Helmholtz resonator natural frequency, optimal drilling fluid flow rate of resonator,drilling fluid flow velocity in forward jet channel, critical impact velocity of cuttings and minimum length of the accelerating cavity. Meanwhile, factors affecting optimal drilling fluid flow rate, critical impact velocity of cuttings and minimum length of accelerating cavity were investigated. Case study showed a good consistency between the calculation results and the related theories. It is concluded that optimal drilling fluid flow rate increases with the increase of inlet and outlet cavity’s diameter, and decreases with the increase of the diameter of the resonant cavity. Critical impact velocity of cuttings increases with the energy conversion factor(β) and ROP, while decreasing with the final size of the cuttings(dt). This effect is obvious when β<0.2, ROP<3.048 mh-1 and dt<0.3 mm. Minimum length of the accelerating cavity decreases with the increase of the resonator’s natural frequency and separation coefficient(α) of drilling fluid flow rate. This study provides a promising solution to remove cuttings bed in horizontal well. 展开更多
关键词 PULSE jet MILL TECHNIQUE CUTTINGS bed HELMHOLTZ RESONATOR optimal flow rate critical impact velocity
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