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알루미늄 입자 크기에 따른 파라핀 혼합연료의 연소 특성 연구
고수한(Soohan Ko),한승주(Seongjoo Han),류성훈(Sunghoon Ryu),김진곤(Jinkon Kim),문희장(Heejang Moon),김준형(Junhyung Kim),고승원(Seungwon Ko) 한국추진공학회 2017 한국추진공학회 학술대회논문집 Vol.2017 No.5
본 연구에서는 알루미늄 입자 크기에 따른 파라핀 혼합연료의 연소 특성에 관한 실험을 수행하였다. 평균 입도 100 nm 및 8 μm 크기의 알루미늄 입자와 Sasol사의 마이크로크리스탈린 파라핀 왁스(Sasol 0907)를 이용하여 연소실험을 수행하였고 순수 파라핀과 알루미늄 입자 5 wt%를 첨가한 파라핀 혼합 연료의 후퇴율과 압력선도, 특성배기속도 등을 비교하였다. 마이크로 입자의 첨가는 산화제 유속이 증가할수록 후퇴율을 향상시켰으나 나노 입자의 첨가는 후퇴율이 감소하는 경향을 보였다. In this study, the combustion characteristics of paraffin blended fuel on aluminum particle size were investigated. The combustion experiments were carried out using aluminum particles with an average particle size of 100 nm and 8 μm and microcrystalline paraffin wax (Sasol 0907). A series of comparison was conducted on the regression rate, the pressure curve and the characteristic velocity of pure paraffin and paraffin blended fuels with aluminum particles. It was found that the micro-sized particles enhance the regression rate as the oxidizer mass flux increased. However, the nano-sized particles decrease the regression rate as the oxidizer mass flux is increased.
Ko, Yeounjoo,Seol, Eunhee,Sundara Sekar, Balaji,Kwon, Seongjin,Lee, Jaehyeon,Park, Sunghoon Elsevier 2017 Bioresource technology Vol.244 No.1
<P><B>Abstract</B></P> <P>Production of 3-hydroxypropionic acid (3-HP) or 1,3-propanediol (1,3-PDO) production from glycerol is challenging due to the problems associated with cofactor regeneration, coenzyme B<SUB>12</SUB> synthesis, and the instability of pathway enzymes. To address these complications, simultaneous production of 3-HP and 1,3-PDO, instead of individual production of each compound, was attempted. With over-expression of an aldehyde dehydrogenase, recombinant <I>Klebsiella pneumoniae</I> could co-produce 3-HP and 1,3-PDO successfully. However, the production level was unsatisfactory due to excessive accumulation of many by-products, especially acetate. To reduce acetate production, we attempted; (i) reduction of glycerol assimilation through the glycolytic pathway, (ii) increase of glycerol flow towards co-production, and (iii) variation of aeration rate. These efforts were partially beneficial in reducing acetate and improving co-production: 21g/L of 1,3-PDO and 43g/L of 3-HP were obtained. Excessive acetate (>150mM) was still produced at the end of bioreactor runs, and limited co-production efficiency.</P> <P><B>Highlights</B></P> <P> <UL> <LI> <I>K. pneumoniae</I> was engineered for co-production of 3-HP and 1,3-PDO from glycerol. </LI> <LI> Co-production improved upon by-products reduction. </LI> <LI> The maximum 21g/L 1,3-PDO and 43g/L 3-HP were obtained in fed-batch bioreactor cultivation. </LI> <LI> Acetate accumulation was serious and limited further improvement of co-production. </LI> <LI> Activation of TCA cycle and ETC is suggested to reduce acetate and improve ATP supply. </LI> </UL> </P>
Sunghoon Park,Hyejoon Kheel,Gun-Joo Sun,Hyoun Woo Kim,Taegyung Ko,Chongmu Lee 대한금속·재료학회 2016 METALS AND MATERIALS International Vol.22 No.4
Cr2O3-functionalized Nb2O5 nanoparticles were synthesized via a facile hydrothermal route. The multiple-networked Cr2O3-functionalized Nb2O5 nanostructured sensor showed enhanced H2 gas sensing performance compared to its pristine Nb2O5 nanostructure counterpart. The Cr2O3-functionalized Nb2O5 nanostructure sensor showed responses of 5.24 to 2 ppm of H2 at room temperature, whereas the pristine Nb2O5 nanoparticle sensors showed responses of 2.29. The former also exhibited a faster response to H2. The multiple-networked pristine and Cr2O3-functionalized Nb2O5 nanostructured sensors were stronger and much shorter, respectively, than other nanomaterial-based Schottky diode-type sensors and Nb2O5-based Schottky diode-type sensors. The underlying mechanism for the enhanced sensing performance of the Cr2O3-functionalized Nb2O5 nanostructured sensor towards H2 gas is discussed in detail. Particular emphasis is placed on the role of the Cr2O3-Nb2O5 p-n junction in the Cr2O3-functionalized Nb2O5 nanostructure sensor.
Enhanced NO2 Gas Sensing Properties of WO3-Coated Multiwall Carbon Nanotube Sensors.
Ko, Hyunsung,Park, Sunghoon,Park, Suyoung,Lee, Chongmu American Scientific Publishers 2015 Journal of Nanoscience and Nanotechnology Vol.15 No.7
<P>WO3-coated multiwall carbon nanotubes (MWCNTs) were fabricated by sputter-deposition of WO3 on MWCNT paste. The outer diameters of WO3-coated MWCNTs ranged from 20 to 40 nm and the lengths ranged up to a few tens of micrometers. The low-magnification TEM image of a typical WO3-coated CNT showed a CNT with an inner diameter of ~20 nm and a tube wall thickness of ~7 nm and WO3 shells with a thickness up to 10 nm at both edges of the tube. The WO3 shells were very nonuniform in thickness not only along the axis of the nanotube but also from one nanotube to the other. The sensing properties of multiple networked WO3-coated CNT sensors toward NO2 gas were examined. The WO3-coated MWCNT sensors showed responses of 120-221% over an NO2 concentration range of 1 to 5 ppm at room temperature. The responses were 1-2 fold higher than those of the pristine MWCNT sensor over the same NO2 concentration range. The origin of the enhancement of the MWCNTs in the response to NO2 by coating them with WO3 is discussed.</P>
Photoluminescence in MgO-ZnO Nanorods Enhanced by Hydrogen Plasma Treatment
Park, Sunghoon,Ko, Hyunsung,Mun, Youngho,Lee, Chongmu Korean Chemical Society 2013 Bulletin of the Korean Chemical Society Vol.34 No.11
MgO nanorods were fabricated by the thermal evaporation of $Mg_3N_2$. The influence of ZnO sheathing and hydrogen plasma exposure on the photoluminescence (PL) of the MgO nanorods was studied. PL measurements of the ZnO-sheathed MgO nanorods showed two main emission bands: the near band edge emission band centered at ~380 nm and the deep level emission band centered at ~590 nm both of which are characteristic of ZnO. The near band edge emission from the ZnO-sheathed MgO nanorods was enhanced with increasing the ZnO shell layer thickness. The near band edge emission from the ZnO-sheathed MgO nanorods appeared to be enhanced further by hydrogen plasma irradiation. The underlying mechanisms for the enhancement of the NBE emission from the MgO nanorods by ZnO sheathing and hydrogen plasma exposure are discussed.
Numerical study of high-speed two-phase ejector performance with R134a refrigerant
Baek, Sunghoon,Ko, Seungbin,Song, Simon,Ryu, Sungmin Elsevier 2018 INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER - Vol.126 No.1
<P><B>Abstract</B></P> <P>An ejector is a passive pumping device to increase the flow rate of a motive fluid and to enhance compression of the fluid flow by geometrically induced secondary flows. In particular, the high-speed two-phase ejector has attracted attention as an alternative to the throttling valve, because by compensating the throttling loss that appears in expansion devices it has the potential to improve significantly the performance of refrigeration systems. However, flows inside the ejector are so complex that it is not easy to characterize the relevant flow and thermodynamic behaviors experimentally. In contrast, the numerical approach is relatively favorable to elucidate the relevant physics inside the ejector, and is considered useful to improve the performance of the ejector. However, there have been few relevant numerical studies, because it is challenging to resolve high-speed flows accompanied with phase transitions. In the present study, we present numerical solutions of the high-speed flows inside a two-phase ejector. An evaporation-condensation model is implemented and the real-fluid properties of refrigerant R134a are input in our RANS simulations to resolve phase transitions. Based on the validated predictive ability of our computational apparatus on the baseline model of the ejector, we present a parameter study to identify the effects of geometry variables on the entrainment performance. Our study provides specific guidelines to be considered when designing supersonic two-phase ejectors, and thus, it is expected to contribute to studies associated with supersonic two-phase ejector-equipped refrigeration systems.</P> <P><B>Highlights</B></P> <P> <UL> <LI> We present numerical solutions of the high-speed flows inside a two-phase ejector with R134a used for low-pressure refrigeration cycles, and explain the detailed flow behavior affected by major geometric parameters of the ejector. </LI> <LI> The results include characteristics of phase transition, compressibility effect, mass and heat transfer at interface of each phase. For example, the length of the diverging nozzle is related to maximizing the mean dynamic pressure at the nozzle exit; the nozzle exit position affects significantly the size of the recirculation bubble observed in the suction chamber which should be avoided or minimized; the entrainment performance of the ejector highly depends on the diameter and length of the mixing tube. </LI> <LI> The numerical study can be taken as a pragmatic reference of designing the two-phase ejector with a high performance. </LI> </UL> </P>