• Design & Manufacturing
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• 제14권4호
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• pp.17-24
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• 2020

Products for heating indoors in low temperature and dry winter are largely divided into products using fossil fuels and products using electricity. The fossil fuels can warm the entire space by convection, but there is a high risk of fire and the frequent ventilation due to the increase in carbon monoxide and carbon dioxide. Heaters using electricity are mainly used because they are convenient to use and are cheap. However, these products can not efficiently warm the air because they use radiation energy. In other words, only the front part exposed to the heater is warm, and the rear part has no heating effect at all. Also, because it emits a large amount of light, fatigue of the eyes is very high. Another problem is that when using electric heaters, the room tends to be dry by high heat. Indoor humidity maintenance is a very important factor in the prevention and treatment of respiratory diseases. Especially, it is essential for health care for infants, bronchial organs and people with weak respiratory because humidity is low in winter. In this study, we conducted a study to develop a product that can improve heating efficiency while maintaining proper indoor humidity by combining heat energy and moisture particles. The concept of humidification and heating at the same time, moisture particles generated in the humidifier pass through the heater, include thermal energy, and the moisture particles with thermal energy are diffused into the space by forced convection, thereby warming the entire space. In addition, the heating time is shortened as the feeling temperature is increased with the high relative humidity, and this has the effect that the heating cost in winter is reduced.

• Journal of the Korean Wood Science and Technology
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• 제17권1호
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• pp.22-54
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• 1989

Seasonal semi-greenhouse type solar-drying of 2.5cm-and 5.0cm-thick lumber of Quercus aliena Blume and Quercus variailis Blume was carried out to investigate the possibility of solar-drying of wood and to decide the active solar-drying period in Korea. In the active solar-drying period obtained solar-dehumidification, semi-greenhouse type solar-, air- and kiln-drying of 2.5cm -thick lumber of oaks were carried out to analyze drying-rates. -defects, and -yield in each drying-method and to calculate daily total absorbed solar-radiation the solar dryers. The energy balance equations were set up, considering all the energy requirements, to analyze the heat efficiencies of semi-greenhouse type solar and solar-dehumidification-dryer. In a seasonal drying the drying rate of semi-greenhouse type solar-dryer was highest in summer, and greater in fall, spring, and winter in order. Solar-drying time was 45% in summer to 50% in winter of the air-drying rime, and more serious drying-defects occurred in air-drying than in solar-drying. In the active solar-drying period. April, May, and June, the average drying rate in solar-dehumidification-drying was 1.0%/day and greater than 0.8%/day in semi-greenhouse type solar-drying. In solar-dehumidification-drying the time required to dry lumber to 10% moisture content was less than 60 days, and solar-dehumidification-drying showed the highest drying-yield, 65.01%, than the other drying methods. The daily total absorbed solar radiations were 8.51MJ on the roof collector and 6.22 MJ on the south wall collector. In the energy blance 69.48% of total energy input was lost by heat conduction through walls, roof. and floor 11.68% by heat leakage, 0.33% by heating the internal structures of the solar-dryer and 5.38% by air-venting. Therefore the heat efficiency of semi-greenhouse type solar-dryer 13.13%, was lower than that of solar-dehumidification-dryer, 14.04%. Solar-drying of lumber in Korea showed the possibility to reduce the air-drying-time in every season and the efficiency of solar-dehumidification drying was higher than that of semi-greenhouse type solar-drying.

• 한국태양에너지학회 논문집
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• 제36권3호
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• pp.53-61
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• 2016

Solar assisted heat pump system uses solar thermal energy as a heat source of evaporator of heat pump. So, COP can be enhanced as well as collector efficiency. For improving performance of this system, some research about hybrid solar collector that has fin-and-tube heat exchanger has been conducted. This collector can get a thermal energy from ambient air for liquid heating, so heated liquid can be used as a heat source of evaporator in heat pump even the solar radiation is not enough. In this study, numerical analysis was conducted for confirming heat gain of liquid according to fin height and pitch of fin-and-tube heat exchanger in collector. As a result, higher heat gain was obtained on lower fin height and narrow fin pitch, but the pressure drop also increased with increment of heat gain. Thus the JF factor considering both heat transfer enhancement and pressure drop was investigated and the maximum value was shown when the fin height and pitch were 40mm and 45mm. So it is considered that this installation condition has a highest heat transfer improvement when comparing with pressure drop. However heat gain of liquid at this condition was less than the other installation conditions of fin pitch on same height. Then, after establishing a proper minimum heat gain of liquid, actual production and experiment of collector will be conducted with fin height and pitch showing maximum JF factor and satisfying selected minimum heat gain of liquid on the basis of results of this study.

• 한국태양에너지학회 논문집
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• 제31권4호
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• pp.57-65
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• 2011

This study proposes a Passive Solar Chamber System (PSCS) as a passive method for reduction of building energy consumption. Through numerical analysis, the study quantitatively analyzes system performance and aims to provide foundational data for system design. For this purpose, the study configures different system operation modes seasonally and also computes thermal and ventilation performance of the system in accordance with design factors(solar radiation, air channel height and distance). System and ventilation efficiency increases along with increase in solar radiation and air channel distance; however, as the air channel height increases, the efficiencies showed a tendency to decrease. Upon installation of PSCS, an average of $98.23W/m^2$ of heat flux was introduced in the daytime for the month of January in comparison to walls with no PSCS installed. For the month of August, natural ventilation of $56.68m^3/h$ was shown to be supplied to the room.

• 한국화재소방학회논문지
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• 제33권3호
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• pp.29-36
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• 2019

다층·다성분 난연성 케이블의 화재시뮬레이션에서 요구되는 연소물성이 콘 칼로리미터를 통해 측정되었다. 난연성 케이블의 주요 재질에 따른 CO 및 Soot yields 그리고 연소열이 검토되었다. 케이블의 난연성능이 우수한 TFR-8(고난연성 PCV 및 XLPE 첨가), TFR-CVV-SB(고난연성 PCV 및 일반 PVC로 구성) 및 VCTF가 각각 대상으로 고려되었다. 주요 결과로서, 난연성케이블인 TFR-8과 TFR-CVV-SB는 입사 복사열유속이 25 kW/㎡에서 50 kW/㎡으로 증가됨에 따라 CO yield(y_CO) 는 각각 23% 와 16% 증가한다. 반면에 VCTF의 CO yield는 복사 열유속의 변화에 큰 영향을 받지 않는다. 마지막으로 Soot yield 및 연소열은 시스의 재질(난연성능)이 강화될수록 복사 열유속에 의한 차이가 증가됨이 확인되었다. 따라서 다양한 열유속이 공존하는 화재환경에서 난연성 케이블의 연소물성의 적용에는 상당한 주의가 요구된다.

• 대한금속재료학회지
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• 제56권11호
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• pp.805-812
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• 2018

High pressure die casting is one of the precision casting methods. It is highly productivity and suitable for manufacturing components with complex shapes and accurate dimensions. Recently, there has been increasing demand for efficient heat dissipation components, to control the heat generated by devices, which directly affects the efficiency and life of the product. Die cast aluminum alloys with high thermal conductivity are especially needed for this application. In this study, the influence of elements added to the die cast aluminum alloy on its thermal conductivity was evaluated. The results showed that Mn remarkably deteriorated the thermal conductivity of the aluminum alloy. When Cu content was increased, the tensile strength of cast aluminum alloy increased, showing 1 wt% of Cu ensured the minimum mechanical properties of the cast aluminum. As Si content increased, the flow length of the alloy proportionally increased. The flow length of aluminum alloy containing 2 wt% Si was about 85% of that of the ALDC12 alloy. A heat dissipation component was successfully fabricated using an optimized composition of Al-1 wt%Cu-0.6 wt%Fe-2 wt%Si die casting alloy without surface cracks, which were turned out as intergranular cracking originated from the solidification contraction of the alloy with Si composition lower than 2 wt%.

• 대한기계학회논문집B
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• 제36권12호
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• pp.1177-1183
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• 2012

본 연구의 목적은 형상계수와 태양추적장치를 이용하여 헬리오스타트에서 흡수기로 복사열전달이 최대화 될 수 있는 시스템을 개발하는 것이다. 헬리오스타트에서 타워 상단에 위치한 흡수기로의 열전달은 대부분 복사에 의해 일어나기 때문에, 복사 열전달에서 사용되는 형상계수를 헬리오스타트 제어에 이용하였다. 태양 추적 및 태양 위치 계산은 CdS 센서와 시뮬링크 프로그램을 이용하였다. 시뮬링크 프로그램을 이용하여 실시간으로 헬리오스타트, 흡수기, 태양 사이의 형상계수가 최대화되는 알고리즘을 적용함으로서, 헬리오스타트에서 흡수기로의 복사 열전달이 최대화 될 수 있도록 하였다. 또한 다양한 조건에 따른 헬리오스타트 제어에 필요한 각을 시뮬레이션 함으로서 각 조건에 필요한 각을 도출할 수 있었다.

• Journal of Biosystems Engineering
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• 제43권1호
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• pp.21-29
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• 2018

Purpose: The objective of this study is to evaluate the performance of the conical solar concentrator (CSC) system, whose design is focused on increasing its collecting efficiency by determining the optimal conical angle through a theoretical study. Methods: The design and thermal performance analysis of a solar concentrator system based on a $45^{\circ}$ conical concentrator were conducted utilizing different mass flow rates. For an accurate comparison of these flow rates, three equivalent systems were tested under the same operating conditions, such as the incident direct solar radiation, and ambient and inlet temperatures. In order to minimize heat loss, the optimal double tube absorber length was selected by considering the law of reflection. A series of experiments utilizing water as operating fluid and two-axis solar tracking systems were performed under a clear or cloudless sky. Results: The analysis results of the CSC system according to varying mass flow rates showed that the collecting efficiency tended to increase as the flow rate increased. However, the collecting efficiency decreased as the flow rate increased beyond the optimal value. In order to optimize the collecting efficiency, the conical angle, which is a design factor of CSC, was selected to be $45^{\circ}$ because its use theoretically yielded a low heat loss. The collecting efficiency was observed to be lowest at 0.03 kg/s and highest at 0.06 kg/s. All efficiencies were reduced over time because of variations in ambient and inlet temperatures throughout the day. The maximum efficiency calculated at an optimum flow rate of 0.06 kg/s was 85%, which is higher than those of the other flow rates. Conclusions: It was reasonable to set the conical angle and mass flow rate to achieve the maximum CSC system efficiency in this study at $45^{\circ}$ and 0.06 kg/s, respectively.

• 한국태양에너지학회 논문집
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• 제29권4호
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• pp.22-27
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• 2009

This study focus on verification of the thermal efficiency of volumetric receiver with 5k Wth Dish-type solar thermal system. Spiral flow path shaped on receiver and working fluid(steam) flow along with this flow path. Porous material for radiation-thermal conversion used in former researches are substituted with the stainless steel wall installed along the spiral flow path. Numerical analysis for the flow path and temperature distributions are carried out. Numerical results are compared with experimental data. Using the numerical model, the heat transfer characteristics of spiral type receiver for dish-type solar thermal systems are known and the thermal performance of the receiver can be estimated.

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2007년도 동계학술발표대회 논문집
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• pp.564-569
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• 2007

This study describes thermal performance of solar cooling and hot water for demonstration system with ETSC(Evacuated tubular solar collector) installed at Seo-gu art center of Kwangju. For demonstration study, a reading room with about 350㎡ was heated and cooled with the solar system. The system was consisted of ETSCs, storage tank, hot water supply tank, subsidiary boiler, subsidiary tank, absorption chiller, chiller storage tank, and cooling tower. The results of the experimental study indicated that the total solar energy gain as daily performance on a sunny day (August 25, 2007) with total daily radiation of $606\;W/m^2$ was 671 kWh, the collecting efficiency of 55%. In the case of supplies to heat source more than $83^{\circ}C$, cooling time operated by solar was driven 8.8 hours, cooling energy generated by solar system was 179 kWh and the solar cooling fraction was 79.2%, and hot water supplied with surplus heat source by the solar system was 201 kWh.