n: (1)vapor and liquid at the outside boundary of the liquid layer are in thermodynamic equilibrium (2)condensate flows downward in laminar flow (3)liquid velocity at the wall is zero 8 Basic assumption: (4)liquid velocity at the outside of the film is not influenced by vapor velocity (5)temperatures of the wall and the vapor are constant (6)vapor superheat is neglected (7)the condensate is assumed to leave the tube at the condensing temperature (8)physical properties of the liquid are taken at the mean film temperature 9 ? Vertical tubes The heat flows through the condensate film solely by conduction. ? solely by conduction ? fxkh?(13.1) Local coefficient 10 ? FIGURE 13.1 Film thickness and local coefficients, descending film of condensate.
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