• Journal of the Korean Solar Energy Society
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• v.37 no.1
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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.

• Proceedings of the Korean Nuclear Society Conference
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• 1999.05a
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• pp.164-164
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• 1999

• Proceedings of the Korean Nuclear Society Conference
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• 1999.05a
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• pp.165-165
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• 1999

• Proceedings of the Korean Nuclear Society Conference
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• 1999.05a
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• pp.166-166
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• 1999

• Proceedings of the Korean Society for Agricultural Machinery Conference
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• 2002.02a
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• pp.558-563
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• 2002

시설원예에서 난방장치를 사용하는 겨울철 재배 농산물의 생산비 중 난방 연료비가 30%~37% 정도를 차지하여 비중이 가장 높다. 따라서 시설원예 농가에서는 난방비를 절감하는 것이 농가소득과 직결되므로, 난방장치의 선정이 대단히 중요하다. 본 연구에서는 겨울철 재배 농산물의 생산비 중 30%-37% 정도를 차지하는 연료비를 절감하기 위해 기존의 온풍난방기와 다른 새로운 방식의 열교환기와 원심식 송풍블로워를 사용하는 블로워 송풍방식의 온풍난방기를 개발하고 개발된 온풍난방기의 가동으로 인한 난방 연료비 절감효과와 온실내의 균일한 온도분포를 획득하기 위해 8연동 비닐온실에서의 시험을 실시하였으며 얻어진 결과를 요약하면 다음과 같다. 가. 저 정압용의 전동기 축직결식 송풍팬을 대신하여 고 정압용의 블로워 송풍팬을 장착하고 열교환 면적을 크게 한 지그재그식 환류의 열교환실을 채용한 온풍난방기를 개발하였다. 나. 공시한 온실에서 기존 온풍난방기의 2일 가동시 DH당 연료 사용량이 평균 1.082$\ell$/$^{\circ}C$.hr 이며, 블로워 송풍방식 온풍난방기의 3일 가동시 DH당 연료 사용량은 평균 0.854$\ell$/$^{\circ}C$.hr로써 21%의 난방 연료비 절감효과가 나타났다. 다. 블로워 송풍방식 온풍난방기는 동일시간대 3$^{\circ}C$의 경시적 온도변화가 발생하였고, 기존의 은풍난방기의 동일시간대 온도변화는 최대 6.1$^{\circ}C$로 나타나 개발된 블로워 송풍방식 온풍난방기가 동일시간대 온실내의 온도변화를 크게 줄일 수 있었고 온도분포를 비교적 균일하게 하는 효과가 있음을 확인하였다.도 33$^{\circ}C$를 기준으로 한 열 회수 시간은 유입공기 온도가 52$^{\circ}C$ 및 64$^{\circ}C$ 일 각각 120분 및 140분으로 나타났다. (3) 제 3종 자갈: 축열조로 공급되는 공기의 온도가 52$^{\circ}C$와 64$^{\circ}C$ 일 때, 축열조 출구의 공기온도가 33$^{\circ}C$에 도달될 때까지 가열되는데 소요된 시간은 가열공기의 온도가 52$^{\circ}C$와 64$^{\circ}C$ 일 때 각각 180분과 150분이었고, 방열에 소요된 시간은 각각 240분 및 270분으로 나타났다. 방열과정 동안 축열조 출구의 최고 공기온도는 가열 공급공기의 온도가 52$^{\circ}C$ 와 $65^{\circ}C$일 때 각각 35.5$^{\circ}C$ 및 39.5$^{\circ}C$였다. 출구 공기온도 33$^{\circ}C$이상을 기준으로 한 에너지 회수시간은 유입공기 온도가 52$^{\circ}C$ 및 64$^{\circ}C$일 때 각각 140분 및 160분으로 나타났다. 이와 같이 자갈이 작을수록 축열조 출구의 공기온도가 기준온도 33$^{\circ}C$에 도달되는 시간이 길었으며, 이것은 축열조내의 공극이 작고 비중량이 커 자갈층을 가열시키는 축열시간이 길어지기 때문인 것으로 사료된다. 또한 작은 자갈일수록 방열시간도 다소 길어져 회수 가능 열에너지가 큰 것으로 나타났다

• Aerospace Engineering and Technology
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• v.3 no.1
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• pp.65-78
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• 2004

This research was conducted for an acquisition of the ramjet engine test facility design technique which are concerned about freejet type test facility. In this research, we concentrated on the design technique and the construction technique of the vitiation air heater(VAH), test section, diffuser and ejector. Based on the operating modes of the basic test facility, ten operating modes in coordinates "Altitude-Mach number" was regenerated from Mach 2, Altitude 0km to Mach 5, Altitude 15km. In this operating modes, we calculated a design parameter of the supersonic nozzle, VAH, diffuser and ejector and acquired a technique for the ramjet test facility operating and repairing.

• Journal of the Korean Institute of Intelligent Systems
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• v.26 no.2
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• pp.147-152
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• 2016

Shape Memory Alloys (SMAs) undergo changes in shape and hardness when heated or cooled, and do so with great force. Since wire-type SMAs contract in length when heated and pull with a surprisingly large force and move silently, they can be used as actuactors which replace motors. These SMA actuators can be heated directly with electricity and can be used to create a wide range of motions. This paper presents the mechanical design and control for a three fingered, six degree-of-freedom robotic hand actuated by SMA actuators. Each finger has two joints and each joint is actuated with two tendons in the antagonistic manner. In order to create the sufficient force to make the smooth motion, the tendon is composed of two SMA actuators in parallel. For controlling the current to heat the SMA actuators, PWM drivers are used. In experiments, the antagonistic interaction of fingers are evaluated.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.48 no.11
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• pp.889-902
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• 2020

In this study, a numerical analysis was performed to confirm the formation of supersonic flow and the stabilization time satisfying the design condition in a Direct-connect supersonic combustor. The process was examined in which the high-pressure gas of vitiation air heater propagates downstream to the supersonic combustor and forms a supersonic flow field. It was confirmed through the analysis of pressure and temperature that the supersonic flow field satisfies the design points of Mach number 2.0 and 1,000 K, and requires a minimum of 4.0 ms for stabilization. These results indicate that the time required for the supersonic flow field stabilization should be taken into account when testing for the supersonic combustion experiment.

• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.6
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• pp.1547-1555
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• 1993

An experimental study on convection heat transfer characteristics from a heated tube to an oscillating flow has been carried out, . This problem is of particular interest in the design of heat exchangers in Stirling cycle machines. Experimental system has been developed to measure temporal variations of temperature inside a heater tube during oscillating modes in a Stirling cycle machine. The dependence of temperature distributions and heat transfer rates on the oscillating frequency as well as the swept volume ratio and the mean pressure of a Stirling cycle machine is investigated in detail. The experimental results indicate that the measured temporal variations of temperature become nearly sinusoidal. The amplitude of temperature variation in the core of the tube is much more substantial than that near the tube wall, whereas the reverse is true for pulsating flows. It is also found that the heat transfer rate is increased significantly as the oscillating frequency or oscillating amplitude or the mean pressure in a tube is increased.

• Journal of the Korean Solar Energy Society
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• v.34 no.6
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• pp.49-56
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• 2014

Research about hybrid solar air-water heater that can make heated air and hot water was conducted as a part of improving efficiency of solar thermal energy. At this experiment, ability of making heating air and hot water was investigated and compared with traditional solar air heater and flat plate solar collector for hot water when air or liquid was heated respectively. Comparing hybrid solar air-water heater that used in this experiment to other solar air heater studied already, it has a lower efficiency at same mass flow rate. Air channel structure, fin's shape and arrangement in the air channel result in these difference then the ability of air heating need to be improved with changing these thing. In case of making hot water, performance was shown as similar with traditional system although the air channels were established beneath absorbing plate. But the heat loss coefficient was shown higher value by installing of air channel. Also the performance of hot water making was shown lower value at same liquid mass flow rate with traditional flat plate solar collector for hot water. So the necessity of performance improvement at lower mass flow rate of each heating medium can be confirmed.