Effects of Surface Roughness

More recently Carre and Schultz [28] have used the Wenzel equation to determine the value of the roughness factor, rf, for various types of solid 

Wenzel s relation has been confirmed in terms of the first two laws of thermodynamics. Huh and Mason, in 1976, used a perturbation method for solving the Young-Laplace equation while applying Wenzel s equation to the surface texture. Their results can be reduced to Wenzel s equation for random roughness of small amplitude. They assume that hysteresis was caused by nonisotropic equilibrium positions of the three-phase contact line, and its movement was predicted to occur in jumps. On the other hand, in 1966, Timmons and Zisman attributed hysteresis to microporosity of solids, because they found that hysteresis was dependent on the size of the liquid molecules or associated cluster of molecules (like water behaves as an associated cluster of six molecules). 

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A number of refinements and applications are in the literature. Corrections may be made for discreteness of charge [36] or the excluded volume of the hydrated ions [19, 37]. The effects of surface roughness on the electrical double layer have been treated by several groups [38-41] by means of perturbative expansions and numerical analysis. Several geometries have been treated, including two eccentric spheres such as found in encapsulated proteins or drugs [42], and biconcave disks with elastic membranes to model red blood cells [43]. The double-layer repulsion between two spheres has been a topic of much attention due to its importance in colloidal stability. A new numeri-... 

The effect of surface roughness on contact angle was modeled by several authors about 50 years ago (42, 45, 63, 64]. The basic idea was to account for roughness through r, the ratio of the actual to projected area. Thus = rA. lj apparent and similarly for such that the Young equation (Eq.-X-18) becomes... 

Lin et al. [70, 71] have modeled the effect of surface roughness on the dependence of contact angles on drop size. Using two geometric models, concentric rings of cones and concentric conical crevices, they find that the effects of roughness may obscure the influence of line tension on the drop size variation of contact angle. Conversely, the presence of line tension may account for some of the drop size dependence of measured hysteresis. 

This case vividly illustrates the potential effect of surface roughness on the propagation of cavitation bubbles. Figure 12.18 represents a surface... 

J. A. Cookson and J. L. Campbell. NucL Instr. Meth. Phys. Res. 216, 489, 1983. Calculated effects of surface roughness on thick-target PDCE. 

A principal aim of the discussion thus far has been to set out a theoretical framework within which it is possible to rationalise the effects of surface roughness on adhesion. It may be useful to summarise this framework before examining practical examples taken from the literature. 

Quantifying the effect of surface roughness or morphology is difficult, however. Surface preparations that provide different degrees of surface roughness also usually produce surfaces that have different oxide thicknesses and mechanical properties, different compositions, or different contaminant levels. The problem of separation of these variables was circumvented in a recent study [52] by using a modified microtome as a micro milling machine to produce repeatable, well-characterized micron-sized patterns on clad 2024-T3 aluminum adherends. Fig. 2 shows the sawtooth profile created by this process. 

Judy J, Maynes D, Webb BW (2002) Characterization of frictional pressure drop for liquid flows through micro-channels. Int J Heat Mass Transfer 45 3477-3489 Kandlikar SG, Joshi S, Tian S (2003) Effect of surface roughness on heat transfer and fluid flow characteristics at low Reynolds numbers in small diameter tubes. Heat Transfer Eng 24 4-16 Koo J, Kleinstreuer C (2004) Viscous dissipation effects in microtubes and microchannels. Int J Heat Mass Transfer 47 3159-3169... 

Fig. 4.7a,b Trapezoidal micro-channels, (a) Effect of surface roughness on Nusselt number (Wu and Cheng 2003). (b) Effect of geometric parameters on Nusselt number (Wu and Cheng 2003). Reprinted from Wu and Cheng (2003) with permission... 

Pandey, A. K. and Pratap, R., Coupled Nonlinear Effects of Surface Roughness and Rarefaction on Squeeze Film Damping in MEMS Structures," 7. Micromech. Microeng., Vol. 14, 2004, pp. 1430-1437. 

Patir, N., Effects of Surface Roughness on Partial Film Lubrication Using an Average Flow Model Based on Numerical Simulation. Ph.D. Thesis, Northwestern University, 1978. 

Sun, H., Faghri, M., Effect of surface roughness on nitrogen flow in a micro-channel using the Direct Simulation Monte Carlo Method (DSMC), Numerical Heat Transfer A 43 (2003) 1-8. 

Effect of surface roughness. CHF for rough surfaces was measured on vertical annular tubes cooled by a downward flow of subcooled water by Durant and Mirshak (1959, 1960). An increase in the apparent critical heat flux of as much as 100% over a smooth surface was obtained at the same coolant velocity, temperature, and pressure. The heated surfaces were 304 SS and Zircaloy-2 tubes about... 

Two questions need to be answered if one wants to develop a method of generating a limiting current gradually while minimizing the effect of surface roughness ... 

The effect of surface roughness has not yet been studied, but in all experiments the surface roughness was small on the scale of particle sizes used. 

Szleifer, I., Ben-Shaul, A. and Gelbart, W. M. (1986). Chain statistics in micelles and bilayers effects of surface roughness and internal energy, J. Chem. Phys., 85, 5345-5358. 

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