| Phase change heat transfer is an efficient method for heat dissipation of high heat flux devices.Boiling-condensation is the core of phase transition heat transfer,in which boiling heat transfer efficiency is an important index to measure heat dissipation effect.The influencing factors of heat dissipation efficiency mainly include the microstructure of the boiling end,the material and the fluid,etc.From the perspective of exploring the correlation between the structure of the boiling end and the interference behavior of the boiling bubbles,we used the method of combining finite element numerical simulation and visualization pool boiling test to build a visual boiling test platform and explore the influence law of different spacing and plane profile on the dynamic behavior of the boiling bubble and related parameters.The main research contents are as follows:(1)Numerical simulation of pool boiling micro-channel with different sizes.Based on the boiling heat transfer mechanism and existing measures to enhance boiling heat transfer,a micro-channel numerical model was established to analyze the nucleation,growth,interference,necking and detachment behaviors of boiling bubbles at different channel spacing,and to establish the correlation between channel spacing and dynamic interference behaviors of bubbles.The influence of wall superheat on the bubble departure diameter and frequency was analyzed.The bubble behavior of different spacing microchannels in the boiling process of the pool was investigated.(2)Test principle design and construction of visual boiling test bed.Set up a set of pool boiling test platform integrating dynamic observation,temperature monitoring and data acquisition.The processing technology of micro-channel structure was explored,and the influence of laser processing parameters(scanning speed,processing mode,repetition frequency)on the surface topography of the channel was analyzed.test specimens of different structures and sizes were prepared by laser technology.test plans and standardized test flow were designed,and verify the test scheme,and device support was provided for boiling test research.(3)Boiling test of bottom plate pools with different sizes under two kinds of microstructures.Pool boiling tests were carried out on four fractal corner profile plates with different channel spacing and "Y" structure of imitating blade veins,to explore the influence of micro-channel structure and profile on boiling heat transfer,capture the image of the whole process from nucleation to separation of bubbles on the bottom plate,and analyze the correlation law between bubble size,channel structure and wall superheat.The results show that under the same size,the average bubble departure frequency of the plate with the vein-like configuration is 11.5%higher than that of the parallel structure during the boiling process.In this thesis,the dynamic characteristics of bubbles are correlated with the effect of enhanced boiling,and the effect of microstructure size of boiling end on bubble behavior is further explained.The research results have important reference value for the kinematic behavior and interference law of bubbles generated by different size microstructure under pool boiling,and provide a new reference for optimizing the structure of boiling end and boiling heat transfer performance. |
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