Experimental Study Of Vapor Bubble On Downward Facing Curved Surface In Subcooled Boiling Liquid

Research of heat and mass transfer about the boiling is very significant in a lot of practical engineering, as we know, there are three mechanisms in the process of the boiling, and bubbles have an important influence in each of mechanisms. So, studying bubble behavior and the interaction with interface in the process of boiling become an important channel that be used to reveal the mechanism of boiling heat transfer. Subcooled boiling is a special period in the process of boiling, with cryogenic fluid become more and more available in many field such as science and technology field, explored about this field has caused widespread concern, makes this study become a hot issue.Although scholars at home and abroad had conducted many researches about the growth, shape variation and trajectory of bubbles in the subcooled boiling. Lots of them concerned the behavior features of bubbles on the horizontal, vertical, and inclined flat surface. As to curve surface, especially the downward faced, the research become less and less. So the present work concern the behavior characteristic of bubble on downward facing curved surface in subcooled boiling liquid. Study that by experimental method using a high speed camera, and compared with the issue on the horizontal flat surface at the same environment. Explored the dynamic trait about the process of bubbles from grow, move to disappear, analyze the difference and why with the horizontal. This work mainly includes the following parts.(1) In order to get the bubble, a way to product bubble must be chose, On this basis, reading a lot of literature, concerning other researchers how to conduct experiment, to design bench and deal with experimental data, choose Methylene chloride as test liquid.(2) To design the experimental component and establish a visual test tank. Refer to other’s work, complete the design and build assignment. As to the experiment on curved surface, the experimental apparatus is made of stainless steel, three faces of the tank are equipped with windows allowing the observation. The test part’material is same to the tank, just a circular tube. The other apparatus is made of tempered glass, test part is same to the former. Both experiment use Iodine nickel wire lamp as fill light, as for the mode of fill light.(3)Digital image processing and data post-processing. Matlab software is applied in the present work, dispose the ideal bubble image with gray and other process by self-made program. Observe the movement and deformation of bubbles on downward facing curved surface. Then use Image Pro-Plus software to extract and analysis the related parameters, such as equivalent diameter of bubbles when just have a movement.(4) Analysis the experimental data and conclude. Through-analyze the experimental information and observe the bubbles, compare the difference between downward facing curve surface and horizontal flat surface, After comprehensive analysis summarizes the conclusion: in terms of curve surface, it has been discovered that bubbles change from a sphere at the growth process on the initial position to an elongated ellipsoid at sliding process, the heat flux had an influence on the equivalent diameter of bubbles beginning movement:with the increase of heat flux, the equivalent diameter increased.