Numerical simulation of bubble dynamics under multi-ultrasonic vibrators

doi:10.11949/0438-1157.20201498

Abstract

Abstract:

Ultrasound plays an important significance in enhancing the boiling heat-transfer of lithium bromide aqueous solution in the generator of absorption refrigeration system, there are few theoretical and experimental studies about the application of ultrasound heat-transfer enhancement technology in the boiling heat-transfer of lithium bromide aqueous solution in the generator, especially in the field of solution bubble dynamics with multi-ultrasonic vibrators at present. In order to investigate the influence of the quantities of ultrasonic vibrators on the characteristics of solution cavitation bubble dynamics, a mathematical model of lithium bromide aqueous solution bubble dynamics is constructed, in addition, the accuracy of the mathematical model is verified with the degassed water, and the effect of different influencing factors on the characteristics of solution cavitation bubble dynamics are discussed. The results indicate that, when the total sound intensity of 1 W/cm², as the quantities of ultrasonic vibrators rise from 1 to 5, the maximum radius of a cavitation bubble is increased by 44.12%, while the maximum radius of cavitation bubble is increased by no more than 1% at the quantities of ultrasonic vibrators of 24—25; The effect of the generating pressure (ambient pressure) on the solution cavitation effect would be increased with the quantities of ultrasonic vibrators increase, in the absorption refrigeration system, the lithium bromide aqueous solution in vacuum generator is more likely to produce steady cavitation process with the single-ultrasonic vibrator, nevertheless, the solution in vacuum generator is more likely to produce transient cavitation process with the multi-ultrasonic vibrators; when the ultrasonic frequency uniformities of ultrasonic vibrators decrease, the intensity of solution cavitation effect would be increased, while the ultrasonic intensity uniformities of ultrasonic vibrators on the intensity of solution cavitation effect could be neglected.

Key words: ultrasonic cavitation, lithium bromide aqueous solution, numerical simulation, multi-frequency ultrasound, bubble dynamics

摘要：

超声对强化吸收制冷循环中发生器内溴化锂水溶液沸腾传热有重要意义，目前开展的相关研究较少，尤其多超声振子气泡动力学方面的理论尚未报道。为探究振子数量对溶液空化特性的影响，构建多振子气泡动力学模型，以纯水为例验证了模型准确性，探讨了不同影响因素对溶液空化特性的影响。模拟结果表明：总声强为1 W/cm²，振子数量由1增加至5时，空化气泡最大半径增加了44.12%，振子数量达到24～25个时，气泡最大半径增加率仅为1%；发生压力对空化效应的影响随着振子数量的增多而增大，单振子在吸收制冷系统的真空发生器更易产生稳态空化，而多振子更易在真空发生器内产生瞬态空化；多振子频率均匀度越小，空化强度越大，声强均匀度对空化强度的影响可忽略。

关键词: 超声空化, 溴化锂水溶液, 数值模拟, 多频超声, 气泡动力学

CLC Number:

TQ 025.2

HOU Zhaoning, WANG Lin, YAN Xiaona, LI Xiuzhen, WANG Zhanwei, LIANG Kunfeng. Numerical simulation of bubble dynamics under multi-ultrasonic vibrators[J]. CIESC Journal, 2021, 72(S1): 362-370.

候召宁, 王林, 闫晓娜, 李修真, 王占伟, 梁坤峰. 多超声振子作用下气泡动力学数值模拟[J]. 化工学报, 2021, 72(S1): 362-370.

Figures/Tables 13

Fig.1 Mechanical model of cavitation bubble

Fig.2 Spherical bubbles in homogeneous media

Fig.3 Comparison of accuracy of bubble dynamics model

Fig.4 Effect of generating pressure on cavitation bubble dynamics

Fig.5 Effect of quantities of ultrasonic vibrators on solution bubble dynamics

Fig.6 Effect of ultrasonic intensity uniformities of ultrasonic vibrators on solution bubble dynamics

Fig.7 Effect of ultrasonic vibrators phase difference on solution bubble dynamics

Fig.8 Effect of ultrasonic frequency uniformities of ultrasonic vibrators on solution bubble dynamics

Fig.9 Effect of solution concentration on cavitation bubble dynamics

Fig.10 Effect of solution temperature on cavitation bubble dynamics

Fig.11 Effect of generating pressure on cavitation bubble dynamics

Fig.12 Effect of ultrasonic frequency on cavitation bubble dynamics

Fig.13 Effect of ultrasonic intensity on cavitation bubble dynamics

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