Research On The Boiling Heat Transfer Enhancement Of Internal Combustion Engine’s Cooling Water Jacket Via Microstructure Surface

Under severe energy and environmental problems,the internal combustion engines continue to develop in the direction of high power and light weight,which leads to a sharp increase in the heat load of the combustion chamber and other components,the further improvement of the heat exchange capacity of the cooling water jacket needs to be solved.The traditional convection heat exchange method has been unable to meet the increasingly heat exchange requirements,while the phase change cooling mode represented by boiling heat transfer has aroused high interest of researchers.As a new type of enhanced heat transfer method,surface modification can not only increase the heat transfer surface,but also change the evolution behavior of bubbles.Studying its effect on boiling heat transfer is of great significance for improving the heat transfer capacity of the cooling water jacket of internal combustion engines.In this paper,the calculation model of the high-precision pool boiling heating system is established through a combination of numerical simulation and experimental research,and the law and mechanism of enhancing boiling heat transfer with different surface morphologies and wetting properties was explored from the phase volume fraction,temperature and heat transfer coefficient of the heat transfer surface.The main contents are as follows:(1)An experimental bench for the pool boiling heating system was designed and completed,The experimental study of the influence of different subcooled temperature on the heat transfer capacity was carried out by changing the coolant temperature.The results show that in the range of superheat(0-40℃),the heat flux under all working conditions increases slowly and then rapidly as the superheat increases.the coolant has a certain effect on the boiling heat transfer ability,before boiling,the lower the coolant temperature,the better the heat transfer ability.However,after boiling,the higher the coolant temperature,the better the boiling heat transfer ability.(2)Four types of heat transfer surfaces with micron-level cavity and pillar are designed,and hydrophilic properties are added to their surfaces.Finally,numerical calculations are carried out based on the VOF model.The results show that when the superheat is low,the truncated coneshaped cavity and cylindrical cavity structure show better heat transfer capacity due to the shorter time required for nucleation;With the increase of superheat,the cylindrical cavity structure is the first to cause film boiling due to the too small microstructure spacing,and the heat transfer capacity is drastically reduced.The truncated cone-shaped cavity structure causes film boiling afterwards due to the narrow outlet;When the superheat is high,the truncated cone-shaped pillar shows the highest heat transfer coefficient and the lowest heat exchange surface temperature,followed by the cylindrical pillar morphology.The truncated cone-shaped cavity and cylindrical cavity structure show poor heat transfer capacity.(3)Based on the structure scheme of the truncated cone-shaped pillar morphology,the wettability surface characteristics of hydrophilic and hydrophobic combination are added to the heat exchange surface,the evolution behavior,heat transfer surface temperature and heat transfer coefficient of the bubbles on the hydrophilic surface and the hydrophilic-hydrophobic combined surface are compared and analyzed.The separation time of the bubbles on the hydrophilichydrophobic composite surface is shortened,the floating speed increases after separation.and the heat transfer surface temperature is decrease by 0.21%,the heat transfer coefficient is increase by29.5%.For the wettable surface with hydrophilic and hydrophobic binding,the Latin hypercube sampling combined with response surface analysis is used to study the influence of each structural parameter of the truncated cone-shaped convex structure and the coupling effect between the parameters on the heat transfer capacity.The multi-objective optimization design of the truncated cone-shaped convex structure is carried out by combining the non-dominated sorting genetic algorithm.The results show that the height of the truncated cone-shaped pillar is the most important parameter.As the height increases,the maximum average temperature rise first decreases and then increases,the average heat transfer coefficient first increases and then decreases,and the bubble separation speed coefficient decreases monotonously.The influence of the length of the lower surface on the heat transfer performance is higher than the length of the upper surface.Compared with the average heat transfer coefficient and the maximum average temperature rise of the hydrophilic non-topography plane,the optimal design has a significant improvement.The average heat transfer coefficient HTC is increased by 194.5%,and the maximum average temperature rise ΔT is reduced by 33.9%.