Extended performance evaluation criteria for enhanced heat transfer surfaces: heat transfer through ducts with constant heat flux

Extended performance evaluation criteria equations for enhanced heat transfer surfaces based on the entropy production theorem are developed to include the effect of fluid temperature Variation along the length of a tubular heat exchanger. The equations originate from various design constraints and generalize the performance evaluation criteria (PEC) for enhanced heat transfer techniques obtained by means of first law analysis. The general evaluation criteria add new information to Bejan's entropy generation minimization method assessing two objectives simultaneously. The application of this more comprehensive treatment of PEC compared with previous references is illustrated by the analysis of heat transfer and fluid friction characteristics of 10 spirally corrugated tubes assessing the benefit of these tubes as an augmentation technique. The results for different design constraints show that the optimum rib-height-to-diameter ratio (e/D) for these tubes is about 0.04. (C) 2000 Elsevier Science Ltd. All rights reserved.