This paper investigates the irreversibilities caused by fluid flowing under the effect of isothermal walls of fin-tube heat exchanger in the presence of longitudinal vortex generators. Inline arrangement of circular tubes with fin-surface mounted rectangular winglet pairs (RWPs) arranged in common flow down configuration are selected for the present three-dimensional numerical study. Initially, thermodynamic performance analysis of different possible RWP locations corresponding to tubes has been examined for a fixed angle of attack. Further, the study is expanded for some specific locations by varying angle of attack ranging from 15° to 60° and flow Reynolds number ranging from 2000 to 4000. Thermodynamic performance of the present system has been evaluated by analyzing the irreversibilities caused due to RWPs and compared with the thermo-hydraulic performance. Thermodynamic analysis is categorized into two parts: the first ‘entropy generation analysis’ and the second ‘exergy analysis’. For entropy generation analysis entropy generation rate, irreversibility distribution ratio and Bejan number are examined. The obtained results indicate that the irreversibility caused by entropy generation in the present system is majorly dominated by the entropy generation rate due to thermal effect. Exergy analysis is studied by calculating the irreversibility rate, exergy destruction number, heat transfer improvement number and exergetic efficiency. The observation of exergetic efficiency variation for different RWP locations demonstrates that the present system with upstream RWP locations delivers higher performance. © 2020 Elsevier Ltd