• 한국광학회지
• /
• 제33권4호
• /
• pp.159-166
• /
• 2022

본 연구에서는 이중 슬릿 회절 실험을 이용하여 박막의 두께와 굴절률을 측정하는 실험을 수행하였다. 투명 기판 위에 입혀진 박막이 만드는 투과광의 위상 단층의 크기를 이중 슬릿을 통과하여 나타나는 회절 패턴을 분석하여 측정하였다. 이로부터 두께와 굴절률을 동시에 결정하기 위해 공기와 증류수 속에서 각각 한 번씩 실험을 수행하였다. 이 방법의 유효함을 확인하기 위해 도파로 결합법으로 측정한 두께와 굴절률과 비교하였다. 본 연구에서 제안한 측정법은 기존의 선행 연구들과 더불어 박막의 두께와 굴절률을 동시에 측정할 수 있는 새로운 방법으로 응용될 수 있을 것으로 기대된다.

• KIEAE Journal
• /
• 제1권2호
• /
• pp.47-54
• /
• 2001

Single sound absorbers such as porous materials, panels, and Helmholts resonators have limited performance with some extents of frequency region. For example, porous materials do not attenuate low frequency sounds, while panels do not absorb high frequency sounds. Composite absorption structure with coverings, porous materials, and air gaps are an alternative for wide band sound absorption. Slits, panels, perforated panels are those materials for coverings, glass wool, mineral wool, polyester, and polyurethane are frequently used porous materials. Air gap between the porous material and background surface is one of major factors which governs the absorption characteristics of composite absorption structures, especially in the low frequency area. Calculations and measurements show that the absorption coefficients of composite absorption structure, in mid and low frequency bands, are getting higher with increased air gaps. Perforated panels rather than slits and panels are good coverings with higher number as far as absorption coefficient is concerned. Perforated panels with porous materials and 37 cm of air gaps in background have high absorption coefficients for all frequency bands, above 0.7 to 1.0. All measurements are performed in reverberation chamber, Mokpo National University, according to ISO 354 and ISO 3382.

• 대한기계학회논문집B
• /
• 제31권7호
• /
• pp.611-619
• /
• 2007

In this study, the droplet size distribution of a slit injector at different surrounding conditions, such as air flow and fuel temperature, were investigated. Phase Doppler anemometry (PDA) was utilized to investigate the initial droplet size distribution and the effect of fuel temperature and air flow on droplet size distribution. The entrained air motion was also evaluated by the temporal velocity profile of droplets. When the air flow velocity increased, the small droplets were more entrained to the upper and central parts of the spray and this tendency was confirmed by plotting the temporal velocity profile of droplets. This entrainment of small droplets at high airflow velocities caused relatively small mean droplet size at upper and central parts of the spray and the large mean droplet size at downstream and edge of the spray, compared to that of low airflow velocities. The total mean droplet size, obtained by averaging the size of all droplets measured at all test locations, decreased when the high airflow velocities were applied. The increased fuel temperature, with an airflow velocity of 10m/s, caused reduced droplet size at all test locations. However, the decreased value of mean droplet size at high fuel temperatures was relatively higher at upper parts of the spray, compared to downstream, as a result of enhanced entrainment of small droplets to upper parts of the spray.

• 대한설비공학회:학술대회논문집
• /
• 대한설비공학회 2008년도 동계학술발표대회 논문집
• /
• pp.519-524
• /
• 2008

In the present study, the air-side heat transfer and pressure drop characteristics of the fin-tube and PF heat exchangers have been experimentally investigated under the cooling standard condition. Fin type of PF heat exchanger is a triangler and squarer form. The experimental data of the slit fin-tube and two kinds of PF heat exchangers are measured using the air-enthalpy calorimeter and the constant temperature water bath. As the inlet air velocity increases, the heat transfer rate and pressure drop of the heat exchanger increased. The heat transfer rate and pressure drop of PF-2 heat exchanger of the squarer fin is larger than that of PF-1 heat exchanger of the triangler fin. As the inlet air temperature increases, the heat transfer rate decreases and the pressure drop is nearly uniform.

• 대한기계학회논문집B
• /
• 제29권9호
• /
• pp.1032-1041
• /
• 2005

This study is performed to investigate the heat transfer characteristics of heat exchanger according to the arrangement of fins as well as fin configuration by using the four times enlarged model. Friction factor, Colburn j factor and goodness factors are compared to each other to estimate performance of each case for 4 different kinds of fins, which are plain, single side slit, double side slit and louver fin. Results show that heat transfer would be altered by fin arrangement and that friction loss is more affected by fin configurations than by the fin arrangements. In particular, heat transfer depends more on the shape of front row than that of rear row. The heat transfer rate of combined fin arrangement increases a lot more under the same pressure drop than that of conventional fin arrangement. This indicates that the heat exchanger of higher efficiency would be designed by the proper combination of fins, of different shapes.

• 대한기계학회논문집B
• /
• 제22권11호
• /
• pp.1555-1563
• /
• 1998

Heat transfer and pressure drop for ${\phi}10.07$ dry surface fin-tube heat exchanger with wave and wave-slit fins were measured for different fin spacings and number of tube rows. Longitudinal and transverse tube spacings of the heat exchangers are 21.65mm and 25mm respectively, and wave depth of wave fin is 1.5mm. The experiments were performed for 4 different fin spacings, 1.3, 1.5, 1.7 and 2.0mm, and the number of tube rows were 1,2 and 3 rows. The present results were compared with the previous results for the wave depth of 2mm. Also hydrophilic coated and bare fins were tested. Correlations for Colburn j-factor and friction factor were developed.

• 한국추진공학회지
• /
• 제24권6호
• /
• pp.53-60
• /
• 2020

액체연료 분무 연소에서 화염 외부에 정상초음파 가진을 통해 압력장을 조절함으로써 초음파 무화액체연료 화염에 미치는 초음파 가진의 영향을 관찰하는 실험을 수행하였다. 초음파에 의해 미립화된 케로신 에어로졸화염은 초고속카메라, DSLR 그리고 슐리렌 촬영기법을 이용하여 가시화하였다. 연소시 소모된 연료량은 정밀유량측정법으로 계측하였고, 이를 통해 수송기체 공연비를 구할 수 있었다. 실험결과, 2차화염영역에 정상초음파를 가함에 따라 액체연료 에어로졸의 연소반응률이 증대되는 것을 관찰할 수 있었다.

• 한국추진공학회지
• /
• 제20권3호
• /
• pp.9-16
• /
• 2016

초음파 진동자에 의해 미립화된 탄화수소계 액체연료 분사화염의 연소특성을 고찰하기 위한 실험이 수행되었다. 초고속카메라를 이용하여 미립화된 액체연료의 화염형상을 획득하였고, 이미지 후처리를 통해 화염의 구조와 거동을 면밀히 분석하였다. 또한 정밀유량계측법을 이용하여 연소반응 시 소모된 연료량도 측정하였다. 그 결과, 수송기체 유량이 증가하면 무화된 연료의 분사량도 같이 증가하였으나, 공연비(air/fuel ratio)와 수송기체 유량의 상관성은 관찰되지 않았다. 화염면적은 공연비 보다는 연료의 분사량과 진동자 인가전력에 종속하였으며, 화염면적의 FFT 분석을 통해 생성화염의 진동특성도 고찰하였다.

• 대한화학회지
• /
• 제37권6호
• /
• pp.549-554
• /
• 1993

티타늄 금속판을 공기산화와 수증기 산화하여 만든 Ti$O_{2-x}$ 박막을 시료로 사용하여 1M NaOH 용액에서 광전기화학적 성질을 연구하였다. 높은 온도에서 제조된 Ti$O_{2-x}$ 전극들은 낮은 온도에서 제조된 전극들보다 더 음의 값으로 주어지는 flat band potential($V_{fb}$)과 더 높은 donor density($N_D$)를 가졌다. 전극전위의 변화에 따른 광전류 측정과 Mott-Schottky plot로부터 얻은 $V_{fb}$는 -0.95 ∼ -1.1 V 사이에서 비슷한 값으로 주어졌다. 자외부 영역의 광을 완전히 차단하는 TiO2 단결정을 필터로 하여 가시부 영역의 광전류를 측정할 때 분해능이 좋은 slit를 사용한 경우 좋은 sub band gap 광반응을 볼 수 있었다.

• 유체기계공업학회:학술대회논문집
• /
• 유체기계공업학회 2003년도 유체기계 연구개발 발표회 논문집
• /
• pp.238-244
• /
• 2003

An experimental study was performed to examine the heat transfer performance of individual rows of fin-tube heat exchangers. The heat transfer performance was measured using air-enthalpy type calorimeter. The examined heat exchangers consists of $7{\Phi}$ tube and fin patterns of them are slit and louver types. Equivalent fin spacing are 18 FPI for all samples, and the number of tube rows were 2. In order to confirm that thermal boundary condition on fins of each row are the same, physically separated between two rows as well as connected heat exchangers were used. The frontal air velocity varied from 0.7 to 2.5 m/s. Heat transfer performance for each row are measured. It was observed that the heat transfer coefficient of the 2nd row were smaller than that of the 1st row at low Reynolds number while larger at high Reynolds number.