• 한국광학회:학술대회논문집
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• 한국광학회 2000년도 하계학술발표회
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• pp.74-75
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• 2000

The past few decades have witnessed the development of very robust technique, known as magneto-optical trap(MOT), for cooling and trapping of neutral atoms using lasers and magnetic fields. This technique can easily produce cooled atoms to a temperature range of nano-kelvin $s^{(1)}$ . These laser cooled and trapped atoms have found applications in various fields, such as ultrahigh resolution spectroscopy, precision atomic clocks, very cold atomic collision physics, Bose-Einstein Condensation, the Atom laser, etc. Particularly, a few isolated atoms of very low temperature are needed in the cavity QED studies in the optical regime. One can obtain such atoms from a MOT using the atomic fountain technique. The widely used technique for atomic fountain is, first to cool and trap the neutral atoms in MOT. And then launch them in the vertical (1, 1, 1) direction with respect to cooling beams, using moving molasses technique. Recently, this technique combined with the cavity-QED has opened an active area of basic research. This way atoms can be strongly coupled to the optical radiation in the cavity and leads to various new effects. Trapping of single atom after separating it from MOT in the high Q-optical cavity is actively initiated presentl $y^{(2.3)}$. This will help to sharpen our understanding of atom-photon interaction at quantum level and may lead to the development of single-atom laser. Our efforts to develop an $^{85}$ Rb-atomic fountain is in progress. (omitted)

• Advances in aircraft and spacecraft science
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• 제7권6호
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• pp.537-551
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• 2020

Investigation of leading edge impingement cooling for first stage rotor blades in an aero-engine turbine, its effect on rotor temperature and trailing edge wake loss have been undertaken in this study. The rotor is modeled with the nozzle for attaining a more accurate simulation. The rotor blade is hollowed in order for the coolant to move inside. Also, plenum with the 15 jet nozzles are placed in it. The plenum is fed by compressed fresh air at the rotor hub. Engine operational and real condition is exerted as boundary condition. Rotor is inspected in two states: in existence of cooling technique and non-cooling state. Three-dimensional compressible and steady solutions of RANS equations with SST K-ω turbulent model has been performed for this numerical simulation. The results show that leading edge is one of the most critical regions because of stagnation formation in those areas. Another high temperature region is rotor blade tip for existence of tip leakage in this area and jet impingement cooling can effectively cover these regions. The rotation impact of the jet velocity from hub to tip caused a tendency in coolant streamlines to move toward the rotor blade tip. In addition, by discharging used coolant air from the trailing edge and ejecting it to the turbines main flow by means of the slot in trailing edge, which could reduce the trailing edge wake loss and a total decrease in the blade cooling loss penalty.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 2004년도 ICCAS
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• pp.730-735
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• 2004

This paper describes an improving cooling system in the composite plant. In order to save the energy, a plate-and-frame heat exchanger has been used to replace the traditional worm cooler. The composite plant in Thailand was studied as an illustrative case study. The experimental results demonstrating the saving in energy costs and some economic benefits of the proposed technique are obtained.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집D
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• pp.546-552
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• 2001

The heat transfer and flow measurements on a pedestal encountered in chip cooling. A uniform wall temperature boundary condition at the plate surface and on a pedestal was created using shroud method. Liquid crystal was used to measure the plate surface temperature. The jet Reynolds number (Re) ranges from 11,000 to 50,000, the dimensionless nozzle-to-surface distance (L/d) from 2 to 10, and the dimensionless pedestal diameter-to-height (H/D) from 0 to 1.0. The results show that the Nusselt number distributions at the near the pedestal exhibit secondary maxima at $r/d{\cong}1.0\;and\;1.5$. The formation of the secondary maxima is attributed to an create in the vortex by the pedestal.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집D
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• pp.286-291
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• 2001

This paper describes an optimal scheduling for ice slurry systems for energy cost saving. The optimization technique applied in the study is the dynamic programming method, for which the state variable is the storage in the ice storage tank and the control variable is the state of chiller's on-off switching. Though the costs during charge period is included in optimization by taking the average cost of ice per hour for slurry making, the time horizon for the simulation is limited building cooling period because accurate charge rate from the ice maker into the ice storage tank cannot be estimated during the charge period. In the operating simulation after optimizing procedure, energy consumption and operating cost for the optimal control are calculated and compared with them for a conventional control with one case of cooling load profile.

• 전기학회논문지
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• 제59권9호
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• pp.1615-1620
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• 2010

A thin film thermoelectric cooler for COB direct assembly was proposed and the COB cooler structure was modeled by electrical equivalent circuit by using SPICE model of thermoelectric devices. The embedded cooler attached between the die chip and metal plate can offer the possibility of thin film active cooling for the COB direct assembly. We proposed a driving method of TEC by using pulse width modulation technique. The optimum power to the TEC is simulated by using a SPICE model of thermoelectric device and passive components representing thermal resistance and capacitance. The measured and simulated results offer the possibility of thin film active cooling for the COB direct assembly.

• 대한기계학회논문집A
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• 제20권7호
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• pp.2134-2140
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• 1996

This study was carried out to anlayze the heat-resistant characteristics of functionally gradient material(FGM) composed with ceramic and metal. The thermal fracture behavior of plasma-sprayed FGM and conventional coating material(NFGM) was exaimined by acoustic emession technique under heating and cooling. Furnace cooling and rapid cooling tests were used to examine the effect of temperature change under various conditions, respectively. At the high temperature above $800^{\circ}C$, it was shown that FGM gives higher thermal resistance compared to NFGM by AE signal and fracture surface analysis.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2002년도 추계학술대회논문집
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• pp.116-121
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• 2002

Axial fans are widely used in heavy machines due to their ability to produce high flow rate for cooling of engines. At the same time, the noise generated by these fans causes one of the most serious problems. This work is concerned with the low noise technique of discrete frequency noise. To calculate the unsteady resultant force over the fan blade in an unsymmetric engine room. Time-Marching Free-Wake Method is used. From the calculations of unsteady force on fan blades, noise signal of an engine cooling fan is calculated by using an acoustic similarity law. Noise optimization is obtained from Neural Network which is constructed based on the calculated flow rate and noise spectrum.

• 한국자동차공학회논문집
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• 제11권1호
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• pp.32-41
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• 2003

For the countermeasure of expected higher thermal load in miller cycle engine, coolant flows in the cylinder head of base engine with several coolant flow methods and drilled hole passages were measured by using PIV technique. And the cooling effect was evaluated by measurements of wall temperatures according to each coolant flow method. It was found that the series flow system was most suitable among the discussed 3 types of coolant flow methods since it had the best cooling effect in cylinder head by the fastest coolant flow velocity It was also found that for drilled water passage to decrease the large thermal load in exhaust valve bridge, nozzle type is more effective compared with round type of water passage, and its size has to be determined according to the coolant flow pattern and velocity in each cylinder.

• Nuclear Engineering and Technology
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• 제46권3호
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• pp.395-406
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• 2014

This study provides a fundamental understanding of a cold finger melt crystallization technique by exploring the heat and mass transfer processes of cold finger separation. A series of experiments were performed using a simplified LiCl-CsCl system by varying initial CsCl concentrations (1, 3, 5, and 7.5 wt%), cold finger cooling rates (7.4, 9.8, 12.3, and 14.9 L/min), and separation times (5, 10, 15, and 30 min). Results showed a potential recycling rate of 0.36 g/min with a purity of 0.33 wt% CsCl in LiCl. A CsCl concentrated drip formation was found to decrease crystal purity especially for smaller crystal formations. Dimensionless heat and mass transfer correlations showed that separation production is primarily influenced by convective transfer controlled by cooling gas flow rate, where correlations are more accurate for slower cooling gas flow rates.