Microchannel diameter

This flow is identical to the bubbly flow of gas-liquid systems. It is characterized by the drops with diameters less than or equal to the microchannel diameter. In a microchannel, this flow pattern typically occurs at relatively high continuous flow velocities and low dispersed phase velocities. The drop size is restricted by channel dimensions. By varying the microchannel dimensions, the flow regimes can be changed from drop flow to slug flow and vice versa [12]. 

Figure 11.1 The Graetz problem for forced convection in a microchannel (diameter c/h) with developed laminar flow. The gray profiles indicate the streamwise development of the concentration profile. The concentration profile near the entrance is unaffected by the fast first-order reaction at the wall. Outside this region, the...

From the gas phase only Chemical Vapour Deposition [CVD] can be applied in certain circumstances for a pwst-coating with catalyst. The deposition rate which is influencing the gas phase content of the sup>port or active sp>ecies ptrecursor will determine the homogeneity of the catalyst along the microchannels. The deposition rate is mainly influenced by the parameters microstructure wall temperature, microchannel diameter and the flow velocity in the microchannels at constant ptressure. These pjarameters relate to the diffusivity of the precursor. Appropriateness of CVD methods for coating with AI2Q5 has been shown very early by Janicke et al. (2000). 

The front opening of such a microchannel element has a diameter of only a few microns, but it is only one element of a whole multichannel array (Figure 31.2). Whereas the orifice to one micro-channel element covers an area of only a few square microns, an array of several thousand parallel elements covers a much larger area. In particular, the area covered by the array must be larger than... 

Chung PM-Y, Kawaji M (2004) The effect of channel diameter on adiabatic two-phase flow characteristics in micro-channels. Int J Multiphase Flow 30 735-761 Colgan E (2005) A practical implementation of silicon microchannel coolers for high power chips. 

The problems of micro-hydrodynamics were considered in different contexts (1) drag in micro-channels with a hydraulic diameter from 10 m to 10 m at laminar, transient and turbulent single-phase flows, (2) heat transfer in liquid and gas flows in small channels, and (3) two-phase flow in adiabatic and heated microchannels. The smdies performed in these directions encompass a vast class of problems related to flow of incompressible and compressible fluids in regular and irregular micro-channels under adiabatic conditions, heat transfer, as well as phase change. 

It was found that the pressure gradient and flow friction in micro-channels were higher than that predicted by the conventional laminar flow theory. In a low Re range, the measured pressure gradient increased linearly with Re. For Re > 500, the slope of the /(c-Re relationship increases with Re. The ratio C was about 1.3 for micro-channels of hydraulic diameter 51.3-64.9pm and 1.15-1.18 for microchannels of hydraulic diameter 114.5-168.9pm. It was also found that the ratio of C depends on the Reynolds number. 

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... 

The experimental data obtained in conventional size channels and micro-channels with diameters between 100 pm and 6.0 mm are examined to further elucidate and understand the differences in two-phase flow characteristics between the microchannels and conventional size channels. Since two separate sets of experiments have been conducted using air and water in acrylic channels with diameters between 500 pm and 6.0 mm, and nitrogen gas-water in fused silica channels with diameters between 50 and 500 pm, the authors refer to the former channels as conventional size channels, and the latter channels as micro-channels for convenience. Two different inlet sections were covered in micro-channel experiments, a gradually reducing section and a T-junction. 

Scale-up of microchannel reactors is based on using the optimal channel dimensions rather than seeking the smallest or the largest microchannel. In some cases, the channels may range from 100 pm in hydrauhc diameter to a few millimeters. The classification of a rigorous size range to designate a reactor as microchannel is not necessary. 

S. Sugiura, M. Nakajima, and M. Seki Prediction of Droplet Diameter for MicroChannel Emulsification. Langmuir 18, 3854 (2002). 

Efforts toward integrating SPE onto a lab-on-a-chip device are currently being investigated by the Collins group. Two complementary approaches are being pursued. One approach is to use small-diameter, Cl8 functionalized silica beads that are packed into a microchannel to form an extraction bed [46], A sample solution containing trace levels of explosives is electrokinetically directed across the microcolumn bed, causing the hydrophobic explosive molecules to adsorb onto the stationary phase with nearly 100% efficiency. Subsequently,... 

The subfibrils with diamters of 39 A contain five helices each of which in turn is built from three polypeptide chains. In this arrangement, microchannels or holes having minimum diameters of approximately 16 A are enclosed between the subfibrils. 

From the assumption that the collagen fibres are expanded, it also follows that the diameter values of calcium phosphate nuclei should exceed the value of 16 A, which is the minimum diameter of the microchannels (i. e. the diameter when the subfibrils are in direct contact). 

Figure 2. Schematic diagram of the imaging apparatus with ion lens. The detector is a dual microchannel plate/phosphor screen assembly (40 mm active diameter) coupled with a CCD camera. Electric field lines are shown to illustrate the ion lens. Equipotential surfaces in the repeller/extractor region are also included.

Microfluidics is about the flow of tiny amounts of liquids. The prefix micro indicates that at least in two dimensions, the liquid should be confined in micrometer dimensions. If we are, for instance, dealing with a channel, its width or diameter should be below 100 /tm to earn the title microchannel . Please note that a microliter is a relatively large volume in microfluidics since it is equal to the volume of (1 mm)3. 

Figure 3. Schematic drawing of a microchannel plate detector for neutron radiography. Channel diameters range from 6 to 12 p.m, and typical wall thickness are about 2 p.m. The high voltage depends on the particular MCP used and can range from 2 to 6 kV.

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