• Journal of Mechanical Science and Technology
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• 제15권1호
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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.

• 한국지역사회생활과학회지
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• 제18권4호
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• pp.681-686
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• 2007

This study was conducted to investigate the effects of the thermally different states of human feet on temperature regulation in winter season. Five healthy female students of age 20 volunteered as subjects to participate in the study. Physiological responses such as rectal temperature and skin temperatures as well as subjective responses of thermal comfort and thermal sensation were observed. Preferred clothing and preferred temperature were also evaluated in terms of behavioral temperature regulation. The results obtained through the experiment were statistically analyzed using paired t test. Rectal temperature was decreased greater (p<.01) and mean skin temperature was maintained higher (p<.01) in feet wanning than in feet cooling. Results of preferred clothing were coincident with those of general thermal sensation. There was a higher tendency to prefer temperature in feet wanning than feet cooling in the morning. It was concluded that keeping feet skin temperature lower in the early morning and higher in the late evening would be effective in terms of regulating circadian rhythm of core temperature.

• 한국식품과학회지
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• 제21권6호
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• pp.735-741
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• 1989

For the accurate prediction of freezing time, probably the most difficult factor to measure and major error source is the surface heat transfer coefficient. In this work, surface heat transfer coefficient were determined for still air freezing and immersion freezing methods by theory of the transient temperature method and confirmed by using a modification of plank's equation to predict the freezing time of ground lean beef. The results showed the cooling rate of immersion freezing was about 11 times faster than that of still air freezing method. A comparison of surface heat transfer coefficient of copper plate and ground lean beef resulted an difference of 25-30% because the food sample surface is not smooth as copper plate. Also, when h-values measured by ground lean beef were applicated to modified model, the accuracy of its results is very high as difference of about 8%.

• Design & Manufacturing
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• 제16권2호
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• pp.46-52
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• 2022

As the consumer market in the eco-friendly vehicle industry grows, the demand for water pump in a electric car parts market. This study intend to propose a mathematical model that can verify the effect of improving thermal properties when a non-conductive cooling filler liquid is introduced into an electric vehicle water pump. Also, the pros and cons of the immersion cooling method and future development way were suggested by analyzing the cooling characteristics using on the derived analysis solution. Thermal characteristics analysis of electric water pump applied with non-conductive filler liquid was carried out, and the diffusion boundary condition in the motor body and the boundary condition the inside pump were expressed as a geometric model. As a result of analyzing the temperature change for the heat source of the natural convection method and the heat conduction method, the natural convection method has difficulty in dissipating heat because no decrease in temperature due to heat release was found even after 300 sec. Also, it can be seen that the heat dissipation effect was obtained even though the non-conductive filling liquid was applied at the 120 sec and 180 sec in the heat conduction method. It has proposed to minimize thermal embrittlement and lower motor torque by injecting a non-conductive filler liquid into the motor body and designing a partition wall thickness of 2.5 mm or less.

• 대한금속재료학회지
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• 제50권9호
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• pp.697-702
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• 2012

In this study, unidirectional and plain woven carbon fiber reinforced magnesium matrix composite laminates were fabricated by the liquid pressing infiltration process, and evolutions of the microstructure and compressive strength of the composite laminates under corrosion were investigated by static immersion tests. In the case of the unidirectional composite laminate, the main microstructural damage during immersion appeared as a form of corrosion induced cracks, which were formed at both CF/Mg interfaces and the interfaces between layers. On the otherhand, wrap/fill interface cracks were mainly formed in the plain woven composite laminate, without any cracks at the CF/Mg interface. The formation of these cracks was considered to be associated with internal thermal residual stress, which was generated during cooling after the fabrication process of these materials. As a consequence of the corrosion induced cracks, the thickness of both laminates increased in directions vertical to the fibers with increasing immersion time. With increasing immersion time, the compressive strengths of both composite laminates also decreased continuously. It was found that the plain woven composite laminates have superior corrosion resistance and stability under a corrosive condition than unidirectional laminates.

• Corrosion Science and Technology
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• 제2권1호
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• pp.36-40
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• 2003

An attractive combination of corrosion resistance and mechanical properties in the temperature range -50 to $250^{\circ}C$ is offered by duplex stainless steel. However, undesirable secondary precipitation phase such as $\sigma$, $\gamma_2$ and $Cr_2N$ may taken place at the cooling stage from the welding processes. Therefore, this paper describes the influence of different welding procedures such as manual metal arc welding (MMA), tungsten inert gas welding (TIG) and vacuum brazing on corrosion resistance of the welded joint for UNS S31803 duplex stainless steel. Microstructure and chemical compositions of the welded joint were examined. The weight loss of specimens immersed in 6% $FeCl_3$ solution at $47.5^{\circ}C$ for 24-hours was determined and used to evaluate the pitting resistance of duplex stainless steel and their welds. The region of heat-affected zone of specimen obtained by the MMA is much wider than that resulted from TIG, therefore, the weight loss of welds by MMA was larger than that of weld by TIG. The weight loss of brazed specimens cooled from slow cooling rate was larger than those of specimens cooled from high cooling rate, because the precipitation of $\sigma$ phase. Beside that, the weight loss of brazed specimen is greater than those of the welded specimens. The galvanic corrosion was observed in brazed duplex stainless steel joints in the chloride solution.

• Corrosion Science and Technology
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• 제6권6호
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• pp.286-290
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• 2007

Biocompatible Hydroxy apatite (HAp) coatings on metallic substrate by plasma spray techniques have been developed. Long-term credibility of plasma spray HAp coatings has been evaluated in physiological saline by electrochemical measurements. It was found that the corrosion resisitance of SUS316L based HAp/Ti conbined coatings was excellent even after more than 10 weeks long-term immersion. It was shown that postal heat treatment improved both the crystallinity and corrosion resistance of HAp. By lowering cooling rate during heat treatment process, less cracks produced in HAp coating layer, which lead to higher credibility of HAp during immersion in physiological saline. The ICP results showed that the dissolution level of substrate metallic ions was low and HAp coatings produced in this research can be acceptable as biocompatible materials. Also, the concentration of dissolved ions from HAp coatings with postal heat treatment was lower compared to those from samples without postal heat treatment. The adherence of HAp coatings with Ti substrate and other mechanical properties were also assessed by three-point bending test. The poor adhesion of HAp coating to titanium substrate can be improved by introducing a plasma spray titanium intermediate layer.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1990년도 한국자동제어학술회의논문집(국제학술편); KOEX, Seoul; 26-27 Oct. 1990
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• pp.1316-1321
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• 1990

Molten steel level information of ladle is very important for process control in steelmaking process. At secondary refining process, measuring lance and snokel have to keep constant thier depth from molten steel surfaces. But, there is much slag on the molten steel surface. Besides, not only the thickness of slag is varied with refining condition, but also molten steel level is largely affected by firebrick errosion. Then, optical measuring method and/or by human eyes cannot detect true molten steel surface, but slag surface. This slag thickness is 300mm at maximum, then huge diameter eddy current sensor will be needed if that type sensor is applied. In addition to, cooling system is necessary because the molten steel and slag temperature is high. This is not practically. To solve this problem, immersion type levelmeter is developed. This sensor is made up from primary and secondary cylindrical coils. High frequency current is applied to primary coil. Electro-motive force from secondary coil is measured, which is varied with molten steel level. This complete set is installed within stainless steel long capsule and attached to top of lance. This sensor is immersed into molten steel bath of ladle or tundish with protection of expendable paper sleeve.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2012년도 제43회 하계 정기 학술대회 초록집
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• pp.151-151
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• 2012

A new plasma process, i.e., the combination of PIII&D and HIPIMS, was developed to implant non-gaseous ions into materials surface. HIPIMS is a special mode of operation of pulsed-DC magnetron sputtering, in which high pulsed DC power exceeding ~1 kW/$cm^2$ of its peak power density is applied to the magnetron sputtering target while the average power density remains manageable to the cooling capacity of the equipment by using a very small duty ratio of operation. Due to the high peak power density applied to the sputtering target, a large fraction of sputtered atoms is ionized. If the negative high voltage pulse applied to the sample stage in PIII&D system is synchronized with the pulsed plasma of sputtered target material by HIPIMS operation, the implantation of non-gaseous ions can be successfully accomplished. The new process has great advantage that thin film deposition and non-gaseous ion implantation along with in-situ film modification can be achieved in a single plasma chamber. Even broader application areas of PIII&D technology are believed to be envisaged by this newly developed process. In one application of non-gaseous plasma immersion ion implantation, Ge ions were implanted into SiO2 thin film at 60 keV to form Ge quantum dots embedded in SiO2 dielectric material. The crystalline Ge quantum dots were shown to be 5~10 nm in size and well dispersed in SiO2 matrix. In another application, Ag ions were implanted into SS-304 substrate to endow the anti-microbial property of the surface. Yet another bio-application was Mg ion implantation into Ti to improve its osteointegration property for bone implants. Catalyst is another promising application field of nongaseous plasma immersion ion implantation because ion implantation results in atomically dispersed catalytic agents with high surface to volume ratio. Pt ions were implanted into the surface of Al2O3 catalytic supporter and its H2 generation property was measured for DME reforming catalyst. In this talk, a newly developed, non-gaseous plasma immersion ion implantation technique and its applications would be shown and discussed.

• 대한약리학회지
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• 제19권1호
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• pp.61-69
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• 1983

Hypothermia is an essential preparatory procedure for cardiac surgery, which lows the metabolic rate and myocardial oxygen demand. However, hypothermia itself is a stress enough to change the tonus of sympathoadrenal system, especially the cardiovascular responses to the catecholamines. It is reported that the positive chronotropic and inotropic response of catecholamines is exaggerated during hypothermia because of decreased norepinephrine uptake at the junctional cleft or decreased catecholamine metabolism. On the other hand, there are evidences of diminished catecholamines responses in low temperature ana further, interconversion of adrenergic receptors is also suggested. Present investigation was planned to observe the cardiovascular changes and its responses to catecholamines during surface hypothermia in cat. Healthy mongrel cats, weighing $2{\sim}3\;kg$, anesthetized with secobarbital(30 mg/kg), were permitted to hypothermia by external cooling technic. Esophageal temperature, ECG (lead II), heart rate, left ventricular pressure with dP/dt, carotid artery pressure and left ventricular contractile force were monitored with Polygragh (Model 7, Grass), and the respiration was maintained with artificial respirator (V 5 KG, Narco). Followings are summarized results. 1) Surface cooling caused progressive decrease of body temperature and reached $l8.8{\pm}0.8^{\circ}C$ and $16.9{\pm}0.6^{\circ}C$ in 120 and 150 min respectively, after immersion into ice water, and ventricular fibrillation was developed at $20.4{\pm}0.65^{\circ}C$. 2) Heart rate, blood pressure and myocardial contractility were decreased after initial increase as the body temperature falls. 3) Systolic and diastolicdd P/dt of left ventricular pressure were decreased and that the decrement of diastolic dP/dt was more marked. 4) On ECG, ST depression, Twave inversion and prolongation of PR interval were prominent in hypothermia, and moreover, the prolongation of PR interval was marked just prior to the development of ventricular fibrillation. 5) The cardiovascular responses to catecholamines, especially to isoproterenol, were suppressed under hypothermia.