Pipes with Trapezoidal Cut Twisted Tape Inserts in the Laminar Flow Regime: Nusselt Number and Friction Coefficient Analysis

Abstract

The thermal behavior of pipes with a twisted tape inside (used to enhance heat transfer through the tube wall) is studied in the laminar flow regime. Oil is used as the work fluid with the corresponding Reynolds Number spanning the interval 200-2000. It is found that in such conditions the 'Nusselt Number' (Nu) gradually increases with reducing the tape twist ratio, whereas the friction factor is detrimentally affected by the presence of the tape (as witnessed by the comparison with the companion case where a plain tube is considered). In particular, it is shown that the heat transfer efficiency can be improved by nearly 69% if tape inserts with a relatively low twist ratio are used. On the basis of these findings, it is concluded that loose fit tape inserts are superior to tight fit tapes in terms of heat transfer and ease of replacement.