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김대현 ( Kim Dae-hyun ),김정근 ( Kim Jeong-guen ),이수영 ( Lee Soo-young ) 경희대학교 입학전형연구센터 2018 입학전형연구 Vol.6 No.-
본 연구는 대학입학 후 중도 포기의 정확한 원인을 파악하여 입학생들의 대학생활 지원 및 입학전형 설계에 활용하고자 기획되었다. 이를 위해 2014년 3월부터 2016년 8월까지 2년 6개월간 경희대학교 서울/국제캠퍼스 학부 재적생 46,331명 중 중도포기자 1,915명을 대상으로 조사하였다. 입학전형별, 단과대학 및 학과별, 입학년도별, 학년별 등 크게 4가지로 구분하였다. 연구 결과 중도포기의 원인은 타대학진학 > 성적경고제적 > 경제사정 순이었다. 입학전형별 중도포기자 수는 수능중심전형이 가장 많았고, 모집인원 대비 중도포기자 비율은 교과중심전형이 가장 높았다. 논술중심전형과 학생부종합전형은 모집인원 대비 중도포기자가 2% 미만으로 매우 낮았다. 연구 결과를 바탕으로 추후 신입생들에 대한 이해, 대학생활 적응 지원, 중도포기 방지를 위한 학사 운영, 입학전형 설계 방안 등을 논의해 볼 수 있을 것으로 기대한다. This study was designed to determine the exact causes of the annual students dropping out of the college. For this purpose 1,915 dropout students out of 46,331 were surveyed at Kyunghee University for two and a half years from March 2014 to August 2016. Large sections were categorized by four categories: admission types, colleges & departments, year of entry and school years. The result is that the main cause of dropping out is to go(transfer) to other colleges, to expell due to academic records, and the economic situations. Based on this study, we hope to understand students' situations, support for college life adaptation and prevent from dropping out and design for admission system.
최종원(Jong Won Choi),김정근(Jeong Guen Kim),최영찬(Young Chan Choi) 대한기계학회 2018 大韓機械學會論文集B Vol.42 No.5
정전분무 기술은 노즐 통해 흐르는 물에 고전압을 하전하여 물분자들 사이의 높은 척력에 의해 매우 작은 하전된 물입자로 분사를 하는 기술을 말한다. 정전분무 기술을 전기집진기에 응용을 하게 되면, 분사된 미립화된 물은 노즐과 반대 극성을 띄는 플레이트를 향해 전기장을 따라 움직이며, 유입된 초미세입자와 직접 충돌 혹은 정전기력에 의한 간접 충돌을 한 후 플레이트에서 중력 방향으로 집진을 할 수 있다. 본 연구에서는 정전분무 분사에 관한 가시화 연구 및 습식 사이클론에 응용하였을 경우 미세먼지 제거 성능을 실험적으로 살펴보았으며, 대표적인 초미세먼지라고 할 수 있는 PM2.5의 경우 사이클론에 약 50 mg/m³의 농도와 10 m/s의 속도(혹은 2 m³/min)로 유입될 경우 35 kV의 운전조건에서 95 % 이상의 제거 효율을 보였다. The electrospray is one of the most well-known spray techniques using highly concentrated free charges from high intensity electrical potential between two oppositely charged electrodes to produce very fine and highly charged water droplets in a conical shape (i.e., Taylor cone). We propose the application of this spray technology to a wet cyclone system to maximize particle collection efficiency. Highly charged droplets impact fine particles inside a flue gas, stick to the collector body, and fall through the cyclone cone in a gravitational direction. We have designed and fabricated an electrospray-driven wet cyclone electrostatic precipitator, investigating particle collection performance with a tangential velocity of ~10 m/s at the cyclone inlet, applying various voltages and water supply flow-rates. Experimental results show that the effective driving voltage for reaching the PM2.5 collection efficiency over 95 % is 35 kV. Comparing performances of previously commercialized wet scrubbers, in terms of the same treatment capacity, we obtained 70 % power and 75 % water consumption savings, respectively.
최종원(Jong Won CHOI),김진한(Jin Han KIM),이영주(Young Joo LEE),박주형(Ju Hyung PARK),이계중(Kye Jung LEE),김정근(Jeong Guen KIM),최영찬(Young Chan CHOI) 대한설비공학회 2018 대한설비공학회 학술발표대회논문집 Vol.2018 No.6
Nowadays the ultrafine particle emission from the vehicles, power plants, and industries has been revealed to cause the critical respiratory diseases like silicosis and asbestosis, thereby the atmospheric particulate matter (PM) concentration is being considered as a proxy indicator of air pollution. In particular, the reduction of ultrafine particle concentration inside a combustion flue gas becomes an inevitable option to many researchers. Differently from the previous dry electrostatic precipitator (ESP), it is necessary to employ water to capture such ultrafine particles in order to satisfy the stricter environmental regulations. Herein, we proposed, designed and tested one of the promising systems that consists of a simple grounded cyclone geometry and electrical insulating high voltage water nozzle, called Electrospary Cyclone Precipitator (ECP). From experimental results, we obtained the maximally 91.5% collection efficiency of Sub-1um particles (PM1.0) with water-gas ratio of 0.1 L/m³, water consumption of 12 ccm for every single nozzle, electrical field strength of 6.7 kV/cm and the specific corona power of 20 W/(m³/min). Comparing the operating parameters of ECP with the previously proposed electrospray ESP, we saved 85% water and 43% power consumptions, respectively.
정전 분무를 이용한 미세 물 액적 생성 및 습식 사이클론 적용 방안에 관한 연구
최종원(Jong Won CHOI),정대헌(Dae Hun CHUNG),이계중(Kye Jung LEE),김정근(Jeong Guen KIM),최영찬(Young Chan CHOI),이욱현(Wook Hyun LEE),우영민(Young Min WOO),오상현(Sang Hyun OH),윤민혜(Min Hye YOUN) 대한설비공학회 2017 대한설비공학회 학술발표대회논문집 Vol.2017 No.6
A historically well-known technique for atomizing the liquid water droplets may be electrospray, which is induced by electrostatic charging inside a confined geometry such as needle, nozzle or slit. Based on the Rayleigh’s theory of instability and Taylor’s theory, the electrospray enables to produce fine water droplets as forming a conical shape (Taylor cone) due to the highly concentrated free charge from high intensity of electrical potential between two oppositely charged electrodes. We herein applied this technology to the wet electrostatic precipitator, especially in cyclone structure. The wet electrostatic precipitator has been reported to possess a few flaws such as un-uniform water film formation on the wall, excessive waste water and large energy consumption. Applying the negative potential to the needles and the positive potential to the collector body, we observed sub-100㎛ water droplets are generated by means of an electrospraying process without any pressure. Such highly charged droplets pull the fine particles inside a flue gas, stick to the collector body and then finally free fall down. In this study, we designed and fabricated the electrospray driven wet cyclone electrostatic precipitator, investigating the particle collection performance with the tangential velocity of ~10 m/s at the cyclone inlet, for various voltages and water flowrates. The experimental results show that the effective flowrate through one needle for reaching the PM2.5 collection efficiency of 95% and the power consumption per a needle are measured as 20 ccm and 0.35 W (35 kV and 0.01 mA). Comparing that the the ratio of water to flue gas and power consumptions of the previously commercialized wet electrostatic precipitators for the treatment capacity of 50 CMM have been reported as 1.0 L/m<SUP>3</SUP> and 840 kW, our measurement gave us 0.2 L/m<SUP>3</SUP> and 175 W, which are merely 20% and 20.8% over those of the commercialized one, respectively