Microscale multiphase flow

The dynamic nature of multiphase microflows imposes unique requirements on the time resolution of the flow characterization techniques. Table 1.1 summarizes different experimental techniques for characterizing microscale multiphase flow and also the spatial and temporal measurement resolutions. Intmsive measurement probes are generally not an option for micro- and nanofluidic systems. 

In summary, the microscale description provides two important pieces of information needed for the development of mesoscale models. First, the mathematical formulation of the microscale model, which includes all of the relevant physics needed to completely describe a disperse multiphase flow, provides valuable insights into what mesoscale variables are needed and how these variables interact with each other at the mesoscale. These insights are used to formulate a mesoscale model. Second, the detailed numerical solutions from the microscale model are directly used for validation of a proposed mesoscale model. When significant deviations between the mesoscale model predictions and the microscale simulations are observed, these differences lead to a reformulation of the mesoscale model in order to improve the physical description. Note that it is important to remember that this validation step should be done by comparing exact solutions to the mesoscale model with the microscale results, not approximate solutions that result... 

In this chapter, we have introduced the basic steps needed to derive the mesoscale model starting from a microscale description of the polydisperse multiphase flow. The first step is to identify a set of microscale variables, denoted here by (X " ... 

As derived from the microscale model in Chapter 4, the GPBE for a polydisperse multiphase flow has the following form ... 

Multiphase processes. Although the above Monte Carlo methods were developed for simulations of gas flows, they can also be used to analyze gas-particle interactions in granular flows, gas-liquid phase interactions in a liquid drop, and particle coagulation and aggregation. The proposed GEMC method will be very helpful for the analysis of multiphase processes in microscale gas flows. 

Figure 1.3 Multiphase systems for performing reactions in microscale segmented flow. The continuous phase (A) is shown in green and the disperse phase (B) is colored blue. (1) Immiscible fluids, either a gas-liquid mixture or two liquids, react with each other. The location of the reaction depends on the reaction rate, as...

Size Microreactor systems incorporate structures for the directed transport or containment of gases or fluids that have a dimensional property in at least one direction usually measured in micrometers, sometimes up to 1 mm. These structures may comprise microscale ducts (e.g., channels and slots) and pores, larger features (e.g., parallel plates) that cause fluid to flow in thin films, and others that cause fluid to flow in microscale discontinuous multiphase flow (e.g., bubbles and emulsions). More specific details of these types of structure are explained in Chapters 9 and 10. In addition, small containment structures such as microwells have been fabricated in an analogous format to traditional microtiter plates, rendering potential compatibility with existing robotic handling... 

Fede, R Fevrier, P. and Simonin, O. Numerical Study of the Effect of the Fluid Turbulence Microscales on Particle Segregation and Collisions in Gas-Solid Turbulent Flows. In Proc. 5th Int. Conf on Multiphase Flow. Paper No 343. Yokohama, Ja-pan 2004. 

On the microscale (tissue level), surface tension forces located at the air-Uquid interface of the progressing bubble subject the EpC lining of closed airways and alveoli to a nonuniform, time-dependent, micromechanical stress field. In order to predict the magnitude of the microscale stresses imparted by the interfacial flows, fluid mechanical models are developed that are founded upon fundamental investigations of multiphase flows. 

Lan WJ, Li SW, Lu YC, et al Controllable preparation of microscale mbes vnth multiphase co-laminar flow in a double co-axial microdevice. Lab Chip 9 3282—3288, 2009. 

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