Intensification of double-tube heat exchangers performance by modified twisted tapes: review perforated and dimpled/baffled twisted tape techniques

The use of twisted tapes as inserts in heat exchanger tubes dates back to the 1960s with the aim of activating thermal performance. However, the limited thermal enhancement and friction losses resulting from these inserts remain a continuing challenge to this day. Many modifications have been made to the twisted tapes to improve their ability to enhance the performance of heat exchangers, like cut, perforated, corrugated twisted tapes, etc. This review, the first of its kind, is concerned with the literature that used perforated and dimpled/baffled twisted tapes as inserts in the internal tube of a double-tube heat exchanger with the aim of identifying the influencing parameters and diagnosing the possibilities for development and performance enhancement. The results of this review indicated, despite some contrary claims, that perforated twisted tapes do not show superiority in thermal enhancement, especially with increasing perforation ratio, compared to conventional twisted tapes, but they are better in terms of hydraulic performance (lower friction losses), which makes them possible to use for this purpose only. On the other hand, dimpled and baffled twisted tapes show higher thermal performance enhancement but with higher friction losses compared to conventional twisted tapes without a clear parameter, which requires further investigation to reach the optimum dimple and baffle sizes that give the best performance to double-tube heat exchanger.