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.
Strip Width = (1/FPI + Fin Height) - (Fin Strip Thickness x 3) + (Fin Strip Thickness x
OLFF fin strip width is again reduced by one FPI. Fin Tip Thickness is also predictable by the following formula:
Fin Tip Thickness = Fin Strip Thickness x Tube Diameter / Finned OD
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:
Weight of Aluminum Fin Per Foot of Tube = Fin Strip Thickness x Fin Strip Width x Tube OD x 3.1416 x FPI x 12 x .1
Weight of Copper Fin Per Foot of Tube = Fin Strip Thickness x Fin Strip Width x Tube OD x 3.1416 x FPI x 12 x .32
CAUTION: Fin Height Hardware for OLFF is specific for each combination of fin height, fin strip thickness and pitch.
Fins Per Inch: 4-12 FPI
Tube Material: Ferrous, Non-Ferrous & Some Alloys
Fin Contact: Interference Fit
Type of Service: More Severe Service
Maximum Tube Wall Operating Temperature: Up to 500°F (260°C)*
Maximum Tube RPM on 1" Tube: 3000
Estimated Production Feet/Hour on 1" X 11 FPI 50 Foot Tube at 90% of Tube RPM and 85% Efficiency Factor: 641 ft/hr or 95 m/hr