• 한국산학기술학회논문지
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• 제15권1호
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• pp.32-38
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• 2014

본 연구에서는 해수용 열교환기 적용을 위한 열분사 코팅의 침지부식 특성 및 열확산율을 조사하기 위해 실험이 수행되었다. 코팅은 아연과 알루미늄을 열분사 코팅한 뒤 실리콘 및 에폭시 수지를 추가 도포한 총 8개의 시편이며 이를 $70^{\circ}C$ 3.5%w NaCl 수용액에 2주간 침지하여 침지 전후의 부식특성 변화를 관찰하였다. 코팅의 부식특성 변화를 관찰하기 위하여 AC 임피던스 측정, SEM 촬영 등을 진행하였으며 레이저 확산법을 이용하여 침지 전후의 열확산율을 측정 및 비교하였다. 침지실험 결과로부터 실리콘 및 에폭시가 추가된 코팅 시편은 표면에 블리스터가 생성되지 않았으며 이에 실러 추가 코팅에 따른 내부식성 향상효과가 있는 것으로 확인되었다.

• 설비공학논문집
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• 제8권1호
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• pp.1-12
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• 1996

In lots of application to heat exchanger systems, closed two-phase thermosyphons are tilted from a horizontal. If the tilt angle, especially, is less than 30$^{\circ}$, the operational performances of thermosyphon are highly dependent on tilt angle. The present study was conducted to better understand such operational behaviors as mech-anni는 of phase change, and flow patterns inside a tilted thermosyphon. For experiment, an ethanol thermosyphon with a 35% of fill charge rate was designed and manufactured, using a copper tube with a diameter 19mm and a length 1500mm. Through a series of test, the tilt angle was kept constant at each of 4 different values in the range 10~25deg. and the heat supply to the evaporator was stepwisely increased up to 30㎾/$m^2$. When a steady state was established to the thermosyphon for each step of thermal loads, the wall temperature distribution and vapor temperature at the condenser were measured. The wall temperature distributions demonstrated a formation of dry patch in the top end zone of the evaporator, with a values of temperature 20~4$0^{\circ}C$ higher than the wetted surface for a moderate heat flux q≒20㎾/$m^2$. Inspite of the presence of hot dry patch, however, the mean values of boiling heat transfer coefficient at the evaporator wall were still in a good agreement with those predicted by Rohsenow's formula, which was based on nucleate boiling. For the condenser, the wall temperatures were practically uniform, and the measured values of condensation heat transfer coefficient were 1.7 times higher than the predicted values obtained from Nusselt's film condensation theory on tilted plate. Using those two expressions, a correlation was formulated as a function of heat flux and tilt angle, to determine the total thermal resistance of a tilted thermosyphon. The correlation formula showed a good agreement with the experimental data within 20%.

• 청정기술
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• 제13권4호
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• pp.281-286
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• 2007

본 연구에서는 폐열회수형 환기장치(전열교환기)로부터의 휘발성 유기화합물이 측정되었다. KS 냉방 및 난방표준조건하에서 휘발성유기화합물의 초기 배출특성을 연구하기 위하여 폐열회수 환기장치로부터 2종류의 열교환소자(L형과 M형)가 평가되었다. 휘발성 유기화합물은 다양한 풍량 변화와 운전시간 변화에 대하여 측정되었다. 본 연구의 분석방법 및 기기상의 한계로 인하여 농도가 비교적 큰 물질만을 살펴보니 페열회수 환기장치에서는 acetic acid, 2-butanone (MEK), 2-(methylthio)ethylamine, toluene, styrene 및 x-acids (Ion 57) 등의 6종의 휘발성 유기화합물이 배출됨을 확인하였다. 배출된 휘발성 유기화합물의 농도는 운전조건에 대해서는 크게 영향을 받지 않았다. 높은 작동온도 때문에 휘발성 유기화합물의 농도는 난방조건보다는 냉방조건에서 더 크게 나타났다.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2010년도 추계학술대회 초록집
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• pp.64.2-64.2
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• 2010

The objective of this study is to make a comparative study of the operation performance of different type of solar collectors. A flat-plate collector, a single-glazed evacuated collector and a double-glazed evacuated collector are used in this study. These 3 type of collectors are connected in series in the order of a flat-plate collector, a single-glazed evacuated collector and a double-glazed evacuated collector. This experimental facility is a kind of a solar system with a controller, a heat exchanger, a storage tank and a circulation pump. Each collector has a different collection area(flat-plate collector-$6.00m^2$ total area/$5.61m^2$ aperture area, double-glazed evacuated collector-$6.04m^2$ total area/$4.92m^2$ aperture area, single-glazed evacuated collector-$7.65m^2$ total area/$5.61m^2$ aperture area) and its performance characteristic respectively. The experiments have been demonstrated at around $70^{\circ}C$ operating temperature(flat-plate collector inlet temperature). The thermal collecting efficiencies of each collector are obtained under the different insolation and operation condition as a result.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2011년도 춘계학술대회 초록집
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• pp.87.1-87.1
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• 2011

The residential Fuel Cell system has high efficiency of 85% with transferring natural gas to electrical power and heat, directly and it is a friendly environmental new technology in that $CO_2$ emission can reduce 40% compared with conventional power generator and boiler. The residential fuel cell system consists of two main parts which have electrical and hot storage units. The electrical unit contains a fuel processor, a stack, an inverter, a control unit and balance of plant(BOP), and the cogeneration unit has heat exchanger, hot water tank, and auxiliaries. 5kW class fuel process was developed and tested from 2009, it was evaluated for long-term durability and reliability test including with improvement in optimal operation logic. Stack development was crried out through improvement of design and evaluation protocol. Development of system controller was successfully accomplished through strenuous efforts and original control logic was optimized in 5kW class PEMFC system. In addition, we have been focused on development of system process and assembly technology, which bring about excellent improvement of reliability of system. The 5kW class PEMFC system was operated under dynamic conditions for 1,000 hours and it showed a good performance of total efficiency and durability.

• 한국가시화정보학회지
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• 제15권1호
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• pp.11-18
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• 2017

A two-phase flow observed in a heat exchanger or nuclear power generation often has a profound effect on undesirable noise or flow characteristics. Void fraction, which refers to the ratio of gas (or liquid) to the total fluid, affects heat transfer coefficient, vibration and so forth. In other words, void fraction is one of most important parameters in two-phase flow since it contributes to comprehend the characteristics of two-phase flow. We developed a two-phase flow visualization system to measure cross-sectional and volumetric void fractions by using quick closing valves and image processing software. With this system, we could observe the plug, slug, and stratified flow patterns of two-phase flow and measure a myriad of void fractions. As a consequence of the experiment, we found that the estimated void fractions were largely coincident with the predictive values by Chisholm model.

• 한국태양에너지학회 논문집
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• 제38권5호
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• pp.37-47
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• 2018

The heating performance of a solar thermal seasonal storage system applied to a glass greenhouse was analyzed numerically. For this study, the gardening 16th zucchini greenhouse of Jeollanam-do agricultural research & extension services was selected. And, the heating load of the glass greenhouse selected was 576 GJ. BTES (Borehole Thermal Energy Storage) was considered as a seasonal storage, which is relatively economical. The TRNSYS was used to predict and analyze the dynamic performance of the solar thermal system. Numerical simulation was performed by modeling the solar thermal seasonal storage system consisting of flat plate solar collector, BTES system, short-term storage tank, boiler, heat exchanger, pump, controller. As a result of the analysis, the energy of 928 GJ from the flat plate solar collector was stored into BTES system and 393 GJ of energy from BTES system was extracted during heating period, so that it was confirmed that the thermal efficiency of BTES system was 42% in 5th year. Also since the heat supplied from the auxiliary boiler was 87 GJ in 5th year, the total annual heating demand was confirmed to be mostly satisfied by the proposed system.

• 생물환경조절학회지
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• 제12권3호
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• pp.107-113
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• 2003

본 연구에서는 온실의 온풍식 난방시스템 연통에 장착할 수 있는 폐열 회수기의 성능 개선을 목적으로 기 설계된 세 가지 열교환 장치와 기존의 장치에서 열교환 면적과 파이프의 두께 및 공기흐름 방향을 개량한 새 열교환 장치에 대해 열회수 성능을 실험적으로 비교 분석하였다. 그 결과 기존의 열 교환장치인 A형, B형 및 C형의 열회수 성능은 동일 송풍전입에서 각각 42.2%, 40.6% 및 54.4% 정도였으나 , 새로 개량된 D형은 69.2%로써 가장 현저히 높게 나타났다. 그러나 열회수용 공기의 흐름방향 변화에 따른 열회수 성능 개선효과 (A형 대비 B형)는 없는 것으로 나타나 적정 송풍기 용량이라면 직선형이 공기의 흐름방향 180${\circ}C$ 굴절시키는 헤어핀형보다 효과적인 것으로 판단된다. 결국 열회수 성능은 열회수 시스템의 열교환 면적과 열교환 파이프의 두께 및 풍속에 크게 좌우되는 것으로 나타났다. 따라서, 열교환 파이프의 내구성 등 을 고려하여 기능한 한 범위 내에서 열 교환면적을 증대시키거나 열교환 파이프의 두께를 앓게 하고 풍속을 증대시키는 것이 열회수 성능 개선효과와 직결됨을 알 수 있었다. 그리고 송풍기 용량이 필요이상으로 큰 경우, 소비전력이 많게 되는 등의 문제가 있기 때문에 적정용량 및 제품의 안정성을 고려하여 선택해야 할 것으로 판단되었다.

• Membrane and Water Treatment
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• 제1권1호
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• pp.1-12
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• 2010

Membrane distillation process was used for purification of pre-treated natural water (tap water). The rejection of inorganic and organic compounds in this process was investigated. The obtained rejection of inorganic solutes was closed to 100%, but the volatile organic compounds (VOCs) diffused through the membrane together with water vapour. The content of trihalomethanes (THMs) in the obtained distillate was two-three fold higher than that in the feed, therefore, the rejection of the total organic compounds present in the tap water was reduced to a level of 98%. The intensive membranes scaling was observed during the water separation. The morphology and composition of the fouling layer was studied using scanning electron microscopy coupled with energy dispersion spectrometry. The influence of thermal water pre-treatment performed in a heat exchanger followed by filtration on the MD process effectiveness was evaluated. This procedure caused that significantly smaller amounts of $CaCO_3$ crystallites were deposited on the membrane surface, and a high permeate flux was maintained over a period of 160 h.

• 대한기계학회논문집B
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• 제28권5호
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• pp.594-603
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• 2004

Several desiccant cooling systems have been developed in terms of cost and performance. In this study a fin-tube exchanger has been used for liquid desiccant dehumidification system. This dehumidifier has been designed to study the absorption characteristic of the aqueous triethylene glycol(TEG) solution which has the flow range from 20 to 50 LPM. The dehumidifier performance characteristics of working factor variables such as inlet solution flow rate, air flow rate, solution concentration and brine temperature have been analyzed. This dehumidifier has the ability to provide running while saving the latent heat load of total energy. The result of this experiment can provide useful data for hybrid air conditioning system.