Spontaneous nucleation and resulting explosive evaporation of liquid impinging on a hot surface with a high speed

当高温液体与易挥发的低温液体接触时，接触界面温度超过低温液体的过热极限时，可能会发生自发形核和由此产生的蒸汽爆炸。本文用快速加热的方法研究了液体与高温固体的接触以及由此产生的气泡成核现象。一台浸泡在乙醇中的小型铂膜加热器由具有两级或三级的矩形脉冲供电。聚结气泡的破裂是由于第一级的高脉冲在加热器表面自发成核而形成的，导致固液二次接触。改变第二级的脉冲功率，以控制接触处的加热器温度。采用电阻测温法测量加热器表面温度。可忽略功率的第三阶段能够在接触期间测量表面温度。在接触过程中会产生细小气泡，当加热温度在液体均匀成核温度附近时，细小气泡的数量最多。在更高的温度下，即使在合并的气泡破裂后，蒸汽膜仍然留在整个表面上。

When a high temperature liquid contacts with a volatile low temperature liquid and the contact interface temperature is beyond the superheat limit of the low temperature liquid, spontaneous nucleation and resulting vapor explosion may occur. In the present study, the contact of liquid with a high temperature solid and the resulting bubble nucleation phenomenon were investigated using a rapid heating method. A small platinum film heater immersed in ethyl alcohol was powered by a rectangular pulse having two or three-stages. The collapse of a coalesced bubble, which is formed as the result of spontaneous nucleation over the heater surface by high pulse of the first stage, causes the solid-liquid re-contact. The pulse power of the second stage was changed in order to control the heater temperature at the contact. The heater surface temperature was measured by means of the resistance thermometry. The third stage of negligible power enabled the surface temperature measurement during the contact. Fine bubbles appeared during the contact and its number becomes maximal when the heater temperature was around the homogeneous nucleation temperature of the liquid. At higher temperatures, the vapor film remained on the entire surface even after the collapse of the coalesced bubble.