**Subscripts**

a; air c; contact area CFD; obtained using CFD based method e; external surface of tube between fins f; fin g; external surface of tube without fins in; inner m; logarithmic mean temperature difference me; measured temperature difference on air side min minimum cross-section area for transversal air flow through the tube array o; outer t; tube to; total air side temperature difference w; water I, II; first and second tube row, respectively
