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Continuum‐scale models used to model and predict two‐phase flow in the subsurface are often based on averaged flow parameters and do not consider pore‐scale fluid flow phenomena, for example, ganglion dynamics and thin‐film flow. As such, a major challenge in upscaling two‐phase flow for groundwater engineering applications is understanding the impact of disconnected flow and ganglion dynamics on continuum‐scale flow functions such as relative permeability‐saturation and capillary pressure‐saturation curves. In this study, we explored how changes in wettability and fluid velocity affect ganglion dynamics. We conducted pore‐scale numerical simulations with OpenFOAM to investigate the displacement of decane by water. Additionally, we examined how displaced phase saturation (a continuum‐scale flow function) responds to changes in dynamic fluid connectivity. We identified three different fluid flow regimes, that is, the connected pathway flow regime, ganglion dynamics (GD) flow regime, and droplet traffic flow regime, and studied the effects of changes in the wettability of the porous medium and the velocity of the invading fluid on the transitions between these different regimes. Our research showed that transitions between connected and disconnected pore‐scale flow regimes, which are induced by changes in fluid velocity and wettability, have a significant impact on both fluid displacement efficiency and average fluid flow transport kinetics. Plain Language Summary: The transport and confinement of hydrocarbons, organic pollutants or carbon dioxide (CO2) within rock pores is a complicated process that occurs on a minuscule scale and is crucial to groundwater engineering activities. The interplay of intricate fluid dynamics and alterations in rock and fluid characteristics at the microscopic level can have a considerable influence on continuum‐scale flow properties. Continuum‐scale models used to predict fluid flow in the subsurface are usually based on averaged flow parameters and do not account for the physics that occur at the pore scale. This often leads to disparities between the flow predictions made at the pore scale and at the field scale. A long‐standing challenge in scaling up flow from the pore scale to the continuum scale lies in addressing the impact of disconnected fluid ganglia and ganglion dynamics on overall flow transport kinetics. This work aims to bridge this gap between the pore and continuum scales. We investigate the behavioral response of the saturation function (a continuum‐scale function) to wettability and flow rate‐induced changes in dynamic fluid connectivity. Key Points: Changes in wettability and fluid flow rate induce transitions between connected and disconnected pore‐scale flow regimesTransitions between pore‐scale flow regimes have significant effects on the saturation function and flow transport kineticsThe Lomeland, Ebeltoft, and Thomas (L‐E‐T) relative permeability model can capture the effects of pore‐scale changes in fluid connectivity [ABSTRACT FROM AUTHOR]

We describe a promising approach to the processing of micro-optical components, where C[O.sub.2] laser irradiation in raster scan is used to generate localized surface melting of binary or multilevel structures on silica, fabricated by conventional reactive-ion etching. The technique is shown to provide well-controlled local smoothing of step features by viscous flow under surface tension forces, relaxing the scale length of etch steps controllably between 1 and 30 [micro]m. Uniform treatment of extended areas is obtained by raster scanning with a power stabilized, Gaussian beam profile in the 0.5 to 1 mm diameter range. For step heights of 1 [micro]m or less, the laser-induced relaxation is symmetric, giving softening of just the upper and lower comers at a threshold power of 4.7W, extending to symmetric long scale relaxation at 7.9 W, with the upper limit set by the onset of significant vaporization. Some asymmetry of the relaxation is observed for 3 [micro]m high steps. Also, undercut steps or troughs produced by photolithography and etching of a deep 64 level multistep surface are found to have a polarization-dependent distortion after laser smoothing. The laser reflow process may be useful for improving the diffraction efficiency by suppressing high orders in binary diffractive optical elements, or for converting multilevel etched structures in fused silica into smoothed refractive surfaces in, for example, custom microlens arrays. [c] 2010 Optical Society of America OCIS codes: 050.1380, 050.1970, 140.3390, 220.4000, 350.3950.

High average power (>50 W) nanosecond pulsed fiber lasers are now routinely available owing to the demand for high throughput laser applications. However, in some applications, scale-up in average power has a detrimental effect on process quality due to laser-induced thermal accumulation in the workpiece. To understand the laser–material interactions in this power regime, and how best to optimize process performance and quality, we investigated the influence of laser parameters such as pulse duration, energy dose (i.e., total energy deposited per unit area), and pulse repetition frequency (PRF) on engraving 316L stainless steel. Two different laser beam scanning strategies, namely, sequential method (SM) and interlacing method (IM), were examined. For each set of parameters, the material removal rate (MRR) and average surface roughness (Sa) were measured using an Alicona 3D surface profilometer. A phenomenological model has been used to help identify the best combination of laser parameters for engraving. Specifically, this study has found that (i) the model serves as a quick way to streamline parameters for area engraving (ii) increasing the pulse duration and energy dose at certain PRF results in a high MRR, albeit with an associated increase in Sa, and (iii) the IM offers 84% reduction in surface roughness at a higher MRR compared to SM. Ultimately, high quality at high throughput engraving is demonstrated using optimized process parameters. [ABSTRACT FROM AUTHOR]

We provide experimental evidence that the laser beam scanning strategy has a significant influence on material removal rate in the ultrafast laser machining of glass. A comparative study of two laser beam scanning methods, (i) bidirectional sequential scanning method (SM) and (ii) bidirectional interlaced scanning method (IM), is presented for micromachining 1.1-mm-thick borosilicate glass plates (Borofloat® 33). Material removal rate and surface roughness are measured for a range of pulse energies, overlaps, and repetition frequencies. With a pulse overlap of ≤90%, IM can provide double the ablation depth and double the removal rate in comparison to SM, whilst maintaining very similar surface roughness. In both cases, the root-mean-square (RMS) surface roughness (Sq) was in the range of 1 μm to 2.5 μm. For a 95% pulse overlap, the difference was more pronounced, with IM providing up to four times the ablation depth of SM; however, this is at the cost of a significant increase in surface roughness (Sq values >5 μm). The increased ablation depths and removal rates with IM are attributed to a layer-by-layer material removal process, providing more efficient ejection of glass particles and, hence, reduced shielding of the machined area. IM also has smaller local angles of incidence of the laser beam that potentially can lead to a better coupling efficiency of the laser beam with the material. [ABSTRACT FROM AUTHOR]

Conventional manufacturing of microfluidic devices from glass substrates is a complex, multi-step process that involves different fabrication techniques and tools. Hence, it is time-consuming and expensive, in particular for the prototyping of microfluidic devices in low quantities. This article describes a laser-based process that enables the rapid manufacturing of enclosed micro-structures by laser micromachining and microwelding of two 1.1-mm-thick borosilicate glass plates. The fabrication process was carried out only with a picosecond laser (Trumpf TruMicro 5×50) that was used for: (a) the generation of microfluidic patterns on glass, (b) the drilling of inlet/outlet ports into the material, and (c) the bonding of two glass plates together in order to enclose the laser-generated microstructures. Using this manufacturing approach, a fully-functional microfluidic device can be fabricated in less than two hours. Initial fluid flow experiments proved that the laser-generated microstructures are completely sealed; thus, they show a potential use in many industrial and scientific areas. This includes geological and petroleum engineering research, where such microfluidic devices can be used to investigate single-phase and multi-phase flow of various fluids (such as brine, oil, and CO2) in porous media. [ABSTRACT FROM AUTHOR]