• Journal of Bio-Environment Control
• /
• v.12 no.3
• /
• pp.107-113
• /
• 2003

This study was carried out to improve the performance of pre-developed heat recovery devices attached to exhaust-gas flue connected to combustion chamber of greenhouse heating system. Four different units were compared in the aspect of heat recovery performance; A-, B-, and C-types are exactly the same with the old ones reported in previous studies. D-type newly developed in this experiment is mainly different with the old ones in its heat exchange area and tube thickness. But airflow direction(U-turn) and pipe arrangement are similar with previous three types. The results are summarized as follows; 1. System performances in the aspect of heat recovery efficiency were estimated as 42.2% for A-type, 40.6% for B-type, 54.4% for C-type, and 69.2% for D-type. 2. There was not significant improvement of heat recovering efficiency between two different airflow directions inside the heat exchange system. But considering current technical conditions, straight air flow pattern has more advantage than hair-pin How pattern (U-turn f1ow). 3. The main factors influencing on heat recovery efficiency were presumably verified to be the total area of heat exchange surface, the thickness of ail-flow pipes, and the convective heat transfer coefficient influenced by airflow velocity under the conditions of allowable pipe durability and safety. 4. Desirable blower capacity for each type of heat recovery units were significantly different to each other. Therefore, the optimum airflow capacity should be determined by considering in economic aspect of electricity required together with the optimum heat recovery performance of given heat recovery systems.

• Proceedings of the Korean Society for Bio-Environment Control Conference
• /
• 2003.04a
• /
• pp.152-156
• /
• 2003

우리나라 시설원예 면적은 최근 정체되는 기미를 보이긴 하지만, 아직도 시설원예 면적이 50,000ha 이상에 달하고 난방면적도 점점 증가되어 전체 면적 중에 난방면적이 차지하는 비율은 현재 12,300ha 정도인 24%이다. 난방기의 보급기의 보급도 매년 증가하여 '00년말 현재 127,560대 정도이다. 최근 국내 버섯 재배면적의 42% 차지하는 느타리(큰느타리 포함)버섯 재배사도 연중재배를 위하여 난방을 실시하는 농가가 점점 늘고 있고, 특히 새송이(큰느타리) 버섯 재배사의 대부분은 간이형 온실에서 냉난방 설비를 갖추어 연중재배를 하고 있다. (중략)

• Proceedings of the Korean Society for Bio-Environment Control Conference
• /
• 2001.04b
• /
• pp.100-102
• /
• 2001

본 연구에서는 온실의 난방에 사용되는 열풍식 난방기 등의 배기 연통에 부착하여 배출되는 가스로부터 열을 회수할 수 있는 장치를 개발함에 있어서 연통과 열회수 장치간의 열 교환 성능을 3가지 상이하게 설계된 열 교환 장치(Fig. 1 참조)에 대하여 실험적으로 비교 분석하였다. Fig. 1-(a)는 열 교회수기 개발을 위해 기존에 사용한 장치로서 회수용 공기의 흐름방향이 배기 연통과 직각을 이룬 형식이며, Fig. 1-(b) 및 (c)는 열 회수 성능 개선을 위해 새로 설계된 형식으로서 각각 열 교환 파이프의 배치형식이 상이하나 회수용 공기의 흐름방향이 180도로 굴곡되는 U-자형 흐름이 이루어지도록 하였다. 실험에 사용된 공기 순환 펜의 용량은 AB-형의 경우에는 최대 25㎥/min이고, C-형 및 D-형의 경우는 공히 최대 42㎥/min으로서 송풍전압 조절장치를 이용하여 풍량을 연속적으로 조절할 수 있도록 하였다. U-자형 흐름형식인 C-형 및 D-형의 경우 흐름 방향의 굴곡으로 인한 마찰저항이 있을 것으로 예상은 했으나 당초 예상했던 것에 비해 마찰 저항이 지나치게 큰 것으로 밝혀졌다. 비록 설계된 열교환 튜브의 배열형식별 열 교환기의 외부 모양이 달라 회수기의 표면을 통한 대류 열 교환이 다소 차이를 보일 것으로 예상되지만 본 연구에서는 열 회수장치에 내장된 열 교환 튜브부분만을 통한 열 회수율을 중심으로 형식간의 성능을 비교하였다. 실험을 통하여 측정된 자료중 대표적인 예는 Fig-2와 같으며, 측정자료를 기준으로 분석된 열회수 성능에 대한 설계형식별 비교 결과는 Table-1과 같으며, 분석된 결과를 요약하면 다음과 같다: 1. AB-형 열회수시스템의 경우, 초기 투자비용과 현재의 농용 전력요금 하에서 에너지 절감규모를 비교하면, 대체로 1년을 전후하여 투자에 대한 보상이 충분히 가능할 것으로 판단된다. 2. C-형 및 D-형 열회수시스템의 경우, 열 회수용 공기의 흐름방향이 동일 공간내에서 180도 굴절됨으로서 저항이 크게 발생되어 송풍 펜의 전압 증가에 따른 유속증가가 미미하였으며, 굴절형의 열교환장치는 비록 열교환면적은 직선형과 유사하더라도 송풍 펜의 공기저항이 커져서 결국 열 회수성능이 기대했던 것만큼 크게 개선되지는 못했다. 3. 송풍펜의 용량은 AB-형에 사용된 용량인 25㎥/min 전후가 적절할 것으로 판단되며, 적정 송풍 펜용량 하에서 열 회수성능은 굴절형이 직선형보다 효과적인 것으로 나타났다. 다만, 곡선형은 물론 직선형에서도 열교환 튜브의 배치밀도, 튜브 길이 및 두께 등의 변화에 따른 최적화 연구가 수반되어야 할 것으로 판단된다.

• Journal of Bio-Environment Control
• /
• v.11 no.3
• /
• pp.101-107
• /
• 2002

This study was carried out to improve the performance of heat recovery device attached to exhaust gas flue connected to combustion chamber of greenhouse heating system. Three different units were prepared far the comparison of heat recovery performance; A-type is exactly the same with the typical one fabricated for previous study of analyzing heat recovery performance in greenhouse heating system, other two types (B-type and C-type) modified from the control unit are different in the aspects of airflow direction (U-turn airflow) and pipe arrangement. The results are summarized as follows ; 1. In the case of Type-A, when considering the initial cost and current electricity fee required for system operation, it was expected that one or two years at most would be enough to return the whole cost invested. 2. Type-B and Type-C, basically different with Type-A in the aspect of airflow pattern, are not sensitive to the change of blower capacity with higher than 25m$^3$.min$^{-1}$ . Therefore, heat recovery performance was not improved so significantly with the increment of blower capacity. This was assumed to be that air flow resistance in high air capacity reduced the heat exchange rate as well. Never the less, compared with control unit, resultant heat recovery rate of Type-B and Type-C was improved by about 5％ and 13％, respectively 3. Desirable blower capacity of these heat recovery units experimented were expected to be about 25m$^3$.min$^{-1}$ , and at the proper blower capacity, U-turn airflow units showed better heat recovery performance than control unit. But, without regard to the type of heat recovery unit, it was recommended that comprehensive consideration of system's physical factors such as pipe arrangement density, unit pipe length and pipe thickness, etc., was required for the optimization of heat recovery system in the aspects of not only energy conservation but economic system design.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.34 no.3
• /
• pp.291-298
• /
• 2010

A conventional EGR cooler, which is used in an EGR system of an automobile diesel engine, has a low heat-exchange efficiency. To maximize the heat transfer between the exhaust gas and coolant, dimples are formed on the surface of heat exchange tubes. When designing the dimpled EGR cooler, the net heat transfer areas in the conventional and dimpled tube-type EGR coolers are compared. Structural integrity evaluations are also performed by combining finite element analysis with a homogenization method. Subsequently, the process of manufacturing the dimpled tube, i.e., the formation of dimples, edge bending, center v-notch bending, compression, and plasma welding, is established and carried out. Thus, the dimpled EGR cooler is developed, and its performance is verified.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.16 no.11
• /
• pp.2196-2202
• /
• 1992

The optimum size combination of heat exchangers in a Joule-Thomson(J-T) circuit for small cryogenic systems has been sought analytically, when the circuit is combined with a two-stage Gifford-McMahon(GM) cooler. Full thermodynamic cycle analysis was carried out to predict the performance of the combined refrigeration system. Relevant convective heat transfer coefficients, the computerized properties of helium, and the refrigeration capacity curve of a typical GM cooler have been used in the analysis. The result showed that, by changing the configuration(heat exchanger area ratio) of the system, the performance of the commonly-used GM/J-T refrigerators could be optimized. For the maximum refrigeration performance, the optimum mass flow rate of the refrigerant and the relative size between the heat exchangers have been obtained, when the cooling load was 0.1W at 3.995K with the total heat exchanger area being given.

• Journal of the Korean Geotechnical Society
• /
• v.31 no.5
• /
• pp.23-33
• /
• 2015

In the present study, a ground heat exchanger was installed for each heat source in the system at the site to evaluate ground heat conductivity, constructability, and economic feasibility; the factors considered in the study included ground heat, groundwater, fillers (such as bentonite and pea pebbles) and the shape of the heat exchange pipe (e.g., U and D-U). The aim was to determine the ground heat exchanger appropriate for the geothermal system in the 3rd-phase construction of Incheon International Airport. A comparative cost analysis of the initial costs based on the above information showed that although the initial costs of the regular vertical closed loop-II and modified vertical closed loop were lower than those of the regular vertical closed loop-I, they could not be expected to deliver high economic efficiency from the viewpoint of constructability (filler injection, heat exchange pipe insertion). The initial costs proved to be higher in the case of Geohil.

• The Magazine of the Society of Air-Conditioning and Refrigerating Engineers of Korea
• /
• v.28 no.5
• /
• pp.389-395
• /
• 1999

냉동공조설비, 발전설비, 화학플랜트설비 등에 사용되는 응축기는 주로 증기가 관의 외부에서 응축을 하고 냉각수가 관 내부로 흐르는 쉘-튜브(shell and tube)형 태를 취하고 있다. 초기투자비용 및 운전비용을 줄이기 위해서는 응축기의 열교환 성능을 향상시키는 일이 필수적이며 이를 위해 코팅 표면(coated surfaces), 거친 표면(rough surfaces), 코일 튜브(coiled tubes), 선회 흐름장치(swirl flow), 전열면적을 넓힌 낮은 핀관과 3차원 형상을 갖는 열전달 촉진관의 사용이 제시되고 있다.

• The Journal of Engineering Geology
• /
• v.9 no.2
• /
• pp.89-100
• /
• 1999

This study was carried out to assess the physicochemical properties of domestic bentonites and zeolites from Tertiary Formation as the candidate material for a engineered barrier of a radioactive waste repository. Natural bentonite and zeolite samples were collected from nine bentonite mines and six zeolite mines in Yeonil-Gampo area. The commercial products of bentonite and zeolite were obtained from local companies. The collected samples were investigated to study the following physicochemical properties: X-ray diffraction patterns, swelling, cation exchange capacity(CEC), specific surface area, montmorillonite content, pH, organic carbon content, thermal property, microstruciure and chemical composition. Based on the physicochemical properties of bentonite and zeolite, the bentonites from U-41 and G-46 mines and the zeolites from Daedo and Y-1 mines are regarded as the most desirable candidate materials.

• Transactions of the Korean hydrogen and new energy society
• /
• v.35 no.3
• /
• pp.290-299
• /
• 2024

In this study, a theoretical study was conducted on the pre-cooling temperature of hydrogen gas and the heat exchanger area in a small-scale liquefied hydrogen system. The small-scale liquefaction system was built and liquid hydrogen production experiments were performed. In this process, the temperature of precooled hydrogen gas was measure to be about 120 K, and then the possibility of a cause was analyzed through pressure analysis of hydrogen gas and container, and analysis of the amount of liquid hydrogen produced. It was found that some reasonable results were obtained from the theoretical approaches. Based on this theoretical approach, we aim to improve the production of liquid hydrogen by optimizing the heat exchange area according to flow rate.