Heat transfer tube for evaporation with variable pore sizes

A metallic heat transfer tube, in particular for the evaporation of liquids from pure substances or mixtures on the outside thereof, comprising integral fins which extend circumferentially annularly or helically on the outside and which are shaped to form essentially closed off channels, whereby the channels extend circumferentially with an essentially uniform cross section and are opened outwardly alternately through pores with at least two variable sizes comprising the following characteristics:

• a) the reciprocal ratio between the average size As of the smallest class of pores and the average size Al of the next larger class of pores is:
• Al/As=1.5 to 4;
• and
• b) the frequency ratio m=number Ns of pores of the smallest class of pores compared to the number Nl of pores of the next larger class of pores is:
• 5 m = N s N l = 12 :
• 1 ⁢ ⁢ to ⁢ ⁢ 1 :
• 5.