A performance evaluation based on exergy analysis was proposed to
evaluate the benefits of different enhancement techniques for flow inside tubes.
The present performance evaluation was developed based on the application of
the principle of entropy generation. A semi-analytical model was developed to
predict the entropy generation and the exergy destruction rates associated with
both flow friction and heat transfer. This model was based on measurements
and empirical correlations for both flow and heat transfer characteristics.
The present performance evaluation was applied on flow through tubes
enhanced with twisted-tapes inserts, spirally internal fins and conical
turbulators for three different fluids. It was found that using specific types of
enhancement techniques reduces the irreversibility owing to heat transfer
across a finite temperature difference and in the same time increases that part of
irreversibility resulting from the flow friction. Therefore, a thermodynamic
optimum at a minimum exergy destruction rate can be achieved for different
enhancement techniques and different flow conditions. |
