Analysis of heat transfer enhancement in coiled-tube heat exchangers

We analyze the phenomenon of steady heat transfer enhancement due to chaoti c particle paths in steady, laminar flow through a tube. The performances o f two different coils, one with regular mixing and the other with chaotic m ixing, are numerically analyzed and compared. For the latter case, axially periodic boundary conditions over a unit cell are used: Velocity vectors an d temperature fields are computed. Poincare maps of fluid particles being r epeatedly mapped from inlet to outlet of this cell are presented as functio n of system geometry. Point and periodic attractors with chaotic windows ar e found. Lyapunov exponents are used to establish the presence of chaotic m ixing. Flow fields and isotherms are examined to reveal the mechanisms of e nhanced heat and momentum transfer through modification of the wall and int ernal boundary layers. Spatially varying local and constant bulk Nusselt nu mbers and bulk friction factors are determined for a range of governing par ameters. (C) 2001 Elsevier Science Ltd. All rights reserved.