Thermodynamic effects of gas adiabatic index on cavitation bubble collapse.

In this paper, an improved multicomponent lattice Boltzmann model is employed to investigate the impact of the gas properties, specifically the gas adiabatic index, on the thermodynamic effects of cavitation bubble collapse. The study focuses on analyzing the temperature evolution in the flow field and the resulting thermal effects on the surrounding wall. The accuracy of the developed model is verified through comparisons with analytical solutions of the Rayleigh-Plesset equation and the validation of the adiabatic law. Then, a thermodynamic model of cavitation bubble composed of two-mixed gases collapsing near a wall is established to explore the influence of the gas adiabatic index γ on the temperature behavior. Key findings include the observation that the γ affects the temperature of the first collapse significantly, while its influence on the second collapse is minimal. Additionally, the presence of low-temperature regions near the bubble surface during collapse impacts both bubble and wall temperatures. The study also demonstrates that the γ affects maximum and minimum wall temperatures. The results have implications for selecting specific non-condensable gas properties within cavitation bubbles for targeted cooling or heating purposes, including potential applications in electronic component cooling and environmental refrigeration.

Analysis of P wave induced second-order harmonic field at solid-fluid interface with potential matrix algorithm.

Based on the second-order harmonic potential theory, the characteristics of the second-order harmonic field generated at the solid-liquid interface induced by P wave incidence are analyzed. A planar model of the solid-liquid interface is established to study the variation of the second-order displacement field versus the incident angles. The homogeneous solution coefficient matrix, refraction and reflection coefficient matrix are introduced. According to the boundary conditions and Lagrange's various parameters method, the second-order displacement field is obtained, and its dependence on the solid-liquid interface is investigated. The different effects of boundary on the tangential displacement and normal displacement are demonstrated. Numerical simulation shows that the complete solution varies slightly at the incident angle, and the tangential displacement and the normal displacement change sharply at a mutation angle θω due to the boundary effect.

Self-Organized Fractal Structures on Plasma-Exposed Silver Surface.

Planar fractal microstructure is observed on the silver film treated by positive corona discharge for the first time. Due to the abundant positive ions driven by the electrical field of positive polarity, surface modification is mainly induced by the plasma oxidation effect, resulting in a large scale of dendritic pattern with self-similarity and hierarchy. In contrast, negative ions dominate the plasma-film interaction under negative corona discharge condition, leading to a different surface morphology without fractal characteristics. A growth model based on the modified diffusion-limited aggregation (DLA) theory is proposed to describe the formation of the dendritic fractal structure, whilst the physics behind is attributed to the electric field directed diffusion of the positive ions around the surface roughness. Numerical simulation verifies the high density of the hot spot in the dendritic pattern, which may enable potential applications in fractal photonic metamaterials.

Thermodynamic of collapsing cavitation bubble investigated by pseudopotential and thermal MRT-LBM.

The thermodynamic of cavitation bubble collapsing is a complex fundamental issue for cavitation application and prevention. The pseudopotential and thermal multi-relaxation-time lattice Boltzmann method (MRT-LBM) is adopted to investigate the thermodynamic of collapsing cavitation bubble in this paper. The simulation results satisfy the maximum temperature equation of the bubble collapse, which derived from the Rayleigh-Plesset (R-P) equation. The validity of thermal MRT-LBM in simulating the collapse process of cavitation bubble is verified. It shows that the temperature evolution of vapor-liquid phase is well captured. Furthermore, the two-dimensional (2D) temperature, velocity and pressure field of the bubble near a solid wall are analyzed. The maximum temperature inside the bubble and wall temperature under different position offset parameters are discussed in details.

Propagation characteristics of interface waves between a porous medium and a sediment-containing two-phase fluid.

Based on the modified Biot theory of Johnson, the propagation characteristics of the various interface waves at an interface between a semi-infinite fluid and a porous medium were studied. First, based on the characteristic equations of open-pore and sealed-pore, which were derived from the wave equations, time-domain waveforms at the interface were obtained by inverse Fourier transform. The effects of the longitudinal frame modulus on the interface waves were investigated. For open-pore and sealed-pore, the effect of porosity on the propagation of the interface waves was studied; the porosity was found to strongly influence the true surface wave. Based on four ultrasonic suspension models-Utrick, Utrick-Ament (UA), Harker-Temple (HT) and McClement, the pseudo-Stoneley wave propagation characteristics were analyzed at the interface between the sediment-containing two-phase fluid and the porous medium solid. The effects of volume fraction and particle diameter on the phase velocity, attenuation coefficient and dispersion for the pseudo-Stoneley and true surface wave were discussed, and the results demonstrated that the properties of the fluid strongly impacted the pseudo-Stoneley wave but exerted very little effect on the true surface wave. The conclusions drawn in this paper could contribute to elucidate the parameters of sediment and porous media.

Study of a peak in cavitation activity from HIFU exposures using TA fluorescence.

Methods of measuring the sound field and focal region of a 1.05 MHz high intensity focused ultrasound (HIFU) are described in this paper. 1.05 MHz pulsed HIFU with intensity 2400 W/cm(2) with a 1:1 duty cycle ("on" phase equaled "off" phase) was used to irradiate terephthalic acid (TA). Pulse periods of 0.5 ms, 1 ms, 3.3 ms, 10 ms, 15 ms, 33 ms, 0.1s and 1s were used. The irradiation time was 2 min. To indicate the intensity of inertial cavitation activity, the fluorescence intensity of hydroxyterephthalic acid (HTA) was measured. The result shows that the cavitation activity of pulsed HIFU peaks at a pulse period of 10 ms, cavitation activity is significantly greater for pulse periods from 2 to 20 ms than for others.