• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.26 no.2
• /
• pp.55-60
• /
• 2014

The present study has been conducted to develope a heating system for a green house with heat from underground air at Jeju Island. The temperature of the air deposited in the underground is $16{\sim}18^{\circ}C$ throughout the year, and it also has a large amount of moisture. Therefore, the air could not directly used for the heating of a green house. In this study, a heat pump with dehumidification function has been developed, which consisted of three evaporators, where the moisture removal occurs, accompanied by temperature drop. The dropped temperature is recovered, while passing through a series condenser. The air temperature increased from $17^{\circ}C$ to 35 with a 2.1 kg/h of moisture removal rate. The developed system moisture removal performance shows 0.91 kg/kWh.

• International Journal of Air-Conditioning and Refrigeration
• /
• v.12 no.3
• /
• pp.148-157
• /
• 2004

Convective boiling heat transfer coefficients of R-22 were obtained in a flat extruded aluminum tube with $D_h=1.41mm$. The test range covered mass flux from 200 to $600kg/m^{2}s$, heat flux from 5 to $15kW/m^2$ and saturation temperature from $5^{\circ}C\;to\;15^{\circ}C$. The heat transfer coefficient curve shows a decreasing trend after a certain quality (critical quality). The critical quality decreases as the heat flux increases, and as the mass flux decreases. The early dryout at a high heat flux results in a unique 'cross-over' of the heat transfer coefficient curves. The heat transfer coefficient increases as the mass flux increases. At a low quality region, however, the effect of mass flux is not prominent. The heat transfer coefficient increases as the saturation temperature increases. The effect of saturation temperature, however, diminishes as the heat flux decreases. Both the Shah and the Kandlikar correlations un-derpredict the low mass flux and overpredict the high mass flux data.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.18 no.5
• /
• pp.418-425
• /
• 2006

An AHX (Accumulator Heat exchanger) consists of a commercial accumulator and an inner heat exchanger located inside of the accumulator. The AHX is used in multi air-conditioners to assure that liquid-phase refrigerant enters into the expansion device. This purpose is achieved by heat transfer between the refrigerant leaving the evaporator and the refrigerant leaving the condenser. In this study, the effects of AHX on the performance of a refrigeration system using R-22 were measured and the test results were analyzed. The operating characteristics of the refrigeration system with the AHX are considerably different from those without the AHX. Therefore, it is required to determine optimum refrigerant charge and optimum operating conditions when the AHX is used in the refrigeration system having a constant flow-area expansion device such as capillary tube.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.14 no.2
• /
• pp.517-522
• /
• 2013

Small size ice-cream maker has two evaporators having different evaporating temperatures of $4^{\circ}C$ and $-8^{\circ}C$. In such case, ice-cream maker system design becomes complicated because multiple capillary tubes affects one another. In this study, performance analysis was conducted for the soft ice-cream maker having two evaporators operating at different temperatures. The compressor was analyzed using efficiency models, the capillary tube was modeled assuming one-dimensional flow, the condenser and the evaporators were modeld based on UA-LMTD method. The refrigeration cycle simulation program was developed applying the enthalpy, pressure and mass balance on each component. Comparison of the test data with the simulated results for R404A revealed that evaporator temperatures of refrigerator and freezer agreed within $3^{\circ}C$.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2012.02a
• /
• pp.341-341
• /
• 2012

Recently, oxide semi-conductor materials have been investigated as promising candidates replacing a-Si:H and poly-Si semiconductor because they have some advantages of a room-temperature process, low-cost, high performance and various applications in flexible and transparent electronics. Particularly, amorphous indium-gallium-zinc-oxide (a-IGZO) is an interesting semiconductor material for use in flexible thin film transistor (TFT) fabrication due to the high carrier mobility and low deposition temperatures. In this work, we demonstrated improvement of flexibility in IGZO TFTs, which were fabricated on polyimide (PI) substrate. At first, a thin poly-4vinyl phenol (PVP) layer was spin coated on PI substrate for making a smooth surface up to 0.3 nm, which was required to form high quality active layer. Then, Ni gate electrode of 100 nm was deposited on the bare PVP layer by e-beam evaporator using a shadow mask. The PVP and $Al_2O_3$ layers with different thicknesses were used for organic/inorganic multi gate dielectric, which were formed by spin coater and atomic layer deposition (ALD), respectively, at $200^{\circ}C$. 70 nm IGZO semiconductor layer and 70 nm Al source/drain electrodes were respectively deposited by RF magnetron sputter and thermal evaporator using shadow masks. Then, IGZO layer was annealed on a hotplate at $200^{\circ}C$ for 1 hour. Standard electrical characteristics of transistors were measured by a semiconductor parameter analyzer at room temperature in the dark and performance of devices then was also evaluated under static and dynamic mechanical deformation. The IGZO TFTs incorporating hybrid gate dielectrics showed a high flexibility compared to the device with single structural gate dielectrics. The effects of mechanical deformation on the TFT characteristics will be discussed in detail.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2013.02a
• /
• pp.352-352
• /
• 2013

국내 에너지 소비량의 21.6%가 건물 분야에 소비되고 있다. 창호는 벽체에 비해 8~10배 이상 낮은 단열 특성을 가지기 때문에 열 손실량이 크다. 유리는 창호를 이루는 요소 중 가장 큰 면적을 차지하고 있으며, 창호의 단열성능을 2배로 향상시키면 30% 이상 건물의 에너지 절감 효과를 가질 수 있다. 창호의 단열 성능을 향상시키기 위해서 Low-e(emissivity) 기술 연구가 진행 중이다. 이번 실험에서는 RF 마그네트론 스퍼터링 시스템을 사용하여 XG 유리기판 위에 ZnO박막을 증착하고, evaporator 장비를 사용하여 metal층인 Ag를 증착하였다. 그리고 다시 한번 ZnO박막을 증착하였다. Low-e 연구에 활용할 수 있는지를 확인하기 위해 XRD, AFM, 투과도를 측정하였다. ZnO박막의 증착 조건은 초기압력 $3.0{\times}10^{-6}$ Torr, 공정압력 $2.0{\times}10^{-2}$ Torr, RF파워 30 W, Ar gas는 50 sccm, 증착온도는 상온으로 하였다. Metal층인 Ag를 증착하기 위해 evaporator의 증착 조건은 Rotate rate 2 rpm, voltage 0.3V, 공정압력 $5.0{\times}10^{-6}$ Torr이며, 변수로 Ag두께를 3,5,7,9,11,13,15 nm로 하였다. AFM 측정결과 Ag두께가 증가할수록 RMS roughness값이 높아졌으며, 최소 0.71 nm의 거칠기를 가지는 것을 확인하였다. XRD분석결과 37도 부근의 피크가 발생하여 ZnO 박막이 결정질 구조임을 확인할 수 있었다. 그리고 UV-Visible-NIR 분광 광도계를 이용하여 광학적 투과를 측정한 결과 Ag두께가 13 nm일 때 가시광 영역의 투과도가 최대 75%, 적외선 영역의 투과도가 최소 28%로 좋은 차단 특성을 가지는 것을 확인하였다. 위 결과들로 ZnO 박막이 Low-e 기술에 활용될 수 있음을 확인하였다.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2013.02a
• /
• pp.351-351
• /
• 2013

한국 전체 에너지 사용량 중약 24%의 에너지가 건축물 부분에 소비되고 있다. 건축물의 벽체나 유리창 등을 통해서 에너지 손실이 이루어지는데 유리창은 벽체에 비해 약 10배 이상 낮은 단열 특성을 가지고 있기 때문에 유리창을 통한 열손실량은 더 크다. 이러한 유리창 부분의 열손실 문제를 해결할 수 있는 방안으로 좋은 단열 특성 및 낮은 방사율을 가지고 있는 Low-e coating 방법을 사용하였다. 본 실험에서는 XG glass 기판 위에 IGZO/Ag/IGZO OMO 구조의 다층 박막을 증착하였다. RF magnetron sputtering방법을 이용하여 OMO 구조의 상부와 하부의 Oxide layer로 IGZO 박막을 증착하였다. 사용된 IGZO 타겟은 $In_2O_3$ (99.99%), $Ga_2O_3$ (99.99%), ZnO (99.99%)의 분말을 각각 1:1:1 mol% 조성비로 혼합하여 소결하여 제작하였다. Thermal Evaporator 장비를 이용하여 OMO 구조의 Metal layer로 Ag (99.999%)를 증착하였다. 실험 기판은 크기 $30{\times}30mm$의 0.7T XG glass를 사용하였다. OMO 구조의 산화층 IGZO 박막은 상/하층 동일 조건으로 기판 온도는 실온으로 고정하였으며, 초기 압력 $3.0{\times}10^{-6}$ Torr, 증착 압력 $3.0{\times}10^{-2}$ Torr, RF 파워 50W, Ar 유량 50 sccm로 고정시키고 증착 시간이 변화하면서 박막을 증착하였다. OMO 구조의 Metal layer로 Ag 증착 조건은 초기 진공도가 약 $6.0{\times}10^{-6}$ Torr 이하로 유지하고 기판을 2 Rpm의 속도로 회전시켰다. 이후 0.3 V로 Ag를 10분간 가열하여 충분히 녹인 후 Film Thickness Monitor로 두께를 확인하였다. OMO 다층 박막의 산화물층 변화에 따라 로이다층 박막의 구조적, 광학적 및 전기적 특성을 분석하였다. XRD 분석결과에 의하여 Bragg's 법칙을 만족하는 피크가 나타나지 않는 비정질 구조임을 확인할 수 있으며, AFM 분석결과에 통해서 최소 1.3 nm의 Roughness를 나타내었다. UV-Visible-NIR 분광광도계를 이용하여 다층 박막은 가시광선 영역에서 평균 80%의 광 투과성을 보여 IR 영역에서 평균 30% 투과하고 좋은 차단 특성을 나왔다. Low-e 특성을 갖는 유리창을 통해서 에너지 절약을 이룰 수 있는 것을 확인할 수 있었다.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2006.11a
• /
• pp.315-316
• /
• 2006

We fabricated GaN nanopores m the etching process of anodic oxidation of aluminum. The aluminum was deposited by using E-beam evaporator on p-type GaN. After the aluminum was anodized GaN structure was exposed to the electric field with the oxidat species. The fabricated nanopore structure provides the enhanced intensity of light emission at the wavelengths 470 nm. We investigated the structure of the GaN nanopores from FE-SEM and EDS measurements.

• International Journal of Air-Conditioning and Refrigeration
• /
• v.7
• /
• pp.22-32
• /
• 1999

A multi-type heat pump controls the mass flow rate of the working fluid to cope with variable heat loads when it is under dynamic load condition. This paper describes the exergy analysis associated with the unsteady response of a heat pump. First, a basic heat pump cycle is examined at a steady state to show the general trends of exergy variations in each process of the cycle. Entropy generation issue for the heat exchangers is discussed to optimize the heat pump cycle. Secondly, the performance of the inverter-driven heat pump is compared to that of the conventional one when the heat load is variable. Thirdly, the exergy destruction rate of the heat pump with On/Off operation is calculated by simulating the thermodynamic states of the working fluid in the condenser and the evaporator. The inefficiency of On/Off operation during the transient period is quantitatively described by the exergy analysis.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.10 no.2
• /
• pp.155-164
• /
• 1998

A multi-type heat pump controls the mass flow rate of the working fluid to cope with variable heat loads when it is under dynamic load condition. This paper describes the exergy analysis associated with the dynamic response of heat pump. First, a basic heat pump cycle is examined at steady state to show the general trends of exergy changes in each process of the cycle. Entropy generation issue in the exchangers is discussed to optimize the heat pump cycle. Second, the performance of the inverter-driven heat pump is compared to that of the conventional one when the heat load is variable. Third, the exergy destruction rate associated with the ON/OFF operations of the heat pump is calculated by simulating the thermodynamic states of the condenser and the evaporator. The inefficiency of the ON/OFF operation during the transient period is quantitatively revealed by the exergy analysis.