Lindinger Bernhard, Söhnholz Hendrik, Mettin Robert
Drittes Physikalisches Institut, Georg-August-Universität Göttingen, Friedrich-Hund-Platz 1, 37077 Göttingen, Germany.
J Chem Phys. 2024 May 28;160(20). doi: 10.1063/5.0205894.
Cavitation in supercooled water has been induced by the short ultrasound pulses of an ultrasonic horn driven at 20 kHz. The cavitation during the ultrasonic pulses and occasionally the crystallization events thereafter have been imaged by a high-speed camera. The probability of ice crystallization in dependence on the pulse duration and temperature showed a high chance for the water to remain liquid if sufficiently short bursts of moderate acoustic power were applied. This regime has been used for the assessment of sonoluminescence (SL) from the generated cavitation bubbles in the supercooled liquid state. To this end, light emitting events were summed up over a number of ultrasonic pulses by an image intensifier. SL appeared mostly directly under the tip of the ultrasonic horn and sometimes also a few millimeters below the tip. The intensity of SL events showed a slight rise for a decrease in temperature, i.e., for an increase in supercooling. This behavior is in accord with the SL dependence on temperature above the freezing point and might be attributed to a further lowering of vapor pressure. An increase in the bubble collapse peak temperature for increased supercooling is calculated on the basis of spherical bubble model calculations, which supports the findings. The simulations predict further that the peak temperature will fall off again beyond a certain supercooling level.
通过以20kHz驱动的超声变幅杆产生的短超声脉冲，已在过冷水中引发了空化现象。超声脉冲期间的空化现象以及随后偶尔出现的结晶事件，已由高速摄像机成像。根据脉冲持续时间和温度，冰结晶的概率表明，如果施加足够短的中等声功率脉冲串，水保持液态的可能性很大。此状态已用于评估过冷液态中产生的空化气泡的声致发光（SL）。为此，通过图像增强器对多个超声脉冲上的发光事件进行了累加。声致发光大多出现在超声变幅杆尖端的正下方，有时也出现在尖端下方几毫米处。声致发光事件的强度随温度降低（即过冷度增加）略有上升。这种行为与冰点以上声致发光对温度的依赖性一致，可能归因于蒸气压的进一步降低。基于球形气泡模型计算得出，过冷度增加时空化气泡坍塌峰值温度会升高，这支持了该研究结果。模拟还预测，超过一定过冷度水平后，峰值温度将再次下降。
