• Transactions of the Korean Society of Mechanical Engineers B
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• v.21 no.10
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• pp.1254-1261
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• 1997

Pulse boiling, the unsteady periodic boiling phenomenon appearing in the evaporator of thermosyphons was investigated by many researchers. In the present study investigations were conducted to examine the evolution of flow patterns at the evaporator, and changes in thermodynamic state that each of liquid pool and vapor experiences through 1 cycle of pulse boiling process. For wall and liquid pool the degree of superheat for the onset of nucleation was examined. It revealed that the degree of superheat increased with the increase of pulse period, reaching to 16.5 deg.C and 23 deg.C for liquid pool and evaporator wall respectively at .tau.=80 sec. The data on flow patterns obtained through series of operation tests were plotted in the coordinates of heat flux and vapor pressure to get a regime map. Further this map could be used to figure out the conditions of pulse boiling for a thermosyphon.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.7 no.1
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• pp.132-141
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• 1995

Characteristics of pressure-drop oscillations(PDO) in a boiling channel were studied numerically and compared with experimental data. Effects of initial and boundary conditions on PDO were investigated in terms of oscillation period and amplitude. The period and amplitude of PDO increased with increasing of the compressible volume in the surge tank and the heat input. PDO occurred within the specific range of the fluid temperature, at which oscillation period and amplitude diminished rapidly with the increase of the fluid temperature. The increase of the loss coefficient in fluid supply line resulted in slightly longer oscillation period and larger amplitude. Numerical results showed good agreement with the experimental data.

• Nuclear Engineering and Technology
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• v.41 no.9
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• pp.1205-1214
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• 2009

The critical heat flux (CHF) levels that occurred due to exponential heat inputs for varying periods to a 1.0-mm diameter horizontal cylinder immersed in various liquids were measured to develop an extended database on the effect of high subcoolings for quasi-steady-state and transient maximum heat fluxes. Two main mechanisms of CHF were found. One mechanism is due to the time lag of the hydrodynamic instability (HI) which starts at steady-state CHF upon fully developed nucleate boiling, and the other mechanism is due to the explosive process of heterogeneous spontaneous nucleation (HSN) which occurs at a certain HSN superheat in originally flooded cavities on the cylinder surface. Steady-state CHFs were divided into three regions for lower, intermediate and higher subcooling at pressures resulting from HI, transition and HSN, respectively. HSN consistently occurred in the transient boiling CHF conditions that correspond to a short period. It was also found that the transient boiling CHFs gradually increased, then rapidly decreased and finally increased again as the period became shorter.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.5 no.3
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• pp.179-186
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• 1993

The characteristics of pressure-drop oscillations(PDO) in boiling channel are studied experimentally. The effects of initial and boundary conditions on PDO are investigated in terms of oscillation period and amplitude. The period and amplitude of PDO are increased with the increase in the compressible volume in surge tank and heat input. However the amplitude of PDO is decreased with fluid temperature under low subcooling condition. Higher initial insurge flowrate resulted in almost invariant oscillation period but lower amplitude. At higher heat input the oscillation of heater wall temperature is significant, whose period is the same as that of pressure-drop instability.

• Journal of Environmental Science International
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• v.5 no.6
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• pp.749-755
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• 1996

In order to grasp a characterization of low boiling point chlorinated organic compounds, this study which were carried out at the 8 stations for precipitation samples in the Pusan area during the period from February to September 1995. As a result, low boiling chlorinated organic compounds were estimated that it was dissolved by a portion of precipitation, and it be able to shift at the surface of the each. Concentration of low boiling point chlorinated organic compounds in precipitation are increased with increase of temperature, and estimated that air pollution compounds of as a rule in atmosphere.

• Proceedings of the KSME Conference
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• 2002.08a
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• pp.403-406
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• 2002

A number of the experiments on the phenomenon in which the thermal energy was transferred from a hot sphere to the surrounding water through the film boiling process had been conducted. As the sphere only carried the thermal energy associated with its initially high temperature but did not contain any other thermal source, the film boiling was only driven by the decreasing temperature of the sphere and, thus, was time dependent. The results from the experiments showed that the temperature of the sphere was slowly decreased in the beginning. This corresponded to the period in which the sphere was penetrating the water surface. Later, when the sphere was fully submerged and the transition film boiling was observed over the whole surface, the temperature of the sphere was decreased relatively much faster. In the last stage, the temperature of the sphere was again slowly decreased. This was considered caused by the relatively low temperature of the sphere, which reduced and later ceased the film boiling process. In addition, the estimation of the departure rate of the steam bubbles from the film layer was also correlated for the experiments.

• Nuclear Engineering and Technology
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• v.53 no.8
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• pp.2464-2476
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• 2021

Direct-contact heat transfer of a single saturated droplet upon colliding with a heated wall in the regime of film boiling was experimentally investigated using high-resolution infrared thermometry technique. This technique provides transient local wall heat flux distributions during the entire collision period. In addition, various physical parameters relevant to the mechanistic modelling of these phenomena can be measured. The obtained results show that when single droplets dynamically collide with a heated surface during film boiling above the Leidenfrost point temperature, typically determined by droplet collision dynamics without considering thermal interactions, small spots of high heat flux due to localized wetting during the collision appear as increasing We_n. A systematic comparison revealed that existing theoretical models do not consider these observed physical phenomena and have lacks in accurately predicting the amount of direct-contact heat transfer. The necessity of developing an improved model to account for the effects of local wetting during the direct-contact heat transfer process is emphasized.

• Journal of Sericultural and Entomological Science
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• v.31 no.1
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• pp.20-24
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• 1989

The purpose of this experiment was to obtain the basic information on heterosis and inbreeding depression of quantitative characters in the silkworm by diallel crosses of seven varieties differing widely in each character. Period of 5th instar cocoon weight, cocoon layer weight, cocoon layer ratio, boiling off ratio, raw silk percent, bave length, bave weight, bave size, weight of first molting larva and fourth molting larva were investigated. The results obtained were summarized as follows : The degrees of positive heterosis of cocoon weight and cocoon layer weight were higher. Period of 5th instar and boiling off ratio were negative heterosis. In F1 generation, cocoon weight and bave weight showed positive heterobeltiosis, while fifth instar-period, cocoon layer ratio and boiling off ratio showed negative heterobeltiosis in the F1 and F2 generation. Inbreeding depression was observed in cocoon layer ratio and boiling off ratio.

• Journal of the East Asian Society of Dietary Life
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• v.24 no.2
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• pp.242-251
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• 2014

The traditional food - jungkwa of Korea, is difficult to manufacture. In this study, jungkwa with carrots was made in a rice cooker to simplify preparation. The boiling times for red color, chewiness and overall acceptability of jungkwa with carrots in a rice cooker as compared to the traditional method were 135 minutes, 150 minutes, 165 minutes, 180 minutes and 195 minutes, respectively. The rice cooker produced a lower moisture content in jungkwa with carrots when cooked for a longer time period, whereas the sugar content increased significantly. The color value of jungkwa with carrots was reduced at a longer boiling time as compared to the traditional method, yellowness increased when boiling time was longer than 195 minutes, whereas it remained the same with the traditional method. The hardness of jungkwa with carrots increased and candied jungkwa's result increased significantly when the boiling time was longer than 165 minutes. The rice cooker created a similar chewiness even when boiling time was over 165 minutes, although not consistently. The sensory evaluation scores of jungkwa made with carrots in terms of appearance, smell, taste, texture and overall preference were highest at 150 minutes and 165 minutes. Boiling jungkwa for 150 minutes in the rice cooker is the traditional method which simmers jungkwa at a lower timethan the preference time. Therefore, the best time for boiling jungkwa in the rice cooker highest was 165 minutes. After storage for 15 days chewiness and moisture content of jungkwa made with carrots at different boiling times, increased and decreases respectively. Therefore, the rice cooker can used to achieve comparable jungkwa without the traditional method.

• Nuclear Engineering and Technology
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• v.55 no.7
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• pp.2591-2603
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• 2023

Simulating the Corrosion-Related Unidentified Deposit (CRUD) on the surface of fuel assemblies is necessary to predict the axial offset anomaly and the localized corrosion induced by the CRUD during the operation of nuclear power plants. A new CRUD model was developed to predict the formation of the CRUD deposits, considering the deposition and erosion mechanisms. The heat transfer and capillary flow within the CRUD were also considered to evaluate the boiling amount within the CRUD layer. This model predicted a CRUD deposit thickness of 44 ㎛ during a one-cycle operation of the Seabrook nuclear power plant. The CRUD deposition tended to accelerate and decelerate during the simulation, by being related to boiling mechanism on the deposits surface. Additionally, during a three-cycle operation corresponding to the refueling period, the CRUD deposition was saturated at a thickness of 80 ㎛, which was in good agreement with the suggested thickness for CRUD buildupin pressurized water reactors. Surface boiling on the thin CRUD deposits enhanced the acceleration of the deposition, even when the wick boiling properties were not favorable for CRUD deposition. To ensure the certainty of the simulation results, sensitivity analyses were conducted for the porosity, chimney density, and the constants employed in the proposed model of the CRUD.