Page 219 - Fluid mechanics, heat transfer, and mass transfer
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TWO-PHASE FLOW    197
































                                                                FIGURE 7.4  Flow pattern as a function of fraction of air in
                                                                air–water flow in a vertical pipe.



                                                                     & Wavy Flow: Gas/vapor flows in the upper pipe section
                                                                       and liquid as waves in the lower section.
                                                                     & Slug Flow: Slugs of gas/vapor bubbles flowing
                                                                       through the liquid.




            FIGURE 7.3  Two-phase flow patterns in a vertical evaporator
            tube.


                & Vapor fraction in the two-phase mixture determines
                  the flow patterns as illustrated in Figure 7.4.
              . What is flashing flow?
                & Flashing flow and condensing flow are two examples
                  of multiphase flow with phase change.
              . Under what circumstances flashing flow occurs?
                & Flashing flow occurs when pressure drops below
                  bubble point pressure of a flowing fluid.
              . Illustrate gas–liquid two-phase flow patterns in hori-
                zontal pipes.
                & Figure 7.5 illustrates gas/vapor–liquid flow patterns
                  in horizontal pipes.
                & Bubble Flow: Bubbles dispersed in liquid.
                & Plug Flow: Plugs of liquid flow followed by plugs of
                  gas/vapor flow.
                & Stratified Flow: Liquid and gas/vapor flow in strat-  FIGURE 7.5  Flow patternsingas/vapor–liquidflowsin horizontal
                  ified layers.                                  pipes.
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