It is well known that a high-power laser could breakdown liquid [1, 2]. Laser-induced breakdown of liquids is characterized by fast plasma formation after evaporation of liquid and subsequent vapor expansion accompanied by shock wave emission [2]. The bubble wall velocity after the shock departure has been found to be sufficiently high to produce emission of light at the collapse point [3]. Recently, bubble formation on the surface of gold nanoparticles irradiated by a high-power laser in water [4, 5] has been studied for medical applications such as cancer diagnosis and possible therapy [5]. However, it is very hard to perform these experiments and to obtain good data from the bubble formation on the surface of laser-irradiated nano-particles because the nanoparticles dispersed in liquid cannot be controlled properly. In this study, laser-induced bubble formation on a micro gold particle levitated at the center of a spherical flask under ultrasound was investigated experimentally. The obtained results are compared with the results for laser cavitation without the gold particle, i.e., typical laser-induced cavitation. Figure 1 shows a schematic of the experimental setup used to investigate the laser-induced bubble formation on a micro gold particle. Two disk-type lead zirconate titanate (PZT) transducers (Channel Industries Inc.; 15 mm in diameter and 5.0 mm in thickness) attached to the side of the wall of the cell produced a velocity stagnation point near the center of the flask. The driving frequency of the PZT transducers was approximately 27.0 kHz which was close to the resonance frequency of the LRC circuit (Its capacitor unis is PZT.) and the acoustic resonance frequency of the water-filled flask. A drop of water containing gold particles with an average diameter of 10 μm are dispersed was injected into a 100-ml pyrex spherical flask filled with degassed water. When the body force of a gold particle in liquid is slightly lower than the Bjerknes force [6] induced by ultrasound, the particle will stay near the pressure antinode, i.e., the center of the flask. A Q-switched Nd:Yag laser delivered a single pulse of 0.5 ns in width with an energy of 7.5 mJ at a wavelength of 1064 nm to the gold particle or liquid at the center of the cell. The laser light was focused at the center of the flask using a lens with an effective focal length of 36.3 mm. Bubble formation and subsequent growth and collapse were visuallized by a high-speed camera (V2511, Phantom, USA) with 0.45 Mfps (million frames per second). The time-dependent radius was also obtained by the light scattering method. The scattering angle chosen was 80 degree where one-to-one relationship exists between the scattered intensity and the bubble radius [7]. The scattered intensity from a bubble illuminated by a 5-mW He-Ne laser was received by a photomultiplier tube (PMT: Hamamatsu, R2027) and was recorded in an oscilloscope. The scattering data were calibrated using the maximum radius for different bubble, which was obtained by high-speed camera. The shock strength during the expansion stage of bubbles was measured by a calibrated needle hydrophone (HPM1, Precision Acoustics, UK) at various distances from the center of the cell for different bubbles. The hydrophone can measure acoustic signals ranging from 1 kPa to 20 MPa. The hydrophone was attached to a three-dimensional micro stage so that fine control of the positioning of the hydrophone was possible.

High fluence time-resolved laser-induced incandescence (TiRe-LII) measurements show a discrepancy between experimental observations and model predictions. Several hypotheses have been proposed to explain this discrepancy, including the possibility of back flow of sublimed species and the possibility of formation of shock waves. This is the first study that uses transient Direct Simulation Monte Carlo (DSMC) to investigate the abovementioned effects in high fluence TiRe-LII. This study verifies that back flow of sublimed species occurs, and must be included in analytical models. On the other hand, shock waves were not observed for the fluences and predetermined temperature curves used in this study.

The autoignition of fatty-acid methyl ester biodiesels and methyl ester biodiesel components was studied in gas-phase shock tube experiments. Ignition delay times for two reference methyl ester biodiesel fuels, derived from methanol-based transesterification of soybean oil and animal fats, and four primary constituents of all methyl ester biodiesels, methyl palmitate, methyl stearate, methyl oleate, and methyl linoleate, were measured behind reflected shock waves for fuel/air mixtures at temperatures ranging from 900 to 1350 K and at pressures around 10 and 20 atm. Ignition delay times were determined by monitoring pressure and chemiluminescence from electronically-excited OH radicals around 310 nm. The results show similarity in ignition delay times for all methyl ester fuels considered, irrespective of the variations in organic structure, at the high-temperature conditions studied and also similarity in high-temperature ignition delay times for methyl esters and n-alkanes.

A cable box is a metal enclosure that provides connections to the main electric power machineries such as switchgear or transformer. Cable terminals housed in cable boxes have a high fire risk because very few cable boxes can withstand the pressure generated by a low impedance arc. And the cable boxes usually suffer from significant damage causing breakage of bushings between the cable box and the electric equipment. In case of transformer, oil is then spilled from the damaged bushing and the released oil generates the fire ignition. In this study numerical prediction for the pressure rise and propagation during the arc inside the cable box has been performed considering the effects of the shock waves, the deformation of the tank and the fluid-structure interactions between the pressure wave and the cable box. Based on the Euler-Lagrange coupling method, flow field and structure analysis has been conducted to predict pressure rise value of the cable box and the stresses of the wall. Two arcing positions such as line to line and line to ground has been chosen in order to consider how the initial arc point affects the pressure wave propagation and the shapes of pressure wave pattern due to the interaction with near wall.

Phase-change through condensation and evaporation processes takes place in many daily-use heating and cooling systems. However, if these processes experience uncontrolled pressure and temperature conditions, shock waves may be generated. Depending on the strength and conditions of the generated waves, they can decrease the effective life of equipment or even cause devastating destruction. Cavitation and water hammer phenomena are examples of flow issues that are well understood and reported in thermal/fluid systems, although not many studies have been published in open literature on condensation-induced shock (CIS) with the applications in refrigeration and air conditioning systems. This study reviews the limited literature on this topic, analyze the complex CIS phenomenon, derives and solves the governing equations, presents the results of typical conditions that may happen in different residential and industrial applications, and provides ways to avoid devastating incidents that may occur as a result of this phenomena.

Nanosecond laser ablation is studied using a theoretical model combined with experimental data from laser ablation of metal films. The purpose of the research is to obtain the recoil pressure boundary condition resulting from explosive phase change. The ablation experiments are performed using a Nd:YAG laser of 1064 nm wavelength and 7 ns pulse width at full width half maximum. Three samples, 200 and 1000 nm aluminum films and 1000 nm nickel films, are used in the experiments. The transient shock wave positions are obtained by a time-resolved shadowgraph technique. A N 2 -laser pumped dye laser with 3 ns pulse width is used as an illumination source and is synchronized with the ablation laser to obtain the transient shock wave position with nanosecond resolution. The transient shock position is used in a model for finding the shock wave speed as well as the pressure, temperature, and velocity just behind the shock wave. A power law is used for fitting curves on the experimentally obtained shock wave position. Knowing the shock wave position, the normal shock equations are used to calculate the thermo-fluid properties behind the shock wave. The solutions are compared with the Taylor-Sedov solution for spherical shocks and the reason for the deviation is described. The thermo-fluid property results show similar trends for all tested samples. The results show that the Taylor-Sedov solution under-estimates the pressure behind the shock wave when compared to the normal shock results.

Laser ablation consists of three coupled processes: i) heat conduction within the solid, ii) flow through a discontinuity layer (evaporation wave) attached to the solid surface, and iii) shock wave expansion of the laser induced vapor. In this paper; a one-dimensional solution for all three coupled processes is presented. The heat conduction and the evaporation wave are solved numerically. The shock wave expansion of the laser induced vapor, how ever, is solved analytically for the first time Analytical solutions for the classic Riemann problem have been employed to solve the transient propagation of the strong shock wave. This model provides a sound theoretical basis for the analysis of the laser ablation process. The effects of the laser intensity, back temperature and back pressure are analyzed. The temperature pressure; density and velocity of the laser induced vapor are calculated and the results are discussed.