Experimental Study Of Initial Temperature Effect On Quenching Boiling Heat Transfer Characteristics Of Surfaces With Different Wettability

Quench initial temperature is an important parameter in the quenching industry as it is of great significance in the fields of material processing,metal forming and steel metallurgy.It has been widely discussed in research in quench-related fields,but the effect of quench initial temperature on the transient pool boiling process has rarely been discussed in depth.Surface properties play an important role in quenching boiling heat transfer,where surface wettability determines the ability of the liquid to wet the surface and has a significant effect on boiling heat transfer.However,there is a lack of studies related to the effect of quench initial temperature on heat transfer in transient pool boiling with different wettability surfaces.In this paper,two nanofluids were used to prepare surfaces with different hydrophobic and hydrophilic properties by depositing nanoparticles on the surface during nanofluid boiling.The effects of different quenching initial temperatures on the quenching and boiling heat transfer characteristics of different wettability surfaces were investigated experimentally,and the changes of quenching curves and boiling curves of various wettability surfaces at different quenching initial temperatures were analyzed qualitatively,and the trends of CHF,MHF and THF and the corresponding temperatures and arrival times with wettability at different quenching initial temperatures were analyzed quantitatively.The variation patterns of surface heat transfer coefficient and vapor film thickness under the combined influence of quenching initial temperature and hydrophobicity are also discussed.Finally,the changes in vapor film morphology of the relevant wettability surfaces at different quenching initial temperatures are recorded,and the relationship between vapor film images and heat transfer data is analyzed and interpreted.The results showed that the increase of hydrophobicity shifted the quenching curve to the right and shifted the boiling curve to the lower left.the corresponding heat flow density and temperature of CHF and MHF decreased with the increase of hydrophobicity,and the corresponding arrival time and quenching time increased with the increase of hydrophobicity.With the increase of the quenching initial temperature,the above-mentioned trends gradually become less pronounced.At the same time,it was found that the number of surfaces with transitionl boiling subzone conditions became more with increasing quenching initial temperature.The heat transfer coefficients and vapor film thicknesses at each stage are generally consistent with the effects of the above-mentioned variation trends.It was also found that hmax does not occur at the CHF point.The increase in hydrophilicity shifted the quenching curve to the left and shifted the boiling curve to the upper right.As the quenching initial temperature increases,the curves for different surfaces show different trends.The CHF,MHF and THF of hydrophilic surfaces as well as the corresponding temperature and arrival time are affected by the corresponding changes in the quench boiling curve.The heat transfer coefficient increases roughly with increasing hydrophilicity,which is less pronounced for the first three surfaces,especially in the nucleation boiling phase.The tendency of the heat transfer coefficient to increase with increasing hydrophilicity is more pronounced when the quench initial temperature increases.The heat transfer coefficient at the hydrophilic surface CHF is also not the maximum heat transfer coefficient.As the hydrophilicity increases,the corresponding equivalent vapor film thickness roughly decreases.This trend becomes less pronounced in the first three surfaces when the quench initial temperature increases.The vapor film thickness of surface I is related to the stage experienced.The vapor film thickness of superhydrophilic surface J is consistently small.The surface vapor film morphology varies with wettability,and the same surface can have different vapor film morphology changes at different quench initial temperatures.