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이대영,정성훈,강병하,홍희기,Lee, D.-Y.,Jung, S.-H.,Kang, B.H.,Hong, H. 대한설비공학회 1999 설비공학 논문집 Vol.11 No.1
An experimental study on the performance enhancement of a screw-compressor-type chiller with 100kW of nominal cooling capacity has been carried out. Performance test facility was developed to investigate the effects of a partial modification from the existing chiller on the performance. By replacing the existing shell-and -tube heat exchangers with plate heat exchangers, the cooling capacity is increased by 15~18% and the COP is also increased by 19~21% depending on the operation temperature range. Charging mixed refrigerant R22/R142b(80 : 20) instead of R22 into the chiller with plate heat exchangers improves the cooling capacity by 4% and the COP very largely by 30%. Each contribution of the plate evaporator, plate condenser, and mixed refrigerant to the performance enhancement is examined by analyzing the refrigeration cycle and the heat transfer processes. It is also shown that the chiller performance can be improved by adapting 2-stage-compression cycle using an economizer.
이대영,강병하,김민수,Lee, D.-Y.,Kang, B.H.,Kim, M.S. 대한설비공학회 1999 설비공학 논문집 Vol.11 No.1
The charge operation of an ice storage system has been analyzed in this paper. The thermal characteristics of major components of the ice storage system. i.e., the refrigerator and the ice storage tank are evaluated from performance tests on an existing ice storage system. Based on the measured data for thermal characteristics, a simulation is carried out for the charge operation and the effect of the refrigerator size on the system performance is investigated. The results indicate that the larger the refrigerator size for a given storage capacity, the lower the inlet temperature of the ice storage tank so that the lower the efficiency of charge operation. It is also found that there exists an optimal size of the refrigerator with which the ice storage at the end of the charge operation is maximized, but the complete charge is not possible even with the optimally sized refrigerator. This leads to the result that the design capacity of the storage tank should be larger than the required amount of cold energy for the daytime cooling considering the practically chargeable amount of cold energy during the nighttime. Where the cooling load sharing of the storage is 40%, the nominal capacity of an ice storage tank needs to be larger than the required storage amount by 30%.
HDD에서 상대습도, 디스크 가속도, 정지시간이 슬라이더-디스크 인터페이스의 마찰대전 발생에 미치는 영향
이대영(D.Y. Lee),이재호(J. Lee),좌성훈(S.H. Choa),황정호(J. Hwang) 한국트라이볼로지학회 2006 한국윤활학회지(윤활학회지) Vol.22 No.2
In hard disk drives as the head to disk spacing continues to decrease to facilitate recording densities, slider disk interactions have become much more severe due to direct contact of head and disk surfaces in both start/stop and flying cases. The slider disk interaction in CSS (contact-start-stop) mode is an important source of particle generation and tribocharge build-up. The tribocharge build-up in the slider disk interface can cause ESD (electrostatic discharge) damage. In turn, ESD can cause severe melting damage to MR or GMR heads. The spindle speed of typical hard disk drives has increased in recent years from 5400 rpm to 15000 rpm and even higher speeds are anticipated in the near future. And the increasing disk velocity leads to increasing disk acceleration and this might affect the tribocharging phenomena of the slider/disk interface. We investigated the tribocurrent/voltage build-up generated in HOD, operating at increasing disk accelerations. In addition, we examined the effects with relative humidity conditions and rest time. We found that the tribocurrent/voltage was generated during pico-slider/disk interaction and its level was about 3~16 ㎀ and 0.1~0.3 V, respectively. Tribocurrent/voltage build-up was reduced with increasing disk acceleration. Higher humidity conditions (75~80%) produced lower levels of tribovoltage/current. Therefore, a higher tribocharge is expected at a lower disk acceleration and lower relative humidity condition. Rest time affected the charge build-up at the slider-disk interface. The degree of tribocharge build-up increased with increasing rest time.
[論文] 비례적분 방식의 피드백 공연비 콘트롤 시스템 해석
이대영(D.Y.Lee),박경석(K.S.Park),고상근(S.K.Kauh),노승탁(S.T.Ro),김응서(E.S.Kim) 한국자동차공학회 1991 오토저널 Vol.13 No.5
Air/fuel ratio control system for gasoline engines has been analyzed to determine the control gain of the system. In this analysis the engine is modelled to be a simple time delaying element and the ramp-and-jump method is used to control air/fuel ratio. The result shows that it is necessary to measure the air flow rate accurately to enhance the control performance. And also it is shown that the control gain must be determined in some bounded region to meet the fast dynamic response and high catalyst conversion efficiency together.
이진영(J. Y. Lee),이대영(D. Y. Lee),김광호(K. H. Kim),남평우(P. W. Nam) 한국유체기계학회 1999 유체기계 연구개발 발표회 논문집 Vol.- No.-
시스템의 영향을 미치는 여러 가지 인자와 시간지연의 영향에 민감한 열유동 시스템에 적합한 제어기를 설계하여 실제 시스템에 적용하여 보고자 압축기 성능시험조건을 자동으로 제어할 수 있는 냉매압축기 성능시험장치를 제작하였다. 성능시험장치 응답특성에서 시간지연은 그리 크게 나타나지 않았지만 응축기와 증발기의 상태변화가 다른 쪽의 변화에 크게 영향을 미치므로 이러한 상호간의 영향을 입력으로 취급하여 보상할 수 있는 제어방법이 요구된다.<br/> PID 제어를 열유동시스템에 적용할 경우, 외란에 대한 제어특성이 상대적으로 취약한 것을 알 수 있다. 본 연구에서는 증발기와 응축기의 상호작용을 고려하기 위하여 시간지연 보상과 다중입력 처리가 용이한 예측제어방법을 소개하였다. 현재 냉매압축기 성능시험장치용 예측제어기를 설계 중에 있다. This paper describes the control characteristics of thermal/flow systems. In thermal/flow systems, the transport lag plays as a dead time causing a deterioration of the controllability. Besides this, such many parameters including the temperature, pressure, and flow rate affect the system response that a control scheme which can deal with multi-input is required. Particularly in a refrigerant compressor test facility, the evaporator and condenser interact each other so that the change in the evaporator pressure cause the condenser pressure to change or vice versa. Therefore, to control the evaporator pressure, not only the cooling water flow rate in the evaporator but also the coolant flow rate in the condenser is considered. Meanwhile, the conventional PID controllers, which is suitable for a single input system, shows a large overshoot for a disturbance input. In this work, the predictive control scheme is introduced and its applicability is discussed for thermal/flow systems.