Image processing methods to obtain symmetrical distribution from projection image.
Flow visualization and measurement of cross-sectional liquid distribution is very effective to clarify the effects of obstacles in a conduit on heat transfer and flow characteristics of gas-liquid two-phase flow. In this study, two methods to obtain cross-sectional distribution of void fraction are applied to vertical upward air-water two-phase flow. These methods need projection image only from one direction. Radial distributions of void fraction in a circular tube and a circular-tube annuli with a spacer were calculated by Abel transform based on the assumption of axial symmetry. On the other hand, cross-sectional distributions of void fraction in a circular tube with a wire coil whose conduit configuration rotates about the tube central axis periodically were measured by CT method based on the assumption that the relative distributions of liquid phase against the wire were kept along the flow direction.
Generalized Abel transform for the analysis of fluid vibration in a tube
Fluid vibrations in axisymmetric geometry according to the first harmonic in the circumferential direction are analyzed. This problem has a practical application in the analysis of transverse vibrations of fluid in an axisymmetric pipe. The numerical model is developed using finite-element techniques in axisymmetric geometry. Irrotational motions of ideal compressible fluid are analyzed. The finite-element model of the system is based on the approximation of nodal displacements via the shape functions. Thus the field of the amplitudes of the circumferential variation of the volumetric strain is calculated, exploiting conjugate approximation techniques. Obtained volumetric strains are used for the numerical construction of the interference pattern of the vibrating fluid. For this purpose the Abel transform, which is usually exploited in axisymmetric problems, is generalized for problems with circumferential variation of displacements. The obtained interference patterns are used in hybrid experimental–numerical procedures and help to interpret experimental results.
Application of neutron radiography to visualization and void fraction measurement of air-water two-phase flow in a small diameter tube
Abstract The purpose of this study is to investigate the feasibility of visualization and void fraction measurement of air-water two-phase flow in a small diameter tube (I.D.: 4.08mm) by using the real-time neutron radiography and image processing techniques. Video images of two-phase flow were taken by using the real-time neutron radiography system (thermal neutron radiography facility No. 2) installed at the Japan Research Reactor 3 M of the Japan Atomic Energy Research Institute. The shape of bubbles and its moving behavior were clearly observed from the video images. The image corrections for dark current, shading, field intensity fluctuation and electrical system drift were examined in order to measure the void fraction from the video images. Though, generally speaking, the effect of the scattered neutron could not be ignored for quantification of the images taken by the neutron radiography, the scattered neutron could not affect the final results of void fraction in the case of a small diameter tube...