中文摘要：

针对汽泡在脱离点和浮升点的力平衡特点，根据受力分析结果对汽泡的动量平衡方程进行了简化。提出了汽泡在竖直加热壁面上脱离和浮升的判据。采用Thorncroft的实验数据进行检验，结果发现，汽泡的脱离及浮升直径预测值与实验值误差在±20％以内。模型分析结果表明，向上流动的汽泡脱离直径随平均流速的增加而减小，随壁面过热度的增加而增加；向下流动情况大致相同；但由于流动曳力对汽泡脱离的作用和浮力的作用相反，从而导致了在0．2～O．3m·s^-1流速范围内出现汽泡不脱离的现象。在向上流动条件下，由于汽泡脱离核化点后的滑动方向和主流方向一致，从而使得汽泡与流体间的相对速度减小，使浮升直径大大增加；向下流动时，汽泡浮升直径随平均流速和壁面过热的关系与脱离直径的变化趋势基本一致，但与壁面过热的关系没有脱离直径的明显。

英文摘要：

With regard to the force characteristics at the point of departure and lift-off, the momentum equations of bubble were simplified according to the result of force balance analysis. The criteria of bubble departure and lift-off point were proposed as well. The predicted results were compared with the experimental results of Thorncroft, the error of bubble departure diameter and lift-off was within ±20%. In up-flow boiling, higher wall superheat or lower mean velocity led to increasing bubble departure diameter. It was generally the same in the case of down-flow. Because of opposite effect of drag force and buoyancy force on departing bubbles, there was no bubble departure of the flow at the velocity ranged from 0. 2-0. 3 m · s^-1. In up-flow boiling, the same direction of the bubble sliding on heated surface and the main flow led to reduced velocity difference between bubble and main liquid and greatly increased lift-off diameter. In down-flow boiling, the bubble lift-off diameter also increased with lower mean velocity and higher wall superheat. However, as compared with departure diameter, the bubble lift-off diameter did not greatly increase with higher wall superheat.