The Knurled Footed Fin is characterized as adding increased tube and fin surface area due to the knurled surface on the fin foot and tube. The fin is consider an interference fit type fin and because of the knurls some heat transfer specialist give the fin added performance ratings due to a mechanical type bond of the fin material to the tube wall surface. Typically, this fin is produced out of aluminum or copper fin strip. This fin type is not suitable for carbon steel or stainless steel fin materials as the material is too hard for the formation of the characteristic L or LL foot. Knurling depth in the tube wall is affected by the hardness of the tube material chosen. The fin, whether W/O or OLFF, is formed using standard fin height hardware.
For W/O fin strip width, standard formulas can be used. But, when establishing your fin strip width use one less FPI; in other words, if you wish to manufacture an 11 FPI tube, use 10 FPI for determination of your fin strip width in the following formula.
When calculating the weight of material per foot of tube be sure to use the revised fin strip width but the actual FPI to be produced. Calculate the weight of fin strip per foot of tube with the following formula:
CAUTION: Fin Height Hardware for OLFF is specific for each combination of fin height, fin strip thickness and pitch.