Micro-geometry

Beskok, A., Kaeniadakis, G. E., Simulation of heat and momentum transfer in complex micro-geometries,... 

Beskok, A. and Karniadakis, G.E., Simulation of Heat and Momentum Transfer in Complex Micro Geometries, J. Thermophysics and Heat Transfer, 1994, 8(4), 647-655. Beskok, A., Karniadakis, G.E. and Trimmer, W., Rarefaction, Compressibility and Thermal Creep Effects in Micro-Elows, Proceedings of the ASME Dynamic Systems and Control Division, 1995, DSC-57-2, 877-892. 

In this work, heat and fluid flow in some common micro geometries is analyzed analytically. At first, forced convection is examined for three different geometries microtube, microchannel between two parallel plates and microannulus between two concentric cylinders. Constant wall heat flux boundary condition is assumed. Then mixed convection in a vertical parallel-plate microchannel with symmetric wall heat fluxes is investigated. Steady and laminar internal flow of a Newtonian is analyzed. Steady, laminar flow having constant properties (i.e. the thermal conductivity and the thermal diffusivity of the fluid are considered to be independent of temperature) is considered. The axial heat conduction in the fluid and in the wall is assumed to be negligible. In this study, the usual continuum approach is coupled with the two main characteristics of the microscale phenomena, the velocity slip and the temperature jump. 

The notion of the critical thickness of the wetting film, h , can preserve its physical meaning if the micro-geometry of a rough surface satisfies some conditions. The necessary condition of a smooth spherical particle attachment Eq. (11.80) can be used for a spherical macroscopically smooth surface, too. 

Chamfer Honed cutting edges Macro geometry Micro geometry Rounded cutting edge... 

Current research focuses mainly on the cutting edge micro geometry (Denkena et al. 2011). The micro geometry describes the wedge geometry within a distance of up to 150 pm from the ideal... 

Cutting Edge Geometry, Fig. 4 Favorable micro geometries for different workpiece materials... 

The term dressing refers to different processes used to prepare and regenerate the macro and micro geometry of grinding wheels. 

Walker, W.C., Popper, P., Tam, A., 2009. Direct formation of textile shapes via a self-interlacing micro-geometry or structure process SpiderWeb. In 2nd World Conference on 3D Fabrics and Theb Applications, Greenville, SC, USA. U.S. Patent 6,107,220 U.S. Patent 6,323,145 U.S. Patent 6,579,815. 

Wang and Sun (2001) developed another numerical method to simulate textile processes and to determine the micro-geometry of textile fabrics. They called it a digital-element model. It models yams by pin-connected digital-rod-element chains. As the element length approaches zero, the chain becomes fully flexible, imitating the physical behavior of the yams. The interactions of adjacent yarns are modeled by contact elements. If the distance between two nodes on different yarns approaches the yam diameter, contact occurs between them. The yarn microstructure inside the fabric is determined by process mechanics, such as yarn tension and interyam friction and compression. The textile process is modeled as a nonlinear solid mechanics problem with boundary displacement (or motion) conditions. This numerical approach was identified as digital-element simulation rather than as finite element simulation because of a special yam discretization process. With the conventional finite element method, the element preserves... 

There are two common approaches. The first approaeh is to combine porous media theory with more generalized flow models such as Stokes flow to take into accoimt micro-geometrie effects. This approach is referred to as micro-modeling. Another approach is to use porous media theory and apply it to the entire mould, macro-flow. Micro-flow models can take into account complex geometry regions of a mould, while macro-flow models can consider larger, more complex moulds [15],... 

Fig. 8 Initial micro-geometry at the apex of the head of inplant no. 4.

The solid friction is calculated by an energetic approach which is described in [1] and in more depth by Bartel [10]. The components of the solid friction are deformation and adhesion. The first one can be calculated from the elastic-, plastic deformations of the macro and micro geometry. To calculate the adhesion force, some assumptions have to be taken into account at the moment Adhesive bonding can only occur if plastic deformation of the material takes place and secondly if local temperatures exceed a critical value which lead to a desorption of the fluid film. Since the simulation program is not able to determine local temperatures yet, the second assumption cannot be tested. But it seems reasonable that the plastically deformed micro asperity also experience local temperature peaks. Since it is quite sophisticated to get reliable values for the shear strength in adhesive bonding, in this work one sixth of the universal hardness or plastic pressure limit of 100Cr6 (SAE 52100), respectively, is used ... 

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