Results of thermal investigations of monometallic tubes finned on both sides used in heat exchangers are presented in this article. Investigated tubes differ in twist and inclination angles of internal fins. In experiments a transform oil was cooled and air was a coolant. Heat transfer coefficient values for the inner side of the tube based on correlation equations from literature were compared with the experimental and numerical ones. The aim of this research is to specify the meaning of correlation equations for determination of heat transfer coefficients of tubes finned on both sides with twisted longitudinal internal fins. The change in heat flux in a tube when the twist angle of the internal fins varies is shown. Results of computations are presented in the form of useful drawings, which can be readily applied in practice. (C) 2012 Elsevier Ltd. All rights reserved.