Papers by Keyword: Leak Rate

Abstract: MEMS vacuum packaging now is the impediment of the MEMS appliance in some specified fields. The major problem of current packaging approach is that the packaging process can not match the requirement of the ultra low leak. But the process now can not be improved with the existing technology. In this situation, authors proposed a novel approach for MEMS vacuum packaging, which can remarkably lower the leak rate. This paper analyzed the vacuum maintaining time of the vacuum packaging and compared the current design and new packaging method.

Abstract: One of the critical issues in designing a planar solid oxide fuel cell (SOFC) is the development of materials to hermetically seal the metal (430 series stainless steel) or ceramic interconnector with the ceramic electrolyte of the cell. The main objective of this sealing material is to achieve a low leak rate, long-term stability at operating temperature and chemical compatibility with other components. One of the compositions has been operated in an SOFC in excess of 30 minutes over the range of 600, 700, 800, and 900°C. The seal is a composition of polymer blend and glass of 1:3, 1:1 and 3:1 by weight. The leakage rate of each seal was measured simultaneously under the compressive force of 100 N, 2 bar Helium. The seal was characterized using a thermogravimetric analysis. The effect of glass composition on operating temperature and compressive forces on the leakage rate have been discussed and correlated.

Abstract: While the fact that abrasion leads to change of surface topography is taken into consideration, the influence of spring pressure both on leakage rate and on friction characteristic of contacting mechanical seals are investigated by fractal theory. Several GY-70 type mechanical seals are tested. Both theoretic analysis and test results indicate that the friction will be more serious because lubrication medium between two end faces reduces as spring pressure increases, though the increase of the spring pressure may not be enough to change the face friction state of mechanical seal. There is an optimum spring pressure for mechanical seal operation. Under different operating conditions, identical type mechanical seals may possess different spring pressure. Appropriate selection of spring pressure is key to the mechanical seal operation under the best condition.

Abstract: A primary water stress corrosion cracking (SCC) and an outside diameter SCC have occurred in the steam generator (SG) tubes of nuclear power plants around the world. It is important to establish the repair criteria for the degraded tubes to assure a reactor integrity, and yet maintain the plugging ratio within the limits needed for an efficient operation. For assessment and management of the degradation, it became crucial to understand initial leak behaviors under a small pressure and leak rate evolution under a constant pressure of SCC flaws. Stress corrosion cracked tube specimens were prepared by using a room temperature cracking technique, and leak behaviors of these tubes were measured at room temperature. Water pressure inside the tube was increased slowly in a step like manner with a designated holding time. Water leak rates just after a ligament rupture were measured by collecting the leaked water in a plastic container for a designated time. A leak rate was calculated by dividing the amount of water by the time. Under 3.45 MPa, a small water droplet was formed, but it did not grow after a 10 minute holding period at a constant pressure of 3.45 MPa. A throughwall crack seemed to open at around 8.28 MPa (1200 psi). Some tubes with 100 % through wall cracks did not show a leakage at 10.8 MPa, which is a typical pressure difference of pressurized water reactors (PWRs) during a normal operation. The higher the pressure was applied, the larger the rates of increase with the time were. Axial cracks showed a lower leak pressure than that of the circumferential cracks, which might be from a higher hoop stress than the axial stress. A large open and long axial crack showed an increasing leak rate with the time at a constant pressure.

Abstract: This study is to estimate the feasibility of acoustic emission(AE) method for the internal leak from the valves. In this study, two types of valve(a 4 inch glove steam valve and 4 inch ball water valve) leak tests using three different leak path and various leak rates were performed in order to analyze AE properties when leaks arise in valve seat. As a result of leak test for specimens simulated valve seat, we conformed that leak sound amplitude increased in proportion to the increase of leak rate, and leak rates were plotted versus peak acoustic amplitudes recorded within those two narrow frequency bands on each spectrum plot. The resulting plots of leak rate versus peak AE amplitude were the primary basis for determining the feasibility of quantifying leak acoustically. The large amount of data attained also allowed a favorable investigation of the effects of different leak paths, leak rates, pressure differentials and AE sensors on the AE amplitude spectrum. From the experimental results, it was suggested that the AE method for monitoring of leak was feasible.

Abstract: The Korea Research Institute of Standards and Sciences has developed and maintained leak standards systems, and has accumulated much data on leak standards that have been disseminated during calibration and testing services. We have found that the indicative value of a leak detector and a halogen leak detector varies a lot, depending on the conditions encountered during sniffer mode operation. Therefore, to measure the reliability of the leak rate or when performing a leak test, proper test conditions are necessary. In addition, we found that the reliability increased when we used a guide tube that could influence the flow of air.

Abstract: Porous composites containing ceramic fiber have been developed for the fabrication of SOFC seals. They were fabricated using glass powder and alumino-silicate chopped fibers. Effect of mixing ratios of ceramic fiber and glass on the leak rates and strength of the composite seals was investigated. In addition, seal performance of commercial glasses was compared with that of SiO2-BaO-B2O3 glass synthesized in this work. The leak rate of the composite seals containing 55 vol% glass was seven times higher than the one containing 75 vol% glass. The flexural strength of the composite seals was reduced to one fourth of the initial value as the porosity increased from 1 to 29%. The incorporation of alumino-silicate chopped fibers into a sealing glass degraded room temperature strength and increased leak rates due to increase in porosity with increasing fiber content. The viscosity of glass at the seal test temperature is presumed to affect the leak rate of the glass seal.