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Influence of Solid Fraction on Gravity Segregation of Sn in A1-20Sn Alloy Casting

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Journal of Materials Science & Technology 2000年第6期16卷 577-580页

作者： Zhang P. Du Y.H. Zeng.D.B. Cui J.Z. Ba L.M. dep. of Mechanical eng. Tsinghua Univ. Beijing 100084 China

The influence of solid fraction of Al-20Sn alloy mushy on gravity segregation of Sn in casting was studied . The relationship between solid fraction and the temperature of alloy mushy and that between solid fraction of alloy mushy and size of Sn particle in ingot were determined. The results show that the relationship between solid fraction and the temperature of alloy mushy was fs=1683-4.86t+0.003 5t2. The extent of gravity segregation of Sn in casting reduced gradually with the increase of solid fraction of alloy mushy. When solid fraction of alloy mushy was larger than 40%, the gravity segregation of Sn in casting could be removed basically, and the relationship between solid fraction of alloy mushy and size of Sn particle in ingot was s=-0.64fs+70.8.

关键词： Metal casting

STUDY ON VERTICAL WATER TEMPERATURE MODEL FOR MIYUN RESERVOIR

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Journal of Hydrodynamics 2000年第4期12卷 75-83页

作者： Li, Y.L. Chen, Y.C. Zhang, B.X. dep. of Hydraulic eng. Tsinghua Univ. Beijing 100084 China

According to the characters of the Miyun reservoir located in northeast Beijing, one-dimensional method is used to establish a mathematical model of temperature for the reservoir. In this model the heat exchange between water surface and atmosphere, effective diffusion, inflows, outflows, and thermal advection are considered comprehensively. The effective diffusion coefficient, decay coefficient of short wave in water, etc, are calibrated based on the observed stratification data of 1991 in the reservoir. The mathematical model is verified through the agreement with the data of 1992. This model can be used to predict the temperature distribution along the vertical direction for the Miyun reservoir and other similar reservoir.

关键词： Computer simulation Heat transfer Mathematical models Temperature distribution

EXPERIMENTAL RESEARCH OF CYLINDER TO BED HEAT TRANSFER IN AGITATED FLUIDIZED BEDS

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Journal of Hydrodynamics 2000年第4期12卷 36-40页

作者： Ma, J.H. dep. of Air-condition eng. Shandong Inst. of Archit. and Eng. Jinan 250014 China

Cylinder-to-bed heat transfer in agitated fluidized beds was studied experimentally. In the experiments, the aluminum particles were used as bed material, the diameter of those ranged from 0.5 mm to 2 mm. The effects of gas velocity, particles size, and agitator rotary speed on heat transfer were studied. From the experimental results, we have come to the following conclusion: (1) there are optimal ranges for airflow velocity and rotary speed to get optimal heat transfer coefficient; (2) the cylinder-to-bed heat transfer is greatly affected by gas velocity, rotary speed and particles sizes, and the effect of rotary speed on heat transfer is similar to that of gas velocity; (3) higher heat transfer coefficient is obtained with smaller particles.

关键词： Fluidized beds Heat transfer Mass transfer Two phase flow

CHANGES OF MEAN VELOCITY PROFILES IN THE WAVE-CURRENT COMBINED FLOW

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Journal of Hydrodynamics 2001年第1期13卷 47-53页

作者： Wu, Y.S. Lian, J.J. Zhang, Q.H. Qin, C.R. dep. of Hydraulic eng. Tsinghua Univ. Beijing 100084 China

A mathematical model is developed to simulate the change in mean velocity for the coexistent case of waves and current. The experimental results of mean velocity profile in a wave-current flume show the following features: Eulerian mean current profile for following current is more uniformly distributed than the corresponding pure current case, whereas , the case of an opposing current leads to the more straight profile. This model is based on Eulerian mean framework, and motions of wave and current are solved simultaneously. The comparisons of numerical results and experimental data show that the mathematical model presented in this paper is reasonable and feasible.

关键词： Computer simulation Hydrodynamics Mathematical models Sediment transport

THEORETICAL STUDY OF HEAT TRANSFER ENHANCEMENT IN PIPE WITH POROUS BODY

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Journal of Hydrodynamics 2001年第1期13卷 111-116页

作者： Gong, W.P. Han, J.T. Cheng. F. dep. of Power eng. Shandong Univ. Jinan 250061 China

A theoretical investigation on the fluid flow and heat transfer in a pipe with porous body of high porosity twisted by metal wire was carried out. A theoretical model of a circular pipe with porous matrix attached at the channel wall and extended inward the centerline was set up. Through analyzing the flow in the porous matrix by the Brinkman-extended-Darcy equation and through including the effect of dispersion by adding the dispersion coefficient into the energy equation, the theoretical solutions of velocity distribution and temperature fields were obtained. Finally the effect of the properties of the porous matrix on the flow and heat transfer in the porous body was studied, which indicates that dispersion can really enhance the heat transfer in pipe.

关键词： Computer simulation Dispersions Mathematical models Pipe flow Porosity Porous materials

Fatigue Behavior of Cemented Carbide Die in Cold Forging of Steel

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Journal of Materials Science & Technology 2001年第1期17卷 51-52页

作者： Z.Wang and K.Dohda dep.. of Mechanical System eng.neering, Gifu University, Gifu, Japan dep. of Mech. Syst. eng. Gifu Univ. Gifu Japan

The fatigue behavior of cemented carbide die under service load in the multistage cold forging of steel was investigated. It was found that the fatigue cracks do not initiate at the stress concentration position and the crack initiation position can be classified to three types. The crack initiation position can be predicted by FEM only when the plastic deformation of the die is considered.

关键词： Fatigue Behavior of Cemented Carbide Die in Cold Forging of Steel

Mechanism of the Forming of Nodular Graphite

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Journal of Materials Science & Technology 2000年第6期16卷 615-618页

作者： Shoukui ZHANG (dep.. of Materials eng.neering, Dalian University of Technology, Dalian 116024, China) [Manuscript received September 6, 1999, in revised form January 21, 2000] dep. of Materials eng. Dalian Univ. of Technol. Dalian 116024 China

This article presents a theory about the growth mechanism of bubble-screw dislocation of nodular graphite. Normally speaking, the crystallizing procedure of most nodular graphite is as follows: firstly, graphite generates nuclei on bubbles and fills them (mainly in the way of screw dislocation) forming the complete nuclei of nodular graphite-graphite bubble nuclei. Then, graphite grows up in the way of screw dislocation. Two important conditions concerning the production of nodular graphite are: (a) there is a relatively big interfacial energy between ferro liquid and graphite, and the one between ferro liquid and graphite prismatic plane is bigger than that between ferro liquid and graphite basal plane; (b) there are a certain amount of micro-bubbles in the melt.

关键词： Mechanism of the Forming of Nodular Graphite

Die Motions of New Forging Process Using Intermediate Die Assembly

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Journal of Materials Science & Technology 2001年第1期17卷 127-128页

作者： T. Umemura, Y.Zhou and S.Kamimura dep.. Mech. eng., Nagaoka Unly. of Technology, Nagaoka, Japan N.Motoi and Y Ohta Johetsu industries Co. Ltd., Ogunimachi, Niigata, Japan N. Yamaguchi COMAC, Ltd. Sanjyo, Niigata, Japan dep. of Mech. eng. Nagaoka Univ. of Technol. Nagaoka Japan

The die motions of a new forging process for automation with an intermediate die assembly called hamburger were analyzed through high-speed video pictures. The results showed that the upper die that is assembled in the hamburger and retained over the lower die collides few times . with the ram and workpiece, but sound products can be obtained with less sticking in spite of the lowered impacts of hit.

关键词： L

VERIFICATION AND COMPARISON OF FORMULAS FOR BED LOAD TRANSPORT

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Journal of Hydrodynamics 2001年第1期13卷 8-11页

作者： Wang, X.K. Li, D.X. Qu, Z.S. Wang, D.C. dep. of Hydraulic eng. Tsinghua Univ. Beijing 100084 China

Several typical formulas for bed load transport are examined based on field data. It is concluded that the Einstein formula provides good estimates for the bed load transport rate while other ones predict much lower transport rates. The main reason for the under-prediction is that Dp, the effective diameter of particles, is too large as a representative diameter of the bed material for gravel streams with partially movable bed. Performance of these formulas can be significantly improved if D35 is adopted instead of Dp.

关键词： Loads (forces) Structural loads