• Nuclear Engineering and Technology
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• v.49 no.6
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• pp.1301-1309
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• 2017

The extinction probability of a branching process (a neutron chain in a multiplying medium) is calculated for a system randomly varying in time. The evolution of the first two moments of such a process was calculated previously by the authors in a system randomly shifting between two states of different multiplication properties. The same model is used here for the investigation of the extinction probability. It is seen that the determination of the extinction probability is significantly more complicated than that of the moments, and it can only be achieved by pure numerical methods. The numerical results indicate that for systems fluctuating between two subcritical or two supercritical states, the extinction probability behaves as expected, but for systems fluctuating between a supercritical and a subcritical state, there is a crucial and unexpected deviation from the predicted behaviour. The results bear some significance not only for neutron chains in a multiplying medium, but also for the evolution of biological populations in a time-varying environment.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.26 no.10
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• pp.1370-1377
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• 2002

This study analyzed the design performance of the bottoming system of combined cycle power plants using a once-through heat recovery steam generator. For a parallel arrangement of the main heater and reheater, parametric analyses were carried out to present the criteria for determining the reheater pressure and the location of the starting point of the reheater in the HRSG. The performance of the bottoming system was presented fer a range from high subcritical to supercritical pressure. The steam turbine power is as high as that of conventional triple-pressure bottoming systems. The serial arrangement of heat exchangers with division of each heater into several segments can achieve similar power level.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2010.11a
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• pp.597-600
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• 2010

Cold flow injection test was conducted to investigate the characteristics of cryogenic liquid nitrogen jet at sub to supercritical condition. Single jet injector element was installed in high pressure chamber to investigate the effect of ambient pressure around the jet, injector geometry and flow conditions. Experimental results showed obvious differences between jet characteristics under subcritical and supercritical condition. Effect of injector inlet shape also was investigated.

• Journal of the Korean Wood Science and Technology
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• v.34 no.6
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• pp.44-50
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• 2006

To characterize thermo-chemical feature of su gar conversion of woody biomass poplar wood (Populus alba${\times}$glandulosa ) by sub- and supercritical water was treated for 60s under subcritical (23 MPa, 325 and $350^{\circ}C$) and supercritical (23 MPa, 380, 400, and $425^{\circ}C$) conditions, respectively. Among degradation products undegraded poplar wood solids existed in aqueous products. As the treatment temperature increased, the degradation of poplar wood was enhanced and reached up to 83.1% at $425^{\circ}C$. The monomeric sugars derived from fibers of poplar wood by sub- and supercritical treatment were analyzed by high performance anionic exchange chromatography (HPAEC). Under the subcritical temperature ranges, xylan, main hemicellulose component in poplar wood, was preferentially degraded to xylose, while cellulose degradation started at the transition zone between sub and supercritical conditions and was remarkably accelerated at the supercritical condition. The highest yield of monomeric sugars amounts to ca. 7.3% based on air dried wood weight (MC 10%) at $425^{\circ}C$.

• Food Science of Animal Resources
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• v.35 no.2
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• pp.265-271
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• 2015

In a previous study, hydrolysates of porcine placenta were obtained and the extraction efficiency for proteins and amino acids was compared between sub- and super-critical water extraction systems; optimum efficiency was found to be achieved using subcritical water ($170^{\circ}C$, 10 bar). In this study, the effects of adding ethanol to the subcritical water system were investigated. The lowest-molecular-weight extraction product detected weighed 434 Da, and the efficiency of extraction for low-molecular-weight products was increased when either the concentration of ethanol was decreased, or the extraction time was lengthened from 10 min to 30 min. The highest concentration of free amino acids (approximately 8 mM) was observed following 30 min extraction using pure distilled water. The concentration of free amino acids was significantly lower when ethanol was added or a shorter extraction time was used (p<0.05). Color change of the solution following extraction was measured. There were no significant differences in color between lysates produced with different extraction times when using distilled water (p>0.05); however, using different extraction times produced significant differences in color when using 20% or 50% ethanol solution for subcritical extraction (p<0.05). The range of pH for the hydrolysate solutions was 6.4-7.5. In conclusion, the investigated extraction system was successful in the extraction of $\leq$ 500 Da hydrolysates from porcine placenta, but addition of ethanol did not yield higher production of low-molecular-weight hydrolysates than that achieved by DW alone.

• Proceedings of the KSME Conference
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• 2001.11b
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• pp.872-877
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• 2001

This study analyzed the design performance of the bottoming system of combined cycle power plants adopting a single-pressure once-through heat recovery steam generator with reheat. A computer program was constructed and parametric analyses were carried out to present the criteria for determining the reheat pressure and the location of the starring point of the reheater in the HRSG. The performance of the bottoming system was presented for the range from high subcritical to supercritical pressures. It was founded that the power of the bottoming system can be as high as that of the present triple-pressure bottoming system even with a higher exhaust gas temperature. A requirement for this high performance is a proper arrangement of the reheater.

• Proceedings of the KIEE Conference
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• 2008.07a
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• pp.1663-1664
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• 2008

Many years ago, most of thermal power plants built in this country were of subcritical pressure, of medium or small size, of constant pressure operations and of drum type steam generators with circulation type boilers. But, nowadays almost all of them were of high efficiency, of supercritical pressure, of big capacity, of sliding pressure operations, and of once through type steam generators. Presently built once through boilers introduce turbine bypass systems to variable pressure operation which eliminates unexpected materials in boiler tube during startup, minimizes fuel loss by short startup period and eventually improve both total efficiency and power system stability.

• Journal of Hydrospace Technology
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• v.2 no.1
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• pp.10-17
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• 1996

If a point impulse travels over free surface of water of finite depth, surface waves consist of divergent waves. The crestlines of those divergent waves are short and end on the cusp line if the impulse travels at a subcritical speed. But the crestlines become infinitely long and there are no cusps if the impulse travels at a supercritical speed.

• Wind and Structures
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• v.11 no.5
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• pp.377-389
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• 2008

An experimental investigation has been conducted to determine the effectiveness of base shield plates in reducing the drag of a rough circular cylinder in a cross flow at Reynolds numbers in the range $3{\times}10^4{\leq}Re{\leq}10.5{\times}10^4$. Three model configurations were investigated and compared: a plane cylinder (PC), a cylinder with a splitter plate (MC1) and a cylinder fitted with base shield plates (MC2). Each configuration was studied in the sub and supercritical flow regimes. The chord of the plates, L, ranged from 0.22 to 1.50D and the cavity width, G, between the plates was in the range from 0 to 0.93D. It is recognized that base shield plates can be employed more effectively than splitter plates to reduce the aerodynamic drag of circular cylinders in both the sub- and supercritical flow regimes. For subcritical flow regime, one can get 53% and 24% drag reductions for the MC2 and MC1 models with L/D=1.0, respectively, compared with the PC model. For supercritical flow regime however, the corresponding drag reductions are 38% and 7%.

• Journal of the Korean Society of Propulsion Engineers
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• v.22 no.5
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• pp.32-39
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• 2018

Supercritical injection behavior of liquid hydrocarbon compounds, which are used as main components of propellant fuel, was analyzed. Decane and Methylcyclohexane (MCH) with different critical points were selected as experimental fluid and Shadowgraphy technique was used. Decane and MCH behave differently in the initial state under the subcritical condition. However, near the critical point, the enthalpy of evaporation became close to 0, so that phase change into supercritical fluid occurred, not vaporization process, and no breakup of both fluids occurred.