• Journal of the Korea Academia-Industrial cooperation Society
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• v.14 no.10
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• pp.4658-4664
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• 2013

This paper presents the effects of the tube materials on the heat transfer performance of double-tube heat exchangers for the development of heat exchangers using deep sea water. Heat exchangers made of titanium, aluminum. stainless steel, iron, copper, and aluminum with carbon black 0.015mm and 0.15mm coating were tested. Also, the heat transfer rate of each heat exchanger was calculated by using EES program. The calculated values were compared with the experimental ones, and the deviations were less than 10%. From the above experiment and analysis, aluminum with carbon black 15 coating can be considered the most promising candidate for the replacement of titanium heat exchanger.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.5 no.4
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• pp.257-264
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• 1993

This is the second report of a three part study on the absorption and heat transfer characteristics of absorber, the correlation of refrigerating capacity and heating capacity. The 2nd report deals with the heat transfer characteristics of a vertical falling film type absorber of inner copper tube. The solute is LiBr-Water solution(60wt%) and the solvent is water vapor. The film Reynoles numbers are varied in the range of 35~130. The states of LiBr solution at the top of absorber are supercooled liquid and superheated liquid. The results are summarized as follows ; Heat transfer results reveal that for the absorption of falling film, the state of LiBr solution appears to be influential in determining the heat transfer. Thus, for the state of supercooled liquid, heat transfer coefficient decreases with increasing the film Reynolds number, but in the condition of superheated liquid, it increases conversely. The mass transfer coefficients that were presented in the 1st.report and heat transfer coefficients of this paper are presented as the dimensionless correlation. The optimum water flowrate which brings about maximum value of heat flux in the film exists, and that increases with increasing the cooling water temperature.

• Journal of Power System Engineering
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• v.10 no.2
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• pp.47-53
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• 2006

This study concerns the performance of condensation heat transfer in plain and grooved thermosyphons. Distilled water, methanol, ethanol have been used as the working fluids. In the present work, a copper tube of the length of 1200mm and 14.28mm of inside diameter is used as the container of the thermosyphon. Each of the evaporator and the condenser section has a length of 550mm, while the remaining part of the thermosyphon tube is adiabatic section. A study was carried out with the characteristics of heat transfer of the thermosyphon 50, 60, 70, 80, 90 helical grooves in which boiling and condensation occur. The liquid filling as the ratio of working fluid volume to total volume of thermosyphon, the kinds of working fluid, the inclination angle, grooves and operating temperature have been used as the experimental parameters. The experimental results show that the number of grooves, the amount of the working fluid, the kind of working fluid, angle of inclination angle are very important factors for the operation of thermosyphon. The maximum heat transfer was obtained when the liquid fill was about 20 to 25 % of the thermosyphon volume. The relatively high rates of heat transfer have been achieved in the thermosyphon with grooves. The helical grooved thermosyphon having 70 to 80 grooves in water, 60 to 70 grooves in methanol and 70 to 80 grooves in ethanol shows the best heat transfer coefficient in both condensation.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.14 no.11
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• pp.5377-5384
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• 2013

This paper presents the effects of the tube materials and corrosion on the heat transfer performance of double-tube heat exchangers for the development of heat exchangers using deep sea water. Heat exchangers made of titanium, aluminum. stainless steel, iron, copper, and aluminum with electro-deposition coatings(Carbon black_$15{\mu}m$, Carbon black_$150{\mu}m$) were tested. Also, the heat transfer rate of each heat exchanger was calculated by using EES program. For the acceleration of corrosion by sea water, the temperature of sea water $70^{\circ}C$ and the concentration of salt 3.5% were considered. And the specimens were immersed in sea water during 6 weeks. From the above experiment and analysis, aluminum with electro-deposition coating(Carbon black_$150{\mu}m$) can be considered the most promising candidate for the replacement of titanium heat exchanger.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.16 no.11
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• pp.1051-1059
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• 2004

Two phase thermosyphone loop for electronics cooling are designed and manufactured to test its performance under the partial load and low environment temperature conditions. The thermosyphone device has six evaporators connected parallel for the purpose of cooling six power amplifier units (PAU) independently. The heater modules for simulating PAUs are adhered with thermal pad to the evaporator plates to reduce the contact resistance. There are unbalanced distributions of liquid refrigerant in the differently heated evaporators due to the vapor pressure difference. To reduce the vapor pressure differences caused by partial heating, two evaporators are connected each other using the copper tube. The pressure regulation tube successfully reduces these unbalances and it is good candidates for a field distributed systems. Under the low environment temperature operating condition, such as $-30^{\circ}C$, there may be unexpected subcooling in condenser. It leads the very low saturation pressure, and under this condition there exists explosive boiling in evaporator. The abrupt pressure rise due to the explosive boiling inhibits the supplement of liquid refrigerant to the evaporator for continuous cooling. Finally the cooling cycle will be broken. For the normal circulation of refrigerant there may be an optimum cooling air flow rate in condenser to adjust the given heat load.

• Nuclear Engineering and Technology
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• v.21 no.2
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• pp.111-122
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• 1989

With the Zircaloy-4 tube oxidized in high temperature (1323 K) steam for 5, 10, 30 and 60 minutes, the expanding copper mandrel test was carried out over a temperature range of 673-l173k at $\varepsilon\;=\;3.0\times10^5S\;^1$. The oxidation parameters $(K_i)$ in the present study were linearly proportional to square root of time $(Ki= \delta_{kit})$ and their rate constants ($\delta_{ki}$) are 0.281, 2.82, and 2.313 for weight gain and thickness of Zr02 and $\alpha$(0) layer, respectively. Activation energy for high temperature (873-1073k) plastic deformation of Zircaloy-4 increases from 251 KJ/mol to 323 KJ/mol with increase in oxidation time from 5 minutes to 60 minutes due to the high strengthened Zr02. With the oxide layer thickness [K ; expressed in "Equivalent Cladding Reacted" (ECR,%)] and the yield stress obtained from the mandrel test, an empirical relation was derived as ($\sigma/C)^n=K^mexp$ (Q/RT) with n=6.9, m=5.7, C=0.155, 0.138, 0.051, and 0.046 MPa for Q=251, 258, 316, 323 KJ/mol, respectively.

• Progress in Superconductivity and Cryogenics
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• v.13 no.1
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• pp.12-16
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• 2011

In this paper, the prototype of the HTS motor with an on-board cryocooler, is fabricated and tested. The overall system is composed of the stator with conventional copper winding, the rotor with superconductor, and the rotating cryocooler designed from the on-board concept. The rotor is fabricated as the race-track coil with 2G, YBCO tape and contacts with the on-board cryocooler while being rotated together. An inline-type pulse tube refrigerator is used as the on-board cryocooler. The cryocooler is fabricated from optimal process to satisfy the structure and thermal stability of the on-board system. Each component is integrated according to carefully defined sequence. Specially, a combining method of torque tubes is an important part for sustaining stability of the rotor and the cryocooler. In the rotating test, the HTS motor is successfully operated with 240 rpm of rotating speed when 75 A current is supplied to the superconducting rotor. In this paper, potential problems of the HTS motor system using the on-board cryocooler are proposed and solved, and realistic possibility of this concept is also confirmed.

• Environmental Analysis Health and Toxicology
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• v.22 no.4
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• pp.339-348
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• 2007

A laboratory experiment was conducted to study the characteristics of leaching of Cr, Cu, and As from chromated topper arsenate (CCA)-treated wood. The wood species tested was hemlock spruce ($10\;cm\;{\times}\;10\;cm\;{\times}\;10\;cm\;tube$). The leaching experiment was conducted over 60 days using I L of leachants whose pHs were adjusted to 2.0, 3.7, and 1.6, respectively with nitric acid, and also using lake water, according to the OECD guideline. Each leachate was analyzed for Cr and Cu using flame-AAS, and for As using vapor generation-AAS. Three metals were loathed at the highest levels at pH 2.0 but almost at similar levels at the other conditions. Cumulative quantifies over 60 days of a leaching period were in order of As>Cu>Cr. As was predicted to leach with an increase in flux over a 10 year period, while Cr and Cu fluxes were predicted to decrease with time. This result suggest that arsenic can pose a health risk to humans over a long period of time, when CCA-treated wood is used for building facilities (e.g., playgrounds, residential purposes, etc.) with which humans frequently contact.

• Journal of Welding and Joining
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• v.15 no.1
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• pp.116-124
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• 1997

A scope of this study is to establish the optimum plasma spray conditions for fine ($5\mu\textrm{m}$) $Al_2O_3$ powder. However, the flowability of the $Al_2O_3$ powder is not so good because of irregular particle shape and fine particle size. Therefore, powder feeding system was modified by 1) change of powder feeding line material from polymer to copper 2) shorten the powder feeding tube length 3) heating the powder feeding system to $80^{\circ}C$4) vibrating the powder feeding line continuously, in order to feed the fine powder homogeneously. The homogeneous powder feeding conditions were obtained with the modified powder feeding system by controlling the powder carrier gas flow and the powder flow rate indicator. The best plasma spraying conditions for the fine $Al_2O_3$ powder were found out as 40kw gun power, 80 g/min. powder feed rate and 50 mm working distance after characterizing the microstructure, hardness and wear loss of the $Al_2O_3$ coating layer.

• Bulletin of the Korean Chemical Society
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• v.35 no.6
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• pp.1687-1691
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• 2014

This study reports on the synthesis of carbon nanofibers via chemical vapor deposition using Co and Cu as catalysts. In order to investigate the suitability of their catalytic activity for the growth of nanofibers, we prepared catalysts for the synthesis of carbon nanofibers with Cobalt nitrate and Copper nitrate, and found the optimum concentration of each respective catalyst. Then we made them react with Aluminum nitrate and Ammonium Molybdate to form precipitates. The precipitates were dried at a temperature of $110^{\circ}C$ in order to be prepared into catalyst powder. The catalyst was sparsely and thinly spread on a quartz tube boat to grow carbon nanofibers via thermal chemical vapor deposition. The characteristics of the synthesized carbon nanofibers were analyzed through SEM, EDS, XRD, Raman, XPS, and TG/DTA, and the specific surface area was measured via BET. Consequently, the characteristics of the synthesized carbon nanofibers were greatly influenced by the concentration ratio of metal catalysts. In particular, uniform carbon nanofibers of 27 nm in diameter grew when the concentration ratio of Co and Cu was 6:4 at $700^{\circ}C$ of calcination temperature; carbon nanofibers synthesized under such conditions showed the best crystallizability, compared to carbon nanofibers synthesized with metal catalysts under different concentration ratios, and revealed 1.26 high amorphicity as well as $292m^2g^{-1}$ high specific surface area.