Influence of the typical twisted tape inserts into the inner tube of double-pipe heat exchanger: A limited review

Abstract

Given the importance of the double-pipe heat exchanger (DPHX) in industry, this article review explores the studies and methods that have enhanced the thermal performance of this heat exchanger using typical twisted tape (3T) inserts into the inner tube as one of the prominent passive techniques. The twist ratio (TR) parameter can be considered the most influential factor on the thermal enhancement percentages, in addition to other less influential parameters, such as the type of 3T material, the clearance between the 3T and the inner tube, the length of the 3T relative to the length of the inner tube, in addition to the operating conditions, including the difference in the inlet temperature between the working fluids and the difference in flow rates. Thermal enhancement is increased when this technique is combined with other techniques, whether passive or active. In general, the use of 3T inserts enhances the thermal performance of the DPHX, especially when reducing the TR, but at the outlay of hydraulic performance, so it is necessary to use the thermal performance factor parameter (TPF) in evaluating the overall performance. The literature indicates that it is possible to obtain a TPF greater than 2 depending on operation conditions, design, and integration with other thermal enhancement techniques. This review can stand as a valuable, clear, and limited reference for those interested in this subject and increasing knowledge, as well as for developers and researchers who want to enhance the performance of DPHX using 3T with or without other techniques.