Engulfment flow

When the Reynolds number is increased, a regime with a flow pattern of broken symmetry is reached, as found by Bothe et al. [54]. At a Reynolds number of about 140 the symmetric flow pattern becomes unstable and an engulfment flow with an increased area of material interface between the two fluids is found. This is illustrated in Fig. 3.13 that shows maps of the computed concentration field over cross sections of the mixing channel for Reynolds numbers ranging from 119 (a) to 239 (f). The increase in material interface is related to an increase in mixing efficiency, thus making a mixing tee more efficient than predicted by simple... 

The constant has unit of m s °-. This corresponds to an energy efficiency of 3-4% (explained in section 4.6). In Example 4.3 the characteristic mixing time is estimated supposing engulfment flow. 

The transition of regimes depends on Re and reactor geometry. In T-mixer, stratified flow is observed at low Re. Engulfment flow is observed at / e> about 100. Engler et al. [11] proposed a parameter (K) to estimate the flow regime in T-mixers. 

The first transition from stratified to vortex flow was observed at about K = 15, whereas the transition to engulfment flow happened at /C = 40. The corresponding Re for two transitions in a 600 x 300 x 300 pm T-mixer are 45 and 150, respectively, which corresponds roughly to the observations presented in Section 4.2. 

Fig. 3.10 Laminar flow regime and engulfment flow regime in a T-shaped micromixer...

As previously discussed, many, if not most, cases of particles adhering to substrates involve at least one of the contacting materials deforming plastically, rather than elastically. Under such circumstances, it would be expected that the extent of the contact should increase with time and, with it, the force needed to detach a particle from a substrate. Moreover, material flow can occur, resulting in the engulfment or encapsulation of the particles. 

One of the principal difficulties faced when employing Lagrangian micromixing models is the determination of tm based on properties of the turbulent flow fields. Researchers have thus attempted to use the universal nature of high-Reynolds-number isotropic turbulence to link tm to the turbulence time scales. For example, in the E-model (Baldyga and Bourne 1989) the engulfment rate essentially controls the rate of micromixing and is defined by... 

The fire engulfed most of the catalyst preparation area. Also, the automatic deluge sprinkler coverage for this area had actuated, hut no water was available. The fire brigade tried to activate a fixed monitor, but again got no water flow. With the limited water supply from the plant fire engine available as a shield, the fire brigade members felt they could reach the lead outside operator. 

AM. Plant fire brigade reaches the emergency location. They see fire engulfing catalyst prep area (automatic deluge sprinkler had actuated, but no water was available) see the lead outside operator down about 40 feet from the catalyst prep area, find the injured (unidentified at that time) service contractor about 120 feet away, Plant fire brigade then tries to activate a fixed monitor, but no water flows, sends one brigade member to fire pump house to check pump status. 

Chemicals may cross the cell membrane via membrane pores. This diffusion depends on the size of the pore and the size and weight of the chemical. The chemical flows through the membrane along with water. Finally, the membrane can actually engulf the chemical, form a small pouch called a vesicle, and transport it across the membrane to the inside of the cell. This process is called pinocytosis. 

Oil and gas deposits are trapped for long periods, stored in permeable rocks that are engulfed by impermeable rocks (no one will claim that these are through-flow systems with active oil or gas recharge). 

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