• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.14 no.11
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• pp.964-971
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• 2002

A numerical investigation of the constrained melting of phase change materials within spherical-like capsule is presented. A single-domain enthalpy formulation is used for simulation of the phase change phenomenon. The solution methodology is verified with the melting process inside an isothermal spherical capsule. Especially, the effect of capsule shape on the heat storage is emphasized. Two shape parameters are considered from the real capsule shape showing good characteristics of heat storage and the effect of these parameters is examined. Early during the melting process, the conduction mode of heat transfer is dominant. Thus the capsule shape with large surface area is desirable. However, the capsule shape with large surface area plays negative role on the strength of buoyancy-driven convection that becomes more important as melting continues.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.58 no.3
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• pp.310-315
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• 2009

This investigation was performed to study the characteristics of electricity and heat transfer that occur in the cylinder of electrode type humidifier during the process of water evaporation. Measurements were made to obtain the amount of water evaporation, the consumption of electric power, electrical conductivity, etc according to the materials and shapes of electrode. When the humidifier was in non-drain controlled mode, the number and amplitude of current cycle per minute increased gradually with the lapse of time, whereas for drain controlled mode, it decreased about 40[%] after draining water. It was found that for non-drain controlled mode, the thermal efficiency of humidifier which used SS400, STS316 and wire net electrode type was about 95~96[%] and it was 2~4[%] higher than that of drain controlled mode. Also, it was shown that the thermal efficiency of humidifier which used neighboring six-phase electrode balanced electrically was 4[%] higher than that of existing six-phase type.

• Journal of ILASS-Korea
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• v.25 no.3
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• pp.119-125
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• 2020

In this paper, we used Helmholtz solver based on 3D finite element method to quantitatively analyze the effects of change of gain, time delay and time delay spread, which are the main variables of flame transfer function, on combustion instability in gas turbine combustor. The effects of the variable of flame transfer function on the frequency and growth rate, which are the main results of combustion instability, were analyzed by applying the conventional heat release fluctuation model and modified one considering the time spread. The analysis results showed that the change of gain and time delay in the same resonance mode affected the frequency of the given resonance modes as well as growth rate of the feedback instability, however, the effect of time delay spread was not relatively remarkable, compared with the dominant effect of time delay.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.29 no.9 s.240
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• pp.997-1005
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• 2005

The extinction characteristics of low strain rate normal gravity (1-g) nonpremixed methane-air flames were studied numerically and experimentally. A time-dependent axisymmetric two-dimensional (2D) model considering buoyancy effects and radiative heat transfer was developed to capture the structure and extinction limits of 1-g flames. One-dimensional (1D) computations were also conducted to provide information on 0-g flames. A 3-step global reaction mechanism was used in both the 1D and 2D computations to predict the measured extinction limit and flame temperature. A specific maximum heat release rate was introduced to quantify the local flame strength and to elucidate the extinction mechanism. Overall fractional contribution by each term in the energy equation to the heat release was evaluated to investigate the multi-dimensional structure and radiative extinction of 1-g flames. Images of flames were taken for comparison with the model calculation undergoing extinction. The two-dimensional numerical model was validated by comparing flame temperature profiles and extinction limits with experiments and ID computation results. The 2D computations yielded insight into the extinction mode and flame structure of 1-g flames. Two combustion regimes depending on the extinction mode were identified. Lateral heat loss effects and multi-dimensional flame structure were also found. At low strain rates of 1-g flame ('Regime A'), the flame is extinguished from the weak outer flame edge, which is attributed to multi-dimensional flame structure and flow field. At high strain rates, ('Regime B'), the flame extinction initiates near the flame centerline due to an increased diluent concentration in reaction zone, which is the same as the extinction mode of 1D flame. These two extinction modes could be clearly explained with the specific maximum heat release rate.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.65 no.1
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• pp.73-80
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• 2016

The preliminary test for the dual mode plasma torch system was carried out to explore the operation properties in advance. The dual mode plasma torch system that is able to operate in transferred, non-transferred, or dual mode is very adequate for melting the mixed wastes including nonconductive materials such as concrete, asbestos, etc. since it exploits both the high efficiency of heat transfer to the melt in transferred mode and stable operation in non-transferred mode. Also, system operation including restarting is reliable and very easy. A stationary melter with a refractory structure was designed and manufactured considering the melting behavior of slags to minimize the refractory erosion. The power supply for the dual mode plasma torch system built with high power insulated gate bipolar transistor (IGBT) modules has functions for both current control and voltage control and is sufficient to suppress the harmonics during the operation of the plasma torch. The power supply provides two different voltages for transferred operation and non-transferred. It is confirmed that the operation voltage in transferred is always higher than non-transferred. The dual mode plasma torch system was successfully developed and is under operation for a melting experiment to optimize operation data.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2017.05a
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• pp.59-60
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• 2017

Combustion instability of gas turbine is performed by adopting dynamic mode decomposition (DMD). The unstable frequencies are calculated and compared with FFT results. The damping coefficient derived from the DMD technique and FFT results were compared and analyzed. OH radical is measured by experimental work and fluctuation field is extracted and FTF was calculated at various points with DMD. The gains of FTF are changed depending on the extraction position of the heat release fluctuation field.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.22 no.3
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• pp.156-164
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• 2010

Combustion instability is a major issue in design of gas turbine combustors for efficient operation with low emissions. Combustion instability is induced by the interaction of the unsteady heat release of the combustion process and the change in the acoustic pressure in the combustion chamber. In an effort to develop a technique to predict self-excited combustion instability of gas turbine combustors, a new stability analysis method based on the transfer matrix method is developed. The method views the combustion system as a one-dimensional acoustic system with a side branch and describes the heat source as the input to the system. This approach makes it possible to use not only the advantages of the transfer matrix method but also well established classic control theories. The approach is applied to a gas turbine combustion system, which shows the validity and effectiveness of the approach.

• Proceedings of the SAREK Conference
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• 2009.06a
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• pp.1449-1457
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• 2009

Combustion instability is a major issue in design of co-generation gas turbine combustors for efficient operation with low emissions. Combustion instability is induced by the interaction of the unsteady heat release of the combustion process and the change in the acoustic pressure in the combustion chamber. In an effort to develop a technique to predict self-excited combustion instability of co-generation gas turbine combustors, a new stability analysis method based on the transfer matrix method is developed. The method views the combustion system as a one-dimensional acoustic system with a side branch and describes the heat source as the input to the system. This approach makes it possible to use not only the advantages of the transfer matrix method but also well established classic control theories. The approach is applied to a simple co-generation gas turbine combustion system, which shows the validity and effectiveness of the approach.

• 한국전산유체공학회:학술대회논문집
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• 2011.05a
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• pp.124-128
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• 2011

The heat transfer rate in an oven is very important for the quality of cooking food. For a robust performance design in an electric oven, forced convection has been used rather than natural convection, in bake and convection mode. Forced convection heat trans for in a vented electric oven has been numerically evaluated using the commercial software FLUENT. CFD modeling of the electric oven involves three-dimensional, steady state, MRF fan model and DO radiation model. In this study, the electric oven cavity and fan modules are not simplified. Other research shows that the boundary condition can often lead to non-physical solutions, such as reverse flaw at the top vent. To remove this non-physical solution, control volume has been expanded at the nearby vent. This numerical analysis has been performed with dedicated experimental support. The results show that there is less than a 2.2% difference between the simulation and experimental data for the temperature profile of food. From this research we can use this oven simulation technique to make a better convection system in an electric oven.

• Journal of the Korean Wood Science and Technology
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• v.48 no.5
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• pp.710-721
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• 2020

This study used a building model made up of cement, brick, and wood to measure temperature and relative humidity for 3 days in a closed environment with a diameter of 900 mm, and performed a comparative analysis of the effect of types of building materials on the indoor temperature environment and heat transfer characteristics. The water installed inside the building model represented the person in the room and was used to assess how the environment effects the person. Wooden building model showed the lowest heat loss due to the higher thermal insulation properties than cement and brick buildings. The thermal comfort of each building model was calculated using temperature and relative humidity, and the wooden building model created a more pleasant environment than the cement and brick building models.