The thermal performance of heat exchangers that are essential units
in power plants can be substantially improved by a number of augmentation
techniques. The entropy generation and exergy destruction rate due to the flow
friction and heat transfer across temperature differences were proposed
numerically to evaluate the benefits of utilisation of these techniques. Enhanced
tubes with either dimples or spiral corrugations that are isothermally heated
were investigated. The combination of spirally corrugated tubes with twisted
tape inserts was also presented. In general, dimpled and spirally corrugated
tubes and the combination of spirally corrugated tubes with a twisted tape
substantially increase the percentage of temperature raise ratio and decrease the
percentage of exergy destruction rate relative to smooth tubes. Increasing both
the additional heat transfer area due to dimpling, and ridge height of
corrugation increases the percentage of temperature raise ratio and decreases
the exergy destruction rate. Also, the combination of corrugated tubes with
twisted tapes is attractive as an augmentation technique based on exergy
analysis, especially at low twisted tape length to inner tube diameter ratio,
and high ridge height of corrugation for high Reynolds number. |
