• Food Science and Biotechnology
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• v.18 no.5
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• pp.1293-1297
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• 2009

In this study, drying kinetics of onion slices was examined in a laboratory scale vacuum dryer at an air temperature in a range of $50-70^{\circ}C$. Moisture transfer from onion slices was described by applying the Fick's diffusion model, and the effective diffusivity was calculated. Temperature dependency of the effective diffusivity during drying process obeyed the Arrhenius relationship. Effective diffusivity increased with increasing temperature and the activation energy for the onion slices was estimated to be 16.92 kJ/mol. The experimental drying data were used to fit 9 drying models, and drying rate constants and coefficients of models tested were determined by non-linear regression analysis. Estimations by the page and Two-term exponential models were in good agreement with the experimental data obtained.

• Nuclear Engineering and Technology
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• v.30 no.5
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• pp.424-434
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• 1998

RELAP5/Mod3.1 code was assessed with the semiscale experiment S-NC-3, and S-NC-4, which simulated the two-phase natural circulation and reflux condensation for the SBLOCA of PWR, respectively . Test S-NC-3 and S-NC-4 calculation results showed that RELAP5/Mod3.1 quite well describes the influence of steam generator secondary side heat transfer degradation on both two-phase natural circulation and reflux condensation. A comparison between the calculated and measured two-phase mass flow rate in test S-NC-3 shows good agreement for primary mass inventory more than 92%. And RELAP5/Mod3.1 have a good mass flow rate prediction capability for the transient such as S-NC-4 except some flow oscillations. The reflux flow rate for S-NC-4 test is under predicted, and the overall results verify that the correct prediction of the reduced liquid level appears to be required for the correct calculation of the overall phenomena.

• JSTS:Journal of Semiconductor Technology and Science
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• v.13 no.1
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• pp.28-33
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• 2013

Spin-torque oscillators (STO) is a new device that can be used as a tunable microwave source in various wireless devices. Spin-transfer torque effect in magnetic multilayered nanostructure can induce precession of magnetization when bias current and external magnetic field are properly applied, and a microwave signal is generated from that precession. We proposed a semi-empirical circuit-level model of an STO in previous work. In this paper, we present a refined STO model which gives more accuracy by considering physical phenomena in the calculation of effective field. Characteristics of the STO are expressed as functions of external magnetic field and bias current in Verilog-A HDL such that they can be simulated with circuit-level simulators such as Hspice. The simulation results are in good agreement with the experimental data.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.55 no.5
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• pp.278-285
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• 2006

A micro hotplate for micro gas sensor was fabricated by MEMS technology. In order to heat up the gas sensing material to a target temperature, a micro hotplate was built on the gas sensor. The sensing material was deposited on the heater and electrodes, and did not contact with the silicon base to minimize the heat loss to the silicon base. The electric power to heat up the gas sensor was measured. The temperature distribution of micro gas sensor was analyzed by a CFD program. The predicted electric power to heat up th sensing material showed a good agreement with the measured data. The design of micro gas sensor could be modified to increase the temperature uniformity and to decrease the electric power consumption by optimizing the layout of micro hotplate and electrodes.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.10 no.6
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• pp.63-70
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• 2001

This study is concerned with Finite Element Analysis on welded part of control link fur automobile. For analysis, control link was modeled into two parts, ring and rod. Heating condition, temperature distributions and fatigue fracture strength were analyzed using "HEAT III" and "NDURE" module of NISA II. Metal flow in the process of welding was simulat- ed by $DEFORM^{TM}2D$.The analyzed results were compared with experimental inspection. Quality of welded part was able to be improved by controlling metal flow in the process of welding by increase the friction constant of ring part. Heat transfer analysis and flow simulations were in good agreement wish welding experiments.

• Nuclear Engineering and Technology
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• v.32 no.6
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• pp.549-558
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• 2000

A transient model for hydrogen generation in molten metal-water interactions was developed with separate models for two stages of coarse mixing and stratification. The model selves the mechanistic equations (heat and mass transfer correlation, heat conduction equation and the concentration diffusion equation) of each stage with non-zero boundary conditions. Using this model, numerical simulations were performed for single droplet experiments in the Argonne National Laboratory tests and for FITS tests that simulated dynamic fragmentation and stratification. The calculation results of hydrogen generation showed better agreement to the experiment data than those of previous works. It was found from the analyses that the steam concentration to be reached at the reaction front might be the main constraint to the extent of the metal droplet oxidized. Also, the hydrogen generation rate in the coarse mixing stage was the higher than that in the stratification stage. The particle size was the most important factor in the coarse mixing stage to predict the amount of hydrogen generation.

• Journal of Ocean Engineering and Technology
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• v.19 no.1 s.62
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• pp.33-38
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• 2005

It has been well documented that plate forming is one of the most important processes in shipbuilding. In the most shipyards, the line heating method is primarily used for plate forming. Since the heating process is carried out for the curved plate and not for the flat plate, a curvature effect on the final deformation must be considered in deriving the simplified prediction models for deformation. This paper investigates the effect of curvature along the heating line on the deformation of the plate. First of all, results of numerical analysis are compared with these of a line-heating test, to justify the elasto-plastic analysis procedure for the present study, which shows good agreement. Then, the present numerical procedure is applied to flat and curved plate models, to investigate the curvature effect on the heat transfer characteristics and deformation by line heating.

• International Journal of Korean Welding Society
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• v.2 no.2
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• pp.1-6
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• 2002

This article presents an integrated modeling approach for coupled analysis of heat transfer and microstructure evolution in welding carbon steel. The modeling procedure utilizes commercial finite element code ABAQUS/Standard as the platform for solving the equation of heat conduction. User subroutines that Implement computational thermodynamics and kinetics models are integrated with the FEA code to compute the transient microstructure evolution. In this study, the integrated models are applied to simulate the hot-tap repair welding of carbon steel pipeline. Microstructural components are treated as user output variables. Based on the predicted microstructure and cooling rates, hardness distributions in the welds were also predicted. The predicted microstructure and hardness distribution were found in good agreement with metallographic examinations and hardness measurements. This study demonstrates the applicability of computational models for the development of welding procedure for in-service pipeline repair.

• Journal of Energy Engineering
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• v.21 no.3
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• pp.254-264
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• 2012

Rayleigh-Benard natural convection experiments were carried out as the preliminary experiment to simulate the natural convection of the core melt at the severe accident conditions. This work focused on the influences of plate separation distance(s), the existence of the side walls and crust geometries of upper and lower plates. Based upon the analogy concept, a cupric acid-copper sulfate electroplating system($H_2SO_4-CuSO_4$) was employed as the mass transfer system and measurements were made for $Ra_s$ ranging from $1.06{\times}10^7$ to $2.91{\times}10^{10}$. The test results measured for a single horizontal plate were in good agreement with the correlation reported by McAdams and those for two horizontal plates showed the similar trend to the existing Rayleigh-Benard heat transfer correlations developed by Dropkin and Somerscales, Globe and Dropkin. The measured heat transfer rate decreased with the increasing separation distance between the two plates and became similar to those for a single horizontal plate. Fin arrays mounted on both upper and lower plates enhanced the heat transfer rates. For all cases, the heat transfer rates measured for open side walls are higher than those for closed ones.

• Clean Technology
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• v.14 no.1
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• pp.53-60
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• 2008

The condensation heat transfer coefficients and pressure drops of hydrocarbon refrigerants (R-290 and R-600a) and hydrochlorofluorocarbon (HCFC) refrigerants were measured in the two horizontal double pipe heat exchangers with inner diameters of 10.07 mm and 5.80 mm at a mass flux of $35.5{\sim}210.4\;kg/m^2s$ and the condensation temperature of $40^{\circ}C$. The average condensation heat transfer coefficients of hydrocarbon refrigerants were higher than that of HCFC refrigerant(R-22). The pressure drop had a magnitude in the order of R-600a > R-290 > R-22. The pressure drops in the tubes with inner diameter of 10.07 mm were approximately $6{\sim}15%$, $9.8{\sim}12.5%$ and $2.1{\sim}4.6%$ higher for R-600a, R-290 and R-22, respectively, than those with inner diameter of 5.80 mm. The condensation heat transfer coefficients were compared with the published experimental data, and showed the best agreement with Haraguchi et al.'s correlation.