Microchannels hydrodynamic diameters

The hydrodynamic diameters of microchannels usually range from 10 to 1000 rm. In such confined flowing spaces, the multiphase flow patterns of Newtonian fluids are more variable compared with the common bubbly or droplet flows in larger vessels and columns. The confined flowing channel first affects the shape of droplets therefore, the flow patterns of liquid/hquid dispersed systems are usually categorized as plug flow and droplet flow, as shown in Fig. 1A and B. Usually, the droplet flow has larger specific surface area, which is fit for the mass transfer enhancement process (Mary et al,... 

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. 

Hydrodynamics, pressure drop, and mass transfer during liquid-liquid flows were investigated in two different systems, viz. in glass microchannels with circular cross section of 0.2 mm ID (Fig. 3.3a, b) using an ionic liquid and deionised water, and in Teflon channels of different sizes, i.e. 0.2-2 mm ID (Fig. 3.3c) using either different TBP/ionic liquid mixtures (30 %, v/v) (Table 3.2) and aqueous nitric acid solutions, relevant to spent nuclear fuel reprocessing, or ionic Uquid and deionised water. The internal diameter of the microchannels was measured using a microscope (Nikon Eclipse ME 600). 

This approach is very simple and however has some limitations. LTM is valid if the particle size is small compared to the device dimensions, and in this version, it is valid for spherical particles. For the Stokes law to be valid, the particle needs to be several diameters away from the solid boundaries and the other particles (to model the hydrodynamic interaction of the particle with the wall, a correction factor needs to be introduced [6]) Moreover, if the disturbance of the flow field is significant due to the presence of the particle (e.g., the number of particles may be high within the domain or the size of the particle may be comparable with the microchannel size), the validity of the LTM is questionable. Since LTM does not include the presence of the particle, the simulation of the flow field can be performed with any standard software which handles the solution of PDFs, and the trajectory of the particles can be obtained at the postprocessing step. 

Entrance Region, Table 1 Maximum Reynolds number, hydrodynamic entrance length and total axial length to entrance length ratio for circular microchannels with a tixed L/D value (L/D = 2000) and pressure drop (Ap = 200 bar) as a function of fhe microtube internal diameter... 

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