Chow R, Blindt R, Chivers R, Povey M
Unilever R&D, Colworth Laboratory, Sharnbrook, Bedford MK44 1LQ, UK.
Ultrasonics. 2005 Feb;43(4):227-30. doi: 10.1016/j.ultras.2004.06.006.
Several different investigations have been carried out to study the primary and secondary nucleation of ice by sonocrystallisation. Firstly, the primary nucleation of discrete ice crystals in a supercooled sucrose solution has been observed. For increasing concentrations of sucrose solutions from 0 to 45 wt%, the nucleation temperature consistently occurs at a higher nucleation temperature in the presence of ultrasound. The nucleation temperature also increases as the power output and duty cycle of a commercial ultrasonic horn are increased. Snap shot images of the bubble clouds obtained from the ultrasonic horn also show that the number of bubbles appears to increase as the ultrasonic output is increased. This suggests that the nucleation of ice is related to the power output and number of cavitation bubbles. The effect of a single bubble on the sonocrystallisation of ice is discussed. High-speed movies (1120 fps) have shown that the crystallisation appears to occur in the immediate vicinity of the single bubble. In most cases, many crystals are observed and it is not known whether a single ice crystal is being fragmented by the bubble or whether many crystals are being initiated. The bubble appears to undergo a dancing regime, frequently splitting and rejoining and also emitting some small microbubbles. A study on the secondary nucleation of ice in sucrose solutions has been carried out using a unique ultrasonic cold stage device. Images taken using a microscope system show that the pre-existing ice dendrite crystals can be broken up into smaller fragments by an ultrasonic field. Cavitation bubbles appear to be important during the fragmentation process, possibly melting any ice crystals in their path. Flow patterns around cavitation bubbles have also been observed, and these may be responsible for the fragmentation of ice crystals.
已经开展了多项不同的研究来探究声结晶法中冰的一次成核和二次成核。首先，观察到了过冷蔗糖溶液中离散冰晶的一次成核现象。对于蔗糖溶液浓度从0 wt%增加到45 wt%的情况，在超声作用下，成核温度始终出现在更高的温度。随着商用超声变幅杆的功率输出和占空比增加，成核温度也会升高。从超声变幅杆获得的气泡云的抓拍图像还显示，随着超声输出增加，气泡数量似乎也会增加。这表明冰的成核与功率输出和空化气泡数量有关。讨论了单个气泡对冰声结晶的影响。高速电影（1120帧/秒）显示，结晶似乎发生在单个气泡的紧邻区域。在大多数情况下，会观察到许多晶体，并且不清楚是单个冰晶被气泡破碎，还是许多晶体被引发。气泡似乎经历一种跳动状态，频繁分裂和重新合并，还会释放一些小气泡。使用一种独特的超声冷台装置对蔗糖溶液中冰的二次成核进行了研究。使用显微镜系统拍摄的图像显示，预先存在的冰枝晶晶体可以被超声场破碎成更小的碎片。空化气泡在破碎过程中似乎很重要，可能会融化其路径上的任何冰晶。还观察到了空化气泡周围的流动模式，这些可能是冰晶破碎的原因。
