tailieunhanh - Heat Transfer Handbook part 68

Heat Transfer Handbook part 68. The Heat Transfer Handbook provides succinct hard data, formulas, and specifications for the critical aspects of heat transfer, offering a reliable, hands-on resource for solving day-to-day issues across a variety of applications. | 664 BOILING upward. One explanation for the instability is that the gravity and shear forces acting on the thin film of liquid of Taylor bubbles become similar in mgnnitdde such that the flow direction of the film oscillates between upward and downward. This flow pattern is a transition regime between the slug flow and annular flow regimes. In small-diameter tubes churn flow may not develop such that the flow passes directly from slug flow to annular flow. Annular flow. Here the bulk of the liquid flows as a thin film on the wall with the gas as the continuous phase flowing up the centerof the tube forming a liquid annulus with a gas core whose interface is disturbed by both large-magnitude waves and chaotic ripples. Liquid may be entrained in the high-velocity gas core as small droplets the liquid fraction entrained may be similar to that in the film. This flow regime is quite stable and is often desirable for system operation and pipe flow. Wispy annular flow. When the flow rate is increased further the entrained droplets congregate to form large lumps or wisps of liquid in the central vapor core with a very disturbed annular liquid film. Mist flow. When the flow rate is increased even further the annular film becomes very thin such that the shear of the gas core on the interface is able to entrain all the liquid as droplets in the continuous gas phase . the inverse of the bubbly flow regime . The wall is intermittently wetted locally by impinging droplets. The droplets in the mist may be too small to be seen without special lighting and or magnification. Flow patterns in horizontal two-phase flows are influenced by the effect of gravity which acts to stratify the liquid to the bottom and the gas to the top of the channel. Flow patterns encountered in co-current flow of gas and liquid in a horizontal tube are shown in Fig. . The commonly identifiable flow patterns are Bubbly flow. The bubbles are dispersed in the continuous liquid with a higher .

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