Experimental Study On The Surface Of Micro- Or Nanostructures For Enhancing The Boiling Heat Transfer In The Cooling Water Jacket Of Internal Combustion Engine

In the cooling water jacket of internal combustion engine,cooling fluid is used to remove heat from combustor to ensure the safety of the combustion components.As the power of engine continues to rise,the temperature of in-cylinder gas will keep going up,and it causes the increase of heat load on combustion components,so enhancing heat transfer in the cooling water jacket is inevitable.The convective heat transfer can not meat the heat transfer requirements of the cooling water jacket,and boiling heat transfer can transfer high amounts of heat with small temperature difference,which has been got more attention from scholars in the world.Compared to the traditional smooth surface of cooling water jacket,the surface with the micro-or nano-structure can further enhance boiling heat transfer.With insufficient research on micro-or nano-structure surface boiling heat transfer,this paper conducted the experiments of pool boiling heat transfer with micro-or nanostructure surface.With the help of visualization,the effects of structure size on bubble dynamics under different heat flux was discussed to reveal the mechanism of enhancing boiling heat transfer on the micro-or nanostructure surface for the foundation for practical application of micro-nano structure surface in the cooling water jacket of internal combustion engine The main contents are included in following three aspects.1)Preparation and characterization of micro-or nanostructure.In this paper,three different micro-or nanostructure surfaces were fabricated:Firstly,UV-LIGA method was used to fabricate to the synergistic microstructure surface with the large groove and small groove array.The structural dimension is19.9×20.1mm~2,the width of small groove is100?m,the width of large groove is 400?m,the fin thickness is 100?m,the width of connection groove is 200?m,the distance of two connection groove is 500?m,and the groove height is 250?m.The surface contact angle is 129o.Secondly,nanostructure was formed on the surface by chemical electrodeposition,and the surface morphology was observed by SEM.The structure size is approximately 200nm.The surface contact angle is109o.Thirdly,the micro-nano structure surface was fabricated by the combination UV-LIGA method and chemical electrodeposition.The nanostructure is attached to the microstructure.The surface contact angle is 139o.2)The design of experiment pool boiling and visualization.The experiment system of pool boiling heat transfer and visualization was established for the superheat(0~50?)and the heat flux on the cooling water jacket of internal combustion engine.In this experiment,bolts were used to make the test surface in close contact with the heating block and the surface was replaceable.The experiments included measurements of the test surface boiling curve and bubble dynamics.3)Experimental study on pool boiling and visualization of micro-or nanostructure surfaces.The experiment of pool boiling heat transfer was conducted and bubble dynamic behavior was observed on the three surfaces with micro-or nanostructue prepared in the second chapter of this paper.The results show that the boiling heat transfer coefficient of micro-synergistic structure surface is increased by 65%compared to the smooth surface at the superheat of 20?.The boiling heat transfer coefficient of the nanostructure surface is increased by 50%compared to the smooth surface at the superheat of 10?.Because the nanostructure has more nano-cavities,which increases the active nucleation,enhances the boiling heat transfer,and reduces the wall superheat for the onset of boiling.The boiling heat transfer coefficient of the micro-and nanostructure surface is increased by 90%compared to the smooth surface at the superheat of 15?.Because the micro-and nanostructure surface combines the characteristics of micro-synergistic structure and nanostructure to further enhance boiling heat transfer.