在直径为8.2 mm的竖直向上均匀加热圆管上进行了干涸型临界热流密度实验研究,加热长度2.4m,压力3.2～19.7 MPa,质量流速963～2 707 kg/(m2·s),进口欠热度34～213℃,出口含汽率0.11～0.78.研究发现:临界热流密度随进口欠热度、质量流速的增加而线性增加,随出口含汽率的增加而迅速减小.通过对临界气液两相参数的分析发现,本实验参数范围内,蒸汽速度是导致干涸的主要原因.当达到临界蒸汽速度时,近壁面液体消失触发临界.随压力的增加,表面张力逐渐减小,液膜更易被撕裂,因而临界蒸汽速度随压力的增加而减小.从高压实验数据出发得到临界蒸汽速度Ucr,参考Steen和Wallis推荐的夹带开始速度U0,建立了预测临界蒸汽速度的模型:Ucr=25U0 +4.利用低压实验数据对预测模型进行了验证,符合较好.%The critical heat flux (CHF) experiment was performed in a tube with inner diameter of 8.2 mm and heated length of 2.4 m.The pressure is 3.2-19.7 MPa,mass flux is 963-2 707 kg/(m2 · s),inlet subcooling is 34-213 ℃ and outlet quality is 0.11-0.78.The results show that the CHF almost goes up linearly while mass flux or inlet subcooling increases,and falls down rapidly while the outlet quality rises.Based on the two-phase parameter analysis,it is found that within the experiment parameter range,the CHF is much related to vapor velocity.Criticality occurs when the liquid near the wall vanishes due to vapor entrainment after reaching the critical vapor velocity.As a result,the surface tension decreases with the increase of the pressure,the liquid film tends to tear out and the critical vapor velocity falls down while pressure rises.Based on the critical vapor velocity Ucr from experimental data of high pressure and the initiation entrainment velocity U0 proposed by Steen and Wallis,a prediction model for the critical vapor velocity was presented.The predicted results by this model agree well with the experimental data of low pressure.
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