Dynamics of a Laser-Induced Bubble above the Flat Top of a Solid Cylinder—Mushroom-Shaped Bubbles and the Fast Jet

The dynamics of a laser-induced bubble on top of a solid cylinder is studied both experimentally and numerically. When the bubble is generated close to the flat top along the axis of the cylinder and its maximum radius exceeds the one of the flat top surface, it collapses in the form of a mushroom with a footing on the cylinder, a long stem and a hat-like cap typical for a mushroom head. The head may collapse forming a thin, fast liquid jet into the stem, depending on bubble size and bubble distance to the top of the cylinder. Several experimental and numerical examples are given. The results represent a contribution to understand the behavior of bubbles collapsing close to structured surfaces and in particular, how thin, fast jets are generated.

Effect of concentric and eccentric porous layer on forced convection heat transfer and fluid flow around a solid cylinder

In this paper, heat transfer and fluid flow around a solid cylinder wrapped with a porous layer in the channel were studied numerically by computational fluid dynamics (CFD). The homogeneous concentric and eccentric porous medium round a rigid, solid cylinder are supposed at local thermal equilibrium. The transport phenomena within the porous layer, volume averaged equations were employed, however the conservation laws of mass, momentum and energy were applied in the channel. This current numerical analysis, the effects of eccentricity ( ), the variable diameter of porous layer (d=0.07,0.08,0.09), permeability, as well as the different Reynolds number and Darcy number on the heat transfer parameters and fluid flow was investigated. The main purpose of this study is analyzed and compared the heat flux of concentric and eccentric porous layer in Reynolds number range of 1 to 40 and Darcy numbers of to . It is found that with the decline of Darcy number, the vortex length is increased behind the solid cylinder surface. In addition, the heat flux rate of the cylinder is raised with the increase of Reynolds number. Finally, The results have demonstrated that with raising Reynolds and Darcy numbers, the increase of the average Nusselt numbers in the eccentric porous layer is higher than the concentric porous layer.

Entropy production and mixed convection within trapezoidal cavity having nanofluids and localised solid cylinder

The entropy production and mixed convection within a trapezoidal nanofluid-filled cavity having a localised solid cylinder is numerically examined using the finite element technique. The top horizontal surface moving at a uniform velocity is kept at a cold temperature, while the bottom horizontal surface is thermally activated. The remaining surfaces are maintained adiabatic. Water-based nanofluids ($$\text {Al}_2\text {O}_3$$ Al 2 O 3 nanoparticles) are used in this study, and the Boussinesq approximation applies. The influence of the Reynolds number, Richardson number, nanoparticles volume fraction, dimensionless radius and location of the solid cylinder on the streamlines, isotherms and isentropic are examined. The results show that the solid cylinder’s size and location are significant control parameters for optimising the heat transfer and the Bejan number inside the trapezoidal cavity. Furthermore, the maximum average Nusselt numbers are obtained for high R values, where the average Nusselt number is increased by 30% when R is raised from 0 to 0.25.

Modeling and investigating of the influence of surface roughness on the strength of electrically conductive fiber

In the framework of the model of locally inhomogeneous electrically conductive nonferromagnetic solid, the near-surface inhomogeneity in a solid cylinder is investigated. It is shown that such inhomogeneity is characterized by three characteristic sizes associated with the structural inhomogeneity of the material, the roughness of the real surface and the electronic subsystem. The charge distribution features a double electric layer. The size effect of fiber strength and its dependence on geometric inhomogeneity parameters of the surface are studied.