Initiation of an explosion of a single bubble and bubble detonation

Interaction of a single chemically active bubble in water with acoustic waves is numerically studied within the framework of the model of a two-dimensional unsteady flow of an ideal compressible medium. The boundaries between the phases are explicitly identified. It is demonstrated that bubble explosion initiation can be determined by the character of bubble deformation. Nonsphericity of deformation and jet formation lead to an explosion even if the bubble does not collapse. The possibility of the bubble explosion in an expansion wave, transfer of detonation from one bubble to another, and, thus, emergence of bubble detonation is demonstrated.     

The effect of bubble size on the detonation wave characteristics

Detonation waves in various monodispersed media containing gas bubbles with a specified diameter were investigated experimentally. The investigation centered on the effect of the bubble size on the critical initiation conditions, the structure and on the properties of the detonation waves in bubbly media. Lower and upper bubble diameter limits were detected for the existence of detonation waves. The behavior characteristics of the gas bubbles of various diameters in the detonation wave are explained. M. A. Lavrent'ev Hydrodynamics Institute, Siberian Division, The Russian Academy of Sciences, 630090 Novosibirsk. Translated from Fizika Goreniya i Vzryva, Vol. 31, No. 5, pp. 83–91, September–October, 1995.     

Critical energy of bubble detonation wave initiation by a wire explosion

Initiation of bubble detonation by a short shock wave generated by exploding a wire located in a chemically active bubbled medium is studied experimentally. Critical energies of detonation initiation are determined for different volume fractions of bubbles. It is demonstrated that this method of initiation transforms the compression wave to a detonation wave at a length of ≈0.3 m. In the case of a wire explosion in a gas-liquid medium, the critical energy of bubble detonation initiation can be reduced by more than two orders of magnitude, as compared with initiation by a gas detonation wave.     

四传感器光纤探针测量气泡速度矢量模型

光纤传感器作为纤维光学领域中的新技术,在两相流动局部参数测量中得到了越来越广泛的应用。在假设气泡对称面垂直于气泡运动方向的基础上,对四传感器探针测量局部瞬时气泡速度的数学原理进行了详细推导,给出了新的计算气泡速度矢量的方法和模型,并运用自制的四传感器光纤探针,对气液两相流动中的气泡运动速度和方向进行了测量。实验中通过探针方法测得气相流速相对于流量计测量值的平均偏差为9%,表明新的探针测量方法精度较高,能够用于两相流中气泡速度矢量测量。进一步的实验研究表明,不同流动条件下,局部空泡份额及界面面积浓度(IAC)沿通道径向呈“壁峰型”或“核峰型”的分布规律。     

竖直加热壁面上汽泡脱离及浮升点汽泡直径预测模型

针对汽泡在脱离点和浮升点的力平衡特点,根据受力分析结果对汽泡的动量平衡方程进行了简化。提出了汽泡在竖直加热壁面上脱离和浮升的判据。采用Thorncroft的实验数据进行检验,结果发现,汽泡的脱离及浮升直径预测值与实验值误差在±20%以内。模型分析结果表明,向上流动的汽泡脱离直径随平均流速的增加而减小,随壁面过热度的增加而增加;向下流动情况大致相同;但由于流动曳力对汽泡脱离的作用和浮力的作用相反,从而导致了在02～03 m·s-1流速范围内出现汽泡不脱离的现象。在向上流动条件下,由于汽泡脱离核化点后的滑动方向和主流方向一致,从而使得汽泡与流体间的相对速度减小,使浮升直径大大增加;向下流动时,汽泡浮升直径随平均流速和壁面过热的关系与脱离直径的变化趋势基本一致,但与壁面过热的关系没有脱离直径的明显。     

加压大型鼓泡床反应器内大小气泡气含率研究

在内径0.3m、高6.6m的加压鼓泡床反应器内采用床层塌落技术测量床层内的大小气泡气含率实验。由于大小气泡上升速度不同,床层塌落曲线存在一水平段,在此基础上,详细考察了表面张力、粘度、系统压力、表观气速对大小气泡气含率的影响,得出大气泡气含率随粘度和表面张力升高而升高,随压力升高而降低;小气泡气含率随粘度和表面张力升高而降低,随压力升高而升高;并根据质量守恒定理,进行了解释。     

Bubble detonation conditions

Initiation of bubble detonation in the system “inert liquid-explosive gas bubbles” by a detonation wave in a gas was studied experimentally. Compression-wave pressure profiles were determined as functions of the length of the initiation section and the initial pressure of the explosive gas mixture in it. It was shown that because of the effect of the explosive-gas volume between the diaphragm and the upper boundary of the bubble medium, the pressure in front of the initiating wave increased much more slowly than the initial pressure. The optimal length of the initiation section was found, and the critical (minimum) initiation pressure in it and at the shock-wave front were determined. It was found that for a fixed gas volume concentration in the bubble medium, the pressure in the initiation section increased insignificantly as the length of the section decreased. __________ Translated from Fizika Goreniya i Vzryva, Vol. 43, No. 2, pp. 84–90, March–April, 2007.     

Model validation for low and high superficial gas velocity bubble column flows

In the present work, gas-liquid flow dynamics in a bubble column are simulated with CFDLib using an Eulerian-Eulerian ensemble-averaging method in a two-dimensional Cartesian system. The two-phase flow simulations are compared to experimental measurements of a rectangular bubble column performed by Mudde et al. [1997. Role of coherent structures on Reynolds stresses in a 2-D bubble column. A.I.Ch.E. Journal 43, 913-926] and a cylindrical bubble column performed by Rampure et al. [2003. Modeling of gas-liquid/gas-liquid-solid flows in bubble columns: experiments and CFD simulations. The Canadian Journal of Chemical Engineering 81, 692-706] for low and high superficial gas velocities, respectively. The objectives are to obtain grid-independent numerical solutions using CFDLib to reconcile unphysical results observed using FLUENT with increasing grid resolutions [Law, D., Battaglia, F., Heindel, T.J., 2006. Numerical simulations of gas-liquid flow dynamics in bubble columns. In: Proceedings of the ASME Fluids Engineering Division, IMECE2006-13544, Chicago, IL], and to validate computational fluid dynamics (CFD) simulations with experimental data to demonstrate the use of numerical simulations as a viable design tool for gas-liquid bubble column flows. Numerical predictions are presented for the local time-averaged liquid velocity and gas fraction at various axial heights as a function of horizontal or radial position. The effects of grid resolution, bubble pressure (BP) model, and drag coefficient models on the numerical predictions are examined. The BP model is hypothesized to account for bubble stability, thus providing physical solutions.     

Theory of solid-state detonation

The Jouguet theory allows one to estimate the detonation velocity from the known shock adiabat of the product of a solid-state chemical reaction initiated by a shock wave. Using manganese and zinc chalcogenides as an example, it is shown that such estimates are close to experimental detonation velocities in these systems. __________ Translated from Fizika Goreniya i Vzryva, Vol. 43, No. 2, pp. 108–110, March–April, 2007.     

Ozone-modified detonation nanodiamonds

XPS, EPR and NMR studies of the ozone-treated nanodiamond (NDO) are presented. Based on the spectra, the nature of the surface chemical functional groups, which were formed as a result of the ozone reaction with the pristine DND surface in the soot, is discussed.     

Theory of aerosol detonation

Odessa. Translated from Fizika Goreniya i Vzryva, Vol. 24, No. 4, pp. 101–109, July–August, 1988.     

Model and experimental visualizations of the interaction of a bubble with an inclined wall

In this paper we derive a model based on lubrication theory to describe the interaction of a bubble with an inclined wall. The model is an extension of the model derived by Klaseboer, Chevailier, Mate, Masbernat, Gourdon [2001. Model and experiments of a drop impinging on an immersed wall. Physics of Fluids 13(1), 45-57.] and Moraga, Drew, Larreteguy, Lahey [2005. Modeling wall-induced forces on bubbles for inclined walls. Multiphase Science and Technology 17(4), 483-505.] in the case of a horizontal wall. We consider bubbles of diameter 1-2 mm, which corresponds to high Reynolds numbers , and moderate deformation effects (with a Weber number of O(1)). Predictions of the model are compared with experimental visualizations of air bubbles rising in water toward an inclined wall. The dynamical behavior of bubbles is observed to depend on the wall inclination. We find that the model reproduces the bubble trajectories for wall inclinations smaller than 55^°-60^°. This critical value for the wall inclination corresponds to an experimentally observed transition in the bubble bouncing behavior, which agrees with the observations of Tsao and Koch [1997. Observations of high Reynolds number bubbles interacting with a rigid wall. Physics of Fluids 468, 271.]. We show that the main features of our lubrication-based model for rebound with an inclined wall can be expressed with a simple force model proposed by Moraga et al., suitable for use in direct numerical simulations of multiphase flow.     

竖直窄流道内过冷流动沸腾的单汽泡生长模型

The process of bubble growth on heating wall in subcooled boiling includes the micro-layer evaporation on heating wall and the bubble top coagulation when the bubbles grow to a certain size and emerge into the subcooled mainstream fluid. Based on this consideration, a model for the single bubble growth of subcooled flow boiling in vertical narrow rectangular channel was proposed.Compared with experimental results, the error of the simulation results using the proposed model is less than ±25%. The simulation results indicated that as the wall superheat increases, the bubble growth gets faster, with the subcooled degree of mainstream increases, the bubble growth in later stage would be slowed, with the contact angle increases, the contact radius of the bubble bottom and the wall tension would be strengthened, resulting in faster bubble growth to make the bubble to be flat and more easily exposed to the mainstream. The velocity of mainstream has no significant effects on bubble growth rate.     

鼓泡塔内气泡羽流周期性摆动的数值模拟

以二维和三维鼓泡塔内气液二相流动的动态特性为研究对象,寻找各自合适的湍流模型和边界条件设置。二维鼓泡塔的进口气速采用2种不同的方法:①实际进口速度法;②均值修正法。湍流模型选用标准k-ε湍流模型、RNG k-ε湍流模型。结果显示二维模拟使用RNG k-ε湍流模型、三维模拟使用标准k-ε湍流模型能够得到周期性的羽流摆动,且二维鼓泡塔的进口气速采用均值修正法能够得到较合理的摆动周期。