• 한국항공우주학회지
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• 제36권1호
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• pp.7-13
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• 2008

본 논문에서는 유한요소법을 기반으로 한 소프트웨어 COMSOL Multiphysics를 이용하여 압전 복합재료 작동기를 이용하여 제작한 무밸브 마이크로펌프의 성능을 연구하였다. 압전 마이크로펌프는 4층의 경량 압전 복합재료 작동기, PDMS으로 된 챔버와 2개의 디퓨저로 이루어졌다. 시뮬레이션에서는 압전 재료 영역, 구조 영역과 유체 영역을 완전 연성하여 해를 계산하였다. 물을 유체로 사용하였으며, 유량을 마이크로펌프의 구조적 파라미터에 대하여 계산하였다. 이 연구에 기초하여 보다 성능이 좋은 마이크로펌프를 제시하였다.

• 한국항공운항학회지
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• 제13권4호
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• pp.92-99
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• 2005

A closed-circuit type wind tunnel is designed, which has a test section with the dimensions $1.2(W){\times}1.2(H){\times}3.4(L)$. A subsonic wind tunnel is designed to improves educational circumstances and promote ground tests. It is constituted of an exchangeable test section, first and second diffusers, a fan, a settling chamber, a contraction, and 4 corners. The maximum velocity in the test section is 70m/s and the contraction ratio is 6.25:1. Input power in the wind tunnel is about 96.1 kw (128.8 hp) and its energy ratio is 3.89. It has the dimension of about $7.4(W){\times}3.6(H){\times}21.7m(L)$. The wind tunnel designed in this investigation will be an effective educational and investigational equipment.

• 설비공학논문집
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• 제10권1호
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• pp.66-78
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• 1998

Adequate ventilation with the proper amount of air to the right place is important factor to achieve a good Indoor air climate. Thus it is of prime importance that the ventilation system is working properly. This requires reliable pressure loss calculation to balance the air flow through duct systems. So a computer program for balancing CAV duct system is developed In this study. The results of CAV duct system is compared with the "Balans" code developed by Larsen from Norway. To obtain the pressure drop characteristics of damper at duct terminal, some experiments are performed using DPM(Dual Pressure Measurement) system. To adjust the resistance of damper, present study suggests that some special diffusers should be designed and damper producers should give the data of air flow vs. pressure drop to the customs when they manufacture the damper. One of the results concludes that the working time can be reduced from several minutes to several seconds per damper in the present experimental site, if the DPM system and the air volume adjusting process are used.

• Journal of Information Display
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• 제7권2호
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• pp.6-11
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• 2006

New photopolymers were designed and prepared using the photosensitive polymer binders. Holographic gratings were successfully fabricated in these photopolymer samples by a conventional optical interference method. We also investigated the effect of photocrosslink in the polymer binder on the diffraction behavior of a new photopolymer. The dynamic behavior of the grating formation was monitored by changing exposure intensity in terms of the diffraction efficiency. Particularly, we focused our efforts in observing the variation of diffraction efficiency during a post UV curing process. The surface topographical change of photopolymer layer before and after Vis/UV light exposure was observed by atomic force microscope (AFM). We inscribed the gratings of the glass diffuser on the surface of the photopolymer and investigated their diffusing properties. The diffusers with photopolymer with the main chain polymer binder showed relatively good viewing angle of around ${\pm}30{\circ}$. Two kinds of photopolymer showed similar uniformity of around 47-54%.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 추계학술대회논문집B
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• pp.447-452
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• 2000

In this study, the design of Free-Fall Simulator was carried out using concept of vertical wind tunnel. Free-Fall Simulator is not an experimental equipment but a training equipment. Therefore Free-Fall Simulator needs a large training section compared with test section of wind tunnel and has critical limit of height. These limits bring about the difficulty of design for a return passage. Due to small area ratio, the downstream flow of training section with high speed is not decelerated adequately to the fan section. High-speed flow leads to great losses in the small area ratio diffuser and corner. So design of diffusers and corners located between training section and fan section has a great effect on the Free-Fall Simulator performance. This study used an estimation method of subsonic wind tunnel performance. It considered each section of Free-Fall Simulator as an independent section. Therefore loss of one section didn't affect loss of other sections. Because losses of corner with vane and $1^{st}$ diffuser are most parts of overall Free-Fall Simulator, this study focused on the design of these sections.

• Journal of Advanced Marine Engineering and Technology
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• 제31권8호
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• pp.939-946
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• 2007

The purpose of this study is to measure and analyze the ship's indoor thermal conditions and also to integrate experimental database of those, supplied and controlled by ship's HVAC. On this study, temperature, humidity and air volume of 6 different needs' cabin are measured on a newly-launched training ship during 2nd through 5th of April, 2007. Followings are the results of this study. (1)Because only partial loads are needed in spring season, the air volume from diffusers are measured as below 20%. (2)The temperatures are ranged between $20{\sim}25^{\circ}C$ and those are within comfort temperature range proposed by AHREA. (3)But humidities in cabins are very low and it could be the reason of a cold and/or a skin disease. (4)From the student cabins' measurements which have different supply diffuser(s), it is clear that the design is suitable for this case. (5)Because of low humidity, only 16.1% among the measured data are satisfied with the comfort standard range proposed by ASHREA. To improve the predictability and the comfort, HVAC should maintain the humidity as $40{\sim}60%$.

• Environmental Engineering Research
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• 제17권1호
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• pp.3-8
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• 2012

A scaled-up bioconversion of fishmeal wastewater (FMW) into liquid fertilizer was performed five times in a $1m^3$ reactor in order to examine the feasibility of commercialization. The importance of aeration was marked. Analyses indicated that dissolved oxygen (DO) level was closely related to the value of oxidation-reduction potential (ORP) and it was crucial to achieve high-quality liquid fertilizer. When pure oxygen was supplied through four diffusers into the reactor, DO levels and ORP values were maintained over 1.2 mg/L and 0.2 mV, respectively all the time during 52 hr of bioconversion. The pH changed from 6.8 to 5.9. The average removal percentages of chemical oxygen demand ($COD_{Cr}$) and total nitrogen (TN) were 75.0% and 71.6%, respectively. Compared to the result acquired in a 5-L reactor, bioconversion of FMW into liquid fertilizer was achieved in a shorter time under the same removal percentages of $COD_{Cr}$ and TN. The 52-hr culture of inoculated FMW was phytotoxic-free and it possessed comparable fertilizing ability to a liquid fertilizer made from the fish waste in hydroponic culture with amino acid contents of 5.93 g/ 100 g sample. From all the above results, transferring lab-scale data to large-scale production appeared to be successful. As a result, the commercialization of a liquid fertilizer made from FMW was feasible.

• 한국자동차공학회논문집
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• 제5권2호
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• pp.136-148
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• 1997

The present study has been carried out to develop a computational procedure for the analysis of the off-design performance in centrifugal compressors with vaneless diffusers by integrating empirical loss models and analytical equations. Losses in centrifugal compressors stem from a number of sources and their exact calculation is not yet possible. This study investigates several modeling schemes and shows that a fairly good prediction can be achieved by a proper selection of the most important flow parameters resulting form a meanline one-dimensional analysis. The performance maps for compressors are calculated and compared with measured performance maps. The off-design performance characteristics in terms of the pressure ratio vs. mass flow produced have generally correct forms. However, no universal means have been found to predict accurately the onset of surge. The prediction method developed through this study can serve as a tool to ensure good matching between parts and it can assist the understanding of the operational characteristics of general purpose centrifugal compressors.

• 신재생에너지
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• 제1권4호
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• pp.30-37
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• 2005

Cycle simulation of Ground Source Heat Pump[GSHP] system was carried out to determine the design specification of basic components such as turbo compressor and heat exchangers. Part load operation characteristics of the designed GSHP system was estimated using the compressor and heat exchanger performance data. A 50RT class turbo compressor for GSHP system is now under development, in which R134a refrigerant is adopted as working fluid. The compressor with variable cascade diffusers is designed to work both in cooling and heating modes so that it can actively keep up with the climate change with high efficiency. The normal running speeds of the compressor are 59000rpm for heating mode and 70000rpm for tooling mode respectively. It has two identical impellers at both ends of the rotor so as to minimize aero-induced thrust force effectively. GSHP system was coupled with a vortical type heat exchanger, and heat gain and heat loss from ground were evaluated per a bore hole. For the optimal integration of the heat pump system, its header for circulating fluid was combined with the ground heat exchangers in parallel and series configuration.

• Journal of Information Display
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• 제5권1호
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• pp.22-27
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• 2004

Photopolymers are quite promising candidates for holographic data storage and diffusers because of their high sensitivity and high refractive index modulation. New photopolymers were prepared using the cellulose ester binder bearing different kinds of monomer. The holographic gratings were elaborated successfully in these photopolymer samples by conventional optical interference method. We investigated the dynamic behavior of the diffraction efficiency and the effect of the functionality of the monomer doped into the polymer binder. Triacrylate monomer doped photopolymer showed the highest diffraction efficiency of around 80-90 %, even under low intensity of writing beam (I=2 mW/$cm^2$). We inscribed the gratings of the glass diffuser on the surface of the photopolymer and investigated their diffusion properties.