Microchannel surface roughness

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... 

An infrared C02 laser (1060 nm) was used to cut through a polycarbonate PC (black) (carbon-coated) wafer of 250-pm thickness to create microfluidic channels. The laser-machined black PC wafer was then thermally bonded between two transparent PC wafers at 139°C under two tons of pressure for 45 min [937], A C02 laser was also used to ablate Mylar sheets (with adhesive). Then the machined Mylar sheets were laminated together [1051]. Moreover, a PMMA substrate was machined by a C02 laser [201,202]. However, the microchannel ( 200 pm deep) has a Gaussian-like cross section and a certain degree of surface roughness [201], The C02 laser has also been used to machine PET substrates [203],... 

Superhydrophilic and superhydrophobic surfaces are more effective at stabilizing two-phase microflows. These surfaces can be obtained by creating roughness utilizing titanium nanoparticles. Titanium modification of a microchannel yields nanometer-scale surface roughness, and subsequent... 

Matsushita et al. (2007) subsequently demonstrated the ability to N-alkylate amines (Scheme 57) under continuous flow, again employing a quartz microreaction channel coated with a Ti02 or Pt-loaded Ti02 layer. As Table 28 illustrates, the illuminated specific surface area per unit of liquid attained within a microchannel is large even without taking into account the surface roughness of the catalyst however, it can be seen that a shallow reaction channel provides optimal photon efficiency. 

M.B. Tmgay and A. Guvenc Yazicioglu, Effect of surface roughness in parallel-plate microchannels on heat transfer, Numerical Heat Transfer 56, 497-514 (2009). 

M.B. Turgay, Effect of surface roughness in microchannels on heat transfer, M.Sc. Thesis, Middle East Technical University, Ankara, Turkey (2008). 

The process time depends on the complexity of the 3D microstructures therefore, it is commonly used for prototyping. An extensive review on stereolithography can be found in Reference 119. The latter method is a subtractive manufacturing process that uses a focused high-intensity laser beam to evaporate the material from the surface. Laser ablation is mostly used to fabricate microchannels in thermosetting polymers such as polyimide due to its physical properties. Microstructures of nanometer scale have been danonstrated, but the surface roughness and properties using laser... 

It can be concluded that the most significant impact on the formation of the flow patterns originated from the fluid properties, channel size, channel wettability, flow rate ratio and interfacial tension. A comprehensive flow pattern map should be dependent on the fluid and microchannels characteristics, and thus correlate the flow regimes using the relative forces responsible as well as the surface roughness. 

Boundary Slip of Liquids, Fig. 6 Slip length versus shear rate for flow of n-hexadecane in microchannel of different channel depths (//) and surface roughness... 

Electrokinetic or pressure-driven liquid flow in microchannels with three-dimensional (3D) surface roughness generated by manufacturing techniques or by adhesion of biological particles from the liquid. 

Hu Y, Werner C, Li D (2(X)3) Influence of 3D surface roughness on low-Reynolds pressure-driven flow through microchannels. Fluid Eng 125 871... 

While experimental evidence indicates that fluid flow in microdevices differs from flow in macroscale, existing experimental results are often inconsistent and contradictory because of the difficulties associated with such experiments and the lack of a guiding rational theory. Koo and Kleinstreuer [6] summarized experimental observations of liquid microchannel flows and computational results concerning chamiel entrance, wall slip, non-Newtonian fluid, surface roughness, and other effects. Those contradictory results suggest the need for applying molecular-based models to help establish a theoretical frame for the fluid mechanics in microscale and nanoscale. 

The large surface-to-volume ratio in microchannels tends to enhance several factors that were neglected in macroscale flow and heat transfer, such as surface frictiOTi, compressibility, surface roughness, viscous, channel surface geometry, surface electrostatic charges, axial wall heat conduction, and measurement errors. Velocity slip flow has been widely studied accurately to model the characteristics of gas flow in the Knudsen layer for aU flow regimes. A review of the slip velocity can be fotmd in Zhang et al. [4]. 

One common conclusion of many of these early studies was that the relatively high surface roughness of the microchannels investigated was a major factor in the observed... 

In microreactors, the friction factor is not independent of wall surface roughness. Moreover, molecular interaction with the walls increases relative to intermolecular interactions when compared to macro-scale flows. In macro-scale systems, two boundary conditions will be applied, that is, a no-slip-flow in which the fluid next to the wall exhibits the velocity of the fluid normally being zero in the most common conditions, and a slip flow in which the velocity of the fluid next to the wall is not zero, and is affected by the wall friction effects and shear stress at the wall. In the case of the slip-flow conditions, a significant reduction in the friction pressure drop and thus reducing the power consumption required to feed the fluid into the microchannel reactor. For most cases in microreactors, the = 0.1 continuum flow with slip boundary conditions is applied. In addition, the pressure drop inside the microreactor is minimal in comparison to that of macro-scale systems (Hessel et ai, 2005b). 

Wu and Cheng [26] derived a Nu correlation based on experimental results in trapezoidal Si microchannels. The surface roughness k is taken into account, in addition to geometric aspects ... 

With copper or brass as base material, the best surface quality is obtained with mechanical precision machining, followed by an electropolishing step. By this means, a surface roughness of down to 30 nm can be reached. Figure 2.7 shows the surface of a single O F copper microchannel after the electropolishing step. For all techniques, details can be found in [1, 4,14—20]. 

The microstructure size, e.g. microchannel width and height, which belongs to the reactor size attributes, is influenced by the microfabrication method. The individual microfabrication methods imply different surface roughness and shapre, and impact on the catalyst incorpxrration technique is obvious. 

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