Patterns mist flow

In annular flow, liquid flows as a thin film along the pipe wall and gas flows in the core. Some liquid is entrained as droplets in the gas core. At veiy high gas velocities, nearly all the liquid is entrained as small droplets. Inis pattern is called spray, dispersed, or mist flow. 

In high heat flux (heat transfer rate per unit area) boilers, such as power water tube (WT) boilers, the continued and more rapid convection of a steam bubble-water mixture away from the source of heat (bubbly flow), results in a gradual thinning of the water film at the heat-transfer surface. A point is eventually reached at which most of the flow is principally steam (but still contains entrained water droplets) and surface evaporation occurs. Flow patterns include intermediate flow (churn flow), annular flow, and mist flow (droplet flow). These various steam flow patterns are forms of convective boiling. 

At a constant low liquid-flow rate with steadily increasing gas flow, the patterns observed will tend to be stratified, wavy, annular and mist flow. At a somewhat higher liquid rate, stratified, plug, slug, annular, and mist flow occur while at high liquid flows the patterns follow the order bubble, plug, slug, annular, and mist, as gas flow increases. 

The basic assumptions implied in the homogeneous model, which is most frequently applied to single-component two-phase flow at high velocities (with annular and mist flow-patterns) are that (a) the velocities of the two phases are equal (b) if vaporization or condensation occurs, physical equilibrium is approached at all points and (c) a single-phase friction factor can be applied to the mixture if the Reynolds number is properly defined. The first assumption is true only if the bulk of the liquid is present as a dispersed spray. The second assumption (which is also implied in the Lockhart-Martinelli and Chenoweth-Martin models) seems to be reasonably justified from the very limited evidence available. 

From (a), we can see that the flow pattern at the entrance is typical dine bubbly flow, and the bubble exist corrugated. At the 1/3 inlet, there are bubble which come from the evaporation of the fluid, close to the wall, and then small bubbles gather together to form the plug-shaped air flow pattern map. From (b) we can see that at the entrance, the fine bubbly flow pattern map exists just for a short time, at the 1/4 inlet, forming a gus slug flow pattern map. From (c) we can see that, there is no existence of gas slug flow pattern map at the entire wall. From (d) we can see that the flow pattern map shows a typical gas mist flow pattern, and with the... 

Mist or Spray Flow. As the gas rate increases, the aimular flow pattern changes to a spray or mist flow. 

Mist Flow. As the gas flow continues to increase, the liquid film from the wall breaks off and entrains in the gas, forming a mist pattern. 

Annular flow. In annular flow there is a continuous liquid in an annulus along the wall and a continuous gas/vapor phase in the core. The gas core may contain entrained droplets—dispersed mist—while the discontinuous gas phase appears as bubbles in the annulus. This flow pattern occurs at high void fractions and high flow velocities. A special case of annular flow is that where there is a gas/vapor film along the wall and a liquid core in the center. This type is called inverse annular flow and appears only in subcooled stable film boiling (see Sec. 3.4.6.3)... 

A standard cross flow ventilation system develops further the horizontal flow concept and provides ventilation to the tankhouse by generating a horizontal flow across the cell area of the tankhouse (see Figure 4 showing typical cross flow layout with flow patterns). The system has an inlet or baffle side and a fan or exhaust side. The fans located at the exhaust side of the tankhouse generate the air flow. The acid mist generated by the cells is removed by means of the cross flow of air. 

---