Surface characteristics of a finned tube heat exchanger were examined to help predict the contact geometry between metal surfaces. Primary characteristics evaluated were the surface roughness and waviness and the material hardness. A scanning electron microscope was used to observe the surface topography of the fins as well as to examine the contact between the aluminum fin and the copper tube.

For a given fin number, surface roughness increased as the expansion increased. Tests also revealed that only a portion of the fin collar was actually in contact with the tube. These results were subsequently used to develop a mathematical model for predicting the heat transfer between the fin and tube.