ABSTRACT
Because of the ever-present problem of heat inleak to a cryogenic fluid transfer system, two-phase flow and boiling heat transfer are not uncommon. Two-phase flow is always encountered in cryogenic liquid gasifiers (vaporizers) used in such applications as self-pressurization systems and LNG (liquid natural gas) gas deli very systems (Filina and Weisend 1996, 1-9). In this chapter, the phenomena of two-phase flow, including techniques for prediction of the flow regimes and pre ssure drop in two-phase flow, will be examined. Physical principles associated with both pool boiling (boiling on a surface immersed in a cryogenic liquid) and forced-convection boiling (boiling within flow passages) will be presented. Twophase flow may involve condensation instead of boiling, and condensation heat transfer in both external flow and internal flow will be considered. Finally, some problems involving solid-liquid phases (such as slush hydrogen) will be examined.
4-1 FLOW REGIMES IN TWO-PHASE FLOW Two-phase flow is generally more complicated than single-phase flow for several reasons. Many different flow patterns are possible for two-phase flow; whereas, in single-phase flow, one encounters only laminar or turbulent flow, with a transition region between the two regimes. In two-phase flow, the flow may be laminar in the liquid phase and turbulent in the vapor phase, or any of the four different
