• Korean Chemical Engineering Research
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• 제52권2호
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• pp.199-204
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• 2014

2성분 응고계에서 다공성 mush 층에서의 조성 대류는 생성되는 제품의 질에 영향을 준다. 본 연구에서는 일정한 속도로 응고되는 mush 층을 고려하였다. 선형 안정성 이론을 사용하여 mush 층에 대한 교란방정식을 유도하였고, 기본상태 온도장과 mush 층에서 기공률의 분포를 수치해법으로 조사하였다. 과열량이 클 때 mush 층의 두께는 열경계층의 두께에 비해 상대적으로 작았다. 과열량이 감소함에 따라 mush 층의 두께를 기준으로 한 Rayleigh 수는 증가하였고, mush 층은 조성 대류에 대해 안정해졌다. mush 층의 윗면에 등온조건을 적용한 경우보다 온도 및 열속의 연속조건을 액체-mush 계면에 적용한 경우에 임계 Rayleigh 수가 더 작게 얻어졌다.

• Journal of applied mathematics & informatics
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• 제29권5_6호
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• pp.1269-1283
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• 2011

Here we consider magneto-convection in a mushy layer which is formed during solidification of binary alloys. The mushy layer is treated as an active porous media with variable permeability. The equations governing the layer are conservation of mass, conservation of heat, conservation of solute, magnetic induction equation, momentum equation governed by the Darcy's law and Maxwell's equations for the magnetic field. To study the second order effects on the flow without solving the second order system, we need to obtain the adjoint system for the flow. This motivates the authors we derive the adjoint system analytically for the mushy layer case. Numerical results of the adjoint system are presented for passive and active mushy layers at the onset of the motion using a set of parameters experimentalists use.

• Korean Chemical Engineering Research
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• 제55권6호
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• pp.868-873
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• 2017

Natural convection is driven by the compositional buoyancy in solidification of a binary melt. The stabilities of convection in a growing mushy layer were analyzed here in the time-dependent solidification system of a near-eutectic melt cooled impulsively from below. The linear stability equations were transformed to self-similar forms by using the depth of the mushy layer as a length scale. In the liquid layer the stability equations are based on the propagation theory and the thermal buoyancy is neglected. The critical Rayleigh number for the mushy layer increases with decreasing the Stefan number and the Prandtl number. The critical conditions for solidification of aqueous ammonium chloride solution are discussed and compared with the results of the previous model for the liquid layer.

• Journal of applied mathematics & informatics
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• 제30권3_4호
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• pp.499-510
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• 2012

Here we consider the inertial effect in a horizontal mushy layer during solidification of a binary alloy. Using perturbation technique, we obtain two systems, one of zero order and the other of first order. We consider a mushy layer with an impermeable mush-liquid interface and of constant permeability. The analysis reveals that the effect of inertial parameter is stabilizing in the sense that the critical Rayleigh number at the onset of motion increases by the inertial effect.

• Korean Chemical Engineering Research
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• 제47권2호
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• pp.174-178
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• 2009

이성분 혼합물의 응고중에 수지상 결정으로 이루어진 mush 층이 형성될 수 있다. 본 연구진이 개발한 전파이론으로 mush 층에서 성분적 대류의 발생을 해석하였다. Emms와 Fowler의 모델로부터 유도한 자기유사 안정성 방정식을 사용하여 대류 발생에 대한 임계 Rayleigh 수를 수치방법으로 계산하였다. 과열량이 아주 크거나 mush 층의 성장률이 아주 작은 극한의 경우에 본 연구 결과는 준정적 안정성 해석 결과와 같아진다.

• Korean Chemical Engineering Research
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• 제50권1호
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• pp.61-65
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• 2012

이성분 용융액의 시간의존형 응고계에서 mush 층의 대류발생을 선형 안정성 이론으로 해석하였다. 본 연구에서는 근공융물 mush 층을 다공성 블록으로 가정한 단순화된 모델에 전파이론을 적용하여 대류발생 임계조건을 구하였다. 본 연구 모델에서는 기존의 실험결과 및 mush층 위의 액체층을 포함하여 고려한 이론적 연구의 결과보다 더 높은 임계 Rayleigh 수가 얻어졌다. mush 층의 윗 경계면에 일정압력(투과)조건을 적용하는 경우가 비투과조건에 비해 임계 Rayleigh 수를 더 작게 하며 염화암모늄 수용액의 응고실험결과와 더 근접한 것으로 조사되었다.

• 한국주조공학회지
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• 제6권1호
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• pp.20-26
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• 1986

In order to investigate the solidification characteristics of CV. graphite cast iron, decantation technique and thermal analysis test were used. Solidification characteristics were studied in the specimens with various compositions and graphite shape. The results were as follows; 1. The first surface solidifcation layer is formed along the mold wall by the growth of austenite dendrites in hypoeutectic composition and thin solid film in hypereutectic composition. 2. The mushy degree of solidifcation of hypereutiectic composition is higher than that of hypoeutectic. 3. In hypoeutectic, the effect of change of the mushy degree of solidification on the graphite shape is small, however, in hypereutectic the mushy degree of solidification becomes higher in order of flake, CV, and spheroidal graphite cast iron.

• 대한기계학회논문집B
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• 제24권11호
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• pp.1437-1446
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• 2000

A numerical analysis on the freeze coating process of a non-isothermal finite dimensional plate with a binary alloy is performed to investigate the growth and decay behavior of the solid and the mushy layer of the freeze coat and a complete procedure to calculate the process is obtained in this study. The continuously varying solid and mushy layers are immobilized by a coordinate transform and the resulting governing differential equations are solved by a finite difference technique. To account for the latent heat release and property change during solidification, proper phase change models are adopted. And the convection in the liquid melt is modeled as an appropriate heat transfer boundary condition at the liquid/mushy interface. The present results are compared with analytic solutions derived for the freeze coating of infinite dimensional plates and the discrepancy is found to be less than 0.5 percent in relative magnitude for all simulation cases. In addition the conservation of thermal energy is checked. The results show that the freeze coat grows proportional to the 1.2 square of axial position as predicted by analytic solutions ar first. But after the short period of initial growth, the growth rate of the freeze coat gradually decreases and finally the freeze coat starts to decay. The effects of various non-dimensional processing parameters on the behavior of freeze coat are also investigated.

• 한국기계가공학회지
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• 제18권12호
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• pp.52-58
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• 2019

This study numerically analyzed the icing process in a U-shaped pipe exposed to the outside by considering the mushy zone of freezing water. Numerical results showed that the flow was pulled outward due to the U-shaped bend in the freezing section exposed to the outside, which resulted in the ice wave formation on the wall of the bended pipe behind. At the same time, the formation of a corrugated ice layer became apparent due to the venturi effect caused by the ice. The factors affecting the freezing were investigated, including the change of the pipe wall temperature, the water inflow velocity, and the pipe bend spacing. It was found that, as a whole, the thickness of the freezing layer increased as the pipe wall temperature decreased. It was also found that the freezing layer became relatively thin when the inflow rate of water was increased, and that the spacing of the pipe bends did not significantly impact the change in the freezing layer.

• 한국기계가공학회지
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• 제17권6호
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• pp.144-150
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• 2018

In this study, the freezing process of L-shaped pipe exposed to the outside was investigated numerically by considering the mushy zone of freezing water. From the numerical results, it was found that the flow was outwardly directed due to the influence of the L-shaped bending part in the outside exposed part of the pipe, and the ice was formed in the shape of longitudinal corrugation on the wall surface of the pipe after the bending part. It is confirmed that this phenomenon is caused by the venturi effect due to the freezing as seen in connection with the velocity distribution in the pipe. It is found that the remelting phenomenon at the end of the freezing section occur simultaneously during the process of forming the ice in the pipe section. In regard of the factors affecting freezing, it was found that the thickness of the freezing layer is increased as the exposed pipe surface temperature is decreased, and the pipe surface temperature had a significant effect on the change of the freezing layer thickness. At the same time, it was found that the freezing layer becomes relatively thin when the water inflow rate is increased. This phenomenon was caused by reducing the exposure time of freezing water due to the vigorous flow convection of the water fluid.