Pressure drop and heat transfer comparison for both microfin tube and twisted-tape inserts in laminar flow

Experiments were carried out to compare pressure drop and heat transfer coe fficients for a plain, microfin, and twisted-tape insert-tubes. The twisted -tape experiments include three different twist ratios each with two differ ent widths. The data were taken at Reynolds numbers well in the laminar reg ion. The heat transfer data were obtained in a single shell-and-tube heat e xchanger where steam is used as a heat source to obtain a uniform wall temp erature and the working fluid in the tube is oil. The twist ratio and the w idth of the tape seem to have a large effect on the performance of the twis ted-tape insert. The results demonstrate that as the twist ratio decreases, the twisted-tape will give better heat transfer enhancement. The loose-fit (W = 10.8 mm) is recommended to be used in the design of: heat exchanger w here low twist ratios (Y = 5.4, and Y = 3.6) and high pressure drop situati ons are expected since it is easier to install and remove for cleaning purp oses. Other than these situations, the tight-fit tape gives a better perfor mance over the loose-fit tape. For the microfin tube tested in this paper, the data shows a small increase in both heat transfer and pressure drop. Th is type of microfin tube is not recommended to be used in laminar flow cond itions. (C) 1999 Elsevier Science Inc. All rights reserved.