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Particle Adhesion to Surfaces Theory of Cleaning
Published in R. P. Donovan, Particle Control for Semiconductor Manufacturing, 2018
However, there is a boundary layer of fluid on the surface of a wafer, so that particles on the surface are not subject to the full force of the fluid moving across the wafer surface. The boundary layer thickness is a function of the direction of fluid flow relative to the surface, but in general it is proportional to the square root of the kinematic viscosity, which is the fluid viscosity divided by the fluid density. Comparing air and water again, the square root of the kinematic viscosity of water is 0.25 times that of air, so that the boundary layer thickness of water is a factor of four less than that of air. Hence, the drag force experienced by a particle on a surface in a liquid is higher than that in air because the liquid boundary layer is thinner at comparable velocities.
Introduction
Published in Greg F. Naterer, Advanced Heat Transfer, 2018
Heat transfer near the surface occurs through a boundary layer. The boundary layer is a thin layer of fluid close to the solid surface of the wall in contact with the moving fluid stream. The fluid velocity varies from zero at the wall (called a no-slip condition) up to the freestream velocity at the edge of the boundary layer, which approximately within 1% corresponds to the freestream velocity. The boundary layer thickness is the distance from the surface up to the point at which the velocity is 99% of the freestream velocity. To determine how the velocity and temperature fields change through a boundary layer, and more generally the entire flow field, the governing differential equations of mass, momentum, and energy conservation must be solved. These three-dimensional equations in Cartesian, cylindrical, and spherical coordinates are shown in Appendix C and will be discussed further in Chapter 3.
Lithography
Published in Andrew Sarangan, Nanofabrication, 2016
Solvent evaporation occurs by diffusion through the stationary boundary air layer above the substrate, as illustrated in Figure 6.10. The thickness of this boundary layer is a function of the airflow pattern in the spinner bowl. A laminar flow free of turbulence has to be maintained to have a predictable boundary layer thickness and evaporation rate. If not, the evaporation rate and the film thicknesses could vary across the substrate surface. Therefore, spin coating is not just about the spinning substrate but also about controlling the airflow around the substrate in the spin bowl. Careful attention to all of these parameters is important to achieve a uniform film thickness.
Surface grown copper nanowires for improved cooling efficiency
Published in Cogent Engineering, 2018
Anagi M. Balachandra, A.G.N.D. Darsanasiri, Iman Harsini, Parviz Soroushian, Martin G. Bakker
The boundary layer forms near the pipe wall surface because the fluid velocity in direct contact with the solid surface goes to zero due to viscous forces acting between the shearing fluid/wall layers. Since fluids deform easily, the wall friction physically forces a parabolic boundary layer profile. Moving away from the wall, flow begins to return to free-stream velocity. The distance from the wall to the location where flow velocity returns to 99% of the free-stream velocity is called the boundary layer thickness. The boundary layer thickness for the pipe flow conditions considered in our experimental work was calculated at about 100 μm. This thickness and the inner structure of the boundary layer are very important as far as the effect of nanowires on heat transfer in turbulent flows is concerned. The thermal boundary layer, which is related to the fluid momentum/velocity boundary layer, is more important in heat transfer. The relative thickness of the thermal boundary layer with respect to the momentum boundary layer depends on the boundary conditions for temperature and velocity, and on the ratio of viscosity to thermal diffusivity (the Prandtl number). Under normal operating conditions, the Prandtl number is close to 1 for both nitrogen and helium, indicating that the thermal and the momentum boundary layers are somewhat similar.
Boundary layer development over non-uniform sand rough bed channel
Published in ISH Journal of Hydraulic Engineering, 2019
Figure 5 shows the measured velocity profiles with respect to flow depth and channel length for no seepage and seepage flow and gives the velocity profiles along the centreline of the developing flow. The boundary layer thickness is defined as the distance from the bed at which flow velocity is 99% of free stream velocity. The boundary layer thickness (δ) in Figure 5 is identified as:
Cutting fluid behavior under consideration of chip formation during micro single-lip deep hole drilling of Inconel 718
Published in International Journal of Modelling and Simulation, 2023
Ekrem Oezkaya, Andreas Baumann, Sebastian Michel, Dirk Schnabel, Peter Eberhard, Dirk Biermann
The application of Computational Fluid Dynamics (CFD) simulations gives here an opportunity to analyze the essential functions of the cutting fluid, the cutting fluid distribution, the removal of the chips as well as the cooling and lubrication of the active elements, in particular, the cutting edge and the guide pads. While the structural mechanical Finite Element Method (FEM) has established itself as an important analysis tool in machining, the use of CFD, in particular, with three-dimensional fluid modelling and simulation, is relatively new for machining tools with geometrically defined cutting edge. Only through detailed knowledge of the cutting fluid behavior (multidisciplinary relationships) and the effects on the production process the energy and resource intensive cutting fluid supply can be controlled in a targeted manner and the process can be efficiently improved [5]. In addition, reliable, economical machining of high-performance materials can only be achieved with an optimized tool geometry, which in turn requires fundamental knowledge of the interactions in the process. The importance of CFD application in machining technology has already been shown in previous studies and promotes in-depth knowledge that leads to a better understanding of the processes [6,7]. However, the modelling and meshing for CFD simulations differ considerably from structural mechanical FEM. In contrast to the definition of the geometry for a static calculation, the flow geometry must be adapted in CFD. Depending on the application, the flow geometry (fluid model) is modelled internally or externally. Problems to be solved internally, for example, drilling, are not only an enormous challenge because of the very small dimensions and complex geometry but also among the most difficult numerical problems to solve in fluid mechanics. In the computation domain, there are often flows that have different mathematical properties. In addition to the boundary conditions to be defined for the inlet and outlet of the flow and the physical properties of the fluid to be simulated, the choice of the turbulence model also plays an important role [8–10]. Just as important is the way of meshing the fluid model. In addition to the fine mesh with more elements in areas where the solution variables have high spatial gradients, the physical phenomena of the coupling of pressure and speed must also be well represented in the mesh in order to ensure the continuity of the fluid mass in the solution domain. An inflation layer, which is a special area in the fluid, is required in all areas near the wall [11]. The boundary layer thickness must be adapted to the fluid geometry and the effective flow parameters and is dependent, among other things, on the Reynolds number and viscosity of the fluid.