Fluid flow characteristics for shell side of double-pipe heat exchanger with helical fins and pin fins

To improve understanding of the heat transfer enhancement for shell side of a double-pipe heat exchanger with helical fins and pin fins, the three-dimensional velocity components for the shell side with and without pin fins were measured experimentally by using laser Doppler anemometer (LDA) under cylindrical coordinate system and the fluid flow characteristics, i.e., the distributions of the axial velocity, secondary flow, stream function as well as vorticity were analyzed by employing orthogonal helical coordinate system. The results showed that, for the shell side only with helical fins at large pitch, there was a pair of vortex near the upper and lower edge of the rectangular cross section; the weakest secondary flow occurred at the center. By pin fins being installed, the three-dimensional velocity components in the helical channel were strongly changed. The extra two vortices emerged at the center of the cross sections. The fluctuation of the velocity at the center of the cross sections before and behind a pin was increased sharply by the pin, especially for the situation behind a pin. (C) 2011 Elsevier Inc. All rights reserved.