• 한국태양에너지학회 논문집
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• 제37권1호
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• pp.47-57
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• 2017

Solar energy is one of the important renewable energy resources. It can be used for air heating, hot water supply, heat source of desiccant cooling system and so on. And many researches for enhancing efficiency have been conducted because of these various uses of solar thermal energy. This study was performed to investigate the air heating performance of hybrid solar air-water heater that can heat air and liquid respectively or simultaneously and finding method for improving thermal performance of this collector. This collector has both liquid pipe and air channel different with the traditional solar water and air heater. Fins were installed in the air channel for enhancing the air heating performance of collector. Also air inlet & outlet temperature, ambient temperature and solar collector's inner part temperature were confirmed with different air velocity on similar solar irradiance. As a result, temperature of heated air was shown about $43^{\circ}C$ to $60^{\circ}C$ on the $30^{\circ}C$ of ambient temperature and thermal efficiency of solar collector was shown 28% to 73% with respect to air velocity. Also, possibility of improvement of thermal performance of this collector could be ascertained from the heat transfer coefficient calculated from this experiment. Thus, it is considered that the research for finding optimal structure of hybrid solar air-water heater for enhancing thermal performance might be needed to conduct as further study based on the method for improving air heating performance confirmed in this study.

• 한국태양에너지학회 논문집
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• 제39권1호
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• pp.77-89
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• 2019

The solar air heater has various performances according to an obstacle installed in the air duct. Many studies on thermal performance have been conducted. But many of these studies were using a kind of rib type obstacle attached at the bottom of absorbing plate, but they are so hard to be manufactured. In this study, characteristics of the heat transfer and pressure drop in the solar air heater with various horizontal rectangular obstacles was investigated by CFD (Computational Fluid Dynamics) analysis. As a result, the heat transfer performance was improved from 1.2 to 3.32 times depending on installation conditions of rectangular obstacle. The pressure drop, however, also increased with increment of heat transfer performance from 2.8 to 180 times only by changing installation conditions of rectangular obstacle. Thus, the performance factor presenting the thermal performance enhancement on the same pressure drop was also confirmed. As a result, the highest value of 0.828 as better performance factor was obtained at the lower height of rectangular obstacle and this value has started to decrease with increment of heat transfer performance. In the end, it could be confirmed that the pressure drop was carried higher than the quantity of improvement of the heat transfer performance when the heat transfer performance was increased by change of installation conditions of rectangular obstacle. Both heat transfer enhancement and pressure drop to be required for system need to be considered before the rectangular obstacles are applied to the solar air heater.

• 동력기계공학회지
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• 제19권4호
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• pp.69-75
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• 2015

In this study, the characteristics of heating performance of a high-performance air-cooled heat pump with vapor-injection(VI) cycle using re-heater was investigated experimentally. Devices used in the experiment is consist of a VI compressor, condenser, oil separator, refrigerant (economizer outlet refrigerant) re-heater, economizer, evaporator. And R410A was used as a working fluid. The experiment was conducted with two cycles(cycles A and B) for investigating heating performance. In case of cycle B, heat exchange was conducted by re-heater between outlet refrigerant of compressor and suction refrigerant of the VI system(Fig.1, re-heater). But the re-heater was not used in case of cycle A. As a result of this experiment, discharge temperature of refrigerator in compressor was shown higher value, when the cycle B was conducted, because of the heat exchange between suction refrigerant of VI cycle and outlet refrigerant of compressor in the re-heater than cycle A that was not use re-heater. it means that liquid hammer and the decrement of heating performance can be decreased by using re-heater. Also, Heating coefficient of performance(COPh) was shown about 2.98 in Cycle B which was 4% higher than Cycle A and from these results, It was confirmed that the improvement of the heating performance of heat pump with VI cycle can be achieved by applying re-heater.

• 한국태양에너지학회 논문집
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• 제24권1호
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• pp.53-61
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• 2004

Absorption potential of desiccant solution significantly decreases after absorbing moisture from humid air, and a regeneration process requires a great amount of energy to recover absorption potential of desiccant solution. In an effort to develop an efficient solar water heater, this study examines a regeneration process using hot water obtained from solar water heater to recover absorption potential by evaporating moisture in the liquid desiccant. In this paper, a solar absorption dehumidifying system with solar water heater is suggested to save the electricity for operating an air conditioner. LiGl(lithium chloride) solution was adopted as a liquid desiccant in the proposed system, and hot water obtained from the solar water heater was used for regenerating the liquid desiccant. As a result, it was clear that the dilute LiCl solution could be regenerated by hot water, and the regeneration rate depends mostly on temperature level of liquid desiccant. The regeneration rates were about 2.4kg/h with $40^{\circ}C$, 4.0kg/h with $50^{\circ}C$, and 6.2kg/h with $60^{\circ}C$ of hot water respectively.

• 전자공학회논문지A
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• 제31A권5호
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• pp.113-120
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• 1994

Silicon flow sensor that can detect the velocity and direction of air flow was designed and fabricated by integrated circuit process and bulk micromachining technique. The flow sensor consists of three-layered dielectric diaphragm, a heater at the center of the diaphragm, and four thermopiles surrounding the heater at each side of diaphragm as sensing elements. This diaphragm structure contributes to improve the sensitivity of the sensor due to excellent thermal isolation property of dielectric materials and their tiny thickness. The flow sensor has good axial symmetry to sense 2-D air flow with the optimized sensing position in the proposed structure. The sensor is fabricated using CMOS compatible process followed by the anisotropic etching of silicon in KOH and EDP solutions to form I$\mu$ m thick dielectric diaphragm as the last step. TCR(Temperature Coefficient of Resistance) of the heater of the fabricated sensors was measured to calculate the operating temperature of the heater and the output voltage of the sensor with respect to flow velocity was also measured. The TCR of the polysilicon heater resistor is 697ppm/K, and the operating temperature of the heater is 331$^{\circ}C$ when the applied voltage is 5V. Measured sensitivity of the sensor is 18.7mV/(m/s)$^{1/2}$ for the flow velocity of smaller than 10m/s.

• 한국산학기술학회논문지
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• 제16권11호
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• pp.7250-7255
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• 2015

본 논문은 전기자동차의 주행 거리 향상을 위한 전기자동차용 연소식 공기 히터를 개발하기 위하여 기존 디젤 연소식 공기 히터의 난방성능에 대한 실험 및 분석을 실시하였다. 본 연구에서 사용된 연소식 공기 히터의 성능 분석을 위하여, 히터의 열용량 계산과 실차 실험을 통한 온도 변화를 고찰하였다. 승차공간으로 공급되는 난방 공기의 온도는 $101.3^{\circ}C$이며 연소식 공기 히터 내부 히트싱크의 표면 온도 편차는 위치에 따라 67.8% 차이를 나타내었고 공기 히터의 난방 열량은 2.0 kW로 산출되었다. 또한 연소식 공기 히터의 실차적용 실험에서 차량 승차공간의 내부 온도는 지속적으로 상승하였고 1800초 후 승차공간의 상부 공기 온도는 $42.5^{\circ}C$이고, 하부 공기 온도는 $25.3^{\circ}C$로 나타났으며 디젤 연소식 공기 히터의 난방 효율은 평균 63.7%로 산출되었다.

• 한국공작기계학회논문집
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• 제11권6호
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• pp.60-67
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• 2002

A precise measurement of field test was performed to estimate the thermal performance of the forced convection electric air heater by experiment. Air temperature, flow rate and electrical power input were measured with the related measurement sensors, and acquisition methods for the measured data were studied to estimate the thermal performance of the tested air heater effectively. To determine the mean air temperature at the flow cross-section, measuring positions were chosen by considering the flow velocity profile and the equally divided cross-sectional area. From the experimental results, thermal efficiency was obtained accurately as an indication of the tested heating system performance.

• 생물환경조절학회지
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• 제22권4호
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• pp.355-360
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• 2013

2개의 단동 수막 비닐하우스에 보조난방으로 경유 온풍기와 적외선 난방등을 설치하고 야간최저온도를 $6^{\circ}C$로 설정하여 '설향' 딸기를 재배하였다. 하우스 내부의 평균 야간온도는 적외선난방이 $6.6^{\circ}C$로 온풍난방의 $7.1^{\circ}C$와 비슷하였지만 외기의 최저온도가 $-10^{\circ}C$ 이하로 내려갈 경우 온풍난방은 내부온도의 변화가 적은 반면 적외선난방은 설정한 온도 이하로 내려가는 경우도 있었다. 상대습도는 보조난방 종류와 관계없이 수막시스템의 영향으로 98% 이상으로 높았다. 엽온의 변화를 열화상 카메라로 촬영했을 때 적외선 난방등이 켜졌을 때와 꺼졌을 때 사이에 $5^{\circ}C$ 정도의 차이를 보였으며 적외선 복사선이 식물체에 직접적으로 미치는 범위는 제한적이었다. 딸기의 화경장과 초장은 적외선등 난방을 한 하우스가 온풍난방을 한 하우스보다 증가하는 경향을 보였고 잎의 크기, 엽수, 1화방 화수, 분지수에서는 통계적인 차이를 보이지 않았다. 수확과수와 당도, 경도, 평균과중 및 수량은 차이를 보이지 않았고 경유 온풍기는 면세유 543L를 사용하여 622,662원이 소요된 반면 적외선 난방등은 농업용(병) 5,685kW를 사용하여 235,284원이 소요되어 약 62.2%의 난방비를 절감할 수 있었다.

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2009년도 하계학술발표대회 논문집
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• pp.218-223
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• 2009

Cost related to building equipment accounts for about 85% of the life cycle cost of buildings. Therefore proper selection of air-conditioning system is important for reducing the overall cost of buildings. In this study, large capacity ice thermal storage and absorption chiller-heater for air-conditioning a building with a floor area of $9,900\;m^2$ are compared economically. For easy input and analysis, an Ms Excel VBA program has been developed. To consider all the factors of initial and operation costs effectively, an annual equal payment method is proposed. Under the assumptions made in this study, overall cost of an absorption chiller-heater is less than that of an ice thermal storage, but this is not absolute and different outcome may result if different assumptions are made. This study is useful for those who are interested in choosing an economical air-conditioning system for large-size buildings with simple calculations.

• 설비공학논문집
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• 제14권1호
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• pp.10-20
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• 2002

A dynamic model of a water heater system heated by a heat pump was developed. The water heater system was composed of heat pump and hot water reservoirs. Finite volume method (FVM) was applied to describe the heat exchangers. A new constraint on electronic expansion valve (EEV) or thermostatic expansion valve (TXV) that can control superheat after the evaporator was developed. Dynamic performances were evaluated for various sizes of the reservoir. In order to compare those performances, time scale was normalized by time constant representing the characteristics of reservoir size. Time constant was determined from quasi steady-state simulation of the system. From the simulation, the size of the water heater reservoir was found to have a large influence on the transient performance of the sys- tem. Therefore, the optimization of the reservoir size is needed in a design process.