• Transactions of the Korean Society of Mechanical Engineers B
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• v.29 no.7 s.238
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• pp.814-819
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• 2005

The phase change heat transfer has been applied to the processes of machines as well as of manufacturing. The cycle in a heat exchanger includes the phase change phenomena of coolant for air conditioning, the solidification in casting process makes use of the characteristics of phase change of metal, and the welding also proceeds with melting and solidification. To predict the phase change processes, the experimental and numerical approaches are available. In the case of numerical analysis, the Enthalpy method is most widely applied to the phase change problem, comparing to the other numerical methods, i.e. the Equivalent Specific Heat method and the Temperature Recovery method. It's because that the Enthalpy method is accurate and straightforward. The Enthalpy method does not include any correction step while the correction of final temperature field is inevitable in the Equivalent Specific Heat method and the Temperature Recovery method. When the temperature field is to be used in the calculation, however, there must be converting process from enthalpy to temperature in the calculation scheme of Enthalpy method. In this study, an improved method for the Equivalent Specific Heat method is introduced whose method dose not include the correction steps and takes temperature as an independent variable so that the converting between enthalpy and temperature does not need any more. The improved method is applied to the solidification process of pure metal to see the differences of conventional and improved methods.

• Journal of Advanced Marine Engineering and Technology
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• v.20 no.3
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• pp.162-170
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• 1996

A numerical study on the Stefan problem occurred in cryosurgery is performed. Crank-Nicholson type finite difference algorithm based on the enthaly method is adapted to solve the phase change problem in this study. As it is a moving boundary problem, special emphasis is put on the estimation of the freezing front location. Two cases selected here are freezings of human tissue by disk type cryoprobe and by hemispherical one. In both cases, the heat flows are considered to be one dimensional. The calculated results using enthalpy method are compared with those using the program TRUMP and with Neumann's solution. These results agree guite well with each other. While it is pretty difficult to get accurate freezing front location by TRUMP due to the so- called "phase change knee" occured during the phase change, the algorithm based on the enthalpy method is proved to be very powerful to cope with this kind of problem.f problem.

• Journal of the Korean Society of Safety
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• v.15 no.3
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• pp.14-22
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• 2000

A numerical analysis has been performed on the two-dimensional rectangular gallium melting problem using the enthalpy method. The major advantage of this method is that the physical domain is discretized with fixed grids without transforming variables and the interface conditions of phase change are accounted for the definition of suitable source terms in the governing equations. But in the fixed method, there is some ambiguity in defining the porosity constant which has no physical interpretation. If the velocity correction is included in the momentum equation, for the appropriate range of porosity constant, the realistic predictions are obtained. The object of the present work is to predict the phase change within the molten steel with thin riser slab using the modified enthalpy-porosity method. The computational procedures for predicting velocity and temperature are based on the finite volume method and the non-staggered grid system. The influence of natural convection on the melting process is considered. A comparison with the experimental results shows that the modified method is better than the previous one.

• Journal of the Korean Society of Industry Convergence
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• v.23 no.3
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• pp.499-505
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• 2020

Capacitor-run single-phase induction motor is cheaper than motors that use permanent magnets and is widely used in home appliances and industries based on relatively high durability and productivity. It can also be operated by line. However speed cannot be controlled because the line frequency is free. In this paper we dealt pole change method one of the method controlling speed of capacitor-run single-phase induction motor. The conventional pole change method is difficult to improve the power and efficiency of the motor because the composition of the pole change device is complex and do not have enough area of the windings because of windings not used according to the driving conditions. In this paper, we proposed the pole change method that is used main windings and auxiliary windings at 4 poles operation and used auxiliary windings as compensation windings at 2 poles operation. The proposed method was verified through finite element analysis.

• Journal of computational fluids engineering
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• v.15 no.2
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• pp.86-94
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• 2010

A thermal-hydraulic code, named CUPID, has been developed for the analysis of transient two-phase flows in nuclear reactor components. A two-fluid three-field model was used for steam-water two-phase flows. To obtain numerical solutions, the finite volume method was applied over unstructured cell-centered meshes. In steam-water two-phase flows, a phase change, i.e., evaporation or condensation, results in a great change in the flow field because of substantial density difference between liquid and vapor phases. Thus, two-phase flows are very sensitive to the local pressure distribution that determines the phase change. This in turn puts emphasis on the accurate evaluation of local pressure gradient. This paper presents a new reconstruction method to evaluate the pressure gradient at cell centers on unstructured meshes. The results of the new scheme for a simple test function, a gravity-driven cavity, and a wall boiling two-phase flow are compared with those of the previous schemes in the CUPID code.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.13 no.12
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• pp.1223-1229
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• 2001

Though conventional calorimetry methods such as differential scanning calorimetry (DSC) and differential thermal analysis (DTA) are used generally in measuring heat of fusion, T-history method has the advantages of a simple experimental apparatus and no requirements of sampling process, which is particularly useful for measuring thermal properties of inhomogeneous phase change materials (PCMs) in sealed tubes. However, random criteria (a degree of supercooling) used in selecting the range of latent heat release and neglecting sensible heat during the phase change process can cause significant errors in determining the heat of fusion. In the present study, it was shown that a 40% discrepancy exists between the original T-history and the present methods when analyzing the same experimental data. As a result, a reasonable modification to the original T-history method is proposed.

• International Journal of Air-Conditioning and Refrigeration
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• v.11 no.1
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• pp.32-39
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• 2003

Though conventional calorimetry methods such as differential scanning calorimetry and differential thermal analysis are used generally in measuring heat of fusion, T-history method has advantages of a simple experimental apparatus and no requirements of sampling process, which is particularly useful for measuring thermophyical properties of in-homogeneous phase change materials in sealed tubes. However, the degree of supercooling used in selecting a range of latent heat release and neglecting sensible heat during the phase change process can cause significant errors in determining the heat of fusion. In the present study, it was shown that a 40% discrepancy exists between the original T-history and the present methods when analyzing the same experimental data. As a result, a reasonable modification to the original T-history method is proposed.

• 전기의세계
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• v.13 no.2
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• pp.1-4
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• 1964

Phase transformation is used to change some phase from phase in A.C. system. We have been used Scott or Fork connection in phase transformation the otherwise phase transformation was constructed from M-G set. From this M-G set, we could make phase shift facilities by mannual. Now, I can derive more easy phase transformation from taking another method. I believe this new phase transformation method in the first thing in the world. And so, I am going to explain about phase transformer construction process. The first, we could devide into equal part of core around the iron core as to be same size. The second, you will make primary and secondary winding on the core. The third, when you will supplied three phase A.C. at the terminal of primary winding you can get e.m.f. inducing of some phase at secondary. And so, we could make phase change from some phase A.C. We can apply this principle in many fields, i.e., freequency changer, phase leader of no use condenser, voltage regulator in keeping balance, and D.C. generator. And more, I will introduce in details concerning main pinciple and theory through following chapter.

• Journal of the Korean Society of Visualization
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• v.21 no.2
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• pp.63-71
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• 2023

Energy storage and distribution technologies are emerging as important factors as research on renewable energy continues. Analyzing the thermal flow of phase change material inside a latent heat storage device and to predict the phase change time is an important part for improvement of thermal performance. However, most of the current research is based on the trial-and-error experimental investigation to measure the phase change time. Therefore, in this study, a can-type phase change material container was designed, and the numerical method for analyzing the thermal flow of phase change material was established and validated. The error rate of the phase change time between the numerical and experimental results was within 5%, which proves its reliability. As a result, the phase change finishing times were found to be 78 minutes with inlet fluid temperature of 80℃ during charging process, and 126 minutes with inlet fluid temperature of 9℃ during discharging process.

• 한국전산유체공학회:학술대회논문집
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• 2005.10a
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• pp.75-80
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• 2005

The present work was undertaken to numerically analyze the defrosting phenomena of windshield glass. In order to analysis the phase change from frost to water on windshield glass by discharging hot air from a defroster nozzle, the flow and the temperature field of the cabin interior, the heat transfer through the windshield glass, and the phase change of frost should be solve simultaneously. In the present work, the flow field was obtained by solving 3-D incompressible Navier-Stokes equations, and the temperature field was computed from the incompressible energy equation. The phase change process was solved by the enthalpy method. For the code validation, the temperature and the phase change of the driven cavity were calculated. The calculation showed a good agreement with other numerical results. Then, the present code was applied to the defrosting problem of a real automobile, and a good agreement with the experimental data was also obtained.