• 한국전산유체공학회:학술대회논문집
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• 2008.03b
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• pp.117-120
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• 2008

Numerical simulations and experiment of a hydrodynamic and thermally developed turbulent flow through square ducts (3.0 ${\times}$ 3.0 cm) with twisted tape inserts and with twisted tape inserts plus interrupted ribs are conducted to investigate regionally averaged heat transfer and friction factors. Turbulent swirl flows having Reynolds numbers ranging from 8,900 to 29,000, a rib height-to-channel hydraulic diameter(e/D$_h$) of 0.067, and a length-to-hydraulic diameter(L/D$_h$) of 30, are considered. The square ribs are arranged to follow the trace of the twisted tape and along the flow direction defined as axial interrupted ribs. The twisted tape has 0.1 mm thick carbon steel sheet with diameter of 2.8 cm, length of 90 cm, and 2.5 turns. Each wall is composed of isolated aluminum sections, and two cases of surface heating are set. The results show that uneven surface heating enhances the heat transfer coefficient over uniform heating conditions, and square ducts with twisted tape inserts plus interrupted ribs produces the best overall transfer performance.

• Journal of Advanced Marine Engineering and Technology
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• v.30 no.5
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• pp.572-579
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• 2006

Accurate heat release analysis based on the cylinder pressure trace is important for evaluating combustion process of diesel engines. However, traditional single-zone heat release models (SZM) have significant limitations due mainly to their simplified assumptions of uniform charge and homogeneity while neglecting local temperature distribution inside cylinder during combustion process. In this study, a heat release analysis based on single-zone model has been evaluated by comparison with computational simulation result using Fire-code, which is based on multidimensional model (MDM). The limitations of the single-zone assumption have been estimated, To overcome these limitations, an improved model that includes the effects of spatial non-uniformity has been applied. From this improved single-zone heat release model (Improved-SZM), two effective values of specific heat ratios, denoted by ${\gamma}_V$ and ${\gamma}_H$ in this study, have been introduced. These values are formulated as the function of charge temperature changing rate and overall equivalence ratio. Also, it is applied that each equation of ${\gamma}_V$ and ${\gamma}_H$ has respectively different slopes according to several meaningful periods during combustion progress. The heat release analysis results based on improved single-zone model gives a good agreement with FIRE-code results over the whole range of operating conditions of target engine, Hyundai HiMSEN H21/32.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09b
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• pp.922-923
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• 2006

Thermal management is one of the critical aspects in the design of highly integrated microelectronic devices. The reliability of electronic components is limited not only to operating temperature but also by the thermal stresses caused during the operation. The need for higher power densities calls for use of advanced heat spreader materials. A copper diamond composite has been developed with high thermal conductivity $(\lambda)$ and tailorable coefficient of thermal expansion (CTE). Copper diamond composites are processed via gas pressure assisted infiltration with different copper alloys. Emphasis has been placed on the addition of trace elements in deisgning the copper alloys to facilitate a compromise between thermal conductivity and mechanical adhesion. The interfaces between the alloy and the diamond are related to the thermal properties of these copper composites.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.12 no.3
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• pp.251-257
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• 2000

District heating and cooling systems offer highly efficient energy utilization and maintenance by centralizing heat management. More pumping power, however, is required because the water has to travel long distance from heat source to the users. In the present study, a trace of drag reduction additives is added to the District Cooling system to achieve a significant drag reduction and save pumping power. Water-soluble polymers, surfactants, and environment-friendly degradable polymers are used as effective drag reducing additives. Time dependent percent drag reductions are compared for various additive solutions at 100 wppm concentration for different water velocity. Without as an anionic surfactant, copolymer was most effective in percent drag reduction. It is found that there exists an optimal condition when copolymer is mixed with SDS. An environment-friendly degradable polymer, xanthan gum, is found to be a significant drag reduction additive. Ice slurry systems, can give less pressure drops compared with chilled water system for certain condtions. Drag reduction additives were also effective for the ice slurry system.

• The Journal of Korean Academy of Prosthodontics
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• v.25 no.1
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• pp.95-118
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• 1987

This study was undertaken to observe the elemental transition of Interface depending on different pretreatment methods, the number of filings, the kinds of porcelain powders and the various alloys in ceramo-metal restoration. The materials used in this study were Pors-on $4^{(R)}$ and Ceramco porcelain powder to compare the differences depending on the pretreatement methods and the number of firings. Ceramco porcelain powder and Vita porcelain powder were used to compare the differences of elemental transition depending on the porcelain powders. The $Parasil^{(R)},\;PGV^{(R)}$ and Pors-on $4^{(R)}$ as Pd-Ag alloy were used to compare the difference of elemental transition depending on the various alloys. The pretreatment methods were : no treatment, treatment under vacuum and air, treatment with 50 % hydrofluoric acid and double heat tretament. The number of firings were 3, 5 and 7 repeated firings All specimens were observed by SEM and concentration of elements were analyzed quantitatively with EPMA The results of this study were obtained as follows : 1. In the groups of air-treatment, concentration of Sn were the highest and widest. A high concentration of In were in the groups of vacuum and air treatment. 2. There were no significant differences in concentration of Sn between the group of vacuum, 5 minutes hydrofluoric acid and double heat treatment. (p>0.05) 3. As the period of time of hydrofluoric acid treatment increased, not only were the trace elements reduced but the main components such as Pd and Ag were also reduced. 4. Concentration of Sn and In increased and diffused with repeated firings but 5 repeated and 7 repeated firings groups had no significant differences. (p>0.05) 5. Sn were more concentrated in the group of Ceramco porcelaion powder than Vita porcelain powder. 6. The higher concentration of trace elements in the alloy, the more increasing concentration of Sn and In in the interface.

• Journal of the Korean Vacuum Society
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• v.6 no.4
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• pp.293-297
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• 1997

Using trace etching method in this study, we measure the energy of argon ions generated in VEBA System which is composed of Marx Generater and Pulse Forming Line. In this system the electron beam of 240 kV, 30 kA, 60 ns is generated. Argon ions are formed through the electron beam ionization of a gas cloud injected by a fast puff valve. Thus argon ions are accelerated into vacuum drift tube by a virtual cathode and seperated with electron beam, consequently, they heat the trace etching plates made of aluminum thin films. The energy of argon ions are determined by the number of aluminum thin films penetrated by the ions. This experimental value corresponds with the theoretical value.

• Journal of Korean Institute of Fire Investigation
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• v.4 no.1
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• pp.62-69
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• 2004

The purpose of this study on the sheath heater having high occurrence of fires in a small work place because of not having the safety device, was to find out the characteristics required in the field examination of the fires in the courses of investigation. The results of the experiments conducted and reviewed on the basis of the fire cases whose conditions of the ignition possibility were divided into A, E, C and D are as follows: When the sheath heater without safety device is left on the condition of the heat accumulation of which the temperature rapidly rise, and then ignite the inflammables of the surroundings. In such cases, it was characterized that the color change trace appeared even if no short trace was discovered in the power line.

• Nuclear Engineering and Technology
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• v.54 no.12
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• pp.4759-4775
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• 2022

The RVACS is a versatile and robust safety system driven by two natural circulations: in-vessel coolant and ex-vessel air. To observe interaction between the two natural circulations, SINCRO-IT facility was designed with two different similarity laws simultaneously. Bo' based similarity law was employed for the in-vessel, while Ishii's similarity law for the ex-vessel excluding the radiation. Compared to the prototype, the sodium and air system, SINCRO-IT was designed with Wood's metal and air, having 1:4 of the length reduction, and 1.68:1 of the time scale ratio. For the steady state, RV temperature limit was violated at 0.8% of the decay heat, while the sodium boiling was predicted at 1.3%. It showed good accordance with the system code, TRACE. For an arbitrary re-criticality scenario with RVACS solitary operation, sodium boiling was predicted at 25,100 s after power increase from 1.0 to 2.0%, while the system code showed 30,300. Maximum temperature discrepancy between the experiments and system code was 4.2%. The design and methodology were validated by the system code TRACE in terms of the convection, and simultaneously, the system code was validated against the simulating experiments SINCRO-IT. The validated RVACS model could be imported to further accident analysis.

• Food Science of Animal Resources
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• v.43 no.6
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• pp.989-1001
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• 2023

Processed foods containing pork fat tissue to improve flavor and gain economic benefit may cause severe issues for Muslims, Jews, and vegetarians. This study aimed to develop an indirect enzyme-linked immunosorbent assay (iELISA) based on a monoclonal antibody specific to thermal stable-soluble protein in pork fat tissue and apply it to detect pork fat tissue in heat-processed (autoclave, steam, roast, and fry) beef meatballs. To develop a sensitive iELISA, the optimal sample pre-cooking time, coating conditions, primary and secondary dilution time, and various buffer systems were tested. The change in the iELISA sensitivity with different 96-well microtiter microplates was confirmed. The detection limit of iELISA performed with an appropriate microplate was 0.015% (w/w) pork fat in raw and heat-treated beef. No cross-reactions to other meats or fats were shown. These results mean that the iELISA can be used as an analytical method to detect trace amounts of pork fat mixed in beef.

• Journal of Microbiology and Biotechnology
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• v.34 no.5
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• pp.1119-1125
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• 2024

Phytase increases the availability of phosphate and trace elements by hydrolyzing the phosphomonoester bond in phytate present in animal feed. It is also an important enzyme from an environmental perspective because it not only promotes the growth of livestocks but also prevents phosphorus contamination released into the environment. Here we present a novel phytase derived from Turicimonas muris, TmPhy, which has distinctive structure and properties compared to other previously known phytases. TmPhy gene expressed in the Pichia system was confirmed to be 41 kDa in size and was used in purified form to evaluate optimal conditions for maximum activity. TmPhy has a dual optimum pH at pH3 and pH6.8 and exhibited the highest activity at 70℃. However, the heat tolerance of the wildtype was not satisfactory for feed application. Therefore, random mutation, disulfide bond introduction, and N-terminal mutation were performed to improve the thermostability of the TmPhy. Random mutation resulted in TmPhyM with about 45% improvement in stability at 60℃. Through further improvements, a total of three mutants were screened and their heat tolerance was evaluated. As a result, we obtained TmPhyMD1 with 46.5% residual activity, TmPhyMD2 with 74.1%, and TmPhyMD3 with 66.8% at 80℃ heat treatment without significant loss of or with increased activity.