Venturi bubble generators have been extensively studied because of having a simple structure and high foaming efficiency, while producing a uniform bubble size. The effect of a noncondensable gas on hydraulic cavitation was considered to improve the Zwart-Gerber-Belamri cavitation model. This improved model and a population balance model were used to study the effect of cavitation on bubble fragmentation. The CFD-PBM results were compared with experimental results, and the accuracy of the improved calculation method was verified in terms of the distributions for the cavitation cavity, gas phase, and bubble size. The calculation results showed that increasing the noncondensable gas content over a certain range promoted the development of hydraulic cavitation, and the cavitation intensity could be indirectly controlled by adjusting the noncondensable gas content. With increasing cavitation intensity, the average bubble size decreased, and the bubble size distribution became narrower. Therefore, a high-pressure pulse generated by cavitation could effectively break bubbles. The development process of Microbubbles was studied. The main controlling factors for bubble formation were determined to be the turbulent shear force of the fluid and the collapse impact force of the cavitation group, which provides a theoretical basis for optimizing the design of bubble generators.

Colloidal Gas Aphrons (CGA), consist of gas bubbles with diameters ranging from 10 to 100 micron, surrounded by a thin aqueous surfactant film. This fluid combines certain surfactants and polymers to create the systems of Microbubbles. The function of surfactant in CGAs is to produce the surface tension to contain the aphrons. Also, a biopolymer needs to be considered in the formulation as a viscosifier as well as a stabilizer. The aphron-laden fluid appears to be particularly well suited for drilling through depleted zones. The unique feature of aphron based fluids is to form a solid free, tough, and elastic internal bridge in pore networks or fractures to minimize deep invasion using air Microbubbles. This microenvironment seal readily cleans up with reservoir flow back as production is initiated, thereby reducing cost associated with stimulation processes. This paper presents a comprehensive, comparative study of rheological behavior and filtration properties of CGA based drilling fluids with various concentrations of polymer and surfactant. Laboratory evaluations showed that the CGA based fluid is one of the ideal engineering materials which can control and kill the loss circulation, save cost and increase productivity in which rheological characteristics and filtration properties of them are greatly influenced by the level of polymer and surfactant concentration.

Background: Microbubbles are widely used in diagnostic ultrasound applications as contrast agents. Recently, many studies have shown that Microbubbles have good potential for the use in therapeutic applications such as drug and gene delivery and opening of blood-brain barrier locally and transiently. When Microbubbles are located inside an elastic microvessel and activated by ultrasound, they oscillate and induce mechanical stresses on the vessel wall. However, the mechanical stresses have beneficial therapeutic effects, they may induce vessel damage if they are too high. Microstreaming-induced shear stress is one of the most important wall stresses. Objective: The overall aim of this study is to simulate the interaction between confined bubble inside an elastic microvessel and ultrasound field and investigate the effective parameters on microstreaming-induced shear stress. Material and Methods: In this Simulation study, we conducted a 2D finite element simulation to study confined Microbubble dynamics, also we investigated both acoustical and bubble material parameters on Microbubble oscillation and wall stress. Results: Based on our results, for acoustic parameters in the range of therapeutic applications, the maximum shear stress was lower than 4 kPa. Shear stress was approximately independent from shell viscosity whereas it decreased by increasing the shell stiffness. Moreover, shear stress showed an increasing trend with acoustic pressure. Conclusion: Beside the acoustical parameters, bubble properties have important effects on bubble behavior so that the softer and larger bubbles are more appropriate for therapeutic application as they can decrease the required frequency and acoustic pressure while inducing the same biological effects.

Conventional Flux Compression generators (FCG"s) are used to generate high power ‎DC pulses. A new kind of (FCG"s) with series capacitance called Capacitive Flux ‎Compression generator (CFCG) will be introduced and explained in this paper. This ‎new kind is used to generate modulated high power pulses. There are some problems ‎to establish a capacitance in high power and high frequency applications. In the ‎present paper several practical methods will be addresed to make capacitance in high ‎power and high frequency applications‎‏.‏