| Rapid cooling technology of hot rolled strip is an important part of TMCP,currently,the rapid fast cooling system of hot rolled strip has been successfully applied to industrial application and it plays an important role in control of microstructure and performance after rolling,therefore,a series of products high quality and economical hot rolled strip have been developed and produced.Whereas,the thin gauge steel with the lower the constraint on deformation is easily prone to local deformation,which eventually affects the performance of product processing.Aiming at the heat transfer mechanism of aerosol spray cooling process in thin slab,this paper combined with the National Natural Science Foundation "No.51404058",as well as the Fundamental Research Funds for the Central Universities "No.N150704005".The main research contents and results are as follows:(1)Build an optimized experiment platform in the laboratory,comparing the mechanism of typical pool boiling heat transfer mechanism,the film boiling,the nucleate boiling and the secondary nucleate boiling,the rewetting process of the high temperature steel plate was analyzed,which provides the theoretical basis for the subsequent research.(2)The wetting state and fluid state of high temperature steel plate during the process of aerosol spray cooling were analyzed,combining the typical curves of temperature drop and heat flux in the process of aerosol jet cooling,and simulated the high temperature field.The results showed that:The steel surface has been subjected to film boiling,nucleate boiling and secondary nucleate boiling heat exchange.Both pressure and flow increase are beneficial to the droplet atomization,increasing the number of droplets per unit area,expanding the area of the cooling zone,and thus accelerating the expansion of the wetting zone.The temperature field corresponding to the atmospheric pressure has a larger low temperature zone in the direction of the width of the steel plate,whereas larger exit flow rates have a slighter temperature drop in the width direction of the steel plate,but the temperature drop gradient increased significantly.(3)Aiming at the process parameters of flow,pressure and cooling temperature,the law of cooling and exchanging heat in aerosol spray was studied,the results showed:The heat flux increases with the increase of flow rate and jet pressure.Increasing the air pressure is more favorable for improving the heat exchange efficiency in the outer region of the impact point.In order to achieve the more atmospheric conditions of the aerosol cooling,the larger flow made the gas-liquid ratio balanced,sufficient atomization,so as to further improve the heat transfer capacity of the steel surface.When the cooling temperature is increased and the heat flux at the impinging point is increased,the rewetting delay is more obvious.The higher cooling temperature is unfavorable to the rapid and uniform steel surface.However,at the higher cooling temperature,the average heat flux is maintained at peak time longer.(4)The heat transfer of nanofluids during the aerosol spray cooling process was studied,the effect of nanofluids with different types,different volume fraction and the concentration of different surfactant on the heat transfer process.The results showed:The contact angle of nanostructures increased with the increase of volume fraction and the surface tension decreased with the increase of surfactant concentration.With the increase of the volume fraction of nanofluid,the heat flux increases,the rewetting delay decreases,and the surface cooling uniformity increases.As the surfactant concentration in the nanofluid increases,the heat flux increases in the cooling zone,the wetting area increases,the rewetting rate increases,and the cooling uniformity increases.Finally,by comparing different types of nanofluids,it can be seen that the overall heat transfer effect of the nanofluid with the surfactant is better than that of the nanofluid without the surfactant,which is better than the conventional aerosol cooling. |
PDF Full Text Request