Study On Boiling Heat Transfer Based On Micro/nanoporous Membrane And Analysis Of Microstr

With the development and innovation of technology,the integration degree and scale of electronic components are continuously improved,leading to growing heat dissipation requirement.The insufficient heat dissipation capacity will lead to the increase of component temperature,which will decrease the performance and reliability of the entire system.Heat transfer enhancement has become a hot issue in the current research.As a new type of phase change cooling method based on nanoporous membrane,thin film boiling is capable to reach ultra-high heat flux of more than 1 000 W/cm2 and maintain the heating surface at a low temperature,which is conducive to efficient heat dissipation and temperature control of heat surface.Thin film boiling is a considerable potential cooling method and can reach the requirement for the heat dissipation of electronic components.In this paper,thin film boiling is deeply studied with the following part:(1)building up a thin film boiling experimental setups to realize the experimental observation of thin film boiling;(2)establishing a comprehensive mathematical model of thin film boiling and quantitatively analyzing the boiling curve;(3)establishing resistor network to analyze metal coating layer on the sample,uncovering the reason leading to the failure and putting forward the optimization of metal nanolayer processing;(4)proposing active regulation schemes to address the potential causes of nano metal layer failure and comparing each active regulation scheme.The specific research contents are as follows:1.A thin film boiling experimental setups is built up,nanoporous membrane coated with nano metal layer is processed as the experimental sample.In the experiment,the metal layer acts as both a heater and a resistance temperature detector.With the increase of heat flux,the liquid film on the sample will go through convection section,thick liquid film boiling section,thin liquid film boiling section and finally reaches critical heat flux as surface dry-out.The performance of the sample continuously enhances with the continuous improvement of processing,ultra-high heat flux of more than 1 000 W/cm2 is finally realized.The"Riverbed shape" on the surface of the sample debris after thin film boiling experiment is discovered after observation by electron scanning microscopy.It is inferred that the appearance of the shape was the direct cause leading to sample failure.2.A comprehensive mathematical model of thin film boiling is established in order to understand the mechanism of it,pool boiling model is treated as a base and appropriate corrections are considered.The thin film boiling curve is divided into four sub-segments for quantitative analysis.The model results of the established mathematical model show good agreement with the experimental results,the decrease of liquid film thickness is the cause of the unique negative slope of thin film boiling curve and potential mechanism for ultra-high heat flux.3.The "Riverbed shape" on the surface of the sample debris is processed by electron discharge spectroscopy analysis.It is judged that the performance of the shape was caused by local melting of the metal layer.The electrical network model of metal layer on the surface of nanoporous membrane is established to calculate and analyze the influence of metal layer thickness uneven to metal layer temperature distribution and melting process.The causes of "Riverbed shape" on the sample surface are revealed.The model results confirms that the uneven metal layer thickness has an important influence on temperature distribution and heat flux,the uneven thickness will significantly reduce the critical heat flux that can be reached.The optimization scheme of metal layer processing is put forward to reduce the influence of metal layer on the experiment,so as to obtain higher critical heat flux.4.The metal layer is simplified to analyze the effect of uneven pore diameter on nanoporous membrane on heating and cooling performance,results show that existence of uneven pore diameter will lead to failure of metal layer with slightly voltage fluctuation.Active regulation schemes including overall regulation and zoning regulating are proposed to improve the local cooling performance to avoid melting of metal layer caused by potential voltage fluctucaiton.Compared with the overall regulation of "flood irrigation",zoning regulation can achieve "fine adjustment" by increasing the liquid pressure for specific zone while other zones can still operate with lower liquid.pressure.The characteristics of these active regulation schemes are compared to provide an important reference for thin film boiling form experiment to practice.