Uneven longitudinal pitch effect on tube bank heat transfer in cross flow

For the optimal operation of steam generation in the HRSG system, the longitudinal pitch distance of the tube banks can be controlled independently for each individual row. To achieve a uniform heat transfer rate for each row of the tube bank, we conducted a full numerical study that includes a variation of the longitudinal pitch for the in-line tube bank geometry. The overall heat transfer across the tube bundles was compared to the existing correlation; it showed good agreement within a Reynolds number range of 500-2000. It was found that the transverse pitch effect can be included in the form of the maximum Reynolds number at the minimum cross section, as in conventional heat transfer formulation. Increasing the longitudinal space for uniformly distributed cylinders enhances the overall heat transfer. An appropriate relationship was obtained as a function of the pitch ratio in each direction. Finally, a general correlation of the individual Nusselt number for each row was obtained by considering the additional effect from uneven longitudinal pitch distances. The proposed correlation could predict the temperature variation across each row of the target HRSG system and was in agreement with the experimental results. (C) 2012 Elsevier Ltd. All rights reserved.