Research On Visualization Measurement And Characteristics Of Bubble In Seawater

With the development of marine resources,construction of large scale water conservancy and shipping engineering,and investigation on underwater equipment,the research on visualization measurement and characteristics of bubbles in seawater plays an increasingly important role in ocean exploration,development and production.Therefore,it is of great significance to study the flow field structure and characteristics of bubbles for revealing the heat and mass transfer mechanism and the reaction kinetics law of the gas-liquid two phases,as well as guiding engineering practice.The seawater bubble generating device and flow field visual measurement system based on high-speed photography and laser scanning technology are built to explore the variations and influence factors of seawater bubble characteristic parameters.The surface tension coefficient is accurately measured based on the implicit representation of the surface tension coefficient and bubble terminal rising velocity.Besides,based on the laser scanning slice images,the three-dimensional(3D)reconstruction of the dense bubbles of seawater is realized,and the void fraction measurement and distribution mechanism are studied according to the reconstruction of flow field structure.The work is summarized as follows:1.To investigate the bubble characteristics and flow mechanism of seawater,the visual measurement system based on high-speed photography and laser scanning is built.The mathematical model of laser scanning is analyzed in detail.And according to the measurement requirements,the error is analyzed thoroughly as well.2.The underwater bubble generation device and image acquisition system are set up to obtain the images of seawater bubble at different salinities,which are captured by high-speed photography.Then the characteristic parameters such as bubble equivalent radius and terminal velocity are extracted,and the factors which affect the seawater bubble characteristics are analyzed.3.Based on the implicit representation of the surface tension coefficient and bubble terminal velocity,the surface tension coefficient is accurately measured through the visual measurement system.A new correlation of the surface tension coefficient is presented by using the least squares fitting.Then the comparative correlations analyses of the seawater surface tension are discussed thoroughly.4.The 3D structure of the flow field is reconstructed based on laser scanning.Then according to the 3D reconstruction of the dense bubbles of seawater,the void fraction measurement and distribution mechanism are studied.