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RISS 인기검색어
- 검색키워드
- 저자 : N. W. Mureithi (검색결과 4 건)
- 무료
- 기관 내 무료
- 유료
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Parametric study of two-phase flow by integral analysis based on power law distribution
심우건,N. W. Mureithi,M. J. Pettigrew 대한기계학회 2010 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.24 No.7
To understand the fluid dynamic forces acting on a structure subjected to two-phase flow, it is essential to obtain detail information on the characteristics of that flow. The distributions of flow parameters across a pipe, such as gas velocity, liquid velocity and void fraction,may be assumed to follow a power law (Cheng 1998; Serizawa et al. 1975). The void fraction profile is, for example, uniform for bubbly flow, whereas for slug flow it is more or less parabolic. In the present work, the average values of momentum flux, slip ratio and other parameters were derived by integral analysis, based on approximate power law distributions. A parametric study with various distributions was performed. The existing empirical formulations for average void fraction, proposed by Wallis (1969), Zuber et al. (1967) and Ishii (1976), were considered in the derivation of the present results. Notably, the unsteady momentum flux for slug flow was approximated.
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A two-phase damping model on tube bundles subjected to two-phase cross-flow
심우건,N. W. Mureithi 대한기계학회 2014 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.28 No.2
An analytical model is developed to estimate the two-phase damping ratio for upward cross-flow through horizontal tube bundles. Thepresent model is formulated based on Feenstra’s model (2000) for void fraction and various models (homogeneous, Levy, Martinelli-Nelson and Marchaterre) for two-phase friction multiplier. The analytical results of drag coefficient on a cylinder and two-phase Eulernumber are compared with the experimental results by Sim-Mureithi (2013). The correlation factor between frictional pressure drop andthe hydraulic drag coefficient is evaluated by considering the experimental results. The two-phase damping ratios given by the analyticalmodel are compared with existing experimental results. The model based on Marchaterre’s model is suitable for air-water mixture,whereas the Martinelli-Nelson’s model is suitable for steam-water and Freon mixtures. The two-phase damping ratio is independent ofpitch mass flux for air-water mixture, but is more or less influenced by the mass flux for steam-water/Freon (134) mixtures. The twophasedamping ratios given by the present model agree well with experimental results for a wide range of pitch mass ratio, quality, andp/d ratios.
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An experimental study on characteristics of two-phase flows in vertical pipe
심우건,B. M. Bae,N. W. Mureithi 대한기계학회 2010 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.24 No.10
The characteristics of two-phase flow in a vertical pipe are investigated to provide information for understanding the excitation mechanisms of flow-induced vibration. An analytical model for two-phase flow in a pipe was developed by Sim et al. (2005), based on a power law for the distributions of flow parameters across the pipe diameter, such as gas velocity, liquid velocity and void fraction. An experimental study was undertaken to verify the model. The unsteady momentum flux impinging on a ‘turning tee’ (or a ‘circular plate’) has been measured at the exit of the pipe, using a force sensor. From the measured data, especially for slug flow, the predominant frequency and the RMS value of the unsteady momentum flux have been evaluated. It is found that the analytical method, given by Sim et al. for slug flow, can be used to predict the momentum flux.
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Kang, H.S.,Mureithi, N.W.,Pettigrew, M.J. Academic Press 2012 Journal of fluids and structures Vol.35 No.-
An analytical model of annular-flow-induced vibration of a pinned-pinned cylinder is proposed. The model is based on three main assumptions: (i) small perturbations in flow components, (ii) negligible radial flow to reduce the annular flow to two-dimensional flow, and axial flow only for reduction to a one-dimensional flow, and (iii) perturbation frictional loss depending on the variation of axial perturbation velocity in terms of space and time. In this study, it is concluded that (a) the difference in fluidelastic forces between two- and one-dimensional flow models mostly depends on cylinder radius, and on whether perturbation flow is mainly allowed in the axial or circumferential direction, (b) the one-dimensional flow model should be limited to 1-d.o.f. vibration analysis or the case of a cylinder having a large radius-to-length ratio, and (c) the perturbation assumption has little effect on the dynamics of annular-flow-induced vibrations; however, the critical flow velocity is diminished considerably. Finally, preliminary results suggest that fluid friction may significantly modify the predicted model dynamics.
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