the tube 40 is in a vertical position and to fig8 where the tube 40 is in a horizontal position the available design flexibility in the configuration of heat exchangers is apparent from fig5 8 the fluid conducting tubes being arrangeable vertically horizontally and angularly as desired moving on to the second embodiment of the invention fig9 shows a rectilinear flat thin wall strip 43 of thermally conductive metal similar to the metal strip 29 of fig1 fig9 a shows the metal strip 43 of fig9 with equalized perpendicular transverse and longitudinal reference lines 41 and 41 39 applied across its surface the dimensions and placement of these lines 41 and 41 39 determine the size of the corrugations and the angle of inclination of the entire fin structure fig9 b depicts the metal strip 43 of fig9 and the reference lines 41 and 41 39 of fig9 a with cutting lines 44 applied across the surface of the strip along each linear edge 46 these cutting lines extend between the edges 46 and the alternative intersections of the longitudinal reference lines 41 39 and the transverse reference lines 41 and together with the transverse reference lines 41 divide the strip 43 into a series of alternating parallelograms 47 which will form the.