Abstract
Accurate detection of air bubbles boundaries is of crucial importance in determining the performance and in the study of various gas/liquid two-phase flow systems. The main goal of this work is edge extraction of air bubbles rising in two-phase flow in real-time. To accomplish this, a fast algorithm based on local variance is improved and accelerated on the GPU to detect bubble contour. The proposed method is robust against changes of intensity contrast of edges and capable of giving high detection responses on low contrast edges. This algorithm is performed in two steps: in the first step, the local variance of each pixel is computed based on integral image, and then the resulting contours are thinned to generate the final edge map. We have implemented our algorithm on an NVIDIA GTX 780 GPU. The parallel implementation of our algorithm gives a speedup factor equal to 17x for high resolution images (1024×1024 pixels) compared to the serial implementation. Also, quantitative and qualitative assessments of our algorithm versus the most common edge detection algorithms from the literature were performed. A remarkable performance in terms of results accuracy and computation time is achieved with our algorithm.
Highlights
Flows are encountered in various industrial equipment such as, chemical reactions, purification of liquids, drag reduction of ships, gas/liquid contactors including bubble columns reactors, stirred tank reactors, evaporators, boilers and plate columns for absorption of gases and distillation
The present study aims to develop an accurate edge detection algorithm performing in real-time, in order to extract edge map of air bubbles floating in static fluid in two-phase flow systems, for further processing later
The proposed algorithm is based on the exploitation of raw images in order to preserve all features details until the final phase of treatment. This edge detection technique is performed on two main steps: in the first step, the local variance of each pixel is computed based on integral image in order to improve computation time, and the resulting contours are thinning to generate the final edge map
Summary
Flows are encountered in various industrial equipment such as, chemical reactions, purification of liquids, drag reduction of ships, gas/liquid contactors including bubble columns reactors, stirred tank reactors, evaporators, boilers and plate columns for absorption of gases and distillation. The knowledge of bubble characteristics is of crucial importance in determining the performance and in the study of various two-phase flow systems. The results of bubble dynamic are useful in extending the knowledge of bubble behavior in gas/liquid systems and in providing data to develop flow models. Due to the action of hydrodynamic forces, the bubble shape would change. The interaction between rising bubbles and liquid determines the shape of the bubble and the extent of the disturbance in the surrounding fluid. Instantaneous bubbles shapes, deformation of surfaces and sizes are very important because they reflect the dynamic changes of their pressures inside the bubbles and in the surrounding liquid. An improved understanding and instantaneous controlling of the flow around a rising gas bubble are required
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