| With the increasing demand for power sources in modern society,the power and integration of internal combustion engines are increasing,resulting in a sharp increase in the thermal load on pistons.At present,most of the pistons of high-power internal combustion engine are using the cooling method of the casting inner cold oil cavity,during the piston reciprocating motion,the oil oscillation in the cavity shocks the surface of the oil cavity for heat exchange,but there is a situation that can not completely cover the surface of the oil cavity,resulting in direct contact between the local surface and the air,the heat exchange coefficient is smaller,the heat exchange capacity is insufficient,so that the oil cavity wall surface local dry pot at high temperature,that is: lubricant deterioration,coked,has become a bottleneck restricting the clean and high development of the internal combustion engine.Simply increasing or improving the structure of the inner cold oil chamber can not solve the problem,so it is necessary to find a solution to the low coverage of the wall oil film.After previous exploration,it was found that the micro-nanostructure super-oil wall surface has super-strong capillary force,so that the oil is more easily spread in the wall attached,forming a stable oil film with a certain thickness,can completely cover the surface;In this paper,through experimental methods,deionized water is used as the cooling quality to explore the mechanism of intra-cavity oscillation heat exchange.It provides a new idea for further strengthening the cooling capacity of the inner cold oil chamber,thus solving the problem of lubricating oil coked.In this paper,the microstructure surface is prepared by laser ablation process,the superhydrophilic surface is prepared by hydrogen peroxide corrosion method,and the two methods are combined to prepare the microstructure super-hydrophilic surface,and the indicative contact angle is close to 0 degrees.The prepared surface is applied to the self-built reciprocating oscillation shock heat exchange and visualization test bench,and the heat exchange characteristics of cooling work material intermittently touching the upper wall surface under reciprocating oscillation are simulated by intermittent spray experiments,and the experimental results show that:(1)When the filling rate is 50%,it can not only ensure the reciprocating shock oscillation,but also can guarantee that the upper wall surface gets enough liquid film coverage,so the heat exchange characteristics are best at this time,the impact on the upper wall surface is enhanced,heat exchange characteristics are strengthened,compared with the four surface heat exchange characteristics,compared with polished surface,the other three surfaces have a certain degree of heat exchange enhancement effect,of which the microstructure super-hydrophilic surface heat exchange characteristics are strongest,an average increase of 18%.(2)At high temperature,the filling rate is still the best at 50%,but in order to prevent the local steaming of the upper wall surface of the cavity,the intra-cavity filling rate should be avoided below 50%,in the thermal flow density range of the experiment,the polished surface and microstructure surface first occurred at the end of the cavity outlet local steaming phenomenon,and then spread to the whole cavity caused the membrane boiling,but the microstructure surface has a certain hydrophilicity,the density of local steamed dry heat flow is 2.3 times that of polished surface,and the other two super-hydrophilic surfaces do not occur,indicating that super-affinity surface can effectively delay critical thermal flow density point.(3)The improvement of the speed makes the heat exchange wall get the impact of cooling quality in time,thus effectively improving the critical heat flow density.At the same time,the use of super-hydrophilic surface can also effectively delay the occurrence of steaming and drying phenomenon,compared to the polished surface up to 66%. |
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