• 한국전산유체공학회:학술대회논문집
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• 2009.04a
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• pp.176-182
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• 2009

In the present study, a numerical simulation for the diffusion of hydrogen jet in a enclosure was performed to aid the leakage test of the hydrogen for the safety of the hydrogen vehicle. The temporal and spatial distributions of the hydrogen concentration in the test chamber are predicted from the present numerical analyses. Flammable region of 4-74% and explosive region of 18-59% hydrogen by volume was identified from the present results. Factors influencing the diffusion of the hydrogen jet were examined to evaluate the effectiveness of forced ventilation for relieving the accumulation of the leaked hydrogen gas in the chamber, which include location of open windows, size of leakage nozzle, and leakage rate among others. The distribution of the concentration of the leaked hydrogen for various cases can be used as a database in various applications for the hydrogen safety.

• Journal of computational fluids engineering
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• v.14 no.2
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• pp.32-38
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• 2009

In the present study, a numerical simulation for the diffusion of hydrogen jet in a enclosure was performed to aid the leakage test of the hydrogen for the safety of the hydrogen vehicle. The temporal and spatial distributions of the hydrogen concentration in the test chamber are predicted from the present numerical analyses. Flammable region of 4-74% and explosive region of 18-59% hydrogen by volume was identified from the present results. Factors influencing the diffusion of the hydrogen jet were examined to evaluate the effectiveness of forced ventilation for relieving the accumulation of the leaked hydrogen gas in the chamber, which include location of open windows, size of leakage nozzle, and leakage rate among others. The distribution of the concentration of the leaked hydrogen for various cases can be used as a database in various applications for the hydrogen safety.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.21 no.10
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• pp.1339-1349
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• 1997

A numerical method of calculating the performance of a scroll compressor for refrigerant R-22 and R-134a is presented in this paper. A series of involute curves are employed for the scroll wrap design and the compression volume is investigated geometrically. The radial leakage flow rate through tip clearance is calculated by the two-dimensional compressible flow. On the basis of the results, quasi one-dimensional leakage modeling can be applied to the performance analysis of a scroll compressor, more effectively. Furthermore, the heat transfer effect between scroll wrap and working fluid in compression chamber is considered for the performance analysis. As the results of this study, the effects of the radial and tangential leakage flow rate and heat transfer on the scroll compressor performance are derived precisely. These results may provide the guideline for the design and development of a real scroll compressor.

• Tribology and Lubricants
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• v.39 no.2
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• pp.61-71
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• 2023

This study proposes a procedure for designing a labyrinth seal that meets both leakage flow rate and rotordynamic performance criteria (effective damping, amplification factor, separation margin, logarithmic decrement, and vibration amplitude). The seal is modeled using a one control volume (1CV) bulk flow approach to predict the leakage flow rate and rotordynamic coefficients. The rotating shaft is modeled with the finite element (FE) method and is assumed to be supported by two linearized bearings. Geometry, material and operating conditions of the rotating shaft, and the supporting characteristics of the bearings were fixed. A single labyrinth seal is placed at the center of the rotor, and the linearized dynamic coefficients predicted by the seal numerical model are inserted as linear springs and dampers at the seal position. Seal designs that satisfy both leakage and rotordynamic performance are searched by modifying five seal design parameters using the multi-grid method. The five design parameters include pre-swirl ratio, number of teeth, tooth pitch, tooth height and tooth tip width. In total, 12500 seal models are examined and the optimal seal design is selected. Finally, normalization was performed to select the optimal labyrinth seal designs that satisfy the system performance requirements.

• The KSFM Journal of Fluid Machinery
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• v.2 no.3 s.4
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• pp.52-58
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• 1999

The leakage and rotordynamic coefficients of see-through type gas labyrinth seals are determined using a two-control-volume-model analysis with Moody's wall-friction-factor formula which is defined with a large range of Reynolds number and relative roughness. Jet flow theory are used for the calculation of the recirculation velocity in the cavity. For the reaction force from the labyrinth seal, linearized zeroth-order and the first-order perturbation equations are developed for small motion about a centered position. The leakage and rotordynamic coefficient results of the present analysis are compared with Scharrer's theoretical analysis using Blasius' wall-friction-factor formula and Pelletti's experimental results. The comparison shows that the present analysis using Moody's wall-friction-factor formula and Scharrer's theoretical analysis using Blasius' wall-friction-factor formula give the same results for a smooth seal surface and the range of Reynolds number less than $10^5$.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.11b
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• pp.799-804
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• 2002

In this paper the leakage prediction and rotordynamic analysis of an annular seal with a smooth rotor and spiral-grooved stator are performed. For developing a theoretical model, the three-control-volume analysis of the circumferentially-grooved seal is expanded by considering pressure reduction due to the pumping effect of spiral groove and pressure flow through the spiral groove. Results by the present analysis are compared with available experimental data. For leakage the analysis results generally show a reasonable agreement to the experimental results. For rotordynamic coefficients the analysis results show the same trend as the experimental results for rotor speed with spiral angles, but their magnitudes show somewhat large deviations.

• Tribology and Lubricants
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• v.24 no.6
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• pp.291-296
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• 2008

In order to improve the leakage prediction and rotordynamic analysis of an annular seal with a smooth rotor and circumferentially grooved stator, CFD analysis using FLUENT has been performed to determine the groove penetration angle a which is the angle of separation line between control volumes II and III in groove section of Ha and Lee's three-control-volume theory. Validation to the present analysis using new penetration angle determined by the CFD analysis is achieved by comparisons with the results of published Ha and Lee's analysis. For the leakage prediction the present analysis shows slight improvement and CFD results yields the best. Direct damping and cross-coupled stiffness coefficients are predicted better to the experimental ones. However, direct stiffness coefficient is predicted worse.

• Journal of the Korean Society for Precision Engineering
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• v.26 no.4
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• pp.55-63
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• 2009

This paper reports on the theoretical and experimental study of the pressure ripples in a pressure unbalanced type vane pump which have widespread use in industry. Because they can infinitely vary the volume of the fluid pumped in the system by a control. Pressure ripples occur due to the flow ripples induced by geometry of side plate, leakage flow, reverse flow from the outlet volume produced by pressure difference between pumping chamber and outlet volume when the pumping chamber connected with the outlet volume. In this paper, we measured the pressure variation of a pumping chamber, reaction force on a cam ring, the mathematical model for analyzing the pressure ripples which included vane detachment and fluid inertia effects in notch area has been presented, and was applied to predict the level and the wave form of the pressure ripples according to operating conditions.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.20 no.6
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• pp.555-560
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• 2007

This paper describes the results of a study on the sealing integrity of polymer housed surge arrester based on the thermal mechanical test. The polymer housed surge arrester employs silicone insulating materials for its housing, instead of the conventional porcelain housing. The polymer housed surge arresters exhibited the highest sealing integrity because it is not air volume between the FRP(fiber reinforced plastics) module and the silicone housing. In accordance, the sealing integrity of station class surge arresters is investigated with moisture ingress test. And, the influence of sealing integrity was evaluated through such as measurement of the deflection, reference voltage, leakage current. In electrical characteristics, reference voltage decreased in the range of $16.45{\sim}16.15\;kV$ with after thermal mechanical test. In contrary, despite the continued moisture ingress, the polymer housed surge arresters exhibited almost the same leakage current value and the resistive leakage current has risen slightly. As a results, It was thought that the polymer housed surge arresters shows good stability with sealing integrity.

• Journal of the Korean Society of Safety
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• v.29 no.6
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• pp.68-75
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• 2014

It is very important to classify explosion hazardous area (EHA) suitably and to use proper explosion-proof electric installations for facilities using flammable gases and liquids. In the past, various examples in the Notification of Ministry of Employment and Labor were referred to in classifying EHA. But, at present, many companies use the hypothetical volume in Korean Standards (KS). This study reviews the validity of EHA classification based on the hypothetical volume by comparing the calculated radii of EHA with those obtained by a consequence analysis program called PHAST and a mathematical approach in British Standards (BS). The radii of EHA by the hypothetical volume were found to be slightly larger than those by the other two methods. This was attributed to rather conservative uses of a safety factor(k) and a correction factor(f) for availability of ventilation in calculating the hypothetical volume. Since the differences are not so conspicuous, however, it is concluded that the hypothetical volume in KS is a valid means for the classification of EHA. This study also presents a table of the radii of EHA for easy reference by small-scale companies using city gas, C3-LPG and flammable liquid(toluene), respectively. The table consists of 25 leakage scenarios corresponding to combinations of 5 pipe(nozzle) sizes and 5 operating conditions for each flammable gas and liquid.