• 한국유체기계학회 논문집
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• 제10권5호
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• pp.27-33
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• 2007

Rarefied gas flows through two-dimensional micro channels are studied numerically for the performance optimization of a nanomembrane-based Knudsen compressor. The effects of the wall temperature distributions on the thermal transpiration flow patterns are examined. The flow has a pumping effect, and the mass flow rates through the channel are calculated. The results show that a steady one-way flow is induced for a wide range of the Knudsen number. The DSMC(direct simulation Monte Carlo) method with VHS(variable hard sphere) model and NTC(no time counter) techniques has been applied in this work to obtain numerical solutions. A critical element that drives Knudsen compressor Is the thermal transpiration membrane. The membranes are based on aerosol or machined aerogel. The aerogel is modeled as a single micro flow channel.

• Bulletin of the Korean Chemical Society
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• 제30권6호
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• pp.1337-1340
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• 2009

Electrical properties of a fluorinated carbon black (CB)-filled high-density polyethylene (HDPE) polymeric switch were investigated as a function of fluorination pressure at 0.1 ~ 0.4 MPa. From the FT-IR results, the absorption spectra of the fluorinated CB show an absorption band at 1400 ~ 1000 $cm^{-1}\;for\;{\nu}_{C-F}$ and the peak intensity increased with increasing fluorination pressure. Also, the analysis of XPS spectra of the fluorinated CB indicated that fluorine content increased with increasing fluorination pressure. Meanwhile, the surface free energy of the fluorinated CB decreased with increasing fluorination pressure. Consequently, the increase of fluorine contents of CB made a disappearance of negative temperature coefficient (NTC) behavior of the polymeric switch, which was probably due to the reduction of CB reaggregation after melting point of the HDPE, resulted from the decreasing of London dispersive component of the surface free energy for CB particles.

• 청정기술
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• 제25권3호
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• pp.238-244
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• 2019

본 연구에서는 온도와 압력의 변화에 따른 석유계항공유(Jet A-1), 바이오항공유(Bio-6308) 그리고 두 항공유를 50:50 (v:v)으로 혼합한 연료의 점화특성의 변화에 대한 분석을 수행하였다. Combustion research unit (CRU) 장비를 사용하여 각 항공유의 점화지연시간을 측정하였으며, GC/MS 및 GC/FID를 사용하여 각 항공유를 구성하는 화합물에 대한 정성 및 정량적인 분석을 수행하였다. 그 결과, 모든 연료의 경우에서 온도와 압력이 증가할수록 점화지연시간이 짧게 측정 되었으며, 특히 압력보다 온도의 영향을 더 많이 받는 것을 확인하였다. 또한, 모든 측정 조건에서 Jet A-1의 점화지연시간이 가장 길게 측정되었는데 이는 Jet A-1을 약 22.48%의 비율로 구성하는 방향족화합물이 산화되는 과정에서 생성되는 benzyl radical이 구조적으로 매우 안정한 특성을 갖기 때문인 것으로 판단되었다. 이러한 benzyl radical은 negative temperature coefficient (NTC) 구간에 영향을 줄 수 있는 반응을 억제하여, Jet A-1의 경우에서는 온도가 증가함에 따라 점화지연시간이 짧아지는 정도가 감소하는 구간이 없는 것을 확인하였다. Jet A-1과 Bio-6308을 50:50 (v:v)으로 혼합한 연료의 점화특성은 Bio-6308 보다는 Jet A-1과 비슷한 경향을 나타내는 것을 통해 기존의 시스템을 변경하지 않고서도 실제로 적용이 가능함을 확인하였다.

• Macromolecular Research
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• 제12권1호
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• pp.53-62
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• 2004

We have prepared polymer composites of low-density polyethylene (LDPE) and ionomers (Surlyn 8940) containing polar segments and metal ions by melt blending with carbon black (CB) as a conductive filler. The resistivity and positive temperature coefficient (PTC) of the ionomer/LDPE/CB composites were investigated with respect to the CB content. The ionomer content has an effect on the resistivity and percolation threshold of the polymer composites; the percolation curve exhibits a plateau at low CB content. The PTC intensity of the crosslinked ionomer/LDPE/CB composite decreased slightly at low ionomer content, and increased significantly above a critical concentration of the ionomer. Irradiation-induced crosslinking could increase the PTC intensity and decrease the NTC effect of the polymer composites. The minimum switching current (Ι$\sub$trip/) of the polymer composites decreased with temperature; the ratio of Ι$\sub$trip/ for the ionomer/LDPE/CB composite decreased to a greater extent than that of the LDPE/CB composite. The average temperature coefficient of resistance (${\alpha}$$\sub$T/) for the polymer composites increased in the low-temperature region.

• 한국산학기술학회논문지
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• 제16권12호
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• pp.8306-8313
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• 2015

개방형 전류측정기는 DC 모터 콘트롤러, AC 가변 콘트롤러, UPS(Uninterruptible Power System)에 주로 사용되며 최근 신재생 에너지의 성장과 전력망의 스마트 그리드화로 인하여 활용성이 점차 확대되고 있다. 이러한 신재생 에너지의 성장으로 관련 핵심기술의 보유여부가 중요해지고 있으며 대부분 수입에 의존하고 있는 개방형 전류측정기의 국산화 및 관련 기술의 확보를 필요로 한다. 본 논문에서는 일반 산업용 개방형 전류측정기의 제작과정과 특성을 측정한 결과를 기술하였다. 개방형 전류측정기를 구성하는 C형 철심의 공극자장분포 해석 및 형상 설계, 홀센서의 선정 및 특성시험, 정전류 전원공급회로와 신호처리회로의 회로설계 과정을 기술하며 DIP(Dual In-line Package) type과 SMD (Surface Mount Device) type의 100A급 개방형 전류측정기를 제작하고 특성을 측정했다. 제작된 전류측정기로 0~100A 범위에서 통전 실험을 실시한 했고 직류전류와 60Hz의 교류전류에서 특성을 측정한 결과 정밀도 오차 2% 이내, 선형도 오차 2% 이내의 성능을 만족하였다. 또한 부 특성 온도계수를 갖는 NTC(Negative Temperature Coefficient) 서미스터를 이용한 온도보상회로를 사용하여 $-35{\sim}100^{\circ}C$의 범위에서 온도보상 효과를 확인하였다.

• 한국미생물·생명공학회지
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• 제11권3호
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• pp.175-180
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• 1983

Lysine의 analogue인 thialysine은 야생주 Candida utilis NCYC-359의 생육을 강력하게 저해했으며 0.1%에서는 18시간까지 9.5%에서는 24시간까지 본 효모의 유도기를 지연시켰다. thialyssine에 의한 야생주의 생육저해의 회복에 미치는 아미노산 및 비타민의 영향을 조사한 결과 glycine, mthionine, arginine, histidine 그리고 trypphan등은 어느정도 효과가 있었으며 비타민은 거의 효과가 없었다. 특히 최소배지에 L-lysine을 thialysine의 1/8량만 첨가해도 thialysine에 의한 생육저해는 거의 일어나지 많았다. NTC 1회 처리시 thialysine에 대한 내성을 나타내는 빈도를 보면 최소배지에 thialysine 0.1% 첨가시 그 빈도가 0.11%, 0.5%시 0.03%로 나타났으며 이 내성맥리주에 의한 lysine 생산능을 검토한 결과 최소배지에 첨가된 thialyslne의 농도와 lysine생산능과는 뚜렷한 관계가 성립되지 않았으며 NTC를 회복처리하여 균체외로 lysine을 다양 분필 하는(450$\mu\textrm{g}$/$m\ell$) thialysine 내성맥리주 Candida utilis TRN-4006을 최종적으로 분리선별하였다.

• 한국연소학회:학술대회논문집
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• 한국연소학회 2014년도 제49회 KOSCO SYMPOSIUM 초록집
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• pp.179-182
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• 2014

A comparative DNS study of the ignition characteristics of dual-fueled reactivity controlled compression ignition (RCCI) and stratification charge compression ignition (SCCI) is investigated using a 116-species reduced primary reference fuel (PRF) mechanism. In the RCCI combustion, two PRF fuels (n-heptane and iso-octane) with opposite autoignition characteristics are separatedly supplied and in-cylinder blended such that spatial variations in fuel reactivity, fuel concentration and temperature are achieved. In the SCCI combustion, however, just a single fuel (PRF50) is used such that only fuel concentration and temperature inhomoginieties are obtained. Because three factors, rather than only two as in SCCI combustion, govern the overall RCCI combustion, combustion timing and combustion duration or heat release rate of RCCI combustion are flexibly and effectively controlled. It is found that the overall RCCI combustion occurs much earlier and its combustion duration is longer compared to SCC combustionI. Moreover, the negative temperature coefficient (NTC) has a positive effect on enhancing RCCI combustion by inducing a shorter combustion timing and a longer combustion duration as a result of the occurrence of a predominant low-speed deflagration-combustion mode.

• Carbon letters
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• 제2권3_4호
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• pp.159-164
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• 2001

In this study, the effects of carbon black (CB) content and anodic oxidation treatment with $AgNO_3$ on positive temperature coefficient (PTC) behavior of CB/HDPE nanocomposites were investigated. Also, the addition of elastomer as a toughing agent was studied. The 20~50 wt% of CB, 0~5 wtt% of elastomer, and 1 wt% of $AgNO_3$-filled HDPE nanocomposites were prepared using the internal mixer in 60 rpm at $160{\circ}C$ and the compression-molded at $180{\circ}C$ for 10 min. As a result, the room temperature resistivity and PTC intensity of the composites were dependent, to a large extent, on the content of CB, addition of elastomer, and surface chemical properties that were controlled in the relative arrangements of the carbon black aggregates in a polymeric matrix. Moreover, the composites with relatively low room temperature resistivity and suitable PTC intensity could be achieved by treatment of $AgNO_3$. Consequently, it was noted that PTC effect was due to the deagglomeration or the breakage of the conductive networks caused by thermal expansion or crystalline melting of the polymeric matrix.

• 한국연소학회지
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• 제18권2호
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• pp.32-41
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• 2013

This study presents both experimental and numerical investigation of ignition delay time of n-heptane and n-butanol binary fuel. The $O_2$ concentration in the mixture was set to 9-10% to make high exhaust gas recirculation( EGR) rate condition which leads low NOx and soot emission. Experiments were performed using a rapid compression machine(RCM) at compressed pressure 20bar, several compressed temperature and three equivalence ratios(0.4, 1.0, 1.5). In addition, a numerical study on the ignition delay time was performed using CHEMKIN codes to validate experimental results and predict chemical species in the combustion process. The results showed that the ignition delay time increased with increasing the n-butanol fraction due to a decrease of oxidation of n-heptane at the low temperature. Moreover, all of the binary fuel mixtures showed the combustion characteristics of n-heptane such as cool flame mode at low temperature and negative-temperature-coefficient(NTC) behavior. Due to the effect of high EGR rate condition, the operating region is reduced at lean condition and the ignition delay time sharply increased compared with no EGR condition.

• Steel and Composite Structures
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• 제44권2호
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• pp.155-169
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• 2022

In the present paper an analytical model was developed to study the non-linear vibrations of Functionally Graded Carbon Nanotube (FG-CNT) reinforced doubly-curved shallow shells using the Multiple Scales Method (MSM). The nonlinear partial differential equations of motion are based on the FGM shallow shell hypothesis, the non-linear geometric Von-Karman relationships, and the Galerkin method to reduce the partial differential equations associated with simply supported boundary conditions. The novelty of the present model is the simultaneous prediction of the natural frequencies and their mode shapes versus different curvatures (cylindrical, spherical, conical, and plate) and the different types of FG-CNTs. In addition to combining the vibration analysis with optimization algorithms based on the genetic algorithm, a design optimization methode was developed to maximize the natural frequencies. By considering the expression of the non-dimensional frequency as an objective optimization function, a genetic algorithm program was developed by valuing the mechanical properties, the geometric properties and the FG-CNT configuration of shallow double curvature shells. The results obtained show that the curvature, the volume fraction and the types of NTC distribution have considerable effects on the variation of the Dimensionless Fundamental Linear Frequency (DFLF). The frequency response of the shallow shells of the FG-CNTRC showed two types of nonlinear hardening and softening which are strongly influenced by the change in the fundamental vibration mode. In GA optimization, the mechanical properties and geometric properties in the transverse direction, the volume fraction, and types of distribution of CNTs have a considerable effect on the fundamental frequencies of shallow double-curvature shells. Where the difference between optimized and not optimized DFLF can reach 13.26%.