Dual phase flow

The application of conventional pressure drop correlations for single and dual phase flow has been examined by Yue et al. [64], They reported that the single fluid behavior still obeys classical theory in microchannels with diameters of several hundred micrometers. For dual phase flow, they proposed a modified correlation, but recognized that further research would be necessary [64],... 

AN ANALYSIS OF DUAL-PHASE FLOW AT THE INLET TO A CENTRIFUGAL CRYOGENIC PUMP... 

Another group of investigators has applied the equations of motion for dual-phase flows of determined flow patterns. 

Some of them used the single-phase analogy while others based their reasoning on various simplifying assumptions. This was done in order to study flow patterns and to obtain some quantitative results on dual-phase flows. Attempts to correlate these results with experimental data have not been very successful to date, Deviations as much as 1 30 per cent have been noted. 

Since the separation process in CEC has a number of attributes similar to those of HPLC, the most important variables affecting the separation are the same for both of these techniques. However, in HPLC mobile phase, flow and separation are independent variables. Therefore, the most important operational variables are the analyte-sorbent interactions that can be modulated by the chemistry of the packing, composition of the mobile phase, and temperature. In contrast, the CEC column has a dual role as it serves as both (i) a flow driving device and (ii) separation unit at the same time. Although the set of variables typical of HPLC is also effective in CEC, their changes may affect in one way or another both column functions. Therefore, optimization of the separation process in CEC is more complex than in HPLC. 

Dual Phase Continuity. Dual phase continuity has been shown to be important in numerous polymer blends and IPN s, to achieve special properties. Dual phase continuity is defined as a region of space where two phases maintain some degree of continuity. An example of dual phase continuity is an air filter and the air that flows through it. A Maxwell demon could traverse all space within the air filter phase, as well as within the air phase. 

Figure 6.1 shows the apparatus diagram. The diffusion flame burner consisted of an air plenum with an exit diameter of 22 mm, forced at a Strouhal number of 0.73 (100 Hz) by a single acoustic driver, and a coaxial fuel injection ring of diameter 24 mm, fed by a plenum forced by two acoustic drivers at either 100 Hz (single-phase injection) or 200 Hz (dual-phase injection). The fuel was injected circumferentially directly into the shear layer and roll-up region for the air vortices. In addition, this fuel injection was sandwiched between the central air flow and the external air entrainment. Thus the fuel injection was a thin cylindrical flow acted upon from both sides by air flow. 

A major interest to sequential IPN s relates to dual phase continuity, defined as a region of space where each of two phases maintain some degree of connectivity. An example is an air filter with the air flowing through it. A Maxwell demon can transverse all space within both the filter phase and the air phase, both phases being continuous. 

For the determination of supplemental vitamin E in infant formulas, Woollard and Blott (222) employed a radially compressed Radial-PAK cartridge. This enabled lipid material to be rapidly cleared by stepping up the mobile-phase flow rate from 2 ml/min to 10 ml/min after elution of the a-tocopheryl acetate. Fluorescence detection, using a filter-type fluorometer, allowed the indigenous a-tocopherol to be conveniently estimated, while UV absorbance detection was used to quantify the a-tocopheryl acetate. Supplemental retinyl acetate could be assayed simultaneously with either added or indigenous vitamin E using the appropriate detection mode. With the aid of a dual-monochromator spectrofluorometer, a-tocopheryl acetate and a-tocopherol could be determined simultaneously with wavelengths of 280 nm (excitation) and 335 nm (emission), but the increased selectivity eliminated detection of the vitamin A esters (233). 

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). 

Dual phase continuity offers many advantages, because rubber/plastic compositions yield tough, leathery materials. Many of the compositions described above, for example, contain two continuous phases, with cylinders of polystyrene meandering within the polybutadiene matrix. Since all IPN s are crosslinked, it may be that their greatest advantage will lie in products which are leathery or rubbery, but can not be permitted to flow. 

In the case of liquid—liquid extraction in mono-segmented flow systems, aliquots of organic solvents can be strategically added to the analytical path for single-phase [196] or dual-phase [195,402] separations. 

The dual beam configuration of LDA is most widely used today, where the Doppler difference frequency is directly measured and the receiving optics may be placed at an arbitrary position with respect to the transmitting beams. Laser-Doppler anemometry has been first applied to measurements of mean velocities and turbulence properties in single phase flows. In this case small particles, which follow the flow and the turbulent fluctuations, need to be present in the flow or must be added to it (i.e. seeding the flow with a tracer). The principles of LDA are, for example, described in detail by Durrani and Greated (1977), Durst et al. (1981), and Durst et al. (1987). 

The thermoplastic IPNs utihze physical cross-hnks, rather than chemical crosshnks. Usually, these materials wiU flow when heated to sufficiently high temperature (hence the terminology thermoplastic), but behave as thermosets at ambient temperature, with IPN properties, often possessing dual phase continuity. Most often, physical crosshnks are based on triblock copolymers (thermoplastic elastomers being the leading material), ionomers, or semi-crystalhne materials. 

The use of the dual-phase gas-diffusion cell allows the hydride to pass immediately through the membrane into a hydrogen acceptor stream. The effect of this process is a decrease of the contact time between the hydride and any transition metal precipitate. The end result is that the interferences observed for this system versus other flow methods generally are significantly diminished. Since the reduced contact time also favorably influences the interference due to hydride competition, the observed reductions are therefore really a combination of the separation techniques obtained in the FIA system and that of kinetic discrimination. 

G. E. Pacey, M. R. Straka, and J. R. Gord, Dual Phase Gas Diffusion Flow Injection Analysis/Hydride Generation Atomic Absorption Spectrometry. Anal. Ghent., 58 (1986) 502. 

The first expansion process would be sufficient for liquefaction, however, Joule-Thomson expansion is applied for the final step (from approx. 26 K down) to avoid two-phase flow in the expander. Variations of the dual-pressure Claude process as a large-... 

Fig. lO Schematic figure of a FI hydride generation AAS system with segmented carrier stream and tubular membrane dual phase gas diffusion separator reponed in ref. 48. S. sample At, aigon flow T, microporous PTFE tubing G, dual-phase gas-diffusion separator, BH, borohydride reductant W, waste and AAS, quartz atomizer cell. 

In systems with a low surface tension, the hole size of the sieve tray with downcomer should be smaller than 2 mm to prevent the continuous phase percolating through. For the treatment of such systems, dual flow trays without downcomers are more suitable. On a dual flow tray, the disperse and continuous phases flow in turn through the base plate holes and between the trays, producing strongly circulating convection cells. 

Lyngaae-Jorgensen, J., Lunde Rasmussen, K., Chtcherbakova, E,A and Utracki, L.A. (1999) Flow induced formation of dual-phase continuity in polymer blends and alloys. Part 1, Polym. Eng. Sd., 39 (6), 1060-1971,... 

Amongst the above mentioned compatibilization methods, the obtaining of IPNs and SIPNs often proved to be a promising and very efficient route. An IPN is a polymer alloy comprised of two or more chemically crosslinked polymers. The difference between polymer blends and IPNs is that the latter ones swell instead of dissolving in solvents and do not creep or flow. Types of IPNs include sequential, simultaneous, latex and gradient IPNs and may also be thermoplastic (i.e. when physical crosslinks are imphed). Thermoplastic IPNs behave as thermosets at ambient temperature, but usually flow when heated at certain temperatures, possess IPN properties and often exhibit dual phase behavior [1]. 

---