CONDENSATION: In film condensation, the condensate wets the surface and forms a liquid film at the surface, and slides down DUE to gravity. The thickness of the film increase in the DIRECTION of the flow.The average heat transfer coefficient for film condensation of a pure saturated vapor on the outside of a single horizontal tube and verticle tube is:\(\overline {{h_H}} = 0.725{\left[ {\frac{{{k^3}{\rho ^2}g{h_{FG}}}}{{\mu D\left( {{t_{sat}} - {t_s}} \right)}}} \right]^{0.25}}\)and \(\overline {{h_V}} = 0.943{\left[ {\frac{{{k^3}{\rho ^2}g{h_{fg}}}}{{\mu l\left( {{t_{sat}} - {t_s}} \right)}}} \right]^{0.25}}\)\(\frac{{\overline {{h_H}} }}{{\overline {{h_V}} }} = \frac{{0.725}}{{0.943}}{\left[ {\frac{l}{D}} \right]^{0.25}}\)when \(\overline {{h_H}} = \overline {{h_V}} \) then the above equation gives \(\frac{l}{D}=2.86\).i.e. when the ratio of length to diameter is 2.86, then for filmwise condensation, the heat transfer coefficient will be equal whether the tube is horizontal or vertical