The effect of fouling on thermodynamic performance can be evaluated by studying the increase of entropy generation rate due to fouling as compared to that for clean surface tubes. In this study, an attempt has been made to correlate the effect of fouling with entropy generation and related operational cost. In the model developed, fouling thickness and tube surface temperature are considered to be the main parameters. Numerical results of entropy generation and related operational cost due to both heat transfer and viscous friction under fouling conditions are presented and discussed. (C) 2000 Elsevier Science Ltd. All rights reserved.