Two-phase flow structures

Janssen, E., 1967, Two Phase Flow Structure in a Nine-Rod Channel, Steam-Water at 1000 psia, Final Summary Rep. GEAP-5480, General Electric, San Jose, CA. (5)... 

The flow structure in a tall vertical bubble column was analyzed using deterministic techniques. The characterization of the two-phase flow structure was realized in the middle section where the flow is fully developed (measuring section). Three cases under different volume fraction of liquid were shown. The results can be resumed as follows ... 

During vaporization or condensation, thermal and hydraulic performances depend essentially on the two-phase flow structure. Furthermore, as very often in industrial processes, the heat exchanger operates in thermosyphon or under natural circulation knowledge of the pressure drop and liquid holdup is of major importance. But there is very little information on two-phase flow characteristics in compact geometries. 

Cui, H. Chaouki, J. Effects of temperature on local two-phase flow structure in bubbling and turbulent beds of FCC particles. Chem. Eng. Sci. 2004, 59, 3413-3422. 

Breast-on-a-chip and splenon-on-a-chip systems have also utilized microfluidic technology. However, their capacities are limited. The breast-on-a-chip devices only mimic the distribution of anatomical vessels of a breast rather than the whole microenvironment containing glandular, fatty, and vascular tissues. The device can be integrated with other tumor-on-a-chip devices to further mimic tumor development in the breast. The splenon-on-a-chip system just simulates the blood filtering function of in vivo splenon using a microfluidic two-phase flow structure. Those chips still lack of accuracy to mimic tissue and cellular level. 

The first area covers low volumetric flow rates, and entrance pressures below Pcr. This sector of two-phase flow in the molding machine is characterized by a complex non-linear dependence of reduced pressure on reduced volumetric flow rate. The structure of foam plastics obtained in this way was called shell structure by the authors in [20, 21] — the extrudate contains huge shell bubbles which are comparable to its section. As CBA concentration increases, or medium volumetric flow rate is increased at low CBA concentration, small bubbles materialize in the melt around the shell bubbles, and the structure becomes shell-bubble . Increase of the volumetric flow rate and the concentration of flowing agent neutralizes the difference in bubble size their lateral dimensions become smaller than their longitudinal ones. 

Two-phase flows in micro-channels with an evaporating meniscus, which separates the liquid and vapor regions, have been considered by Khrustalev and Faghri (1996) and Peles et al. (1998, 2000). In the latter a quasi-one-dimensional model was used to analyze the thermohydrodynamic characteristics of the flow in a heated capillary, with a distinct interface. This model takes into account the multi-stage character of the process, as well as the effect of capillary, friction and gravity forces on the flow development. The theoretical and experimental studies of the steady forced flow in a micro-channel with evaporating meniscus were carried out by Peles et al. (2001). These studies revealed the effect of a number of dimensionless parameters such as the Peclet and Jacob numbers, dimensionless heat transfer flux, etc., on the velocity, temperature and pressure distributions in the liquid and vapor regions. The structure of flow in heated micro-channels is determined by a number of factors the physical properties of fluid, its velocity, heat flux on... 

Peles YP, Yarin LP, Hetsroni G (2000) Thermohydrodynamic characteristics of two-phase flow in a heated capillary. Int J Multiphase How 26 1063-1093 Peng XF, Wang BX (1994) Cooling characteristics with micro-channeled structures. J Enhanced... 

Slug flow. As a very complex, unsteady, turbulent two-phase flow, slug flow typically has high acceleration and decelerations of liquid, which causes steep pressure drops. Dukler and Hubbard (1975) considered the basic hydrodynamic structure of a slug unit as consisting of several regions (Fig. 3.39) ... 

Wyllie, G., 1965, Evaporation and Surface Structure of Liquid, Proc. Roy. Soc. A197.383. (2) Yadigaroglu, G., 1993, Instabilities in Two-Phase Flow, in Workshop on Multiphase Flow and Heat Transfer Bases, Modeling and Applications, chapter 12, University of California, Santa Barbara, CA. (4)... 

The chaotic behavior is an interesting nonlinear phenomenon which has been intensively studied during last two decades. The deterministic techniques have been used to understand the d3mamical structure in several nonlinear systems [5], [6], [42]. Particularly, the two-phase flow systems present nonlinear d mamical behavior which can be studied by means of chaos criteria behavior [2], [17], [25], [31], [45], [51]. Two-phase flows they provide a rich variety of cases whose dynamics lead to oscillatory patterns. The following published results are example ... 

C7. Chien, S.-F., An experimental investigation of the liquid film structure and pressure drop of vertical, downward, annular, two-phase flow. Ph.D. thesis, Univ. Minnesota, Minneapolis, Minnesota, 1961. 

For the gas-solids two-phase flow in a CFB riser, there is no clear separation between the micro-scale (fine-grid scale of TFM continual and the meso-scale (cluster scale), as discussed in Goldhirsch (2003) and Wang and Li (2007). Thus, the meso-scale structure does not vanish... 

Albeit originally proposed for gas-solid fluidization, the concepts of structure resolution and compromise between dominant mechanisms embodied in the EMMS model can be generalized into the so-called variational multi-scale methodology (Li and Kwauk, 2003) and extended to other complex systems (Ge et al., 2007). One typical example out of these extensions is the Dual-Bubble-Size (DBS) model for gas-liquid two-phase flow in bubble columns (Yang et al., 2007, 2010). 

Bridging the gap between micro- and macro-scale is the central theme of the first contribution. The authors show how a so-called Energy-Minimization Multi-Scale (EMMS) model allows to do this for circulating fluid beds. This variational type of Computational Fluid Dynamics (CFD) modeling allows for the resolution of meso-scale structures, that is, those accounting for the particle interactions, and enables almost grid-independent solution of the gas-solids two-phase flow. 

Hartge, E.-U., Li, Y. and Werther, J. (1986). Analysis of the Local Structure of the Two Phase Flow in a Fast Fluidized Bed. In Circulating Fluidized Bed Technology. Ed. P. Basu. Toronto Pergamon Press. 

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