The effect of surface texture and roughness on shear and pressure forces in tribological applications in the lubrication regime is analyzed by means of lattice-Boltzmann simulations that take the geometry of real surface elements into account. Topographic data on representative surface structures are obtained with high spatial resolution with the application of an optical interference technique. The three-dimensional velocity field past these surfaces is computed for laminar flow of Newtonian fluids in the continuum regime. Subsequently, pressure and shear flow factors are obtained by evaluating the velocity field in accordance with the extended Reynolds equation of Patir and Cheng (1978, ASME J. Tribol., 100, pp. 12–17). The approach allows an efficient determination of the hydrodynamic characteristics of microstructured surfaces in lubrication. Especially, the influence of anisotropy of surface texture on the hydrodynamic load capacity and friction is determined. The numerical method used in the present work is verified for a simplified model configuration, the flow past a channel with sinusoidal walls. The results obtained indicate that full numerical simulations should be used to accurately and efficiently compute the characteristic properties of film flows past rough surfaces and may therefore contribute to a better understanding and prediction of tribological problems.
The objective of this paper is to analyze the laminar flow of a Newtonian fluid, pressurized and sheared, through a twodimensional channel with one sinusoidal wall. The motivation of this work is the investigation of shear flows in lubrication. The effects of Reynolds number and the geometrical dimensions on the velocity distributions and on the flow factors are studied numerically using the lattice Boltzmann method (LBM). The results are verified with analytical and other numerical solutions.
a b s t r a c tMembrane distillation (MD) is a promising thermally driven membrane separation technique. In MD, water vapor is being separated from the hot feed water solution using a microporous hydrophobic membrane, due to the difference in temperature, and hence vapor pressure, across the membrane. Air gap membrane distillation (AGMD) process is one of the common configurations of applying the MD process for water desalination and other applications. In AGMD, a stagnant air gap is introduced between the membrane and a condensation surface within the membrane module to reduce the conduction heat loss through the membrane. In this review article, design characteristics and operating conditions of AGMD and its modified designs to enhance the productivity and reduce the energy consumption are surveyed and discussed. Previous work on pilot AGMD systems and multi-stage or multi-effect systems with energy saving modules is highlighted. Membrane materials and developments used with the AGMD modules are presented with discussion of membrane fouling and scaling problems. In addition, modeling techniques based on the heat and mass transfer equations and simulation approaches of the AGMD process are presented. The merits of operating the AGMD systems with solar and other renewable energies are discussed along with the economic aspects. The future research directions of AGMD are highlighted in this review. This will help researchers to direct their research without repetition of previous known studies.
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