Condensation on vertical and horizontal tubes

Condensation on vertical and horizontal tubes The Nusselt equation 

If vapour condenses on the outside of a vertical tube of diameter do, then the hydraulic mean diameter for the film is  

If G is the mass rate of flow of condensate, the mass rate of flow per unit area G is G/S and the Reynolds number for the condensate film is then given by  

This is approximately the same as equation 9.173 for vertical tubes and is a universal equation for condensation, noting that for vertical tubes M = G/ndo and for horizontal tubes M — Gjl, where / is the length of the tube. Comparison of the two equations shows that, provided the length is more than three times the diameter, the horizontal tube will give a higher transfer coefficient for the same temperature conditions. 

For j vertical rows of horizontal tubes, equation 9.175 may be modified to give  

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