• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.13 no.11
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• pp.1089-1096
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• 2001

The cool-down performance after soaking is very important in an automotive air-conditioning system and is considered as the key design variable. Therefore, understanding of the overall transient characteristics of the system is essential to the preliminary design as well as steady-state characteristics. The objective of this study is to develop a computer simulation model and estimate theoretical1y the transient performance of an automotive air-conditioning system. To accomplish this, a mathematical modelling of each component, such as compressor, condenser, expansion valve, and evaporator, is presented first of all. For a detailed calculation, condenser and evaporator are divided into many subsections. Each sub-section is an elemental volume for modelling. In models of expansion valve and compressor, dynamic behaviors are not considered in an attempt to simplify the ana1ysis, but the quasi-static ones are just considered, such as the relation between mass flow rate and pressure drop in expansion device, polytropic process in compressor, etc. The developed simulation model is validated with a comparison to laboratory test data of an automotive air-conditioning system. The overall time-tracing properties of each component agreed fairly well wish those of test data in this case.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.28 no.12
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• pp.1475-1483
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• 2004

Loop thermosyphon(LTS) has many good characteristics such as low thermal resistance, no power consumption, noiseless operation and small size. To investigate the overall performance of LTS, we have performed various experiments varying three parameters: input power of the heater, working fluid(water, ethanol, FC3283) and filling ratio of the working fluid. At a combination of these parameters, temperature measurements are made at many locations of the LTS. The temperature difference between the evaporator and the condenser is used to obtain the thermal resistance. In addition, flow visualization using a high speed camera is carried out. The thermal resistance is not constant. It is lower at higher input power, which is one of the distinct merits of LTS. Flow instabilities are frequently observed when changing the working fluid, the input power and the filling ratio. The results show that the LTS can be readily put into practical use. Future practical application in electronic cooling is recommended.

• 한국태양에너지학회:학술대회논문집
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• 2011.04a
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• pp.86-91
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• 2011

Thermal design was conducted for a solar thermal storage system in a medium-temperature range between $200^{\circ}C$ and $400^{\circ}C$. The system was composed of heat pipes as heat carrier and molten salts as phase-change storage material. Each heat pipe penetrated through the storage system and had two heat-exchanging sections at both ends to interact with high-and low-temperature steams, while it exchanged heat with molten salts in the middle section. During a heat-storage mode, the heat pipes transferred heat from the hot steam at one side to the molten salts and it transferred heat from the molten salt to the cold steam at the other side during the heat-dissipating mode. A tube-bank type heat exchanger theory was applied to this design task to meet the required inlet and outlet temperatures of the steams depending on the operation modes. Several design variables were considered including the lengths of evaporator and condenser of a heat pipe, traverse and longitudinal pitches of the pipe, and the number of rows of the heat pipes for two different molten salt baths. An optimum design results were presented with discussion.

• Journal of the Korean Vacuum Society
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• v.11 no.1
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• pp.1-7
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• 2002

We deposited $Ba_{0.5}Sr_{0.5}TiO_3$(BST) thin-films on Pt/Ti/$SiO_2$/Si substrates using RF magnetron sputtering method. A Substrate temperature was fixed at room temperature, while working gas flow ratio and RF Power were changed from 90:10 to 60:40 and 50 W, 75 W respectively. Also after BST thin films were deposited, we performed annealing in oxygen atmosphere using Rapid Thermal Annealing. For capacitor application we deposited Pt using E-beam evaporator of UHV system. In a structural property study through XRD measurement we found that crystallization depends on annealing rather than working gas ratio or and RF Power. Electrical properties showed relatively superior characteristic on the annealed sample with 50 W of RF Power.

• Journal of IKEEE
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• v.23 no.4
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• pp.1128-1133
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• 2019

This paper proposed colored front panel glass for Building Integrated Photovoltaic (BIPV) systems using multi-layered thin films composed of transition metal oxide (TMO) layers. Molybdenum oxide (MoO₃) and tungsten oxide (WO₃) provided complementary and suitable materials in making effective interference of reflected light from interfaces with significant difference in refractive indices. A simple, fast, and cheap fabrication method was achieved by depositing the multi-layer films in a single thermal evaporator. Magenta colored glass with optical transmittance of more than 90% was achieved with MoO₃ (60nm)/WO₃(100nm) multi-layered film. This technology could play in a critical role in commercial BIPV system applications.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.18 no.11
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• pp.915-922
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• 2006

Considering heat pipe design principles in fabrication and operational performances, water is one of the most recommended working fluids to make mid to low tempera lure heat pipes. But the conventional water heat pipes might encounter the failure in a cold start-up operation when socked at a chilling temperature lower than the freezing point. If they are subjected to a heat supply for start-up at a temperature around $-20^{\circ}C$, the rate of the vapor flow and the corresponding heat transfer from the evaporator to the condenser is so small that the vapor keeps to stick on the surface of the chilling condenser wall, forming an ice layer, resulting in a liquid deficiency in the evaporator. This kind of problems was resolved by Kang et al. in 2004 by adopting a gas loading heat pipe technology to the conventional water heat pipes. This study was conducted to examine a chilling start-up procedure of gas loading heat pipes by investigating the behaviors of heat pipe wall temperatures. And the thermal resistance of the gas loaded heat pipe that depends on the operating temperatures and heat loads was measured and examined. Two water heat pipes were designed and fabricated for the comparison of performances, one conventional and the other loaded with $N_2$ gas. They were put on start-up test at a heat supply of 30 W after having been socked at an initial temperature around $-20^{\circ}C$. It was observed that the gas loaded one had succeeded in chilling start-up operation.

• Transactions on Electrical and Electronic Materials
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• v.9 no.6
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• pp.223-226
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• 2008

$Ge_1Se_1Te_2$ chalcogenide amorphous materials was prepared by the conventional melt-quenching method. Samples were processed bye-beam evaporator systems and RF-sputtering systems. Phase change characteristics were analyzed by measuring glassification temperature, crystallization temperature and density of bulk material. The thermal characteristics were measured at the temperature between 300 K and 700 K, and the electrical characteristics were studied within the range from 0 V to 3 V. The obtained results agree with the electrothermal model for Phase-Change Random Access Memory.

• Proceedings of the IEEK Conference
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• 2000.06b
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• pp.115-118
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• 2000

Uncooled pyroelectric infrared detectors based on BST(B $a_{-x}$S $r_{x}$Ti $O_3$) thin films have been fabricated by RF magnetron sputtering and surface Micromachining technology. The detectors form BST thin film ferroelectric capacitors grown by RF magnetron sputtering on N/O/N(S $i_3$ $N_4$/ $SiO_2$/S $i_3$ $N_4$) membrane. The sputtered BST thin film exhibits highly c-axis oriented crystal structure that no poling treatment for sensing applications is required. This is an essential factor to increase the yield for realization of an infrared image sensor. surface-Micromachining technology is used to lower the thermal mass of the detector by giving maximum sensor efficiency Gold-black is evaporated on top of the sensing elements used the thermal evaporator. fabricated uncooled pyroelectric infrared detectors is highly output voltage at the low temperature(1$^{\circ}C$).).).

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.10 no.2
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• pp.227-237
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• 1998

A numerical simulation has been carried out for the automotive air conditioning system. The purpose of this simulation is to present the methods for simulating car air conditioning components, systems and cool-down performance by computerized mathematical model and to analyze the performance of A/C system. In analyzing the heat exchanger(evaporator and condenser), the finite volume model which has a merit in predicting the temperature field in detail because it can consider partial variation of thermal property and heat transfer coefficient is used. In analyzing the compressor, the polytropic approach which regards the actual compression process as a reversible polytropic process is employed. In analyzing vehicle passenger compartment, the thermal network is employed to simulate the car cool down process. This A/C system program can be used for analyzing a component performance when a component is alternated or designed and for analyzing the engine cooling system when A/C system is operated.

• Journal of Advanced Marine Engineering and Technology
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• v.27 no.2
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• pp.305-311
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• 2003

This Paper Presents an information about the heat transfer characteristics of a separate type thermosyphon in electronic equipments. The heat removal problem of electronic equipments is regarded as an important factor and a separate type heatpipes can be utilized as a cooling device of electronic equipments (such as CPU of a Personal computer or notebook). In this study. heat source ($50\times50\times2 mm $aluminum Pseudo CPU) was used for the experiment. The device can transfer heat from the evaporator to the condenser through natural circulation (without any external driving forces) and the results indicate that the device is capable of dissipating over 60W of thermal energy and keeping the heating plate surface temperature under $50^{\circ}C$.