Energy conservation through heat transfer enhancement techniques

Enhanced heat transfer surfaces have been successfully used in the heat transfer industry to obtain more compact and efficient units. Conservation of the useful part of energy (exergy) can be reached through higher heat transfer than that for standard surfaces and flow configurations. There are numerous ways for heat transfer augmentation which have been marketed or tested in laboratories. In this paper, we review some of the passive techniques for single-phase flow. One of the most promising heat transfer enhancement techniques is the compound augmentation method, in which different enhancement techniques are used simultaneously. Extended performance evaluation criteria (PEC) 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 and assess two objectives simultaneously. The need for this more comprehensive treatment of PEC compared to previous references is illustrated by the analysis of heat transfer and friction characteristics of ten spirally corrugated tubes. These PEC are used to assess the multiplicative effect when a corrugated tube is combined with twisted tape insert.