• Nuclear Engineering and Technology
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• v.43 no.3
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• pp.205-216
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• 2011

Recently, many research studies have investigated the enormous critical heat flux (CHF) enhancement caused by nanofluids during pool boiling and flow boiling. One of the main reasons for this enhancement is nanoparticle deposition on the heated surface. However, in real applications, nanofluids create many problems when used as working fluids because of sedimentation and aggregation. Therefore, artificial surfaces on silicon and metal have been developed to create an effect similar to that of nanoparticle deposition. These modified surfaces have proved capable of greatly increasing the CHF during pool boiling, and good results have also been observed during flow boiling. In this study, we demonstrate that the wetting ability of a surface, i.e., wettability, and the liquid spreading ability (hydrophilic surface property), are key parameters for increasing the CHF during both pool and flow boiling. We also demonstrate that when the fuel surface in nuclear power plants is modified in a similar manner, it has the same effect, producing a large CHF enhancement.

• Journal of Fisheries and Marine Sciences Education
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• v.28 no.5
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• pp.1388-1394
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• 2016

This paper presents a experimental study of two-phase flow boiling of FC-72 in multi channels. Flow boiling heat transfer coefficients are obtained with mass flux ranging from 152.9 to $353.9kg/m^2s$ and heat flux from 5.6 to $46.1kW/m^2$. The experimental results show that the heat transfer is governed by nucleate boiling mechanism in the low heat flux region. However, it is found that the effects of nucleate boiling and forced convection boiling are combined as the heat flux increases. A new correlation to predict the heat transfer coefficient is developed by using the dimensionless number such as Reynolds number, Weber number, boiling number. This correlation shows good predictive accuracy against the measured data.

• Korean journal of food and cookery science
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• v.15 no.4
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• pp.382-387
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• 1999

This study was conducted to investigate the changes of mineral contents in radish leaves, soybean sprout and chwi namul by cooking method(boiling, steaming, sauting) and cooking time(1, 3, 5 min.). The residual rate of minerals(such as Calcium, Sodium, Potassium, Iron and Magnesium) in radish leaves, soybean sprout and chwi namul by 1 minute sauting was the range of 83.2 to 99.1%. It was shown that sauting was desirable method for all three vegetables. The residual rate by the cooking method was sauting, steaming, boiling, in that order, but boiling in radish leaves and chwi namul were more desirable method than steaming for Calcium use. At the cooking method and cooking time, Potassium content in soybean sprout was reduced remarkably in 5 minutes boiling. Boiling of radish leaves and soybean sprout showed that Sodium was reduced remarkably after 5 minutes of boiling, 54.4% for radish leaves and 19.9% for soybean sprout, respectively.

• Culinary science and hospitality research
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• v.9 no.2
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• pp.85-97
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• 2003

This study is an attempt that Rheology changes are occurred by boiling, frying, and boiling potatoes with soy bean sauce. Three different methods are tested for chemical analysis, fine potato starch grain structural change, sensory evaluation. 1) Alkaline number and acidity number are changed (+)2.17 in raw, decreased (+)1.76 by boiling, increased (+)2.38 by frying, and (-)2.22 by boiling with soy bean sauce. 2) Potatoes are completely dissolved into the gelatinization when they are boiled at 10$0^{\circ}C$ for 15minutes(PB III), fried at 18$0^{\circ}C$ for 3 minutes(PF IV), and boiled with soy bean sauce l0$0^{\circ}C$ for 30 minutes(PS III). 3) The pectin content ratio is decreased according to frying (31.78$\mu\textrm{g}$/$m\ell$), boiling(44.20$\mu\textrm{g}$/$m\ell$), boiling soy bean sauce(36.37 $\mu\textrm{g}$/$m\ell$), Hemicellulose content ratio is decreased according to frying(1.19%), boiling(1.17%), boiling soy bean sauce(0.92%). And the contend of cellulose and lignin is still regardless of any cooking method. 4) The sensory evaluation conducted by 30 university students as panelists showed that there are more significant differences among four samples in appearance, flavour, texture. As a result, the optimum cooking condition for potatoes is that potatoes are boiled l0$0^{\circ}C$ for 15minutes, fried at 18$0^{\circ}C$ for 3minutes, and boiled with soy bean sauce at 1$0^{\circ}C$ for 30minutes.

• Nuclear Engineering and Technology
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• v.38 no.2
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• pp.139-146
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• 2006

An experimental study was performed to evaluate the effects of surface coating and an enhanced insulation structure on the downward facing boiling process and the critical heat flux on the outer surface of a hemispherical vessel. Steady-state boiling tests were conducted in the Subscale Boundary Layer Boiling (SBLB) facility using an enhanced vessel/insulation design for the cases with and without vessel coatings. Based on the boiling data, CHF correlations were obtained for both plain and coated vessels. It was found that the nucleate boiling rates and the local CHF limits for the case with micro-porous layer coating were consistently higher than those values for a plain vessel at the same angular location. The enhancement in the local CHF limits and nucleate boiling rates was mainly due to the micro-porous layer coating that increased the local liquid supply rate toward the vaporization sites on the vessel surface. For the case with thermal insulation, the local CHF limit tended to increase from the bottom center at first, then decrease toward the minimum gap location, and finally increase toward the equator. This non-monotonic behavior, which differed significantly from the case without thermal insulation, was evidently due to the local variation of the two-phase motions in the annular channel between the test vessel and the insulation structure.

• Journal of Power System Engineering
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• v.17 no.2
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• pp.21-28
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• 2013

Phenomenon of droplet impingement with high temperature wall needs to be investigated because atomization process of droplet and cooling process of the wall by the impingement are very important in industry, thus studies concerned with temperature of piston wall have been conducted in spray characteristics analysis of diesel engine. Hence, in this study, we defined $DT_{sat}(=T_w-T_{sat})$ superheat degree of the wall by difference between $T_w$ considering surface temperature of piston in the actual engine and $T_{sat}$ saturation temperature of the fuel and then investigated spray behavior of wall impinging with variance of the boiling process. In this study, in order to analyze wall impingement of droplet in accordance with difference of boiling condition, calculational conditions were set as $DT_{sat}=40K$(nucleate boiling), $DT_{sat}=140K$(transition boiling), and $DT_{sat}=240K$(film boiling). As a result, it can be found that fuel vapor increases and droplet mass decreases in the order of the nucleate boiling, transition boiling, and film boiling.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.20 no.4
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• pp.1406-1415
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• 1996

Several recent studies have revealed that boiling heat transfer may be considerably enhanced in a narrow restricted region. In his study, the narrow restricted region was formed by attaching a perforated plate on top of a boiling surface. Through systematic experiments, effects of the hole size, hole pattern, gap width between the perforated plate and the boiling surface were investigated using water or R-113. Results show that perforated plates considerably enhance the boiling of water or R-113. For water, especially, they have outperformed commercial enhanced tubes, which confirms that boiling enhancement mechanism of the perforated plate (thin film evaporation beneath the elongated bubble) is very effective to the boiling of high surface tension liquids such as water. Optimum configuration was found - 3.0 mm hole diameter, 15 mm * 15 mm hole pattern, 0.3 ~ 0.5 mm gap width for water, and 2.0 mm hole diameter, 3.5 mm * 3.5 mm hole pattern, O.5 mm gap width for R-113. A correlation which correlates most of the data within .+-. 30% was also developed.

• Journal of Mechanical Science and Technology
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• v.15 no.1
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• pp.98-107
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• 2001

Continuing efforts to achieve increased circuit performance in electronic package have resulted in higher power density at chip and module level. As a result, the thermal management of electronic package has been important in maintaining or improving the reliability of the component. An experimental investigation of thermosyphonic boiling in vertical tube and channel made by two parallel rectangular plates was carried out in this study for possible application of the direct immersion cooling. Fluorinert FC-72 as a working fluid was used in this experiment. Asymmetric heated channel of open periphery with gap size of 1, 2, 4 and 26mm and uniformly heated vertical tubes with diameter of 9, 15 and 20mm were boiled at saturated condition. The boiling curves from tested surfaces exhibited the boiling hysteresis. It was also found that the gap size is not a significant parameter for the thermosyphonic boiling heat transfer with this Fluorinert. Rather pool boiling characteristics appeared for larger gap size and tube diameter. The heat transfer coefficients measured were also compared with the calculation results by Chens correlation.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.12 no.11
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• pp.963-971
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• 2000

In order to investigate the effects of an electric field on EHD(Electro-hydrodynamic) nucleate boiling hat transfer characteristics in a nonuniform electric field under saturated pool boiling, the basic study has been performed experimentally. In the present study, the working fluid is R-113 and the plate-wire electrode system is used to generate a steep electric field gradient. Boiling parameters are investigated by using a high speed camera. The electric field distribution around a wire is obtained to understand the effect of an electric field on bubble departure/movement. The experimental results show EHD effects are much more considerable when the applied voltage increases. Bubbles depart away from the heated wire in radial direction. It is confirmed that the mechanisms of EHD nucleate boiling are closely connected with the dynamic behavior of bubbles. The boiling parameters are significantly changed by the electric field strength. With increasing applied voltages, the bubble size decreases and the nucleation site density, bubble velocity and bubble frequency increase.

• Nuclear Engineering and Technology
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• v.35 no.4
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• pp.274-285
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• 2003

Film boiling heat transfer coefficients for a downward-facing hemispherical surface are measured from the quenching tests in DELTA (Downward-boiling Experimental Loop for Transient Analysis). Two test sections are made of copper to maintain Bi below 0.1. The outer diameters of the hemispheres are 120 mm and 294 mm, respectively. The thickness of both the test sections is 30 mm. The effect of diameter on film boiling heat transfer is quantified utilizing results obtained from the two test sections. The measured heat transfer coefficients for the test section with diameter 120 mm lie within the bounding values from the laminar film boiling analysis, while those for diameter 294 mm are found to be greater than the numerical results on account of the Helmholtz instability. There is little difference observed between the film boiling heat transfer coefficients measured from the two test sections. In addition, the higher thermal conductivity of copper results in the higher minimum heat flux in the tests. For the test section of diameter 120 mm, the Leidenfrost point is lower than that for the test section of diameter 294 mm. Destabilization of film boiling propagates radially inward for the 294 mm test section versus radially outward for the 120 mm Test Section.