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• Impact of inclined wall on rising bubbles with shape and path instabilities are investigated. • Wall-induced zigzag and helicoidal bubble path analyzed by 3D reconstruction. • Restitution coefficient of helicoidal bubble likens droplet impact on horizontal wall. • Breakdown of bubble kinetic and surface energies highlights path instability modes. In this study, the dynamics of a single ellipsoidal air bubble rising in an inclined cylindrical vessel is experimentally investigated. The three-dimensional bubble trajectory reconstruction shows that the spirally rising bubble maintains two out-of-phase modes of oscillations, while the zigzagging bubble maintains a two-dimensional motion , despite the irregular rebounds with small amplitude. Assessing the bubble-wall rebounds for the helicoidal rising bubble shows that the normal restitution coefficient correlates with a modified normal Stokes number in the same manner as the normal wall collisions of liquid droplets [Legendre et al., 2005, Physics of Fluids 17, 097105]. A similar contribution of normal-to-wall and tangent-to-wall components of the kinetic energy in helicoidal bubble rise is maintained up to the highest inclination angle, i.e. 15°. However, for the zigzag rising bubble, despite the bubble rebounds on the wall, the wall-normal contribution of the kinetic energy is much less than its tangent-to-wall component. [ABSTRACT FROM AUTHOR]

Crack pinning by tougher heterogeneities is in principle an interesting way to toughen brittle materials. To study the impact of highly heterogeneous toughness field, we investigate numerically the propagation of a tensile penny-shape planar crack within an axisymmetric heterogeneous toughness field. In particular, we take into account the large crack front deformations induced by high toughness contrasts. To compute the variations of stress intensity factor along the crack front arising from its progressive deformation, a perturbation approach based on Bueckner-Rice weight function theory is used iteratively. For low enough toughness contrasts, the crack front deforms until reaching an equilibrium shape for which the local stress intensity factor equals the local toughness value at each point of the front. For larger contrasts, however, this equilibrium shape is never reached. Instead, some points of the crack front remained pinned by strong impurities, while some other part of the front advances continuously. The mechanism at the origin of this fingering instability is finally discussed. [ABSTRACT FROM AUTHOR]

Abstract: We examine the shape instability of dislocation-free strained islands in heteroepitaxial growth, using continuum elasticity theory. Using the dipole interaction approximation for the strain-energy proposed by Pimpinelli and Villain, we have calculated the critical island size at which the shape instability may occur, and found that our expressions for the strain-energy and corresponding critical island size are very similar to those obtained by Li, Liu, and Lagally (Phys. Rev. Lett. 85 (2000) 1922). In addition, for the case of Cu/Ni(100) submonolayer islands we have carried out a direct comparison between the continuum elasticity predictions for the force monopole density and dipole interaction energy and atomistic calculations. Our results indicate that while the continuum elasticity expressions significantly underestimate both the force monopole density and the dipole interaction energy, the use of atomistic calculations leads to reasonable agreement between the two approaches. Our results also confirm that the experimentally observed ramified islands in Cu/Ni(100) submonolayer growth cannot be explained by equilibrium energetics arguments. [Copyright &y& Elsevier]

Abstract: The equilibrium shapes of bilayer islands under anisotropic misfit stress have been theoretically characterized from a thermodynamics point of view. Based on an energy variation calculation, it is found that when the ratio σ between the components of the misfit stress is such that σ =−1, both square and rectangular shaped bilayer islands may coexist depending on the island volume and stress level. When σ ≠−1 and σ <0, the possibility of formation rectangular islands along both perpendicular directions is also discussed. [Copyright &y& Elsevier]

This paper aims at (a) comparative assessment of the different volume of fluid (VoF) based numerical schemes for a rising, single air bubble in isothermal liquid (water) layers and (b) investigation of bubble rise in thermally stratified liquid (therminol) layers. For numerical investigation of bubble rise in isothermal liquid layers, three available numerical schemes, Upwind, Quadratic Upstream Interpolation for Convective Kinematics (QUICK) and Monotonic Upwind Scheme for Conservation Laws (MUSCL) schemes, combined with the pressure-velocity coupling(p-v) approaches, such as, Pressure Implicit with Splitting of Operators (PISO) and Semi Implicit Method for Pressure-Linked Equations (SIMPLE), are considered. The wake analysis revealed that the region of influence grows beyond 10 times the diameter of the bubble. Moreover, based on the comparative assessment, MUSCL scheme with PISO is selected, for investigating the bubble rise in thermally stratified therminol layers. Based on these investigations, a 3D diagram, describing bubble shape as f (Ra, Eo, Ga), is proposed, and a new insight to the micro-convection, inside the rising bubbles is provided. Furthermore, a time-scale analysis is performed to describe the heat transfer mechanisms, (a) inside air bubble, and (b) between air bubble and the external surrounding liquid. Thus, the findings will be useful for the design of heat exchangers or cooling devices, which rely on the heat transfer augmentation with rising air bubble. [ABSTRACT FROM AUTHOR]