Numerical Simulation of Microstructure Evolution in Solidification Process of Ferritic Stainless Steel with Cellular Automaton

In order to study the basic principles of vibration-excited liquid metal nucleation technology, a coupled model to connect the temperature field calculated by ANSYS Fluent and the dendritic growth simulated by cellular automaton (CA) algorithm was proposed. A two-dimensional CA model for dendrite growth controlled by solute diffusion and local curvature effects with random zigzag capture rule was developed. The proposed model was applied to simulate the temporal evolution of solidification microstructures under different degrees of surface undercooling and vibration frequency of the crystal nucleus generator conditions. The simulation results showed that the predicted columnar dendrites regions were more developed, the ratio of interior equiaxed dendrite reduced and the size of dendrites increased with the increase of the surface undercooling degrees on the crystal nucleus generator. It was caused by a large temperature gradient formed in the melt. The columnar-to-equiaxed transition (CET) was promoted, and the refined grains and homogenized microstructure were also achieved at the high vibration frequency of the crystal nucleus generator. The influences of the different process parameters on the temperature gradient and cooling rates in the mushy zone were investigated in detail. A lower cooling intensity and a uniform temperature gradient distribution could promote nucleation and refine grains. The present research has guiding significance for the process parameter selection in the actual experimental.

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Optimization of Process Parameters for Unidirectional Solidification of Magnesium Alloy

Materials Science Forum ◽

10.4028/www.scientific.net/msf.750.228 ◽

2013 ◽

Vol 750 ◽

pp. 228-231

Author(s):

Ming Chen ◽

Xiao Dong Hu ◽

Hong Yang Zhao ◽

Dong Ying Ju

Keyword(s):

Magnesium Alloy ◽

Temperature Gradient ◽

Process Parameters ◽

Solidification Process ◽

Optical Microscope ◽

Field Method ◽

Unidirectional Solidification ◽

Grain Structure ◽

Phase Field Method ◽

Gradient Distribution

The unidirectional solidification process of magnesium alloy needs to establish a specific temperature gradient in casting mold, the direction of crystal growth and heat flow are in the opposite direction in the unidirectional solidification. The process can better control the grain orientation, and eliminate the horizontal grain boundary, so to attain columnar grain structure and excellent performance of magnesium alloy. In this paper, Numerical simulation is carried out by orthogonal experiments in order to obtain the optimal process parameters according to the actual experimental device. Different process parameters are taken into account, including pulling speed, cooling time and cooling intensity. FEM (finite element method) is employed to calculate the temperature field and reached a straight shape of temperature gradient distribution which is conductive to achieve unidirectional solidification microstructure. PFM(phase field method) is adopted into the microstructure calculation. The microstructure obtained by PFM is in agreement with the actual pattern by the optical microscope observation.

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Liquid phase stratification induced by large temperature gradient during spinodal decomposition in Fe–Cr alloys: A phase-field study

Modern Physics Letters B ◽

10.1142/s0217984921503747 ◽

2021 ◽

pp. 2150374

Author(s):

Lifei Du ◽

Runbo Tian ◽

Tiantian Shi ◽

Youqi Cao

Keyword(s):

Liquid Phase ◽

Temperature Gradient ◽

Spinodal Decomposition ◽

Phase Field ◽

Anisotropic Diffusion ◽

Phase Field Model ◽

Solute Diffusion ◽

Large Temperature ◽

Cahn Hilliard Equation ◽

Kinetics Of

The spinodal decomposition in Fe-40at.%Cr binary alloy is numerically studied by implementing the phase-field model based on Cahn–Hilliard equation. Effects of different temperature gradients on the solute distributing characteristics during the spinodal decomposition are investigated. In the system with a temperature gradient, the phase decomposition happens gradually from low temperature to high temperature, and a metastable stratification is achieved with specified temperature distribution. The critical temperature and corresponding temperature gradient are specified for the obvious solute stratification in the binary Fe–Cr alloy. The kinetics of the solute diffusion during the spinodal decomposition is discussed to reveal the liquid phase stratification induced by the anisotropic diffusion with the nonuniform temperature field. Therefore, tailoring the heat treatment during the spinodal decomposition in Fe–Cr binary alloys might be an efficient way to obtain nanometer coherent microstructures with specified solute distribution.

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Addressing Paraffin Deposition Challenges Through New Technologies

10.2118/207789-ms ◽

2021 ◽

Author(s):

Saugata Gon ◽

Christopher Russell ◽

Kasper Koert Jan Baack ◽

Heather Blackwood ◽

Alfred Hase

Keyword(s):

Temperature Gradient ◽

Surface Temperature ◽

New Technologies ◽

Test Methods ◽

Large Temperature ◽

Mixing Condition ◽

Cold Finger ◽

Cold Surface ◽

Bulk Oil ◽

Conventional Test

Abstract Paraffin deposition is a common challenge for production facilities globally where production fluid/process surface temperature cools down and reach below the wax appearance temperature (WAT) of the oil. Although chemical treatment is used widely for suitable mitigation of wax deposition, conventional test methods like cold finger often fail to recommend the right product for the field. The current study will present development of two new technologies PARA-Window and Dynamic Paraffin Deposition Cell (DPDC)to address such limitations. Large temperature gradient between bulk oil and cold surface has been identified as a major limitation of cold finger. To address this, PARA-Window has been developed to capture the paraffin deposition at a more realistic temperature gradient (5°C) between the bulk oil and surface temperature using a NIR optical probe. Absence of brine and lack of shear has been identified as another limitation of cold finger technique. DPDC has been developed to study paraffin deposition and chemical effectiveness in presence of brine. Specially designed cells are placed horizontally inside a shaker bath to achieve good mixing between oil and water for DPDC application. A prior study by Russell et al., (2019) showed the effectiveness of PARA-Window in capturing deposition phenomena of higher molecular weight paraffin chains that resemble closely to field deposits under narrow temperature gradient around WAT. Conventional test methods fail to capture meaningful product differentiation in most oils under such conditions and hence can only recommend a crystal modifier type of paraffin chemistries. PARA-Window technique can expand product selection to other type of paraffin chemistries (paraffin crystal modifiers, dispersants and solvents) as shown earlier by Russell et al., (2021). The usage of DPDC allows us to create a dynamic mixing condition inside the test cells with both oil and water under a condition similar to production pipe systems. This allows DPDC to assess water effect on paraffin chemistries (crystal modifiers and dispersants). This study presents the usage of these two new technologies to screen performance of different types of paraffin chemistries on select oils and their advantages over cold finger. The results identify how mimicking field conditions using these new technologies can capture new insights into paraffin products.

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Cellular automaton simulation of molten pool migration due to temperature gradient zone melting

Acta Physica Sinica ◽

10.7498/aps.68.20181587 ◽

2019 ◽

Vol 68 (4) ◽

pp. 048102

Author(s):

Hui Fang ◽

Hua Xue ◽

Qian-Yu Tang ◽

Qing-Yu Zhang ◽

Shi-Yan Pan ◽

...

Keyword(s):

Temperature Gradient ◽

Cellular Automaton ◽

Molten Pool ◽

Zone Melting ◽

Gradient Zone

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Numerical Simulation of Temperature Distribution in a Containment Vessel of an Operating PWR Plant

Journal of Nuclear Engineering and Radiation Science ◽

10.1115/1.4026389 ◽

2015 ◽

Vol 1 (1) ◽

Cited By ~ 1

Author(s):

Yoichi Utanohara ◽

Michio Murase ◽

Akihiro Masui ◽

Ryo Inomata ◽

Yuji Kamiya

Keyword(s):

Numerical Simulation ◽

Temperature Distribution ◽

Temperature Gradient ◽

Heat Release ◽

Gas Phase ◽

Large Temperature ◽

Measured Temperature ◽

Average Temperature ◽

Containment Vessel ◽

Large Temperature Gradient

The structural integrity of the containment vessel (CV) for a pressurized water reactor (PWR) plant under a loss-of-coolant accident is evaluated by a safety analysis code that uses the average temperature of gas phase in the CV during reactor operation as an initial condition. Since the estimation of the average temperature by measurement is difficult, this paper addressed the numerical simulation for the temperature distribution in the CV of an operating PWR plant. The simulation considered heat generation of the equipment, the ventilation and air conditioning systems (VAC), heat transfer to the structure, and heat release to the CV exterior based on the design values of the PWR plant. The temperature increased with a rise in height within the CV and the flow field transformed from forced convection to natural convection. Compared with the measured temperature data in the actual PWR plant, predicted temperatures in the lower regions agreed well with the measured values. The temperature differences became larger above the fourth floor, and the temperature inside the steam generator (SG) loop chamber on the fourth floor was most strongly underestimated, −16.2 K due to the large temperature gradient around the heat release equipment. Nevertheless, the predicted temperature distribution represented a qualitative tendency, low at the bottom of the CV and increases with a rise in height within the CV. The total volume-averaged temperature was nearly equal to the average gas phase temperature. To improve the predictive performance, parameter studies regarding heat from the equipment and the reconsideration of the numerical model that can be applicable to large temperature gradient around the equipment are needed.

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