• 태양에너지
• /
• 제13권2_3호
• /
• pp.120-132
• /
• 1993

본 연구의 목적은 터어빈 회전차를 모델로한 복합회전형 히이트파이프의 전열특성을 실험과 유한요소의 해석법에 의하여 연구한 것이다. 입열량과 회전수에 따른 Nu, Re, Pr 그리고 무차원 응축액막두께가 변수로 사용되었다. 해석과 실험치는 거의 유사한 경향으로 일치하였으며, 연구결과는 복합히이트파이프 성능예측을 하는데 도움을 주었다. 복합회전형 히이트파이프에서의 열저항은 응축액막두께가 감소함에 따라 응축부의 열전달은 급격히 증가하였고, 응축액막두께는 복합회전형 히이트파이프의 전열 특성에 가장 큰 영향을 주었다. 주어진 Pr에서 Re가 변화함에 따라 무차원 응축액막두께가 일정한값으로 나타났고,무차원 응축액막두께는 회전수의 역수의 제곱근에 비례하였다. 본 연구의 해석적 방법에 의해서 Nu=A$({\delta}({\omega}/v)^{-1/2}Re^B)$라는 식을 구했고, 이때 A=0.963, B=0.5025의 값을 얻었다.

• 한국태양에너지학회 논문집
• /
• 제29권5호
• /
• pp.35-44
• /
• 2009

In this study, boiling heat transfer coefficients(HTCs) and critical heat flux(CHF) are measured on a smooth square flat copper heater in a pool of pure water with and without carbon nano tubes(CNTs) dispersed at $60^{\circ}C$. Tested aqueous nanofluids are prepared using multi-walled CNTs whose volume concentrations are 0.0001, 0.001, 0.01, and 0.05%. For dispersion of CNTs, polyvinyl pyrrolidone(PVP) is used in distilled water. Pool boiling HTCs are taken from $10kW/m^2$ to critical heat flux for all nanofluids. Test results show that the pool boiling HTCs of the nanofluids are lower than those of pure water in entire nucleate boiling regime. On the other hand, critical heat flux is enhanced greatly showing up to 200% increase at volume concentration of 0.001% CNTs as compared to that of pure water. This is related to the change of surface characteristics by the deposition of CNTs. This deposition makes a thin CNT layer on the surface and the active nucleation sites of heat transfer surface are decreased due to this layer. The thin layer acts as the thermal resistance and also decreases the bubble generation rate resulting in a decrease in pool boiling HTCs. The same layer, however, maintains the nucleate boiling even at very high heat fluxes and reduces the formation of large vapor canopy at near CHF resulting in a significant increase in CHF.

• 에너지공학
• /
• 제2권2호
• /
• pp.179-186
• /
• 1993

평판형 태양열 집열기에 적용되는 열파이프는 증발부에 상대적인 낮은 열유속으로 길이가 길고 가느다란 형상을 갖는다. 이러한 열파이프는 증발부의 하단부에서 액체 Pool이 형성하는 경향이 있다. 그리고 이 Pool에서 과열, 급속한 기포의 생성, 기포의 폭발적인 성장과정과 Flooding 등의 복잡한 증발과 유체 역학적 현상이 발생한다. 본 논문에서는 4개의 열파이프와 3개의 열사이폰을 이용하여 주 설계변수인 작동유체의 충전량과 위크의 설치 영역을 조절함으로써 이러한 문제를 해결하도록 하였다. 이에 대한 결과들은 다음과 같이 요약할 수 있다$^{1)}$ . 열파이프의 유효 열전도도는 단열부와 응축부에 위크를 제거함으로써 상당히 개선할 수 있었다$^{2)}$ .액체의 충전량은 위크를 적실수 있는 양보다 약 40%정도 증가시켜야 한다$_{3)}$ . 증발부에서 위크는 핵비 등의 단속적 발생에 의한 불안정한 작동과 포기 시동과정에서 응답시간을 줄이는데 유용한 효과를 갖는다.

• 한국신재생에너지학회:학술대회논문집
• /
• 한국신재생에너지학회 2007년도 추계학술대회 논문집
• /
• pp.281-284
• /
• 2007

Recently, we have developed p-i-n a-Si:H single junction thin film solar cells with RF (13.56MHz) plasma enhanced chemical vapor deposition (PECVD) system, and also successfully fabricated the mini modules ($>300cm^2$), using the laser patterning technique to form an integrated series connection. The efficiency of a mini module was 7.4% ($Area=305cm^2$, Isc=0.25A, Voc=14.74V, FF=62%). To fabricate large area modules, it is important to optimise the integrated series connection, without damaging the cell. We have newly installed the laser patterning equipment that consists of two different lasers, $SHG-YVO_4$ (${\lambda}=0.532{\mu}m$) and YAG (${\lambda}=1.064{\mu}m$). The mini-modules are formed through several scribed lines such as pattern-l (front TCO), pattern-2 (PV layers) and pattern-3 (BR/back contact). However, in the case of pattern-3, a high-energy part of laser shot damaged the textured surface of the front TCO, so that the resistance between the each cells decreases due to an incomplete isolation. In this study, the re-deposition of SnOx from the front TCO, Zn (BR layer) and Al (back contact) on the sidewalls of pattern-3 scribed lines was observed. Moreover, re-crystallization of a-Si:H layers due to thermal damage by laser patterning was evaluated. These cause an increase of a leakage current, result in a low efficiency of module. To optimize a-Si:H single junction thin film modules, a laser beam profile was changed, and its effect on isolation of scribed lines is discussed in this paper.

• Journal of Biosystems Engineering
• /
• 제36권3호
• /
• pp.211-216
• /
• 2011

According to the result of the first report and the second report of this study, it was expected that soil heating in a protected cultivation in winter season would affect the initial growth and development of fruit. Based on the result of previous study, we compared height, leaf number, leaf area, fruit weight, crop growth rate (CGR), features and quantity of cucumber for 3 months after planting between the soil heating group and the non-heating group. The result were summarized as follows: The height, leaf number, leaf area and fruit weight of cucumber in the soil heating group were 12.5%, 14.6%, 21.4% and 22.8% higher, respectively, compared to those of cucumber in the non-heating group. Although both the soil heating group and the non-heating group similarly showed an increasing pattern in CGR after transplanting, the soil heating group showed the increased CGR by 12.1% compared to that of the non-heating group. The quantity of cucumber in the soil heating group was about 26% higher than that of the non-heating group. It is assumed that the activation of initial growth and development of fruit in the heating group resulted in the increase of quantity.

• 태양에너지
• /
• 제12권3호
• /
• pp.37-46
• /
• 1992

상변화 물질로 Paraffin wax를 사용한 잠열축열 시스템의 축열성능을 실험을 통하여 조사하였다. 가열유체로는 ethylene glycol을 사용하였고 왁스로의 전열을 위해 열싸이폰을 사용하였다. 왁스의 유효열전도율을 높이기 위해 여러장의 구리망을 왁스에 넣었고 실험은 체적비 2%, 3%, 4%에 대해 유량을 변화시키며 수행하였으며 몇가지 주요결과는 다음과 같다. (1) 구리망은 열전도를 촉진시켜 왁스의 온도를 균일화 하는 역할을 한다. (2) 구리망수의 증가는 열전도를 향상시키는 반면 응해된 왁스의 대류작용을 억제한다. (3) 축열시스템에 최적인 구리망의 수가 존재하며 이 연구에서는 체적비로 나타낼 때 $3{\sim}4%$인 것으로 나타났다.

• 태양에너지
• /
• 제15권3호
• /
• pp.15-27
• /
• 1995

본 연구는 상변화물질로써 무기염수화물계 물질인 피로인산나트륨($Na_4P_2O_7{\cdot}10H_2O$)이 채워져 있는 직육면체형 잠열축열조 내에서 축열과정시 일어나는 상변화물질의 온도특성, 열전달현상, 축열량 등을 실험적으로 측정하고 그 결과들을 수치해석결과들과 비교 검토한 것이다. 축열과정시 상변화물질인 피로인산나트륨은 용융상태가 액체상태가 아닌 gel상태이므로 액체상태에서의 주된 열전달현상으로 나타나는 자연대류 유동현상이 일어나지 않아 전도에 의한 열전달현상이 지배적인 것으로 나타났다. 무기염수화물계 상변화물질은 공극율(공기 함유율)이 작을수록 열용량이 커지므로 축열과정시 공극율이 큰 경우보다 온도가 서서히 상승되었으며, 실험으로 측정된 온도값과 수치해석적인 방법으로 계산된 온도값은 최대 15%의 차이가 났다.

• 태양에너지
• /
• 제15권3호
• /
• pp.29-38
• /
• 1995

본 연구는 화학열펌프 개발을 목적으로 비교적 고온영역에서 화학축열에 응용 가능 할 것으로 판단되는 무기수화물계 $Ca(OH)_2/CaO$ 가역 반응싸이클을 이용한 수화 탈수반응에 따른 충진층내 열이동에 대하여 실험적 검토를 행하였다. 그 결과 본 실험에서 얻은 열교환특성은 $Ca(OH)_2$ 열분해 탈수반응시 반응기 내의 시료층 상단부가 하단부에 비해 탈수반응이 느리게 진행되었으며 이러한 현상은 탈수반응이 하부에서 상부로 진행됨을 알 수 있었다. 또, 반응기내 반경방향에서의 $Ca(OH)_2$ 열분해 탈수반응에 따른 온도변화는 시료 중심부에서 상 하단부로 나타났으며 이는 열전도도에 의한 온도 강하로 중심부의 축열온도가 높음을 알 수 있었다.

• 한국태양에너지학회 논문집
• /
• 제31권5호
• /
• pp.77-84
• /
• 2011

Korea and some other countries located in the northern hemisphere employ the air conditioner for the space cooling in the hot summer season and also some kinds of heaters for the space heating in the cold winter season. Especially in Korea, a great number of air conditioners of about 12,700,000 sets have been used these days. However, they are used for a short operation period of only 58 days a year, which results in the material and economic losses. To solve this problem and employ this system for the emergency shelter, a new conversion unit which could convert the existing air conditioner to a heat pump system for simultaneous heating and cooling was developed in this study, and the thermal performance was tested. The results indicated that the indoor air could be heated from $27^{\circ}C$ to $39^{\circ}C$ by the air conditioner converted to a heat pump system with the ambient temperature variation of $-10^{\circ}C{\sim}10^{\circ}C$, and cooled from $20^{\circ}C$ to $15^{\circ}C$ by the converted system with the ambient temperature variation of $20^{\circ}C{\sim}35^{\circ}C$. And also the heating COP increased from 3.3 to 5.3 in case of the heat exchange of the super cooling(HESC) circuit and from 3.0 to 4.0 in case of the By-pass with the ambient temperature variation of $-10^{\circ}C{\sim}10^{\circ}C$, respectively, whereas the cooling COP decreased from 3.1 to 2.1with the increase of the ambient temperature from $20^{\circ}C$ to $35^{\circ}C$.

• 한국태양에너지학회 논문집
• /
• 제25권4호
• /
• pp.111-118
• /
• 2005

The purpose of this study is to address the progress of the heat island phenomenon and the scheme to decrease in heat island phenomenon through analysis of micro-climates according to land use and make a plan to construct wind ways. The result is: 1) Analysis of temperature and humidity at 6 spots for 24 hours showed that heat island phenomenon was considerably intense around center road of Gwangju and can be mild through making lakes and green zones. 2) Analysis of the direction and velocity of the wind at 2 spots for 24 hours showed that the direction of the wind at the center of Gwangju was SSW(South-South-West) and average velocity of the it was $1.2{\sim}1.5\;m/s$. To make the inflow of the low-temperature air current from Mt. Mudeung into the city through Gwangju river, efficient management of Gwangju riverside parks should be considered for Gwangju river itself to be wind way. 3) Analysis of mobile temperature measurement on 3 courses for 24 hours showed that the low-temperature air current of Mt. Mudeung and a micro-climate of Gwangju river can lighten thermal storage phenomena of the city in that the temperature was lowest at Gwangju riverside. These outcome is from a day term measurement. So, to figure out accurate condition of heat island phenomenon in Gwangju City, it is needed to have long term measurements and accumulation of those information.