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나노유체를 적용한 태양열집열시스템 열전달 성능향상 연구
손지훈(J. H. Son),정정열(J. Y. Jung),이호생(H. S. Lee),김현주(H. J. Kim) 한국해양환경·에너지학회 2013 한국해양환경·에너지학회 학술대회논문집 Vol.2013 No.11
해양온도차발전의 경우 적도 및 아열대 해역에서는 1년 내내 효율이 유지가 되지만, 고위도에서는 하절기와 달리 동절기에는 표층수의 온도가 떨어져 심층수와의 적정온도차를 만족하지 못해 효율이 하락하는 등의 문제점이 발생함으로 인해 동절기에 해양온도차발전 운전시 해양표층수를 대체할 온열원의 공급이 필요하다. 동절기에 해양온도차발전의 온열원 확보를 위해 같은 전력으로도 좀 더 높은 온도의 온열원 공급을 위해 산화알루미늄 나노유체를 태양열집열시스템에 적용하였다. 이에 본 연구에서는 평판형 태양열집열기를 기반으로 하는 태양열집열시스템의 큰 관을 적용하여 실험장치 2개 set를 제작하였고, 실제 태양열의 평균일사량 대비 평판형 태양열집열기의 평균 집열열량을 기준으로 가동을 하여 순수물과 산화알루미늄 나노유체의 비율별 가동실험을 수행하여 열전달 성능을 비교하였다. In case of OTEC, its efficiency is maintained all through the year in tropical and subtropical regions. However in high latitude region, the efficiency of OTEC decreases due to less temperature difference between surface and deep waters in winter while the temperature difference is enough for OTEC in summer. Because the temperature of surface water goes down in winter, an additional heat source is necessary to compensate the energy of surface water to operate OTEC. In this study, solar energy is considered as the additional heat source because it is the most abundant energy resource on earth. Also nanofluid, a colloid with suspended nanoparticles, is used to enhance the heat transfer rate of solar collecting system. Al2O3/water nanofluids were prepared to used as an working fluid for solar collecting system. We installed same two sets of solar collecting system with flat-plate solar collectors and carried out experiments to compare heat transfer performances of pure water and Al2O3/water nanofluids.
Model for predicting the critical size of aggregates in nanofluids
정정열,구준모,Yong Tae Kang 대한기계학회 2013 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.27 No.4
Stable suspension of the nanoparticles in the base fluids is inevitable to have the nanofluids be operated properly. Here we report the theoretical model to find the critical size of aggregates in nanofluids for the first time. The concept of relaxation time r τ is adopted,which reflects the probability of encountering the particles. The hydrodynamic diameter of the aggregates in nanofluids must be kept below the critical size to be stably suspended, which is in good agreement with the experimental results.
정정열(Jung-Yeul Jung),유정열(Jung Yul Yoo) 대한기계학회 2007 대한기계학회 춘추학술대회 Vol.2007 No.5
In this study, the mechanism of enhanced thermal conductivity is elucidated on the bases of both electric double layer (EDL) and kinetic theory. A novel expression for the thermal conductivity of nanofluids is proposed and verified by applying to Al₂O₃ nanofluids with regard to various temperatures, volume fractions and particle sizes. In dilute nanofluids, the effects of Brownian motion and particle interaction on enhancing the thermal conductivity of nanofluids are quite comparable while the effect of particle interaction due to EDL is more prominent in dense nanofluids. The model presented in this paper shows that particle interaction due to the electrical double layer is the most responsible for the enhancement of thermal conductivity of nanofluids.
CO2 absorption characteristics of nanoparticle suspensions in methanol
정정열,강용태 대한기계학회 2012 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.26 No.8
Recently there have been growing concerns that anthropogenic carbon dioxide (CO2) emissions cause the global warming problem. Therefore, the cutting-edge technologies for the reduction, separation and collection of the CO2 are very important to alleviate this problem. The best methods for reducing the CO2 emission are to increase the energy efficiency and to remove it from the power plant. The CO2 absorption from the syngas in the integrated gasification combined cycle (IGCC) might increase the energy efficiency of the power generation systems, which also contribute to mitigate the global warming. In this study, the suspensions of nanoparticles in methanol (called the nanofluid) are developed and estimated to apply it to absorb CO2 gas in the IGCC systems. The nanofluids are prepared by the ultrasonic treatment and show the good stability. It is found that the CO2 absorption rate by the nanofluid is enhanced up to ~8.3% compared to the pure methanol.
흡수식 시스템 적용을 위한 이성분 나노에멀젼(O/S)의 열물성 측정 실험
설혜연(Hea Youn Sul),정정열(Jung-Yeul Jung),강용태(Yong Tae Kang) 대한기계학회 2010 대한기계학회 춘추학술대회 Vol.2010 No.5
이성분 나노에멀젼이란, 흡수식 시스템의 열 및 물질전달 향상을 위해 나노 크기의 오일액적 입자를 작동 유체인 H₂O/LiBr에 분산시킨 것을 의미한다. 본 연구에서는 DLS 법을 이용한 입도 측정과 비정상 열선법을 이용한 열전도도 측정 연구를 수행하였다. 실험 결과 단성분 나노 에멀젼(Oil in water nanoemulsion)의 경우 0.1 vol %의 오일이 분산되었을 때 약 6.4%, 이성분 나노에멀젼(Oil in solution nanoemulsion)의 경우 30 wt% H₂O/LiB의 모유체에 1 vol%의 오일이 분산되었을 때 약 3.6%의 유효열전도도 상승을 나타내었다. 따라서 모유체 보다 낮은 열전도도를 갖는 오일을 나노 크기로 분산시킴으로써 이성분 나노에멀젼의 열전도도를 상승시킬 수 있었다. Binary nanoemulsions, nano-sized oil-droplet suspensions in a binary solution (H₂O/LiBr), are developed to enhance the heat and mass transfer performance of absorption refrigeration systems. In this study, the droplet size and the thermal conductivity of binary nanoemulsions are measured by the DLS method and the transient hot-wire method, respectively. It is found that the measured thermal conductivity of the oil-in-water nanoemulsion enhances up to 6.4 % at 0.1 vol% of oil, and the binary nanoemulsion enhances up to 3.6 % at 1.0 vol % of oil in 30 wt % H₂O/LiBr compared with the estimated one from the Maxwell's model. Therefore it is proposed that the thermal conductivity of the binary nanoemulsion could be enhanced by adding nano-sized droplets of n-decane oil, which has a lower thermal conductivity than that of the base fluid.
정정열(Jung-Yeul Jung),오후석(Hoo-Suk Oh),곽호영(Ho-Young Kwak),최경빈(Kyong-Bin Choi),고창복(Chang-Bok Ko) 대한기계학회 2005 대한기계학회 춘추학술대회 Vol.2005 No.5
Convective heat transfers of a nanofluid in rectangular microchannel were measured. An integrated microsystem consisting of a single microchannel on one side and two localized heaters and seven polysilicon temperature sensors along the channel on the other side were fabricated. Aluminum dioxide (Al₂O₃) suspended nanofluids with various particle volume fractions were used in experiment to investigate the effect of the volume fraction of the nanoparticles to the convective heat transfer and fluid flow in microchannels. The convective heat transfer coefficient with Al₂O₃ suspended nanofluid was measured to be increased up to 30 % compared to the distilled water at a volume fraction of 1.8 vol.% without major friction loss. A new type of convective heat transfer correlation was proposed to correlate experimental data of heat transfer for nanofluids in microchannels.
전자장치 냉각을 위한 콘 형상 모세관을 이용한 모세관 펌프 루프
정정열(Jung-Yeul Jung),오후석(Hoo-Suk Oh),곽호영(Ho-Young Kwak),이대근(Dae Keun Lee),고창복(Chang-Bok Ko) 대한기계학회 2005 대한기계학회 춘추학술대회 Vol.2005 No.11
A capillary pumped loop (CPL) was developed using cone shaped capillary structure for cooling electronic device. Cone shaped capillary structure was constructed by sand blast with 32 ㎛-diameter Al₂O₃ nano particles. The CPL fabricated was tested under various conditions such as different relative heights, fill ratios and heat fluxes. The operation conditions of CPL were varied depending on relative height, fill ratio and heat flux. With an allowable temperature of 55 ℃ on the evaporator surfaces, the CPL can handle a heat flux of about 0.8 W/㎝². Steady state operation condition was achieved within 10 minutes.