Visual Experimental Study On The Effect Of Nano-porous Structure And Thermal Resistance On Cryogenic Nitrogen Boiling

With the development of science and technology,cryogenic fluid is more and more applied to aerospace and superconducting field.In practical application,the initial temperature of the equipment is much higher than that of the cryogenic liquid,and the quenching heat transfer will occur immediately.The rapid cooling of the equipment can effectively reduce the consumption of cryogenic liquid and make the equipment enter the working state as soon as possible.At present,it is found that surface modification can greatly improve the heat transfer performance,so the influence mechanism is worth further research.In this paper,the effects of the nanostructure and thermal resistance of the boiling surface on the quenching heat transfer are studied by the visualization experiment.The main work focuses on the following aspects:1.The electrochemical reaction conditions of electrolytic polishing and anodic oxidation is mainly studied.The contrast experiment is conducted to determine the optimal technique for preparing the surface with aluminum anodic oxide layer,which provides the surface with nanoporous structure and hydrophilicity.2.Based on heat transfer inverse problem method and the simplified model of the quenching heat transfer experiments,the exact solutions of the boiling surface temperature,heat flux and heat transfer coefficient is calculated through discrete analysis and data reduction.3.A visual experimental study is carried out to learn how the boiling surfaces with different surface structure properties and heat resistance influence the quenching heat transfer in liquid nitrogen.The study focuses on the cooling curves,boiling curves and heat transfer coefficient change,combined with the analysis of the dynamic process of gas-liquid phase transition image.The experimental results show that both the nanostructure and thermal resistance can significantly improve the Leidenfrost temperature and critical heat flux of the heat transfer,especially in the transition and nucleate boiling regime and the nanoporous structure is more effective.