• Title/Summary/Keyword: surface pressure measurement

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Measurement of the Film Cooling Effectiveness on a Flat Plate using Pressure Sensitive Paint (압력감응페인트를 이용한 평판에서의 막냉각 계수 측정)

  • Park, Seoung-Duck;Lee, Ki-Seon;Kim, Hark-Bong;Kwak, Jae-Su;Kim, Jae-Hwan
    • Journal of the Korean Society of Propulsion Engineers
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    • v.12 no.5
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    • pp.67-72
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    • 2008
  • The film cooling effectiveness on a flat plate measured by pressure sensitive paint technique. Six film cooling hole were fabricated on a flat plate with 30 degree angle with respect to the surface and three blowing ratios of 0.5, 1, and 2 were tested. Results showed that PSP technique successfully evaluated the distribution of film cooling effectiveness and showed similar results with references. The film cooling effectiveness near the film cooling holes was higher for lower blowing ratio case. As the blowing ratio was increased, the film cooling effectiveness near the film cooling hole decreased due to the lift off of the coolant. At far downstream, the film cooling effectiveness for higher blowing ratio was higher due to the coolant reattachment.

In-situ spectroscopic studies of SOFC cathode materials

  • Ju, Jong-Hun
    • Proceedings of the Materials Research Society of Korea Conference
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    • 2012.05a
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    • pp.70.1-70.1
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    • 2012
  • In-situ X-ray photoelectron spectroscopy (XPS) and infrared (IR) spectroscopy studies of SOFC cathode materials will be discussed in this presentation. The mixed conducting perovskites (ABO3) containing rare and alkaline earth metals on the A-site and a transition metal on the B-site are commonly used as cathodes for solid oxide fuel cells (SOFC). However, the details of the oxygen reduction reaction are still not clearly understood. The information about the type of adsorbed oxygen species and their concentration is important for a mechanistic understanding of the oxygen incorporation into these cathode materials. XPS has been widely used for the analysis of adsorbed species and surface structure. However, the conventional XPS experiments have the severe drawback to operate at room temperature and with the sample under ultrahigh vacuum (UHV) conditions, which is far from the relevant conditions of SOFC operation. The disadvantages of conventional XPS can be overcome to a large extent with a "high pressure" XPS setup installed at the BESSY II synchrotron. It allows sample depth profiling over 2 nm without sputtering by variation of the excitation energy, and most importantly measurements under a residual gas pressure in the mbar range. It is also well known that the catalytic activity for the oxygen reduction is very sensitive to their electrical conductivity and oxygen nonstoichiometry. Although the electrical conductivity of perovskite oxides has been intensively studied as a function of temperature or oxygen partial pressure (Po2), in-situ measurements of the conductivity of these materials in contact with the electrolyte as a SOFC configuration have little been reported. In order to measure the in-plane conductivity of an electrode film on the electrolyte, a substrate with high resistance is required for excluding the leakage current of the substrate. It is also hardly possible to measure the conductivity of cracked thin film by electrical methods. In this study, we report the electrical conductivity of perovskite $La_{0.6}Sr_{0.4}CoO_{3-{\delta}}$ (LSC) thin films on yttria-stabilized zirconia (YSZ) electrolyte quantitatively obtained by in-situ IR spectroscopy. This method enables a reliable measurement of the electronic conductivity of the electrodes as part of the SOFC configuration regardless of leakage current to the substrate and cracks in the film.

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Open-jet boundary-layer processes for aerodynamic testing of low-rise buildings

  • Gol-Zaroudi, Hamzeh;Aly, Aly-Mousaad
    • Wind and Structures
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    • v.25 no.3
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    • pp.233-259
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    • 2017
  • Investigations on simulated near-surface atmospheric boundary layer (ABL) in an open-jet facility are carried out by conducting experimental tests on small-scale models of low-rise buildings. The objectives of the current study are: (1) to determine the optimal location of test buildings from the exit of the open-jet facility, and (2) to investigate the scale effect on the aerodynamic pressure characteristics. Based on the results, the newly built open-jet facility is well capable of producing mean wind speed and turbulence profiles representing open-terrain conditions. The results show that the proximity of the test model to the open-jet governs the length of the separation bubble as well as the peak roof pressures. However, test models placed at a horizontal distance of 2.5H (H is height of the wind field) from the exit of the open-jet, with a width that is half the width of the wind field and a length of 1H, have consistent mean and peak pressure coefficients when compared with available results from wind tunnel testing. In addition, testing models with as large as 16% blockage ratio is feasible within the open-jet facility. This reveals the importance of open-jet facilities as a robust tool to alleviate the scale restrictions involved in physical investigations of flow pattern around civil engineering structures. The results and findings of this study are useful for putting forward recommendations and guidelines for testing protocols at open-jet facilities, eventually helping the progress of enhanced standard provisions on the design of low-rise buildings for wind.

Optimization of the deposition condition on hetero-epitaxial As-doped ZnO thin films by pulsed laser deposition (PLD를 이용한 hetero-epitaxial As-doped ZnO 박막 증착 조건의 최적화)

  • Lee, Hong-Chan;Jung, Youn-Sik;Choi, Won-Kook;Park, Hun;Shim, Kwang-Bo;Oh, Young-Jei
    • Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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    • 2005.07a
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    • pp.207-210
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    • 2005
  • In order to investigate the influence of the homo buffer layer on the microstructure of the ZnO thin film, undoped ZnO buffer layer were deposited on sapphire (0001) substrates by ultra high vaccum pulsed laser deposition (UHV-PLD) and molecular beam eiptaxy (MBE). After high temperature annealing at $600^{\circ}C$ for 30min, undoped ZnO buffer layer was deposited with various oxygen pressure (35~350mtorr). On the grown layer of undoped ZnO, Arsenic-doped(l, 3wt%) ZnO layers were deposited by UHV-PLD. The optical property of the ZnO was analyzed by the photoluminescence (PL) measurement. From $\Theta-2\Theta$ XRD analysis, all the films showed strong (0002) diffraction peak, and this indicates that the grains grew uniformly with the c-axis perpendicular to the substrate surface. Field emission scanning electron microscope (FE-SEM) revealed that microstructures of the ZnO were varied with oxygen pressure, arsenic doping level, and the deposition method of undoped ZnO buffer layers. The films became denser and smoother in the cases of introducing MBE-buffer layer and lower oxygen pressure during As-doped ZnO deposition. Higher As-doping concentration enhanced the columnar-character of the films.

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Improvement of In-Situ Stress Measurements by Hydraulic Fracturing - Focusing on the New Standard by Japanese Geotechnical Society (수압파쇄를 이용한 초기응력 측정 결과의 신뢰도 제고 방안 - 일본 지반공학회 표준시험법 개정안을 중심으로)

  • Kim, Hyung-Mok;Lee, Hangbok;Park, Chan;Park, Eui-Seob
    • Tunnel and Underground Space
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    • v.32 no.1
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    • pp.1-19
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    • 2022
  • In this report, new standard, published by Japanese Geotechnical Society, on in-situ stress measurements by hydraulic fracturing was reviewed. In the standard, modification was made for the calculation of fracture re-opening pressure in consideration of fracture surface roughness and residual aperture. The standard also presents how much the system compliance influences the estimation of the fracture re-opening pressure and subsequent in-situ stresses. It is shown that the stiffer the rock mass is, the system compliance should be sufficiently small enough so as to obtain in-situ stress measurement with higher confidence.

Evaluation of Uplift Force Acting on Foundation of Underground Structure (지하구조물 하부에 작용하는 양압력 평가)

  • Kim, Jin-Man;Han, Heui-Soo
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.21 no.11
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    • pp.662-671
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    • 2020
  • The uplift force acts directly on the foundation and causes a building to float to the upper ground. To examine the stability of a structure according to the uplift force, four sites (Paju, Anyang, Osan, and Gangneung) were selected, and sensors were installed on the foundations for the field tests. The rainfall characteristics were analyzed around June~September, and the changes in the water level of the adjacent river were considered. The maximum uplift force except for Gangneung did not exceed 72% of the water pressure when the groundwater level was up to the surface. On the other hand, the maximum uplift force in Osan was approximately 67%, but the reliability was slightly inferior because the difference from the average (46%) was large. The minimum uplift force was within 10% except for Anyang (~ 41%). At the Gangneung site on soft rock where the permanent drainage facility was installed before the measurement, the maximum and minimum uplift force was approximately 14% and 3.5%, respectively. Based on the measurement results, the possibility of overdesigning or underdesigning comes from the design by the hydrostatic pressure when the groundwater level is up to the surface.

An Experimental Study on Mode ll Fracture Toughness Determination of Rock (암석의 전단 파괴인성 측정에 관한 실험적 연구)

  • 윤정석;전석원
    • Tunnel and Underground Space
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    • v.13 no.1
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    • pp.64-75
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    • 2003
  • This study presents a newly suggested test method of Mode II fracture toughness measurement called "Punch Through Shear Test" which was originally proposed by Backers and Stephansson in 2001. The purpose of this study is to check the validity of the suggested testing method by performing Mode II fracture toughness tests for Daejeon Granite. In addition, the optimal specimen geometry for the testing and the relation between Mode II fracture toughness and confining pressure were also investigated. Fractured surface was observed to be very smooth with lots of rock debris which came off fracture surface which obviously implies that the surface was sheared off. This confirms that Mode II fracturing actually occurred. In addition, numerical analyses including continuum analysis, particle flow code analysis and crack propagation simulations were performed. Results of these numerical analyses indicated that the cracks occurred in the specimen were predominantly in Mode II and these cracks led to failure of the test specimen. From this investigation, it can be concluded that the newly suggested "Punch Through Shear Test" method provides a reliable means of determining the Mode II fracture toughness. fracture toughness.

Measurement of Adiabatic Wall Temperature on an Impinging Surface by Under-expanded Jet (과소팽창된 충돌제트에 의한 단열벽면 온도 측정)

  • Yu, Man-Sun;Lee, Jang-Woo;Kim, Byung-Gi;Cho, Hyung-Hee;Hwang, Ki-Young;Bae, Ju-Chan
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.33 no.4
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    • pp.79-84
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    • 2005
  • An experimental investigation for impingement of under-expanded, axisymmetric jets on a flat plate has been conducted, and the surface pressure, the adiabatic wall temperature distributions on the plate have been measured in detail. For the explanation on the wall temperature distributions, the total temperature distributions along a free jet have also been measured with total temperature probes. In this study, the under-expansion ratio and the nozzle-to-plate distance have been considered as experimental parameters. Depending on nozzle-to-plate distances, different distributions of adiabatic wall temperature are shown by the energy separation at a jet edge and a impinged surface. Also, the recovery factor on a stagnation point decreases significantly due to the isolation of fluid particles in a central region.

A Study on Failure Mode of Pipe Elbows with Wall Thinning (두께 감소된 배관 엘보우의 파손 모드에 대한 연구)

  • Shin, Kyu-In;Yoon, Kee-Bong
    • Journal of the Korean Institute of Gas
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    • v.12 no.2
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    • pp.57-62
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    • 2008
  • Difference of failure modes was studied by finite element analysis for elbows with local wall thinning area particularly at inner surface of intrados of the elbow. Longitudinal wall thinning length, minimum thickness were kept constant but circumferential wall thinning width was varied to get $90^{\circ}$, $180^{\circ}$ and $360^{\circ}$ thinning width. Elastic-plastic analysis were carried out under the combined loading conditions of internal pressure and in-plane bending moment closing the elbow. Von Mises stress were obtained from the outer surface central surface location in intrados, extrados and crown parts in elbow. The results showed that the plastic deformation and failure started from the crown location when the thinning width small ($90{\sim}180^{\circ}$). However, plastic collapse started from the intrados location when the thinning width is approaching $360^{\circ}C$. This should be reflected to assess structural integrity of elbows after wall thinning measurement is made.

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A Study on the Injection Mold with Superhydrophobic Surface Properties Using Nanosecond Laser Machining (나노초 레이저 가공을 활용한 초소수 표면 특성을 가지는 사출 금형에 관한 연구)

  • Jung-Rae Park;Hye-Jin Kim;Ji-Young Park;Si-Myung Sung;Seo-Yeon Hong;Ki-Hyeok Song
    • Design & Manufacturing
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    • v.17 no.3
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    • pp.48-54
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    • 2023
  • In this study, an injection mold with ultra-small surface properties was manufactured using nanosecond laser processing. A superhydrophobic characteristic analysis was performed on the PET specimen manufactured through this. To this end, a hydrophobic pattern was defined using the Cassie-Baxter model. The defined features were selected with a spot diameter of 25um and pitch spacing of 30um and 35um. As a result of the basic experiment, it was confirmed that the fine pattern shape had an aspect ratio of 1:1 when the pitch interval was 35um and 20 iterations. Through the determined processing conditions, a hydrophobic pattern was implemented on the core surface of KP4. A specimen with a hydrophobic pattern was produced through injection molding. The height of the molded hydrophobic pattern is 20 ㎛ less than the depth of the core and the contact angle measurement results are 92.1°. This is a contact angle smaller than the superhydrophobic criterion. Molding analysis was performed to analyze the cause of this, and it was analyzed that the molding was not molded due to the lack of pressure in the injection machine.