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1

Motion of a sphere in vicinity of the wall

Mikielewicz D., Wajs J.

Transactions of the Institute of Fluid-Flow Machinery

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2006

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nr 118

127-138

EN

The paper is focused on studies of particle's path deflection near the wall. Particle is modeled by a rigid sphere suspended on the thread. A specially designed rig has been constructed where systematic experiments were done to obtain sphere trajectories for its three different sizes. Mathematical analysis led to correlation describing the influence of wall on particle movement in function of initial distance of the sphere to the wall and its Reynolds number. The analysis was based on original model postulated by authors. Comparisons of experimental data against correlations available from literature shows a satisfactory agreement.

2

Improved model of void fraction distribution in two-phase flow in the boundary layer

Mikielewicz D., Wajs J.

Archives of Thermodynamics

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2006

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Vol. 27, no. 3

95-116

EN

The aim of present work is investigation focused on experimental verification of forces acting on bubble flowing along the wall and subsequent implementation of the findings into the model of void fraction distribution, developed earlier by one of the co-authors [6]. In experimental investigations the bubble is represented by a solid sphere suspended on a thin string. Authors are convinced that the presented model of a bubble motion captures at least a qualitative behaviour of a bubble in the bubbly flow and will compliment the transverse force balance acting on the bubble. Such transverse balance of forces forms one of equations involved in the model of void fraction developed by Mikielewicz [6]. Presented results of experimental research show periodic character of sphere movement (simplified bubble model) along the wall of vertical channel, which is in line with findings of the experiments preformed on bubbles in vicinity of wall. Sphere trajectory visibly changes, which are caused by non-uniform velocity distribution of fluid around the sphere related to non-uniform pressure field around it, giving in such a way rise to the repelling force. The wall force was introduced to the model of void fraction distribution and improved results were obtained.

3

Evolution of flow patterns, gas fraction profiles and bubble size distributions in gas-liquid flows in vertical tubes

Lucas D., Krepper E., Prasser H. M.

Transactions of the Institute of Fluid-Flow Machinery

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2003

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nr 112

37-46

EN

Air-water flow at ambient conditions in a vertical pipe an inner diameter of 51.2 mm is investigated. An electrode wire-mesh sensor enables the measurement of the phase distribution with a very high resolution in space and in time. Local bubble size distributions are calculated from the data. The measurements were done in distances from the gas injection device. As a result, the development of bubble size distributions as well as the development of the radial gas fraction profiles can be studiet. It was found, that the bubble size distribution as well as local effects determine the transistion from bubble flow. The data are used for the development of a model, which predicts the development of the bubble size distribution and the transition from bubble flow in the case of stationary flow in a vertical pipe.

4

A new model of bubble - liquid interaction in the boundary layer

Mikielewicz D.

Zeszyty Naukowe Politechniki Świętokrzyskiej. Mechanika

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1999

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Z. 67

283--292

EN

In the present work a new approach to modelling of the void fraction in the upward flow in the boundary layer is presented. The circulation around the bubble is modified to what has been previously assumed in the literature. The circulation is composed of two mechanisms which rotate in opposite directions. The resulting model predicts the wall peaking as well as the core peaking depending primarily on the bubble diameter. The proposed mechanism is entirely new in the available approaches. It is relatively general and enables future modifications.