Nonisothermal Flows in Channels and Tubes

Note that at U = 0 relation (5.7.11) turns into formula (5.7.10). 

Film condensation in a vertical tube. To present a theoretical description of film condensation in tubes is much more difficult, since there may arise a strong dynamic interaction between the moving vapor and the flowing condensate film. If the direction of the vapor motion coincides with the direction of the condensate motion due to gravity, then, owing to viscous friction on the phase boundary, the velocity of the film flow increases, its thickness decreases, and the coefficient of convective heat transfer also increases. If the direction of the vapor motion is opposite to that of the condensate flow, then we have the opposite situation. If the vapor velocity increases, then the film may partially separate from the wall and convective heat transfer can increase sharply. 

For the calculation of the local coefficient of convective heat transfer a when the condensation takes place in tubes provided that flow in the condensate film is laminar, the following relation based on experimental data was proposed in [200]  

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