Developing a method for digital image processing of two phase fluid flows

A new image processing technique was developed in the current study to understand the effects of various hydrodynamics and geometric parameters on local phase distribution phenomena in non-equilibrium two-phase flow systems. While image processing has been employed extensively in velocimetry, its application to explain the two-phase flow phenomena is new. The present study consisted of developing the technique and using it to extract phase distribution data. This, technique presents an advantage of providing measurements and extracting the bubbles of the two-phase bubbly flow compared with the traditionally used methods: point by point measurement technique or digitization. The image processing method proposed in this study is based on the detachment and tracing of the edges of the bubbles and their background. The conclusions are summarized below. (i) High speed photographic results show different behaviors of the bubbles. Some bubbles slide along the wall and detach by rapid ejection into the flow. The motion of these bubbles into the liquid core cause a violent agitation of the liquid near the heated surface. It was also noted that some bubbles detach the surface and sweep downstream and recondensing slowly in the bulk flow. This difference in bubble behavior indicates that the ejection mechanism is influenced by hydrodynamics or thermal condition and will be of interest for further study. (ii) Vapor bubble departure diameters in forced convection subcooled boiling, have been experimentally obtained over a range of mass flux, D, and heat flux, qw, for the subcooled flow boiling region. (iii) For the flow conditions experimentally investigated, the overwhelming majority of the bubbles leave the nucleation sites by sliding a finite distance along the heating surface lifting off the wall. The results can be utilized in explaining the mechanism of subcooled nucleate flow boiling especially in determining the dynamics of the local void distribution and void behavior, particularly, near the point of net vapor generation. The values of the bubble size and shape, interfacial area, information about void formation. bubble growth or collapse and its size and position as well as the velocity of the bubbles for particular conditions, are also evaluated. (Original)