• 한국태양에너지학회 논문집
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• 제32권4호
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• pp.9-16
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• 2012

Nanofluids using Carbon Nanotubes have a excellent thermal characteristic. In this study, for increasing the efficiency of solar collector, the thermal conductivity and viscosity of Ethanol-Oxidized Multi-walled Carbon Nanofluids were measured. Nanofluids were manufactured by ultra-sonic dispersing Oxidized Multi-walled Carbon Nanotubes(OMWCNTs) in ethanol at the rates of 0.0005 ~ 0.1 vol%. The thermal conductivity and viscosity of manufactured nanofluids were measured at the low temperature($10^{\circ}C$), the room temperature($25^{\circ}C$) and the high temperature($70^{\circ}C$). For measuring thermal conductivity and viscosity, we used transient hot-wire method and rotational digital viscometer, respectively. As a result, under given temperature conditions, thermal conductivity of the 0.1 vol% nanofluids improved 33.74% ($10^{\circ}C$), 33.14% ($25^{\circ}C$) and 32.36% ($70^{\circ}C$), and its viscosity increased by 37.93% ($10^{\circ}C$), 31.92% ($25^{\circ}C$) and 29.42% ($70^{\circ}C$) than the base fluids.

• 설비공학논문집
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• 제17권4호
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• pp.285-296
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• 2005

In order to reduce the compression power and to use the overall energy contained in LNG effectively, a combined cycle is devised and simulated. The combined cycle is composed of two cycles; one is an open cycle of liquid/solid carbon dioxide production cycle utilizing LNG cold energy in $CO_2$ condenser and the other is a closed cycle gas turbine which supplies power to the $CO_2$ cycle, utilizes LNG cold energy for lowering the compressor inlet temperature, and uses the heating value of LNG at the burner. The power consumed for the $CO_2$ cycle is investigated in terms of a production ratio of solid $CO_2$. The present study shows that much reduction in both $CO_2$ compression power (only $35\%$ of power used in conventional dry ice production cycle) and $CO_2$ condenser pressure could be achieved by utilizing LNG cold energy and that high cycle efficiency ($55.3\%$ at maximum power condition) in the gas turbine could be accomplished with the adoption of compressor inlet cooling and regenerator. Exergy analysis shows that irreversibility in the combined cycle increases linearly as a production ratio of solid $CO_2$ increases and most of the irreversibility occurs in the condenser and the heat exchanger for compressor inlet cooling. Hence, incoming LNG cold energy to the above components should be used more effectively.

• Journal of the Optical Society of Korea
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• 제20권3호
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• pp.389-395
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• 2016

A Carbon Fiber Composite (CFC) framework was designed for a small lightweight space camera. According to the distribution characteristics of each optical element in the optical system, CFC (M40J) was chosen to accomplish the design of the framework. TC4 embedded parts were used to solve the low accuracy of the CFC framework interface problem. An integrated optimization method and the optimization strategy which combined a genetic global optimization algorithm with a downhill simplex local optimization algorithm were adopted to optimize the structure parameters of the framework. After optimization, the total weight of the CFC framework and the TC4 embedded parts is 15.6 kg, accounting for only 18.4% that of the camera. The first order frequency of the camera reaches 104.8 Hz. Finally, a mechanical environment test was performed, and the result demonstrates that the first order frequency of the camera is 102 Hz, which is consistent with the simulation result. It further verifies the rationality and correctness of the optimization result. The integrated optimization method mentioned in this paper can be applied to the structure design of other space cameras, which can greatly improve the structure design efficiency.

• 한국전산구조공학회논문집
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• 제30권5호
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• pp.381-387
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• 2017

섬유강화 복합재료는 열팽창 계수의 방향성을 갖고 있을 뿐만 아니라 제작과정 온도와 실제 사용온도 사이의 차이 때문에 필연적으로 열응력 효과를 받게 된다. 이러한 열응력에 의한 파손현상은 실제 항공우주산업에서의 응용이 증대되고 있는 두꺼운 복합 적층판의 경우에 더욱 현저한 현상으로 적층판의 역학적 기능 및 파단강도에 큰 영향을 미치게 된다. 본 연구에서는 복잡한 재질로 구성되고 높은 세장비를 가진 블레이드 날개 구조의 차원축소 및 열 응력 복원 이론을 소개하고 3차원 유한요소모델과 비교결과를 통해 효율성과 정확성을 입증한다. 또한 차원을 축소한 모델링을 구성하고 복원이론를 이용하여 열적 환경에 적용된 복합재 보 단면의 열응력을 차원 복원하고 시각적으로 형상화하는 효율적인 복원해석 과정을 소개하고자 한다.

• Elastomers and Composites
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• 제48권3호
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• pp.232-240
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• 2013

자기치유형 아스팔트를 구현하기 위하여 치유제로 디메틸페놀을 사용하여 내부층을 이루고 바깥층이 멜라민 수지로 이루어진 마이크로켑슐을 제조하였다. 마이크로캡슐이 내재된 아스팔트는 일반 아스팔트에 비해 높은 기계적 성질을 나타내었다. 그대로 길어질수록 마이크로캡슐이 함유된 아스팔트는 함유되지 않은 아스팔트보다 더 높은 충격 강도를 나타내었으며 15일의 휴식기간에 최초의 물성을 회복하였다. 이는 X-선 사진에서 보듯이, 깨어진 아스팔트 경계면에 있던 마이크로캡슐이 아스팔트와 동시에 깨지면서 캡슐 안에 있던 단량체인 디메틸페놀이 흘러나와 외부의 반응촉매 투입 없이 아스팔트 자체의 금속촉매와 아민촉매 및 공기 중의 산소분자에 의하여 열가소성 고강성 플라스틱 고분자인 폴리페닐렌옥사이드가 자율적으로 중합되면서 깨어진 아스팔트의 경계면을 메우면서 최초의 물성으로 복구된 것이다. 이는 마이크로캡슐을 함유한 아스팔트는 자가복구능을 갖고 있음을 의미한다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2013년도 제44회 동계 정기학술대회 초록집
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• pp.299-299
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• 2013

Indium Tin Oxide (ITO) has widely been used as a transparent conductive oxide (TCE) for photovoltaic devices. Lately, flexibility of ITO becomes an issue as demand of flexible device increases. Several scientists have tried to substitute ITO to different materials such as conductive polymer, graphene, CNT, and metal nanowire because of ITO brittleness. Among the substitute materials, PEDOT:PSS has mostly paid attention because PEDOT:PSS has excellent flexibility and good conductivity. The conductivity of PEDOT:PSS increases up to 1000 S/cm with additives such as DMSO, EG, sorbitol, and so on. In our research group, we introduce a conductive polymer PEDOT:PSS as a buffer layer to improve not only flexibility but also conductivity. As PEDOT:PSS layer forms beneath ITO thin film (20 nm), sheet resistance decreases from $230{\Omega}$/${\Box}$ to $85{\Omega}$/${\Box}$ and crack initiation decreases from 4.5 mm to 3.5 mm as well. We have fabricated organic photovoltaic device and power conversion efficiencies using conventional ITO electrode and ITO/PEDOT:PSS hybrid electrode. The photovoltaic property such as power conversion efficiency for ITO/PEDOT:PSS hybrid electrode is comparable to the value obtained using conventional ITO electrode on glass substrate.

• Environmental Analysis Health and Toxicology
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• 제11권1_2호
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• pp.31-39
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• 1996

Leachate from municipal solid waste (MSW) landfill, effluent from leachate treatment plant, and ground water sample from a monitoring well near landfill site were tested for an acute toxicity. Microtox toxicity test was used for testing the acute toxicity of leachate and other samples. EC$_{50}$ values which a concentration of pollutant for reducing 50% light output from luminescent bacteria, Photobacterium phosphoreum were determined to assess the toxicity of pollutants as well as the relative toxicity. In addition, characteristics of leachate were studied and compared to those of phenol and pentachlorophenol (PCP) which are typical aquatic toxic pollutants. For leachate, EC$_{50}$ for 30 min incubation was 10.8%, while for phenol and PCP, 46 ppm and 1.2 ppm, respectively. the relative toxicity of treated leachate by in situ aeration with activated sludge was reduced to more than 75% of toxicity of the untreated leachate. Microtox toxicity test was failed to figure out EC$_{50}$ values for groundwater from a monitoring well since the relative toxicity of the unconcentrated sample was too low to estimate EC$_{50}$. Addition of activated carbon to leachate was reduced the relative toxicity. The reduction Pattern of the relative toxicity of leachate by mechanical aeration was similar to that of PCP, but different from that of phenol. These findings suggest that the toxicity of leachate may come from PCP-like toxic compounds rather than phenol-like one. In conclusion, the process of aeration with activated sludge might be very important to reduce the environmental toxicity of leachate. And Microtox test could be a reasonable bioassay for screening and monitoring the environmental toxicity of leachate from municipal solid waste landfill as well as for determining the reduction efficiency of the leachate toxicity by various treatment processes in leachate treatment plant.

• Environmental Engineering Research
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• 제24권4호
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• pp.630-637
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• 2019

The present study aimed to investigate the potential of Enterococcus faecalis (E. faecalis) and Bacillus cereus (B. cereus) in improving the properties of bio-concrete. E. faecalis and B. cereus strains were obtained from fresh urine and an acid mire water at cell concentration of 1.16×10¹² and 1.3×10¹² cells mL^-1, respectively. The bacterial strains were inoculated in a liquid medium into the concrete with 1, 3 and 5% as replacement of water cement ratio (w/c). The ability of E. faecalis and B. cereus cells to accumulate the calcite and the decrement of pores size within bio-concrete was confirmed by SEM and EDX analysis. The results revealed that E. faecalis exhibited high efficiency for increasing of compressive and splitting tensile strength than B. cereus (23 vs. 14.2%, and 13 vs. 8.5%, respectively). These findings indicated that E. faecalis is more applicable in the bio-concrete due to its ability to enhance strength development and reduce water penetration.

• Journal of Advanced Marine Engineering and Technology
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• 제23권4호
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• pp.488-503
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• 1999

The present paper considers the constraint effect on J-R curves under the two-parameter $J-A_2$ controlled crack growth within a certain amount of crack extension. Since the parameter $A_2$ in $J-A_2$ three-term solution is independent of applied loading under fully plasticity or large-scale defor-mation $A_2$ is a proper constraint parameter uring crack extension. Both J and $A_2$ are used to char-acterize the resistance curves of ductile crack growth using J as the loading level and $A_2$ are used to char-acterize the resistance curves of ductile crack growth using J as the loading level and A2 as a con-straint parameter. Approach of the constraint-corrected J-R curve is proposed and a procedure of transferring the J-R curves determined from standard ASTM procedure to non-standard speci-mens or real cracked structures is outlined. The test data(e.g. initiation toughness JIC and tearing modulus $T_R$) of Joyce and Link(Engineer-ing Fracture Mechanics 1997, 57(4) : 431-446) for single-edge notched bend[SENB] specimen with from shallow to deep cracks is employed to demonstrate the efficiency of the present approach. The variation of $J_{IC}$ and $T_R$ with the constraint parameter $A_2$ is obtained and a con-straint-corrected J-R curves is constructed for the test material of HY80 steel. Comparisons show that the predicted J-R curves can very well match with the experimental data for both deep and shallow cracked specimens over a reasonably large amount of crack extension. Finally the present constraint-corrected J-R curve is used to predict the crack growth resistance curves for different fracture specimens. over a reasonably large amount of crack extension. Finally the present constraint-corrected J-R curve is used to predict the crack growth resistance curves for different fracture specimens. The constraint effects of specimen types and specimen sizes on the J-R curves can be easily obtained from the constrain-corrected J-R curves.

• 제어로봇시스템학회논문지
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• 제17권4호
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• pp.388-396
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• 2011

Sun tracking system is the most important subsystem in parabolic dish type solar thermal power plant, since it determines the amount of thermal energy to be collected, thus affects the efficiency of solar thermal power plant most significantly. Various types of sun tracking systems are currently used. Among them, use of photo sensors to located the sun(which is called sensor type) and use of astronomical algorithm to compute the sun position(which is called program type) are two of the mostly used methods. Recently some uses CCD sensor, like CCD camera, which is called image processing type sun tracking system. This work is concerned with the analysis of sun tracking performance of various types of sun tracking systems currently used in the parabolic dish type solar thermal power plant. We first developed a sun tracking error measurement system. Then, we evaluate the performance of five different types of sun tracking systems, sensor type, program type, hybrid type(use of sensor and computed sun position simultaneously), tracking error compensated program type and image processing type. Experimentally obtained data shows that the tracking error compensated program type sun tracking system is very effective and could provide a good sun tracking performance. Also the data obtained shows that the performance of sensor type sun tracking system is being affected by the cloud significantly, while the performance of a program type sun tracking system is being affected by the sun tracking system's mechanical and installation errors very much. Finally image processing type sun tracking system can provide accurate sun tracking performance, but costs more and requires more computational time.