Selection of tube inserts in heat exchanger retrofit applications for increased energy recovery

Abstract

To improve the thermal performance of conventional heat exchangers, the use of tube inserts to increase heat transfer is a suitable option. The number of new geometries that keep appearing in the open literature makes it necessary to develop practical comparison methods for their selection in real life applications. Most performance comparison methods provide an indication of how the heat transfer increases in relation to friction. This is useful but still the decision is qualitative since the whole picture in terms of the actual size and pressure drop cannot be anticipated as in the case of retrofit of existing heat exchangers. This paper introduces an alternative approach for the comparison of tube inserts for use in retrofit applications. The methodology is confirmed by comparing the performance predictions using the thermodynamic quantity of irreversibility. The comparison results are graphically displayed and allow to quickly identify the most suitable promoter from the thermal and hydraulic points of view. The results show that among the different turbulence promoters analysed in this work, the best performance is obtained from the perforated twisted tape that provides heat load increments between 4.2% and 6.4% with pressure drops 3.4 times larger than the plain tube.