• Bulletin of the Korean Space Science Society
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• 2011.04a
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• pp.23.4-23.4
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• 2011

MIRIS is the main payload of the Science and Technology Satellite-3 (STSAT-3). which is being developed by KASI for infrared survey observation of the Galactic plane at Paschen alpha wavelength. Wideband filters in I and H band will also be used to observe cosmic infrared background. The MIRIS will perform astronomical observations in the near-infrared wavelengths of 0.9~2 ${\mu}m$ using a 256 ${\times}$ 256 Teledyne PICNIC FPA sensor providing a 3.67 ${\times}$ 3.67 degree field of view with a pixel scale of 51.6 arcsec. The flight model of the MIRIS has been recently developed, The system performance tests have been made in the laboratory, including opto-mechanics test, vibration test, thermal vacuum test and passive cooling test down to 200K, using a thermally controlled vacuum chamber. Several focus tests showed good agreements compared to initial design parameters. Recent efforts are being concentrated to improve the system performances, particularly to reduce readout noise level in electronics. After assembly and integration into the satellite bus, the MIRIS will be launched in 2012.

• ETRI Journal
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• v.24 no.5
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• pp.349-359
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• 2002

With Ni/Au and Pd/Au metal schemes and low temperature processing, we formed low resistance stable Ohmic contacts to p-type GaN. Our investigation was preceded by conventional cleaning, followed by treatment in boiling $HNO_3$:HCl (1:3). Metallization was by thermally evaporating 30 nm Ni/15 nm Au or 25 nm Pd/15 nm Au. After heat treatment in $O_2$ + $N_2$ at various temperatures, the contacts were subsequently cooled in liquid nitrogen. Cryogenic cooling following heat treatment at $600^{\circ}C$ decreased the specific contact resistance from $9.84{\times}10^{-4}$ ${\Omega}cm^2$ to $2.65{\times}10^{-4}$ ${\Omega}cm^2$ for the Ni/Au contacts, while this increased it from $1.80{\times}10^{-4}$ ${\Omega}cm^2$ to $3.34{\times}10^{-4}$ ${\Omega}cm^2$ for the Pd/Au contacts. The Ni/Au contacts showed slightly higher specific contact resistance than the Pd/Au contacts, although they were more stable than the Pd contacts. X-ray photoelectron spectroscopy depth profiling showed the Ni contacts to be NiO followed by Au at the interface for the Ni/Au contacts, whereas the Pd/Au contacts exhibited a Pd:Au solid solution. The contacts quenched in liquid nitrogen following sintering were much more uniform under atomic force microscopy examination and gave a 3 times lower contact resistance with the Ni/Au design. Current-voltage-temperature analysis revealed that conduction was predominantly by thermionic field emission.

• Proceedings of the SAREK Conference
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• 2009.06a
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• pp.1096-1101
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• 2009

The plate heat exchanger(PHE) in heat pump has two flow streams of the refrigerant and water. The flow direction of the refrigerant, unlike that of water, can be changed by a 4-way valve depending on operating condition. Therefore the flow arrangement is a parallel flow for heating and a counter flow for cooling, respectively. In this study, the effects of the flow direction of the water on the heat transfer rate are investigated experimentally. The experiments are carried out for brazed plate heat exchangers under a parallel and counter flow conditions in evaporation and condensation. The experimental parameters in this study include the mass flux of the refrigerant 410A from 3 to $14\;kg/m^2s$ and the flow patterns for the pressure of PHE fixed at 0.97 and 2.46 MPa. The results show that both the heat transfer rate and frictional pressure drop across the PHE increase with the mass flux. The heat transfer rate of the refrigerant 410A for evaporation show great sensitivity to flow direction of the water. The heat transfer rate for evaporation with a counter flow are 5-30% higher than that with a parallel flow.

• Journal of the Microelectronics and Packaging Society
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• v.12 no.4 s.37
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• pp.331-338
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• 2005

The rapid advances in high power light sources and arrays as encountered in incandescent lamps have induced dramatic increases in die heat flux and power consumption at all levels of high power LED packaging. The lifetime of such devices and device arrays is determined by their temperature and thermal transients controlled by the powering and cooling, because they are usually operated under rough environmental conditions. The reliability of packaged electronics strongly depends on the die attach quality, because any void or a small delamination may cause instant temperature increase in the die, leading sooner or later to failure in the operation. Die attach materials have a key role in the thermal management of high power LED packages by providing the low thermal resistance between the heat generating LED chips and the heat dissipating heat slug. In this paper, thermal transient characteristics of die attach in high power LED package have been studied based on the thermal transient analysis using the evaluation of the structure function of the heat flow path. With high power LED packages fabricated by die attach materials such as Ag paste, solder paste and Au/Sn eutectic bonding, we have demonstrated characteristics such as cross-section analysis, shear test and visual inspection after shear test of die attach and how to detect die attach failures and to measure thermal resistance values of die attach in high power LED package. From the structure function oi the thermal transient characteristics, we could know the result that die attach quality of Au/Sn eutectic bonding presented the thermal resistance of about 3.5K/W. It was much better than those of Ag paste and solder paste presented the thermal resistance of about 11.5${\~}$14.2K/W and 4.4${\~}$4.6K/W, respectively.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2000.10a
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• pp.11-14
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• 2000

This paper describes a thennally stimulated displacement current(TSDC) of polyamic acid alkylamine salts(PAAS) Langmuir-Blodgett(LB) films, which is a precursor of polyimide(PI). The TSDC measurements of PAAS LB film were performed from room temperature to about $250^{\circ}C$ and the temperature was increased at a rate of $0.2^{\circ}C/s$. This show that this is TSDC peaks at about $70^{\circ}C$ in the arachidic acid LB films, and at about $70^{\circ}C$ and $160^{\circ}C$ in the PAAS LB films. Results of this measurements indicate that one small peak at $70^{\circ}C$ is resulted from a softening of the alkyl group and the large peak at $160^{\circ}C$ is possibly due to dipole moment of C-O group in the PAAS molecule. We have calculated the vertical component of dipole moment of the P AAS LB film out of the TSDC curves. It shows that the dipole moment of PAAS LB film is about -40mD at $70^{\circ}C$ and about 200mD at $160^{\circ}C$ in the first measurement of TSDC. In the second measurement of TSDC of PAAS LB film after cooling down to room temperature, the TSDC peaks are almost disappeared.

• Journal of Korean Society for Atmospheric Environment
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• v.22 no.2
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• pp.249-257
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• 2006

In this work, the adsorptive and desorptive behavior of reduced sulfur compounds (RSC) was investigated using the combination of the Peltier cooling (PC)/thermal desorption (TD) unit with the gas chromatographic (GC) detection technique. To examine the adsorptive characteristics of RSC on clothing materials, a total of nine experiments were conducted in a stepwise manner. Once small towel pieces are exposed to significant quantities of RSC standards with high concentrations (10 ppm), the desoprtion stage was then induced by deloading RSC with ultrapure $N_2$ at three different flow rates (FR) of 20, 40, and 60 mL/min. At each FR, the total deloading volume of 400, 800, and 1,600 mL were maintained. These results were then compared in terms of odoring efficiency by dividing the total amount of desorption with the total amount used for exposition or RSC loading. The results indicated that desorption reaction of certain compounds ($CH_3SH$ and DMS) can be influenced significantly with the reducing FR, while they are not affected directly by the total deloading volume. In addition, when the extent of adsorption was compared for most S compounds by the odoring efficiency term, the extent of absorption generally occurred at approximately 1/1000 level of original exposition.

• Architectural research
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• v.17 no.3
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• pp.109-115
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• 2015

The dynamic pricing of electricity, where the electricity rate increases in a time zone with a high demand for electricity is typically applied to a building whose power reception capacity is greater than a certain size. This includes the time of use(TOU) electricity pricing in Korea which can induce the effect of reducing the power demand of a building. Meanwhile, a VRF (Variable Refrigerant Flow) system that uses electricity is regarded as one of the typical heating and cooling systems along with central air conditioning (central HVAC) for its easy operation and application to the building. Thus, to reduce power energy and operating costs of a building in which the TOU and VRF systems are applied simultaneously, we suggested a control for changing the indoor temperature setting within the thermal comfort range or limiting the rotational speed of an inverter compressor. In this study, to describe the features of the above-mentioned control and verify its effects, we evaluated the results obtained from the analysis of its operation data. Through the actual measurements in winter operations for 73 days since mid- December 2014, we confirmed a reduction of 10.9% in power energy consumption and 12.2% in operating costs by the new control. Also, a reduction of 13.3% in power energy consumption was identified through a regression analysis.

• Journal of Astronomy and Space Sciences
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• v.14 no.2
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• pp.259-268
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• 1997

We present the development process of a prototype CCD imaging system which is being built at Korea Astronomy Observatory(KAO) for astronomical applications. The CCD imaging system requires very low noise and high stability characteristics and is widely used for astronomical purposes from infrared to ultraviolet wavelength regions. However its system design, particularly for the controller design technique, as heart of the system, is not secured in Korea so far. The prototype electronics developed in this study consists of a signal chip controller which was implemented in an EPLD(Erasable Programable Logic Device) and an analog driver, a video processor with a LN2 cooling cryostat. A PC system was employed to control the whole system and to store the image data considering compatibility of the system. We have successfully obtained the first image in the laboratory with the prototype of this imaging system, and an image of the M15 at Sobaeksan Astronomy Observatory.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.19 no.12
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• pp.842-849
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• 2007

For a $CO_2$ two-stage twin rotary compressor used for heat pump water heater system, changes of $CO_2$ solubility in PAG oil were investigated along the gas passages from the first stage suction to final discharge. Only slight changes in solubility took place in suction chambers for both of the first and second stages, but for compression chambers, solubility variation ranged from 0.115 to 0.136, and from 0.133 to 0.182, respectively for the first and second stages. Calculation of gas flashing in parts of leakage oil flows and of oil contained in control volumes due to solubility changes was conducted and included in gas pressure calculation. For the second stage, gas flashing amounts to around $5%\sim6%$ for most leakage flows. Cooling capacity, compressor input, and COP obtained by calculation were well compared to the experimental results. Effects of operation speed on the compressor performance was also studied: as the shaft speed increased, adiabatic efficiency decreased rapidly due to increased over-compression loss.

• Journal of the Microelectronics and Packaging Society
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• v.24 no.2
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• pp.17-21
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• 2017

Horizontal thin-film thermoelectric cooler has been simulated using a commercial software (ANSYS Workbench Thermal-electric). The thermoelectric cooler consists of thin-film n-type $Bi_2Te_3$, p-type $Sb_2Te_3$ thermoelectric elements, and Au electrode, respectively. The hot spot was placed under the center of device which represents Joule heating. Numerical analysis was conducted by geometric variable, and a maximum temperature difference of $13^{\circ}C$ was obtained. As from the simulation parameters, we presented an optimized design for high efficiency cooling.