• Proceedings of the KSME Conference
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• 2007.05a
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• pp.1836-1841
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• 2007

Based on three-dimensional (3-D) FE limit analyses, this paper provides plastic limit and TES(Twice-Elastic-Slope) loads for pipe bends under combined pressure and out-of-plane bending. The plastic limit loads are determined from FE limit analyses based on elastic-perfectly-plastic materials using the small geometry change option, and the FE limit analyses using the large geometry change option provide TES plastic loads. A wide range of parameters related to the bend geometry is considered. Based on the FE results, closed-form approximations of plastic limit and TES plastic load solutions for pipe bends under out-of-plane bending are proposed.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.27 no.9
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• pp.1317-1326
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• 2003

The maximum temperature limit at which liquid boils explosively is called the superheat limit of liquids. The superheat limits of hydrocarbon liquids and their mixtures were measured by the droplet explosion technique. Also the fully evaporated droplet at the superheat limit and subsequent bubble evolution from the fully evaporated droplet were visualized. The pressure wave emanating from the evaporating droplet and subsequent bubble evolution process were measured by a piezoelectric transducer.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.22 no.6
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• pp.549-555
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• 2009

Based on three-dimensional(3-D) finite element limit analyses, this paper provides limit and TES (Twice-Plastic Load) loads for mitred pipe bends under bending and pressure. The plastic limit loads are determined from FE limit analyses based on elastic-perfectly-plastic materials using the small and large geometry change option. A wide range of parameters related to the mitred bend geometry is considered. Based on the finite element results, closed-form approximations of plastic limit and TES plastic load solutions for mitred pipe bends under bending are proposed.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.15 no.1
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• pp.18-27
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• 2019

The Advanced Power Reactor 1400 (APR1400) Steam Generator (SG) uses alloy 690 as a tube material and SA-508 Grade 3 Class 1 as a tubesheet material to form tube-to-tubesheet joint through hydraulic expansion process. In this paper, the residual stresses in the SG tube-to-tubesheet contact area was investigated by applying Model-Based System Engineering (MBSE) methodology and the V-model. The use of MBSE transform system description into diagrams which clearly describe the logical interaction between functions hence minimizes the risk of ambiguity. A theoretical and Finite Element Methodology (FEM) was used to assess and compare the residual stresses in the tube-to-tubesheet contact area. Additionally, the axial strength of the tube to tubesheet joint based on the pull-out force against the contact joint force was evaluated and recommended optimum autofrettage pressure to minimize residual stresses in the transition zone given. A single U-tube hole and tubesheet with ligament thickness was taken as a single cylinder and plane strain condition was assumed. An iterative method was used in FEM simulation to find the limit autofrettage pressure at which pull-out force and contact force are of the same magnitude. The joint contact force was estimated to be 20 times more than the pull-out force and the limit autofrettage pressure was estimated to be 141.85MPa.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.20 no.8
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• pp.2572-2592
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• 1996

A low-Reynolds-number second moment turbulence closure was developed with the aid of DNS data. Model coefficients of nonlinear return to isotropy term were derived by use of Cayley-Hamilton theorem and two component turbulence limit condition as the functions of invariances of anisotropy and turbulent Reynolds number. Launder and Tselepidakis' cubic mean pressure strain model was modified to fit the predicted pressure-strain components to the DNS data. Two component turbulence limit condition was the precondition to be satisfied in developing the second moment turbulence closure for the realizable Reynolds stress prediction. But the satisfactions of Reynolds stress level and pressure-strain level of each component were compromised because the satisfaction of both levels was impossible.

• Journal of the Korean Society of Safety
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• v.15 no.4
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• pp.95-100
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• 2000

This study was performed in Hartmann type dust explosion apparatus in order to research the dust explosion characteristics of hydroxypropyl methyl cellulose(HPMC): minimum explosive limit, minimum ignition energy, limiting oxygen concentration, maximum explosion pressure, rate of pressure rise, etc. The samples of HPMC dust were distributed into 120-140 mesh, 170-230 mesh and 325 under, and the gap distance of the discharge electrode was setted up at 5mm. The experimental results were obtained as follows: (1) The minimum explosive limit for HPMC dust was founded at 180g/㎥. the minimum ignition energy at 9.8mJ and the limiting oxygen concentration at 12%. (2) The maximum explosion pressure of HPMC dust was $8.1kg/cm^2\;{\cdot}\;$abs at the concentration of $500g/m^3$ and the maximum rate of pressure rise was 203.98 bar/sec at the concentration of $480g/m^3$ for 325 under.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.22 no.11
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• pp.1564-1570
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• 1998

In-situ particle monitors(ISPMs) are widely used for monitoring contaminant particles in vacuum-based semiconductor manufacturing equipment. In the present research, the performance of a Particle Measuring Systems(PMS) Vaculaz-2 ISPM at subatmospheric pressures has been studied. We created uniform upstream conditions of particle concentration and measured the detection efficiency, the lower detection limit, and the size response of the ISPM using uniform sized methylene blue aerosol particles. The effect of particle size, particle velocity, particle concentration, and system pressure on the detection efficiency was examined. Results show that the detection efficiency of the ISPM decreases with decreasing chamber pressure, and with increasing mass flow rate. The lower detection limit of the ISPM, determined at 50 % of the measured maximum detection efficiency, was found to be about $0.15{\sim}0.2{\mu}m$, which is similar to the minimum detectable size of $0.17{\mu}$ given by the manufacturer.

• 한국연소학회:학술대회논문집
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• 1999.10a
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• pp.111-115
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• 1999

In order to enhance the burner performance of household gas fired absorption chiller/heaters, the operating condition(excess air $\approx$ 10%) of the burner currently being used was required to be optimized. In this regard, we examined where the $CO_{\min}$. emission limit was located between blow off and yellow tip limit and how much amount of excess air was exhausted by means of observing blow off and yellow tip limit. It was found that the $CO_{\min}$ limit(excess air ${\approx}$ 4%) was determined near the yellow tip limit. The effect of exhaust pressure on the $CO_{\min}$. limit was that, if exhaust pressure was higher than that in steady condition, higher air blower fan rpm is demanded to maintain the $CO_{\min}$ limit. Therefore, it was necessary to optimize the operating condition of burner in terms of a thermal efficiency and safety.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.15 no.2
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• pp.71-80
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• 2019

In this study, limit load equations of thick-walled pipes with inner and outer circumferential surface cracks were derived based on force and moment equilibrium conditions. Since the limit load equations based on the mean radius at uncracked ligament, previously proposed by Kanninen et al., are based on the premise that the pipe wall thickness is relatively thin, the existing limit load solutions are only applicable to thin-walled pipes. In order to analyze the effect of the pipe thickness and surface crack depth on the limit load results, the predictions using the present limit load equations are compared with those using the existing solutions for thin-walled pipes. Being derived considering the thickness effect, the limit load solutions from this paper are believed to be more accurate for thick-walled pipes than the limit load equations presented for thin-walled pipes, and thus to be valuable equations for integrity assessment of thick-walled pipes.

• Nuclear Engineering and Technology
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• v.53 no.3
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• pp.901-910
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• 2021

KHNP recently has obtained the approval for the commercialization of the modified 37-element (or 37 M) fuel bundle and now is loading the 37 M fuel bundles in CANDU-6 reactors in KOREA. One of the main issues for approval was the burnup limit. Due to CANDU design and neutronic characteristics, there was no specific burnup restriction of a fuel bundle. The absence of a burnup limit does not mean that a fuel bundle can stay in the CANDU reactor without a time limit. However, the regulator requested traditional design values as well as the burnup limit reflecting the computer code uncertainty. The method for the PWR burnup limit was not applied to the CANDU fuel bundle. Since there was no approved methodology to build the burnup limit with uncertainties, KHNP introduced a Monte-Carlo method coupled with a 95/95 approach to determine the conservative burnup limit from the viewpoint of the centerline temperature, internal pressure, strain measurement deviation. Moreover, to consider the uncertainties of various computing models, a converted power uncertainty was introduced. This paper presents the methodology and puts forward the limits on burnup, evaluated for each of the existing and modified fuel bundles, in consideration of the pressure tube aging condition.