In this study, the impact of the number of bubbles on the velocity of laser-induced microjet is numerically investigated, focusing on the pressure wave propagation generated by multiple laser-induced bubbles. First, we show that the microjet velocity increases with the increasing impulse of the pressure wave propagating to the meniscus direction. This result indicates that it is possible to study the structure of the pressure field generated from bubbles to investigate the effect on microjet generation. In addition, it is found that the microjet is weakened with the increase in the number of bubbles. Next, we show that the propagation of the pressure waves has two types. The first type is propagating from a bubble to a meniscus. The second type is propagating round trip between nearby bubbles or by the bubble itself. Finally, we explain the reason for the decrease in the microjet velocity with the increasing number of bubbles by an expansion history of the bubbles, which depends on their interaction with the pressure waves. These results could help to design not only laser-induced microjet generation but also devices that use laser-induced bubbles generated in a microchannel.

A device generating high-speed microjets from a liquid-filled microtube with laser-induced bubbles gets attention due to possibility of various engineering applications. In this study, we optimized the placement and bubble size of the laser-induced bubbles to maximize the efficiency of microjet generation. In the optimization, we use the Covariance Matrix Adaptation Evolution Strategy, which is one of the evolutionary algorithms. And a compressible multiphase flow solver based on the 5-equation model is used to evaluate the solution. Furthermore, data mining techniques using correlation analysis and dimensionality reduction algorithms are applied for extracting features related to the efficiency of microjet generation. Our result shows that it is effective to generate a laser-induced bubble near the tube wall. In addition, it is found that smaller volume and lower energy bubbles can provide efficient microjet generation. These results from the optimization and data mining are important for producing high-speed jets at low energy.

No abstract

No abstract

Laser-induced microjets are advantageous for yielding high-speed and convergent microjets shape. However, owing to the need for high-power laser devices, reducing the required laser power is a prerequisite for convenience in practical use. This study aimed to optimize initial multiple bubbles design and find the dominant parameters for efficient microjet generation. For this purpose, the bubble design was optimized using an evolutionary algorithm-the covariance matrix adaptation evolutionary strategy. In addition, the dataset of solutions obtained through the optimization process was analyzed via principal component analysis (PCA). The optimization and analysis revealed that a higher microjet velocity could be obtained when a single bubble was generated near the tube wall, and an optimal total bubble volume was observed corresponding to this optimization. In addition, this approximate optimal solution we obtained was confirmed to reduce 88% of total initial energy compared to that of the typical solution. The result shows possibility to improve the efficiency of microjet generation and reducing the laser power.