• Korean Journal of Mathematics
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• v.7 no.1
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• pp.27-35
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• 1999

As seen from the ammonium chloride experiment (Chen & Chen [1], Roberts & Loper [11], the interface near chimneys has an up-rising shape and we observe thickening of mush next to chimney. We analyze the thermal boundary layer around chimney that forms as the mush is cooled locally by the fluid rising through the chimney. We obtain solutions of the temperature, the solid fraction, and the pressure in the chimney wall. Also, our expression of the pressure shows that the fluid flow can require a huge pressure in order to pass through the chimney wall if its permeability is very small. We present a simple analytic description of the up-rising shape near the exit of the chimney, due to the fact that the comparatively solute (i.e. $NH_4Cl$ in the case of the ammonium chloride experiment)-rich fluid near the chimney tends to crystallize as it is chilled by the rising jet of cold fluid in the chimney.

• Journal of Mechanical Science and Technology
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• v.17 no.12
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• pp.2034-2041
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• 2003

This study introduced a lattice Boltzmann computational scheme capable of modeling thermo hydrodynamic flows with simpler equilibrium particle distribution function compared with other models. The equilibrium particle distribution function is the local Maxwelian equilibrium function in this model, with all the constants uniquely determined. The characteristics of the proposed model is verified by calculation of the sound speeds, and the shock tube problem. In the lattice Boltzmann method, a thermal fluid or compressible fluid model simulates the reflection of a weak shock wave colliding with a sharp wedge having various angles $\theta$$\sub$w/. Theoretical results using LBM are satisfactory compared with the experimental result or the TVD.

• Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
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• 2006.05a
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• pp.49-53
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• 2006

In this paper the thermal aging characteristics of transformer fluid were considered. First, the temperature rise characteristic in transformer winding was discussed. The temperatures were rapidly increased immediately with applying load and then the temperature was followed the exponential temperature rise model. Next, Capacitance and leakage current characteristics of the transformer fluid were measured during the over-loading operation. The capacitance of vegetable fluid and leakage current were evidently increased wit aging time. So the simple methods could be applied to diagnosis of the transformer aging

• 한국신재생에너지학회:학술대회논문집
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• 2006.06a
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• pp.103-106
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• 2006

The Plate reformer consisting of combustion chamber and reforming chamber for 25 kW MCFC stack has been operated and computational fluid dynamics was applied to estimate reactions and thermal fluid behavior in the reformer. The methane air 2-stage reaction was assumed in the combustion chamber, and three step steam reforming reactions were included in the calculation. Flow uniformity, reaction rate and species distribution, and temperature distribution were analyzed. In particular, temperature distribution was compared with the measurements to show good agreement in the combustion chamber, however, inappropriate agreement in the reformer chamber

• Transactions of the Korean Society of Mechanical Engineers A
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• v.35 no.10
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• pp.1161-1170
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• 2011

This paper presents a solution to the inverse problem for the service boundary conditions of thermal-flow and structure analysis in a catalyst substrate. The exhaust-gas purification efficiency of a catalyst substrate is influenced by the shape parameter, catalyst ingredients and so on and is estimated by the thermal flow uniformity. The formulations of the inverse problem of obtaining the thermal-flow parameters (inlet temperature, velocity, heat of reaction, convective heat-transfer coefficient) and the direct problem of estimating from a given outlet temperature distribution are described. An experiment was designed and the response-surface optimization technique was used to solve the proposed inverse problem. The temperature distribution of the catalyst substrate was obtained by thermal-flow analysis for the predicted thermal-flow parameters. The thermal stress and durability assessments for the catalyst substrate were performed on the basis of this temperature distribution. The efficiency and accuracy of the inverse approach have been demonstrated through the achievement of good agreement between the thermal-flow response surface model and the results of experimental vehicle tests.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1996.04a
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• pp.635-640
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• 1996

A thermo-elastic system in the production machine has highly nonlinear dynamic characteristics. In general, the finite element method is utilized for accurate analysis. However, it requires large computing time. Thus, thermo-elastic systems are usuallymodeled as electric and fluid system using lumped para,eter. In this paper. we propose the bondgraph model and transient simulation methodology of thermo-elastic system in consideration of various boundary and joint contact conditions. Consequently, the proposed method ensures a possibility of its on-line compensation about undesirable phenomena by using real time estimate process and electronic cooling device for thermal appropriate behavior. Thermo-elastic model consisting of bush and shaft including contact condition is presented.

• Journal of the Korean Solar Energy Society
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• v.23 no.2
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• pp.43-49
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• 2003

The thermal performance of the glass evacuated tube solar collector is numerically investigated. The glass evacuated tube solar collector consists of a two-layed glass tube, a copper tube, and the working fluid. The length and the diameter of the glass tube are 1,200mm and 38mm, respectively. The diameter, thickness, and length of the copper tube and the flow rate of air are considered as the important design and operating parameters of the collector. The effect of these parameters on the thermal performance of the collector are investigated. The results show that as the diameter, the thickness, and the length of the copper tube increase and the flow rate of the air decreases, the thermal performance and the outlet mean temperature increase.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.41 no.11
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• pp.699-707
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• 2017

This study presents a comparative thermodynamic analysis of subcritical and transcritical organic Rankine cycles for the recovery of low-temperature heat sources considering nine substances as the working fluids. The effects of the turbine inlet pressure, source temperature, and working fluid on system performance were all investigated with respect to metrics such as the temperature distribution of the fluids and pinch point in the heat exchanger, mass flow rate, and net power production, as well as the thermal efficiency. Results show that as the turbine inlet pressure increases from the subcritical to the supercritical range, the mismatch between hot and cold streams in the heat exchanger decreases, and the net power production and thermal efficiency increase; however, the turbine size per unit power production decreases.

• Journal of Advanced Marine Engineering and Technology
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• v.36 no.8
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• pp.1030-1035
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• 2012

In this research, we analysed design and CFD analysis of an inflow radial turbine for OTEC with an output power of 8kW using an working fluid of ammonia. The inflow radial turbine consists of scroll casing, vain nozzle with 18 blade numbers and rotor blade with 13 blade numbers. Mass flow rate, and inlet temperature are 0.5kg/s and $25^{\circ}C$ respectively, and variable rotational speeds were applied between 12,000 and 36,000 with 3,000 rpm intervals. As the results according to the rotational speeds, the designed speed is 24,000 rpm where maximum efficiency exists. The maximum efficiency and output power are 88.66% and 8.52kW, respectively. Through this study, we expect that the analysed results will be used as the design material for the composition of the turbine optimal design parameters corresponding to the target output power under various working material conditions.

• Journal of Advanced Marine Engineering and Technology
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• v.35 no.2
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• pp.216-223
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• 2011

TVC is a kind of ejector which entrains low pressure working fluid by using the high pressure working fluid. While most papers relating with ejectors treat the working fluid as an ideal gas for convenience, the fluid doesn't behave as the ideal gas when phase change occurs. In this study, numerical analysis is conducted by applying Redlich-Kwong equation of state instead of ideal gas equation of state. Two turbulent models are compared for the better prediction and SST k-${\omega}$ model is preferred rather than realizable k-${\epsilon}$ model by comparison. Energy loss at the diffuser inlet and throat using the real gas equation of state is relatively greater than that using ideal gas law. For the real gas case, pressure increase due to shock train at the diffuser outlet is relatively smaller than the ideal gas case, but both cases have the same pressure increase due to a pseudo shock.